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Question posted - October 16 to October 23, 2015:

How does the concave or convex curvature of a surface affect the dry film thickness reading?

Selected Answers

From M. Halliwell of Thurber Engineering Ltd. on October 23, 2015:
I think it will also depend on how ham-fisted the person doing the application is, how thick/heavy and "wet" the coating is and the radius of the curvature. It is at least theoretically possible to have variations in the thickness due to the curvature (i.e. minor coating flow at high slopes). As noted, the probe makes a difference, too. Overall, there could be some variation, but a good application and  using an instrument intended for tighter curves should minimize it.

From Tom Swan of M-TEST on October 23, 2015:
If you are using a Type 2 (electronic) gauge and you calibrate the gage to the surface being measured, how concave or convex the surface is does not effect the accuracy. With a Type 1 gauge, it will effect the readings. A convex surface will flatten out the magnetic field and a convex cave will cause the magnetic field to arch higher. Even with a bowling ball, if you zero to the same conditions you are measuring, it should not effect the accuracy. Just don't measure too close to the finger holes.

From David Zuskin of EXCET/US NAVAL RESERACH LAB on October 23, 2015:
If you use a mini probe or micro probe, there should be no effect.

From Warren Brand of Chicago Coatings Group on October 20, 2015:
It will depend on the angle of the curved surface. Either way, using a type 2 pencil gauge should give you an accurate reading unless the surface is curved like a bowling ball or other severe curve, in which case you may, if the full tip of the pencil is not able to come into full contact with the surface,  get readings which are inaccurate.

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Tagged categories: Coating / Film thickness; Dry Film Thickness (DFT); Quality control

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