Monday, November 29, 2010

Design Flex Force/Deflection Tensioning

We often get questions from customers about the force/deflection tensioning recommendations on a Design Flex printout. The report lists the "Rib/Strand Deflection Distance" and the "Rib/Strand Deflection Force" for both a new and used belt. If you have never used this method of measuring tension, our Belt Drive Preventive Maintenance and Safety Manual has thorough instructions.

Some people think that you can measure the tension by only measuring deflection. However, in order to properly tension a belt, you must measure both the force and deflection distance. Measuring one inch of deflection with 5lbs of force is a very different tension than one inch of deflection that requires 100lbs of force.

Some confusion arises from the "Rib/Strand" portion of the title. For a synchronous drive, there is almost always only one belt, so you can use the listed force/deflection values. V-belts however, often have more than one belt on the same drive. In order to properly tension the drive you must multiply the deflection force by the number of strands that you will be deflecting. Even though your PowerBand belt looks like a single belt, you must multiply the force by the number of ribs. The deflection distance is not multiplied by the number of ribs and is calculated as 1/64 of an inch per inch of span length.

People also wonder what is considered to be a used belt. Any belt that has not been run more than about 24 hours is considered a new belt. If you are reassembling a drive with the same belt that was used previously, it is recommended that you measure the tension before dis-assembly and reinstall it at the same tension. If you did not measure the tension, you can reinstall with the used belt values.

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