Re: [ATM] Microwave heating of glass

["Thomas Janstrom" <thomas@moiler.com>]

I have a feeling that the SiC surrounding the glass will be a great help
here, was not only is it transparent to IR but a reasonable microwave (MW)
suseptor (sp?), so it absorbs the MW energy and re-radiates it in the IR to
the glass.

Use a thermocouple to (at this stage of the process) govern when the
magnetron is on and off.

And yes for an 8" by 2" blank you're looking at about 7 to 10 days for the
anneal that is to go from 600'C to 500'C (I'm using round figures, if you
want the exact numbers let me know, I have them), the rest of the way down
to room temp can go faster.

Cheers, Thomas.

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Dale Eason
Sent: Thursday, 10 January 2008 5:02 AM
To: atm@atmlist.net
Subject: Re: [ATM] Microwave heating of glass

So what is your plan to do about annealing?  You will
not be able to use the microwave for that.  Once the
glass is no longer hot enough to be a microwave
receptor then the microwave will not work but the
glass will still need to be annealed.
 
I think standard annealing takes many days of slowly
reducing the temperature. 

Dale Eason

--- Ian Williams <i.r.williams@bristol.ac.uk> wrote:

> So, how does this sound for the next draft of the
> microwave powered 
> glass furnace method?:
> 
> Assumptions:
> 1) That fire-brick is a very poor absorber of
> microwave radiation.  If 
> anyone here can test this by trying to heat a mug of
> water enclosed in 
> fire-bricks I would be very grateful.
> 2) That plaster of paris/Alumina is also a poor
> absorber of microwaves 
> and is suitable for making a refractory mould for
> glass.
> 3) Suitable lab-safety is followed at all times.
> 
> Method (draft 2):
> * Purchase/reclaim a microwave oven with 'microwave
> stirrer' type of 
> magnetron, fire-bricks, glass of desired quality,
> several SiC sharpening 
> blocks, and Plaster of Paris/Alumina to make a
> mould.
> * Make a block of plaster of paris/alumina of
> dimensions 10"x10"x5" with 
> a cylindrical depression in the top surface, of
> diameter ~8" and depth 2".
> * Machine fire-bricks to make an enclosure that
> completely fills the 
> space of microwave leaving enough room inside for
> the mould and SiC 
> blocks.   Don't forget to fire-brick line the base
> of the microwave 
> underneath the mould.
> * Break up required amount of glass into pieces of
> size ???? cm^3.
> * Place microwave where, if it catches fire, the
> fire won't spread. e.g. 
> outside.
> *  Place fire-bricks, mould, broken glass and SiC
> blocks into said 
> microwave.  The SiC blocks could be:
>     a) all around the mould, thus absorbing all the
> microwaves, or,
>     b) only on the sides of the mould away from the
> magnetron, thus 
> allowing the glass to absorb microwaves directly
> too.
> * Set timer to somewhere around 15 minutes, press go
> and stand well back.
> 
> If you can spare some more criticism of these ideas,
> I would appreciate 
> your time.
> 
> Thanks again,
> Ian
> 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 



 
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