Due to the many advances in belt technology, they are now able to meet high-power demands while being extremely safe, efficient and durable. In this article, we shall take a detailed look at the different types of modern belt drives and belt types.

What Is a Belt Drive?

A belt drive is a frictional drive that transmits power between two or more shafts using pulleys and an elastic belt. In most cases, it is powered by friction but it may also be a positive drive. It can operate at wide ranges of speed and power requirements. It is also highly efficient.

When it comes to cost, a belt drive is considerably cheaper than gear and chain drives. It costs less to install as well as maintain. Belt drive sheaves or pulleys undergo little wear compared to chain drive sprockets over extended periods of use.

Contrary to most chain and gear drives, a belt drive can handle some degree of misalignment. Correct alignment, however, increases service life. Excessive misalignment is responsible for issues such as improper belt tracking, uneven pulley wear, noisy operation and belt edge wear. The intensity of these issues is directly proportional to the belt’s width.

Belt tracking refers to the belt’s ability to be centrally located on the pulley and not shift to either side when in operation. Crowned pulleys can alleviate belt tracking issues.

It is also worth noting that a belt drive usually reduces shaft speed. For this reason, the driving pulley is usually smaller than the driven pulley. This provides a greater wrap angle on the driven pulley which is beneficial in friction-based drives. Designers may also use an idler pulley to increase the wrap angle and to maintain the recommended belt tension.

Belt Tension and Slack

The belt is subjected to tension when the driving pulley pulls it. This belt tension, in addition to the static belt tension, is responsible for the transfer of mechanical force. High belt tension prevents heat buildup, slippage and alignment problems as there is little to no relative motion between the belt and the pulleys.

On the other side, the driving pulley pushes the belt away towards the driven pulley. This causes slacking of the belt. Thus, a belt drive sets up fluctuating loads in the belt. If these loads are not considered in the design process, premature belt failure can occur. Fatigue is responsible for more belt failures than any other issue.

It is easy to identify the slack side from the side under tension. Whichever side of the belt approaches the driving pulley is under tension. The other side is the slack side.

Types of Belt Drives

As discussed above, belt drives today are capable of handling a wide range of speeds and power transmission needs. This has prompted further R&D, providing us with an array of different belt drive designs. All engineers should be familiar with the different types to facilitate an informed choice when selecting a belt drive for their application.

We can classify belt drives into seven main types, these are:

• Open belt drive
• Closed or crossed belt drive
• Fast and loose cone pulley
• Stepped cone pulley
• Jockey pulley drive
• Quarter turn belt drive
• Compound belt drive

Open belt drive

This is the simplest type of belt drive where two or more pulleys are connected with a belt wrapped around them. When power is supplied to the driving shaft, it rotates the driving pulley. The belt moves with it and rotates one or more driven pulleys.

In an open belt drive, both pulleys rotate in the same direction. With a horizontal pulley arrangement, the tight side of the belt is at the bottom and the slack side is at the top to increase the belt’s angle of contact with the pulleys.

Cross belt drive

This type of drive is used when two pulleys need to rotate in opposite directions or require a greater wrap angle for power transfer. In a crossed belt drive (aka twisted or closed belt drive), after passing over the top of the driven pulley, the belt contacts the driving pulley from the bottom. Thus, the belt’s shape resembles the number 8.

Between the two pulleys, the belt comes in contact with itself and the rubbing causes the belt to wear off. This can be mitigated by placing pulleys at the maximum allowed distance and running the system at slow speeds.

The crossed belt drive can transfer greater power for the same pulley dimensions and centre distance as the contact angle is higher. However, a longer belt is required as is evident by its crossed positioning.

Stepped cone pulley

This type of belt drive uses a driven pulley with multiple diameters. As the pulley resembles a stepped cone, it is known as a stepped cone pulley drive.

This drive is used when the driven shaft needs to be rotated at different speeds. Speed of the driven shaft can be increased or decreased by shifting the belt to a smaller or larger diameter step on the pulley respectively.

Common applications for this type of drive are lathes and drilling machines. A stepped cone pulley enables to use the same drive motor to obtain different output speeds.

Fast and loose cone pulley

As the name suggests, this drive consists of two pulleys – one fast and the other loose. Both of these pulleys are mounted on the driven shaft.

The fast pulley is keyed to the driven shaft so it rotates at the same speed as the shaft. The loose pulley is mounted without a key so it rotates freely relative to the shaft. This pulley is incapable of power transmission.

To hold the loose pulley in its place, a gun-metal or cast-iron bushing with a collar on one end is used. This prevents any axial movement. The diameter of the loose pulley is smaller than the fast pulley’s to allow the belt some slack.

This drive permits the immediate start and stop of the driven shaft without changing the speed of the driving shaft. When power needs to be transferred, the belt is shifted from the loose pulley to the fast pulley and when it needs to be stopped, the belt shifts back to the loose pulley.

Fast and loose cone pulley drives find use in applications where one line shaft powers multiple driven shafts. Switching to the loose pulley stops power transmission without having to stop the driving shaft which may be powering other shafts at the same time.

Jockey pulley drive

The dimensions of the smaller pulley decide the maximum force that the belt drive system can transmit. But what if both pulleys are small? Smaller pulleys lead to a smaller contact area between the belt surface and the pulley. If the pulley diameter is too small for meaningful contact with the belt’s surface, the power transmission capacity reduces.

Alternately, if the pulleys are required to be really close to each other, the wrap angle around the smaller pulley is reduced. This limits its power transmission capacity.

The solution for the aforementioned cases is to use a jockey wheel or an idler pulley. In mechanical systems, a jockey wheel refers to a machine element that steers or guides another element.

The idler pulley is placed on the slack side of the belt. They improve the belt drive’s performance as they reduce vibration by supporting the belt.

Idler pulleys can increase the wrap angle for smaller pulleys, ultimately increasing the surface area between the drive belt and the pulley.

Quarter turn belt drive

Most belt drives can only work with parallel shafts. But this may not always be the case. In situations where rotating shafts are at the right angles, we can use quarter turn belt drives.

Quarter turn belt drives (aka right angle belt drives) have a belt that goes around two perpendicular shafts after making a quarter turn. For the belt to stay in place, the pulley’s width must be at least 40% wider than the belt’s cross-section.

In some cases, guides or idler pulleys are used to promote better belt tracking and prevent slip off.

Compound belt drive

A common application for belt drives is to reduce shaft speed. This is part of the reason why most belt drives transfer motion from a smaller pulley to a larger pulley. But sometimes the speed ratio achieved from one set of pulleys may not be enough. In such cases, the designers can opt for compound belt drives as they allow for have higher speed ratios to be achieved.

A compound belt drive consists of more than two shafts with multiple pulleys keyed to at least one of the shafts. The driving pulley transfers power from one shaft to another through multiple shafts.

This setup improves the speed ratio without requiring a larger driven pulley or too much extra space.

Types of Belts

As with belt drives, belt designs have been specialized for various applications too. Each of them offers various benefits over others in specific situations. We will take a look at five of the most popular types of belts used in belt drives today. These five types are:

• Round belt
• Flat belt
• V belt
• Toothed belt
• Link belt

Round belt

Round belts have a circular cross-section and fit into U or V-shaped grooves in a pulley. They are also known as endless drive, endless round and O ring type belts.

Round belts are used in motion control as well as power transmission applications. These belts find use in line shafts, industrial conveyors, packaging machinery, photocopiers, printers, etc.

In applications where belts are expected to twist and turn a lot, contacting multiple pulleys in the process, round belts are highly suitable. Due to their very nature, these belts can transmit power and provide friction from any part of their circular surface.

Some other beneficial features of round belts are:

• Available in different sizes, colours and textures
• No fraying
• Economical
• Strong and durable
• Easy to clean
• Fit various pulley shapes
• Non-marking
• Can be reinforced for greater strength
• Features such as abrasion and UV resistance can be improved on need

Flat belt

Flat belts are one of the most common types of industrial belts. These belts have a rectangular cross-section and rest on top of flat pulleys for operation. They transmit power from one or both sides depending on the design. Flat belts find use in many industrial machines such as compressors, separators, fans, belt conveyors, sawmills, water pumps and machine tools such as grinders.

A leather belt was originally used in flat belt applications. But over time, with the discovery of new materials such as rubber and synthetic polymers, the use of leather belts has somewhat diminished.

Flat belts work best with crowned or tapered pulleys.

Some excellent features of flat belts are:

• A flat belt can deliver high power at high belt speeds
• Low noise operation
• High efficiency (up to 98%)
• Small bending loss due to small bending cross-section
• High flexibility
• No need for grooves
• Long service life as they handle dust and dirt reasonably well
• Can be reinforced for greater strength

V belt

Flat belts are not suited for applications where the centre distance between pulleys is small. V belts have largely replaced them in such areas. In fact, V belts are the most common belt type in use today.

A V belt has a trapezoidal (V-shaped) cross-section that fits into a similar groove on pulleys and sheaves. As V belt drives have a larger contact area between the pulley and the belt section (bottom + 2 sides), they can transmit greater power for the same dimensions.

V belts find use in various machine tools such as lathes, drills, milling machines and power tools. They are also widely used in non-industrial applications.

For a more complete understanding of V belts, there are two special types that need further explanation. These are hex belts and kraftbands.

A hex belt is something that we would get if we glued together the top surface of two V belts. The result is a hexagonal-shaped belt that can wedge into pulleys from both sides. Another apt name for a hex belt is a double V belt. They are perfect for applications with one or more reverse bends.

Kraftbands are a special type of V belt that looks as if several V belts are connected side by side at their top edges. It can work as multiple belts in one by increasing the contact area for power transmission. Up to five V belts can connect to form a single kraftband.

Some important features of V belts are as follows:

• Available in a wide range of sizes, strengths, and materials
• High power transmission capacity at high belt speeds
• Low cost
• Easy installation
• Compact arrangement
• Can combine with multi-grooved pulleys for many operational advantages
• Lower efficiency than flat belts due to the wedging effect with pulleys.

Toothed belt

While flat, round and V belts are excellent at transferring motion, they have some limitations. For example, belt slip cannot be eliminated in any of them. In applications where having no slip is a requirement, we must use toothed belts.

A toothed belt is a positive transfer belt that does not need friction for power transfer. It transfers force via teeth similar to chain or gear drives but with much lower noise levels and without the need for excessive lubrication.

The belts have teeth on the engaging side of the belt. These teeth fit into corresponding grooves machined onto the pulley. Toothed belts do not slip at all and are used in applications where maintaining accurate timing and position is critical. As a result, these belts are also known as timing belts or synchronous belts. They are commonly used in automobile and motorcycle engines to power and time camshafts.

Link belt

Link Belt Installation

Link belt is a special belt type that consists of many individual links. These links can be attached and detached as needed to change the length of the belt. The links are typically made from polyurethane and reinforced by a multilayer woven polyester fabric.

Link belts offer features similar to endless belts and do not need special pulleys to function. They have the same power and speed ratings as similarly-sized endless belts. They are easy and fast to install as the machine does not need to be disassembled.

Link belts are costlier than other alternatives which may restrict their use in budget-conscious applications. However, they offer excellent vibration dampening features and they can resist environmental factors much better than rubber belts.

Belt Drive Selection

To select the right belt for the right application, many factors must be considered. These factors help us determine the belt and pulley characteristics required for belt drive design. Some of these important factors are:

• Power transmission requirements
• Shaft separation
• Service environment
• Space constraints
• Type of driven load
• Speed ratio

Power transmission requirements

Belts can transfer power in a wide range of applications. We need accurate data with the appropriate safety factor to determine the type of belt that is best suited for the application.

Shaft separation

Every belt drive has an optimal distance at which it performs best. A small distance between the shafts would suggest the use of jockey pulley drive while long distances would permit an open belt drive for cost savings.

Service environment

Service environment factors such as oil, moisture, high temperatures, dust, snow etc. can affect many parameters such as belt wear, belt life, material, function and slip. The selection of belt drive must focus on the service environment that the belt must endure for a satisfactory wear life.

Space constraints

Limited available space can direct us towards more compact assemblies. Compact setups with hex belts or compound drives can significantly reduce the amount of space a belt drive requires.

Type of driven load

The loads driven by belts can be jerky, shock-prone or reversible. The selection process must opt for belts and pulleys that can manage such loads to ensure compatibility.

Speed ratio

Most belt drives have speed ratio greater than one which means that the driven pulley is larger than the driving pulley. In order to achieve this speed ratio, the designers can either increase the size of the driven pulley or reduce the size of the driving pulley.

But there are certain limitations in both. Increasing the size of the driven pulley drives up the costs and space requirements. Decreasing the size of the driving pulley can only be done to a certain extent as the belt must be capable of bending and wrapping around the driving pulley. Small pulleys increase the elongation of the belt’s outer fibres, exacerbating belt wear and life expectancy.

To add to this, both pulleys cannot be too small as that would result in a high belt velocity which is detrimental to belt life as well.

Advantages

• Belt drives are quite affordable thanks to low component cost and high efficiency
• They can transmit power over long distances, contrary to gears, couplings and lead screws
• Compared to chain drives, they operate smoother and more quietly
• They can absorb shock and vibrations
• Overload protection through the slipping of the belt
• Lightweight and relatively durable
• Low maintenance costs

Disadvantages

• Belt slippage can vary the velocity ratio
• They apply a heavy load on the bearings and shafts
• Finite speed range
• Short service life if not maintained well
• They need an idler pulley or some adjustment of center distance to compensate for belt stretching and wear

Conclusion

Belt drives are very common in the industry today. They are used in light as well as heavy-duty applications in many different configurations.

Round and toothed belts can measure the slightest relative movement in applications such as motion control, encoders and precision manufacturing. Flat, V and timing belts are widely used as power transmission belts. They find extensive use as material handling equipment too.

Belt drives are preferred in these applications for their salient features such as low cost, low weight, reliability, flexibility, durability, easy installation and maintenance. Generally, they can also be fitted into tight spaces.

They do have certain drawbacks though. Often times the belts are not repairable and must be replaced. Their tension needs to be adjusted every now and then. And most belt materials are sensitive to the environment and chemicals such as oils and lubricants.

Thus, due consideration and attention must be paid when choosing a belt drive system that is as compatible as possible with the application at hand.

The post Belt Drives & Types of Belts appeared first on Fractory.

Lead screws are sometimes confused with threaded rods. Although they might look identical to an untrained eye, the threads on a threaded rod are a lot finer. Thus, increasing the risk of thread deformation under load.

In this article, we’ll take a closer look at different lead screw types, their design, use-cases, advantages and disadvantages. So let’s get to it.

What is a Lead Screw?

Lead screw is a power transmission linkage used in modern machines. It can generate very high forces with a small moment, thus providing a large mechanical advantage. It can be thought of as a wedge wrapped around a cylindrical rod.

In applications such as screw jacks and mechanical presses, it is used to create large forces. They also find use in applications needing extremely precise motion transfer and control, such as linear actuators and linear stages.

As the sliding contact area between the screw and the nut is high, a lead screw has more friction losses compared to other alternatives such as gear trains and chain drives. This characteristic generally limits a lead screw’s use to light- and medium-duty applications.

How Does a Lead Screw Work?

A lead screw works in one of two ways:

1. The shaft is stationary and the power is supplied to the nut
2. The shaft rotates and transfers power to the nut

In the first case, manually applied force or a motor rotates the nut. This pushes the nut along the shaft’s axis. Ultimately, the torque applied to the nut is transformed into linear motion.

In the second case, the nut’s rotational motion is restricted and the screw shaft rotates. The nut moves along the screw axis in the process. Thus, the torque on the screw shaft converts into linear motion of the nut.

Lead Screw Components

The lead screw itself is a small component in many complex assemblies. But even a basic lead screw can be broken down into three main components/features. These are:

• Screw shaft
• Threads
• Nut

The screw shaft is a cylindrical rod with threads or grooves along its length. At times, it may be referred to as an ACME rod, buttress rod or square-threaded rod as per the thread geometry. The most common materials used for lead screw shafts are carbon steel, stainless steel and aluminum. PTFE-based coatings are often used in harsh environments for durability and to remove the need for oil and grease.

The threads are present on the screw shaft and the nut. Although it is not a separate component in itself, the thread’s structure is responsible for converting rotational motion into linear motion. The external threads are in direct contact and mesh with the nut’s internal threads.

The nut is a fairly simple component but does not offer much use by itself. Typically, it will have some means, such as tapped or through holes, to connect it to supporting components like a clamp. The clamp connects the nut to a guide rail, restricting the nut’s rotation and only allowing linear motion. Nuts can be made from plastic or bronze to add self-lubricating properties.

Apart from these components, lead screws may require additional parts depending on the function. For instance, to control backlash, precision lead screws are fitted with loaded springs that create an axial load to prevent unintended axial movements.

Lead Screw Design

The lead screw is a fairly straightforward actuator with few components and a simple yet effective design. But an engineer must be aware of certain lead screw terminologies to understand, manage and develop products that use lead screws. The following terms come up in lead screw design.

Crest and root

For a lead screw, the top of the thread is known as the crest. Similarly, the base of the thread where it connects to the screw shaft is known as the root of the lead screw.

Major, minor and pitch diameter

Major diameter is the distance of the thread crest from the shaft’s center axis measured perpendicular to the axis. Minor diameter is the distance of the thread root from the center axis. Pitch diameter is the diameter at which the screw threads contact the threads on the nut.

Helix and lead angle

The angle formed between the helical thread with the perpendicular axis of the lead screw shaft is known as the helix angle. A larger helix angle requires more torque to move the nut but it results in lower friction losses, thus making the setup more efficient.

The lead angle is the complementary angle of the helix angle. It is the angle between the helical thread and the axis of rotation.

Number of starts

A start refers to the starting point of a thread at the end of the screw shaft. When greater speeds and loads are required of the lead screw system, the screw shaft may have more than one start. It may have one, two, or four starts. Screws with multiple starts are basically independent threads running parallel to each other in the helical path around the shaft.

Screw lead and pitch

Screw lead is the linear distance moved by the nut in one revolution (360°) of the nut or the shaft. The smaller the lead, the tighter the thread, resulting in more precise linear motion.

The pitch is the distance between two adjacent crests or troughs measured parallel to the axis of rotation.

For single start screws, lead and pitch values are equal. In the case of multiple starts, the pitch is multiplied by the number of starts to obtain the lead.

Types of Lead Screw Threads

Lead screws are classified on the basis of their thread geometry. Threads used in lead screws must have high precision, accuracy and strength. Three of the most common types of threads used in lead screws are:

• Square thread
• Acme thread
• Buttress thread

Square thread

The square thread has square-shaped threads whose flanks are perpendicular to the axis of the lead screw. This 0° thread angle prevents any radial pressure on components and reduces friction between them. 

This design also minimises the contact surface between the nut and the screw. Thus, square threads have the lowest friction losses and the highest efficiency. As a result, they provide greater load-bearing capabilities for the same dimensions or require smaller motors for the same load transfer. Square threads are, therefore, the first choice in motion transfer and heavy load applications.

Square threads are also desirable in products that need to be compact in size while maintaining their functional requirements. However, these threads are the most difficult and expensive to machine out of all the different types. In most cases, they require a single-point cutting tool for fabrication.

Acme thread

The acme thread is a trapezoid-shaped thread with a thread angle of 29°. It is based on the imperial standard but is accepted throughout the world.

This thread was developed as a stronger alternative to the square thread. Due to the sharp 90° angle between the flank and the root, square threads are relatively weak at the base. Widening the base adds strength as well as makes it easier to machine. Multi-point cutting tools can be used more easily to machine acme threads than square threads.

Many times, acme threads are incorrectly referred to as trapezoidal threads. The trapezoidal thread follows the metric standard and has a thread angle of 30°. The exact specifications for trapezoidal threads can be found under DIN 103. 

Buttress thread

The buttress thread is a triangular-shaped thread that is used when force needs to be transmitted in one direction only. It has a 7° inclination on the load flank and a 45° inclination on the trailing flank.

Such a steep inclination enables it to carry the load as efficiently as square threads while the trailing flank adds additional strength thanks to the wider base. This thread is also very precise and can be used to create small accurate movements in one direction. Buttress threads exhibit poor performance when the axial load is applied in the other direction.

Lead Screw Application Examples

Lead screws are available in virtually every size and thus, they serve in a wide range of applications. In day-to-day use, lead screws are found in appliances such as printers, disc drives, lifting equipment and robots. 

In industries, lead screws are present in machines such as lathes, vices, jacks and CNC machines. Processes like engraving, fluid handling, data storage, rapid prototyping, 3D printing, measuring and inspection rely extensively on high-precision lead screws. 

The smallest commercially available lead screws can be as small as 0.5 mm in diameter. But for special cases, modern manufacturing methods can fabricate lead screws even smaller in dimensions. These special screws are used in medical devices for automated surgery and drug delivery. The medical industry also requires precision lead screws for medical imaging equipment such as X-ray, MRI, IMRT, PET and CT scan machines.

The Difference Between a Lead Screw and a Ball Screw

Ball screws are an alternative to lead screws offering similar functions. Sometimes they are even categorized as a type of leadscrew. The decision of whether to choose a ball screw or a lead screw can be a confusing one because of the similarities between the two.

Ball screw uses metal balls found in ball bearings for motion transfer. Instead of having internal threads, ball screws house balls in the lead screw nut. These balls fit into the grooves on the screw and are responsible for power and motion transfer. The balls have a small contact area with the lead screw shaft, resulting in very low friction. This reduces running temperatures and imparts high efficiency. A ball screw also has higher positional accuracy, speed and lead options.

The main drawbacks of ball screws are that they are expensive, don’t have self-locking properties and are not as shock-resistant as lead screws. They’re generally also a bit bulkier than lead screws and are

How to Select the Right Power Screw for Your Application

Every application is unique. The designer must understand the constraints and the service conditions before making a decision. This selection will not only affect the product design but also dictate the overall system performance.

However, due to the wide variety of screw types and sizes, choosing the right one can be a daunting task. Here’s an overview of the most important power screw features to consider when making the selection.

Load capacity

The load capacity of a power screw is the most important factor in the selection process. The service load affects many power screw features. For starters, the diameter of a lead screw is directly proportional to the required thrust.

There are two types of loads – peak and continuous. Peak load refers to high forces during sudden acceleration or deceleration and can be up to five times the continuous load. Continuous load is a calculated average value (RMS value) and sometimes applies consistently over the nut’s entire travel distance. It also directly affects the L10 life of a component. An engineer must consider both values and go for a design that can manage all the expected loads.

Plastic lead screw nuts can comfortably handle loads up to 50 kg, but they can be designed to manage up to 150 kg loads. On the other hand, bronze leadscrew nuts can handle several tonnes.

Speed

The second most important factor in power screw selection is speed. The speed at which a nut rotates or translates can be controlled by its helix angle and diameter. A small helix angle and large diameter will reduce the linear and rotational speed respectively.

Low speeds mean low operating temperatures, preventing any need for reducing the duty cycle. Operating speed is limited by the critical speed of the power screw. When exceeding this critical rpm (revolutions per minute), excessive shaft vibrations will affect the function and safety of the components. It is generally recommended that the operational speed does not exceed 80% of the evaluated critical speed.

Pressure-velocity factor

Pressure-velocity or the PV factor is an important parameter that expresses the actual load on a power screw. It is the combination of contact surface pressure and sliding velocity between the screw shaft and the nut. It is the key design parameter for lead screw assemblies using polymer nuts.

As the load increases, the rpm must be reduced to prevent permanent damage due to frictional heat. The opposite is also true, more speed means less available load capacity.

By ensuring that the actual PV value is less than the PV limit of the chosen material, we can warrant a longer service life.

Lubrication

Lubrication can be an issue with power screws, especially with those working under heavy loads and/or high speeds. The service environment conditions would need to be evaluated to make an appropriate selection in this regard.

In environments with high debris or particulate concentration, contaminated grease can actually cause abrasion. But lubrication is still necessary to prevent overheating, increase loading potential and improve service life. 

In such cases, one option is to either clean the grease along with the particles and reapply the film. Or use a dry film lubricant. Even bronze nuts with self-lubricating features need damping grease for satisfactory function. Analysing the service environment and the functional demands will help with selecting the appropriate power screw for your application.

Besides the above-mentioned factors, parameters such as backlash, service life, efficiency, accuracy, repeatability, material, resolution and the extent of customization required can help further narrow down suitable choices when selecting lead screws.

Advantages of Lead Screws

• Lead screws are cheap and reliable as they only have a few parts
• They require little to no maintenance
• Smooth and quiet operation
• Capable of lifting heavy loads
• Some power screws have self-locking property
• Low pitch screws can give highly precise measurements, which are vital in machine tool applications

Disadvantages of Lead Screws

• In comparison to other mechanical power transmission methods, leadscrews have a high wear rate
• Not suitable for applications with a very high torque demand
• They have relatively poor efficiency

The post Lead Screws Explained appeared first on Fractory.

In this article, we’ll take a look at chain drives and their various types. They are a crucial part of many machines and they can also be used in applications other than just transmitting power, but more on that later. Let’s start from the beginning.

What Is a Chain Drive?

Chain drive is a type of mechanical power transmission system that uses chains to transfer power from one place to another. A conventional chain drive consists of two or more sprockets and the chain itself. The holes in the chain links fit over the sprocket teeth.

When the prime mover rotates, the chain wrapped on the shaft’s sprocket rotates with it. This applies mechanical force onto the driven shaft, transmitting mechanical power in the process.

One of the main advantages over a belt drive is that a chain drive maintains a constant speed ratio, thanks to its zero slip feature. There is no lag in power transfer and hence, it serves as a timing chain in applications such as internal combustion engines. Having no slippage also ensures high mechanical efficiency. The only losses in a chain drive are due to friction between the chain links and the sprocket.

Compared to gears, chain drives are way more versatile when it comes to operating distances. They come into play when shafts are separated at distances greater than that for which gears are practical. Chain drives are efficient at varying distances while still keeping the setup rather compact. They’re found in short-distance applications such as bicycles and long-distance applications such as 5-storey high marine engines. A single chain can power multiple shafts at a time.

Types of Chain Drives

There’s a wide variety of different chain drive designs developed due to finding use in many different mechanical applications. They can be classified into various categories depending on what we choose as a yardstick. When classifying based on their function, chain drives can be divided into three main types.

• Power transmission chain drive
• Conveyor chain drive
• Hoisting and hauling chain drive

Power transmission chain drive

This type of chain drive is specifically used for transmitting power between two shafts. Most machines that produce power cannot consume it at the same place, e.g. pumps with attached motors. Transmission systems convey power to the consumer through different methods. When chains are used for this process, they are known as power transmission chains.

Common examples are bikes, agricultural machinery, compressors, engine camshafts, etc. All these applications use chain drives for power transmission.

Conveyor chain drive

Another common application for chain drives is conveyor chains. Conveyors use chain drives that are crafted especially for material transportation. They come in hundreds of different designs and sport features such as low friction, high temperature- and chemical resistance. They can also be anti-static and magnetic.

Conveyor chain drives find use in industries such as packaging, automotive, food and beverage production, pharmaceuticals and textiles. Attachments can be fitted to conveyor chains to adapt them for various uses.

Hoisting and hauling chain drive

Chain hoists are probably the most common piece of machinery used to lift and lower equipment. They can lift massive weights with very little effort using pulleys.

Hand chain hoists or chain blocks are a common sight in garages, workshops, construction sites, ship engine rooms and in many factories. They can lift/lower heavy loads going up to 20 tonnes. Hoisting chains can be pneumatic, electrical or manual.

We will be focusing on the different types of chains in the next section but since hoisting chains are rather straightforward in their design and field of application, we’ll be covering them here. Hoist chains can be divided into two categories:

• Oval link chains
• Stud link chains

Oval link chains

Oval link chains are also known as coil chains. They are commonly used as hoisting chains for low to medium loads and are generally meant to be used in low-speed lifting applications. The chain link is oval-shaped and each one is welded after interlocking.

Sometimes, square link types of chains may be used but they are generally avoided due to poor stress distribution and kinking issues.

Stud link chains

Stud link chains are a better alternative for high-load applications. Each chain link is fitted with a stud across its inner width. The studs prevent kinking and increase strength and durability. Stud link chains find use in ship anchors and in other heavy-duty lifting machines.

Types of Chains in Use

There are many types of chains used in chain drives, each with its own advantages and disadvantages. The five most common types in use are as follows:

1. Roller chain (bush roller chain)
2. Silent chain or inverted tooth chain
3. Leaf chain
4. Flat-top chain
5. Engineering steel chain

Roller chain

When talking about chains, roller chain is probably the one that comes into most people’s minds. Roller or bush roller chains are widely used for power transmission in bicycles, motorcycles and other applications in the transportation industry. They are usually made from plain carbon steel or from steel alloys.

A roller chain is made up of an inner plate (roller link plate), outer plate (pin link plate), bushes, pins and rollers. The rollers are placed equidistantly between chain links. These rollers engage with the sprocket teeth and transfer power through the chain. An important advantage of roller chains is that they rotate as needed when they come into contact with the sprocket teeth, thus reducing power losses.

In transmission chains, the height of the roller chain link plates (on each side of the roller) is greater than the rollers. This prevents the side plates from making contact with the sprocket during operation. In addition to that, they also act as guides and prevent the roller chain from slipping off.

For roller chains in conveyors, the roller diameter is relatively larger than the height of the sidebars. This prevents contact between the sidebars and the conveyor track and improves efficiency by eliminating translational friction. Larger rollers also reduce rotational friction.

For greater power requirements, designers can opt for multi-strand roller chains. Having multiple strands permits the use of low speeds and small chain pitches for the same load requirements.

Silent chain (inverted tooth chain)

Most chain drives are infamous for their high operational noise. In noise-sensitive environments such as enclosed spaces, mines and residential areas, a quieter chain is more suitable. This keeps the disturbance to the surrounding environment under control and promotes worker well-being.

Enter silent chains, also known as inverted tooth chains. A silent chain can transmit large amounts of power at high speeds while maintaining a quiet operation. The chain consists of flat plates stacked in rows and connected through one or more pins. Each link has the contour of sprocket gear teeth on the underside where it engages with the sprocket teeth.

The load capacity for a silent chain increases with the number of flat plates in each link, and so does the tensile strength and the chain width.

Leaf chain

These are the simplest types of chains in use. They consist only of pins and link plates. The link plates are alternated as a pin link and an articulated link. They don’t mesh with sprocket teeth as leaf chains are designed to run over sheaves for guidance.

Leaf chains find use in lifting and counterbalancing applications. Some common examples of applications using leaf chains are lifts, lift trucks, forklifts, straddle carriers and lift masts. In all of these low-speed machines, the lift’s chain endures high static loads and a small amount of working load. Leaf chains can handle shock and inertia better than other chain designs.

All lift chains must be capable of handling high tensile stresses without elongating or breaking. They must have sufficient ductility to endure fatigue. As always, lubrication and service environment must be given their due thought already in the design process.

Flat-top chain

Flat-top chains are intended only for conveying. They can replace conveyor belts and belt drives as the material can be carried directly on its links. An individual link is usually made out of a steel plate with barrel-shaped hollow protrusions on its bottom side. The links are connected to preceding and succeeding links by passing a pin through these protrusions underneath the links. The nature of these joints allows movement only in one direction.

There are special types of flat-top chains that can flex sideways. The pin construction permits sideways movement in both directions to enable the conveyor chain to go around curves.

Flat-top chains are used in low-speed conveyor machines for material transportation in assembly lines.

Engineering steel chain

The engineering steel chain has been around since the 1880s. This chain was designed to handle the toughest environments and the most demanding applications. They were made of hot-rolled steel and sometimes heat-treated for extra strength.

Engineering steel chains are just as relevant today. However, their strength, wear rate, loading capacity and pitch have increased to match present-day industrial needs.

These chains consist of links and pin joints. The clearance between this chain’s components is larger than other chains as it has to handle dust, dirt and abrasives under normal operating conditions.

Most engineering steel chains function as conveyor chains for material handling but some are also used in drives. They can be seen in applications such as conveyors, forklifts, bucket elevators and oil drilling machines.

How to Select the Right Chain Drive for Your Application

With the amount of variety in the form and function of various chain designs, selecting the right chain drive for an application can become a bit overwhelming. The right way to go about this selection is to eliminate unsuitable options by evaluating the chain’s application and features. This will help to narrow down viable options before the final selection. The most important factors in chain drive selection are as follows:

• Loading
• Chain speed
• Shaft layout
• Distance between the shafts
• Service environment
• Lubrication

Loading

When selecting the right chain drive for your application, the most important question to focus on is how much power needs to be transferred. The chain must be able to handle the power produced by the prime mover.

The safety of the crew and the chain drive system depends upon the correctness of the calculations at this stage. It is recommended to work with an adequate factor of safety.

Chain speed

Not all chain drives can handle high-speed applications. Some chain drives are specifically designed for low speeds. The specifications can be obtained by carrying out calculations and ensuring that the speed is within the recommended range. This evaluation will considerably narrow down the number of designs that can be used for the application.

Shaft layout

Most chain drives cannot work with non-parallel shafts. If the shafts aren’t exactly aligned, the designers may have to look towards gear drives as an alternative.

Distance between the shafts

It is recommended that the center distance between shafts be in the range of 30-50 times the chain pitch. The designer must also ensure that a minimum arc of contact of 120 degrees is obtained on the smaller sprocket. If the number of sprocket teeth is small, at least five teeth must be in contact with the chain at any given moment.

Service environment

The service environment will dictate the expected resistance of the chain drive to moisture, dirt, abrasives, corrosion and high temperature. It will also affect other parameters such as vibration, noise levels and fatigue strength. For instance, in areas where noise is a concern, the designers can opt for the use of an inverted tooth chain.

Lubrication

Most chain drives require lubrication for a satisfactory wear life. Chain type, size, loads and operating speed will dictate the need and extent of lubrication. Depending on the application, designers may prefer manual, drip feed, oil bath or forced feed lubrication.

Some chains are self-lubricated and do not require any external lubrication throughout their service life. Such chains use bushings made from oil-infused sintered plastics or metals that provide uninterrupted lubrication during operation.

Advantages of Chain Drives

• Able to transfer torque over long distances
• Contrary to a belt drive, a chain drive does not slip
• A chain drive is more compact than a belt drive and can fit into relatively tight spaces
• Multiple shafts can be powered by one chain drive
• Versatile drive that can work at high temperatures and in all kinds of service environments (dry, wet, abrasive, corrosive, etc.)
• It is a low-friction system that guarantees high mechanical efficiency

Disadvantages of Chain Drives

• Cannot work with non-parallel shafts
• Chain drives are known to be noisy and they can also cause vibrations
• Misalignment may cause the chain to slip off
• Some designs require constant lubrication
• An enclosure is usually needed
• They require chain tensioning from time to time in the form of a tightening idler sprocket

The post Chain Drives & Types of Chains appeared first on Fractory.

There are four main types of power transmission – mechanical, electric, hydraulic and pneumatic. In this article, we shall learn about mechanical power transmission, its types and the pros and cons of each type.

What Is Mechanical Power Transmission?

Mechanical power transmission refers to the transfer of mechanical energy (physical motion) from one component to another in machines. Most machines need some form of mechanical power transmission. Common examples include electric shavers, water pumps, turbines and automobiles.

In most cases, the rotational movement of the prime mover is converted into the rotational movement of the driven machinery. However, the speed, torque and direction may change.

Occasionally, they may convert rotational motion into translational motion (back and forth movement) depending on the application’s functional requirements. Such change may be carried out using linkages or other machine elements.

Types of Mechanical Power Transmission

Different machine elements can transmit power between shafts in machinery. The most common mechanical power transmission methods in use in the engineering industry today are:

• Shaft couplings
• Chain drives
• Gear drives
• Belt drives
• Power screws (lead screws)

Shaft couplings

Shaft couplings connect two shafts and transmit torque between them. The shafts may be in line, intersecting but not parallel, or non-intersecting and non-parallel. To cater to the needs of various applications and environments, many different types and sizes of couplings are produced.

Broadly, there are two types of shaft couplings- rigid and flexible. Rigid couplings do not permit relative motion between shafts, whereas flexible couplings do. Hence, flexible couplings can handle some shaft misalignment.

Some couplings, such as the split muff couplings, can be fixed onto shafts without moving them. In contrast, most others require shaft movement for installation/removal.

Advantages

• Shaft couplings are low-maintenance machine elements
• They can absorb shock and vibration
• They can handle radial and axial misalignment
• They provide heat isolation
• Maintenance-free and permanently lubricated designs are available

Disadvantages

• Shaft couplings cannot be used for non-intersecting parallel shafts
• Rigid couplings may damage the shaft if misalignment creeps in
• Backlash may develop over the service life, putting the couplings, bearings and drive components under additional stress
• Some couplings may loosen over time, damaging the drive components

Belt drives

Belt drives are a fairly common sight in industrial applications. A belt drive system consists of two pulleys and a belt (or rope). The belt firmly grips both pulleys and transfers power from the driving shaft to the driven shaft through friction. The belt drive works equally well for slow and very high speeds and thus finds use in high-speed applications such as air compressors.

Just like other drives, there are many belt drive designs that are great for specific applications. Belts can power multiple parallel pulleys and change the speed as needed. They can also absorb shock loads to a certain extent, protecting other drive parts. Both pulleys rotate in the same direction unless it is a cross-belt drive. There are three main types of belts in belt drives – flat belts, V belts and toothed belts.

Cross belt drive animation

Flat belts are great for general-purpose applications with low to medium torque demands. Typical applications include grinders, separators, roller conveyors, fans, water turbines, etc. Flat belts are reversible and can transfer power from both sides. There is no wedging effect in flat belts. This makes the energy losses negligible, and the mechanical efficiency can be over 98%. It can handle dust and dirt reasonably well and thus, has a longer service life compared to other alternatives.

V belts are better for medium to high torque demands. A V belt has grooves on the inside surface that fit into wedges on the pulleys. The driving shaft pulls the belt by the grooves, which pulls the driven pulley on the other end. Such an operation causes wedging losses, which, in effect, decreases the efficiency of a V belt. V belts cannot handle dust and dirt as well as flat belts.

Toothed belt, also known as timing belt, has teeth on the inside surface of the belt that fit onto toothed pulleys or sprockets. This belt drive is used for high-power transmission and timing applications. Toothed belts are used in automobile and motorcycle engines to power and time camshafts.

Advantages

• Belt drives are more affordable than other drives due to low component cost and high efficiency
• They can transmit power over long distances
• Smoother and quieter operation compared to chain drives
• They can absorb shock and vibrations
• Belt drive provides some degree of overload protection through the slipping of the belt
• Lightweight and relatively durable
• Low maintenance costs

Disadvantages

• Belt slippage can vary the velocity ratio
• Short service life if not maintained well
• Finite speed range
• They apply a heavy load on the bearings and shafts
• To compensate for wear and stretching, they need an idler pulley or some adjustment of center distance

Chain drives

Chain drives are used to transmit power between two components that are at a greater distance. These drives consist of a roller chain and two or more sprockets. The driver sprocket’s teeth mesh with the roller chain and transfer torque to the driven sprocket. Chains can be commonly seen in power transmission in bicycles and motorcycles, but they are also quite common in industrial machines.

They can fit into tight spaces by using idler sprockets. Chain drives are also used in applications where timing is critical and any delay caused by slippage would result in problems. This is why they are used in marine diesel engines, as timing chains to transfer power from the crankshaft to the camshaft. The camshaft operates the exhaust valve and the fuel injection timing. If the timing is off, the engine will suffer.

Advantages

• A chain drive is more compact than a belt drive and can fit into relatively tight spaces
• It can transfer torque over long distances
• Contrary to belt drives, chain drives do not slip
• One chain drive can power multiple shafts at a time
• It has high mechanical efficiency thanks to little friction
• A chain drive can work in all kinds of service environments (dry, wet, abrasive, corrosive etc.) and at high temperatures

Disadvantages

• They are noisy and can also cause vibrations
• A chain drive cannot work with non-parallel shafts
• Some designs require constant lubrication
• Misalignment may cause the chain to slip off
• A chain drive usually needs an enclosure
• It requires an arrangement for chain tensioning in the form of a tightening idler sprocket

Gear drives

Gear drives use gears for motion and power transmission from one shaft to another. They consist of a driving gear (on the input shaft) and a driven gear (on the output shaft). Power transmission from the power source to the load takes place through the meshing of the gear teeth. Due to the many available designs, they can work in a number of orientations and applications.

A gear drive can handle higher loads compared to a chain drive but is only suitable for short distances, as the gears need to be in direct contact with each other. Using multiple gears in a gear train makes it possible to change the gear ratio, rotational speed, torque and direction as needed. Too many gears in a single system will, however, reduce mechanical efficiency.

Gear drives do not slip but they may develop some backlash over time. Backlash is the gap between two meshing gear teeth at the pitch circle. At lower outputs, it may only result in some minor calculation errors. But at higher power outputs, the backlash will send a shock through the entire gear train. On occasion, it can even cause damage to the gear teeth.

Advantages

• Suitable for high mechanical power transmission applications
• Gears are sturdy and have long service lives
• Compact setup
• Gears have high efficiency and do not slip

Disadvantages

• Not suitable when distances between shafts are high, a direct connection is needed
• Prone to vibration and noise
• Metal gears are heavy and increase the weight of the machine
• They do not offer any flexibility
• They require lubrication
• Shock loads can damage gears
• Costlier than other drives (chain, belt, etc.)
• Meshing gears require precise alignment

Power screws

Power screws, also known as lead screws (leadscrews) or translational screws, are screws that either transmit or receive power. They are different from screw fasteners that are used to create temporary joints in machines. Power screw consists of a screw and nut that mesh with each other for power transmission.

In some cases, the nut is stationary while the screw moves for power transmission (screw jack and vice). In other cases, the nut is the power source and the screw is stationary (lathe lead screw).

Power screws are subject to considerable axial, horizontal and vertical forces in operation. They must have sufficient strength and bearing area to withstand them.

Lead screws can be seen in action in screw jacks, lathes, vices, mechanical presses, etc. They use the same principle as screw fasteners of converting rotational motion into linear motion to reduce the effort required to do work. The lower the pitch, the easier it is to lift, move or tighten objects with power screws. The most common thread profile for power screws is a square thread, followed by acme and buttress threads.

Advantages

• Power screws are cheap and reliable as they only have a few parts
• Some lead screws have self-locking property
• It requires little to no maintenance
• Capable of lifting heavy loads
• Smooth and quiet operation
• Low-pitch screws can give highly precise measurements, which are vital in machine tool applications (A micrometer works on the same principle)

Disadvantages

• High wear rate compared to other methods of mechanical power transmission
• Power screws have poor efficiency
• Not suitable for mechanical power transmissions with a very high torque demand

Choosing the Correct Power Transmission Method

Choosing the right power transmission method can be tricky. From the data above, it is clear that every type has its pros and cons. The differences may be very obvious in some areas, but subtle in others.

Sometimes, subcategories within a particular type will help improve performance in some aspects. But if engineers work backwards from their expectations from the drive, it will narrow down viable options and even help with the final selection.

In this section, we shall see five important power transmission factors that will help you select the correct method for your application:

• Angle between shafts
• Distance between the prime mover and the load
• Torque
• Temperature
• Maintenance concerns

Angle between shafts

Shafts can be parallel, intersecting, non-parallel but intersecting or non-parallel non-intersecting. Some mechanical power transmissions require that there is no relative motion between shafts (e.g. gear, chain & belt drives). In contrast, others can handle minor misalignment (e.g. flexible shaft couplings).

Distance between the prime mover and the load

The distance between the power source and load can further narrow down the choice. Where there is a considerable distance between shafts, a belt drive or a chain drive can be used. For short distances, shaft couplings and gear drives are more suitable.

Torque

For high torque applications, chain drives can be used as belt drives may slip. On the other hand, for low torque needs, flat belt drives and power screws are better.

Temperature

Materials such as rubber and synthetic compounds are not compatible with high-temperature environments. If such materials are used to manufacture belts in belt drives, they will start wearing out soon.

Alternatives such as chain and gear drives are better suited to high temperatures as they can quickly acclimatise to such environments and work efficiently. Such systems can also work with oil cooling methods. The same oil that is cooling the engine can be used to lubricate the drive. On the other hand, oil cooling is not possible with rubber as it will degrade the material.

Maintenance concerns

Maintenance issues such as tensioning, wear rate, alignment and lubrication can help an engineer determine the suitable mechanical power transmission method for the application.

Conclusion

Mechanical power transmission methods ensure that the load receives the power needed safely and efficiently. Different industries use different mechanical power transmission products and sometimes a combination of all to suit their respective needs.

At times, more than one method may be suitable for the same application. It will come down to comparing the pros and cons of each alternative to determine the most appropriate mechanical power transmission option for your design.

The post Mechanical Power Transmission appeared first on Fractory.

As a result, designers and engineers have designed many variations of couplings for specific service conditions and environments over the years.

This article will familiarise you with the different types of couplings and discuss choosing the right option for your application.

What is a Coupling?

A coupling is a mechanical device that connects similar or dissimilar shafts in machines to transmit power and movement. It is usually a temporary connection (but can be permanent in some cases) and capable of removal for service or replacement. A coupling may be rigid or flexible.

What is a Coupling?

Due to the availability of many designs, there can be stark differences in the construction and function of two types of mechanical couplings. Some couplings can connect to shafts without moving the shaft, while most will require shaft movement for fitting.

In most cases, a coupling does not change the direction of motion or angular velocity, unlike gears. It cannot be connected or disconnected mid-operation, unlike clutches. Couplings can only transfer torque over short distances, for longer distances chain drives and belt drives are better alternatives. Couplings are often paired with lead screw assemblies to connect the screw shaft in-line to a motor.

The coupling works by maintaining a strong but flexible connection at all times between two shafts to transfer motion from one shaft to another. It does so at all values of loads and misalignment without permitting any relative motion between the two shafts.

The Purpose of Couplings

A shaft coupling can perform multiple functions in a machine. The design may incorporate more than one of these coupling features into the product’s function in advanced applications.

Let us take a brief look at what these are:

• Power transmission
• Shock and vibration absorption
• Misalignment accommodation
• Heat flow interruption
• Overload protection

Power transmission

The primary purpose in most cases is power and torque transmission from a driving shaft to a driven shaft — for example, a coupling connecting a motor to a pump or a compressor.

Absorb shock and vibration

A shaft coupling can smooth out any shocks or vibrations from the driving element to the driven element. This feature reduces the wear on the components and increases the service life of the setup.

Accommodate any misalignment

Misalignments between shafts can result from initial mounting errors or may develop over time due to other reasons. Most couplings can accommodate some degree of misalignment (axial, angular and parallel) between shafts.

Interrupt heat flow

A shaft coupling can also interrupt the flow of heat between the connected shafts. If the prime mover tends to heat up during operation, the machinery on the drive side is protected from being exposed to this heat.

Overload protection

Special couplings known as Overload Safety Mechanical Coupling are designed with the intention of overload protection. On sensing an overload condition, these torque-limiting couplings sever the connection between the two shafts. They either slip or disconnect to protect sensitive machines.

Types of Couplings

Couplings come in a host of different shapes and sizes. Some of them work great for generic applications, while some others are custom-designed for really specific scenarios.

To make an informed choice, it is important to be aware of the capabilities and differences between the different types of couplings. This section presents information about the following types of couplings and how they work:

• Rigid coupling
• Flexible coupling
• Sleeve or muff coupling
• Split muff coupling
• Flange coupling
• Gear coupling
• Universal joint (Hooke’s joint)
• Oldham coupling
• Diaphragm coupling
• Jaw coupling
• Beam coupling
• Fluid coupling

Rigid coupling

As the name suggests, a rigid coupling permits little to no relative movement between the shafts. Engineers prefer rigid couplings when precise alignment is necessary. 

Any shaft coupling that can restrict any undesired shaft movement is known as a rigid coupling, and thus, it is an umbrella term that includes different specific couplings. Some examples of this type of shaft coupling are sleeve, compression and flange coupling.

Once a rigid coupling is used to connect two equipment shafts, they act as a single shaft. Rigid couplings find use in vertical applications, such as vertical pumps.

They are also used to transmit torque in high-torque applications such as large turbines. They cannot employ flexible couplings, and hence, more and more turbines now use rigid couplings between turbine cylinders. This arrangement ensures that the turbine shaft acts as a continuous rotor.

Flexible coupling

Any shaft coupling that can permit some degree of relative motion between the constituent shafts and provide vibration isolation is known as a flexible coupling. If shafts were aligned all the time perfectly and the machines did not move or vibrate during operation, there would be no need for a flexible coupling.

Unfortunately, this is not how machines operate in reality, and designers have to deal with all the above issues in machine design. For example, CNC machining lathes have high accuracy and speed requirements in order to perform high-speed processing operations. Flexible couplings can improve performance and accuracy by reducing the vibration and compensating for misalignment.

These couplings can reduce the amount of wear and tear on the machines by the flaws and dynamics that are a part of almost every system. As an added bonus they’re generally rather easy to install and have a long working life.

“Flexible coupling” is also an umbrella term and houses many specific couplings under its name. These couplings form the majority of the types of couplings in use today. Some popular examples of flexible couplings are gear coupling, universal joint and Oldham coupling.

Sleeve or muff coupling

Sleeve coupling is the simplest example of a rigid style coupling. It consists of a cast-iron sleeve (hollow cylinder) or muff. It has an internal diameter equal to the external diameter of the shafts being connected. A gib head key is used to restrict the relative motion and prevent slippage between the shafts and the sleeves.

Some sleeve couplings and shafts have threaded holes that match up on assembly to prevent any axial movement of the shafts. The power transmission from one shaft to the other occurs through the sleeve, the keyway and the key. This shaft coupling is used for light to medium-duty torques.

The sleeve coupling has few moving parts, making it a sturdy choice as long as all the parts are designed keeping in mind the expected torque values.

Split muff coupling

For easier assembly, the sleeve in a sleeve coupling can be divided into two parts. By doing this, the technician no longer needs to move the connected shafts for assembly or disassembly of a coupling.

This is what a split muff coupling or a compression coupling is. The two halves of the sleeve are held in place using studs or bolts.

Similar to sleeve coupling, these couplings transmit power through the key. Split muff couplings are used in heavy-duty applications.

Flange coupling

In flange couplings, a flange is slipped onto each of the shafts to be connected. The flanges are secured to each other through studs or bolts and onto the shaft by a key. Using set screws or a tapered key ensures that the flange hub will not slip backwards and expose the shaft interfaces.

One of the flanges has a protruding ring on its face, while the other has an equivalent recess to accommodate it. This type of construction helps the flanges (and, in turn, shafts) maintain alignment without creating any undue stress on the shafts.

Flange coupling is used in medium to heavy-duty applications. They can create effective seals between two tubes, and hence, in addition to power transmission, they are used in pressurised fluid systems. Flange couplings are of three major types:

• Unprotected type flange coupling
• Protected type flange coupling
• Marine type flange coupling

Gear coupling

A gear coupling is very similar to a flange coupling. However, it is a flexible type of coupling and can be used for non-collinear shafts. Gear couplings accommodate angular misalignment of about 2 degrees and parallel misalignment of 0.25…0.5 mm. 

The setup for gear couplings consists of two hubs (with external gear teeth), two flange sleeves (with internal gear teeth), seals (O-rings and a gasket) and the furnished fasteners.

The power transmission between the two ends of the coupling occurs through the internal and external gears in the gear coupling.

Gear couplings are capable of high torque transmission. As a result, they find use in heavy-duty applications. They require periodic lubrication (grease) for optimum performance.

Universal joint (Hooke’s joint)

When two shafts aren’t parallel and intersect at a small angle, we use a universal joint. This joint can accommodate small angular misalignment while providing high torque transmission capacity.

The universal joint consists of a pair of hinges connected through a cross-shaft. The two hinges are positioned at 90 degrees to each other. The cross-shaft maintains this orientation and is also responsible for the power transfer. The universal joint is not a constant velocity coupling, i.e., the driving and driven shafts rotate at different speeds.

They find use in a variety of different applications, hence the name. The most popular uses of universal joints are in car gearboxes and differentials.

Oldham coupling

Oldham Coupling

Oldham coupling is a special shaft coupling used exclusively for lateral shaft misalignment. When two shafts are parallel but not collinear, an Oldham coupling is most suitable.

The design consists of two flanges that slip onto the shaft and a middle part known as the centre disc. The centre disc has a lug on each face. The two lugs are actually rectangular projections that are perpendicular to each other and fit into the grooves cut out into the flanges on each side.

The flanges are fixed to the shaft through keys. Thus, the power transmission takes place from the driving shaft to the key to the flange to the centre disc and then through the second flange to the driven shaft.

Oldham coupling is ideal for scenarios where there is a parallel offset between two shafts. Such parallel misalignment can happen in cases where power transmission is needed between shafts at different elevations. When the shafts are in motion, the centre disc goes back and forth and adjusts for the lateral variation.

Diaphragm coupling

Diaphragm couplings are great all-rounder shaft couplings. They can accommodate parallel misalignment as well as high angular and axial misalignment. They also have high torque capabilities and can transmit torque at high speeds without the need for lubrication.

Diaphragm couplings are available in various styles and sizes. The structure consists of two diaphragms with an intermediate member between them. The diaphragm is basically one or more flexible plates or metallic membranes that connect the drive flanges on the shafts to the intermediate member through bolts on both sides.

Diaphragm couplings were initially developed for helicopter drive shafts. But over the years, they have found much use in other rotating equipment as well. They are most commonly used in turbomachinery due to their high-speed function. Applications today include turbines, compressors, generators, aircraft, etc.

Jaw coupling

Jaw coupling is a material flexing coupling. It finds use in general low power transmission and motion control applications. It can accommodate any angular misalignment. Similar to diaphragm couplings, jaw couplings do not need lubrication.

This coupling consists of two hubs with intermeshing jaws that fit into an elastomeric spider. The spider is usually made of copper alloys, polyurethane, Hyrtel or NBR and is responsible for torque transmission.

Due to the elastic nature of the spider, it is suitable for the transmission of shock loads. It can also dampen reactionary forces and vibration pretty well.

Engineers use jaw couplings in applications such as compressors, blowers, mixers and pumps. 

Beam coupling

A beam coupling is a machined coupling that offers high flexibility in terms of parallel, axial and angular misalignment. It is one of the best low-power transmission couplings.

A beam-style coupling has a cylindrical structure with helical cuts. The attributes of these cuts, such as their lead and the number of starts, can be modified to provide misalignment capabilities of varying degrees. In fact, engineers can make these changes without sacrificing the structure’s integrity as it is made of a single piece. Thus, a second name for beam coupling is helical coupling.

In essence, beam couplings are actually curved flexible beams. They are available in single-beam and multi-beam versions. Multi-beam couplings can handle greater parallel misalignment than single-beam couplings.

A beam coupling is more suitable for low-load applications as torsional windup can be a real issue. Thus, it is used in servo motors and motion control in robotics.

Fluid coupling

Fluid Coupling Working Principle

A fluid coupling is a special type that uses hydraulic fluid to transmit torque from one shaft to another. 

The shaft coupling consists of an impeller connected to the driving shaft and a runner connected to the driven shaft. The whole setup is fixed in a housing, also known as a shell.

When the driving shaft rotates, the impeller accelerates the fluid, which then comes into contact with the runner blades. The fluid then transfers its mechanical energy to the runner and exits the blades at a low velocity. 

A fluid coupling is used in automobile transmission, marine propulsion, locomotive and some industrial applications with constant cyclic loading.

Parameters for Choosing

Shaft couplings are an integral component of motion control and power transmission systems. They provide incredible advantages and combat many assembly and service environment issues when applied correctly.

To do this, designers must consider many factors to make the right choice. Being aware of them helps reduce instances of coupling failure and improve system capabilities. These factors are:

• Torque levels
• Alignment limits
• Rotational speeds
• Lubrication constraints

Torque levels

Most manufacturers use rated torque as a basis for classifying coupling. The value of torque depends on whether a coupling is used for motion control or power transmission applications. The former has lower torque and loads compared to the latter. Knowing the expected torque levels in an application will narrow down the selection of the right coupling.

Alignment limits

Different applications have different alignment needs. Similarly, some shaft couplings can only accommodate one type of misalignment, while others can handle multiple types.

Manufacturers also mention the misalignment limits for different types of misalignment for every coupling. This consideration helps further narrow down the search and pair the right coupling with the right machine.

Maximum rotational speed

Every coupling also has a maximum allowable RPM. This limit is also published with shaft couplings. General-purpose couplings cannot be used as-is for high RPM applications. High RPM couplings need static and dynamic balancing to ensure safe, smooth and noise-free service.

Such balanced designs are created by precise machining and appropriate fastener distribution. Using the expected RPM as a yardstick can help with the correct coupling selection. 

Lubrication constraints

Sometimes, service conditions may prevent frequent relubrication of shaft couplings that need it. On the other hand, some shaft couplings are designed without the need for any lubrication over their entire life.

If the torque requirements are low, modified versions of conventional couplings are also available. These versions come with metal-on-metal lubrication or metal and plastic combinations to eliminate lubrication altogether. Designers must make the right coupling choice by evaluating the service conditions and application needs.

The post Types of Couplings appeared first on Fractory.

Some of these mechanical parts are elementary mechanical elements, whereas some others are in an assembly with other parts and perform a specific function in the car. The alternator, engine and carburettor are examples of such parts.

Learning about machine elements is the first step in creating efficient machines that solve pressing problems. They reduce human effort and surpass their capabilities significantly. In this post, we shall learn about machine elements and their types.

What Are Machine Elements?

In mechanical engineering, a machine element is the smallest mechanical part or part assembly in a machine. They usually perform a single function and cannot be replaced with multiple parts. For example, a bearing may be made of smaller parts such as balls, rings and seals, but it cannot perform its function if it were split up into its constituent mechanical parts.

Thus, a machine element may be defined as a part constituent (such as a fastener) or a distinct part (e.g. clutch) in machines. Broadly, machine elements can be divided into two main types.

• General-purpose machine elements
• Special purpose machine elements

General-purpose machine elements

These elements are the basic building blocks in many types of machines. Parts such as fasteners (screws, nuts and bolts, rivets, etc.), chains, shafts, keys, bearings and belts are examples of general-purpose machine elements. They usually perform the same function in all these machines.

In most cases, general-purpose machine elements come in sizes and shapes defined by international standards.

For example, hex bolts can be manufactured as per 18 different standards, the most popular being DIN 931 and DIN 933. In most of these standards, they are available in sizes from M3 to M48. This increases their usability in a variety of different machines, as replacements are easily available.

Special-purpose machine elements

These are mechanical elements that find specific use in machine design. Examples of such parts are the turbine in a jet engine, blades in a fan, pistons, crankshaft, etc. The mechanical design of these parts is customised as per requirements.

Let us consider the example of ship engines. They come in different designs, with the number of cylinders ranging from 6 to 14.

For each type of engine, the size of every component is redesigned. The exhaust valve, cylinder head, liner, piston, piston rings, connecting rod and crankshaft all come in different sizes for two different types of engines.

Types of Machine Elements

Both general and special purpose machine elements are elementary mechanical components that function together to make a machine work. Let’s see the various types of common machine elements and their uses.

Bearings

Bearings are one of the most common machine elements in machine design. Their job is to eliminate the friction between two moving parts. The mechanical design of rotating machines is incomplete without it. The primary purpose of bearings is to prevent direct metal-to-metal contact of the two parts and enable smooth relative motion between them.

They come in various shapes and sizes. The abundance of available bearing designs enables designers to select the most suitable bearing for different applications, ensuring maximum reliability, efficiency, performance and durability.

Bearings find use in a range of different motions, such as linear (conveyors), rotational (crankshafts), hinge (doors, windows) and spherical (ball and socket joint). They transmit radial loads, axial loads (thrust bearings), or a combination of both from the rotating element to the bearing housing.

Some applications of bearings are:

• Sliding doors/windows/drawers
• Engine crankshaft
• Conveyor pulleys and idlers
• Wind turbines
• Motors

Shafts

Shafts are long, cylindrical components used for the transfer of torque and mechanical power between two components. Designers use them when the distance between drive train components is too great for a direct connection, or if they operate in different environments.

For instance, in the case of a ship propeller, the distance is too great between the engine and the propeller warranting the use of a long shaft with multiple bearings along the way.

Similarly, the steam turbines powering the cargo oil pumps in oil tankers are isolated from the pumps by a bulkhead to eliminate the chances of ignition (different environments application). Only the shaft passes through the bulkhead from the engine room to the pump room.

The steam turbines in the engine room become extremely hot during operation. Even in the unlikely event of the atmosphere in the pump room becoming combustible (if cargo oil leaks), the mechanical design is such that the turbines will not act as sources of ignition.

A shaft may be solid or hollow, depending on the need. Solid ones are more compact, but their hollow counterparts have a greater load-carrying capacity for the same weight. For shafts under heavy loads during operation, designers prefer a hollow shaft as it has higher rigidity, stiffness and bending moments.

Some applications of shafts are:

• IC engine crankshafts/camshafts
• Vehicle axles
• Clocks and watches
• Motors
• Pumps

Keys

In machine design, keys are small mechanical components that connect shafts to rotating elements. In some cases, they may be solely responsible for the transfer of torque between the two elements.

Keys are placed between the shaft and the rotating element and have provisions cut out in both of them to fix the key in place. The cutout in the hub is known as the keyway. The bottom of the keyway where the key rests in the shaft is known as the keyseat. The complete assembly is known as a keyed joint.

A keyed joint permits no relative rotational motion but may allow axial motion to a small extent as keys are inserted in the axial direction. Due to such a function, keys must endure high compressive and shearing stresses. Thus, crushing failure and shearing failure are important considerations in a key’s mechanical design.

The various types of keys in machine design come in many standard shapes. The five main types of keys are round, saddle, spline, sunk and tangent.

Sunk key is the most common of them all. It comes in various sizes and shapes such as rectangle, square, parallel sunk, woodruff, gib-head and feather.

Some applications of keys are:

• Motors
• Marine propellers
• Gear drives
• Pulleys
• Sprockets

Couplings

Couplings are mechanical components that connect two rotating in-line shafts, with the primary purpose of transmitting power in mechanical design. The entire assembly rotates at the same speed. A coupling may be rigid or flexible, depending on the need.

A flexible coupling can absorb any mounting errors as well as any minor misalignments between the shafts that may develop over time. They also absorb shocks and vibration, increasing the service life of the machines in the process. Unlike clutches, couplings do not engage and disengage.

These machine elements also isolate the heat transfer between the two ends in some applications. For instance, a motor can heat up considerably during operation. A coupling prevents this transfer of heat from the motor to the paired machine.

Some couplings work like fuses. If the torque exceeds a certain limit, they break and sever the connection between the driving and driven components to protect sensitive machinery. Such a coupling is known as Overload Safety Mechanical Coupling and is normally used for the protection of motors and drive systems in power transmissions.

Some applications of couplings are:

• Generators
• Motion control in robotics
• Automotive steering linkages
• Paddle steamers
• Car differentials

Fasteners

In mechanical engineering applications, different types of fasteners are used to hold together two or more machinery components. They create temporary joints which can be disassembled when needed. Some machines work under extreme conditions. The primary purpose of fasteners is to protect these machines against high pressures, excessive forces and vibration.

In machine design, it is important to be as specific as possible about the design or selection of fasteners in applications. This is to ensure that these machine elements can manage the forces that the product will be subjected to in service and the machines can function without failure. Fasteners are usually made from carbon steel, stainless steel, or alloy steel.

Some examples of fasteners are screws, nuts/bolts, split pins, rivets and circlips. And they are used everywhere, independent of the industry. The only question to ask is whether the assembly will need to be disassembled for maintenance or not, as in the choice of rivets vs bolts and nuts.

Gears

Gears are elementary machine elements with toothed wheels to transfer power and rotation between two shafts. They can increase or decrease angular velocity while simultaneously decreasing or increasing torque, following the laws of energy conservation. In essence, they act as levers in a translating mechanical system.

The teeth on two gears mesh with each other and transfer power from the driving shaft to the driven shaft. Usually, the shafts are parallel, but special gears are capable of transferring power between intersecting as well as non-parallel, non-intersecting shafts.

The capability to work efficiently in any orientation means they also come in a variety of shapes. Most gears are cylindrical in shape with teeth along the circumference. Others come in shapes that resemble a shaft (worm gear) or a rod (rack and pinion). Yet others have teeth on the face instead of the circumference (face gears).

While it is important to select the general gear type, due attention must also be paid to factors such as precision grade standard (DIN, AGMA, ISO), need for ground or heat-treated teeth, dimensions (face width, helix angle, module, number of teeth, etc.) and more.

Some applications of gears are:

• Clocks and watches
• Vehicle gearboxes
• Clocks and watches
• Mixers and blenders
• Washing machines and dryers

The post Types of Machine Elements appeared first on Fractory.

Another thing to keep in mind during the product design phase is the ease of maintenance. Any machinery requires certain maintenance routines after specified running hours. The design must be such that engineers and technicians can access and dismantle as many parts as necessary to service, repair, or replace them. As a result, it is necessary to secure machinery components using non-permanent means.

The sometimes extreme forces combined with the necessary flexibility means that a high degree of variability is required from the different types of fasteners. Their sole purpose is holding machine parts in place against excess vibration, force and pressures while maintaining the possibility of easy disassembly in case of non-permanent fasteners.

Permanent vs Non-Permanent Fasteners

As the name suggests, fasteners may be broadly classified as permanent and non-permanent fasteners. For example, rivets and some types of couplings are permanent and cannot be removed and reused once in place.

Most other fasteners are non-permanent. The term “non-permanent” does not mean that the joint is weak. In fact, hydraulic studs and bolts (a type of non-permanent fastener) are used in some of the most intensive applications.

The term only refers to the fact that they allow the parts to be separated for maintenance/inspection purposes. But when they are in place, they hold steady under the most ruthless conditions provided they are tightened up to the recommended torque.

In this article, we shall learn about the different types of fasteners available for use.

Bolt Types

Bolts are the most common type of fasteners. These machine elements are usually used to hold two unthreaded components together. A bolt has external male threads on one end and a hexagonal head on the other.

The bolt is normally fastened with a nut on the other end. Sometimes, one of the parts has a threaded hole to replace the bolt and minimise the number of components.

There are many different types of bolts to choose from. Each type provides some trade-offs. Let’s take a look at some popular bolts types.

Hex-Head Bolts

Hex head bolts have the bolt head in the shape of a hexagon and can be tightened easily using a wrench. The six sides offer a good granularity of angles to approach the bolt from. This is especially important for bolts fastened in difficult to reach spots.

Hex head bolts have machine threads extending halfway or all the way up to the bolt head. Partially threaded bolts deliver a higher shearing capacity. Hex head bolts are extensively used in machinery as they are easy to assemble and disassemble.

The tools needed are also quite commonly available. Regular spanners are affordable and easy to use. Socket set may be used to reach bolts in difficult to reach areas. A single adjustable wrench is all one needs to fasten or unfasten many different sizes of hex head bolts and nuts but this should not be made common practice.

Double End Bolts

This type of bolt resembles a simple threaded rod. The main difference between the two is that a double end bolt has a thread in both ends instead of having it for the whole length of the piece.

They can be used with a nut at one or both ends, with the other end mating with a hole that has a respective thread size.

Eye Bolts

Eye bolts have a thread at one end and a loop at the other end. The loop’s purpose depends on machine design and size.

For example, a few eye bolts can be used together to support the weight of the structure during lifting. Another possibility is using a series of eye bolts to direct wires or cables through them all.

Penta Bolt

Basically the same as a hex-head bolt with one distinctive difference – the head of the bolt has 5 sides. This means that the most common tools can not be used for fastening or unfastening these bolts.

That adds an extra layer of precautionary dimension, as anyone with a wrench cannot disassemble a structure.

Carriage Bolts

Carriage (or coach) bolts have a convex metal head followed by a square neck and thread. This type is mostly used to fasten wood elements. It is designed to fit its square neck into a wood piece through pressure. This feature gives carriage bolts the self-locking element.

The bolt is hammered gradually while securing the other side with a nut. This creates a pocket for the square neck in the wood, holding the bolt firmly in place.

Socket Head Bolts

Also called Allen bolts, these types of fasteners typically have a cylindrical head with a hexagonal hole inside them. An Allen wrench or a hex socket tool can be used for tightening.

Other designs come with a domed button or a flat head countersunk head.

They require less space the method of tightening allows to have the head level with or below the surface of the material in case there are pre-drilled holes in the material.

U-Bolts

These bolts come in the shape of a horseshoe. While there is no thread on the bent section, the straight ends are usually threaded all the way.

U-bolts are excellent for securing the position of tubes and pipes or the position of other parts relative to tubes without making any holes in the tube itself.

There are many other variations of bolts available in the market. Some of them are:

• Flange
• Plow
• Shoulder

Screws

Screws have a structure similar to bolts. They have a male thread starting from the tip and the head can be of various shapes. However, there are some key differences between a bolt and a screw. While bolts can easily hold unthreaded objects together with a nut, a screw usually needs internal threads to maintain a grip.

Commonly, screws are self-threading (self-tapping), meaning that they create the thread into the material during installation. So no previous tapping is necessary.

Many different screw designs are in use. They all have specific pros and cons and the application will decide which one to select. Following is a list of the types of screws:

• Countersunk screw
• Deck screw
• Hex lag screw
• Self-drilling screw
• Machine screw
• Sheet metal screw
• Wood screw

We shall discuss some important screws that we need to be aware of as it is important to choose the right kind depending on the use.

Self-Drilling Screws

Self-drilling screws, aka self-tapping screws, are screws that create an internal thread during installation. The defining feature of a self-drilling screw is the fully threaded shaft from tip to head. The material used for the screw is harder than the objects to be joined.

The screw tip is available in different shapes but generally, a small taper is provided with a notched tip so that the screw can easily create space for itself in the substrate while being turned.

Sheet Metal Screws

Sheet metal screws are used to join two metals together. They have a shank with the thread covering the entire length with a head on one end. The head may be flat or rounded.

The tip on sheet metal screws is extremely sharp to help it pierce the substrate and lodge itself into the material firmly. The thread is also made of hard material to ease the creation of the internal thread for the screw.

This screw is very versatile and is used for plastic and wood besides metal.

It comes in two types: self-drilling and self-tapping. The self-tapping screw only requires a hole in the object body. The internal threads are created during installation. The self-drilling screw comes with drilling tips.

Machine Screws

Machine screws are a type of screw used in most machinery today. It has a structure similar to the aforementioned screws and it also comes in a variety of head and tip shapes. Machinery screws also contain a Phillips or slotted socket on the head to tighten it into the substrate.

Typically, machine screws are installed into pre-drilled holes as opposed to creating the hole during installation. But some machine screws also have the ability to tap the hole during installation.

Nuts

A nut is a fastener with an internal thread. It is used in conjunction with a mating bolt of the same size. During the early stages, nuts (as well as bolt heads) were in the shape of a square. They were easier to manufacture by hand but they do not find much use today except in certain special scenarios.

The square nut provides a better grip and high torque than hex nuts to the user due to the increased length and surface area that the spanner comes in contact with when tightening or loosening the nut.

Hex nuts are the most common types of nuts due to them providing more ways of approach (6 instead of 4. Spanners are also usually offset at 15 degrees to increase the number of approaches from 6 to 12). This is especially required in spaces that restrict spanner movement or flat surfaces.

Nuts also come in various other designs such as wingnuts (for use without tools) and cage nuts for cramped spaces.

Cap Nuts

Also known as acorn or dome nuts, these nuts have a closed end in the shape of a dome. This ensures that the bolt-nut assembly is better protected from the environment and also provides a nice finish.

Castle Nuts

Castle, or castellated nuts have notches at one end. The design enables the insertion of a pin through the notches (the bolt also has to have a hole in it then) to fix the nut’s position.

They are suitable for situations where the torque requirements are low. For example, holding a simple ball-bearing in place may be an appropriate job for a castellated nut.

Weld Nuts

The name says it all – these nuts are welded onto the surface of a part. Welding helps to fasten parts in hard-to-reach places that could make a traditional bolt-and-nut assembly difficult.

Hex Nuts

The most common of them all, these are cheap and easy to assemble with a wrench.

Nylon Lock Nuts

Nylon lock nuts are similar to hex nuts in their build but have an extra collar to accommodate a nylon ring. The ring pushes into the bolt’s thread to prevent loosening of the nut.

Rivet Nuts

A great substitute for weld nuts in places where there is little room. The price can be greater but at the same time there is no need for extra operations in the form of welding.

Round rivet nuts may have the problem of sliding. Thus, the best option is to use hexagonal rivet nuts. Of course, the hole shape has to reflect the shape of the nut which rules out the possibility of simple drilling and replacing it with the need for laser cutting.

However, if the parts are laser cut anyway, the shape of the hole will almost not matter at all int he final costs.

Some other types of nuts include:

• Barrel nut
• Coupling nut
• Flange nut
• Slotted nut
• T-nut
• Wheel nuts

Washers

Washers are small, circular, metal discs in the shape of an annulus. They are a type of fastener that is normally used in conjunction with bolts and nuts. They are placed under nuts, joints or axle bearings. A washer serves multiple functions such as:

1. Alleviation of friction.
2. Even distribution of pressure from nut/bolt on the fastened component.
3. Elimination of leakage
4. Isolation of components.
5. Prevention of loosening due to excess vibration.

Metals, as well as non-metals (plastic), are used as washer material. Washers come in many varieties and can be broadly classified into three major types:

Plain washers

Plain washers are used to isolate the component being fastened from the nut/bolt being used for fastening. This may be for insulation purposes or to protect the surface of the substrate, especially in case the part has a paint coating.

Another important purpose of plain washers is to distribute the load by increasing the surface area that comes in contact with the substrate. If a hole is too big for a fastener, a plain washer can correct the size difference. Plain washers may be one of the following types:

• Flat washer. Made for general use. Used for even load distribution and diminishing hole size difference. Also known as Type A washer.
• Torque washer. Used in woodworking projects with carriage bolts to prevent the bolt from spinning while the nut is being fastened.
• Fender washer. Derives its name from the fact that it is used on car fenders. It has a small inner diameter and large outer diameter to distribute forces over a large area. Used especially with thin metals.
• C-washer. A C-washer has a section cut from a general-purpose flat washer. This washer is needed where the washer might have to be replaced without unscrewing the fastener all the way.
• Finishing washer. Designed for use with countersunk screws, it is also known as a countersunk washer.

Spring washers

Spring washers act like springs due to the small modifications made in their circular shape. They develop axial flexibility which makes the joint more elastic. This ultimately averts unintended loosening or fastening of the fastener due to machine vibration. Spring washers come in many variations. Let’s discuss a few important ones.

• Belleville washer. This washer has the shape of a hollow cone with the top cut off. This gives the washer some flexibility in the axial direction. They can support axial forces with a small deflection. Belleville washers are used in applications that are prone to thermal expansion.
• Crescent washer. When a flat washer is slightly curved to give it the shape of a crescent, we get the crescent washer. Unlike a Belleville washer, a crescent washer can only support small axial forces. This washer is used to absorb small movements.
• Dome spring washer. Dome spring washer looks like a hollow cylinder connected to the base of a cone with the top lopped off. It acts similarly to a Belleville washer but is used when a flatter surface is needed.
• Wave spring washer. These washers have alternating bends in the axial direction that resemble a wave. Wave washers are less effective than Belleville washers. They are used as a cushion or a spacer for fasteners.

Locking washers

Locking washers lock the nut/bolt in place much better than spring washers. Lock washers are used where there is a chance of the fastener losing friction or undergoing rotation during operation. Some very effective lock washers are:

• External tooth lock washer. This washer has teeth that extend radially outward at a small angle. When the external washer is placed between the nut and the substrate and the nut is tightened, it bites into the bearing surface and holds the fastener in place. This washer is generally preferred when the substrate is a soft material such as plastic or aluminium.
• Internal tooth lock washer. This washer has teeth that extend radially inward. They bite into the fastener when it is tightened and prevent any relative motion. Besides, they also assist with absorbing shock and vibration.
• Split lock washer. Split washer looks similar to what you would get if you cut a flat washer from center to edge and bent the two ends in opposite directions. The two ends of the split washer lodge slightly into the mating surfaces when the fastener is tightened and hold it in place.
• Tab washer. A tab washer has a side tab that extends outward. Before tightening, this side tab is bent and placed against the nut to prevent relative motion.

Retaining Rings

Retaining rings are metal fasteners used to hold a shaft or an assembly in place. They come in various designs.

Retaining rings are employed in many applications in machinery. One such instance is the retaining ring (circlip) used to hold the gudgeon pin of an IC engine piston in place. It is also used to hold the assembly together in a diesel generator’s high-pressure fuel pump.

Most retaining rings are used once and replaced when the machinery is overhauled but some may be reused. Retaining rings can be categorised into four major types. These types are further divided into sub-types. The four major categories are:

• Constant section retaining ring
• Tapered section retaining ring
• Spiral retaining ring
• Circular push-on

Rivets

Rivets are permanent fasteners used to secure many different types of materials. They are lightweight and offer great support against shearing forces. The presence of a head at each end enables the rivet to support axial loads up to a certain extent. A special tool known as a rivet gun (or a riveter or a pop riveter) is used for installing rivets. Holes do not need threads when rivets are to be installed.

Unlike threaded fasteners, rivets create a permanent joint and cannot be removed and reused. Rivets offer an excellent strength-to-weight ratio. They are also easier to inspect (compared to welded joints). A visual check is sufficient for inspection (unlike in welding, where special tools are needed to inspect joint integrity).

These reasons have made the rivet the preferred fastener in the aerospace industry. They can create butt as well as lap joints. Some of the most common types are:

• Blind rivet
• Drive rivet
• Large flange rivet
• Semi-tubular rivet
• Tri-fold rivet

Anchors

Anchors are a unique type of fastener used to secure metal to concrete or other materials such as epoxy, vinylester, and polyester resin. Some anchors are installed while the concrete is still drying while others are installed directly into hardened concrete.

Anchors are used to secure a variety of different objects and thus, they come in various designs. An anchor transfers tensile as well as shear force to the substrate. There are many types available in anchors. Some well-known anchor types are:

• Acoustical wedge anchor
• Bonded anchor
• Double expansion shield anchor
• Drop-in anchor
• Hammer drive pin anchor
• Plastic anchor
• Screw anchor

Inserts

Inserts come in different forms. Their shapes can vary a lot as they perform a range of tasks in machinery as fasteners. Inserts are used for reinforcing joints, fixing eroded internal threads, used as keys in rotating machinery, or fastening anchor bolts to hanging pipelines.

Some inserts have internal as well as external threads. The external threads of the insert fit on to the original hole with the eroded thread in the substrate. A smaller sized stud or bolt is then mated with the internal thread of the insert for a tight grip.

Insert fastenings can be classified into the following groups:

• Dowel pin
• Threaded rod
• Unthreaded rod
• Helical threaded inserts
• Keys in shaft key-ways

The post Types of Fasteners appeared first on Fractory.

Different gear types are used in machines as they can be designed for a range of forces from a range of materials. They can also be used to increase/decrease rotational velocity as well as change the direction of rotation.

Gears can also be used to pump liquids as in the case of gear pumps for fuel oil and lubrication oil for instance. They mesh so well (forming a positive displacement pump) that the liquid is pushed ahead with high delivery pressures.

They are also used in chain blocks to lift heavy objects easily. Thus, gears are a core component of most equipment as they are quite versatile and able to perform a variety of tasks.

Difference Between Gears & Sprockets

Gears and sprockets both use teeth to transfer torque. While at the outset, they both are similar-looking components, there are some marked differences that can help us identify them with ease.

• Gears are the preferred solution for short-distance transmissions. Using a sprocket and a chain helps to transmit the power over a considerably longer distance, using a chain.
• While the teeth of two gears mesh perfectly with each other, it is not so for a sprocket. A sprocket tooth is actually designed to fit into a cavity such as the chain of a bicycle or the tracks of a military tank.
• While gears are capable of transmitting torque in parallel, perpendicular, and any other orientation in between, sprockets can only do so along the parallel axis.
• Gears transfer torque in the opposite direction. If the driving shaft is rotating clockwise, the driven shaft will rotate anticlockwise. With sprockets, the rotational direction remains the same.
• Gears with a broken tooth may not be as effective as a perfect system but they will work. In case of sprockets, one or more broken teeth can cause the chain to leave its position and the system will come to a halt.

Different Types of Gears and Their Uses

There are many types of gears and each one offers some trade-offs. It comes down to what expectations a designer has from a gear train. The factors that may be considered are as follows:

• Torque/duty cycle needs
• Rotation speed/gear ratio
• Service environment
• Space availability/restrictions
• Budget

Based on these factors, the selection is further narrowed down to whether the gears will be operating on parallel/non-parallel and intersecting/non-intersecting axes. Let’s learn a little more about what choices one has and what each one of them offers.

Spur Gear

The most common type of gear used. Its simple and effective design creates a possibility for a wide range of applications. The teeth on spur gears are parallel and straight-cut on a cylindrical gear body.

Spur gears use the parallel axes configuration in mated pairs. They work great for moderate load and moderate speed applications and are generally used in applications where noise and vibration are not a concern.

Two differently sized spur gears can be used to change torque and RPM. The simple design allows for a high degree of manufacturing precision. One of its advantages is providing high transmission efficiency while not causing axial loading of the shaft.

Some disadvantages include high noise and vibration in high-speed applications and the great amount of stress the teeth are subjected to in this simple design. This limits its loading capacity.

Gear Rack

It is possible to combine spur gears with a rack to convert rotational motion to linear motion. A rack consists of teeth cut in a straight row on a flat surface. These teeth have the same profile as the spur gear.

The spur gear teeth mate with the teeth on the rack similar to how they would mesh with another spur gear. When the gear rotates, it pushes the rack in a straight line.

The gear rack system, also known as rack and pinion system, finds use in many products such as automobiles, stairlifts, railways etc. It is used to fine-tune machinery parameters to, for example, control the amount of fuel that enters a diesel generator through a high-pressure fuel pump.

Internal Gear

Spur gears may also be combined with an internal gear to create a planetary gear system. An internal gear has teeth on the inside of an annulus-shaped gear body. This gear mates with spur gears placed inside it to transfer motion.

Internal gear mechanisms are of three types: planetary, solar, and star. Depending on the application and other pertinent factors, a variety of speed transmission ratios may be produced along with the desired rotational direction.

Internal gears are employed in a variety of industries where they are commonly used as reduction gears. They are perfect for changing gear ratios in bicycles, watches, and automatic transmission in cars.

Helical Gear

Helical gears are similar to spur gears in construction and application as they use the same parallel axes configuration with parallel teeth. The teeth, however, are angled such a way that if we were to extend them, they would form a helix around the shaft, hence the name.

Unlike spur gears, helical gear teeth come in contact gradually with each other. This avoids impact loading of teeth. Due to this feature of gradual loading, more than one tooth pair are in contact at a time. Load sharing takes place, allowing helical gears to sustain higher loads compared to spur gears.

The gradual loading also reduces noise and vibration, making this type ideal for high loads and high-speed applications.

Use of helical gears produces axial loads and hence they need to be supported by thrust bearings. A pair of mating helical gears consists of one left-hand twist and one right-hand twist gear, unlike spur gears where the teeth are always parallel with the axis.

Double Helical Gear

Double helical gears are a special type of helical gear. They were created to overcome the high axial thrust associated with single helical gears.

Double helical gears combine two opposite orientations of teeth together, usually along the middle of the gear face. The axial thrust produced by the left-hand tooth is nullified by the right-hand tooth, thus eliminating the need for a thrust bearing.

Typical use-cases for double helical gears include prime movers such as gas turbines and generators. They also find use in fans, pumps, and compressors.

As in the case of single helical gears, double helical gears also provide smooth and silent operation at all speeds.

Herringbone Gear

Herringbone gear is a special type of double helical gear. Whereas the helical gear has a groove in the middle between the teeth, the herringbone gear does not.

Such a design helps to cancel out the axial forces on each set of teeth. Thus, larger angles are allowed as there is less danger of failure.

It normally uses the intersecting axes configuration where the two shafts are perpendicular to each other. The power is transmitted from the herringbone gear to a regular double helical gear.

Herringbone gear does not produce any axial thrust and ensures a quieter, smoother, and effective operation at all speeds and loads.

Screw Gear

Screw gear is also known as crossed helical gear. They are used for motion transmission between non-parallel non-intersecting shafts.

While helical gears usually engage between parallel shafts, screw gears do so at 90 degrees.

The teeth on a screw gear are in the form of a helix. They form a point of contact between two gears and hence are not very suitable for high load and high-speed applications. They also have low efficiency compared to other helical gears.

A unique trait of screw gears is that they use the same hand pair when engaging. Motion is transmitted as the same hand pairs slide against each other. Lubrication of screw gears is therefore a necessity. There are no limitations on the combination of the number of teeth.

Bevel Gear

The types of gear we call bevel are cone-shaped, placing the teeth on the conical surface. The cone top is lopped off. The two mating gears are generally placed on perpendicular intersecting shaft axes.

One of the most common uses for bevel gears is for changing the power transmission axis. While doing so, RPM and torque may be changed as necessary by varying the gear size.

There is also the option to increase or decrease the angle between the shafts. The two shafts need not be exactly perpendicular.

Due to the design of bevel gear, when two mating teeth come in contact, the contact takes place all at once instead of gradually. Thus, a similar problem of high stress as in the case of spur gears occurs.

This high impact mating produces more noise and causes excessive stress on the gear tooth. The high stress ultimately affects the durability and service life of the bevel gear.

It also affects the sort of applications they are used for. Straight bevel gears are generally used at low RPM (less than 500 RPM or 2 m/s circumferential speed).

Despite these limitations, they find use in many different industries. Some of the equipment that uses bevel gears are automobiles, pumps, machine tools (milling and turning), food packaging equipment, fluid control valves, and gardening equipment. They are also the easiest to manufacture and hence, are quite affordable and available in a variety of sizes.

Spiral Bevel Gear

Spiral bevel gears are used to overcome the limitations of straight bevel gears. As the name suggests, the teeth on a spiral bevel gear are arranged in the form of a spiral.

When two spiral gears come in contact, they do so gradually. This avoids impact loading of the teeth as the previous gear teeth pair (that are now losing contact) are still carrying some of the load. From this pair, the new mating pair assumes the load slowly.

This makes the operation smooth and quiet. It also increases the safe loading capacity of the gear. Thus, spiral bevel gears find use in highly demanding applications (speeds greater than 500 RPM) for safe and reliable operation.

Some of these applications are power transmission, car differentials, robotics, bow and stern thrusters in ships.

Mitre Gear

Mitre gears are bevel gears with a speed ratio of 1:1. An engaging pair will always have the same number of teeth. They transmit power between intersecting axes.

Mitre gears are used in machines to change the direction of rotation only. They do not cause a change in the shaft speed or torque.

A mitre gear may be of straight or spiral type. Straight mitre gears offer the advantage of not having to deal with any axial thrust. But they come with the limitations of straight bevel gears. Spiral mitre gears produce axial thrust necessitating the need for thrust bearings.

Mitre gears usually engage at 90 degrees. But they may be produced to mate at other angles as well. If they mate at any other angle between 0 and 180, they are known as angular mitre gears. Most common range for angular mitre gears is between 45 and 120 degrees.

Hypoid Gear

Hypoid gear

Hypoid gear resembles a spiral bevel gear but there are some marked differences. Unlike spiral gears, hypoid gear shafts do not intersect.

The hypoid gear is placed offset to the crown wheel which is usually a spiral bevel gear. This positioning of the hypoid gear results in greater contact when mating. This improves load-carrying capacity as well as the durability of the transmission system.

Another difference is the shape of the hypoid gear. The gear body is in the shape of a revolved hyperboloid.

A cone forms when a right-angled triangle revolves around one of the edges that form the right angle. If we replace the hypotenuse (which is a straight line) of the right-angled triangle with a hyperbola and revolve it around the same edge, we get the hyperboloid shape.

This shape matches perfectly without any interference with the spiral bevel gear as the two mating gears are placed a little to the side.

Compared to bevel gears, hypoid gears achieve higher speed reduction due to their large contact ratio. The increased contact also permits higher load transmission while suppressing noise and vibration.

The meshing is, however, complex and the production is also difficult. Hypoid gears are used in automotive differential systems.

Hypoid gears bear some similarity to worm gear systems but they have certain advantages over them. Firstly, less sliding occurs, reducing power consumption. Secondly, the offset between the two gears is less which saves space. Finally, both gears can be heat-treated which imparts higher rigidity reducing the size of gears used.

Worm Gear

In a worm gear drive, a worm engages with a worm wheel and motion transfer takes place. A worm gear resembles a screw and as it rotates it meshes with a cylindrical gear, sometimes also known as worm wheel.

This system is used to transfer motion between two non-parallel, non-intersecting shafts. Worm gears offer one of the highest gear reduction ratios.

A unique characteristic of this gear drive is that the gear pair rotation can be locked. This is because the worm wheel cannot turn the worm gear if it is set at a certain angle. However, the worm gear can turn the worm wheel at any angle. This property is utilized in applications that require self-locking mechanisms.

Worm gears come with certain disadvantages though. The transmission efficiency is not as good compared to other gears. Also, the fact that sliding occurs between the worm and worm wheel during transmission makes lubrication a factor to pay attention to. Continuous lubrication is the basis for smooth operation.

Worm gears are common in automobiles, steering systems, lifts, and material handling systems.

Gear Parameters

Now that we have a general idea of the different types of gears, we are in a better position to get a bit technical and understand the meaning of various terms that one may come across while learning about gears.

Outer Diameter

This is the maximum diameter of a gear. It is the distance from the gear body centre to the tooth tip. The outer diameter signifies the outermost extent of a gear.

Pitch Circle

The pitch circle of two engaging gears touch each other at the point where the mating teeth come in contact with each other. It runs roughly around the centre of the gear tooth. Pitch circle is where the motion transfer takes place and hence, this circle is used for all calculation purposes. The point at which the gears touch is known as pitch point.

Centre Distance

It is the distance between the centres of two mating gears of a system. It is important that this distance is set properly for effective transfer of torque. It is calculated by adding the pitch circle diameter of the two gears and dividing by two.

Root

Root is the point where the tooth connects to the gear body. It is the trough between the bottom-most part of two adjacent gear teeth.

Root diameter is the distance between the centre of a gear body and the base of a gear tooth. The tooth height of two mating gears must be cut in a way that it does not exceed the root of the gear to prevent contact of tooth tip with the other gear’s root during rotation.

Pitch

Pitch is defined as the distance between the same point on two adjacent gear teeth. It can be calculated easily by dividing the circumference of the gear at that point by the number of teeth.

But the word ‘pitch’ can be confusing as at different points along the tooth height, the value will be different. Thus, the diameter needs to be specified. Some popular pitches are circular pitch, normal base pitch, and angular pitch. Circular pitch is the distance between the same points on two teeth faces along the pitch circle.

Diametral Pitch

Diametral pitch informs us of tooth density. It is calculated by dividing the total number of gear teeth by the pitch circle diameter. Its unit is the number of teeth per meter.

Tooth Profile

Tooth profile refers to the shape of a gear tooth. There are many different options we can choose from. We could make them rectangular, triangular, in the shape of a circular arc, or move on to more complex shapes such as a parabola or an involute.

Simple shapes such as rectangles and triangles, however, create high vibration, noise, and would be very inefficient due to excessive sliding. Complex shapes improve efficiency and enable quiet operation. Let’s see what types of profiles are in use today.

Involute Tooth Profile

It is the most widely used tooth profile. There are certain advantages of using involute gears, such as:

• Easy and inexpensive to manufacture

• Can accommodate small deviations in the centre distance.

• High root thickness imparts strength

• Constant pressure angle during operation makes operation smooth

Cycloidal Tooth Profile

The cycloidal tooth profile is the second most common profile in use. This profile ensures the same wear occurs on the entire tooth. Cycloidal gear teeth find use in watches and instruments. It is seldom used for intensive applications as it is difficult to produce.

Arc of Circle Profile

This profile is not as popular but it has the advantage of slow wear as the arc is uneven. It is classified into two types: single arc and compound arc.

As the name suggests, the tooth has a cylindrical shape which mates with the other gear. Sometimes, a convex arc may fit into a concave arc for better transmission. This profile, however, is difficult to produce compared to the involute profile.

Gear Materials and Surface Treatment

Gears are produced using a variety of material and this selection will also affect the surface treatment method that may be chosen to improve performance.

Gears may be produced from different types of metals as well as non-metals such as steel, cast iron, plastic, nylon, and fibre. Each material has its own salient features:

• Steel is used for intensive applications. It provides high strength and hardness. Carbon and alloy steel are common choices.
• Cast iron is easy to produce and is generally preferred when gears are to be mass-produced. Precision is, however, lost in this type of production.
• Nylon is an inexpensive, lightweight and non-corrosive option as a gear material. Nylon is a good choice for low load, corrosion-prone applications.

Surface treatment of gears is usually necessary before putting them into service. Two useful techniques for gear surface finishing are grinding and heat treatment.

Grinding gear teeth makes them smooth and leads to quiet operation. It does increase the final cost of production though.

Many heat treatment techniques are available for improving the strength, surface finish, and durability of gears. Some of these procedures are carburising, annealing, tempering, surface hardening, and normalising.

Depending on the material used and procedure employed, the gears can be made strong, heat-resistant, hard, and durable.

The post Types of Gears appeared first on Fractory.

Bearings are a crucial tribological component of many types of machinery and exist in a variety of forms and shapes. They can be defined as a machine element that supports/permits only a specific type of motion (restriction of degrees of freedom) in a system that may be under static or dynamic loading.

An example is a sliding door. The door cannot be lifted or removed from its place. It only permits sliding to open it. The possible movement is restricted to sliding motion by bearings.

What Is the Purpose of Bearings?

The main purpose of bearings is to prevent direct metal-to-metal contact between two elements that are in relative motion. This prevents friction, heat generation and ultimately, the wear and tear of parts. It also reduces energy consumption as sliding motion is replaced with low-friction rolling.

They also transmit the load of the rotating element to the housing. This load may be radial, axial, or a combination of both. A bearing also restricts the freedom of movement of moving parts to predefined directions as discussed above.

Rolling Element Bearings

Rolling element bearings contain rolling elements in the shape of balls or cylinders. We know that it is easier to roll a wheel than slide it on the ground as the magnitude of rolling friction is lower than sliding friction. The same principle is in work here. Rolling element bearings are used to facilitate the free movement of parts in rotational motion.

Even when we need linear motion in applications, it is easy to convert rotational motion to sliding motion. Consider an escalator or a conveyor. Even though the motion is linear, it is powered by rollers that are driven by motors.

Another example is a reciprocating pump that can convert rotational energy from a motor into translational motion with the help of linkages. In each of these applications, ball bearings are used to support motor shafts as well as shafts of other rollers in the assembly.

Rolling elements carry the load without much friction as the sliding friction is replaced with rolling friction. Rolling element bearings can be subdivided into two major types: ball bearings and roller bearings.

Ball Bearings

Ball bearings are one of the most common types of bearing classes used. It consists of a row of balls as rolling elements. They are trapped between two annulus-shaped metal pieces. These metal pieces are known as races. The inner race is free to rotate while the outer race is stationary.

Ball bearings provide very low friction during rolling but have limited load-carrying capacity. This is because of the small area of contact between the balls and the races. They can support axial loads in two directions besides radial loads.

Ball bearings are used for controlling oscillatory and rotational motion. For example, in electrical motors where the shaft is free to rotate but the motor housing is not, ball bearings are used to connect the shaft to the motor housing.

Depending on the application, different types of ball bearings are available to choose from.

Advantages of ball bearings:

• Good wear resistance
• Do not need much lubrication
• Provide low friction, thus little energy loss
• Long service life
• Easy to replace
• Small general dimensions
• Comparatively cheap
• Can handle thrust loads

Disadvantages of ball bearings:

• May break due to shocks
• Can be quite loud
• Cannot handle large weights

Deep Groove Ball Bearings

Deep groove ball bearings are the most widely used ball bearing type. Trapped between the two races is a ring of balls that transmit the load and allows rotational motion between the two races. The balls are held in place by a retainer.

They have very low rolling friction and are optimized for low noise and low vibration. This makes them ideal for high-speed applications.

They are comparatively easy to install and require minimal maintenance. Care must be taken during installation to prevent denting of the races as they have to be push fit onto shafts.

Angular Contact Ball Bearings

In this ball bearing type, the inner and outer races are displaced with respect to each other along the bearing axis. Angular contact roller bearings are designed to handle greater amounts of axial loads in both directions in addition to radial loads.

Due to the shift in the inner and outer races, the axial load can be transferred through the bearing to the housing. This bearing is suitable for applications where rigid axial guidance is required.

Angular contact bearings are widely used in agricultural equipment, automobiles, gearboxes, pumps, and other high-speed applications, such as CNC machining tool spindles.

Self-Aligning Ball Bearings

This type of ball bearing is immune to misalignment between the shaft and the housing which may happen due to shaft deflection or mounting errors.

The inner ring has deep grooves similar to deep groove ball bearings followed by two rows of balls and the outer ring. The outer ring has a concave shape and this grants the inner ring some freedom to rearrange itself depending on the misalignment.

Thrust Ball Bearings

Thrust ball bearings are a special type of ball bearings designed specifically for axial loads. They cannot sustain radial loads at all.

Thrust ball bearings exhibit low noise, smooth operation and are capable of high-speed applications.

They are available as single-direction or double-direction bearings and the selection relies on whether the load is unidirectional or bidirectional.

When to Use Ball Bearings?

So let’s outline some of the working conditions that may require a ball bearing.

1. Thrust loads are present. Ball bearings’ design makes them capable of withstanding axial loads.
2. No heavy loads. Due to having ball-shaped rolling elements, the bearings concentrate all the force onto a few points of contact. This can result in early failure with high loads.
3. High speeds. The ball bearing’s small point of contact also means less friction. So there is less resistance to overcome and thus it is easier to achieve high speeds with these types of bearings.

Roller Bearings

Roller bearings contain cylindrical rolling elements instead of balls as load-carrying elements between the races. An element is considered a roller if its length is longer than its diameter (even if only slightly). Since they are in line contact with the inner and outer races (instead of point contact as in the case of ball bearings), they can support greater loading.

Roller bearings are also available in various types. The appropriate type may be selected after considering the type and magnitude of loading, service conditions, and the possibility of misalignment among other factors.

Advantages of roller bearings:

• Easy maintenance
• Low friction
• Can take high radial loads
• Tapered roller bearings can withstand high axial loads
• Great accuracy
• Used to adjust the axial displacement
• Low vibrations

Disadvantages of roller bearings:

• Noisy
• Quite expensive

Cylindrical Roller Bearings

Cylindrical roller bearings are the simplest of the roller bearings family. These bearings can face the challenges of heavy radial loading and high speed. They also offer excellent stiffness, axial load transmission, low friction, and long service duration.

The load capacity can be increased further by obviating the use of cages or retainers that are usually in place to hold the cylindrical rollers. This permits the fitting of more rollers to carry the load.

They are available as single-row, double-row and four-row types. They also come in split and sealed variants.

Split variants are used for areas that are difficult to access such as engine crankshafts. In sealed variants, the bearing contamination is prevented and the lubricant is retained making it a maintenance-free option.

Spherical Roller Bearings

Heavy radial and axial loads can be a greater challenge when the shaft is prone to misalignment.

This situation can be handled very well by spherical roller bearings. Spherical roller bearings have high load-carrying capacities and can manage misalignment between the shaft and housing. This reduces maintenance costs and improves service life.

Spherical roller bearing raceways are inclined at an angle to the bearing axis. Instead of straight sides, the rollers have spherical sides that fit onto the spherical raceways and accommodate small misalignments.

Spherical roller bearings have a wide range of use cases. They are used in applications where heavy loads, moderate to high speeds and possible misalignment occur. Some examples are off-road vehicles, pumps, mechanical fans, marine propulsion, wind turbines, and gearboxes.

Tapered Roller Bearings

The tapered roller bearing contains sections of a cone as a load-carrying element. These rollers fit between the two races that are also sections of a hollow cone. If the races and the axes of rollers were extended, they would all meet at a common point.

Tapered roller bearings are designed to handle higher axial loads besides radial loads. The larger the half-angle of this common cone, the more axial load it can sustain. Thus they work as thrust bearings as well as radial load bearings.

Tapered roller bearings are used in back-to-back pairs so that axial forces can be supported equally in either direction.

Needle Roller Bearings

Needle roller bearing is a special type of roller bearing that has cylindrical rollers that resemble needles because of their small diameter.

Normally, the length of rollers in roller bearings is only slightly more than its diameter. When it comes to needle bearings, the length of rollers exceeds their diameter by at least four times.

As needle roller bearings have a smaller diameter, more rollers can be fit in the same space which increases the surface area in contact with the races. Thus, they are capable of handling high loads. The small size can also prove helpful in applications where space is limited as they require smaller clearances between the axle and the housing.

Needle bearings are used in automobile components such as transmission and rocker arm pivots. They are also used in compressors and pumps.

Thrust Roller Bearings

Thrust roller bearings are designed to sustain high axial loads and are available with three types of rollers: cylindrical, tapered and spherical. These bearings offer high axial rigidity and are well-suited for heavy loads.

Cylindrical roller thrust bearings have good axial load-carrying capacity and are relatively cheap. These bearings should be avoided if there are any radial loads present. Compared to thrust ball bearings they tend to wear quicker due to higher friction. They are not suited for high speeds due to the differential sliding of the rollers.

Tapered roller thrust bearings can tolerate slight eccentricity that occurs between the shaft and housing during operation. There is no real difference between tapered roller thrust bearings and tapered roller bearings and the amount of axial loads these bearings can tolerate, alongside radial loads, depends on the half angles of the cones. They can support greater thrust loads than thrust ball bearings due to the larger contact area but are more expensive to manufacture. 

Spherical roller thrust bearings are designed to take heavy axial loads in one direction and accommodate some radial loads as well. They are self-aligning and are thus unaffected by mounting errors and shaft deflection.

When to Use Roller Bearings?

Roller bearings are the most common alternative to ball bearings. So let’s determine what kind of working conditions are best suited for this type of bearing.

1. Heavy loads. Roller bearings provide a considerably larger area of contact, distributing the load more evenly. Thus, they are less prone to failure and can withstand high forces.
2. Lower speeds. This, again, comes down to the contact area. There is more friction which can result in higher temperature generation and quicker wear.

Plain Bearings

A plain bearing is the simplest type of bearing. It usually only consists of a bearing surface. There are no rolling elements.

The bearing is basically a sleeve mounted on the shaft and it fits into the bore, thus it is sometimes referred to as a sleeve bearing. Plain bearings are inexpensive, compact and lightweight. They have high load-carrying capacity.

Plain bearings are used for rotational, sliding, reciprocating or oscillatory motion. The bearing remains fixed while the journal slides on the bearing’s inner surface. To facilitate smooth movement, material pairs with low coefficients of friction are selected. Different types of copper alloys, for example, are pretty common.

This bearing can accommodate some misalignment, multi-directional movements, and is suitable for static as well as dynamic loads. Plain bearings are used extensively in applications in the agriculture, automotive, marine, and construction industries.

The gudgeon pin that connects the piston to the connecting rod in diesel engines is connected through a plain bearing.

The spherical bearing is also a plain bearing, although it consists of 2 parts – the inner ring and the outer ring. Although it looks similar to ball and roller bearings from the outset, they have no rolling elements between the two rings.

Fluid Bearings

Fluid bearings rely on pressurised gas or liquid to carry the load and eliminate friction. These bearings are used to replace metallic bearings in applications where they would have a short life in addition to high noise and vibration levels.

They are also increasingly being used to cut costs. Fluid bearings are used in machines that work at high speeds and loads. While the initial costs are higher, the longer lifespan in tough conditions makes up for it in the longer run.

When the machine is running, there is zero contact between the two elements (except during the start and stop) and hence it is possible to achieve near zero wear with fluid bearings.

Fluid bearings are classified into two types: hydrostatic and hydrodynamic bearings.

Hydrostatic Bearings

In this type, an externally pressurised fluid is forced between two elements that are in relative motion. The pressurised fluid forms a wedge between the moving parts and keeps them apart. The fluid layer may be very thin but as long as there is no direct contact, there will not be any wear.

The fluid is circulated by means of a pump. The exit orifice diameter may be adjustable to ensure the fluid is always under pressure at all shaft speeds and loads. Thus, precise gap control is possible.

Hydrodynamic Bearings

This type of bearing utilises the motion of the journal to force the fluid between the shaft and the housing. The journal motion sucks the lubricating fluid between the moving parts creating a constant wedge.

This, however, means that during start-stop as well as at low loads and speeds, the wedge formation may not be good enough to prevent wear. Only at designed speeds will the system work exactly as needed.

Magnetic Bearings

Magnetic bearings use the concept of magnetic levitation to hold the shaft mid-air. As there is no physical contact, magnetic bearings are zero-wear bearings. There is also no limitation on the maximum amount of relative speed it can handle.

Magnetic bearings can also accommodate some irregularities in shaft design as the shaft’s position is automatically adjusted based on its centre of mass. Thus, it may be offset to one side but will still function just as satisfactorily.

They are broadly classified into two types: Active and passive magnetic bearings.

Active Magnetic Bearings

Active magnetic bearings use electromagnets around the shaft to maintain its position. If a change in position is picked up by sensors, the system adjusts the amount of current being fed to the system and returns the rotor to its original position.

Passive Magnetic Bearing

Passive magnetic bearings use permanent magnets to maintain a magnetic field around the shaft. This means there is no power input needed. The system is, however, difficult to design due to limitations as this technology is still in its early stages.

In many cases, the two types of magnetic bearings may be used in tandem where the permanent magnets handle the static loading while the electromagnets are used to maintain the position to a high degree of accuracy.

The post Types of Bearings appeared first on Fractory.