What’s a flat pulley?

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Flat belt pulleys are used to drive machinery with a single power source. They have a slight pitch and work with an opposite pulley to keep the belt on the equipment. They were used in early manufacturing plants to power all machinery with a centrally located motor, saving costs and reducing heat. Flat pulleys can be slid along the drive shaft to any position and changing the diameter can alter the speed and torque. They were also used in outdoor farm equipment to drive stationary machinery.

A flat pulley is used to drive machinery commonly operated by a single power source. Although it appears flat, the flat belt pulley actually has a slight machined pitch and works in concert with the opposite pulley on the drive shaft; the pulley on the machinery or tool helps keep the belt on the equipment and operate without throwing the belt. The typical flat belt pulley design is a very heavy cast iron pulley with a keyed center hole. This keyed hole allows the pulley to slide onto a solid steel drive shaft and prevent it from slipping with a key and retaining bolt. To remove some unnecessary weight and to help the unit stay cool, most flat pulley designs use a spoked center rather than a solid steel center in the pulley.

In early manufacturing plants, a single engine was used to power all of the plant’s machinery and tools. This was accomplished through a series of drive shafts and pulleys that span the factory ceiling. Each workstation had its own flat belt and flat belt pulley which was driven by the overhead drive shaft system and powered the particular equipment into the individual workstation. The worker simply hooked up a tensioner which tightened the belt and the workstation was powered. It was very much like a type of clutch that brought work station tools and machinery to life.

The centrally located motor and use of a flat belt pulley drive system allowed the plant to operate without the added heat that individual motors would have produced at work stations. This also saved costs, as only one engine operator had to be hired per shift. A flat pulley was also able to be slid along the drive shaft to any position required by a new workstation. By changing the diameter of a flat pulley, the speed of a machine could be altered. Typically, a larger diameter flat pulley would make the car run slower, but with additional torque, a smaller diameter flat pulley would result in a faster machine with less torque.

Some outdoor farm equipment was equipped with a flat belt pulley to drive stationary machinery. Both threshers and sawmill equipment used flat belts driven by the tractor’s flywheel to operate. The belt tension was adjusted in these configurations by changing the position of the tractor.




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