Jim Watt wrote:
> On Sun, 08 Jul 2007 12:04:26 +0100, Tim Jackson
> <tim@tim-jackson.co.uk> wrote:
>
>> Jim Watt wrote:
>>> On Thu, 08 Mar 2007 01:44:38 GMT, dr@him.com wrote:
>>>
>>>> Microwave is just plain stupid.
>>> Why?
>>> --
>>> Jim Watt
>>> http://www.gibnet.com
>> I couldn't resist this.
>>
>> The idea looks good to me so I just tried it. It works and is quick and
>> easy.
>>
>> I put the CD on a wire microwave pie rack to lift it off the metal base
>> plate and prevent screening. I put in a cup of water to protect the
>> microwave from over-voltage and to limit the power density.
>>
>> After about 15 seconds at 1kW the CD was hot, bowed, crazed and smoking
>> a bit.
>>
>> Effectiveness looks roughly equivalent to shredding into 5mm fragments.
>> Destruction is clearly visible. See http://www.tim-jackson.co.uk/cd.JPG
>>
>> It's harmless to the microwave as long as there is something there, or
>> enough CDs, to absorb any excess power, and as long as you don't make
>> too much smoke and fume. The CD absorbs a lot of power, so I guess with
>> half a dozen you'd have no risk of over-voltage or excessively rapid
>> temperature rise and can omit the water.
>>
>> You'd need some sort of (dielectric or wire) frame to support the CDs
>> far enough apart to expose them roughly equally, for doing quantity.
>>
>> So I can definitively state that the idea is not stupid. It may not be
>> the best solution, maybe relatively labour intensive compared to
>> chemistry, but it certainly is a contender: cheap, produces minimal
>> pollution and uses readily available equipment.
>>
>
> Some hints:
>
> 1. The last thing you need in there is a wire frame !
> although plastic would be fine
>
The wire frame came with my microwave. I assure you it is metal and it
works fine. It is intended for heating pies and pizzas, so that
moisture is not trapped underneath. A sturdily built welded steel wire
space-frame structure does not get noticeably hot because the path
lengths are too long for eddy current losses to be significant, and it
is not a very good reflector because the gaps are larger than the
wavelength of the radiation. But it is not a good idea to build your
own unless you understand the nature of microwaves rather well.
If I laid the CD straight on the turntable (also steel) it was fairly
effectively screened and only a small patch was burnt.
> 2. You do not need smoke or to melt the disks the beauty
> of the idea is that a short exposure causes the total
> destruction of the metallic film in the polycarbonate
> sandwich without affecting that.
>
You probably don't, but any less energy and the damage wasn't very
visible. The disk didn't melt, just warped a bit (see photo). But by
the time it had crazed evenly all over there was just a little smoke and
fume from the hottest spots. It seemed to me that maximum undamaged
run-length was a fairly critical parameter in the original specification.
> 3. I do it without the cup of water as its only for around
> three seconds burn, you see the flashover.
>
Sure you do, but it stinks, and the burn tends to be localised. I had a
gone-cold cup of coffee waiting to go in next, so I didn't want to
contaminate the oven.
> If you have any free AOL disks they are ideal for testing the
> method.
>
LOL. I've got a big stack of freebies that come in junk mail. I used
some for pivot bearing washers in my custom-built reclining computer
chair too.
My favourite is the employer's CD the Revenue and Customs dept. send out
every year for tax calculation.
Tim Jackson
Re: Best method For CD destruction 
Linear Mode
