How to focus microwaves?

[Eric R Snow]

A man named David Reid has figured out a way to melt small
quantities, up to .25 kg, of silver and other non-ferrous metals, in a
microwave oven. He describes his method here:
http://home.c2i.net/metaphor/mvpage.html
Metalworking is my vocation as well as an avocation. I have the
experience and the equipment to do conventional lost wax casting.
Using microwaves to melt the metal is intriguing to me so I'm going to
try David Reid's method of melting metal in the microwave.
Mr Reid notes that his method is not as efficient as it could be. I
am wondering if changing the focus of the microwaves would help much
and if adding another magnetron is practical. I know that the second
magnetron will need its own power supply.
So the questions are:
1) How to focus microwaves?
2) Can two magnetrons be used?
3) Will a new chamber with a different shape need to be made?
4) How to insure that a new or modified chamber will not allow any
microwaves to leak out?
Thanks,
Eric

 

[Rich Grise]

A man named David Reid has figured out a way to melt small
quantities, up to .25 kg, of silver and other non-ferrous metals, in a
microwave oven. He describes his method here:
http://home.c2i.net/metaphor/mvpage.html
Metalworking is my vocation as well as an avocation. I have the
experience and the equipment to do conventional lost wax casting. Using
microwaves to melt the metal is intriguing to me so I'm going to try David
Reid's method of melting metal in the microwave.
Mr Reid notes that his method is not as efficient as it could be. I
am wondering if changing the focus of the microwaves would help much and
if adding another magnetron is practical. I know that the second magnetron
will need its own power supply.
So the questions are:
1) How to focus microwaves?
2) Can two magnetrons be used?
3) Will a new chamber with a different shape need to be made? 4) How to
insure that a new or modified chamber will not allow any microwaves to
leak out?

They don't do any of this stuff. Here's what they do:
"Both waxes are coated with a patent ceramic shell slurry containing some
graphite.
These are then stuccoed with a magnetite sand."

It's the crucible that absorbs the microwaves and heats up to the
melting point of the metal.

You can't heat metal directly with microwaves because it's a conductor.

Have Fun!
Rich

 

[Eric R Snow]

They don't do any of this stuff. Here's what they do:
"Both waxes are coated with a patent ceramic shell slurry containing some
graphite.
These are then stuccoed with a magnetite sand."

It's the crucible that absorbs the microwaves and heats up to the
melting point of the metal.

You can't heat metal directly with microwaves because it's a conductor.

Have Fun!
Rich

Greetings Rich,
I understand that the microwaves are absorbed by the graphite and
magnetite and that is what heats up the metal. What I'm wondering is
if the microwaves can be concentrated on the shell and if it's worth
the trouble to try it.
Thanks,
Eric

 

[Rich Grise]

I understand that the microwaves are absorbed by the graphite and
magnetite and that is what heats up the metal. What I'm wondering is if
the microwaves can be concentrated on the shell and if it's worth the
trouble to try it.

Oh, sure you can focus microwaves. In fact, in the early days of microwave
design, one of their major problems was _de_focusing the RF - they went
through all kinds of gyrations to get rid of hot spots in the chamber.

Just a resonant cavity with the thing at the right point should do the
trick.

Is it worth it? I guess, like anything else, "it depends". What do
you want to invest in designing a resonant cavity?

Have Fun!
Rich

 

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Oh, sure you can focus microwaves. In fact, in the early days of microwave
design, one of their major problems was _de_focusing the RF - they went
through all kinds of gyrations to get rid of hot spots in the chamber.

Just a resonant cavity with the thing at the right point should do the
trick.

Is it worth it? I guess, like anything else, "it depends". What do
you want to invest in designing a resonant cavity?

The cavity is easy. What's hard is an easily removable door!

And note that microwave leakage is dangerous not because of skin
burns, but because it tends to fry your corneas and cause permanent
blindness. Safely working with home-built microwave equipment is
sort of like safely working with home-built x-ray machines or
explosives: those without sufficient fear and knowledge will remove
themselves from the breeding pool.