So there is a long list of instructions on building a metal melting furnace. But I have decided to show you my process anyway.
I have turned an old beer keg into a portable metal melting furnace, This will cover both the furnace and the propane torch burner. I being in Canada relay heavily on Canadian Tire store and online product availability.
The metals were acquired locally at a metal recycler and the chems were from a not so local chem supplier, OH and the melting material from a previous employer.
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Step 1: Destroy the Keg
NOTE: No beer was harmed in this step.
I acquired a defective stainless keg from a local brewery.
Measure and cut the top portion away. I needed a lid to control the burn so I cut away the top 3 inches of the keg using an angle grinder and custom make bottle cutter jig. The keg drop tube was removed leaving a perfect vent hole in the lid.
Next I cleaned the cut line of all metal burrs.
Finally I cut a 2 inch hole approximately 4 inches from the bottom if the keg in the sidewall as shown.
Step 2: Fiddling With Science
I have found over a long experimental range that a two bottle per bag ratio seems to work best. I am referring to a 1L bottle of Sodium Silicate 37 to 40% from my favorite online store to 1 bag of Perlite from my favorite local store.
This mixture is thoroughly packed into the open cavity of the Keg using any mechanical means necessary.
Step 3: Pack Until Full
I used a concrete form and old plumbing pipe for this bit.
Wrap the forms in wax paper to prevent sticking.
Place the forms as shown and carefully pack the Perlite to fill the sides and top.
NOTE: This may need more than 1 week to dry depending on your environmental conditions. Too soon and the mixture will fall apart. I actually needed 8 days for mine due to the cold nights.
Carefully peel the cardboard tube out and remove the plumbing tubing. The wax paper may stick but be sure the Perlite doesn't crumble. if it does then coat the surface with more Sodium Silicate liquid to adhere it together then let it dry.
Step 4: Refractory Lining
I mix a 1 to 1 ratio of Prolab Sodium Silicate with 1200 grit white aluminum oxide abrasive.
This is used as a refractory lining to prevent degradation of the Perlite. Without, I find that the Perlite will melt and become brittle after only 1 or 2 burns.
NOTE: Sodium Silicate eats Nitrile gloves. I am shown here with Nitrile gloves but these didn't last more than a couple of minutes in the mixture. luckily i had no allergic reaction.
Carefully and completely coat the entire surface of the furnace with the mixture. this will form a kind of ceramic coating over the Perlite and allow for hotter burns in the future.
Fire the furnace to set the Aluminum oxide coating. A nice glow of orange will indicate the completion of the set.
Step 5: Make It Portable
As shown. Fabricate a frame and moving platform for the keg. measurements are based on the keg size.
I used some pneumatic wheels and 2X1 steel tubing.
The frame houses the base of the keg yet allows for quick moving via a dolly like design.
The bolts are sized to attach the wheels. In this case they are 3/4 but they may vary depending on your wheel of choice.
The handle is galvanized conduit so if welding make sure to use a respirator or open air or safety.
By the way... a flap disc is the bad welders best friend. Massive metal removal and smooth finish. get one and thank me....
Step 6: The Burner
Now that you have waded through the furnace it is time to reveal the quiet burner.
This utilizes a .20 mig tip as the primary orifice.
I also use a commercial propane torch as a regulator as shown.
The mig tip is fitted into a 1/4in waterline adapter as shown. The adapter is then threaded into another brass fitting as prepared earlier.
I have found that drilling at a 45 degree angle air inlet holes in relation to the airflow greatly reduces the amount of noise generated. In this case I have made 5 holes that are approx 3/8 in diameter. These are intersecting with the point of the mig tip as shown.
The brass is 1 inch in diameter and will expand to 1.25 inside diameter with an adapter.
Inside of the 1.25 pipe is a steel screen that will produce turbulence and make the flame burn hotter.
There is exact science here but I circumnavigated it to produce a hot and reliable flame. On full power it will not stay lit outside of the furnace but will work properly when in place.
It takes about 20 minutes to melt the contents of the crucible with this torch and furnace.
Step 7: The Firey Crucible
OK so there is a problem that needs to be addressed.
The crucible I use is actually steel tube with a laser cut steel circle for a base.
These were all found at the scrap recycler over the course of a couple of months.
basicly there are 2 holes drilled at 180 degrees near the top and a full base cover welded in position.
I find that a 6 inch tube will allow to melt a hard drive case without any folding or breakdown.
I use a 1/4 inch steel rod bent into a handle to pick and pour the metal.
Step 8: Between Projects
So I have decided to melt aluminum but have no current project.
The scrap is melted and poured into cast iron pans. This yields ingots of high purity and ease of use.
I have a project coming soon that will use these ingots and more...