Annealing Question?

[colonel4bin]

So I finally got my big Cress clamshell kiln up and running again. I am annealing some thick glass, around 0.50 thickness. I have a good annealing schedule set up, but am unsure what a good cool down rate is. More specifically what rate in degrees F/per hour to you drop after soaking at annealing temp for borosilicate? I have it set-up at 75 degrees per hour right now, but that seems slow.

What do you use? Does it anneal well?

[somewhere]

I was going to refer you to bullseye Annealing Thick Slabs here:
http://www.bullseyeglass.com/email/20050721.html
bottom of the page but the pdf isn't working.

I'll see if I have a hard copy of the schedule and get back to ya.
Off the top of my head it's about naaa I better check

[somewhere]

Hey found my chart but now after a second read I see we are talking boro. I would say 75 an hour is definitely slow.
Use the search engine and you will find a good chart someone kindly posted on there GAorg page.
What exactly are you making? and where did you find large sheets of 1/2" boro?

[jane clifton]

Boro or not at that thickness, you need to go slow. 75 an hour is overkill though in my opinion. I would think between 150 and 200 would be okay. Lower to be safe.

Jane

[menty666]

Here's a place 1 town over from me that does boro sheet in pretty much any thickness you can dream up:

http://www.howardglass.com/home.htm

What he heck I'd use it for...that's the real question.

[Kaj Beck]

My ramp schedule...... 1 hour at 1050, drop to 950 over an hour, hold at 950 for an hour then crash, works just fine, no problems even when I am dealing with large 3 inch+ mibs and large opals. Hope that helps G

[Skye Perry]

I anneal all my boro under 3'' at 1075 F for 1hour .Why 1075 F because when striking color this is the ideal temprature and not all brands of clear boro anneal at exactly 1050 F. Corning 1055 F ,kimble/kimax 1060 F not sure about UST,simax or eighenshaft .From 1075 to 950 (the stress point of most clear boro) at 1 degree per minute .From 950 to 300 at 3 degrees per minute and from 300 it is about 15 degrees per minute . Though because the fire brick in the kiln holds plenty of heat I just let my kiln shut off at 950 F and cool to room temprature or close to it before removing anything from it .Henry from GA tough me this cycle in his color certifacation class a couple of years ago and I have had less checking issue's ever since .

[Swampy]

I see Wesley Fleming has put some great info already into the Wiki, good one Wes.

Annealing comes up now and again and folks post their recipes, it would beneficial to have a fixed reference work in the Wiki describing the whys and wherefores eh.

So here's a great link to some killer info (http://www.pegasus-glass.com/simax.asp)discussing the thermal conductivity of borosilicate glass.

I can relate a lot of what they taught me from my engineering days but for the life of me, I can't figure the calculation using the chart on the Northstar website/leaflet because the conversion from degF to degC gives differing results.

I would say the core temp can differ from the skin temp by a set amount, for instance the figure for float glass (below the strain point) is 3degC. For boro that would be wider, given it's greater resistance to thermal shock. Because the skin:core temp has a greater tolerance.

If anyone is interested in putting some good reference stuff in the Wiki I'd be happy to help out with that.

[colonel4bin]

Thanks for the replies everyone. I got one answer I think. I have a good schedule set for annealing and ramping down, which is what most people are replying with.

I am looking for the rate/per hour that you ramp up and down with such as 100 degrees and hour or 250 degrees an hour. When you program your kiln it asks rA for the rate in which you want it to heat up and down at. So Kaj, you use 100 degrees an hour? Sounds about right. Trying to get it right to save a little on electricity, not really having any annealing problems. Right now it is set at 125 degrees an hour.

Somewhere: I am annealing 1/2" thick boro cells/boxes I made for a chemical company, Basically a 3" square box with no top that a chemist will use! It was a tough job since the plate was thick and had to be sealed hot since they will be heating the cells up and down. Usually I would just UV glue it!

[nickglassdood]

yur the man g sic
'

u got pics???????

this kid pulls off some unreal stuff

[colonel4bin]

Thanks Nic, hope your doing well bro. I'll see if I can get a few pics before I ship them out tomorrow. Looks like I will stick to 150 degrees and hour for now, keep'em coming!!

[Swampy]

Garrett if I remember when I come back from the post office I'll write post mine.

[Ro's Glass World]

i used to use bandhus schedule from cont. lampworking, but found, using a polariscope it was to fast. for larger pieces i hold for 1 inch per hour and ramp down at about 60 an hour to 900 then off.
ro

[colonel4bin]

Rosanne...that sounds about right, I follow his schedule too for the most part. Looks like I might just leave it where I have it for now, everything looks good under the polariscope after annealing.