Types of Belt Drive: Material, Applications, Advantages & Disadvantages :- A belt drive is referred to as that mechanism wherein the power gets transmitted by the movement of a continuous flexible belt. This is used in order to transmit the rotational motion from one mechanical element to another. A belt is referred to as a looped strip of flexible material which is used to mechanically link either two or more rotating shafts. A belt drive is found in almost every possible modern engine available in the market.
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There are five different types of belt drive which are commonly known to mankind which are mentioned below:
Open belt drive
Closed or crossed belt drive
Fast and loose cone pulley
Stepped cone pulley
Jockey pulley drive
1. Open Belt Drive
: ( Types of Belt Drive )
Open belt drive is referred to as that drive which comprises of the shafts rotation in the similar direction which means that the direction of rotation is found to be same as the driving and the driven pulley.
The shafts seem to be arranged in the parallel directions. In case the shafts are found having more distance within the driver and the driving pulley then there must be the upper side, which can be the slack side and the below side, the tight side.
2. Crossed Belt Drive
: ( Types of Belt Drive )
Crossed belt drive also known to be closed belt drive and is referred to as that drive which has transmitted more power but there is a problem that it cannot run that faster. This is the reason which creates rubbing between belts and leads to wear and tear.
In this type of belt drive, the shafts are found to rotate in the opposite direction. At the junction side, it is found to rub and therefore it wears and tears off. If you wish to keep your belt away from wear and tear then you must place more distance within the pulley and also run it at lower speed.
3. Fast and Loose Cone Pulley
: ( Types of Belt Drive )
As the name indicates that fast and loose pulley means that there are two pulleys inside it. But it needs to be understood how these two pulleys are placed inside each other.
The fast pulley is found to be mounted on a shaft accompanied with a key joint and the loose pulley is found to run freely on the shaft due to which it is incapable of transmitting any power. Another term in that is when the multiple machines are found working from a single power source then in this type of condition, each machine has provided with this fast and loose cone pulley.
4. Ste
pped Cone Pulley Drive
: ( Types of Belt Drive )
Stepped cone pulley is also referred to as speed cone. There are more pulleys which are attached to the different diameter wherein one is attached adjacent to another.
Stepped cone pulleys are used where there is a need to change gear or speed of driven shaft, or change frequently like in the case of a machine lathe, milling etc.
The diameter of the driving and driven pulley is such that whenever one wishes to shift to another pulley the same belt can operate.
5. Jockey Pulley Drive
: ( Types of Belt Drive )
Jockey pulleys are referred to as those pulleys which are used in the steering section of any system. Jockey pulley is termed to be an idle pulley which is found to be used in increasing the angle of contact in an open belt drive. By increasing the angle of the contact steer, the power of the transmission capacity of the drive gets increased.
This one pulley is found to be mounted nearer to the smaller pulley wherein we can say that this is placed on the slack side of the belt. It is found to help in increasing the angle of contact of the belt, so that the belt tension can be increased and also the drive is found providing a high-velocity ratio.
There are various applications of a belt-drives which are used in various places like:
A belt drive is used for transferring the power.
The belt drive is used in the Mill industry.
The belt drive is used in the Conveyor.
The belt drive is powered by only a single belt.
Belt drives are usually made up of synthetic material.
This is not stronger as compared to the belt drive.
Belt drives are used in mills.
Difficult to repair if damaged.
Low or medium in price
The belt drive does not require lubricating system
The belt drive is quieter as compared to the chain drive.
The belts are found to be categorized into four different types which are stated below:
● Flat belt
● V belt and
● Circular belt
● Timing belt
1. Flat Belt
Drive
A flat belt is referred to as a kind of rectangular cross-section which is used at the places that require low power and more speed. Generally, the distance of the shaft is found to be within 5 to 10 meters.
Flat belt transmits power by the help of friction which gets produced within the belt and the pulley. The rotation of the pulley is found to be in the same direction in the flat belt. The flat belt is found to have an efficiency of around 98 percent, which results in very little noise in this belt.
2. V Belt
Drive
V belts are referred to as those kinds of belts which are found to be in the trapezoidal cross-section. These belts are mostly used whenever the distance of the shaft is considered less than 2 meters and is also used for a moderate speed and high power.
In these types of belt there is a possibility of multiple drives.
3. Circular Belt
Drive
Circular belt is referred to as that in which there is a circular cross-section. These are the belts which are used at places where there is more than 5-meter shaft distance.
Circular belts are used mostly for high transmission of power and are also used at places where there is smaller initial tension required and absence of vibration and noise is present.
4. Timing Belt
Drive
Timing belt is referred to as an alternate type of belt which is mainly used inside in the system to transmit power. Timing belts are mostly found to have a positive drive and is a precise and reliable type of belt.
For selecting the belt type of material, you should follow some of the below mentioned properties which will help you in buying an ideal belt:
The belt should be flexible
It should be reliable and durable.
The material should be capable of withstanding high tensile stress.
Higher temperature should be resisted.
The weight per unit length should be less.
Higher coefficient of friction within the belt and pulley.
It should have an excellent resistance to wear and fatigue.
It is important to know that there are 5 different types of material which are used for making the belts:
Leather belt
Rubber belt
Cotton or Fabric belt
Plastic belt
Balata belt
1. Leather Belt
Leather belts are referred to as one of the most important type of belt which was first found in Egypt. These belts are commonly found in day to day life.
Leather belts are found to be more expensive as compared to the other belts which are made of cloth or any recycled materials. In order to make leather belt strong, one layer of the leather is joint to another layer in order to make it stronger and to also increase the thickness of the belt.
2. Rubber Belt
A rubber belt is referred to as that belt which is made up of fabric and is commonly used in sawmills, paper mills etc.
3. Cotton or Fabric Belt
Cotton or fabric belt is referred to as that type which is mostly used in the farm machinery and belt conveyor. This type of belt is cheaper and also best suited for warm climates and a damp atmosphere.
4. Plastic Belt
Plastic belts are the ones which are made up of plastic sheets and rubber layers. The main advantage of a plastic belt is that it can be designed in almost any size which depends on the site requirement.
5. Balata Belt
Balata belts are referred to as those belts which seem similar to the rubber type belts but are found to be stronger than them. The balata gum is used here to stick the belt properly.
This type of belt is found to be waterproof and has a high resistance to acidic, alkaline material so this is mostly used for food packaging conveyor. This is not meant for high temperatures as the balata becomes sticky gum at a higher temperature.
The selection of belt drive depends on various factors. Some of them are listed here, for you to select the best belt drive:
It should have a positive drive.
The Centre distance within the shaft and pulley should be proper.
The speed of the driver and driven pulley should be tested and considered.
Power transmission system of the drive should be considered.
The layout of shafts should also be considered.
By now, you all must be aware about the types of belt drive, along with materials. So now, here we aim to discuss the advantages of a belt-drive which are mentioned below:
It can be easily installed and removed.
The price of the belt drive is not too high.
Simple in construction.
Low maintenance cost.
No additional lubrication is needed.
Capable of transferring power vertically, horizontally and in inclined plane too.
Power consumption is quite low.
Knowing just the advantages is not important, therefore here are some disadvantages of the belt drives which are mentioned below:
Loss of power due to slip and creep.
Cannot be used for a very short distance.
Speed is limited to an extent.
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Works very silently.
No possibility of longer life.
Chances of breaking are very frequent.
The operation temperature is just limited within -35 to 85 degrees Celsius. As soon as it exceeds the temperature then it can cause extreme wear and tear.
The angular velocity ratio is not necessarily constant or equal to the ratio of pulley’s diameter due to the slipping.
The chain drive is also used for transferring the power.
Chain drives are usually made up of metal which is stronger and more durable.
The chain drive is used in bicycles, motorcycles etc.
The chain drive is found to be powered via a chain loop.
It is easier to either change or fix it whenever it gets damaged
The chain drive needs a lubricating system
The chain drive is not silent as compared to a belt drive.
Slip in Belt Drive
It is important to have a firm frictional grip within the belt and shaft but at times it becomes insufficient. This can result in some motion in the forward direction of the belt without carrying the driven pulley with it. This is referred to as a slip of the belt which is usually expressed in percentage.
Creep in Belt Drive
Whenever it is found that the belt passes from the slack side to tight side, a certain portion of the belt is found to extend and when the belt passes from tight sight to slack side it gets contacted. Due to these changes in the length, there is a relative motion within the belt and the pulley surfaces. This relative motion is referred to as creep.
Difference Between Slip and Creep in Belt Drive
Creep is referred to as a phenomenon which is caused due to the elastic property of the belt whereas, the conventional slip happens due to insufficient frictional grip within the belt and the pulley. Whereas, the effect of creep and slip, is found to reduce the ratio of the speed along with the power transmission.
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In this article, learn more about the different types of belts and their application, as well as the respective advantages and disadvantages.
Flat belts
The simplest type of belt is the flat belt. It has a rectangular cross-section and was often made of leather in the early days. Today, however, steel or high-strength synthetic materials such as polyamide or aramide are used for tension cords. These force-transmitting cords are embedded in a rubber core between a top cover and a bottom cover. The bottom layer where the belt has contact with the pulley, can be coated with special rubber to increase friction and wear resistance. The top layer on the opposite side only has a protective function.
Figure: Flat belt
Due to their design, flat belts can in principle run on both sides around the pulleys. In this case, both sides of the belt are specially coated. The belt can then be used for multiple belt drives and for crossed belt drives.
Flat belts allow high speeds and high torques to be transmitted (and thus high power). To prevent the flat belt from jumping off the pulley, the cross-section of the pulley has a slight convex crown. Depending on the width of the pulley, this hump usually ranges between 0.3 mm and 1.2 mm. This achieves self-centering of the belt and prevents it from running off and the belt keeps track.
Figure: Pulley for flat belts
Flat belts generally generate very little noise. This also has positive effects on the service life and the efficiency (approx. 98 %) and thus on the maintenance of the belt. Due to the relatively small belt thickness, the belt can be very strongly bent and thus allows the use with relatively small pulleys. A disadvantage of flat belts, however, is the relatively high bearing load caused by the high pretensioning forces.
Flat belts have high efficiency and flexibility as well as low wear and low noise levels; however, they require relatively high pretensioning forces!
V-belts
The high bearing load when using flat belts can be significantly reduced by using V-belts. The wedge-shaped cross-section leads to high frictional forces on the flanks due to the “wedge effect”. Therefore, only relatively low preload forces are necessary to generate the required frictional forces for power transmission. Accordingly, the bearing load is also significantly reduced.
Figure: Standard V-belt (wrapped)
Conversely, with the same pretensioning forces, much higher torques can be transmitted when using V-belts instead of flat belts. To further increase the power transmission, two or more V-belts can also be arranged parallel to each other.
Figure: V-belts
V-belts can transmit significantly higher torques with the same bearing load than flat belts; however, the efficiency is lower!
The so-called groove angle \(\alpha\) is 38° or 32°, depending on the pulley diameter, whereby the belt only has contact with the pulley on the inclined flanks. The V-belt must therefore not touch the groove bottom, as the contact force must only come about by the flanks. Otherwise there would be no wedge effect! For the same radial force (bearing load), the total friction force is significantly higher for V-belts.
Figure: Forces acting on a V-belt
The figure above shows that the radial force \(F_b\) must be balanced with the two resulting normal forces \(F_n\) on the flanks. In this way, a relationship between the radial force and the normal forces can be established using the groove angle \(\alpha\):
\begin{align}
\sin\left(\tfrac{\alpha}{2} \right)&= \frac{\tfrac{F_b}{2}}{F_n} = \frac{F_f}{2 \cdot F_n} \\[5px]
F_n &= \frac{F_b}{2 \cdot \sin\left(\tfrac{\alpha}{2} \right)} \\[5px]
\end{align}
Since the friction force \(F_f\) is proportional to the normal force \(F_n\) according to Coulomb’s friction law, the following equation applies:
\begin{align}
F_{f} & \sim F_n \\[5px]
F_f & \sim \frac{F_b}{2 \cdot \sin\left(\tfrac{\alpha}{2} \right)} \\[5px]
\end{align}
Note, that this frictional force acts equally on both flanks, so that there is a total of twice the frictional force. The following therefore applies to the total frictional force:
\begin{align}
&F_{f,total} = 2 \cdot F_f \sim F_b \cdot \frac{1}{\sin\left(\tfrac{\alpha}{2} \right)} \\[5px]
&\boxed {F_{t,total} \sim F_b \cdot \frac{1}{\sin\left(\tfrac{\alpha}{2} \right)}} ~~~\text{valid for V-belts} \\[5px]
\end{align}
In comparison, the frictional force of flat belts is only proportional to the radial force \(F_b\):
\begin{align}
&\boxed {F_{f,total} \sim F_b } ~~~\text{valid for flat belts} \\[5px]
\end{align}
Consequently, V-belts with the same bearing load \(F_b\) can transmit higher forces by the factor \(\frac{1}{\sin\left(\frac{\alpha}{2} \right)}\) (due to the increased frictional force). Expressed in figures, a factor of 3.1 or 3.6 for groove angles of 38° or 32°.
Since the V-belts only rest on the flanks, they are specially designed for a certain range of pulley diameters as well as for certain wrap angles. Otherwise, for example, belts designed for larger pulleys would bend too much and the flanks would buckle and then no longer rest flat.
Animation: V-belt cross section
Due to the greater belt thickness of V-belts compared to flat belts, the energy required to bend the belt around the pulleys is higher. Therefore, V-belts have a slightly lower efficiency than flat belts (approx. 95 %).
While the transmission ratio for flat belts is determined by the outer diameter of the pulleys, in the cas of V-belts the so-called pulley pitch diameter must be taken as a basis for calculating the transmission ratio due to the special geometry. The pitch diameter \(d\) is defined by the nominal belt width \(b_w\). The nominal width corresponds to the belt width at the level of the neutral axis. Thus, according to the definition of the neutral axis, the nominal width always remains constant even when the belt is bent (i.e. when rotating around different pulley diameters).
It must be noted that V-belts must run in after initial assembly before they can be put into operation. This requires a correspondingly increased preload of approx. 30 % during initial operation.
Over the course of time, different types of V-belts have developed, depending on the application. The most important ones are described in more detail in the following sections.
Standard V-belts
“Classical” V-belts are standardized in Germany according to DIN and have a height to width ratio of 1:1.6. Tension cords made of steel, aramid, polyester or glass are embedded in an elastomer core covered by a top layer. The tension cords run at the level of the nominal width (neutral axis).
Figure: Standard V-belt (wrapped)
To increase friction or wear resistance and to protect the belt from harmful external influences, the V-belt can be covered with a special rubber fabric. This is then referred to as a wrapped V-belt. Such wrapped V-belts are used, for example, in drives for pumps in the chemical industry to convey aggressive media.
Wrapped V-belts offer additional protection against harmful environmental influences!
If, on the other hand, such a rubber casing is missing, the edges of the belt are “raw”, so to speak, and one speaks of an raw edge V-belt. Due to this missing of the relatively stiff sheathing, raw edge V-belts thus have better flexibility. In addition, the force transmission from the pulley to the tension cords does not take place through the sheathing but is transmitted directly throught the core. This results in increased power transmission. To improve the transverse rigidity, elastomer fibres are incorporated transversely to the running direction of the belt.
Figure: Standard V-belt (raw edge)
The advantage of raw edge V-belts compared to classical V-belts is the lower wear due to the lack of wear-prone sheathing and the associated low-noise operation. In addition, the raw edges can be ground in comparison to wrapped V-belts so that belts with narrower tolerances can be produced.
Raw edge V-belts show less wear and higher efficiency than wrapped V-belts!
Narrow V-belts
Compared to standard V-belts, narrow V-belts have a more favourable height to width ratio of 1:1.2. The greater height (at the same width as a classic V-belt) ensures greater power transmission. Conversely, the belt width can be much smaller with the same power transmission. The associated lower belt mass of the narrow V-belt reduces the centrifugal forces occurring during operation, so that higher belt speeds can be achieved.
Figure: Narrow and standard V-belt in comparison
However, the increased belt thickness has an adverse effect on the flexibility. To compensate for this and to be able to use narrow V-belts even with relatively small pulley diameters, they are therefore cogged (so-called narrow cogged V-belts). This increases flexibility even with strong curvatures. This is why narrow V-belts are usually found in the raw edge version.
Figure: Raw edge narrow V-belt (cogged)
The increased power transmission combined with the high flexibility of the cogged narrow V-belts results in a relatively space-saving design of such belt drives. In addition, the lower flexural stiffness reduces the deformation energy required when the belt runs around the pulleys, which increases the efficiency compared to the classic V-belt. For this reason, classic V-belts have to give way more and more to (cogged) narrow V-belts.
Figure: Raw edge narrow V-belt (cogged)
Narrow V-belts offer higher transmittable powers than classic V-belts!
Wide V-belts (variable speed belts)
So-called wide V-belts with a height-width ratio of over 1:2 are used for heavy power transmissions and for applications where large speed changes occur. Therefore they are also referred to as variable speed belts.
Figure: Raw edge wide v-belt (variable speed belt)
Variable speed belts are usually cogged to reduce flexural stiffness. Such belt types are used in continuously variable transmissions in which the pulley diameter is changed by an axial shift to adjust the transmission ratio.
Double V-belts (hex-belts)
Double V-belts are basically two V-belts, that are put on top of each other. Both sides of the belt can therefore be used to transmit power. Due to their cross-sectional shape, double V-belts are also referred to as hex-belts. Hex-belts are able to drive two pulleys with opposite sense of rotation. The double V-belt can also be used when the direction of rotation is to be reversed.
Figure: Wrapped double V-belt (hex belt) Animation: Double V-belt (hex belt)
Kraftbands
If several individual V-belts are connected to each other by a cover plate, this is referred to as a kraftband (“kraft” = German word for “power” and “band” = German word for ribbon). Such a combination of several V-belts ensures, among other things, that individual V-belts do not jump off the pulley under impact loads. Kraftbands usually consist of cogged narrow V-belts in the raw edge version.
Figure: Wrapped kraftband Figure: Raw edge kraftband
Poly V-belts (serpentine belts)
The poly V-belt (also called serpentine belt or V-ribbed belt) is a mixture of a flat belt and a V-belt, whereby the tension cords run over the entire nominal width (neutral axis) in contrast to the kraftband. Such a multible ribbed belt thus combines the advantages of both belt types to a special degree, i.e. high flexibility combined with high power transmission and relatively low bearing load. Serpentine belt are used, for example, in multiple drives in which one pulley drives several other pulley. This is the case in automobiles, for example, where the engine has to drive not only the alternator but also the pump for the servomotor, the air conditioning compressor, the fan and the water pump.
Figure: Raw edge poly v-belt (serpentine belt)
Round belts
Round belts are special belts that are used almost exclusively for motion transmission and less for power transmission. Due to their symmetrical cross section, round belts can very easily be guided in different directions with the aid of guiding pulleys. The figure below shows the motion transmission of a round belt for centripetal force measurement.
Figure: Round belt
Timing belts (synchronous belts)
With friction-locking belt types such as flat belts and V-belts, slippage will occur, which reduces the efficiency and control accuracy accordingly. However, this can be prevented by toothed belts, as the teeth attached to the belt surface then transmit the force positively. Slippage cannot take place. Therefore, toothed belts are always used when precise positioning is required. For this reason toothed belts are also called timing belts or synchronous belts.
Figure: Timing belt (synchronous belt)
The figure below shows the timing belts used to control the printhead of a 3D printer.
Figure: Timing belt for positioning a 3D-printer head
Belt drives are widely used in many industries for power transmission since they are cheap and easy to maintain. However they are often a source of vibration due to misalignments, belt resonance, and belt wear.
The main purpose of belt drives is to transfer power between machines such as motor and fan. They are subject to rotary and push-pull motions with varying dynamic characteristics. Belts are friction drives, which mean they depend on friction between the belt and pulley/sheave to transmit power.
The most common types of belt drives include:
Round belts
Round belts are are generally made of rubber. This type of belt is generally used for light loads, such as in a sewing machine or a vacuum cleaner.
V belts
V belts are arguably the most widely used belts in industry. V belts have a V shaped cross-section, which rests against the side of V pulley under tension. The V shaped cross-section prevents belt from slipping off.
Flat belts
Flat belts are also used to transmit power from one shaft to another. They are generally classified as either small woven endless belts or higher power flat belts. The woven endless belts are especially useful where minimum vibration is required at the driven pulley due to semi-elastic material used in construction. The higher power flat belts are often useful because they eliminate the need to high belt tension used to grip pulleys, which in turn reduces the load on the shaft bearings. The material used for high power flat belts is sticky yet abrasion-resistant rubber compounds.
Timing/toothed belts
Timing belts are toothed belts that use their teeth for power transmission, as opposed to friction. This configuration results in no slippage, and therefore, the driving and driven shafts remain synchronized. It’s more expensive to manufacture due to complexity of the belt and pulley shapes.
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