Posted by Gordon England (62.252.0.12) on 17:41:52 04/04/06
In Reply to: Re: T800 Coating Thickness limit by HVOF posted by Alex
Hi 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.
Regards Gordon
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