Glass Melting in Kiln

[Byrne]

So I had a quick question; if you hold your glass in the kiln at 1050 for longer than 1 hour, will it melt? I've melted some pieces, and the problem seems to be leaving the kiln at a temp of 150 for a few hours, but I don't understand why the kiln would accumulate heat. As I understand it, unless you take glass to slumping temperature it won't melt, right? So why would there be a difference between holding glass at temp of 1050 for 1 hour, and holding it for 6?

[maxtsunami]

So I had a quick question; if you hold your glass in the kiln at 1050 for longer than 1 hour, will it melt? I've melted some pieces, and the problem seems to be leaving the kiln at a temp of 150 for a few hours, but I don't understand why the kiln would accumulate heat. As I understand it, unless you take glass to slumping temperature it won't melt, right? So why would there be a difference between holding glass at temp of 1050 for 1 hour, and holding it for 6?

It shouldn't melt. Check your thermocouple. However, there's not reason to garage at 1050, hold it at 1000 then take it up to 1050 for 30 minutes or so (depending on thickness of work) to anneal.

[Byrne]

Well to give a little background on the situation, I brought the kiln to 1050 and fell asleep; it wasn't until 6 hours later that we began the cooldown process. A number of glassblowers and I share the kiln, and now I am to be held responsible for the sum of our product. I can accept financial responsibility, but I'm not convinced that the meltdown was entirely due to my slumber.

[Firekist]

no, borosilicate glass will not slump or "melt" at 1050 for hour upon hour upon hour. you could leave glass in the kiln for days before you might see a dent where the glass was sitting on the kiln floor (yes, i have done exactly this..today i had a kiln full of work to strike at 1170 all day long. no ill effects at all.) .. (UNLESS you are working super super thin pieces, 1mm and less wall thicknesses or so.. then you might see significant slumping)

work that is closer to the kiln elements tend to get a bit hotter than what the thermocouple is reporting.. more than likely, as said before, it sounds like the thermocouple is not reporting or positioned correctly.

i'm not saying you're off the hook, but maybe, mr. sleepyhead.

---seth

[Aymie]

It shouldn't melt. Check your thermocouple. However, there's not reason to garage at 1050, hold it at 1000 then take it up to 1050 for 30 minutes to anneal.

Annealing time is based on thickness of the glass. 30 minutes doesn't cut it for thick work or marbles. I believe it's 1 hour for every 1/4" of thickness.

I garage at 1050 all day, so I only have to worry about annealing time for the last piece I put in.

What kind of kiln? Your temp is off. Check your thermocouple like said above. My paragon is off and will slump and strike at 1050. If the temp is truly 1050, you shouldn't get slumping. I forgot to turn my kiln off for a good 8 hours after we stopped working yesterday.

[LooseSeal Baller]

yeah my kiln stays around 1050 all day no slumping prob. i'd say your pyrometer is wrong

[yoloswag420]

My guess is the kiln has analog controls and after setting it at 1050F and a six hour nap, 'mid' settings became 'high' and 1050F became 1500F.

[kq9ak]

As a kiln heats up the bricks retain heat and your setting on a analog setup needs to be adjusted, if you want to take a nap you need a digital controler.

[kage]

Just to be clear, was all the work borosilicate?
When you went to sleep it was 1050, but what temp did it read when you woke up?

[dmas0n]

I'm a procrastinator... I like to take long breaks between batches of work sometimes I run two cycles a day but sometimes my stuff garages for long periods at 1050. I've never had any slumping even on things more near to the elements.

[apixdesign]

As a kiln heats up the bricks retain heat and your setting on a analog setup needs to be adjusted, if you want to take a nap you need a digital controler.

This sounds right. My large kiln I have to set full power for an hour then turn down the elements to 30% to keep it at 1050 then constantly check the temp to anneal pieces. Takes forever but I'd never imagine leaving it unatended for more then 30 mins

[Aymie]

I once forgot an analog on high over night. I was just starting and it was my super best most proud if ever batch. Pretty little puddles.

[yoloswag420]

glue puddles to windows, call it "stained"

[menty666]

15 minutes per 1/4" of the thickest section, if I recall correctly.

It gets more annoying if you're getting into fusing because you have to account for the glass AND the mold.

[glasspyromania]

Boro slumps at around 1472. If the kiln is at 1050 you could hold boro at that temp indefinitely without slumping.

Either what ever your using to temp with is way off or you have an analog control and it drifted up to slumping temp while yeh where sleeping.

[Byrne]

We use a digital controller -- and I wasn't the one to shut it off, so I'll have to ask what the temp was. Thanks for all the input! Hopefully I can keep working glass. :)