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GAS FIRED FURNACE.

Page 2.

I still needed a furnace for melting bronze. I decided to build a small crucible furnace as the bronze castings I required were small and few in number I will go into greater detail in describing this furnace. The following drawings illustrate it.

Fig.3 is a cross section giving the main dimensions
Fig.4 external views.
Fig.5 external views.
Fig.6 external views.
Fig.7 Shows the design of the lifter for lifting the crucible out of the furnace.
Fig.8 Shows how the refractory lining is cast.


Construction.

The furnace is simple in design and is fabricated out of flat 1/8" steel plate. No rolling is required. Plates are welded across the inside comers to cut down od refractory. I used a vacuum cleaner type blower that I had been given. It was used in some small spray painting unit. The drawings show how the furnace was originally built. However I had to remove the blower and connect the air pipe to a larger centrifugal blower. This is many years ago and I am not clear on it. On the first furnace. Fig.1. I used my wife's vacuum cleaner as a blower and using town gas was able to melt bronze.

The burner is the same simple design that I used on the other furnaces. The flame is directed low at the bottom of the crucible. The bottom is made removable. This cops the hardest use, with solidified metal building up in the bottom and the projection the pot sits on breaking away. It is necessary to replace this more often than the lining. A drain hole in the bottom is for spilled metal to drain out. Actually there is never enough splash over the side of the pot to run. However should a pot split in the furnace it will allow the metal to drain out instead of collecting in the bottom of the furnace, if this happened the lining would have to be smashed out.

To start as much metal as will allow the closing of the lid is put in the pot. Metal that has to be added as melting proceeds is laid on the cover slightly overlapping the hole so that it is preheated. If it will allow it is pushed into the hole in the cover as required. As this is a one-man operation I had to design a lifter for lifting the pot out of the furnace Fig.7 shows what I came up with. Studying the drawing will give an understanding of how it works.

On the front of the furnace two bars projected out to hold the ladle shank. When the crucible of molten metal was lifted out it was lowered into the shank so that dross could be skimmed up, it was lifted off to pour the castings. Of the shank was an insulated disk to protect the hand from the heat of the pot.

Casting the Lining.

Fig.8. Shows how the lining is cast. A sheet metal sleeve with a soldered lapped joint locates in the cutout hole in the furnace bottom. A wooden mandrel is turned and cut to fit the sleeve This fits into the hole for the burner and is nailed to the sleeve. The heads of the nails are left protruding so that they can be withdrawn later. The outside of the sleeve and the mandrel are coated with grease. A wooden mould is made for the bottom, and a soldered sleeve fitted around it. The inside of this and the mould are greased. The cover frame is set on paper on the floor and a small sleeve for the hole is centered. This is greased. Not shown are short rods welded to the inside of the frame that will prevent the lining falling out when it is set.

The refractory cement is mixed and shoveled into the shelf, cover and bottom mould. As the refractory settles it will be necessary to add a little to the top of the furnace part and trowel it off to give a flat surface for the cover to seat. When everything is set, the nails holding the plug are withdrawn and a torch applied to all the soldered joints. Everything falls away. The plug is knotted out and the bottom mould turned over, rapped and lifted off. If I remember, I let the furnace stand for a couple of days before lighting the burner. A low flame was let burn for a day to dry the lining out before hitting it with the high temperature required to melt bronze

WARNING ----- Do not play around with LPG unless you know what you are doing.

Being heavier than air it is a dangerous gas. It does not rise up out of harm's way but lays on the floor and you don't know it is there. Myself and the chap who took it over have been using the furnace (Fig- 1) now for about twenty years and have never had a mishap. The simple burner design would not be permitted under today's regulation on the use of LPG. However these rules apply to its use in industry and would not apply to a hobbyist building this design of furnace and using it in the back yard shed.