Posted by Gordon England (220.127.116.11) on 17:41:52 04/04/06
In Reply to: Re: T800 Coating Thickness limit by HVOF posted by Alex
Good to hear your making progress in solving your problems. I can only suggest a few other things that may or may not be practical in your situation. Generally your procedures look good.
Preheat 120 -130 C and keeping part temperature around this during spraying sounds about right. Depending on your substrate material it may be worth experimenting with higher preheat and spraying temperatures , just make sure surface oxidation does not become a problem. The aim is to try to maintain a constant temperature throughout the process.
I think you should try to reduce or eliminate the need to use "stop-spray method" time dwells between spray passes to control temperature if possible (easy said then done). Benefits not only to the coating but also improved efficiency (time and material).
Some additional cooling positioned to extract heat from the hottest parts before heat has chance to soak in. Ideally cooling would move relative to the spray gun.
Is it necessary to have the coating right up to the edge? Could a small shoulder be used to contain the coating edge? (would require component modification at machining stage).
Could the coating thickness requirement be reduced?
Experiment with small changes in spray angle, this could have a significant effect on the nature of the coating build-up at the edge.
Another thought, I assume you are traversing spray in a forward then back cycle. Try doing this cycle in only one direction so that all parts of the coating area have an equal time dwell between coating layers.
Removing excess coating at edges requires a lot of care, ensure coating is only put under compressive stress towards substrate and that any grinding process does not produce excessive localised heating.
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