Just a few simple questions? LOL Not for the faint of heart!!

Discussion in 'Furnaces and their construction' started by KC M@, Dec 29, 2020.

  1. KC M@

    KC M@ Copper

    I am new to the forum. My introduction is posted. I am mid build and my thoughts as usual are racing. I have several questions on my build. Technical type over thinker stuff but the kind of things you wish you would have thought of before it cost you additional headache, time, and money.

    Preface:
    Im sorry for the wide spectrum of questions, working out the details ahead of time is what I get paid to do professionally. My thinking that spending a little extra time on the front end can save lot time, money, and materials has never steered me wrong.

    So here goes: (in one breath)

    Calculating hole size for the burner entrance?, does it need/should it be chokeable for rich/lean fine tuning?, should it be sleeved to the hot face?... by metal or refractory?, is it better for the flare to be cast in the hot face?, if diameter is great enough does it need to be off the floor?, floor construction, specifically would fire brick be a sufficient replaceable or should I cast a disc of refractory?, modular/replaceable hot face panels?, should I run the metal on my lid to the vent hole or cast a refractory cylinder through the lid to keep it from scorching the can, and many, many more...

    I understand I might not get everything right the first time but why not try my hardest. Aim small.

    thx
     
  2. Zapins

    Zapins Gold

    Calculating hole size for the burner entrance?
    I don't think the diameter of the burner entrance to furnace (tuyere) is terribly important. You want enough space so you can force enough air in around the burner tube and small enough it doesn't cool the furnace. It should be approximately the same as the vent hole in the roof of the furnace lid. Usually 3 to 4 inches in diameter is what most of us use. Mine is 3 inches across and I run propane.


    does it need/should it be chokeable for rich/lean fine tuning?
    Yes but this is usually done by choking the intake of the blower fan with a pivoting cover.


    should it be sleeved to the hot face?... by metal or refractory?
    Unsure what you mean by sleeved. But I think you are asking if the tuyere should be aimed at the wall - yes. You need flames to slide along the wall and spiral around the crucible. So flames don't directly touch the crucible.

    is it better for the flare to be cast in the hot face?

    Yes I cast the slightly flared/angled opening inside the refractory.

    if diameter is great enough does it need to be off the floor?
    I'd make a small lip between the bottom of the furnace and the tuyere opening. This protects you if your crucible ever fails. Then molten metal doesn't drain out your tuyere and ignite the propane hose.

    Floor construction, specifically would fire brick be a sufficient replaceable or should I cast a disc of refractory?
    You could use firebrick but the insulating type sucks for durability long term in a fire atmosphere. You'd need to coat it with satanite if you used bricks. I'd just cast a disc from refractory and then cast the furnace body on top of it before it fully dries. Then it bonds together well.

    modular/replaceable hot face panels?
    Not needed

    should I run the metal on my lid to the vent hole or cast a refractory cylinder through the lid to keep it from scorching the can
    Metal corrodes quickly when exposed to the games in a furnace if it doesn't have a refractory hot face it won't last long.

    Here is one of my furnace build threads. Might help you sort through questions.

    Abbreviated furnace build thread:
    http://forums.thehomefoundry.org/index.php?threads/furnace-wax-burnout-3-0-zapins.317/

    Some videos of furnace running: http://forums.thehomefoundry.org/index.php?threads/flames-coming-out.1361/#post-31551

    Original thread with many photos of the furnace build including start to finish photos. Of course the old forum is kind of broken so you'll have to open photos individually.
    http://www.alloyavenue.com/vb/archive/index.php/t-9501.html
     
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  3. KC M@

    KC M@ Copper

    Here’s a few more...

    How much heat is lost between the lid and the main body? Would it be worth casting a lip on the lid to sit just inside the barrel? Would it improve efficiency? Exterior coatings? Will powder coat hold up or high temp paint? What temperatures can the exterior housing expect to see? Here’s a quick sketch of what I’m thinking: Thoughts on any of my quandaries? My wife just let me know my food is now cold so I’ll post some pics of the build when I return.

    To all the traditional drafters: I know. It’s not to scale. :D
     

    Attached Files:

    Last edited: Dec 29, 2020
  4. Zapins

    Zapins Gold

    I reposted the original furnace build thread here: http://forums.thehomefoundry.org/index.php?threads/furnace-build-1-0-zapins.1462/

    Have a look at the photos towards the end of the thread that show the inside of the burner tube and how I insulated it.

    There is a good amount of heat lost between the lid and top of furnace. I see flames normally come out on my furnace in that location. A tongue and groove design was suggested by others to trap more flame/heat inside. But it seems to work well enough without that on my furnace. I'm unsure if sealing this gap would really help that much as most of the heat still goes out the top vent and it might serve to choke down the volume of air/propane you can get into the furnace.

    Outer coating use 2000F engine paint from any automotive store. It doesn't hold its color forever but it does prevent rust which is the main point of paint. Powder coating won't hold up over time, not even the 2000F paint really holds up. Exterior temp seems a couple hundred degrees. But this depends on your furnace design. If you do a solid cast refractory furnace like mine it transfers more heat to the outer shell and gets hotter, but a ceramic fiber blanket insulation around the outside would cool it down to touchable temperature.

    Yeah your plans are about right for dimensions. I can't clearly see the size of the vent on top, I'd do 3-4 inches on that. 4 might be better so you can fit in ingots without opening the furnace during a melt. I wish mine had been a tad bigger for this purpose. Especially if you seal the lid and wall area so flames don't leak.

    It is also difficult to make a crack free cylinder like you want to of castable. It will almost certainly crack. Which can be patched but isn't pretty. If you pour thicker it reduces cracking issues. But I know some on the forum have managed it like you want to do.

    Here are my old plans internal diameter 10 inches, and I later extended the height of the inner chamber so it was about 15 inches tall. This lets me use an A16 crucible inside which can melt almost 50 lbs of bronze in one go.
    [​IMG]
     
  5. Jason

    Jason Gold

    Good job Zap. I just didn't have the energy to tackle this one.

    KC, don't get too wrapped around the axle man. It's only a furnace and most people build a bigger and better one later after the lessons are learned.
    Mine is too tall, but still works like a champ!
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Hey Matt, a few questions for you and apologies in advance if you have already posted the answers....on a quick glance I didn't see them.

    What type of castings do you have planned? What metal and how many lbs do you want to be able to cast in a single pour? The usual train of thought in designing a furnace is to identify a crucible size that will do the deed and design around that. Many of your questions can depend on this starting point.

    Best,
    Kelly
     
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  7. KC M@

    KC M@ Copper

    Most of what I want to cast to begin with would be simple items around the house either practical or decorative. Watching myfordboy’s and others videos has made me realize just how many things are cast so sky’s the limit eventually. As far as my build goes I’m sizing it to an A12 crucible. My can is 16” so I plan to do two 1” layers of kaowool with a 1” cast refractory hot face. Single burner, with a 4” vent on the top. I think based on what I’ve read and input from several members that these are tried and tested numbers.
     
    Zapins likes this.
  8. KC M@

    KC M@ Copper

    I wanted to give a thanks to zapins for all the useful info. I’ve seen the videos of your furnace burning before you linked it. Really, really cool. Almost looks like a black hole with all the light spinning around it.

    Update: I had another marathon day in the garage and I am beaming with glee. Bring on the dawn!!

    Here’s my progress so far. Started this bad boy on Saturday. I’m off for the week so I’m powering through it. Hopefully I can start casting on Saturday. The wheels are easily removable after transporting. I did this for two reasons: I was worried the heat from the pivoting lid would melt the soft inflatable tires and if I went with solid metal wheels they wouldn’t melt but it would beat it to death while rolling it to the area where I will be working. It also has the benefit of being super stable on the legs as well as not having to maneuver around the big wheels. Once set up there is a 10”x5/8” bolt with a foot that replaces the tire on the side where the lid swings. It adds stability when all that extra weight is hanging outside the stable base.
    Note: the hole in the side is not for the burner. It was a port that I removed and I still need to cut and weld a filler for it.

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  9. DavidF

    DavidF Administrator Staff Member Banner Member

    Well thats moving right along! Looking good!
     
  10. Jason

    Jason Gold

    Rock and ROLL.. Looks great!
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Good fab work and great start.

    Best,
    K
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    You are very right to plan on removing the tires. The lid would melt one in about 30 seconds if it were hanging over one of them. I screwed 2x4’s to the frame to act as outriggers. The wood is quick on and off using Torq drive screws and an impact driver. On the lid side I covered them with flashing. Otherwise theywould light up from radiant heat from the open lid.

    Denis
     
  13. Tobho Mott

    Tobho Mott Gold Banner Member

    That's going to be a very nice furnace!

    I built one of my furnaces with a 1" dense castable hot face too, to run with a waste oil burner. There are lots of pictures and explanations of how I dealt with the formwork, floor, tuyere, and so on in my build thread (linked in sig).

    If you cast your tuyere bigger than it needs to be to accept your burner, you may have to plug up the extra tuyere space to prevent flames from blasting back through the gap toward your burner's fuel lines and control valves. But that is much easier to do than drilling out a larger tuyere if you decide you want a bigger burner later on. I just stuffed the gap with small scraps of ceramic blanket.

    You can see how I got a pretty good seal where the lid of mine meets the bore. A tiny bit of flame does leak out there but IMO it is negligible. A lid that fits tighter using some sort of interlocking lip or recess (if I have understood your idea correctly) runs the risk of getting stuck shut if the lid expands a little differently than the bore when it gets hot. We have seen that happen before here:

    http://forums.thehomefoundry.org/in...urnace-for-melting-iron.26/page-25#post-15917

    IIRC Pat cracked his hotface badly enough to need patching, trying to pry open a stuck-on hot furnace lid... :eek:

    So, I don't think the benefit outweighs the risk. Sometimes simple is best. :D

    Jeff
     
  14. KC M@

    KC M@ Copper

    Expansion is a great point. Sometimes simple is the best. Thanks for the compliment and thanks for the great info Jeff.
     

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