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topic 59420

Slip Coated pre-galvanized Steel



October 3, 2013

Q. I am working on a project, and the specifications calls for "Slip Coated pre-galvanized Steel to ASTM A527 / ASTM A525 [affil. link to spec at Techstreet] / JIS G3302 [affil. link to spec at Techstreet] having zinc coating done at the rate of 270 g/sqm.

I would like to know what is "slip-coated pre-galvanized steel" and the difference in "hot-dipped galvanized Steel". Could this be clarified please?

We are UL certified fire-rated door manufacturers and have over a period of time found that hot dip galvanized steel is ideal for value addition.

Regards,

B.K. Harish Moorthy
- Al Qusais, Dubai, U.A.E.


A. Hi Harish.

Pre-galvanized means the material was galvanized in sheet form before fabrication. Therefore there will be no zinc at the sheared edges or the edges of holes, etc. If the item were post-galvanized, that would mean it was galvanized in its final fabricated shape.

Galvanizing can be done by hot-dipping (dipping the sheet or the finished item in molten zinc) or it can be done by electrogalvanizing (zinc electroplating the sheet or the finished item). Note that some people don't think that zinc plating should be called "galvanizing", but in your case ASTM A525 [affil. link to spec at Techstreet] requires hot-dip galvanizing anyway. . ASTM A527 is/was a spec for galvanizing to "lock form quality"; I believe it was withdrawn in 1994 though, and replaced by ASTM A653 [affil. link to spec at Techstreet].

A slip coat, to my limited understanding, is a water-soluble temporary coating that is put on the metal to discourage cargo like coal from sticking to it, by filling any small porosity, and by virtue of easily washing away (slip coat and tiny remnants together) after the cargo is unloaded.

Regards,

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Ted Mooney, P.E. RET
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finishing.com - Pine Beach, New Jersey

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