Taking into account the glass AREA when annealing...

[Catharine Newell]

Without resorting to a complex mathematical formula, how do I compute an anneal soak for AREA + thickness of a panel? For example: 35x14x5/8"... It has come to my attention that I am not paying enough attention to the area of glass involved when programming my soak at 960. BE glass, top and side elements, fibre shelf, 46dph from 960-775, 70dph to 500...

What d'you say?
Catharine

[Bert Weiss]

Without resorting to a complex mathematical formula, how do I compute an anneal soak for AREA + thickness of a panel? For example: 35x14x5/8"... It has come to my attention that I am not paying enough attention to the area of glass involved when programming my soak at 960. BE glass, top and side elements, fibre shelf, 46dph from 960-775, 70dph to 500...

What d'you say?
Catharine

Catherine

In my float glass work, I ignore area and anneal for thickness. When I put the largest piece of 10mm glass that will fit in my kiln in to the tempering furnace and it heated to 1100ºF in 5 minutes without breaking, I figure that my schedules are working.

I think that the part of the schedule that you need to worry most about is heatup. The various stresses caused by different glasses pushing and pulling on one another is going to be more problematic relative to heatshock than it will have a problem equalizing in temperature when annealing.

[Lauri Levanto]

As I understand, the *area* is relevant only to a side
element kiln. The heath escapes the shortest way. A flat
sheet loses heat over the top surface, and maybe thru the
shelf. I do believe that even the shelf is cooled mainly
thry the glass.
*Under* a large sheet near the bottom of the kiln, there
may be a hot air pocket, releasing heath only around
sides, that may cause uneven annealing and warrant
a slower pace.

I need both elements to reach the fusing
temperature, but I use only the top element for annealing.
This prevents the top surface cooling too fast, and helps
to keep the temp even thru the thickness of glass+mold+shelf.
-lauri

[Brian and Jenny Blanthorn]

Without resorting to a complex mathematical formula, how do I compute an anneal soak for AREA + thickness of a panel? For example: 35x14x5/8"... It has come to my attention that I am not paying enough attention to the area of glass involved when programming my soak at 960. BE glass, top and side elements, fibre shelf, 46dph from 960-775, 70dph to 500...

What d'you say?
Catharine

In addition

Go 4 the thickest area

It thick / thin go 4 the thickest area then add a bit

[Bert Weiss]

In addition

Go 4 the thickest area

It thick / thin go 4 the thickest area then add a bit

Thick and thin is a totally different problem than uniform thickness. Stress is relieved when the entire piece of glass stabilizes at the right temp. Thick and thin takes longer to do that than just thick.

[Catharine Newell]

Well then, if top and side elements are in use during the entire firing, am I correct in understanding that my main concern is the thickness of a relatively uniform panel rather than area? I'm thinking that area must have something to do with this process. Re: the 35x14x5/8 panel I mentioned... I'm soaking for 2:30 @960, then doing the drop I mentioned in the first post. Does this sound appropriate, or too short at 960? I generally take 8:30 plus to reach my tack/full fuse temps...

Catharine

[Catharine Newell]

Well then, if top and side elements are in use during the entire firing, am I correct in understanding that my main concern is the thickness of a relatively uniform panel rather than area? I'm thinking that area must have something to do with this process. Re: the 35x14x5/8 panel I mentioned... I'm soaking for 2:30 @960, then doing the drop I mentioned in the first post. Does this sound appropriate, or too short at 960? I generally take 8:30 plus to reach my tack/full fuse temps...

Catharine

Let me amend this to say that I take 9:30, at least, to reach targeted temps[/u]

[S. Klein]

I always try to think like the glass and like the kiln. A piece of glass wants to be the same temp throughout. Going up and down the kiln must accomplish that. If a kiln has only top elements and fibre board is under the piece than cooling could go faster. When you put side elements on, the edges are getting more heat than the center even if top elements are on as well. A kiln shelf retains heat much longer than fibre board, therefore when a kiln shelf is used, the bottom of the piece will be significantly hotter than the top of the piece. For me the ideal situation is fibre board below and only top elements. If the kiln has side elements I baffle all around. All this being said, after putting 3 or 4 weeks into a piece, I never hesitate to err on the side of caution..................steve

[Bert Weiss]

I always try to think like the glass and like the kiln. A piece of glass wants to be the same temp throughout. Going up and down the kiln must accomplish that. If a kiln has only top elements and fibre board is under the piece than cooling could go faster. When you put side elements on, the edges are getting more heat than the center even if top elements are on as well. A kiln shelf retains heat much longer than fibre board, therefore when a kiln shelf is used, the bottom of the piece will be significantly hotter than the top of the piece. For me the ideal situation is fibre board below and only top elements. If the kiln has side elements I baffle all around. All this being said, after putting 3 or 4 weeks into a piece, I never hesitate to err on the side of caution..................steve

Steve

I couldn't agree more on every point.

[Lauri Levanto]

Just learned it by the hard way!

The area does count ! !
Take a one inch button and a ten inch plate.
What ever is the residue of stress after annealing,
in the 10" plate it has a tenfold moment to break
the glass. So you must be more careful in annealing.

This applies to the warm up stage, too.

As Lani stated earlier, it is possible to "over anneal" in
a kiln with uneven temp distribution. You are just keeping
on the difference.

In a kiln with nearly perfect evenness, the cooling
takes place all over the piece simultaneously.

-lauri