Slumped glass platen is it possible?

Fred.Rowe

Fred.Rowe

Knifemaker / Craftsman / Service Provider
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May 2, 2004
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I want to try slumping 2" wide by 1/4 thick glass to make a radiused platen. [48 inch radius] I've read a bit on temperatures to slump the glass, they can easily be handled by the elec. kiln.

The form could be made using castable clay with the resulting glass platen being epoxied to a mild steel base. I think the glass would run cooler and would not gouge as easily as steel.

The temps I believe are around 1200 to 1500fh to slump followed by tempering of the glass. If you have any insight I would appreciate it.

Fred
 
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I would think grinding the glass would be easier than tempering and such, but I don't know much about it. I'll be watching for some answers.


-Xander
 
I have slumped old beer and coke bottles, but not tried any glass of the type you would need.
The problems with heating and curving a pyroceramic glass platen would come in not having it crack.
If it works, I would use the actual curved steel base plate to slump it on so the fit will be exact.
 
I'm going to try it. I think you may be correct about slumping over the actual base. I see three radius-ed pieces of 1/4 inch mild steel attached to a flat attachment base.
The tutorials I've read talks about the heating and cycling required to keep the glass from cracking. I'll try some test pieces first and see what transpires. I will post picks when I get this together.
 
It's worth a shot. The type of glass you use will vary you temperatures greatly. So just like steel you need to know what you are using. The other problem I see is that it will slump! You will have a smooth surface but maybe not a flat surface. I would have the glass ground for best results but it's worth a shot!
 
amamachinist said:
It's worth a shot. The type of glass you use will vary you temperatures greatly. So just like steel you need to know what you are using. The other problem I see is that it will slump! You will have a smooth surface but maybe not a flat surface. I would have the glass ground for best results but it's worth a shot!
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Good points; I've considered what you are saying about smooth but maybe not flat. Will the heat cause the glass to slump more in some areas that others, so as to leave a cobblestone surface. With a 36 or 48 inch radii the glass should not have to slump very far. I'll get my trig book out.

I have a local friend who is a glass jewelry maker and she works with an electric kiln. I'm going to pick her brain on temperatures and times. It's said glass is much like steel as to time at temperature.

Thanks for posting, Fred
 
I think it will pucker a bit.

Surface tension type puckering, High, or less likely low at the edges.

Easy enough to dress that out after slumping though.
 
Fred.Rowe said:
Good points; I've considered what you are saying about smooth but maybe not flat. Will the heat cause the glass to slump more in some areas that others, so as to leave a cobblestone surface. With a 36 or 48 inch radii the glass should not have to slump very far. I'll get my trig book out.

I have a local friend who is a glass jewelry maker and she works with an electric kiln. I'm going to pick her brain on temperatures and times. It's said glass is much like steel as to time at temperature.

Thanks for posting, Fred
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The annealing is what is going to be the hard part. Most glass needs a very gradual lowering in temp. Sometimes taking 24 hours to cool. But that is when you have had it molten you won't be getting it anywhere near that hot. Most importantly is that you start with a known glass type.
 
Do you know what type of glass you have? I can't find any good charts online but I do have some old books I can go thru from my glass blowing days.

Also when I first read your post I was picturing slumping the glass down on the ends (think upside down bowl) but now I'm thinking you might be better off slumping the middle down onto a flat surface. This might make your working side of the glass more flat as it forms to your mold. The downside being that you won't have a backing piece like Stacy suggested.
 
Viscosity of Borosilicate Glasses
Working Point 1270 °C
Softening Point 820 °C
Annealing Point 560 °C
Strain Point) 518 °C
Transformation Temperature (Tg) 525 °C


Borosilicate glass will be your best bet because it will be able to withstand being heated and cool repeatedly by your belts.
 
Lining up the glass should be next I think.

I was picturing the slumping, ends moving down. But you may be on to something center moving down.

I'll draw the large radii on paper today so I can see how far the glass has to move.

Thanks for your input, Fred
 
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