I built this propane furnace about 3 years ago. The case is a couple of disposable PU foam canisters that we’re used to spray insulate an aircraft hanger. One was cut just below the radiused top, while the other was cut a couple of inches below the radius to give a decent sized lid. I made the trolley from 1” square steel tube with a foot pedal to lift the lid and an insulated handle to swing it open/closed. The refractory is a mix and of silica sand, perlite and Portland cement, cured over a three week period where the temperature was increased gradually. The burner is a design I found on Alloy Avenue, made from iron pipe fittings brass tube and a carburettor jet. I’ve only cast aluminium parts so far but it has held up well. The crucible is a cut down pub CO2 cylinder with two lift lugs cut in and a tilt lug welded on. I’ve just bought a graphite crucible, but haven’t tried it yet.
That looks well constructed Jim. You may find the limits of the home brew refractory if you venture into higher temp metals. Perlite has a fairly low melting temp. It'd probably still be ok if there was an inch or so of hot face to drop the temp. There were quite a few examples of furnaces that had a commercial refractory hot face and then backed by sand and/or perlite mixtures. There's only one way to find out......turn the thermostat up! Best, Kelly
Hi Kelly, I accept that the refractory that I’m using is limited on temperature so, for the moment, I’ll be sticking to aluminium. If I decide to expand to brass etc, I’ll come back to the forum members for advice. Jim
This is very similar to the propane furnace I started making this past weekend. I am at looking at buying refractory right now. Any of you guys have any good tips on what kind and how much of refractory would be the best...and the cheapest?LOL
You won't need tro tough a build for AL, but for iron, you will stress the most robust refractory you can use. I have been very favorably impressed by the BluRam segmental build. I think the segmental construction method is important. How important the refractory choice is less clear---it sounds like various folks like Mizzou and other dense refractories have their proponents. I do not think satanite/wool will be durable enough for iron. Thin (1/2") dense segmental refractory with wool back up of 2-3 inches seems like a good choice. Denis
I have a few blocks of the blu-ram I was going to do the bottom and the lid with. I was thinking about just using castable for the sides. Any idea how much coverage you get out of it...like weight/inches? I need to know how much to order.LOL
Mizzou, kastolite30 (both are harbison walker) and blueram (Vesuvius) seem to be the most popular here. All are 3000f or greater. When I built my last furnace I wanted to use kastolite because I was backing it with sand/fireclay, and kastolite is insulating, but mizzou was what my supplier had on hand (free), so that's what I used. It takes a bit to get up to temp but it's tough as hell. So far so good. Pete
Yes! Free would be what I would use as well! LMAO Any idea how much coverage you get out of them? I have roughly 480 cubic inches I will need.
I built my cut-down 50 gallon barrel furnace with less than 3 50-lb boxes of Blu-Ram. Walls were 1/2" and floor and lid 3/4 or so. Denis
I found some numbers that looks like the kast-o-lite comes out very close to 10 cubic inches per pound.
I just measured the OUTSIDE of a 55 pound box of Blu-Ram at 10 X 7 x 11.5 So, a little less than 800 cu in is 55 pounds or 1 cu in is a little less than 1.1 oz. I just measured the outside of a 55-pound Blu-Ram box at 10 x 7 x 11.5 . So 1 cu inch is about 1.1 ounces of refractory---a ball park figure. My impression of Kastolite is that it is significantly less durable in an iron furnace than is a denser refractory---much much less durable than Blu-Ram for sure. Denis
That is what I suspected would be the case. I think I would rather go heavy duty for iron melts. You would think I would be able to buy from my company and save a ton on shipping cost, but no such luck. We apparently just made a new rule that employees can no longer buy supplies. Good thing the melt supervisor has a couple of tons that is about to exceed its shelf life and he is going to give me what I want.LOL He says he has the perfect stuff. Ill let you know what it is after I talk to him again. .....Now if I can just find some sand and propane that the shelf life has ran out on.LOL
BluRam is 170lb/ft3 Mizzou is about 140lb/ft3 Kastolite 30 is about 90lb/ft3 In general, insulating castable refractories are lighter but also less strong. I pasted the data sheets below. BluRam is Phos-bonded and good choice for high temp iron service and MelterSkelter has thus far very good results with his. Those Phos-bonded plastics are common patch materials for Cupolas too. Mizzou has been well tested, is economical and a good castable for the hot face. Monolithic shapes like a cup shaped lift out furnace crack because of uneven heat and thermally induced stress. Most people just live with the cracks which are usually minor. Segments allow you to choose the location of the crack and are stress relievers. Though it is popular to cast a cup shaped dense refractory monolith with integral base, I think you are better off with just a cylinder sitting on a disc shaped base. It is lower stress and allows replacement of the base which can get pretty crudded up with slag and glaze after use. Might be good to start a separate build thread Billy. If you need data sheets on refractories, I have quite a few or can point you to them on line. Best, Kelly
Just an update....I received four bags of uni-ram which is more than enough to do it. In fact it is enough to make me think about going ahead and building a bigger furnace while I have the supplies to do so. I have a 35 gallon drum I was thinking about using, but I may opt for 55 gallon instead.
