GSM to Microns. Converting galvanizing weight to thickness

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A. The density of zinc is 7.4 ^7.14 g/cm^3; there are 10^4 µm in a cm, so there are 10^12 µm^3 in a cm^3. Therefore 1 µm/m^2 is equivalent to 7.4 ^7.14 X 10^-4 g of zinc.

A. Trevor, the danger in this type of calculations is that one gets confused about all the different dimensions. The calculation I use is (using dimensions that are commonly used in the world of coatings): Weight of coating/mtr2 [grams/m2] = Film thickness [µ] x specific weight [grams/cm3].

In the case of Zn: specific weight is 7,4 ^7,14 grams/cm3: Zn weight/sqm = 7,4 ^7,14 grams/µ

Calculation is applicable with any coating, p.e. powder:

How much powder is on a part of 3 m2 with an average DFT of 80 µ and a specific weight of powder of 1.3 kg/dm3? Answer: 80 x 1.3 x 3 = 312 grams.

A. I can Simplify the calculation method for converting gr/m2 to micron or micrometer.

D(density) = Wt. (weight)/ V (volume)
for Zinc
D = 7.4 ^7.14 g/cm3
= 7.4 ^7.14/cm*cm*cm.
1 cm = 10000 micron or micrometer.
= 7.4 ^7.14/cm*cm*10^4 µ.
so:
10^4 µ = 7.4 ^7.14 g/cm*cm.
1 m = 100 cm.
10^4 µ = 7.4 ^7.14 g*100*100/(100*cm)*(100*cm).
10^4 µ = 7.4 ^7.14 g* 10^4/m*m.
1 µ = 7.4 ^7.14 g/m2 for one face.
1 µ = 14.8 ^14.28 g/m2 for two face.

ex:
for galvanization layer
25 µ = 185 ^178.5 g/m2 for one face
and 25 µ = 370 ³⁵⁷g/m2 for two faces.

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A. Hi Ashok. They can measure the thickness of the galvanizing with a magnetic thickness meter if they wish confirmation.

Remelt has told us that 1 micron is about 7.4 ^7.14 GSM; so 90 GSM would apparently be somewhere around 12 microns. However, as Nagy implies, it is conventional that 90 GSM refers to the total amount of zinc applied to both sides of the strip, so I would expect the thickness to be about 6 microns per side.

You are welcome to refer them to this page where the question has been answered. Good luck.

Regards,

A. Most sources give the density of pure zinc as 7.14 g/cc. It will be slightly higher for Prime Western Zinc which is a zinc-lead alloy (up to 1.4% lead) but not much. The vast majority of hot dip galvanizing, until recently, was done with Prime Western Zinc. Other alloying components (aluminum, nickel, etc.) will have calculable effects on the density of the coating.

  Thanks for the more refined answer, Tom. 90 GSM then equals about 12,6 microns.

Regards,

A. Hi Omprakash,
"7.4" was intended to be the density of zinc in grams per cubic centimeter, but that was a typo that was accidentally propagated across the whole page :-(
Then Tom advised us that it should actually be "7.14" :-)
After your inquiry we went back and corrected it throughout the page.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. ISO 1461 standard states the thickness of zinc on steel in both formats, and says 85µ is 610 g/m2