Page 183 - Root Cause Failure Analysis

GEARBIOXESLREDUCERS

A gear is a disk or wheel with teeth around its periphery, either on the inside edge
(Le., internal gear) or on the outside edge (Le., external gear). A gear provides a posi-
tive means of power transmission, which is effected by the teeth on one gear meshing
with the teeth on another gear or rack (Le., straight-line gear).

Gear drives are packaged units used for a wide range of power-transmission applica-
tions. They are used to transmit power to a driven piece of machinery and to change or
modify the power that is transmitted. Modifications include reducing speed and
increasing output torque, increasing speed, changing the direction of shaft rotation, or
changing the angle of shaft operation.

CONFIGURATION
Several different types of gears are used in industry. Many are complex in design and
manufacture and several have evolved directly from the spur gear, referred to as the
basic gear. Types of gears are spur, helical, bevel, and worm. Table 14-1 summarizes
the characteristics of each gear type.

Spur
The spur gear is the least expensive of all gears to manufacture and the one most com-
monly used. It can be manufactured to close tolerances and is used to connect parallel
shafts that rotate in opposite directions. The spur gear gives excellent results at mod-
erate peripheral speeds, and the tooth load produces no axial thrust. Because contact
is simultaneous across the entire width of the meshing teeth, it tends to be noisy at
high speeds. However, noise and wear can be minimized with proper lubrication.

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