Thermal Spray ID Temperature
07-18-2007, 05:32 AM,
Thermal Spray ID Temperature
hi, may I know the temperature that should be maintain during spraying ID of a cylinder? Last time I plasma spray (I forgot use what powder) ID, maintain it around 90 degree C, but the whole coating come out from the base material when it cool down. It become my 'famous' product Ashamed0002, the whole cylinder is made of coating material.

The ID I have machined thread before blast.

If I spray zirconia (Metco 204) or alumina (Metco 105) ID, what temperature should I maintain?
07-18-2007, 08:32 PM,
RE: Thermal Spray ID Temperature
Hi Powerman

Preheat can be very important with internal diameters. Also the properties of your substrate and thermal coefficient of expansion compared to that of your coating material requires consideration. You need to be careful with coating thickness, as the coating thickness limitation for ID's is less than that for OD's. The idea is that you expand the substrate through preheating, so that on cooling the substrate shrinks to take up some of the tensile stresses developed in the coating. Also spraying ID's can be more problematical from the point of view of trapping unwanted over-spray material, so ventilating ID's becomes more of an issue.
07-19-2007, 03:51 AM, (This post was last modified: 07-28-2007, 04:27 AM by Gordon.)
RE: Thermal Spray ID Temperature
Bond coat can be used to help mitigate the differences in thermal expansion between ceramic top coat and metal substrates. How do you check the thermal coefficient of expansion of the coating materials? I can not find it in Metco powders reference (It has coating materials hardness, melting point, size, spray parameters and others but does not have thermal coefficient of expansion), the reference book was quite old, i think it has more than 10 years old.

For TBC coating, normally bond coat I spray 0.15mm thickness, top coat 0.30mm thickness.
07-24-2007, 12:31 PM,
RE: Thermal Spray ID Temperature
Hi Powerman

Approximate coefficient of expansion (in/in degree C x 10^6)

Metco 204 10 (source Metco )
Alumina ~8

Which is generally a little less, but similar to your typical steels and nickel chromium alloys, but very different (1/2 to 1/3 less) to austenitic stainless steels and aluminium.

The stress build-up in the coating due to particle solidification is probably a much larger consideration. Knowing the coatings thickness limitation is a very useful guide. Coefficient of expansion differences between coating and substrate will probably be more important with regard to high temperature changes during service than the relatively small temperature changes seen during spraying (100 C or so), but it can have an accumulative positive or negative effect on stress levels.

Quote:For TBC coating, normally bond coat I spray 0.15mm thinkness, top coat 0.30mm thickness.
I don't think you should really have any problems at these thickness's.
07-28-2007, 12:23 AM,
RE: Thermal Spray ID Temperature
Hi Gordon,

Thanks for your advice.

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