Posted by Gordon England on August 28, 2003 at 10:36:35:
In Reply to: Grit blasting titanium and nickel posted by Steve Smith on August 20, 2003 at 10:39:22:
: Looking for information on grit blasting precision made titanium and nickel products prior to coating.
Hi Steve
Alumina grit is usually used for these materials. The grit size required depends on the coating system or roughness required, generally fine grits for thin fine coatings and course grits for thick coatings.
Blasting parameters such as blast pressure and stand-off distance will be dependant on equipment used and nozzle size, the aim is to produce an even etch with no "shine", but not to over blast.
Grit blasting should be the final preparation step prior to coating ideally with minimum delay in between. It is very important that the condition of the grit is monitored for contamination and breakdown in grit size. Ensure parts are cleaned and degreased before grit blasting.
Titanium in particular is prone to retaining embedded grit after blasting. Most aerospace specifications stipulate a maximum of around 20% coating/substrate contamination and in some cases 35% for titanium. This will sometimes require optimising the blasting process (pressure, stand-off, angle, grit condition and time) to provide a balance between achieving an adequate etch and low contamination. The natural break down of alumina grit during use will cause a build up of grit fines and this can make the problem of embedded grit contamination worse.
Hope this helps.
Regards Gordon
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