Posted by Gordon England on July 24, 2003 at 18:27:26:
In Reply to: Zinc metallizing - grit blasting posted by Sandeep Jaikishen on July 24, 2003 at 07:35:52:
: Sir
: Indian Standard IS 3196 (Specification for LPG cylinders) recommends both Shot as well as Grit Blasting before Zinc Metallizing of LPG cylinders.
: we would like to specify for Grit Blasting, Grit Size, Surface preparation specification, Idle time before metallizing and after shot blasting, importance for pretreatment etc.
: Whether their will be practical test result difference
: between
: 01. Shot and grit blasted & metallized surface.
: 02. for different Grit sized surface prepared & metallizing
: 03. different surface preparation grade
: 04. different idle time
: 05. between non pretreated and pretreated surface
: please suggest how to go about it and how can we establish practically the above.
: Regards
: Sandeep
Hi Sandeep
I know some LPG cylinder makers only use shot blasting prior to zinc coating. The main reason being that grit (chilled iron or alumina) causes very rapid wear to their automated blasting equipment. Grit blasting will most definitely improve coating adhesion. If you want to employ both methods use shot blasting first to do the brunt of the cleaning and then finally lightly grit blast to achieve the desired etch for coating adhesion.
You will need to evaluate the quality of your blasted surfaces and the coatings from your tests.
Visual inspection and roughness measurement will need to be taken. Adhesion/bond strength of the coatings is the main property to test for. Tensile bond strength test for quantitative results or scribe test or bend test to give qualitative results. If you apply paint to zinc coating, then evaluate effect on paint finish as well.
Regards Gordon
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