The primary good thing about worm gears is their capability to provide high reduction ratios and correspondingly high torque multiplication. They can even be utilized as rate reducers in low- to medium-acceleration applications. And, because their lowering ratio is founded on the number 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 suitable for hoisting and lifting applications.
Although the sliding contact minimizes efficiency, it provides extremely quiet operation. (The make use of dissimilar metals for the worm and gear also plays a part in quiet operation.) This makes worm gears suited to use where noise should be minimized, such as in elevators. In addition, the use of a softer material for the apparatus means that it can absorb shock loads, like those knowledgeable in serious equipment or crushing equipment.
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 actions causes friction and heat, which limits the proficiency of worm gears to 30 to 50 percent. As a way to minimize friction (and for that reason, heat), the worm and equipment are constructed of dissimilar metals – for instance, the worm may be made of hardened metal and the gear made of bronze or aluminum.
Just like a ball screw, the worm in a worm gear may well have an individual start or multiple starts – and therefore there are multiple threads, or helicies, on the worm. For a single-start worm, each full switch (360 degrees) of the worm advances the gear by one tooth. Thus a gear with 24 teeth provides a gear reduction of 24:1. For a multi-start worm, the apparatus reduction equals the number of teeth on the gear, divided by the number of starts on the worm. (This is different from most other types of gears, where in fact the gear reduction is a function of the diameters of both components.)
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