Our vibration analyst recently discovered an increase in vibration levels in the bearings of a 100hp DC motor, prompting a recommendation for bearing replacement. Upon disassembly, it was apparent that the motor shaft had been rubbing against the end bell. The motor is connected to a gearbox using a timing belt without a tensioning idler, instead relying on shimming the motor to adjust belt tension. The friction between the shaft and end bell was in line with the belt tension, indicating excessive tension as the likely culprit. I have heard of a formula for calculating the force needed to deflect the belt one inch when the tension is correct, based on center-to-center distance and belt width, but I am struggling to locate it. Can anyone provide guidance on how to properly check and adjust belt tension?
Thank you for sending over the chart, Sam. However, it seems that the information pertains to V belts rather than timing belts. I actually came across the same chart on Browning V belts' webpage. It's important to note that timing belts typically require less tension than V belts.
The formula you're referring to is most likely the 'Static Tension' method. According to this, the proper tension for a V-belt drive can be determined by the force needed to deflect the belt approximately 1/64th of an inch for every inch of belt span length. So, if the center-to-center distance of your motor and driven equipment is 32 inches, you should be able to deflect the belt about 1/2 inch with a force of about 4 pounds. However, your situation seems more complicated due to a potential issue of misalignment. Considering you had to shim the motor to adjust the tension suggests that there could be additional problems at play beyond just tension. I'd recommend getting a professional to evaluate your system for alignment, tension, and proper pulley installment. Regardless, don't forget to check your manufacturer's guidelines for proper tension specs. It's always best to follow their advice.
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Answer: - Excessive belt tension can cause increased friction between the motor shaft and end bell, leading to issues such as shaft wear and bearing damage due to increased vibration levels.
Answer: - While tensioning idlers are commonly used for adjusting belt tension, some systems may rely on shimming the motor for tension adjustment. It is important to ensure the tension is within the manufacturer's specifications.
Answer: - The formula for calculating the force needed to deflect a timing belt can be based on factors such as center-to-center distance and belt width. It is essential to accurately determine the correct tension for optimal motor performance and longevity.
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