worm gear shaft

The primary benefit of worm gears is their ability to provide high reduction ratios and correspondingly high torque multiplication. They may also be utilized as acceleration reducers in low- to medium-speed applications. And, because their reduction ratio is based on the amount of gear teeth only, they are smaller sized than other types of gears. Like fine-pitch business lead screws, worm gears are usually self-locking, which makes them ideal for hoisting and lifting applications.

Although the sliding contact reduces efficiency, it provides extremely quiet operation. (The usage of dissimilar metals for the worm and gear also plays a part in quiet operation.) This makes worm gears suited to use where noises should be minimized, such as in elevators. Furthermore, the use of a softer material for the gear means that it can absorb shock loads, like those skilled in weighty equipment or crushing devices.

The meshing of the worm and the gear is a mixture of sliding and rolling actions, but sliding contact dominates at high reduction ratios. This sliding actions causes friction and high temperature, which limits the performance of worm gears to 30 to 50 percent. So that you can minimize friction (and for that reason, temperature), the worm and equipment are constructed of dissimilar metals – for instance, the worm could be made of hardened steel and the gear made of bronze or aluminum.

Like a ball screw, the worm in a worm gear could have a single start or multiple starts – meaning that there are multiple threads, or helicies, on the worm. For a single-start worm, each complete switch (360 degrees) of the worm increases the gear by one tooth. So a gear with 24 teeth will provide a gear reduction of 24:1. For a multi-begin worm, the apparatus reduction equals the quantity of teeth on the apparatus, divided by the amount of begins on the worm. (This is different from most other types of gears, where the gear reduction is a function of the diameters of the two components.)

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