Summary for slip coated pre-galvanized steel Discussion
Slip coated pre-galvanized steel is explained as sheet steel that was galvanized before fabrication, so cut edges and punched holes may not have zinc protection. In the thread, the questioner asks how this differs from hot-dipped galvanized steel and cites ASTM A527, ASTM A525, and JIS G3302 with a 270 g/sqm zinc coating. The answerer says pre-galvanized means the coating was applied in sheet form, while post-galvanized means the finished part was galvanized after fabrication. He also notes that galvanizing can be done by hot-dipping or electrogalvanizing, though ASTM A525 requires hot-dip galvanizing in this case. On ASTM A527, he says it was a lock-form quality spec and believes it was withdrawn in 1994 and replaced by ASTM A653. He adds that a slip coat is a temporary, water-soluble coating used to keep cargo from sticking and to wash away easily after unloading.
October 3, 2013
Q. I am working on a project, and the specifications calls for “Slip Coated pre-galvanized Steel to ASTM A527 [inactive] / ASTM A525 / JIS G3302 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 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 ASTM A527 is/was a spec for galvanizing to “lock form quality”; I believe it was withdrawn in 1994 though, and replaced by ASTM A653.
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,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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