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Glass furnace
The evolution and making of a glass furnace. Still in process
This is a combined project between my husband and I to try to get a glass furnace to be able to use in the back yard. Originally it was to make a glass furnace to be able to take to events but with my injuries we have decided that it will most likely live in the garage and be wheeled out to the drive way to be used. We both liked the idea of the little Dragon glass furnaces https://www.mobileglassblowingstudios.com/#/ but not the price tag. I also did not like some of the features of the furnace having used a one that a friend owns. I also wanted to be able to re-do maintenance any furnace that I have without calling a company and shipping it back. With some internet digging we found the Mini Melt Glass furnace in England which had some design features we liked as well http://minimeltglass.co.uk/
What are the design features and characteristics that I wanted in a furnace.
1. Small and mobile (on wheels)
2. Large enough opening to do a bowl
3. Re-heating (glory hole) furnace combo
4. Side burner, not top burner.
5. Adjustable doors that can keep heat in be closed off for the being melt but can be opened up to be able to re-heat a bowl.
6. Propane powered.
Reference books
Glass Notes: A reference for the Glass Artist Third Edition by Henry Halem
A Glassblower’s Companion: A compilation of Studio Equipment Designs, Essays, & Glassblowing Ideas 1st Edition
by Dudley F. Giberson (Author), Fritz Dreisbach (Editor), Linda Burdick (Editor), Dudley F. Giberson;Jr. (Illustrator)
The above books were referenced to tolerances and how to build a furnace. Both books are assuming that you will have a furnace and separate glory hole. To save space, as well as energy sources we were looking for a combo idea. Neither company who has put out pictures and videos of there combo systems have put out a how for there systems either. We also did not want to rip off an idea or a construction from either artist as they make very nice systems.
The starting point was sketching what we wanted to try.
We then broke this picture down into components.
1. Burnner
2. Bottom or the pot
3. Top the furnace / glory hole /re heating chamber
4. Doors
5. Wheels and movement.
All of these parts need to work together and complement each other.
1. Starting with the burner since Eric has made burners before we started with the burner. The burner is a ribbon burner made out of refractory cast with holes and pipe burner with a oxygen source.
The top of the burner has a piece of metal inside the box is a plate that has holes drilled into it to spread the gass and allow the gass and oxygen to mix. There is a tub that allow the blower to be attached to the burner and the gas line is attached in front of the blower. By having gas and air mixing it allows for a hotter flame.
Spreading the flame out makes a larger heated area and keeps hot spots to a minium to spread the flame out from a 1 in flame to a 4 x 8 in ribbon, cast a set of holes with refractory to create a large flame area.
The burner was cast by creating a mold out of 2X4 wood pieces and setting straws into a plate at the bottom. The castable refractory used is what is considered soft refractory. We used the same refractory that we use for forge bottoms as we had some left over from making forges.
This allowed us to have a refractory face to a large burner. The burner shoots flames about 4 feet when lite and not contained.
Video of the test burn on Eric Campbell’s facebook
2. The bottom of the furnace we decide was going to be a welded metal box with a lining of fire brick and then refractory with a invested crucible. We start with the crucible to determine the size of the box. The crucible I chose is 25 lb glass crucible that is 11 in external diameter by 8 inches external depth.
SO working out from the crucible we want to have a industructable refractory that is high temp and also with stand a high amount of klas so is not going to degrade quickly. I was pointed to Kast-o-lite 30 or Econcast -30 both good for high temps but not good for glass. The MORCO 95 from Hi -temp is near bullet proof which is what we want in contact with glass and glass fumes. MORCO 95 was from Hi -temp in WI and Larkin in GA does the Econocst-30 At this point we have yet to purchase refractory because we want to know the amount that will be needed on the top and the bottom of the furnace.
So the bottom has the crucible at the center 2 in of cast able refractory then 2 lays of high temp fire brick and then a metal box. We want the Morco 95 castable around the crucible so when it breaks the glass does not get to the fire brick because hot glass will liquify the fire brick and dissolve it.
These sizes though made the calculations for the size of the bottom. The box was created on a metal frame that is on wheels so that the furnace can be wheeled into the drive way to run. The height was determined by a comfortable height for me to spin and move a blow pipe. Most of the metal in the project to this point was donated from a friend or was blacksmith shop scrap. The high temp fire brick was acquired from a friend and was trapezoidal shape and need to be cut to be square to line the box.
3. The top after much discussion we decided to make a trapezoidal top to the furnace. This the shape of the out side of the box as we want a dome on the inside to reflect the heat and allow for a 12 in diameter piece to be made. The inside of the top will be lined with accordion folded Ceramic fiber blanket and refractory. Our plan is to accordion fold in the ceramic blanket and then attach it to the top with the refractory sealing it in place. We did have to purchase some sheet metal to finish the top.
For now we have the top as a box that is still being welded.
1. The doors I want to be able to open and close the door so I am hoping for a split circle door with and inner and out part. This will mean at least 2 cased doors put on hinges and hung on either side of the re-heating chamber. At this point the way to hang the doors needs to welded an added to the furnace before we start with the refractory. The refractory in the door will be the econ-cast 30 as it will hold the heat the best.
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