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What are Worm Gears?

Worm-gear motors are used in elevator manufacturing.
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  • Written By: M. McGee
  • Edited By: Lauren Fritsky
  • Last Modified Date: 15 July 2014
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    Conjecture Corporation
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Worm gears are a type of gearing system. The object of a worm gear is the transferal of power by 90 degrees, often with a change in torque and reduction in size. Since the entire assembly may exist in a single plane, these operate in locations where the gear system needs to be either very small or low-profile. Unlike many gear systems, worm gears usually work in one direction only; the shafts spin and the gears turn in one direction. These gears are typically found in elevator and escalator motors, as well as small electric motors and large industrial machinery.

The term worm gear can be confusing. It is used to describe the entire assembly or either of the gears. Depending on where a person lives, the term worm drive or worm wheel may be much more common.

Regardless of what the parts are called, a typical worm gear consists of two shafts and two gears. One shaft feeds into a screw, usually called a worm screw. This screw is connected to a standard spur gear. When used in this setup, the spur gear’s name is technically the worm gear, but that is only when the entire assembly isn’t called by that name. The spur gear is connected to a shaft that runs out at a 90-degree angle.

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This assembly, with the exception of the shaft connected to the spur gear, works within a single plane; this means it is flat. This allows power to come into the system in one direction and leave on a 90-degree turn. The shaft connected to the spur gear is often connected directly to the movement system, allowing the worm gears to sit flush to the item it works with. This small profile allows it to work within walls, next to frame pieces or inside an engine without making a large impact on the item’s size.

Since the spur gear may be of nearly any size in relation to the screw, it is possible to change the torque of the gear using this system. As a result, worm gears are often used as a reduction system. They reduce the size of the assembly while outputting as much or more force than what was put into them.

Worm gears are single-directional. The screw can easily turn a spur gear, but it is nearly impossible for the gear to move the screw. As a result, these gears are used in locations where power shouldn’t transfer backwards through the system. This is common in industrial motors, where an unexpected backwash of power could result in a loss of human life.

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