The primary benefit for worm gears is their capability to provide high reduction ratios and correspondingly high torque multiplication. They can also be employed as acceleration reducers in low- to medium-quickness applications. And, because their reduction ratio is founded on the quantity of gear teeth only, they are smaller sized than other types of gears. Like fine-pitch lead screws, worm gears are typically self-locking, which makes them perfect for hoisting and lifting applications.
Although the sliding contact decreases efficiency, it provides very quiet operation. (The utilization of dissimilar metals for the worm and gear also contributes to quiet operation.) This makes worm gears suited to use where noises should be minimized, such as for example in elevators. In addition, the use of a softer material for the gear means that it could absorb shock loads, like those experienced in major equipment or crushing devices.
The meshing of the worm and the apparatus is an assortment of sliding and rolling actions, but sliding contact dominates at high reduction ratios. This sliding action causes friction and high temperature, which limits the performance of worm gears to 30 to 50 percent. In order to minimize friction (and therefore, high temperature), the worm and equipment are made from dissimilar metals – for example, the worm may be made of hardened metal and the gear manufactured from bronze or aluminum.
Like a ball screw, the worm in a worm gear may possibly have an individual start or multiple starts – meaning that there are multiple threads, or helicies, on the worm. For a single-start worm, each total turn (360 degrees) of the worm increases the equipment by one tooth. Thus a gear with 24 teeth will provide a gear reduction of 24:1. For a multi-commence worm, the gear reduction equals the number of teeth on the apparatus, divided by the number of begins on the worm. (That is different from almost every other types of gears, where in fact the gear reduction is normally a function of the diameters of the two components.)
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