Posted by Gordon England (220.127.116.11) on 13:31:35 16/03/06
In Reply to: Re: stop Zirconia from cracking posted by Alexei Goncharov
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.
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