What’s a pulley assembly?

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Pulleys consist of a wheel and a belt, rope, chain, or cable to reduce the force needed to lift a load. There are three types of simple sheave sets: fixed, movable, and compound. Pulley assemblies are used in manufacturing, mechanical, industrial, and automotive industries, and can be found in everyday items like bicycles. Each part is adapted to the type of work performed.

In its simplest form, a pulley assembly consists of a wheel that spins freely on its axle and a belt, rope, chain, or cable that runs over the wheel. The purpose of pulleys is to reduce the amount of force required to lift a load, otherwise known as mechanical advantage. The manufacturing, mechanical, industrial and automotive sectors use the pulley assembly. The parts of the pulley differ according to the context in which they are used. For example, the wheel, or wheels, used for an assembly may be grooved to accommodate a rope or rough for a belt that will turn under friction.

There are three different systems of simple sheave sets: the fixed sheave, the movable sheave, and the compound sheave. Fixed pulleys consist of an axle that remains fixed in a certain position, while a rope, belt, chain or cable runs over it. Mobile pulleys consist of a fixed shaft, a free shaft and a rope, belt, chain or cable. A compound sheave set is a combination of the fixed and movable sheave systems. These compound assemblies can significantly increase the value of mechanical advantage in a system.

In manufacturing, mechanical, industrial and automotive industries, pulley assemblies follow the same basic patterns as simple pulley systems. Pulley parts can differ in their construction, how force is exerted, and whether or not the directional movement is continuous. Depending on the use of a pulley, each individual part and action is adapted to the type of work performed by the pulley.

A winch and rope sheave assembly, for example, may consist of a strap wrapped tightly around two axles/wheels. While a motor spins one axle/wheel, the friction of the tightly coupled belt spins the two axles/wheels simultaneously and indefinitely. The flanges of the axles/wheels can also be grooved inward specifically to make sure the belt does not come loose.

Pulley assemblies can also be found in everyday items such as bicycles, which use a chain drive pulley assembly between the rear wheel and the pedals. At the base of the pedals and rear wheel are two splined axles in the shape of ‘teeth’, around which a chain is placed to connect the two. The chain is made up of interlocking links, where the “teeth” fit into the spaces between the links. When the bicycle is pedaled, the pedal axle pulls on the chain links, causing both the pedal axle and the axle in the center of the rear wheel to turn.

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