Tension & Relaxation Data


	Tension & Relaxation Data Initial Tension and Relaxation Data Pyramid recommends that belts produced from our Pyrathane® materials be engineered to a length that will provide a given amount of stretch when installed on the application. This percentage of stretch varies from material to material. Stretch recommendations can be found on our Material Comparisons page. The percentage of stretch applied to a belt is arrived at by taking into consideration the tension relaxation that is expected and determining how much resultant tension, measured in pounds of tension, will be required to drive the application properly. The tension relaxation (also called tension decay) that is experienced with the Pyrathane® belt is present in all polyurethane (urethane) 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 tension than is required, knowing that this tension will relax or decay by approximately 50%. Tension begins to drop rapidly immediately upon installation, losing approximately 30% in the first hour, 10% more after 24 hours then another 10% over the next number of days. at which time the tension will have leveled off to a stable condition and remain substantially constant for the remainder of its working life. Belt lengths recommended by Pyramid Inc. take into consideration this tension relaxation or decay An example would be when the Pyrathane® 83A durometer belt is installed with 10% stretch, initial tension will be approximately 200 lbs. of tension per square inch of cross section of the belt. However, within the first several days of static or running application, the tension will relax to approximately half the initial tension (approximately 100 lbs. per square inch of cross section) and remain substantially constant thereafter. A second example would be when the Pyrathane® 92A durometer belt is installed with 7-1/2% stretch, initial tension will be approximately 300 lbs. of tension per square inch of cross section of the belt. And again, within several days 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. 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 find that in the majority of applications our 83A Pyrathane® is most suitable. It combines a high co-efficient of friction, high abrasion resistance and has an excellent flex life. However, in more specialized applications, such a requirement for higher load carrying capacity, static dissipation, ultraviolet light resistance or where a greater torque carrying capacity is required, one of our other Pyrathane® materials may be more suitable. 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.