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April 10 - April 14, 2017

What errors are most likely to occur when measuring dry film thickness on steel, and how can I avoid them?

Selected Answers

From Rob Weber of Fischer Technology on April 12, 2017:
I will agree with previous answers; adjust your Type II gauge with certified, traceable standards on a substrate matching your project (same metallurgy, shape and surface roughness). As Mr. Edmonds says, "calibration" is performed by the manufacturer or certified lab. Gauge "verification" and "adjustment" are performed in the field by the user. It's also good practice to make sure the Type II gauge & probe are appropriate for the measurement task (proper range, edge effect capability, part shape, surface roughness, etc.).

From Mark Edmonds of Placer Inspection on April 11, 2017:
As an instructor of inspector certification classes, I agree with most of what Mr. Brunner says. The only issue is the word "calibration." Calibration of DFT instruments can be accomplished only by certified labs. The process described by Mr. Brunner is officially known as "verifying the accuracy" of the gauge. Also note the process described by Mr. Brunner is for a Type II gauge. While not used very much anymore, Type I gauges have a completely different method for verification of accuracy.

From Steve Brunner of WPC Technologies on April 10, 2017:
Most errors are a result of calibration. What the person measuring dry film thickness (DFT) needs to do is to zero and calibrate the instrument comparable to the substrate, that is, with the same metal grade, blast profile and curvature (if any). In addition, calibration with two shims bordering the anticipated DFT will increase accuracy. A non-calibration error is attempting to measure DFT too soon, while the coating is not fully cured. This allows the probe to enter the coating, resulting in low readings.

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

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