Stretch
Recommendations
Pyramid
generally recommends that belts manufactured of Pyrathane¨ 83A
durometer be engineered with 10% initial stretch.
When
the Pyrathane 83A durometer belt is installed with 10% stretch,
it will exert approximately 200 lbs. of tension per square inch
of cross section of the belt.
However,
within the first 24 to 48 hours of static or running application,
the tension will drop to approximately half the initial tension
(approximately 100 lbs. per square inch of cross section) and
remain substantially constant thereafter.
We
find that in most applications the 83A Pyrathane is most suitable
because of its higher co-efficient of friction and its excellent
flex life. However, in applications where a greater torque carrying
capacity is required, the 92A Pyrathane may be more suitable.
Pyramid
generally recommends that belts manufactured of Pyrathane 92A
durometer be engineered with 7-1/2% initial stretch.
When
the Pyrathane 92A durometer belt is installed with 7-1/2% stretch,
it will exert approximately 300 lbs. of tension per square inch
of cross section of the belt.
Within
24 to 48 hours of static or running application, the tension
will drop to approximately half the initial tension (approximately
150 lbs. per square inch of cross section) and remain substantially
constant thereafter.
The
tension decay that is experienced with the Pyrathane belt is
present in all polyurethane to some extent and is predictable.
The tension after the belt has taken its set is what is termed
the resultant tension. This resultant tension is what we rely
on to actually drive the application and it is important that
it be adequate to transmit the torque desired while maintaining
positive tension on the slack side of the drive belt. Therefore
the belts are typically loaded with more initial tension than
is required or desirable, but this tension decays by approximately
50% rather rapidly and normally causes no ill effects.
Flex Life
of PYRATHANE Belts
The
flex life of both Pyrathane belts and cord is directly related
to the combination of many aspects of each application over
which Pyramid Inc. has no control, such as pulley diameters
and center distances, rpm's, cross sectional dimensions, belt
configurations, ambient temperature, exposure to environmental
contaminates, ultraviolet light, humidity and many others. Because
of this, the flex life of a Pyrathane belt on an application
while usually very good is impossible to predict.
We
recommend that users test a number of prototype belts under
the same conditions in which the belt will be expected to operate
to determine its suitability for the proposed application. Pyramid
Inc. assumes no responsibility for any application.
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