A thin hotface medium/low mass beer keg (drum size) furnace for melting Iron

Discussion in 'Furnaces and their construction' started by PatJ, Aug 24, 2017.

  1. PatJ

    PatJ Silver

    I got really bored today and so I layered up and went outside to finish "operation-dryout" with the oil burner, and also build the metal base for the furnace to sit on.

    I ran the oil burner very low for about three hours; no combustion air and very little compressed air pressure (perhaps 5 psi).
    I ramped up the compressed air and oil a bit and ran it for another couple of hours.
    And finally I cranked up the leaf blower and used that for combustion air, and ran the furnace for about 10 minutes at full burner output (about 3 gal/hr).

    Everything seemed to go well.
    A couple of minor cracks; one in the shell at the top, and one in the lid at the opening.

    I will add a stainless band around the top of the furnace shell to prevent future cracks, and to keep the crack that developed today from propagating.

    I welded up a metal base.
    I wanted to use angle iron, but I had to use what I had on the shelf (round pipe).

    And I buffed the outside beer keg shell a bit to pretty it up for the photo, but nothing like a mirror finish.

    Next step will be adding the ceramic blanket, then the stainless shell, and a few minor additions, and at that point it will be show time.

    It was a bit breezy here today but the sun was out. It did not get above 32 F, which is very cold for around these parts, but a heat wave compared to what is going on up north of here.
    There was no problem lighting or running the oil burner on diesel, although the hoses were very stiff.

    Edit:
    I did not like the way this steel base turned out, and ended up building a different one later in this thread, and discarded this one.


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    Last edited: Nov 29, 2018
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  2. PatJ

    PatJ Silver

    I started cutting ceramic blanket today.

    I used three 1" layers under the refractory shell (which crushed down to 2"), and two 1" layers around the exterior of the shell and on top of the lid.
    (Edit: The ceramic blanket under the refractory shell was not stable enough, and I ended up using insulating fire bricks under the shell to rigidly support it.)

    I cut another beer keg section and will patch that in, and will probably add a 2" band at the top to cover the ceramic blanket.
    And maybe some sheet metal on top the lid blanket to protect the blanket there.

    Any ceramic blanket edges that are still exposed are going to get sprayed with rigidizer.

    I think one layer of 1" ceramic blanket would be sufficient, but I decided to err on the side of caution and go with two layers.

    I still need to cut the hole in the beer keg for the burner exit, and add a collar of refractory around the tuyere, and then I will be ready to try it out on some iron.

    I did order another 20 lbs of Mizzou for my inner lid, and will ram that up weather permitting.



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    Last edited: Sep 14, 2018
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  3. Tobho Mott

    Tobho Mott Gold Banner Member

    Looks good! I used insulating firebrick to insulate the floor of my furnace to prevent the weight of refractory from crushing the ceramic blanket I used for the rest of it. I am guessing having your blanket get crushed down to 2/3 its original height won't make a noticeable difference though. I bet you'll be melting iron before you know it!

    Jeff
     
  4. PatJ

    PatJ Silver

    I have gone back and forth between using ceramic blanket and insulating fire bricks, and actually have a set of bricks that I cut.
    But my sheet metal base is not exactly flat, and the bottom of the furnace shell is not exactly flat either, so I am worried about there only being a few points of contact, and putting too much pressure on the bricks and shell.

    I guess I could use a little furnace cement as a shim, but I was hoping to keep things modular so that if I needed to replace the refractory shell, I would not have to chisel it out.

    Maybe I will use a layer of parchment paper (or maybe aluminum foil) on the steel, to prevent the cement from sticking to it, and another layer between the brick and the refractory shell, or maybe just cement the bricks to the steel.

    At any rate, the bricks would prevent crushing the ceramic blanket over time.


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  5. Ironsides

    Ironsides Silver

    PatJ

    Good to see that you are progressing well with your low mass furnace.

    Back in reply 40 you asked me how the ceramic blanket holds over time?

    I get between 35 – 40 melts in iron, each melt is 14 Kg. So with 35 melts a total of 490 Kg (1078 lbs) has been melted over the life of the furnace linings.

    I occasionally use a larger crucible which melts 24 Kg each time. If I used that crucible every time it would melt 840 Kg (1848 lbs) before it has to be relined. As you can see using the largest possible crucible in your furnace is the most economical way to use your furnace but it may not be the most convenient way to use your furnace.

    For me 14 Kg of iron each time is more than enough for my needs. I think most hobby melters would not come close to melting 490 Kg (1078 lbs) in their entire lifespan of this hobby.

    The ceramic blanket I use is only rated for 1260 C continuous use. Just before I pull out the crucible the temperature of the furnace atmosphere is between 1550 – 1570 C, so it has a hard life. I use the low temp blanket because I got a lifetimes supply really cheap from an auction.

    I did inquire about the high temp ceramic blanket (1550 C), It was sooo expensive that I would not even consider using it.

    I like my low mass furnace because it is so reliable and quick to melt metals. Aluminuim, bronze and cast iron are routinely melted in this furnace every time with no fuss or bother. The one thing I have to watch for, it is so easy to over heat aluminium and bronze in this furnace.
     
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  6. PatJ

    PatJ Silver

    If this shell does not hold up well I am going to try the zircon-coated ceramic blanket.
    The coated blanket seems like a fair trade-off between durability, melt time, mass, and furnace build/rebuild time.

    I guess another option would be the 1.25" thick hard fire bricks stacked in a circle, but they seem to crack in half when exposed to an oil burner running flat out after a short period of time, and the joints would be prone to leakage most likely if exposed to an oil burner. But hard fire bricks would be easily replaceable.

    I would definitely use hard fire bricks for any future aluminum-only furnace that I may build.

    The Mizzou seems to have a reputation for durability at high temperatures, with the trade-off that it is not as insulating as some other refractories due to its high density.
    For multiple iron melts, the refractory needs to be as durable as possible, since iron temps are very hard on the equipment.

    I think scavenger's furnace was/is high/higher mass then some, and he does not seem to have much trouble with melting iron, but he seems to have longer melt times than ironsides, and uses more fuel, and also I think scavenger often does back-to-back iron pours (not positive of that), and the second pour goes much faster since the furnace mass is already heated.

    When I cranked up my oil burner at the end of the second dry-out period and added the full combustion air, the furnace got that super-heated glow to it inside, so I guess that is a good sign.
    I have had times when I could only get a dull red glow inside the furnace, and dull red does not bring iron to pour temperature, the furnace has to reach that almost white hot glow.
    When my old furnace was working correctly, I had to wear gas-welding glasses with UV/IR protection to avoid getting sunburn in the eyes. That is when you can tell you are really getting a hot melt.
     
  7. PatJ

    PatJ Silver

    We had sunshine and some moderate temps, so I made some progress on the furnace today.

    I decided to rigidize the ceramic blanket on the lid, in lieu of a metal cover.
    I used furnace cement thinned with water, and sprayed it on with a sand blasting gun.
    I am trying to keep the metal skins away from the hot shell, to prevent a heat sink effect.
    For an aluminum furnace, I would skin it all in sheet metal, but for a cast iron furnace, I want every degree of temperature I can get to stay inside the furnace.

    I made a stand for the leaf blower, and found an old oval-to-round adapter I made a few years back, which luckily fit perfectly.

    I decided to use insulating fire brick under the shell and I used furnace cement to adhere the pieces together and to the base.
    I added a few thin strips of ceramic blanket on top the brick as a buffer since the bottom of the shell is not exactly flat, and the bricks are not completely flat either.

    I am still working on the beer keg shell. I wish it were not so springy; I cannot get it bent into the correct diameter, and so I will have to put a band around it and pull it into the correct size.

    I added a bit of refractory at the tuyere in order to get a complete seal around the burner tube, and so I can use a square-ended tube.
    I split the PVC pipe so that I can remove it once the refractory sets.

    I will need to add a strip around the top of the keg shell to raise the height a bit.

    This furnace will not win any awards for looks, but hopefully it will function very well with iron melts.

    Edit:
    This tuyere extension should have been cast at the same time and as an integral part of the refractory hot face. I ended up having to secure this tuyere extension to the furnace refractory using a stainless strap, which works, but is a less than ideal solution.


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    Last edited: Nov 29, 2018
  8. Tobho Mott

    Tobho Mott Gold Banner Member

    Coming along great, looking forward to seeing it in action!

    Jeff
     
    Last edited: Jan 24, 2018
  9. PatJ

    PatJ Silver

    Thanks, I am excited about the potential for this furnace.

    This is the culmination of 7 years of watching other's build furnaces, and operating one of my own.
    I have tried to incorporate some of the better features I have seen, plus a few features of my own.

    If the weather holds, I hope to be ready to test it in the next few weeks.
    Its iron or bust this year.
     
  10. Negativ3

    Negativ3 Silver

    Really like your tuyere design. I'm going to steal that for next time :)
     
  11. PatJ

    PatJ Silver

    Thanks, help yourself.

    I will have more photos tonight.
    I am trying to get the stainless cover installed.

    I may put a little furnace cement around it to adhere it to the shell, but so far it seems to be stuck onto the shell pretty rigidly.
    I was originally going to incorporate it monolithically into the shell, but could not get worked out the details of it when I rammed the shell.
     
  12. PatJ

    PatJ Silver

    Here is today's work on the furnace.

    The lid looks like a pig with the rigidized ceramic blanket, and patching the stainless sheet metal back together has become a piecemeal affair, and rather rough looking.

    If I had to do over I would have used either a 55 gal drum, or better yet a stainless 55 gal drum.
    The exterior is all cosmetics though; its the performance I am after.

    I will add one more level of stainless sheet metal around the top, and then rigidize the top of the ceramic blanket, and I will be ready for an iron test.

    I cemented the refractory shell to the insulating bricks, and the bricks are cemented to the metal base.
    I don't want the refractory shifting around inside the sheet metal cover.
    And I added some cement around the tuyere extension just to make sure it does not separate from the refractory shell.

    The refractory has two 1" layers of ceramic blanket wrapped around it, and the lid also has two layers of 1" blanket on top of it.

    I will probably smear some thinned ITC-200 around the interior to fill in the small holes.

    There is no sheet metal touching any of the hot refractory surfaces.
    I guess I could do a test melt with this setup, and then an identical test melt with a sheet metal cover over the lid ceramic blanket, to see if the sheet metal acts as a heat sink.

    Lid lifting is via two arms (human arms), using the handles embedded in the lid.

    I found a thermometer with four probes that I bought last year, and I will drill a couple of holes in the shell and put the probes up against the outside of the refractory shell (in between the refractory shell and the ceramic blanket).
    I guess I will put the probes on the left side, with one at tuyere level, and one about 4" down from the top of the refractory shell. This arrangement will tell me if there is a temperature differential between the upper and lower furnace areas.
    Hopefully this will tell me if the burner is getting the furnace hotter or colder as I make adjustments to the oil flow.

    Today's burner oil adjustment will consist of the following highly scientific method (pun intended):
    1. Start the burner on compressed air and a little diesel.
    2. Ramp up the diesel flow until the mixture is rich.
    3. Turn on the leaf blower at the lowest speed setting (the same setting that poroisitymaster uses to melt iron).
    4. Adjust the fuel needle valve until it looks about right (a little flame coming out the lid).
    5. Play with the needle valve while reading the temperature probes.
    6. Pray fervently to the casting gods for success.

    I will have to wait until the furnace reaches its maximum temperature before doing step 5.
    Step 6 may need to precede all the other steps, perhaps with some type of beer drinking ritual involved (just kidding, I don't drink, but if I did, I would not do it while I am trying to melt iron).

    I was using stainless sheet metal screws tonight, and those things are too soft to be of use.
    Most of them stripped out, so I need to get some better sheet metal screws.

    I may just spray on some rigidizer on the exposed ceramic blanket tomorrow without finishing the upper sheet metal and give it a whirl. I would really like to see how it is going to operate.

    I do have a good feeling about this furnace, and I think it will go well.
    It would be nice if it went record-breaking well, but I don't really see that happening with 100 lbs of mass; but I would settle for just well.

    I am going to try and make a video of the entire startup process, and the attempted iron melt.



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    Edit:
    This was a bad idea since the outside of the hot face gets to hot that it melted the temperature probes.


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    Last edited: Nov 29, 2018
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  13. Tobho Mott

    Tobho Mott Gold Banner Member

    That again. :D

    Jeff
     
  14. PatJ

    PatJ Silver

    I am off to the hardware store for more fasteners and furnace cement.
     
  15. PatJ

    PatJ Silver

    (Edit: My last post was on January 26, 2018, and due to a very heavy work project load, I was not able to make it back out into the shop for six and a half months. In the previous post it was freezing cold, and in this post it was heat stroke weather).


    I went out to the shed to work on the furnace.
    The thermometer is sitting on 100F, and so I lasted about 10 minutes.
    It would be nice to have AC in the shed, but that is not going to happen.

    I think the furnace is far enough along to be tested at any rate, perhaps with the addition of a little rigidizer on the top of the ceramic blankets.

    I need to cut three or four holes in the metal shell and install the thermocouples up against the outside of the refractory shell.

    If all works well, I can tidy things up a bit later after the "proof-of-concept" phase is complete.

    Edit:
    The actual inside dimensions are 13" diameter, and 14" tall, which is slightly smaller than what I posted on the burner thread.
     
    Last edited: Sep 14, 2018
  16. Jason

    Jason Gold

    14" tall sounds more like it. Mine is 18"+ and its way too tall. Long and thin may get you in, but short and thick does the trick.:D
     
  17. PatJ

    PatJ Silver

    You can always just stack soft fire bricks in the bottom, with a final top layer of hard fire brick, as a quick and dirty way to shorten a furnace.

    Below are the dimensions I ended up with (from post #43), and as you can see from the second sketch, I arrived at these dimensions by allowing almost 2" clear between the side of a #20 crucible (the largest crucible I thought I would regularly use), and 1" clear above a #20 crucible to the lid. These dimensions are all based on Morgan clay-graphite "Salamander-Super" crucibles.

    And I do plan on using a 5" tall plinth when I use a #10 crucible, to keep the crucible up in what I think is the hottest part of the furnace.

    I tried to keep it all within a beer keg, but that was not to be, and so I have a cut up beer keg, franken-furnaced together.
    Oh well, if it performs well with iron, then I won't complain about the looks.
    I am still in prototype mode with my foundry builds.


    Edit:
    My final design used one 1" layer of ceramic blanket around the hot face shell, followed by one layer of 2600 F insulating fire brick.
    I also used a domed lid as detailed later in this build.


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    Last edited: Nov 29, 2018
  18. PatJ

    PatJ Silver

    The chances of me building another furnace from cast refractory is basically zero.
    Its just more than I have time for these days.

    But a zircon-coated ceramic blanket furnace would be quick enough, and as ironsides demonstrates, they work well for iron.

    Here are a few sources of zircon that I found.
    I am not sure how much would be required for a 13" dia x 14" tall furnace (maybe ironsides can answer that).

    https://www.mtixtl.com/1800c3270fhi-purityzirconiacoatingquart.aspx


    About $600/ton from asia, but shipping would surely be a problem?

    Edit:

    Looks like zircon comes in two temperature ratings, 2,732F (1,500C), and 3,272F (1,800C).
    I would say the 3,272F would be the one you would want to use with an iron furnace.
    https://www.earthwaterfire.com/ceramiccoatings/refractory-coating.htm


    Edit02:
    Here is a zircon coating discussion.
    Not sure how old this thread is:
    http://www.potters.org/subject119531.htm


    Here is a supplier, but it is only rated for 2,600F, which is too low for iron:
    https://www.axner.com/rigidizer.aspx


    Edit03:
    Here is a source, but I can't access the prices.
    https://www.zircarceramics.com/product-category/coating/zirconia/
    https://www.zircarceramics.com/wp-content/uploads/2017/01/ZC-2.pdf


    Edit04:
    Pyropaint:
    https://www.aremco.com/news-item/pyro-paint-634-zo-coats-induction-heating-coils/


    Edit05:
    Finally found a gallon of the high-temperature zircon paint for sale:
    Not cheap, but this may be enough for several furnaces.
    http://www.graphitestore.com/pyro-paint-634-zo-zirconium-oxide-protective-coating?custcol_size=5

    Shelf life is 6 months.
    Also comes in pint, quart, and 5 gallons.
    The gallon is pretty much the best buy, if you can use it all in 6 months.



    Edit:
    This site says shelf life is 6 months.
    That is not good, and means you pretty much have to buy it and use it immediately.
    Whatever you do not use may go bad before you try to use it again, which is the same with cast refractory.
    https://www.mtixtl.com/1800c3270fhi-purityzirconiacoatingquart.aspx

    The site sells 17 oz for $55.00.
    I wonder how much that is per quart/gallon?
     
    Last edited: Aug 12, 2018
  19. PatJ

    PatJ Silver

    As an afterthought, the zircon coating is a bit pricey, and if the shelf life is really 6 months (it may be longer), then I am not too keen on the ceramic blanket furnace idea.

    If I build another 13" dia x 14" tall furnace, what method would I use?
    (Edit: After further consideration, I would definitely make another cast refractory shell from Mizzou.
    I still have the forms to make this, and it was pretty easy to make.
    I would not use hard fire bricks as I suggest below.)


    I will most likely make it out of hard fire bricks, similar to this smaller furnace that I put together a few years ago as a proof-of-concept.
    I use this furnace for small aluminum melts, and fire it with propane using a Hybrid Burners burner.

    I have a wet tile table saw, so it would be easy to cut a bevel on the edges of the hard bricks, and use two layers to get the necessary height.

    I would probably buy a diamond hole saw to cut the tuyere (I sort of hacked out the hole in the furnace below in a crude way, due to it being a prototype).
    I would make a wood jig so that I could cut the tuyere into the brick at the correct angle.

    A hard fire brick furnace would weigh no more than the Mizzou thin-shell furnace I am building, and the bricks are readily available.
    I would band the bricks on the outside with steel wire or bands, similar to what I did below, and then use two layers of ceramic blanket around the whole thing.

    The lid would probably still need to be cast in refractory, but if you were good enough with the tile saw, and made a jig, I think you could cut tapered pie-shape pieces for the lid that could assume a dome shape, and could be secured with a steel band at the bottom. Probably easier just to cast a domed lid in Mizzou though than make all those cuts.
    For aluminum melts, I use half of a pottery kiln shelf, and that works fine, albeit a bit crude of a lid solution.

    There is really no need to cement the bricks together if the joint is even and tight, and so hard fire bricks would be easy to replace, either individually or as a whole.

    I know of at least one guy who has dabbled in iron work that has used hard fire bricks, but not for an extended period of time, so I am not sure of their long-term durability for iron melts.

    A furnace made from cast refractory does make for a very nice and completely round furnace, but is a considerable amount of form making and ramming work.

    I guess there is no free lunch if you want an iron-rated furnace that will last for a while.


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    Last edited: Nov 29, 2018
  20. So why not soft 3,000F firebrick with a coating? They are lightweight, don't hold much energy, and are good insulators. Hard brick holds a lot of energy and is not a good insulator. I wrapped my lightweight brick in Kaowool and when I melt copper the outside skin does not get hot.

    Satanite is advertised as good for 3,200F. Do we think that is correct?
     

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