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Shot Blasting of chrome [India] 

October 13, 2009

I want to shot blast a metal roll made of HARD CHROME STEEL. Whats grits to be used and what size to use to get considerable roughness on the roll surface.

Venkatesh K
Engineer - Tirupur, Tamilnadu, India

For better understanding, Shot blast normally means steel shot or glass bead or possibly cut wire. This has sieve sizes.
Abrasive blasting uses a media like sand or aluminum oxide or one of the carbides and has grit sizes that equal the sieve that a given percentage will pass thru.
If you shot blast your roll, it will dent the chrome and very probably much of it will peel off as it is highly internally stressed.
If you are going to abrasive blast it, I would use one of the carbides. 16 grit if you want it extremely rough and 24 or 110 more likely. Here again, excessive blasting will probably cause it to peel.
Normally, you would blast the metal roll a bit rougher than desired and then chrome plate it for a rough chromed surface, rather than the other way around.

James Watts
- FL

I read Venkatesh's query differently from the way that James does.

I believe that he has a roll made of a hard, chrome-containing, steel. Not that he has a chrome-plated steel roll.

If I am reading it correctly, then the fact that the steel contains some chrome is not important. The only important thing is the hardness of the roll, because that will affect the necessary abrasive grit size needed to achieve a given degree of roughness.

I suggest that the term "considerable roughness", applied to an article of completely unknown dimensions, conveys no real information at all.

Venkatesh, again assuming I am reading the post correctly, what is the hardness of the roll, and what roughness do you want?

Bill Reynolds    consultant metallurgist Ballarat, Victoria, Australia

From what he is saying I think he may be referring to a hardened chrome molybdenum press or crush type roller like those used to roll foodstuffs or crush out oils. It may not be chrome plated at all. I suppose if he could tell us what he is doing with the roller, EXACTLY! It may make it possible to give him some hints as to how to go about it.

Rod Henrickson     gunsmith Edmonton, Alberta, Canada