Slip, Grip, Friction and Temperature

It’s winter in New England and another snowstorm is on the way. If you watch the news, you’ll hear about travel delays, airline cancellations and the associated costs of disruptions to business during this time of year. I often wonder how they calculate the actual economic impact and yesterday provided a tiny bit of insight.

At CMT, delivery trucks must reverse or back-up into our driveway in order to load or unload goods. The driveway has about a 30 degree incline. Looking out the window yesterday, I noticed several delivery trucks were struggling to maneuver up the driveway. The tires at the front end of the trailer were spinning and causing the truck to slip sideways. Unable to complete the delivery, both FedEx and UPS trucks drove off to the next scheduled stop. Such are the exigencies of global logistics.

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What does this have to do with thermoforming? As it turns out, everything!  The plug/sheet interface performance is all about friction…yet nearly impossible to define with any level of accuracy. Temperature, substrate, surface finish, motion, dust and many other factors affect the Coefficient of Friction (CoF) value. Different surface conditions as a result of machining or polishing a plug material, or even a few degrees of temperature variation in a mold, will affect CoF values. The value changes for each specific plastic relative to plug material. There is both a static (objects at rest) value and a kinetic (objects in motion) value for the frictional coefficient. The only suitable method for determining a CoF value is experimentation with the actual plug and sheet to be used. 

We continue to work with industry and academic partners to investigate these variables and we’ll continue to share our findings. If you have specific questions on your application, just let us know and we’ll be happy to lend a hand.

(And in case you doubt the efficacy of our wonderful freight companies, both FedEx and UPS returned yesterday after the driveway was plowed and then sanded, which created more friction. . .)

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