Problems using regular enamel paint in microwave oven?

We used to use[1] Humbrol model kit paint without any problems, indeed, the 'proper stuff' came from the Humbrol factory and looked and smelled exactly like the model enamel, only five times the price!

[1] back in the days when microwave oven repairs were financially viable

Ron(UK)

Sam:

I think you are 100% correct. There should be no hot spots anywhere on the uwave oven liner as it is a solid metal sheet except where the uwaves come into the chamber. There is obviously a fault of some type that is making that area of the uwave get hot or there would not be any smoke. That may be why there was a fault in the original paint at the location.

BTW - I think you are right on in just about everthing you recommend, and your repair faq stuff is a great resource.

H. R.(BOb) HOfmann

Some black paints are electrically conductive, but even that should be no problem unless it was across an insulator like glass. Probably just the residuals from a little heat and moisture from normal cooking. The oven should have been baked. Did I say that right? At least a hot air gun or hair dryer shold ahve been used to treat the paint first.

greg

Come to think of it, materials can be lossy at microwave frequency, so even if it were not dc conductive, a material could heat up if were suspended across an insulator.

My black electrically conductive seal on the old Heathkit microwave, use to kind of melt.

greg

Sam:

A couple of things come to mind, both of them pretty remote:

a) the batch of paint used had Titanium Dioxide as the white pigment. It is just possible that the paint as-applied was more absorbtive than the OEM paint & metal combination and so that area turned into a 'hot- spot'. If they did an area say the size of a business card or more, that would be the second thing that came to mind and that based only on very careful prep... see b) below. b) conversely and more likely, the prep-work took the microwave- reflective primer off and exposed the steel. BAD MOVE as without that reflective coating the metal will get very hot no matter what sort of finish coating may be on top.

Just my random thoughts.

Peter Wieck Wyncote, PA

Does anyone agree with this?

To understand what the walls of the oven are made of or what material one could use to partially keep food from cooking, you have to have some knowledge of 'dielectric constant' and 'loss tangent'. The materials used for protectors can be plastics, ceramics.... all depends on the dielectric constant and the RF properties at 2.45 GHz. The walls are usually a light sheet metal (or plastic with a layer of metal foil) with a dissipative coating.

from: Ronna Erickson Radio Astronomy, Univ. of Mass. - Amherst

Remove that dissipative coating and Bob's your Uncle...

In any quality oven, that coating is fired enamel and pretty tough. In the cheaper versions, it is a powder-coating that is fragile at best if abrasives are used to clean. On some others, it is back-coated onto a tough plastic... That is the hardest to damage.

Peter Wieck Wyncote, PA

Does that apply only if there's a coating on top of the metal? Because we have a microwave oven with a stainless steel interior

So how is stainless steel different than steel, microwave-wise? To reflect microwaves implies a conductive material. The conductivity may be different, but not dramatically.

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quoted text -

There are several patterns to how the magnetron works, and several methods to spread the pattern over the food. "Better" ovens use a combination of reflection and absorbtion to make the food cook evenly,

*in addition* to either a turntable or even the figure-8 pattern turntables on some higher-end ovens. In these cases, the Turntable platter and mechanism serves as the absorber, the vertical surfaces will be the refectors.

In the cheaper fixed-position ovens where one is required to rotate items or turn them over, the niceties of such designs are ignored and the magnetron pretty much blasts in whatever pattern it is masked to do. Scatter is to be absorbed by the surfaces of the oven.

There is a great deal of thought and design that is hidden in these beasts. It is absolutely possible to put out an oven at US$39 that will both cool and still make a profit for the retailer even after it is shipped from China. It is also possible to spend $600 for an oven that will not only cook but have all of these design niceties included and still make a profit for the dealer even after it has been shipped from China.

Point being that everything inside that oven, right down to the paint, has been chosen for the purpose. And if they are stainelss steel lined, that steel has also been 'designed' for the purpose. Can't go by smell on the paint, can't go by looks on the steel.

Peter Wieck Wyncote, PA

I'm not sure why some people appear to be turning this into rocket science.

Here is a reply from John Gallawa of Microtech at

generally regarded as the most comprehensive site for microwave ovens on the Web.

First my question (similar but not word-for-word what I posted here) and then John's reply:

In fact, I have now been able to determine from testing done by the person who originally was complaining that it is probably just residual odor at this point. I had them run the oven with just a water load to see if the area of the new paint heated up or behaved strangely. It did not. They'll have to try the coffee grounds I guess. :)

Thanks to all who responded.

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Maybe you dont repair microwaves.

NT

Put as simply as possible, I would not, no. And this from someone whose hobby (amongst others) is restoring vintage radios and audio equipment from the 20s - 70s.

Peter Wieck Wyncote, PA