|
 Summary: " Flat
Belts--Are They Still Around?
" With
trilingual summary
From the earliest application of
electric motors to industrial loads, belt drives have been a common
means of reducing motor speed to that required by the driven
machinery. Flat leather belts were most often used. Power was
transmitted through friction between belts and the surfaces of
driving and driven pulleys. Commencing about 75 years ago,
elastomeric V-belts began replacing most flat belts, largely because
of much greater friction created by the wedging action of V-belts in
grooved pulleys. Also, V-belts were quieter; they could readily be
added or removed to suit varying power requirements; and belt
tension was easy to recheck periodically.
However, flat belts (usually made now
with a polymer core for high strength, faced with rubber or leather
for oil resistance) remain useful for drives in which motor pulley
diameters are too small for V-belts, or in which centrifugal force
due to high speed might cause V-belts to fly out of their grooves.
Also, the pulley groove wear that leads to belt damage is not
present in a flat belt drive.
The shaft stress and bearing loading
imposed on a motor by a V-belt drive is easily calculated. Also,
drive design is simplified by the existence of only a few standard
belt cross sections, as well as motor standards governing allowable
driving pulley diameters. With flat belts, a multiplicity of belt
thicknesses and materials makes drive design and load calculation
more complex, although basic formulae relating belt tension and
friction force were developed a century ago.
Motor manufacturers in the 1920s
standardized on certain calculation procedures, and pulley diameters
were agreed upon by a leather belting trade association. However,
those standards have either lapsed, or were never extended to motor
sizes of several hundred hp at speeds of 1200 rpm and below. Typical
calculations indicate that a flat belt drive for a modern large
motor may involve much higher shaft stress and bearing loading that
would result from the use of V-belts. Close coordination between
motor manufacturer and drive designer is necessary to ensure a
trouble-free application.
From
" Flat Belts--Are They Still Around?
" ...by
Richard L. Nailen, EA Engineering Editor -
published in Electrical Apparatus June 2004
© 2004
Barks Publications, Inc. All Rights Reserved.
|
