Simple Brick Furnace

Discussion in 'Furnaces and their construction' started by oldironfarmer, Mar 30, 2018.

  1. oldironfarmer

    oldironfarmer Silver Banner Member

    My situation is different than others, I have a dedicated space for a foundry furnace so mine does not have to be portable. That affects the design. I'm also very concerned about the health hazards of airborne ceramic fiber particles. Maybe overly concerned, however I decided to make a brick furnace to avoid dryout and spalled refractory. Firebrick is also lighter than most refractory and individual bricks can be replaced if necessary. This is what I came up with.


    First a page of history.

    I started melting aluminum in a loose stacked brick furnace with a home made propane burner.


    This was hard firebrick I had laying around. Next step was to buy some soft firebrick and make a burner tile.


    Tapered wooden plug with Greencast 94 refractory. Greencast 94 is a high alumina refractory which is rated for 3,500F. Several outdated bags were given to me.


    Then I melted aluminum in this furnace for a year or so.


    It was surprising to me how good this worked. The outside of the firebrick stayed cool, less than 100F. The brick lasted well with direct flame impingement, but there were lots of air leaks and I wanted to be able to go to higher temperatures eventually for brass and bronze. After a little research and study I decided to build an all brick furnace in a 55 gallon drum.


    It's working good for me so if there is interest I'll detail my build in a few posts.
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  2. oldironfarmer

    oldironfarmer Silver Banner Member

    After determining the inside of the furnace would be big enough in a 55 gallon drum I cut the wall firebrick on that table saw. Soft firebrick cuts like a dream with any old wood cutting blade. I have a good dust collection system and wore a respirator with dust cartridges when cutting.


    The 26 is for 2,600F rated firebrick. They start at 2,400F rating and go to 3,000F rating, getting more expensive as they go up. 2,600F seemed a good middle ground to me.

    I cut a drum off short and put a layer of firebrick in the bottom. I don't worry too much about the edges which will be covered by the wall.


    Some of the brick were out of the old furnace and I used drops to fill in the corners best I could. Cut a ring of brick to lay flat to add to the depth.


    Stacked in the wall (plan is to have ceramic fiber blanket behind the wall mainly to hold the brick snug)


    And made a form for a burner tile. That was a change of plan. I was going to drill a hole in brick for the tuyere but it was going to leave small areas of brick remaining which I thought would fail too soon. Turned a cone, cut it off and cast the burner tile.


    Cured the tile and assembled everything.

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  3. oldironfarmer

    oldironfarmer Silver Banner Member

    Now it's time to build the lid. I'll apologize, that I learned to call the roof in a furnace the arch, whether it is flat or not. And the floor is the hearth. I wanted to make a gas tight seal between the wall and the arch. I decided to try building a conical shaped arch all of brick with only a rim of steel to hold the brick. Laid it out in Fusion360 and came up with the cut angles. Cut the proper angle on the tablesaw with the blade tilted.


    Made a ring out of sheet metal and turned a 1/2" lip on the bottom.


    Test fit the 8 long brick.


    Brick is very stable.


    The ring is slightly larger than the furnace so there is a full refractory joint. Added 8 short triangular brick to finish out the arch. The cone is a 10 degree angle.

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  4. oldironfarmer

    oldironfarmer Silver Banner Member

    Added a trapeze to the arch so it will always hang level to set down.


    The crossbar is mounted on a bolt to allow adjustment to accurately center the arch.

    Added two rounds of ceramic fiber rope to seal the wall/arch joint. Here's the view from the inside.


    The rope and the fiber got rigidizer after a few heats and the rope had set. The rim was painted yellow to show whether it is getting too hot. If the rim gets too hot the arch could fail.

    Filled gaps in the arch with 3,000F brick mortar to take up space both between brick and around the rim. I want the joints to crack so the brick can move with thermal expansion (the cone will rise in the middle). I had left space for ceramic fiber blanket above the brick but have decided it is better to leave that off, trapping heat would just help the rim get warm. They only get to about 150F with an aluminum melt.


    Added a ring of loose brick inside the furnace to take up space while I'm using a smaller crucible.


    After sixteen heats the arch rim shows no discoloration so I think I've got a good seal.


    It heats as quickly as the small stacked brick furnace. I'm going to try a siphon waste oil burner in it later.

    Attached Files:

    Last edited: Apr 5, 2018
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  5. oldironfarmer

    oldironfarmer Silver Banner Member

    Going to make a warming tray to fit over the furnace flue. Decided it needs to flip up and swing side to side. Since my pole is installed I decided to make a clamp to hold the tray support. I could weld one up pretty quickly with a split pipe, but I want to try lost foam so here we go.


    Cut on the bandsaw while I think about a hot wire.

    Added sprues


    My funnels are not up to Kelly's standards.


    First one cast mighty fine


    I got worried about my sections and added a boss at the last minute to the support half. Foam is quick!! It's drying in the sun while the charge is getting hot in the crucible.


    I had sanded the faces smooth however post pour things are different. Does the foam have a grain which needs to be matched?


    The second section from the right has shrunk.
    Last edited: Apr 6, 2018
  6. oldironfarmer

    oldironfarmer Silver Banner Member

    Fit looks good


    I had printed my name backward on the 3D printer and used it to stamp into the foam.


    That worked OK.

    Removed the sprues, drilled 5/16" holes for bolts and 1/2" hole for the arm pivot


    The glue seams are all very shallow. I'm going to try some wax I have. It melts at 137F. I'm not sure about using it.



    I'm very pleased with it.


    Fast and easy, the only porosity was at the top of the boss. There was none in the sprue cut and none in the drilled hole.

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  7. Jason

    Jason Gold Banner Member

    Looks like a winner man! Isn't it nice when you need something, you can now make it exactly like you want it?
  8. Tobho Mott

    Tobho Mott Silver Banner Member

    That came out nice, good job!

  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Congrats OIF, that's a nice looking part. -Now you're hooked.

    There can be a lot of nuance things to positioning/spruing and detailing the foam patterns but it really depends on the degree of finish you're trying to achieve and sometimes the type of foam you used.

    1. Most people on their first LF pour get surprised by the hesitation that occurs between the initial metal contact and filling of the sprue and when the part starts taking metal. Did you notice that?
    2. I can't tell for certain if the patterns were made from extruded polystyrene (XPS) board - typically pink or blue, or expanded polystyrene (EPS) beads -typically white. Both work fine but XPS machines and sands much better and you can achieve nice finishes with it. Worn 220 grit is a usually a happy medium.
    3. On the glue joints, I lay a piece of sand paper on a machine surface and lap the joint faces a little then clamp or weight before cutting. I try to keep the glue away from the cut edges if I can. Even so, you can get such great detail in LF you still can usually detect the joint albiet usually just a hint of a line. What did you use for glue?
    4. On the shrink, Sometimes if the foam joints aren't secured well with glue they can move a little as the foam is consumed during the pouring/casting process and it may not be metal shrink. I really haven't had any shrink problems with LF but most all my parts are relatively thin and uniform walled. For thicker sections shrink bobs can be installed and treated like any other casting process. Do you know the pour temp?
    5. I like the 3D printed imprint. Was that just done with pressure or also a little heat?

  10. Tobho Mott

    Tobho Mott Silver Banner Member

    I like it too, you got that to work a lot better than I did on my spooky belt buckle (I did not use 3DP or heat, just a letter stamp set and pressure), which had to be filed and sanded a lot to reveal the text:

    View attachment 1014

    (Mind you I did not invest the foam pattern for that one)
    (recycled attachment showing up as a link instead of a pic for me... How can I change that?)

    I'm considering making some foam castings similar to this for my muller, to attach the dangly bits from the crossbar and keep some adjustability. It'd be nice to include at least a couple castings in the build anyhow, and my melting/pouring space is currently free of snow and ice...

  11. DavidF

    DavidF Administrator Staff Member Banner Member

    That came out good, you well on your way to making those tractor parts you are thinking about now :)
  12. oldironfarmer

    oldironfarmer Silver Banner Member

    It is exhilarating! I've forged, welded, and machined for years. Always knew I wanted to make castings but was hesitant. When I added on to my shop last year I added a foundry room for my pottery kilns and compressor with no real foundry plans but knowing it was time to get started before arthritis takes over. I am very glad I did. I also loaned out a 250 gallon propane tank twenty or more years ago, he wanted to buy it but really couldn't afford to. He and his wife had since died and I retrieved it from the heirs to have a good supply of propane to melt with. It is a lot cheaper into a big tank than the 20# portables.


    The more advice the merrier. I have trouble sorting through all the advice in various threads and repetition will help others, so thanks for the input!

    Of course even though this was 3D printed it was essentially stamped as far as the foam is concerned. What do you mean you did not invest the foam pattern? No mud?

    I intend on making the same pieces cast for my muller. And I think it is wonderful irony to use lost foam to facilitate sand casting.

    Of course the goal now is to do more casting and I have no tractor parts in mind.:eek: I'm think I'm not alone in the quest for a skill I don't really need. When I got my first lathe it was to just make simple bushings and sleeves, nothing fancy. Then I figured out most lathe operations are pretty simple. This casting can stand a lot of improvement but yet is more complex than I envisioned. My initial goal was to cast large pieces (like a 1-1/2" diameter rod) to be machined away to make what I wanted. Now I see it is easy to get close to what you want with much less machining. This little casting is a big milestone to me. Thanks to each one for your inspiration and help.
  13. Tobho Mott

    Tobho Mott Silver Banner Member

    No mud, correct. More formally referred to in backyard casting circles as "bare-doggin' it" :D
    More pix can and video be found in my 2017 Hallowe'en casting contest thread. Check out Kelly's entry as well while you're there, it's beyond impressive and if the criteria for judging entries had been different IMO he would have won.

    I could make patterns to sand cast the muller parts, but aside from taking a lot longer to get it right before I can pour them, I also broke my "Quick 'n Dirty" muller (a kitchen mixer beater chucked into a drill) last time I used it, and I don't have the patience for hand-mulling. But yeah, I also appreciate the irony of lost foam casting greensand muller parts. :D

  14. Jason

    Jason Gold Banner Member

    Drywall mud isn't necessary at all. Bury the foam in a bucket of sand and dump the aluminum onto the sprue. Cant get more simple than that.
  15. oldironfarmer

    oldironfarmer Silver Banner Member

    I guess I'll have to try it without the mud. Does that affect the surface finish? That would make adding the soft wax a non-issue, I guess, so long as the wax disappears.
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    What's necessary depends on what you're trying to achieve. The use of drywall mud enhances surface finish of the casting and will reproduce the quality of surface finish you can achieve on your pattern. Without, it will take on the finish of the sand grain size. If you have very fine sand, that may be satisfactory or if you're unconcerned with surface finish. With mud, the type of sand used becomes a non-issue. The other benefit of mud is it prevents sand from becoming embedded in the casting surface. Most of the time the sand can just be brushed off, media blasted, or wire wheeled but if you cant get at the area very well, sand is hell on cutting tools.

    You don't need to use a foil sprue either but I have found I get less misruns, sandwash, folds, and oxide defects by doing so. You can just use a foam sprue with no coating or foil if casting quality is less of a concern. You might try using HVAC tape for the foil sprue and a pouring cup. It only takes a couple minutes and the foil funnel is very strong and stable and the pouring cup provides a good solid well to pour into. The aluminum shrinks enough I can just pull the cup off afterward, as long as it is round and not beat up.

    If you've put a fair amount of effort into making a foam pattern, why not attend to some details?

  17. oldironfarmer

    oldironfarmer Silver Banner Member

    Thanks for that review. The mud is easy to apply. Looks like I'm going to be doing more lost foam so I'm planning on making a hot wire cutter and a sand screen. I'd better do more, I bought some foam board, 1" and 2". It's really not expensive and the heavier sections mean less gluing.

    I tried using HVAC tape to make a sprue and pouring basin but the adhesive fought me. I find it easier with foil. I don't think I could have removed my tape basin. Do you reuse them?

    I did get my warming tray welded out today so I'm ready to make the hinge piece. That's the Hastelloy wire mesh I have. Good to 1,500F or more.

    Last edited: Apr 8, 2018
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The foil sprues are consumable. Also, I use steel pouring cups 2-2 1/2" in diameter and 3-4" long. If you keep them round and don't ding and beat them up, they can be pulled off the cup metal after quenching and the cup metal shrinks. I reuse mine over and over and they get a nice oxide layer built up on them.

    I posted a thread on foil sprues here.

  19. oldironfarmer

    oldironfarmer Silver Banner Member

    Thanks for that post on foil sprues. I was going to say I didn't know how I'd missed it, until I saw it was posted today. I wasn't smart enough to make a cone out of tape, it was easy to fold a cone out of a larger piece of foil. I'll sure try that.
  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I could never get the folded aluminum foil sprues I made to stay put but when I went to the HVAC tape, problem solved. Sometimes even the ink on the foil prints through!

    Sprue Printing.JPG


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