GAS FIRED FURNACE.
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.
||is a cross section giving the main dimensions
||Shows the design of the lifter for lifting the crucible
out of the furnace.
||Shows how the refractory lining is cast.
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
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
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.