PowerGrip® GT® Belt Drives

Polyflex ® JB ® Belt Drives
Benefits of 60° Design Angle
Fig. 14 shows the 60° angle sheave groove
provides more support to the tensile cord than the
36° angle sheave groove. This additional undercord
support reduces differential tensile cord tension
caused when the center tensile cords relax due to
the belt collapsing under heavy loading. Differential
tensile cord tension means that the cords located at
the belt edge have a higher tension than the cords
in the belt center, as illustrated in Fig. 15. Tension
variation reduces belt performance and horsepower
capacity, since all the tensile cords do not share the
applied load equally. Therefore, the 60° Polyflex JB
system permits overall higher horsepower load
carrying capability.
Sheave support
area under cordline
36 angle system
°
60°
Angle
36°
Angle
Sheave support area
under cordline with
Polyflex JB
Figure 14 – Increase in cordline support in
60° sheave
Figure 15 – Differential tensile cored
tension
The reduced cross-sectional area and lighter
polyurethane material combine together to help
reduce both bending and centrifugal tension.
Bending and centrifugal tension decrease the
allowable working tension. Since bending and
centrifugal tension are lower for Polyflex JB belts,
more effective tension is available for useful work,
resulting in higher horsepower ratings.
Initial reduction of operating tension in a V-belt is
the result of the belt seating in the sheave groove
while operating under a load. The belt effectively
runs on a smaller diameter because of seating in
and results in a tension loss that requires belt
takeup or retensioning. With the 60° Polyflex JB
system, longer running time is possible before
takeup is required.
The amount a V-belt can seat in the sheave and lose
operating tension depends on these factors:
(1) Abrasion resistance of the belt.
(2) Abrasive effect of dust or dirt on the sheave
groove sidewall.
(3) Compression modulus (permanent
compression set, a stress/time
phenomenon, causes tension decay).
Items (1) and (3) above were discussed in the first
part of this section under the Polyurethane heading.
To briefly review, a high abrasion-resistant material
in the belt and a high compression modulus mean
less belt tension deterioration.
However, if some belt and sheave wear does occur,
the effect on seating in the groove is less for the
60°angle compared to the 36° angle. Any seating
due to wear is only 2/3 as great in the Polyflex JB
60° angle as the same wear in a conventional 36°
sheave angle. This is illustrated in Fig. 16.
Figure 16 – Seating in 60° and 36°
Sheave Grooves
In summary, three characteristics of the Polyflex JB
belt in the 60° angle sheave – abrasion resistance,
high compression modulus and less movement in
the sheave groove (if wear does occur) – all mean
less tension decay. For a Polyflex JB drive, the
result is a reduced frequency of retensioning.
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