Microwave oven question

[Peter Morrill]

Whilst cleaning my (very cheap) Hinari microwave, a bit fell off from inside the cooking area. It's a rectangle of silver card-like substance, presumably something more exotic. I think the aperture it covered is where the microwaves come out. It is very slighlty discoloured (charred). What is it, is it vital and can I get similar from my local electronics shop? Forgive my ignorance of microwaves, but I am loth to replace the cooker or get an expensive repair done if it is something simple.

[Frank Erskine]

How did it fall off? How was it attached?

You can buy a sheet of this from CPC and cut it to size.

[Ian Stirling]

It's the waveguide cover, where the microwaves come through.

will probably have it, but their website is a pile of shit. Order code SHPCOVPA308WRE1 for example. Find a bigger one, and you can trim it with scissors to the right size. OTOH, if you haven't damaged it, you should be able to replace it.

google-uk for "waveguide cover"

[Harry Bloomfield]

What ever is used to fix the cover, may have been the cause of the charring. Sometimes self-tappers are used and if these become loose the RF can cause heat build up in the metal contact areas if they are not firmly bonded to each other. So basically make sure the fixing screw is good and tight.

[Ian Stirling]

'what ever' pretty much has to be stuff designed for it. I tried replacing one with a 2mm bit of glass. Put it on for 15 min, to do some rice, and came back later to rice with glass on.

The glass had melted out of the way of the microwave exit, and after the microwave shut off, cooled and cracked. (As it reassembled into one continuous shape)

[meow2222]

In that case I suspect you had another fault as well, probably the fault that caused the destruction of the first coverpiece. Glass would be fine normally, if a little OTT. If charcoal collects on the waveguide exit, as tends to happen, it ends up being excited by the intense microwaves and burning its surroundings, so the charcoal grows. When replacing these covers I would always clean around the mouth of the guide thoroughly to prevent recurrence of the problem.

The nuke would work with no waveguide cover, but this will ruin it after a while, once a short builds up inside the guide. I had one once where you could see the anode directly with the waveguide cover of, glowing red during cooking, but it scared people.

Waveguide covers are normally fixed on with plastic press in fixings. Press it in the hole, then push the head down and it splays.

NT

[Ian Stirling]

Not a fault as such - well, a user fault, operating after cooking a chicken in 'oven' mode, without cleaning.

Was completely clean behind it.

Many glasses are not completely transparent to microwaves.

Most recently, I placed a half cup of milk in the microwave, in a large glass bowl. The glass bowl was actually quite warm, when the milk had boiled.

If the power density is maybe 100w/cm^2 or so, even a few percent is quite enough to melt glass. Not to mention that once the glass hits 2-3-400C, it'll start to absorb much, much more.

(put half a cup of milk into a cup, with a spoon of sugar and custard powder, put it on for a minute, and you've got custard)

[Dave]

What purpose does it serve? Is it a diffuser of some sorts?

Dave

[Ian Stirling]

It stops chicken grease and other stuff getting to where the microwaves come out of and causing fires.

[Tim S]

As a result, they use that fact in the choice of glass for the turntable plate. That is designed to absorb stray microwave energy as a means of protection in case you turn the oven on with nothing, or very little in it.

I believe you can get the glass to glow red if you try it long enough, but my oven's new s I'm not going to try it yet!

Tim

[Dave]

So it's just a window then.

Thanks :-)

Dave

[Ian Stirling]

Nope. There is simply not enough power there to make it all glow red. It'll get quite warm. The waveguide cover is a special case - the outlet is maybe 5*5cm, and most of the energy comes out in a smaller hole than that.

[meow2222]

I guess the OP's Windows crashed, on his 2.45GHz machine. Perhaps after using the ramdisk utility with a large pizza.

NT

[Peter Morrill]

Many thanks to those of you who replied. The problem is now fixed. Knowing the name of the item was a great help when getting a replacement.

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