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Q: Metal rack in Microwave oven. ( Answered 5 out of 5 stars,   2 Comments )
Subject: Metal rack in Microwave oven.
Category: Science > Physics
Asked by: mc4bbs-ga
List Price: $2.00
Posted: 28 Nov 2002 17:45 PST
Expires: 28 Dec 2002 17:45 PST
Question ID: 116150
Microwave oven manufacturers say not to use metal in the oven;
however, they have been making more and more ovens that feature a
removable metal rack in them.  How does this seemingly ordinary metal
rack differ from other metal objects inside the microwave?  Is it safe
to use the metal rack as opposed to running the microwave without the
rack?  Is there any more/less damage to the magnito with the presence
of the rack?

Request for Question Clarification by tutuzdad-ga on 28 Nov 2002 17:51 PST
Hi mc4bbs-ga;

Your question will likely require more research than the average
question of this price normally entices a researcher to do. You may
want to consider revising the price in order to attract a sufficient
answer. Here is a link to guidelines about pricing your question: 

If you choose to revise the price please post a clarification here
after doing so. The system will notify me and I will take another look
at your question.

Until then, best regards;
Subject: Re: Metal rack in Microwave oven.
Answered By: digsalot-ga on 28 Nov 2002 18:57 PST
Rated:5 out of 5 stars
Hi there mc4

The microwave ovens which are sold with a metal rack are combination
ovens which have a 'browning' feature.

"Why metal rack can be used in the combination mode?

In the combination mode, the microwave is used only for a short
duration in the microwave mode when metal rack cannot and shouldn't be
used. The rack has no sharp edges and the gap between the rods of the
rack is large enough to prevent sparking and to allow the microwave to
pass through.

Please note the grill rack is only to elevate the food to come closer
to quartz heater element for faster browning."

The above quoted explanation is from Bajaj Electricals - FAQ's On
( )

When you are just microwaving, then remove the rack.  While the
sentence from the website above is rather vague, the meaning is quite
clear, the rack is for browning and any exposure to microwaves is
minimal at best.

Your combination setting may look something like this:
Combination cooking (30% microwave plus 70% grill - or - 55% microwave
plus 45% grill)- it is used only for recipes which require both
microwave for cooking/ baking and grilling for browning.

As for damage to the magnito, if you operate an empty oven, there can
be damage.  The microwaves, after reflection from the empty, cavity
will fall back on the magnetron to affect its life and will lead to
magnetron failure.  Food in the oven absorbs the microwaves and
protects the magnetron.  Once again, don't have the rack in when just
using the microwave.

Search - google
Terms - metal rack +in microvave ovens, combination microwave ovens

If I can clarify anything, please let me know.


Request for Answer Clarification by mc4bbs-ga on 28 Nov 2002 19:39 PST
The microwave I own, and the one my friend asked me about do not have
any other "heating" element; nor any options that state
"convectional", "browning", nor "combination mode".  It's a normal
microwave oven with a metal rack in it.  I found this cool website that explains the
physics of the microwave oven; however, no site that discusses what
happens to the microwaves that bounce off of a metal rack.

Clarification of Answer by digsalot-ga on 28 Nov 2002 20:42 PST
Other than re-arrange the microwaves somewhat, I doubt if the metal
rack will cause many problems if it does not have any sharp points.

"This sparking around sharp points is one of the reasons why you are
warned never to put metal in                                          
     microwave ovens. The other reason for the ban is that thin pieces
of metal can overheat as the microwaves                               
                propel currents through them, thereby starting fires.
But metal isn't always a problem in microwave oven.                   
                            A thick, rounded item such as a
good-quality stainless steel spoon doesn't cause any significant
problems. I                                                leave such
spoons in my coffee or tea frequently. While the spoons rearrange the
microwaves slightly,                                               
they neither spark nor overheat." - Quote from Physics Central - which
is the website mentioned by bobthedispatcher-ga in the comment below.
( )

Also, not just any metal rack will do. "Metal racks are physically
proportioned so as not to disrupt the energy pattern." - Quote from
"How do Microwaves cook food"
( )

As for what happens to microwaves that bounce off the rack. 1 - The
rack re-arranges the microwaves but the microwaves still exist.  2 -
Some are absorbed by the cooking food 3 - Some are absorbed by the

The material from which the rack is made may also have quite a bit of
bearing on its use.  "One of the basic characteristics of microwave
energy is that it is reflected by metal. The extent to which
microwaves are reflected varies with the type of metal. For example,
aluminum and stainless steel reflect microwaves, while certain
compositions of cold-rolled steel will absorb microwave energy to some
extent" - Quote from "Microwaves, Metal and Arcing"
( )

As far as damage to the magnetron from the use of the rack, I can find
nothing.  Since the metal rack came with the microwave (assuming you
bought it new and the rack wasn't just added as an afterthought) It
can probably be used with no complications.  Just don't operate the
oven empty.

I appreciate you asking the question as I have also learned somethng
new.  My unit is a combination oven, I never knew metal racks came
with 'microwave only' ovens till this question.  Getting around the
"no metal" barrier may also be something new enough that it hasn't
been addressed thoroughly on the Internet yet.  Even such complete
websites about microwave ovens as the site quoted above
still list questions about metal racks and microwaves as something to
be addressed in the future.

mc4bbs-ga rated this answer:5 out of 5 stars and gave an additional tip of: $3.00
Great answer!!  Great service!

Subject: Re: Metal rack in Microwave oven.
From: bobthedispatcher-ga on 28 Nov 2002 18:35 PST
I'm  not an expert, but have used microwave ovens quite a bit and many
manufaturer do state that small amounts of aluminum foil, or a spoon,
will be OK.  The key problems are sharp points (where arcing may
occur) and thin metal melting.

Metal IS used in some microwave trays for it's heating effect, and
many ovens can deal with a shallow metal tray (TV dinner type).  But
be carefull - it also acts as a shield, reflecting waves away from

for some other inforation
Subject: Re: Metal rack in Microwave oven.
From: flajason-ga on 03 Dec 2002 12:39 PST
From personal experience, I agree... avoid thin metal.

I have always been cautious about putting metal in the microwave, but
one day while heating up some leftover chinese food, I neglected to
remove the metal handle.

It did not spark at all, but it got hot enough to give me a nasty burn
when I reached in to take it out!

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