In one way of the other power must be transferred from one source of energy to another in a mechanical device, the most common and cheapest form is to use a belt and pulley. This power is either gotten from an electrical or mechanical generator to transfer a rotational motion to the application.
Pulley is always mounted on a rotary part of the energy source so that power can be transferred through a belt to the device. Thus, serving as a source of power to that device.
Apart from the above explained, some specific types of pulleys are design similar to levers, to lift loads. These pulleys are wheel-shaped with a groove that allows a cord to fit inside the groove. This will further explain.
Talking about power transmission, a belt is the cheapest form. It’s a loop of flexible material used to link two or more rotating shafts mechanically, often in a parallel form. These belts may be used as a source of motion as it transmits power more efficiently.
Today we’ll be discussing the definition, functions, applications, selection consideration, types, specifications, working, as well as advantages and disadvantages of belt and pulley.
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Definition of pulley and belt
Pulleys can be seen in more than one form as they serve a variety of purposes in the industrial world. First of all, a pulley is a wheel on an axle or shaft designed to support movement and change direction of a belt or taut cable. The device helps in power transmission using a cable or belt.
In a belt and pulley system, a belt runs along a pulley’s groove so that the power can be transfer either from one pulley to another or from the pulley directly to the application that requires power.
Pulley is also used to guide a cable or exert a force and it changes the direction of force, making pulling down easier than lifting up. These kinds of pulley may be called “Sheave”. Well, a drive element of a pulley system can be rope, cable, belt, or chain.
A belt drive is a loop of a flexible material that transfers movement from one rotating pulley to another. Each are held on a shaft.
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Functions of belt and pulley
Below are the functions of a belt drive and pulley in their various applications:
The primary function of a belt is to transfer power (rotary energy) from one source to another. Whereas pulley that has a groove around its circumference allows a belt to smoothly through it when transmitting rotational motion.
A pulley design to attain different diameter functions as it’s used to increase or decrease the speed of the application of its powers.
A specific type of pulley is used to change the direction of the force. This pulley is often seen on heavier applications and they are not used for transmission of rotational motion.
Finally, the function of a belt is to exert force from one direction to either vertical or horizontal direction, depending on the position of the energy source and position of application it will be powering.
Pulleys that are not used to transmit rotational motion functions as they are used to lift heavy loads. The pulley helps o reduces the amount of force required to lift a load.
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Applications of belt and pulley
Below are the applications of a belt and pulley:
In applications where belt drives on a pulley, they are used in automotive engines such as cars, trucks, buses, stationary power generators, marine engines, aviation engines, etc.
Belt and pulley are also used in air compressor engines, agricultural equipment, conveyors, etc.
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In fact, a belt and pulley are purposely designed on any application that requires a rotational motion from another source. There are tons of machines and equipment out there from larger ones to smaller ones such as winches, treadmills and washing machines, etc.
A single pulley that changes the direction of force is used on cranes, well to lift out a bucket, raising a flag, adjusting a window blind, etc.
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Below are examples of the application of a belt and pulley:
- In a bulldozer, it’s used to do its lifting
- An extended ladder
- Using a crane in a construction site
- The working of an escalator going up or down
- Opening and closing a garage door
- Belts and pulley in a vehicle
- Elevation uses several pulleys in its working
- Various fitness or exercise equipment uses a pulley
- Curtain at a theater hall uses pulley, making them easy to pull apart.
- A hoisted-up flagpole or when it’s taken down
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Below are things to consider while selecting a drive and pulley for a device:
- The source of energy use in transmitting energy.
- Center distance between the shaft and pulley.
- The speed of the driver and driven pulley.
- Power transmitted between the system.
- The layout of shafts.
- The flexibility of the belt
- Reliability and durability of the belt
- How much high tensile stress it can withstand.
- Low weight per unit length.
- Resistance to wear and fatigue
- High coefficient of friction between belt and pulley.
- A temperature that can be resisted.
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Belt and pulley Material
Below are materials often used for making belt:
- Leather belt
- Cotton or fabric belt
- Balata belt
- Plastic belt
- Rubber belt
A pulley is made of a metal material often made from cast iron, aluminum alloy, etc. the material used is depending on where the pulley will be used.
Diagram of a belt and pulley system:
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Types of pulleys
Below are the various types of a pulley and their functions:
Open belt drive (Pulley)
In these types of pulleys, the shafts rotate in the same direction. which means, the direction of rotation is the same as the driven pulley. The shafts are arranged in a parallel direction.
The distance between a pulley and the driver will determine whether the upper side will be the slack side of the blow side will be tight.
Crossed belt drive (pulley)
In crossed types of pulleys, the transmitted power is more, but it cannot run faster. This may cause wear and tear to the belt. The shaft rotates in opposite with the pulley. To eliminate wear and tear in these pulley types, more distance should be placed between the pulley, and then it should be run at low speed.
Fast and loose cone pulley
In these types of pulleys, there are two pulleys in it, the first one is faster than the other. The fast pulley is mounted on a shaft with a keyed joint whereas the loose pulley runs freely on the shaft. This loose pulley does not transmit any power.
These types of pulleys are suitable for multiple machines that derive power from a single source.
Stepped cone pulley
The stepped cone pulley is also known as the speed cone. In these pulley types, there are more than one pulleys of different diameters attached to be adjacent to each other. Stepped cone pulley is used in applications that required changing of gear or where the speed of driven shaft change frequently like machines. The same belt is used for different speeds attained.
A jockey pulley is used in a steering section of a system. it’s similar to an idle pulley which is used for increasing the angle of contact in a one belt drive. The function of a jockey pulley is to increase the angle of contact of a belt. This is to help the belt tension is increased and also to offer a high-velocity ratio to the drive.
All the above-explained pulley are used to transmit rotational motion in one way or the other. Some other types of pulley include:
Complex pulley system:
A complex pulley system has a block and tackle system that contains two or more individual drums. Each of these drums has two or more wheels that rotate on the same axle. A rope is looped back and forth between the drums and pulley to help it multiplied so as to accomplish the operations. The complex pulley system is used to move an extremely heavy load.
A compound pulley has both fixed and moveable pulleys, making the load feel lighter. With this, the direction of the force can be easily changed, making the system suitable for moving heavy loads. Sometimes, more motion is required for the work to be properly done.
This system is also called a combination pulley system. it’s designed to make heavier load be lifted with less force. It is often used on a construction site to lift heavy objects like concrete and steel.
The moveable types of pulley consist of a drum that moves while moving an object. There is no change in direction of the force but the object still feels much lighter than it supposes to. A moveable pulley moves more freely. It’s often seen in an elevator.
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Types of belts
Below are the various types of belt used in different applications:
Flat types of belts are used where low power and more speed is required. They are rectangular cross-section types and the shaft distance must be between 5 to 10 meters. These belts transmit power by using friction produce between the belt and pulley. Finally, the pulley’s rotation in flat belts is in the same direction and the efficiency of the belt is around 98%. However, the belt makes little noise.
The v belt types are used where shaft distance is less than 2 meters. They offer moderate speed and high power, unlike flat belts. V belts are in trapezoidal cross-section. Multiple drives are possible in these types of belts.
A circular belt is used where the shaft distance is more than 5 meters. It’s a circular cross-section and it is used to transmit high power. Circular types of belts are used on applications that require smaller initial tension and vibration and noise will not be produced.
Timing belts are popular types of belts that serve alternative purposes. They are mainly used in internal combustion engines to transmit power. They are known as positive drives as they are more reliable and precise.
Some other types of belt include:
- Spring belt
- Multi-groove belt
- Ribbed belt
- Film belt
- Specialty belt (belt used for transmitting power on the tension side of the loop)
- Rolling road (belts used in rolling roads for wind tunnels).
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The working of belt and pulley is less complex and can be easily understood. With the above explanation, am sure you are now familiar with the basics of belt and various types of pulley including their applications. The video below will give you practical knowledge of how a belt-driven pulley works. It will also be exposed to the working of pulley that’s used to carry heavier loads.
Watch videos below:
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Advantages and disadvantages of belt and pulley
Below are the benefits of a belt and pulley in their various applications:
- Low power consumption
- Low maintenance cost
- Easy to install and dismantle
- Simple in construction
- Lubrication is not required
- Can be easily replaced, due to its low cost.
- Power can be transfer vertically, horizontal, or incline.
Despite the good advantages of a belt and pulley system some limitations still occur. below are the disadvantages of belt and pulley systems:
- Power loss could occur due to slip and creep.
- Can’t be used in a very short distance
- Speed is limited to some extent
- It’s very quiet
- Limited operation temperature between 35 to 85 degrees.
- They don’t serve long
- Chances of breakage are common.
- The angular velocity ratio is not necessarily constant or equal to the ratio of pulley’s diameter due to slipping.
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Belts and pulley are great components that can be seen in almost all applications today. They are very important as they help to transmit rotational motion and pulley alone is used to carry heavier loads with ease. In this article, we’ve enlightened on the definition, functions, diagram, types, and working of a belt and pulley system. we also saw their advantages and disadvantages.
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