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Ray-Vin Melting Furnace

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Our first furnace was a Mifco multipurpose furnace. It took 50 minutes to melt 10 pounds of bronze. Also, the crucible had to be lifted chest high to get it out of the furnace. I decided a conventional furnace would be safer and more economical. I started with Dave Gingery's book and asked a lot of questions on hobbicast. I didn't have to ask all the questions since at any given time there will be several people building furnaces.

First I needed a shell. I based the size on a 10" cavity which would be about right for a #10 crucible. To this I added 3" per side for insulation and refractory. Then I called the local well driller and asked if he had any old water tanks I could have. I got two identical diaphram tanks that were just 15-3/4" diameter. On the left is an un-cut tank and on the right the lid and the body for our furnace.

Next came the design phase. After much correspondence on hobbicast, I decided to go with the two types of refractory. An insulating layer 2000F and a refractory layer 3200F. I used Kaocrete 32CM and Kolite 2000HS from Superior Brick & Refractory Service. For my design work I use SolidWorks. It is a 3D parametric solid modeling PC application that is second to none. With SW I modeled in the crucible and plinth. Then I took the water tank and cut the top off to make it the right height for What has to go inside and the 3" of furnace stuff at the bottom. I then modeled the top of the tank to make the lid for my furnace. The different sections you see in the view above show the 2000 & 3200 materials. SW provides the exact volume and weight of refractory for each item taking the guess work out of the equation. SW indicated 55 lbs of 2000HS. At two pounds (52 lbs) into the second bag all that remains is the fillet at the bottom.

(L)The lid showing the reinforcment wires prior to placing the insulation and refractory.
(C)Insulation and refractory in place.
(R)Outside of lid.

Here is the body with burner hole and lid lift bits attached. I brazed all these items to the shell.
If the outside gets hot enough to melt the braze then the furnace is useless anyway!

Here is the body with the bottom layer of insulation in place. The core in the middle is 1" pvc pipe to provide a drain hole incase a crucible breaks.

Here is the body with the side layer of insulation in place. A cardboard tube core is taped in place to create the opening for the burner.

The internal forms are made using Dave Gingery's design. However, I find that styrofoam spacers are easier to make than wood ones. A taper helps with removing them later.

When the 'castable' (read ramable) in tamped in sufficent to hold the form you may remove the spacers that keep it centered. Fill the holes a little at a time and tamp. Don't fill them to the top and tamp because the material at the bottom will not get packed.

Burner and flair forms. I turned a cone to leave a flair in the refractory and placed it all in the burner hole and then packed it with 3200. When it set, I removed the cone to the inside and the tube to the outside.

The burner is made from a piece of steel pipe. The refractory should not be counted on to support the burner so I welded a piece of angle iron there to take the load of the pipeing and valves.

I tried a normally aspriated burner first, but it didn't seem to have the power. Lacking a blower, I decided to try air injection. The air comes in throught the end and the gas comes in through the side. Holes in the pipe allow more air to get sucked in.

Here is a lost foam cast-in-place burner bell I am now using. We got our gas line pressure brought up from 10psi to 30psi. Here are links to more photos of this lost foam burner bell:
Photo 1, Photo 2, Photo 3, Photo 4, Photo 5, Photo 6, Photo 8

I call the furnace Fatman since it looks like that thing we dropped on Japan. Behind it is our Mifco multipurpose. The crucible is lifted out of the top (about chest high) and it has doors on the sides so I think I will keep it for forge work.

When the lid is over to the side it radiates lots of heat downward. When I noticed the plastic parts on the regulator were getting deformed I realized a heat shield was necessary! The unit has completed 18 heats so far, mostly bronze to 2000+F and the 3200 shows no signs of cracking.

What I would do different the next time:
  • I would make the lid flat on the top. It is difficult to put metal on the dome for pre-heat.
  • I would make a bit of a funnel on top of the drain hole.
    As it is now it is slightly off-center and the plinth has to be placed too carefully.
  • I would weld a wide base to the bottom to keep it from rocking.