Worm gear system is comprised of worm shaft and worm wheel. Worm gear is similar to a spur gear, whereas worm shaft is like a screw thread. Worm gear system is used to reduce the input speed and transmit torque to the further system.
As compared to typical spur gear system, the size of worm gearbox will be small. Depending on the number of starts, the gear ratio can be maintained. A worm wheel having 30 teeth will have a reduction ratio of 30:1.
Types of worm gear:
Throated, non throated and double throated worm gears. In single throated worm gears, the worm wheel is the component which is throated. In non throated worm gears, the machining process is done around the worm wheel circumference. In double throated system, both gears are throated. This results in higher torque loading capacity.
Hourglass worm has one or more teeth, and the diameter is higher on the sides and smaller at the center.
Double envelope worm gear are completely mated worm wheel and shaft.The advantages of using a worm gear system is that it can be self locked. When using a single start worm, and a large ratio gear, the direction of transmission is not reversible. Though, this effect reduces considerably when using a multi start worm shaft. The self locking of the worm gear is dependent on pressure angle, lead angle and the friction coefficient.