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Galvanizing coating thickness requirement




What is the minimum coating requirement allowed on galvanized G60 material. Is a Delfelsko gage sufficient enough to check coating thickness requirement?
We currently did a research on coating thickness on G60 material from the past year. It ranged from .25 mils to .75 mils and the certs specifically stated that the coating was a G60.

Jerry Lopez
Quality Manager - Oklahoma City, OK, US
November 24, 2009



November 27, 2009

Jerry,

My two part article in Metal Finishing: "MAGNETIC THICKNESS GAUGES AND STANDARDS PART 1," METAL FINISHING, March 1994, and "MAGNETIC THICKNESS GAUGES AND STANDARDS PART 2," METAL FINISHING, April 1994, shows you the capabilities of the DeFelsko Gauges. (Unfortunately I do not seem to have the page numbers; Check interlibrary loan at you library.) DeFelsko gauges are not named in the article, but were consistently the best in each class. For hot dip galvanizing coatings I prefer the banana type, of course calibrated in the range of interest. I think DeFelsko has four gauges of this type to chose from. Two in metric and two in English with two ranges of thicknesses. (1 mil = 25.4 microns) With this type gauge you must calibrate with a coating which is fixed to the steel (not a shim). Such traceable standards are available from DeFelsco or the US government. For electronic (push down gauges) the coating must be quite smooth and automobile brass shims can be used as standards once they are measured with a micrometer. The banana gauges must be blown out with air periodically to remove small iron grit, and can be calibrated by unscrewing the dial screw and rotating the dial face. It takes some experience to get a good result. The banana gauges give better precision (reproducibility), than the electronic gauges, especially on rough coatings. For many years I wanted an electronic thickness gauge and now I rarely use it. In my experience DeFelsko gauges give the best accuracy once they are properly calibrated. They are a one-point calibration gauge.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA



November 30, 2009

1. DeFelsko good gauges. But there are other brands also that have good accuracy and repeatability. (Elcometer is an example)

2. Units of measurement.
As England uses Metric, what are "English" units? Should that not be "American". Isn't America the last country to change to metric?

geoff_crowley
Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
crithwood logo



December 1, 2009

Geoff,

A few years ago I found out from my cousin that my English ancestors came to America on the Mayflower. All along I thought I was a hybrid "mutt," which I am. Anyway my ancestors brought the English system of units to America and I still use it.

Elcometers are typically two point calibration thickness gauges, which in theory, one would think are more accurate. After taking several hundred thousand thickness measurements on exactly the same samples and using the same calibration standards of USA NIST traceable standards, I assure you the clear winners in accuracy and precision are the DeFelsko thickness gauges. The second place winners are manufactured in Germany.

My two part article is very comprehensive with many shapes, rounds of different diameters, down to wires, different types of steels, different thicknesses of steels, different roughnesses, etc., etc. The work took close supervision of 2 students and 2 years, but was certainly worth the effort. I even went to the trouble to get replacement gauges (directly from the mfgs. when we had "break downs").

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA




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