Yet another keg furnace

Discussion in 'Furnaces and their construction' started by Mark's castings, Aug 3, 2018.

  1. Here's some pics and a short video of my keg furnace so far. Today I made some stainless collars for both pivot shafts: these prevent the two rods from moving sideways during operation and misaligning the lid to the barrel. Everything threaded was slathered in copper antiseize and assembled. All I need to do now is fabricate some legs, a bracket to hold the lid when in open position and weld some 4" tube into the side for the burner entrance. I may line the burner tube entrance with refractory so 4" should be a good diameter.

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    Last edited: Aug 4, 2018
    oldironfarmer likes this.
  2. PatJ

    PatJ Silver

    I like that lid lifter.
    Works well, and no danger of it getting stuck in the partially closed position (as happened to me mid-melt one time).
     
  3. Full disclosure: it has a balance problem if you open the lid and lower it close to the ground so it has maximum horizontal extension. I have to weld a tab to the body so the lid can only swing open enough to fully clear the body and once the 150 odd lbs of refractory is installed it should be fine. The engineer who designed it back in the late 50's early 60's just passed away this last October at age 93, here's Laurie's website: http://www.turbofast.com.au/astrotel/furnace1.html
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    I really like the sloped bottom with puke plug. Wish I had though of that on my build. Right now my furnace floor is pretty much a pile of slag with the plinth melted to the floor over the drain hole. :confused:
     
  5. The current owner hasn't kept that feature and we could have used it a few weeks ago when a worn out silicon carbide crucible split from the top to about 1/3rd the way down: the wall was thin and the bronze ingot inside it from cold startup was too much weight. Now it has half an inch of bronze in the bottom, it'll have to be chipped out and Pete has some relining product to put over the old refractory to give it a new lease of life.

    That reminds me: the original furnace has a bolt on bottom and the plinth and bottom are cast as a one piece refractory plug. I'll cast the walls and lower the base and plinth in from the top so it can be hopefully removed and replaced as needed.
     
  6. Jason

    Jason Gold

    Fancy Schmancy! I wanna see how you form the bottom. I visited that old farts webpage. He was a pretty smart guy. I wonder how long that info will stay on the net? Probably until the next bill comes in. Wonder if we should grab it now?
     
  7. Peter tells me that I'll have to fit a removable, bolt on hatch to the furnace base the diameter of the furnace bore. That way the damaged base refractory can be knocked out and a precast base can be fitted, I'll use the domed lid that I cut off the keg and weld some stainless studs to the base.

    Laurie was quite a character, he was a tradesman pattern maker, then tool and die maker when he started his career before WW2 and the company helped him get an engineering degree. The website should stay up indefinitely, it was always part of his son's website so I guess Ray will keep it alive from here on out. Ray turbocharges high end vehicles for very well heeled customers out of the same workshop.
     
  8. joe yard

    joe yard Silver

    There are many things to like about this design. The first reincarnation of my first and only furnace 20 years ago had a lid movement like that. It worked perfectly with minimal effort. The furnace was electric, mostly built of local clay with a refractory lining wrapped in ceramic wool.
    It sounds like a great idea. To have the bottom the same size as the bore. If you wanted to make it a lift off. It would be easy enough to have keg set on top of the bottom inside the stainless shell.
    With mine I expanded the burn chamber 2 inches to help with burning oil. This made the side walls around the hottest part of the furnace the thinnest. It also made it a real pain to form up. If I had it to do again. I would seriously considered a furnace with a side door. Jason posted this in post 43 of another keg foundry furnace.jpg
     
  9. Hi Joe, having that side door has got to be one of the more practical furnace designs: just open the door and grab the crucible. I'd imagine the door has to be swung wide open to face the hot radiant side away from the user and if the opening and door had tapered sides cast into the refractory then it would wedge tight and seal well.

    Burning oil seems (to me) to be a bit slower to crack the oil molecules and release the heat compared to propane and my experience so far seems to bear that out. It was suggested to me to have a longer, refractory lined tuyere/tube so the oil nozzle could spray into it and travel a longer path to give it extra time to burn fully. There was another version of the one I'm building that had this modification and at full throttle it would melt some of the best castable refractories available.
     
  10. Jason

    Jason Gold

    I think that thing was for sale on fleabay. I like the side door setup personally.

    Ya know mark... EVERYONE over at AA pissed and moaned when I did my build thread... Look it up. My furnace lid hinges back and faces right at me when it's open. The naysayers said it would radiate me to an early death. It's actually not hot at all. The furnace is running when it's open and all the heat from the forced air goes STRAIGHT UP. My hinge was idiot proof and dead simple to build. I believe my oil combusts inside the furnace due to the hot chamber. Now diesel is a different story, that's on fire right at the end of the burner. At least this is how it works in my narrow mind. :p
     
  11. The dodgy home made furnace I'm using loses a lot of white vapour out the cracks and rust holes so I can't increase the rate of burn by boosting the forced air pressure: it's just not airtight enough to do that. So with a new relatively air tight furnace like yours, the rate of burn should increase enough to burn oil readily with forced air supercharging. That's plan 'A' with plan 'B' being a longer tuyere if required. Right now I have thick soot deposits on the bottom half of the crucible and soot free upper half of the crucible, melting refractory on the top third and spectacular flames out the top. To my unscientific eye that looks like the bottom of the furnace is running cool and the top is running too hot.

    Regarding the radiant heat, I just want to minimise it a bit and the lid mechanism also lets me keep preheating ingots on top. My dark blue leather gloves smoke immediately and the pale grey ones seem to run a bit cooler to me but then that difference could be imaginary.

    radiant.jpeg
     
    Last edited: Aug 6, 2018
  12. My firebox is big inside but my oil won't burn in the tuyere. I can see it blow in but the flame starts where the radiant heat is high. I think trying to get it to burn back in the tuyere will just cause more to run down the side. I do have my burner tube 10 degrees down into the furnace to make sure all oil goes to the fire.
     
    Jason and Mark's castings like this.
  13. Petee716

    Petee716 Gold Banner Member

    I don't ordinarily put much total weight on my lid but definitely use it for preheating, particularly aluminum because like one of our members (or AA, I can't remember which) recently related, I keep my Al ingots outside and although they're not swimming, it's a good way to assure they're dry. The flat surface is pretty handy. I also have a reverb furnace made from a horizontal compressor tank that has a lid that opens about 95deg. That's a tilt and pour setup so I only open it to clear out, squeeze, or scrape dross. I load through a top hole or down the chimney. I choose to get in close to scrape so I'm not banging on my lining, and that lid is so f'n hot I end up changing my glove at least once during the 60 second operation.
    I've found with my oil burner regardless whether it's veg, WMO, or kerosene, if it touches the tube I end up with pooling oil and sometimes a fire where I don't want it.
    I'm not sure what type of fuel you're burning Mark, but I'm wondering if your not suffering from residual pooled oil in the lining of your furnace. Then subsequently introducing more oil into a not quite hot enough furnace in your next session is just perpetuating the problem. Perhaps a good burnout with LPG would allow it to get cleared and thereafter a preheat with lighter oil or LPG so that when you switch over to heavier stuff your bore is hot enough to burn it all before it has a chance to accumulate.
    Just a thought.

    Pete
     
  14. The old experimental setup had burn problems from design issues and more than few mechanical failures, there's no doubt at all that there was oil pooling at one stage during the last run. If I start with a decent conventional furnace body that should eliminate some of the issues. As far as burners go, I'm wide open to ideas as my initial experiments are almost exhausted with only a few more to go.

    Ideally I'll match the current propane performance that my furnace is based on but with waste oil: an A20 of bronze in under 25 minutes from cold and 15 minutes thereafter. If I can minimise heat on the user through design then I'll do it.

    There was a guy who ran one on waste oil, like I mentioned earlier and I only have an eyewitness account of the setup used in the 1980's (The owner passed away ten years ago) : The sump oil (pre synthetic days) was strained and waste water removed, then it usually spent some time settling. The 44 gallon drum had the oil pickup several inches off the bottom to avoid crud and it was pumped by an old Holden red motor oil pump. The red 202 cubic inch 6 was based on a GM grey motor made in Canada back in the 1940's. The gear oil pump has an integral spin on oil filter and an internal spring loaded bypass valve and was driven by electric motor. The pump needs modification to address oil leaks on the drive shaft and a pressure adjust screw can be fitted to vary the pressure setting, after that there's nozzles to consider.

    Holden oil pump.jpg
     
  15. Made some slow but steady progress....a word of warning: anyone distressed by poor quality stick welding of stainless steel had better look away NOW :eek:.

    The lid was recycled into the removable base with about two inches of overlap of the cover around the circumference and is held on by wingnuts over captive stainless bolts tack welded from the inside. As they were welded with them angled outwards it caused a bit of distress when it came time to remove the cover after welding the bolts, but now with trimmed bolts and oversize holes in the cover it goes on fine. The lid stops are welded on and prevent the lid from shifting the centre of balance too far sideways. I split a section of 4" tube and welded a 4/5" wide strip to make the oversize tube to accept the 4" burner tube.....the welding to the keg is going to need a good grind and tidy up :rolleyes:. I just have fabricate the formwork and start casting the refractory, I'll try a badly out of balance DC motor strapped to the side with a ratchet strap for vibration to help the compaction.

    inlet pipe split.jpg furnace 6.jpg furnace 5.jpg furnace 4.jpg
     
    Last edited: Aug 8, 2018
  16. PatJ

    PatJ Silver

    I have not welded stainless in a long time, but I seem to remember it being a bit more tricky than a regular rod.
    And couple that with welding sheet metal, which is a bit of a trick itself, I would say your welds are looking good.
     
  17. Thin sheet is always a pain, but I quite like 316 stick welding, it's lower current than mild steel and the poor thermal conductivity helps a bit. Here's a close up of the tube entry weld minus most of the slag....at least there's more metal there for next time round :oops:. The feet are galvanized pipe with enough clearance to remove the base, I'll have to source some tubing for the wall lining, it looks like the outer diameter of 250mm bore PVC drain pipe will be ideal for the job. I should be able to make it split in 2-3 sections for easy removal and tape around a couple of MDF discs until the refractory cures.

    I was thinking I could sell it on Ebay "as is" as salvaged Skylab space junk :D


    stick welding yay.jpg


    mock up.jpg
     
  18. PatJ

    PatJ Silver

    I like to make welds that look good an professional, but I will settle for welds that are structurally strong.
    Sometimes I don't have time to get the pieces to fit exactly, and so I add a filler rod to fill gaps that are too large, and weld over it all.
    There is only so much time in a day, and so my mantra is "Function over form".
    I admire furnaces that look great, and I envy those who have the time to make them look great, but I admire furnaces and burners that function very well more, regardless of their looks.
    In the end, if it does not work well, then it is just eye candy.

    Edit: All my foundry work seems to be stuck in "prototype land", where I don't quite seem to have it all figured out, and my stuff looks pretty notchy. Perhaps that is part of the fun of it in the quest for casting perfection, but I like it when I finally arrive at a solution that works well, and better yet looks well.

    I need to stop chatting and get back to work on my furnace.

    All these furnace posts are giving me iron fever again.

    Edit:
    I have never tried to vibrate refractory.
    I just add it in about 2" thick layers, and then ram it with a wood dowel rod, perhaps 1/2" or 3/4" thick rod. Seems to work well. With the vibrating, I worry about settling out the heavier materials from the water and lighter elements, but some seem to use that method with success.
    And I used stainless needles in my latest furnace build, and don't want those settling to the bottom, or top as the case may be depending on density.
     
    Last edited: Aug 9, 2018
    Mark's castings likes this.
  19. It can't hurt to add some vibration to the casting process, I still plan to ram in small sections. As far as reinforcing goes, I'll leave out any metal in case the difference in expansion co-efficients induces cracking. By containing the lining in the steel body it should stay together even if it cracks due to the cylindrical geometry wedging the refractory (hopefully). I'm fortunate to have an existing successful unit to copy and crib design cues from, such as the lid having those bottom retainer tabs to hold the lid refractory in place and casting the lid in place last so it conforms to the top of the cylinder and seals better.

    All that remains is to sort out a good burner unit: I found a paper on spinning cup geometry which mentions that finest atomisation is not that proportional to cup diameter or speed but rim surface features like points/spikes. The more points the better the atomisation of the liquid, so after a few more tests the idea will be exhausted. After than it'll be on to more conventional tests....apparently a preheater coil for the oil reduces the viscosity and helps a conventional spray nozzle function better. I'll be recreating as much as possible the oil burner used for this furnace that was capable of melting the refractory: the company that made the refractory accused the end user of melting it in an electric arc furnace when sent a sample.
     
  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    You should give it a try Pat. I think you'd be pleasantly surprised. I can't imagine casting castable refractory without vibe. The settling of heavier constituents is really not a problem unless you vibrate for long periods of time. It depends on the level of energy you are putting into the mold and the mass of the mold but with one turbine vibratory on a spring table with a 100lbs sitting on it, the refractory began to flow the instant it was exposed to the vibration and settled out in the first 10-15 seconds. After that it's just a few air bubbles that surface. Wands will keep the vibration localized but do pretty much the same thing. I just can't pass up being able to dump in the mixed refractory and let it find home by itself under vibe......especially in complex shapes and hard to reach pockets.

    Here's short video example when I made a crucible hat.



    Best,
    Kelly
     

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