float glass fusing problem - bends

[mundek.glass]

Dear ALL,

I am new here and also, quite new in fusing. Probably, the topic is somewhere here but it is not so easy to me with my english to find it.

I am trying to fuse 2 pieces of float glass (900x300x4 + 900x300x6). Firing shedule I have found here on the forum as a standard for a float. The problem I have is, that glass bends during the process. Could you help me somehow, please?

[Brad Walker]

Could you tell us what you mean by "bends"?

Is the piece being fused on a flat shelf and bows upward slightly or is it something else?

Also, it would help to have your firing schedule.

[mundek.glass]

Hello,

Yes, fusing was done on flat shelf (on ceramic paper). And yes, saying 'bends' I meant, that bows upward slightly (like you can see on photo attached).
Below you can see firing schedule:

0 C – 482 C in 120 min stay 15 min
482 C – 593 C in 20 min stay 0 min
593 C – 676 C in 90 min stay 30 min
676 C – 801 C AFAP stay 10 min
801 C – 520 C AFAP stay 0
520 C – 400 C 140 min
400 C – room temp

Regards,
Mundek

[Brad Walker]

It's not unusual for long narrow pieces to bow slightly.

To solve the problem, I recommend stopping just above the annealing temperature and holding for at least half an hour That gives the glass time to relax and even out the internal temperature before annealing.

Your schedule is unusual in that you're annealing WAY below the standard annealing temperature for float. That's 1000F/540C, and you appear to be annealing at 750F/400C, which is below the annealing zone for float and is probably of little value.

Instead, hold for 30 to 60 minutes at just above the annealing range (try 1150F/620C), then go down to an annealing temperature of 1000F/540C and hold for the thickness of your piece (140 min should be ok).

[mundek.glass]

Thank you very much for a suggestion.

Below is new schedule, could you check and let me know did I understood right your suggestions ?

0 C – 482 C in 120 min stay 15 min
482 C – 593 C in 20 min stay 0 min
593 C – 676 C in 90 min stay 30 min
676 C – 801 C AFAP stay 10 min
801 C – 620 C AFAP stay 30 to 60 min
620 C - 540 C AFAP stay 140 minutes
540 C - room temp.

Mundek

[Brad Walker]

Yes, that's right. You don't really need to program the last step all the way down to room temperature.

As your final step, I would program 45 dph down to 375C, then turn the kiln off and let it cool with the lid closed to room temperature.

[mundek.glass]

Thank you very much.

Will conduct tests and till the end of coming week let you know about the progress.

Regards,
Mundek

[mundek.glass]

Hello Brad,

After tests as per your recommendation, result is still the same - only 900x300x4 + 900x300x4 is better (almost flat). All pieces where we melt 6 mm thick glass plus 4 mm are bent.
Do you have any other idea whats wrong?

Mundek

[jim simmons]

Do you mean that the total thickness is 10 mm?
The other Jim

[mundek.glass]

Yes, we fuse 2 pieces:

900 x 300 x 4 + 900 x 300 x 6 (6 mm thick piece lays on 4 mm thick piece). Total is 10 mm. Both are float, 4mm - guardian, 6mm - pilkington.

Mundek

[The Hobbyist]

Looks like a clear case of incompatibility. Not all float glass is the same COE. You are using two different manufacturers which would most likely mean they are different glass formulas.

Jim "The Hobbyist"

[mundek.glass]

Yes, I have been thinking about this but pieces 4 mm + 4 mm both were guardian cut from the same sheet of glass and still, they are not completly flat (but definitly better than 4 mm gluardian + 6 mm pilkington).

Mundek