Mechanical engineering Types of belts

 

Mechanical types of belts 

What is mechanical belt..? 

          A belt is a loop of flexible material used to link two or more rotating shafts mechanically, most often parallel. Belts may be used as a source of motion, to transmit power efficiently or to track relative movement.

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

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. 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. 

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. 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. But sometimes the speed ratio achieved from one set of pulleys may not be enough. This is part of the reason why most belt drives transfer motion from a smaller pulley to a larger pulley. Fatigue is responsible for more belt failures than any other issue.

It is easy to identify the slack side from the side under tension. This limits its power transmission capacity.

The solution for the aforementioned cases is to use a jockey wheel or an idler pulley. 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. But what if both pulleys are small? Smaller pulleys lead to a smaller contact area between the belt surface and the pulley. This belt tension, in addition to the static belt tension, is responsible for the transfer of mechanical force. This can be mitigated by placing pulleys at the maximum allowed distance and running the system at slow speeds.

Mechanical types of belts 

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 machine 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 Kraft bands.

 hex belt 

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 Or timing 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 drive 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 

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.

The crossed belt drive can transfer greater power for the same pulley dimensions and centre distance as the contact angle is higher. 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. 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. 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. 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. If these loads are not considered in the design process, premature belt failure can occur. This causes slacking of the belt. 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. It costs less to install as well as maintain. 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. 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. In this article, we shall take a detailed look at the different types of modern belt drives and belt types.

Table of Contents  hide 

I What Is a Belt Drive?

II Belt Tension and Slack

III Types of Belt Drives

IV Types of Belts

V Belt Drive Selection

VI Advantages

VII Disadvantages

VIII Conclusion

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. This prevents any axial movement. The use of these highly efficient mechanical drives is increasing with every passing year.

Due to the many advances in belt technology, they are now able to meet high-power demands while being extremely safe, efficient and durable. Whichever side of the belt approaches the driving pulley is under tension. It can operate at wide ranges of speed and power requirements. 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. 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. 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. These factors help us determine the belt and pulley characteristics required for belt drive design. 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. 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. 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. When power is supplied to the driving shaft, it rotates the driving pulley. Crowned pulleys can alleviate belt tracking issues.

It is also worth noting that a belt drive usually reduces shaft speed. This has prompted further R&D, providing us with an array of different belt drive designs. 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.

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Belt Drive Selection

To select the right belt for the right application, many factors must be considered. 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. Correct alignment, however, increases service life. 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. This provides a greater wrap angle on the driven pulley which is beneficial in friction-based drives. The loose pulley is mounted without a key so it rotates freely relative to the shaft. 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. 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. For this reason, the driving pulley is usually smaller than the driven pulley. It is also highly efficient.

When it comes to cost, a belt drive is considerably cheaper than gear and chain drives. 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. Compact setups with hex belts or compound drives can significantly reduce the amount of space a belt drive requires.

. can affect many parameters such as belt wear, belt life, material, function and slip. Excessive misalignment is responsible for issues such as improper belt tracking, uneven pulley wear, noisy operation and belt edge wear. The belt moves with it and rotates one or more driven pulleys.

In an open belt drive, both pulleys rotate in the same direction. 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. Thus, a belt drive sets up fluctuating loads in the belt. But this may not always be the case. 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. Drives & Types of Belts

A belt drive is one of the most popular types of power transmission methods besides gears, chain drives, shaft couplings and lead screws. 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. 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. 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.

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