J. Stanton McGroarty, CMfgE, CMRP, is senior technical editor of Plant Services. He was formerly consulting manager for Strategic Asset Management International (SAMI), where he focused on project management and training for manufacturing, maintenance and reliability engineering. He has more than 30 years of manufacturing and maintenance experience in the automotive, defense, consumer products and process manufacturing industries. He holds a bachelor of science degree in mechanical engineering from the Detroit Institute of Technology and a master’s degree in management from Central Michigan University. He can be reached at
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When was the last time you checked slippage? Belts are supposed to be simple, quiet, low-maintenance drive systems, and they are. But the fact is that while we’re paying attention to the more complex systems, belts are getting worn, dirty and oily. Then they quietly rob the plant of a lot of electrical cost. The amount varies from plant to plant, of course, but a quick review of the number and horsepower of your pumps, compressors, fans, conveyors and other belt-driven equipment will probably be an eye-opener. An enterprising team of one engineer and one or two mechanics should be able to use a strobe or ultrasound device to identify the shaft speeds of the pulleys that are running your equipment. The readings are best taken under load, as long as safe access is available. The percentage of slippage in the system is an easy calculation once you have the working diameters of both pulleys and the shaft speeds. Given the horsepower at which the equipment is running, converting the slippage to kilowatt hours and then to dollars is pretty straightforward. You’ll also want to give the bearings a listen and maybe a thermographic look to see if they need attention, too. If you take the system down, you’ll also want to check alignment when you put it back to work.
Sometimes a little ingenuity can pay off. For instance, if your system is doing its job in spite of a lot of slippage, maybe a lower-speed ratio will be adequate after cleaning and alignment. Likewise, if someone has blocked half of a fan’s discharge vent, perhaps less horsepower is needed with the vent reopened. Low- to no-cost repairs or refits can yield exciting results at today’s electric power rates. A check figure can be developed by computing the slippage again when the system is recommissioned. That’ll give you a savings number you can bank on.
If you don’t have enough belts to score exciting savings, you can perform a compressed air leak audit or a thermographic scan of walls and roof when the weather’s hot or cold. All energy leaks are fair targets, but who hasn’t seen ancient, dirty belts humming away through nights and holidays, keeping the electric company warm and cozy?
Thanks, Tim.
Read Stanton McGroarty's monthly column, Strategic Maintenance.
