Pu Belt

Stretch Recommendations

Pyramid generally recommends that belts manufactured of PyrathaneЁ 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.

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 MM Inches MM Inches MM Inches MM Inches MM Inches MM Inches MM

.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 2 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 2.5 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 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 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 4.5 114.30 4.5 114.30 1.245 31.633 1.245 31.633 1.245 31.633

.197 5 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 5.5 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 6 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 7 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 8 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 11 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