Question: Can a microwave kiln be used to melt or anneal metal?

[Spajo]

Certain materials will absorb microwaves of the frequency used for those used for cooking. When I was working for a battery manufacturer in thr seventies, I tried using our home microwave for drying some manganese dioxide, the object being to determine water content without decomposing the manganese dioxide. I placed a small sample in a Pyrex petri dish and turned on the microwave for 30 seconds. The sample was glowing red, the petri dish broke,as did the glass plate of the microwave.

Wire twist ties as commonly used for closing bags of bakery goods will arc nicely in in the microwave although that is because they make a fairly good receiving antenna for the microwave radiation. On the other hand, our last two microwaves came with metal racks.

The question is why would you want to use microwaves as an energy source? A resistance heating element is less expensive, more trouble free, and more efficient.

I've had a similar experience with a wire tie. Agree to all said in first two paragraphs.

Is an electric kiln more efficient? I agree that getting the heating element hot is effective use of power, but that heat hast to transfer to the object via convection and radiation. Plus, the whole inside of the kiln has to come to temperature. In the microwave only the metal is being heated. Which is more efficient at cooking a potato? Microwave or conventional oven?

I don't know what the heating mechanism actually is: molecular absorption of microwaves or heating by induced eddy current or both?

I guess that I will add this to my almost infinitely long things to try.

Spajo

 

[Spajo]

Best wishes to all who commented. It seems clear now that microwave ovens are not commonly used in a shop setting. That is more than I knew before I opened this post.

Spajo

 

[Spajo]

OK, I watched the second video and there is some merit in melting metal with a microwave for small amounts of metal. Nearly all of the microwave elegy is absorbed by the crucible and the thick insulation prevents energy loss due to infrared radiation. This allows much higher temperatures to be achieved,

An induction heater heats the metal by virtue of eddy currents induced in the metal itself. IMO, microwave heating would have limited application in annealing, hardening, or tempering steel as there is no means of controlling temperature to the degree necessary.

Speaking only for myself, there are things to be learned about this.

Spajo

 

[pontiac428]

A potato has a high water content compared to metallics. Molecular dipole interaction with energy waves being the main mechanism.

Microwaves modulate their own duty cycles, that's why the sound changes throughout the cooking period. You aren't getting all 1800 watts for the entire 5 minutes it takes to cook your popcorn, the microwave has a microprocessor that was programmed by engineers who were instructed to make the appliances last longer, that's why you get nearly 3 full years of performance out of your appliance before purchasing another and another on a vicious cycle your whole life. If those engineers accidentally made a microwave that lasts 5 years, we'd all know about it by now!

Here's an upside to this path- when you toast a microwave (free or otherwise), you can take out the power supply transformer for the magnetron and use it to make a nice mag chuck!

 

[pdentrem]

Our induction furnace is 10K cycle at 30K watts.

I heard some people do use microwave ovens for Aluminum. One time use?

 

[homebrewed]

A potato has a high water content compared to metallics. Molecular dipole interaction with energy waves being the main mechanism.

Microwaves modulate their own duty cycles, that's why the sound changes throughout the cooking period. You aren't getting all 1800 watts for the entire 5 minutes it takes to cook your popcorn, the microwave has a microprocessor that was programmed by engineers who were instructed to make the appliances last longer, that's why you get nearly 3 full years of performance out of your appliance before purchasing another and another on a vicious cycle your whole life. If those engineers accidentally made a microwave that lasts 5 years, we'd all know about it by now!

Here's an upside to this path- when you toast a microwave (free or otherwise), you can take out the power supply transformer for the magnetron and use it to make a nice mag chuck!

We're using a microwave oven we got from my wife's mother's estate more than 20 years ago. NO we didn't use it all that time....but we have been using it for 10 years after our older one finally died, no idea how long the MIL had been using it. It was a middle-of-the-road Panasonic. Still going strong. Can't complain, that's for sure!

 

[homebrewed]

OK, I watched the second video and there is some merit in melting metal with a microwave for small amounts of metal. Nearly all of the microwave elegy is absorbed by the crucible and the thick insulation prevents energy loss due to infrared radiation. This allows much higher temperatures to be achieved,

An induction heater heats the metal by virtue of eddy currents induced in the metal itself. IMO, microwave heating would have limited application in annealing, hardening, or tempering steel as there is no means of controlling temperature to the degree necessary.

I agree on all points, having watched that video as well. I had thought the heat source might be from a graphite crucible but the idea of using SiC is a nice thing to know. Using sodium silicate solution AKA waterglass as a binder makes a lot of sense. Once the water is burned out it basically becomes a true glass.

Silicon carbide is a semiconductor. In impure form, as it's sold as an abrasive, it is fairly conductive so that's why the microwave energy can heat it up. Pure SiC melts at a bit over 5,000F, very respectable indeed -- but the presence of impurities like sodium silicate will likely significantly lower the melting point. Just saying, don't expect to melt steel in your home-made SiC crucible that has a glass binder in it. Probably not going to happen. But....maybe there are other binders that could do.