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I have much hobby experience with 2-part resins, but this time I'm looking to make a repair part for the inside of a microwave oven (everything I've tried so far heats up, but the original part does not). I need the result to be hard enough (shore durometer D ~ 75) to rotate the glass turntable tray within the oven, withstand ~ 250 degrees Fahrenheit (it will not be in contact with food) and be radio-transparent at the frequency of 2.4 GHz.

I've reached out to over a dozen epoxy/resin manufacturers, but am having trouble finding such a product. Thank you in advance.

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You might not be able to find a home-usable thermosetting resins such as epoxy or RTV silicone rubber that meets your needs: low dielectric loss (dissipation factor), moderate hardness and stability at microwave cooking temperatures.

Bakelite (urea-formaldehyde thermosetting resin) might be usable, as it's hard and temperature resistant, though its dissipation factor is ~0.005, a tiny bit higher than ideal. However, one-off molding of Bakelite is non trivial, requiring pressurized and temperature controlled molds.

A table of electrical properties of some plastics shows polystyrene, polypropylene and some fluorinated plastics such as polytetrafluoroethylene with dissipation factors <0.001, but these are less hard than Bakelite.

Glass-filled plastics such as glass-epoxy laminate (printed circuit board, PCB, material) and RO4000® hydrocarbon ceramic laminates might be better choices. However, instead of casting a part, you'd need to machine the part from one or more PCB's laminated together. This might actually be easier, for a one-off part, than casting.

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  • $\begingroup$ He needs a plastic that won't absorb the microwaves emitted within a convention microwave oven. $\endgroup$ – MaxW Jul 17 at 23:48
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    $\begingroup$ @MaxW, that's what the dissipation factor shows The lower the factor, the less absorbed. That said, the factors are usually given for 1 MHz, rather than 2.4 GHz, but the glass-filled PCB material cited is ~0.003 at 10 GHz. $\endgroup$ – DrMoishe Pippik Jul 18 at 0:34
  • $\begingroup$ @DrMoishe_Pippik Thank you for your answer. The FR4 approach is interesting! I wonder what modern microwave oven turntable tray couplers are made of. (I don't know whether one can tell by looking at it in the oven under the glass tray.) $\endgroup$ – kackle123 Jul 18 at 17:53
  • $\begingroup$ @DrMoishe_Pippik If you're still around, I have a side question: How would one laminate/glue PCBs together; wouldn't I have the same heating problem since the glue is not microwave transparent? $\endgroup$ – kackle123 Jul 24 at 13:38
  • $\begingroup$ Possibly, but the amount of energy absorbed depends on the geometry and size of the material. You could use a non-carbon based cement, such as a ceramic cement. See sauereisen.com/wp-content/uploads/HIGHTEMP.pdf $\endgroup$ – DrMoishe Pippik Jul 25 at 0:37

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