Gordon England Surface Engineering Forum



Re: Pull Off Adhesion strength of Shot and Grit Blasted metallizing


Posted by Gordon England on January 08, 2004 at 03:40:56:

In Reply to: Pull Off Adhesion strength of Shot and Grit Blasted metallizing posted by sandeep on January 01, 2004 at 10:35:03:

: Dear Sir

: WISH U A HAPPY NEW YEAR..........

: 01.
: What would be the approximate pull off adhesion strength (psi) value of thermal spray metallizing (Zn) for surface prepared by Shot and Grits to Sa 2.5 grade.

: 02
: Whether Coarser grits give better pull off adhesion strength against finer grits.

: 03
: What would be the pull off adhesion strength of thermal spray metallizing if surface is prepared by MS or Chilled Cast Iron Grits.Chilled iron grits may cause rapid wear and tear to blasting facilities. Can we recommend MS Grits for LPG cylinder surface preparation.

: Regards

: Sandeep

01. Many specifications call for around 600 or 800 psi as a minimum tensile bond strength for flame spray zinc coatings. It is difficult to give a more precise answer as there are too many factors in addition to the differences in test methods (most commonly accepted methods ASTM D4541 and ASTM C633). Also be aware that coatings in excess of about 0.020" thickness need to be tested to reduce the effect of adhesive absorption interfering with the results. I can only predict that shot blasting will produce lower bond strengths than grit blasting. You will need to conduct test for your particular set-up.

02. I have found in some cases that finer grit blast finishes provide higher tensile bond strengths, but this probably will not apply to shear strength.

03. The problem using soft grits is that they will very quickly blunt and act in a peening action as opposed to grit blasting action.

Hope this helps

Regards Gordon


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