The basic function of a gear is to produce mechanical advantage and any gear device is able to change the speed, torque and direction of its power source. One such gear which has the ability to produce higher torque and also lower speed gear ratio is the worm gear. This worm gear is actually a special form of helical gear. In this context one must mention that gears are broadly classified into spur gears and helical gears on the basis of their teeth. While the spur gears have teeth projecting radially. The helical gears have teeth set at an angle which are not parallel to the gear axis. The method to differentiate between worm gears and helical gears is that they have at least one tooth which persists for an entire rotation.(More Info: Worm Shaft and Worm Gears)
The worm gears have a large helix angle which is not specified but the lead angle is given which comes to ninety degrees minus the helix angle. These gears which resemble screws basically have two major components which are the worm or the screw and the worm gear which is the wheel. Among the two the worm can drive the gear but not always vice versa. Worm gears are very simple and effective buy they have lower efficiency. They can be used to reduce speed but not to increase the drive. Worm gears therefore have specialised applications in mining, elevators, conveyors, rolling mills, rudders and various other industries.(More Info: Turbine Gear)
Another gear which is used for specific applications is the crane gear. These gears are mainly effective when it comes to pulling or pushing away objects. Crane gears must be made of heavy iron and the edges need to be sharp. This is specifically so that the crane does not slip, because that would impede the functioning of the crane gear. These gears include winches and freight elevators among others.
Source By: Industrial Gears Manufacturers
Crane Duty Helical Gearbox 