- May 27, 2011 at 12:16 pm #9589
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,May 28, 2011 at 5:53 am #12077AnonymousInactiveMay 28, 2011 at 11:55 am #12078
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!
KeithMay 30, 2011 at 8:55 pm #12079Stephen RichardParticipant
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 RichardMay 30, 2011 at 10:56 pm #12080AnonymousInactiveJune 1, 2011 at 11:55 am #12081
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.June 1, 2011 at 12:00 pm #12082
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!!!
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