Float glass schedule and rates

[Havi]

Dear friends,
Happy new year to all of you,

I have 2 blocks of float which I made ages ago.
Now I want to kilnform them, kind of slump. I have no idea about working with float glass.
Both blocks are about 9" by 11".
One is 9/16" - 1.4 c'm
the second is 12/16" - 1.8 c'm

at what temprature does float get formed, and what is the rate to raise the temps.? Anybody knows?

Your response will be much appreciated.

Many thanks in advance,


Havi

[Bert Weiss]

Havi. heatup rates are dependent on your particular kiln configuration. Float generally needs 80ºF hotter to slump, fuse, or anneal, than Bullseye.

For your thick piece, I think an overnight (8 hour) heatup should be conservative enough, as well as a practical solution. The thinner one should tolerate a much faster heatup. Unless there is a large thickness differential across the shape.

The lower COE of float glass makes it a bit less susceptible to heat and cold shock than the higher COE fusing glasses.

[Havi]

Thanks,Bert
I shall try follow your advises.


Shavu'a tov....


HAVI

[Brad Walker]

The lower COE of float glass makes it a bit less susceptible to heat and cold shock than the higher COE fusing glasses.

This is an interesting assertion, Bert. As I recall most float is around 82 to 84 COE, about as far below Bullseye as Bullseye is below Spectrum. So are you suggesting that Bullseye is less susceptible to heat and cold shock than Spectrum? That hasn't been my experience. I suspect that float is less susceptible due to factors other than COE.

[Bert Weiss]

The lower COE of float glass makes it a bit less susceptible to heat and cold shock than the higher COE fusing glasses.

This is an interesting assertion, Bert. As I recall most float is around 82 to 84 COE, about as far below Bullseye as Bullseye is below Spectrum. So are you suggesting that Bullseye is less susceptible to heat and cold shock than Spectrum? That hasn't been my experience. I suspect that float is less susceptible due to factors other than COE.

I was careful to include the modifier "a bit". Since I don't have extensive experience using 96 and 90 glasses one after the other, I can't comment on the practical aspect of this. I do know that my float glass is less prone to cold shock at the bottom of a firing, relative to Bullseye. There is more than one factor at play, though. A monolithic glass has less pushing and pulling going on than an amalgamation of different glasses. My gut feeling is that float is less finicky than Bullseye. COE is an answer that fits in with the theories of why.

In theory, I know the statement is true. However that does not mean that your question is not entirely valid. A few points may not make much practical difference. Borosilicate, that does act significantly different, has a COE in the 30's.