Posted by Gordon England on May 22, 2003 at 17:28:43:
In Reply to: Ceramic Coating for Electrical Insulation posted by Ray Roberts on May 19, 2003 at 17:06:57:
: We are using 0.8 mm thick mica board (inorganic bonded muscovite) for electrical insulation between mating surfaces of Inconel 600 parts. The parts cycle daily between room temperature and 600 C.
: We are sometimes experiencing local failure due to crushing and/or cutting-through of the mica board, which has a crushing strength of approximately 25,000 psi (172 MPa).
: The electrical voltage across the insulation is about 100 V.
: It has been suggested that we replace(or augment)the mica board with a plasma sprayed ceramic coating on the Inconel.
: Is this a good application for such a coating?
: What ceramic should we use?
: How thick should the coating be?
: What could we expect the compressive strength of such a coating to be?
: Will the temperature cycling cause the ceramic coating to eventually spall off? If so, in how many cycles?
Hi Ray
A good plasma sprayed alumina coating may be good for this application.
Generally the dielectric strength of these coatings is in the range of 100 - 500 volts per 0.001" of thickness (at room temperature and usually sealed) At 600 C
this may be different and traditional sealers will not work, so any moisture absorption at low temperatures may have an effect. I would suggest trying around 0.005 - 0.010" to start.
The coatings should be ok under these compressive loads. The last question is difficult to answer. The best thing is to test or trial some coatings to see how they perform.
Regards Gordon
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