Posted by Gordon England (62.252.0.12) on 13:31:35 16/03/06
In Reply to: Re: stop Zirconia from cracking posted by Alexei Goncharov
Hi Hong
These problems are usually associated with poor temperature control
during spraying and or excessive coating deposit per pass.
"1. Increase the preheat of the part (with the bond coat)"
- Only if existing preheat is below 100 C and substrate is
compatible with this heat. Part temperature should not go above
about 175 C during preheat or spraying.
"2. Reduce the front cooling air jet flow/pressure on coating" -
Only if coating/substrate temperature is falling below preheat
levels.
"3. Use/increase gun dwell time" - Not sure what you mean here.
Assuming you mean a time pause between spray passes to control
temperature. I would only consider this if all other forms of
temperature control failed.
Ideally, coating/substrate wants a constant uniform temperature
throughout the process. Spray particle quenching obviously produces
very large temperature gradients, but should be a microscopic
effect. These coatings should be applied at less than 0.001"
(0.025 mm) per pass which helps control heat input.
Regards Gordon
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