Muller Page NEW
A FEW OTHER FURNACES OF INTEREST
If you are building or have built similar projects I am interested in seeing and hearing about your methods and ideas.
A few notes on the furnace assembly:
The furnace is built around a number 20 crucible (20lbs Aluminum, 60lbs of iron) however it should accommodate a number 30 as well. The exterior skin/structure is a surplus 55-gal steel drum. The drum is lined with 2.5 inches of 1800 degree F Wescolite 18-HS insulating lining. Inside that layer is another 2.5 inches of Tex Kast 80, which is a 3200 degree F high strength refractory. The total wall thickness is 5”. Both are cast. The inside diameter of the furnace is about 12.5”. Lifting up and out such a large crucible size did not seem very appealing. Therefore I decided for a side unloading "Gingery type" furnace for safety and accessibility reasons. The entire furnace portion weighs about 435 lbs. The lid and body (parts that are lifted) weigh approximately 290 lbs. together. Gingery's lifting mechanism handles a furnace for a number 8 well but was not convincing for the increased weight and size of my design. The amount of force required would be more than I would want to handle and offered limited travel distance. I decided to utilize a winch and carriage system. With this system I could achieve as much travel as needed with a minimum amount of effort. I bought the winch from Harbor Freight Tools for $12.99 (30905-2VGA). It is rated at 1000lbs and handles the furnace well. However I would go for a higher capacity model with a lower reduction gear for easier cranking. Overall the lifting mechanism works well.
Directly under the furnace is sand filled 6” barrel bottom to serve as a catch can for crucible failure. The furnace has a 2” hole in the bottom to allow molten metal to drain in case of crucible failure. The pan is removable and will hold the entire contents of the crucible.
The entire system is mounted on wheels. The total weight (furnace, cart, full propane, blower, etc.) weighs about 675lbs. It is difficult for one person to push however still movable around the shop. The cart is mounted on 5” casters from Harbor Freight Tools ($2.99 each). The cart includes a holder for the propane bottle. However, the furnace is not intended to be operated with the bottle on the cart. It is simply for transporting. A long hose allows for the bottle to be positioned a safe distance from the furnace. The cart is painted with “Ford Tractor Blue” implement paint purchased from Tractor Supply Company. I paint all of my homemade equipment with such. It is oil and gas resistant, durable and about $18 a gallon. Available in a variety of tractor colors as well. It does not keep well so use it up within a few months.
I was concerned about the body lining attachment to the barrel. It seemed without any mechanical bond it could easily slide out when lifted and would break up quickly due to applied stress. As a result I decided to have it sit on a 4” “shelf”. I welded 4" steel angle supports to the barrel that support the refractory lining. The supports carry a sheet metal ring that carries the lining. The lining overhangs inside the supports 1” that then sets on a ceramic rope gasket (like one used for fireplace doors) to protect the steel and keep the heat in. It seems to work great so far. The lining just sits on the steel shelf so expansion and corrosion should not be a problem.
For lifting a 1” square tube is suspended from the carriage that is engaged with pins to lift the furnace body and lid. The 1” square tube slides into a 1-1/4" square tube that is welded to the barrel for the entire height of body and lid. A hole on each side of the lid and body is drilled though both tubes which a bolt or pin is slid into. The lid is bolted since it is always lifted. The body has removable pins to slide in and out for lifting with the lid. This system works well in distributing the weight to the entire metal skin. It eliminates the chances of bending or failure of the lifting points. It also eliminates two separate lifting systems. The 1" square tube that slides into the furnace tube is pointed on the end to ease alignment when lowered. Never had to manually align so far. The furnace could possibly swing from the carriage and knock over the crucible. As a result I added some braces from the lid to the carriage to stabilize it. They were added late and were not painted in the picture. Stabilizing it could be done in a variety of ways and is essential. The lifting carriage rollers are stacked washers that are pressed and tack welded to a 1 / 2” round tube that turns on a 5/16" bolt (axle). The inner washers carry the load while larger outer washers act as guides. This was the cheapest and easiest method of a high strength roller that I could come up utilizing my capabilities. Purchasing bolt, washers, nuts, etc. from farm supply stores is typically the cheapest place I have found. They usually sell them by the pound and not the bolt. Now that the furnace is complete casting and machining them would be the best method. I used 8 but as little as four could be used. I was on a "roll" building them so I went for 8. The sliding lift carriage is attached to a cable and routed to the winch with 3 pulleys. I wanted to be away from the furnace while lifting, however it could easily be altered to almost any location. The cable pulleys are for a garage door cable system. They were a mere $2.84 each at the home depot. They are now destroyed. They just could not handle the weight. I will cast and machine some as my first project.
The burner is a modified Reil burner. It is a 3" intake pipe into a 3" to 2" bell. The burner tube is a 2" pipe that can slide in and out of the furnace for tuning. The injection of the propane is done through a 1/4" pipe penetrating the bell. In the middle of the 1/4" pipe is a T fitting with a plug cap aimed to the furnace. The plug is drilled with a 5/64" hole to form an easily replaceable "jet". I tried an assortment of jets and the 5/64" seemed to work the best. I made the blower from sheet metal and an old washing machine ˝ hp motor. The motor has exposed windings that could be dangerous so I made a sheet metal cover. The bower/motor assembly took a lot of time to fabricate and I would recommend purchasing one if the budget allows. The propane bottle is a 100lb bottle that I purchased from Tractor Supply Company for $79.99. This is not an advertisement plug for Tractor Supply Company I promise. I also purchased the high-pressure regulator from TSC. The regulator works great and is priced good as well. It is adjustable 0-60psi. It is stable at very low pressure and has fine adjustment. It does not include the high and low pressure gauges. I ordered them from MSC industrial supply for about $8.00 each. They are not absolutely necessary but I find them helpful. By the time I purchased fittings, regulator, and gauges it may have been cheaper and less trouble to purchase a complete one made for a propane-cutting torch. The lifting shank in the photo is homemade as well. It is basically a two-person shank for a number 20 crucible with a lock rod that slides over the crucible once in place to secure the crucible while pouring. The lock rod is 5/8" and slides though elevated washers. One end of the tong has a 90-degree handle for tilting. The main bar is a #7 rebar (7/8"). The crucible can be rotate a full 360-degree and not fall out or shift. I have not seen such a system but I have seen very few.
This furnace is by no means the simplest, most inexpensive, or best way of making one. It worked well for me and I considered it a successful experiment. I plan to use it for many years so I did not mind spending some extra time and money. However, If doing over I would simplify and change several components of the assembly.