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We have been asked to galvanize a large shaft which is part of a drive mechanism. Now the design engineer has stated that in order to properly size the motors, he needs to know the coefficient of friction of the zinc coating. Where can I find this information?

The coefficient of friction? You got that question out of your kids high school physics book just to try and fool Dr. Galv, didnt you? Nice Try! I cant give you information on the coefficient of friction, but I can give a value for the slip factor, which should satisfy the engineers need. The information is from W.H. Munse paper on High Strength Bolting of Galvanized Connections; which states the slip factor for a conventional galvanized coating is about 0.14, as compared to 0.35 for clean as-rolled steel. This means that the galvanized surface is more slippery than bare steel. However, as the galvanized surface weathers, or is roughened, the slip factor increases:

 Average Slip Factor
Weathered Galvanized0.20
Galvanized Wire Brushed0.31
Galvanized  Grit Blasted0.31
Bare Steel, As Rolled0.35

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