Posted by Gordon England on October 07, 2003 at 12:32:06:
In Reply to: Thermal spray zinc metallizing posted by sandeep jaikishen on October 07, 2003 at 06:46:42:
: Dear Sir
: I would like to know about the followings:
: 01.How long can we hold a piece after grit blasting without metallizing for a marine and non marine atmosphere.
: 02.What should be the ideal grit size for surface preparation, if we ve to specify
: 03. what should be the ideal wire dia for metallizing
: Regards
: Sandeep
:
Hi Sandeep
1. The period of time between blasting and spraying should be as short as possible. The longer an item is left, the higher the risk of corrosion and contamination. I have seen many specifications that quote 4 hours maximum, but really, if you need to specify a maximum time, it will depend on the environment in which the item is kept. If the item is kept in a controlled dry low humidity and clean environment, it may be possible to leave it for days. In high humidity, marine or dirty environment, every minute may count.
2. The ideal grit size depends on your blasting equipment set-up and blast media, your substrate material and condition etc. The aim should be to produce a SHARP etch (not a peened etch) with complete coverage with minimal over-blasting. The actual surface roughness is not really that important with thin coatings, it is the quality of the etch that is important. Typically -10 +30 mesh or grit No. 20 are used, but go finer or coarser to meet your own requirements.
3. Thick wires like 3/16 are used mainly because they yield slightly higher spray rates. Depending on your equipment, if through put is important, then the thicker wires would be ideal.
Regards Gordon
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