The primary advantage of worm gears is their ability to provide high reduction ratios and correspondingly high torque multiplication. They may also be applied as velocity reducers in low- to medium-speed applications. And, because their reduction ratio is founded on the number of gear teeth alone, they are more compact than other types of gears. Like fine-pitch business lead screws, worm gears are typically self-locking, making them ideal for hoisting and lifting applications.
Although the sliding contact reduces efficiency, it provides very quiet operation. (The usage of dissimilar metals for the worm and equipment also contributes to quiet operation.) This makes worm gears ideal for use where noises should be minimized, such as for example in elevators. In addition, the utilization of a softer materials for the apparatus means that it can absorb shock loads, like those skilled in weighty equipment or crushing equipment.
The meshing of the worm and the apparatus is a mixture of sliding and rolling actions, but sliding contact dominates at high reduction ratios. This sliding actions causes friction and heating, which limits the performance of worm gears to 30 to 50 percent. To be able to minimize friction (and therefore, heat), the worm and gear are made from dissimilar metals – for instance, the worm may be made of hardened metal and the gear manufactured from bronze or aluminum.
Such as a ball screw, the worm in a worm gear could have an individual start or multiple starts – meaning that there are multiple threads, or helicies, on the worm. For a single-start worm, each complete change (360 degrees) of the worm increases the equipment by one tooth. Consequently a gear with 24 teeth will provide a gear reduced amount of 24:1. For a multi-commence worm, the apparatus reduction equals the quantity of teeth on the apparatus, divided by the amount of starts on the worm. (This is different from almost every other types of gears, where the gear reduction is usually a function of the diameters of both components.)
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