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Summary:
"Is
there still a place for gearmotors?"
Very
much so; here are their forms and their many applications
With
trilingual summary
By
Richard L. Nailen, EA Engineering Editor
Yes, there's still a place for gearmotors
A "gearmotor" is considered to be an enclosed gear drive
combined with an electric motor so that the frame of one supports the
other. The low-speed output shaft may be either concentric with,
parallel to, or at right angles to the high-speed input (motor)
shaft. In contrast to an adjustable speed inverter drive, the
gearmotor is intended to provide a single low speed that remains
constant. Sizes range from fractional horsepower to 150 hp or more,
with common speed reduction ratios from 5:1 to 100:1 (3000:1 or more
is possible) in as many as four separate stages.
Either helical or worm gearing, alone or in combination, is most
often used. Worm gears provide higher ratios; are quieter; and don't
involve impact loading as the teeth mesh. Helical gears, involving
less friction, are more efficient.
Some gearmotor designs include coupling arrangements permitting
the use of any standard motor of the proper rating. In others, the
high-speed pinion is mounted directly on the motor shaft.
Because the gearing normally operates in an oil bath, the user
must be careful to use the proper grade of oil for the application,
and to pay close attention to lubricant level, leakage, and
temperature.
Gearmotor load ratings are quite different from those applicable
to motors alone. Because gear teeth experience wear due to friction,
the continuous power rating is determined by wear. Lubricant life and
oil seal integrity depend upon temperature--including the ambient,
which is only 24 degrees C for standard gearmotors (unlike the 40 C
standard for motors).
Peak overload capability is a torqur function, determined by gear
tooth strength, and will vary with the frequency, severity, and
duration of the peak loads. Various standard gearing classes or
standard service factors are available to suit the operating
conditions of different types of industrial machinery. The gearing
service factor, as high as 2.0, does not affect the rating of the
driving motor.
As with motors, gearing service life cannot be accurately
predicted. No "normal value" applies. However, a correctly
applied unit, properly maintained, can give many years of reliable
operation.
Copyright 2002, Barks Publications, Inc., Chicago.
Reproduction by any means prohibited.
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