Programming the Kiln - Sentry 2.0

Erwin Timmers: Hello, I am Erwin Timmers and we're here at the Washington Glass School and in this segment I am going to tell you a little bit about working the kiln and the different temperatures that we need to melt the glass.

These kilns have this little computer on the side here. This computer comes on the lot of different types of kilns, not necessarily only on this kiln. There are larger kilns that are run by the same kind of computer and I have seen very small kilns, very universal. I mean it has very logical series of steps that you take to enter the temperature that you want to take. We've just put the glass in the kiln and so we've closed the door, so the temperature is now just a little bit above room temperature because it's still, you can see on the readouts, it's now a 171 degrees inside the kiln, the other temperature is the last routine temperature which was 200 degrees that we used for drying the kiln shelf.

Now, in order to melt this glass into a bowl that is all fused together, you want about 1450 degrees and that is something that's every glass manufacturer has a different temperature that they want to detain. Window glass typically melts at lot higher temperature, there's other glasses that melt at much lower temperatures. But for this manufacture bowls 1450 degrees is the temperature used to make everything flat surface fused glass, full fused is what they call it. Now, in order to get the glass to that temperature, you need to bring it up slowly. If you heat up the glass too quickly, it will shatter. So, you go start from present temperature at rate of about 350 degrees per hour. Now, since this is a small plate, you can do it a little bit more quickly, but as soon as you get the bigger plates 12 inch, 20 inches and you really want to make sure that your glass warms up at a very slow gradual rate.

So, what I do here is I am just going to start the computer and first asking for user number which doesn't really matter which user it is and then it asks me for a ramp and then I am going to enter that number that I was talking about, 350 degrees per hour. It asks me for a temperature, well how warm do I want the glass to get. Well, Bullseye specifies and it's great to use their glass because they give a full temperature range of everything you need to enter in this computer to get the glass to come out successfully.

Okay, 900 degrees, they have like a strain point at which they want you to hold the glass, so that all the glass becomes the same temperature and there's not parts the glass, that are still a little bit colder, parts of glass a little bit hotter and that temperature is 900. So we bring it up to 900 degrees and we hold it there for 15 minutes, then the next ramp can be a lot quicker because at this point, your glass is already quite hot and you don't have the chance of thermal shock -- and the glass already start to get little bit soft. So, you can bring it up much quicker to the 1450 degrees that we talked about. So, the second ramp, see it's asking for the second ramp, 700 degrees per hour, okay. Then, I have entered again.

Now 1450 degrees was the final temperature and where everything melts together. Before that, I want to step at about 1250 degrees where all the glass is soft and starting to take on -- it can take on a different shape and it will actually that is the temperature also you use in the final step where you're shaping it into your mould. But at this point, you want all the glass to kind to be flat and make it so that there's no bubbles. All the air from the bubbles will be squished out at this point. So we bring it up to 1250 degrees, okay? We enter it and we hold it there for about 20 minutes. That is enough time for all of the air to escape and the glass is now quite soft.

The next ramp can be as fast as you want it to be which in this case is symbolized by 9999 and then we're going to go up to that 1450 degrees which is the full fuse temperature for Bullseye glass. There I am going to hold it for 20 minutes. This is all specified by the factory and now, this is the end of the full fused soak. Now the glass needs to come down and you want it to cool off as quickly as possible in the first segment because the longer it stays hot, the more chance you have that it melts all over the place, things are going to happen that you don't want to happen.

So, you bring it down again as quickly as possible again, symbolized by this 9999. Now, this is quickly as the kiln will cool off and some people actually open the kiln at this point to allow the hot air to escape and the kiln to cool off quicker. It's asking me for temperature. Well, we want to bring it down to an annealing temperature and we've talked about annealing, annealing is like controlled cooling. There's a big difference in ceramics and glass there, even though the kiln is going to be very similar, glass needs to anneal in order for it to remain stress free once it's cold. Annealing basically means that you hold it at a certain temperature to allow all the parts of the glass inside to outside to attain that same temperature, all the molecules are moving at the same rate and there won't be any stress when it cools down further and for Bullseye that is 960 degrees. So we're going to bring it to 960, enter and we hold it there.

For a small plate like this, 45 minutes would be sufficient, an hour is kind of like a standard that we do for most projects. If you have a thicker slab like a big -- we did an inch and a half thick slab recently for a floor panel that had to an hour, had to anneal six hours at one temperature, then four hours another temperature. So it basically the thicker and bigger, you start to work, the more difficult these process would become. We're going to hold it for one hour and after that pretty much you're done. Some people like to have the kiln cool off a little bit more controlled to say 700 degrees, so we can add that into -- say we're going to let it go down 100 degrees an hour which is quite slow to 700 degrees temperature and hold it there, really you don't need to hold it there for more than a minute because it's basically only the rate at which it cools off that's important, the whole time is not important at this point, one minute is the minimum amount you can enter.

Then the next ramp, we'll just leave it zero, that way the computer knows that the program over, and this is the final step. And now program has been entered, the computer is idling. I am going to press Enter again, and it will start up and you will see that the elements are going to start clicking. The lights come on that means there's now power being produced that will heat up the elements. You see that this one has both elements in the side and in the top. Glass kilns generally don't need elements in the side just because of the danger that if there are elements in the side, they could heat up the edges of the glass more than the center of the glass. So the top elements are the most crucial so this one is on high that's where the electricity is used most. The side elements are only on a great low setting just to give it a little bit more of a boost to it.

So when we come back, I'll show you what comes out of the kiln the next day and we'll go, evaluate it and see what we're going to do with it next whether we slump it into a bowl or keep it at tile.