Efficiency Of Worm And Worm Gearing

Machine Design

Gear Drives

Introduction:

The efficiency of worm gearing may be defined as the ratio of work done by the worm gear to the work done by the worm.

Expression for the efficiency of worm gearing:

Mathematically, the efficiency of worm gearing is given by

The efficiency is maximum, when

In order to find the approximate value of the efficiency, assuming square threads, the following relation may be used :

 ...(Substituting in equation (i), φ = 0, for square threads)

where φ₁ = Angle of friction, such that tan φ₁ = μ.

The coefficient of friction varies with the speed, reaching a minimum value of 0.015 at a rubbing speed 

  between 100 and 165 m/min. For a speed below 10 m/min, take μ = 0.015. The following empirical relations may be used to find the value of μ, i.e.

Note :

If the efficiency of worm gearing is less than 50%, then the worm gearing is said to be self locking, i.e. it cannot be driven by applying a torque to the wheel. This property of self locking is desirable in some applications such as hoisting machinery.