Glass fracturing

[kpearman]

I am experiencing alot of breakage for larger pieces during the initial heating process. Usually this is the second time the piece has been fired. The piece usually fractures into several large pieces. I am certain this happens during the initial heating long before the hotter temps are reached.I am using a small ramp rate of 100C per hour up too 1100 F and I have tried both side and top filamants. I heard that this not too unusual and happens around 500 F. Should I put a long soak step in around 500C. Does anyone have solution?

Thanks,

[Anonymous]

What kiln (make and model) are you using and what kind of slump or drape?

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

 

[kpearman]

I have a olympic 146gfe 120v. This has happened during drapes to form a vase and slumps in several different plate molds and also flat tack fuse of two sheets of glass. Usually the bottom plate when tack fusing breaks. I assume the bottom plate just is not heating due to the top plate acting as an insulator. Thanks for any help!

Keith

[Stephen Richard]

From your description and the fact that you don’t mention annealing, I am betting on inadequate annealing.  Annealing consists of two stages – first a soak at the annealing temperature for a length of time adequate to equalise the temperature throughout the glass, second – a slow steady cool down to about 370C  (for 6mm, 80C/hr should be adequate).

 

If the piece has not been adequately annealed, it will break easily upon the heat up.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

[Anonymous]

It is breaking before the slump, correct?

Draping in that kiln is almost impossible due to the shallowness. Your glass is so close to the elements thermal shock is almost guaranteed.

 

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

 

[kpearman]

I do anneal starting at 1050 F soak for 30 min, ramp at 200F/Hr to 750 F and hold for 30 min and 200 F/hr down to room temp. Sounds like I may be ramping down too fast.

[kpearman]

Yes, I have brekage before the slump and drape starts. I will use only side filaments in the future for draping. I assumed that the top flament would heat more uniformly. I really appreacite all the advice!!!

Thanks, Keith

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