Pu Belt
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Stretch Recommendations
Pyramid generally recommends that belts manufactured of PyrathaneÐ 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, rpms, 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.
Belt and Round Cross Sectional Sizes Including Minimum Belt Lengths and Minimum Inside Diameters
Cross Section of Cord
Minimum Belt Lengths
Minimum Belt I.D.
For 83 Durometer Materials
For 70 Durometer Material
For 92 Durometer Materials
For 83 Durometer Materials
For 70 Durometer Material
For 92 Durometer Materials
Inches
Inches
Inches
Inches
Inches
Inches
Inches
.062
3.75
95.25
3.75
95.25
3.75
95.25
1.132
28.744
1.132
28.744
1.132
28.744
.070
3.75
95.25
3.75
95.25
3.75
95.25
1.124
28.541
1.124
28.541
1.124
28.541
.078
3.75
95.25
3.75
95.25
3.75
95.25
1.116
28.338
1.116
28.338
1.116
28.338
.093
3.75
95.25
3.75
95.25
3.75
95.25
1.101
27.957
1.101
27.957
1.101
27.957
.100
3.75
95.25
3.75
95.25
3.75
95.25
1.094
27.779
1.094
27.779
1.094
27.779
.103
3.75
95.25
3.75
95.25
3.75
95.25
1.091
27.703
1.091
27.703
1.091
27.703
.118
3.75
95.25
3.75
95.25
3.75
95.25
1.076
27.332
1.076
27.332
1.076
27.332
.125
3.75
95.25
3.75
95.25
3.75
95.25
1.069
27.144
1.069
27.144
1.069
27.144
.139
3.75
95.25
3.75
95.25
3.75
95.25
1.055
26.788
1.055
26.788
1.055
26.788
.157
4.00
101.60
4.00
101.60
4.00
101.60
1.116
28.353
1.116
28.353
1.116
28.353
.187
4.75
4.50
114.30
114.30
114.30
1.245
31.633
1.245
31.633
1.245
31.633
.197
4.50
114.30
4.50
114.30
4.75
120.650
1.235
31.379
1.235
31.379
1.315
33.400
.210
4.75
120.65
4.75
120.65
4.75
120.65
1.302
33.070
1.302
33.070
1.302
33.070
.218
4.75
120.65
4.75
120.65
4.75
120.65
1.294
32.867
1.294
32.867
1.294
32.867
.236
5.00
127.00
5.00
127.00
5.00
127.00
1.356
34.431
1.356
34.431
1.356
34.431
.250
5.00
127.00
5.00
127.00
5.00
127.00
1.342
34.075
1.342
34.075
1.342
34.075
.274
5.50
139.70
5.50
139.70
5.75
146.05
1.477
37.508
1.477
37.508
1.556
39.530
.312
6.00
152.40
6.00
152.40
6.00
152.40
1.598
40.586
1.598
40.586
1.598
40.586
.375
7.50
190.50
7.50
190.50
7.50
190.50
2.012
51.113
2.012
51.113
2.012
51.113
.437
8.50
215.90
8.50
215.90
8.50
215.90
2.269
57.623
2.269
57.623
2.269
57.623
.500
9.25
234.95
9.25
234.95
9.50
241.30
2.444
6.087
2.444
6.087
2.524
64.108
.562
12.00
304.80
12.00
304.80
13.50
342.90
3.258
82.746
3.258
82.746
3.735
94.874
We manufacture and stock the “PC Belt” in several standard sizes and will custom manufacture other sizes.
Ambient Operating Temperature Limits Are -10 to +150 F
Pyrathane materials will operate in temperatures below -10o F.; however, if allowed to rest, they take a set which is difficult to overcome and may indeed cause fracturing upon start up.
For applications with