From: SFPhysics@aol.com
Date: Mon Oct 20 2003 - 16:40:23 PDT
From: SFPhysics@aol.com Message-ID: <73.3669693b.2cc5cc67@aol.com> Date: Mon, 20 Oct 2003 19:40:23 EDT Subject: Microwave Ovens
>Our 6th grade science club collects and dissects donated appliances each
year. >We have just received our first microwave. Is there anything we should
know about >before looking inside this appliance?? Should these be on our no
thank you list???
>Thanks for the advice.
>Sherry Anderson >>
Greetings Sherry:
Microwave ovens use either a klystron vacuum tube or a magnetron vacuum tube
to produce the microwave energy. Both types of tubes are powered by a high
voltage power supply which includes filter capacitors. While most modern
circuits include a bleed off resistor to discharge the filter capacitors when the
unit is off there is always the odd brand that does not include this feature.
Thus, it is always a good idea to use an insulated handle screw driver to short
across the capacitor terminals with the metal blade as a safety precaution.
If the timer is of the electronic kind, and not electromechanical, you will
have a pc (printed circuit) board with lead/tin soldered connections. This is
not a serious health risk but it is a good idea for the students to wash their
hands after handling the board and before they go to use their hands to eat
something.
Try not to puncture any of the capacitors. Older microwave units contained
capacitors with PCBs (PolyChlorinatedButyls) that gave rise to fears of
environmental damage and carcinogen risks. If any of the caps are leaking try not to
let the students come in contact with the oils.
The other main safety risk is the sharp edges on the sheet metal construction
inside. Microwave ovens are mass produced and interior sharp points and
edges are left in the construction process. You can get a nasty cut from some the
exposed sheet metal parts.
The microwave producing tube has a thin glass window to let out the microwave
energy into the oven cavity. It is under a high vacuum and the window will
implode/explode if subjected to a mechanical shock. The usual safety goggles
and slow methodical disassembly can avoid this. Primitive Pete disassembly
with a hammer is discouraged here.
Other than those few concerns your experience should be a safe one. You will
find two motors, one to operate the microwave stirrer and the other for the
tube cooling fan, a power supply with power transformer, a timing device, and
some really powerful magnets if the unit is of the magnetron type. Have fun.
Al Sefl
Who thought "microwave" was some kind of hair treatment...
And that is my he has no hair left...
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