Gear Products and Suppliers | Gear Knowledge Menu
New gears contain surface imperfections or
roughness that are inherent to the manufacturing process.
During the initial run-in period, these imperfections are
reduced through wear. Smoothing of the gear surfaces is to
be expected . Mild wear will occur even when adequate
lubrication is provided, but this wear is limited to the
oxide layer of the gear teeth. Mild wear is beneficial
because it increases the contact areas and equalizes the
load pressures on gear tooth surfaces. Furthermore, the
smooth gear surfaces increase the film thickness and improve
The amount of wear that is acceptable
depends on the expected life, noise, and vibration of the
gear units. Excessive wear is characterized by loss of tooth
profile, which results in high loading, and loss of tooth
thickness, which may cause bending fatigue.
Wear cannot be completely eliminated. Speed,
lubricant viscosity, and temperature impose practical limits
on gear operating conditions. Gears that are highly loaded,
operate at slow speeds, i.e., less than 30 m/min (100
ft/min), and rely on boundary lubrication are particularly
subject to excessive wear. Slow-speed adhesive wear is
highly dependent upon lubricant viscosity. Higher lubricant
viscosities provide significant wear reduction, but
viscosities must be carefully selected to prevent
The following guidelines should be observed
to minimize the onset of adhesive wear in gear units:
Gear teeth should have smooth surfaces.
If possible, the run-in period for new
gear units should be restricted to one-half load for the
first hours of operation.
Use the highest speeds possible.
High-load, slow-speed gears are boundary lubricated and
are especially prone to excessive wear. For these
applications, nitrided gears should be specified.
Avoid using lubricants with
sulfur-phosphorus additives for very slow-speed gears
(less than 3 m/min, or 10 ft/min).
Use the required quantity of cool,
clean, and dry lubricant at the highest viscosity