Worm gears – contact stress analysis

The coefficient of friction, f, varies widely depending on variables such as plant materials, lubricants, temperature, surface finishes, precision mounting and sliding velocity. The friction coefficient is typical of well lubricated worm gears brought in Fig.15.10.

Fig. 15.10 Friction of well lubricated worm gears, A for cast iron worm and gear and B for case hardened steel worm and phosphor bronze worm gear

Sliding velocity is vs associated with the worm and gear pitch line velocities and the angle worm spread by:



a) Eqn. 15:20 shows that a relatively high coefficient of friction, gear tangential force becomes zero, and the equipment set “self-locks” or not “reform.”

b) With this condition, no amount of torque producing worm bid.

c) Self-locking occurs, if at all, with the drive gear.

d) This is desirable in many cases and helps hold the burden of the recession, such as self-locking screw power.

The worm gear set self-locks where the force to zero, occurs if:


Can series worm gear always be overhauled or ever overhaul, depending on the coefficient value selected friction (ie, λ and a point less φn).