Cast-Iron Furnace Build Using Partially 3D-Printed Molds

Discussion in 'Furnaces and their construction' started by k.kuhn, Dec 21, 2020.

  1. k.kuhn

    k.kuhn Silver

    In a previous post I used an electric heating element to slowly heat to 150C and held it for several hours to drive off the moisture (the schedule I followed asked for only 30 minutes per inch of thickness). But yes, I think I overlooked exactly how slow the schedule is for the rest of the ramp up actually should have been. I find the manufacturer recommendations pretty ridiculous though, at least for my situation. I live in a residential area and the burner/blower fan is really quite loud, not to mention I wouldn't feel comfortable leaving it to run on its own. Doing a heat up by the book would simply take too much time for it to be worthwhile for me. Maybe this means that using refractory is just not practical for me to do. Anyway, time will tell with this one and next time maybe I'll try and find someone with a kiln or other way to heat it in a more controlled manner.

    Edit: I forgot to specify that the inside of the furnace was what was more than 500C, but the outside was still only 200-300C. This large temperature differential probably contributed to any cracks. In the future, I will wrap insulation before performing a first heat up.
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Like I said, I wouldn't sweat it.....on with the build.

    This is true, probably more so with insulation castable. If it had wool around it the gradient would likely be smaller. Many people just finish the build in the uncured state and then do the cure after the build is complete. It steams for a while but will be driven off.

    Best,
    K
     
  3. I'd suggest Satanite for your inside lining. A thin coat of ITC-100 over that but the Satanite works great.
     
  4. Melterskelter

    Melterskelter Gold Banner Member

    Kelly's advice is good.

    Those cracks have surfaces that interlock. As long as they stay stacked side-by-side and on top of eachother they will likely make a wall that will hold together. Afterall, I built my furnace in bore in 4 segments 1/2" thick. They have stayed side-by-side for at least 50 hours service now because they are wrapped in 3 inches of wool and the whole works is enclosed in a steel barrel. Do the equivalent here (could involve steel bands or wire even outside wool) and all will be good for a good while.

    OIF was posting while I was typing. I will echo his suggestion for Satanite. It is really tough with respect to resisiting the harsh fuel/oxgen environment and will add measurably to the life of your hot face. Applied to even wool it can hold flame at bay for quite a while before needing patching.

    Denis
     
    Last edited: Jan 5, 2021
  5. The valuable thing about Satanite for me is that it's like drywall mud. You can mix too much and let it dry in the container. Later you can add water and mix up for application. I misunderstood and tried to put a 1/2" layer in my floor. It would not dry but curled and cracked. I pried it out and was disgusted I had wasted so much. Then I found I could rewet it and use it. I'm still using out of the plastic bucket I first stored the old floor in. I break off a piece and mix it up when I need more. It's very forgiving.

    By the way, I figured out I didn't need floor protection (I have a brick furnace), I spill enough aluminum my floor is covered in a tough layer of aluminum oxide. I cleaned it out once but asked myself what harm was it doing. I've got about 460 melts on the furnace now. The floor looks like aluminum hell but it is not an issue.
     
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  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    +1 The Satanite will have more chemical resistance to fluxes and slag which will become more important for iron. I'd apply it very thin. If may sluff off a little locally with use but is easily patched. Kastolite 30 has decent temp rating but being an insulating castable is probably more vulnerable to reducing agents than dense castable. ITC-100 is a primarily a reflective coating and may also reduce the effective surface temps but is pricey stuff.

    Best,
    Kelly
     
  7. OMM

    OMM Silver

    I have a non-mortored insulated fire brick interior. I literally have hundreds of cracks and leaks. I'm not going to fix them ever. I might replace the bricks as needed. And I might fix with (Satanite or) the high temperature motor I have on hand. Structurally I know my furnace leaks into the 2"ceramic wool. But I do not care, no. Yes, I do get a little bit of smoke exhausting from the ceramic wool. But, again I do not care, no. I use the furnace outside.

    I am using the light insulated fire brick 2.5 inches thick with 2 inches of ceramic wool. My whole furnace weighs in at 150 pounds. It is not light but it is also not heavy. It can melt 5lbs of aluminum in less than 20 minutes with a cold start.

    I can melt scrap copper, but, 2ish pounds of this takes 20 minutes. Crucibles are now my consumables. I am now considering a new A10 (or A8) for copper.
     
    Last edited: Jan 5, 2021
  8. k.kuhn

    k.kuhn Silver

    Added the ceramic wool insulation today. I had enough to do two layers (~2") around both the main body and the lid. I wrapped each layer with several loops of baling wire to secure it in place (was originally going to use kanthal, but thought better of it because I might want to make that electric heating element insert later). The tuyere presented a challenge because a straight loop around would block it, so I made a ring of wire to go around it so I could still have a loop at that level. I tightened the baling wire pretty tight, but not to an extremely high degree because I figured overly compressing the insulation would be counterproductive. If this level of insulation turns out to not be sufficient I will get more ceramic wool and wrap a further layer or two.

    The only part of the furnace that is not insulated with ceramic wool is the bottom, which I figured would benefit from some low-density firebrick instead to help support the weight a little better. I'll be making a square base for it from 5 standard size (4.5"x9") firebricks with three lined up horizontally (4.5*3=13.5) with 1 and a half lengthwise on one end (9+4.5=13.5).

    I took my time when measuring the wool to make sure it would line up perfectly:
    20210108_120511.jpg
    First layer wrapped with baling wire:
    20210108_123330.jpg
    I found that just a simple hook on each end to connect the wire was strong enough. I would make one hook first, wrap the wire around the wool, and then pull the wire tight through the hook for leverage and then snip it off. This photo also shows the loop around the tuyere. We'll see it it remains tight throughout being heated:
    20210108_123338.jpg
    Very similar method for the lid, used an extra bit of bailing wire to secure the wool on top of the lid:
    20210108_134347.jpg
    Only one layer of wool on so far:
    20210108_134416.jpg
    Both layers of wool around the lid now, ready for a coat of ceramic wool rigidizer:
    20210108_140934.jpg
    Still enough room to grab the handles with large gloves on, even with the thick insulation (that's why I made them so long):
    20210108_140939.jpg
    Sprayed with rigidizer, after which I was able to remove my respirator for the first time during the entire process:
    20210108_143915.jpg
    Coated the bottom of the lid with ITC-100 and also the wool that was exposed just above the vent on the top side:
    20210108_150124.jpg
     
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  9. OMM

    OMM Silver

    In the end, it looks like you're gonna have a good performer! One thing that faulted me is this is not a race car, it's more like a Sherman tank. Slow and steady always wins the race. Try to warm her up slow and steady and don't be too ambitious to close the lid for the first five minutes-ish.... Then get ready to tweak the fuel and air so that you have 4 to 8 inch torch tip coming out of the lid hole. I found that increasing the fuel just a little bit, nearing the end of my burn... Lead to less oxygen and more impurities floated to the top. I'm still new to this, and maybe I'm wrong, but this is just what I've been playing with.
     
  10. Tobho Mott

    Tobho Mott Gold Banner Member

    That looks great, I doubt you will feel a need for more insulation unless you compressed the blanket more than it appears in your pic.

    I run my furnace the same way (close to neutral but a little rich/reducing) for copper alloys to limit oxidation, and from what I have seen people melting iron do the same, but for cast aluminum I tweak it so the flame doesn't quite poke up out of the lid (just a little oxidizing/lean) to limit the available hydrogen that can get dissolved into the Al. At least that is what I think I am doing, and why.

    Does the bottom part of your lid fit inside the bore or only sit on top of it? If the former, how much clearance do you have between them? PatJ once built a furnace where the lid fit down inside the hot face to limit leaks, but at some point it got stuck closed due to expansion when the furnace was hot and he busted the hot face prying it open, wound up doing a big repair, or maybe it was even a rebuild...:eek: I tried to find a link to that post/thread but Search doesn't recognize his username anymore and I had no luck picking the right keywords. :( Something to keep an eye on, perhaps.

    Jeff
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It's in this Anaconda Jeff. Some of the 28 pages are even about the furnace.

    http://forums.thehomefoundry.org/in...er-keg-drum-size-furnace-for-melting-iron.26/

    His real Humpty Dumpty moment was when he disassembled it to move it to one of the exhibitions and the hot face fell apart. Never seen a guy spend so much time on equipment and so little time casting. It would not be the thread I'd choose for a teaching moment if you want to cast iron. I think MelterSkelter's journey is more instructive.

    Best,
    Kelly
     
  12. Tobho Mott

    Tobho Mott Gold Banner Member

    Thanks for finding the link Kelly. Now tell us how you really feel! ;)

    Apologies, it was not my intention to reignite old grudges best left alone or start a side-track about iron casting. K.kuhn mentioned taking inspiration from a PatJ build here, so I got to thinking it might be the same furnace that broke because of that recessed lid design. Someone had to raise this potential issue, and it wasn't about to be Pat. As you point out, he really does have a lot of experience building furnaces. I'm quite sure he would have plenty to add at this point if he was still here.

    Jeff
     
  13. k.kuhn

    k.kuhn Silver

    Yes, it protrudes into the furnace about 1" and has 1/8" all around for clearance. If it does get stuck while heating I think I'll just leave it until it cools and then figure something else out for the lid. This lid is a temporary one and also an experiment with the rebar inside.
     
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  14. Tobho Mott

    Tobho Mott Gold Banner Member

    Hopefully you have enough clearance; if it doesn't stick, it should be good for preventing flames leaking out and wasting heat. Test it before you melt anything, as a crucible of molten metal that is allowed to freeze again and cool down is basically toast. Good luck!

    Jeff
     
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  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    No grudge here. I wish him well. I had a few exchanges with him privately that were less than gratifying but I don't even know the details of what led to him being banned, but he obviously stepped over the line. It's probably worth noting he had a long history of being banned from other sites including AA so I don't think his exit from this site could come as a surprise.

    OK. :) I think a number of the things he claimed to be firsts were not firsts, many of the things he did in his build were nonsensical and ill-advised, and a furnace that falls apart after small number of heats is not worthy of repeating. While he was a member here he poured more metal onto the ground than he ever did into a mold but claimed to have mastered iron.......I don't get it........I'm not saying it to smite him, but why I don't recommend it to new members as the example to follow.

    Best,
    Kelly
     
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  16. Petee716

    Petee716 Gold Banner Member

    I noticed that protruding lid too. I think it's a really good idea in this build for a couple reasons, the biggest reason being it should be quite effective at minimizing flame leakage. 1/8" clearance will probably work fine without binding. I have to say I'm a little iffy about not having a hard shell on the furnace and lid. One reason of course is because I've never seen it done that way. The other reason is because of my own experiences with my own furnaces. My furnace exteriors take some abuse moving, storing, and in use. The exhaust hole and lid top in particular take some real abuse from material being lowered in or set on top to either preheat or partially cover the hole. The edges of that exhaust hole will take a beating from the heat and flame force. You will probably see some erosion in that area. I have no doubts this furnace will do what it's designed to do, but I have some durability concerns. I'll be very interested to follow your progress.
    So far so good!
    Pete
     
  17. One lid seal I'd been thinking about would be a 45 or 60 degree tapered cone, 45 degrees would give you 40% more length of contact and it would also be possible to get some abrasive grit to lap the two surfaces into contact which could then be "refreshed" from time to time. The only problem with this is if the heating of the lid is faster than the walls, it's going to expand faster and cause cracks.
     
    Last edited: Jan 9, 2021
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  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I'm with Petee on that. You've done a lot of nice work to not finish it with an outer metal skin? Have you tried to scrounge up a barrel to suit? If it's a matter of metal working skills, even some thin gauge steel wrapped and cinched with wire would be better than nothing. -You've come this far.

    Best,
    Kelly
     
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  19. Melterskelter

    Melterskelter Gold Banner Member

    I agree with putting a little hard shell on the furnace. All it might take is a trip to the local heating and air conditioning shop. Get a piece of light gauge galvanized and bend and band or wire it around the furnace. The wool will become more friable with heat exposure. Just a bit of protection while go a long way. I did not hard face the top of my lid—- the wool is exposed. But the top is far less vulnerable and it has held up well.

    Good work so far.

    I use a gasket made from a 2” wide strip of wool that is glued to the body with Satanite. The lid rests on it. The surface of the lid and the top of the furnace are rather crude and quite irregular. The wool makes a gas-tight seal. I replace the gasket after ten melts or so and protect its inner (hot) side with Satanite.

    Denis
     
  20. OMM

    OMM Silver

    Kelly, that is your opinion. I fully respect your opinion in high regards, but I'm a little bit more democratic. And I do believe you are on the Democratic decisions of the forum discussion with the other moderators of members. I'm sure you were allowed to give your personal recommendation or thoughts on a particular member before any harsh decision was made. Maybe you were, ...and maybe you were not. Is this the situation?

    Whatever decision with other moderators you may or may not have had, ... I am sure decisions were done democratically as a team, that I think you are part of... but, I do not know,.......but, I can't reach out to Mr. PatJ through this platform anymore... This may or may not be your personal preference(or not), but somewhere a decision was made.

    You stated that "he obviously stepped over the line" what line? What did he do wrong and where and how? Please explain so others don't step over the same line.

    In my opinion, a member is a member. A banner member supports financially this website and tries to contribute with good content.

    I try my best to do the banner member. Was PatJ a paid member at the time of the team decision of his membership (banner member)?

    I tried to keep this only 3 questions that can be elaborated on.
     
    Last edited: Jan 9, 2021

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