Different types of Belt-Drives used in Mechanical applications
Do you want to transmit power from your engine to your mechanism using belt drives but don’t know which to use? Well then, I just have the right blog for you. Before I answer your question, look at other forms of drives mentioned below that you could possibly use and if they don’t suit your application, continue reading the blog and choose your belt drive accordingly.
Why Drives are used?
Available energy/power is required to be transmitted to get the desired motion and work. When the power is transmitted from input to output using mechanical elements it is known as mechanical power transmission or a drive. Mechanical elements like friction disc, various types of belts, rope, chain, gears, couplings, etc. are used for power transmission.
So, there are two types of drives — Flexible Drives and Fixed Drives.
In all those drives where driver and driven shafts are connected by an intermediate flexible element are classified as flexible drive. Belt drive, chain drive and rope drive fall under this category as flexible element such as belt, chain and rope exist in between driver and driven shafts. On the other hand, when driver and driven shafts are connected by two rigid bodies, then it is termed as rigid drive. Any intermediate flexible element does not exist here. Gear drive comes under this category.
Belt Drives:
Belt drive is a mechanism that transmits rotational motion from one pulley mounted on a shaft to another by means of a belt.
· It is used to transfer the power from one system to another system.
· The belt drive is used for continuous power transmission.
· The belt transmits torque from the driving pulley to the driven pulley by means of the forces of friction that arise between the belt and the pulleys.
· The belt is a flexible element of a mechanical system.
Why to choose a belt drive?
1. Belts permit flexibility ranging from high horsepower drives to slow speed and high-speed drives.
2. Belt drives are less expensive than chain drives for low horsepower and low ratio applications.
3. Belts require no lubrication.
4. Single belt drives will accept more misalignment than chain drives.
5. Flat belts are best for extremely high-speed drives.
6. Belt drives cushion shock loads and load fluctuations.
7. Belts will slip under overload conditions, preventing mechanical damage to shafts, keys, and other machine parts.
Types of belt drives
1.Open belt drive
2. Closed or crossed belt drive
3. Stepped cone pulley
4. Fast and Loose pulley Drive
5. Jockey pulley drive
Open Belt Drive
In open belt drive, belt proceeds from top of one pulley to the top of other pulley without crossing.
When to choose open belt drive?
1. When the two shafts are horizontally placed or little bit inclined and are parallel.
2. When low power transmission is required.
3. When you want the direction of rotation of the output shaft same as that of input shaft.
4. Torque and speed conversions over a distance.
5. Open belt drive is not suitable for small distances between centres of pulleys.
6. To carry material from one location to another over a straight line.
Examples: Conveyor Belts (Carrying the material), Flour Mills (Torque Conversion over large distance). Both the examples also need the direction of rotation of output shaft to be the same.
Cross Belt Drive
In crossed belt drive, belt proceeds from top of one pulley to the bottom of another pulley and thus crosses itself.
When to choose?
- When the two shafts are horizontally placed or little bit inclined and are parallel.
2. When high power transmission is required.
3. When the required rotation of pulleys is in opposite direction.
4. For greater angle of contact between belt and the pulleys.
5. Cross belt drive works even for small distances between centre.
Stepped Cone Pulley
A pair of pulleys, each with a set of steps of increasing diameter, mounted on parallel shafts such that the smallest and largest diameters of one are aligned with the largest and smallest diameters of the other, thereby allowing a wide range of speed ratios to be achieved by shifting a belt from one end of the pair to the other.
When to choose?
To obtain different speed and torque ratios using one driving shaft(pulley) and one driven shaft (pulley).
Jockey Pulley Drive:
The term jockey wheel predominantly refers to a wheel-based mechanical system used for steering or guidance. It is a guide wheel — usually operating as a pair — which is used to move, retain, locate and (usually) add tension to a belt.
When to choose?
1. When open belt drives angle of contact is less.
2. When required belt tension is not achieved.
3. Idlers should be used to reduce belt vibration by supporting a segment of belt that is prone to vibration/oscillation.
Example: Idler pulleys are used in IC engines for positive clutching action by running the idler pulley on the slack side of the flat-belt drive from engine to transmission.
Fast and Loose Pulley Drive:
This type of belt drive is used when the driven or machine shaft is to be started or stopped whenever desired without interfering with the driving shaft. A pulley which is keyed to the machine shaft is called a fast pulley and run at the same speed as that of the machine shaft. A loose pulley runs freely over the machine shaft and is incapable of transmitting any power. When the driven shaft is required to be stopped, the belt is pushed on to the loose pulley by means of a sliding bar having belt forks.
Quarter Turn Drive:
It is useful when the power is to be transmitted in perpendicular direction of driving pulley or the shafts at a right angle with each other, as shown in the figure.
Now that you have selected the type of arrangement or mechanism for your drive. Let’s select the type of belt which will running that drive.
Now that you have chosen the suitable belt drive on the basis of required geometric arrangement, it’s time for choosing a belt.
Types of Belt
Flat Belt
This is a kind of rectangular cross-section. It is used where low power is required and speed is more. Generally, the shaft distance is between 5 to 10 meters. Flat belt transmits power by using friction produce between the belt and the pulley. The pulley rotation in the flat belt is in the same direction. The flat belt has an efficiency of around 98 percent. Very little noise comes in this belt.
Flat belt are best-suited for applications with smaller pulleys and large central distances. This type of belt is used in many power transmission applications.
V — Belt
V belts are in the trapezoidal cross-section. V belts are used where shaft distance is less than 2 meters and used for moderate speed and high power. In belt the multiple drives are possible.
V- belts are used in variable-speed drives. They offer the best combinations of traction, speed, bearing load and service life. At the same level of tension, they transmit higher power than flat belts. These are generally used for centre distances ranging from 1m ~ 2m as they are not suitable for large distances.
Circular Belt
It is a circular cross-section. Circular belts are used where more than a 5-meter shaft distance. It is used for high power transmission. Circular belts are also used where smaller initial tension is required and absences of vibration and noise are there.
There are two types of grooves for the pulley — trapezoidal with an angle of 40° between the sides and half round with a radius equal to that of the belt.
Timing Belt
Timing Belt can be best described as Belt with integrally moulded teeth on its inside which makes positive engagement with axially grooved pulley. Timing Belt is also known as synchronous Belt or positive-drive Belt. It is a precise and reliable type of belt. Timing belts are mainly used inside (internal combustion type) the system to transmit power. Timing Belts exhibit important properties such as fixed speed ratio, no re-tensioning after installation, low maintenance with wide variety of power transmission capacities and drive speeds. Timing belts use teeth that mesh with grooves in a pulley to synchronously drive the system. Its unique feature enables it to use in positive drive resulting in precise movement of drive components.
Timing belt are used to drive camshafts or for the secondary transmission of some motorcycles. They are also used on many industrial or agricultural machines. These are used in applications where positive drive is required and slipping can’t be tolerated.
It’s quite important to choose the correct belt material so that one does not have to change the belt regularly because of damage.
Factors considered while choosing a material for belt.
1. More flexibility.
2. Reliability and Durability.
3. Material should be able to withstand high tensile stresses.
4. It should resist high temperatures.
5. Should have low weight per unit length.
6. The material should have a high friction coefficient.
7. It should have excellent resistance to wear and fatigue.
Belt Materials:
Plastic belt
o These types of belt materials are made up of plastic sheets and rubber layers.
o The main advantages of a plastic belt are that it can design almost any size.
Balata belt
o Balata belts are like rubber type belts, but they are stronger than rubber belt.
o This is used for food packaging conveyor.
o This is not used for high temperatures because balata becomes sticky gum at a higher temperature.
Leather Belt
The leather is the most significant material for flat belts. Leather belts are made from steer leather (cut from either side of the backbone of a steer). It ensures the greater tensile stress on the outer side of the belt is on the flesh side of the belt.
Rubber Belt
They are made by impregnating fabric or canvas with rubber and have a thin layer of rubber on the surface of the belt. They are suitable where the belt exposed to moist, e.g. sawmills, paper mills.
Cotton or Fabric Belt
The fabric belts are commonly used for temporary application. The advantage of this type includes they are suitable for a warm climate, in damp and exposed positions. Normally used in farm machinery and belt conveyor since they need a little attention.
Industrial Applications of Belt Drives
CVT — Continuously Variable Transmission
- CVT is an advanced technology of automatic transmission.
- Unlike traditional automatic transmissions, continuously variable transmissions do not have a gearbox with a set number of gears.
- It varies the transmission ratio continuously.
- Shifts automatically with an infinite number of ratios.
References
[1] V.B.Bhandari, Text book on Machine Design, Tata McGraw Hill, New Delhi.
[2] Module for belt drives, ME Dept., IIT Kharagpur.
[3] www.wikipedia.com/Belt drives, belt transmission.
[4] Learnmechanical.com/Belt drives
[5] Theengineerspost.com/Belt drives