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How to focus microwaves?

Discussion in 'Electronic Basics' started by Eric R Snow, Jun 7, 2007.

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  1. Eric R Snow

    Eric R Snow Guest

    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:
    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?
  2. Rich Grise

    Rich Grise Guest

    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
    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!
  3. Eric R Snow

    Eric R Snow Guest

    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.
  4. Rich Grise

    Rich Grise Guest

    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

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

    Have Fun!
  5. Guest

    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.
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