G90 means that the average to minimum weight measured at three points on both sides of the galvanized sheet is 0.9oz/ft2, that is, the SI unit is 275g/m2. The conversion relationship between them is 1oz=0.0284kg, so 0.9oz=0. 02556kg=25.56g 1ft2=0.093m2 25.56g/0.093m2=275g/m2.
So the SI unit is labeled Z275. Based on the above conversion, the corresponding relationship between G and Z labels is as follows:
G90——Z275, G75——Z230, G70——Z215, G65——Z200, G60——Z180, G50——Z150, G40——Z120 The density of zinc is 7.14 g/cm3; so 275/7.14=38.5154cm3 =38515.4mm3, that is, the average thickness per square meter is 38.5154 microns. (Single sided) Double sided is half that.
The weight of 1 micron zinc plating per 1m2 is 7.1g, 275g/7.1≈31 microns (average thickness). If a thickness gauge is used for acceptance, the average thickness measured may be higher than 31 microns, because the roughness of the steel surface and the roughness of the coating will affect the test results. The greater the roughness, the greater the measured thickness.
In the ASTM A653 specification, the galvanized layer code G90 means that the total amount of galvanizing on both sides is 0.9 oz/ft2 (average of three points on both sides to a minimum value) or 0.8 oz/ft2 (a single point on both sides to a minimum value) oz/ft2= g/m2 x 0.00328
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