Another melt "learning opportunity"

Discussion in 'General foundry chat' started by chris.trotter, May 12, 2018.

  1. chris.trotter

    chris.trotter Copper

    Ok, so I'm pretty fed up with the furnace at this point. I tried the suggestions from other threads, but no dice, the furnace still takes ~1.5-2.0 hours to heat up. If I could just leave it running somewhere and go and do other stuff, this would be workable, but with little kids and suburbia, not an option.

    Had yesterday afternoon off, fired it up at ~1:45pm (after 20m messing around getting it started), set the air to minimal help, propane to 20psi (more fuel = more hot?), by 2:40pm still nothing melted, so I set it up with the full air as before. By 3:30pm not much happening, but stuff starting to droop in the crucible, so left the heat on. By 4:00pm things definitely started melting. 4:15pm the initial charge was fully melted, 4:30pm another 3 hard drive chassis melted and I poured.

    Protip: 6 hard drives = 3 muffins (these came out just as shiny - will try and get a picture of slag to muffin ratio)

    Pretty frustrating to spend all afternoon out there and get 4 muffins out of it, haha. Gonna take me all summer to melt my scrap at this rate.

    I am starting to suspect there are two or three major issues:
    1. Gap between crucible and hotface is too large - there is ~3-4" space around the entire crucible, plus 3-4" of head room.
    2. Propane burner only ever puts out yellow flames, and as soon as the lid goes on, the flames die down (or become invisible) and the areas I could see getting red before cool down. Also stinks of excess propane when I'm running at 20psi and no air.
    3. Suspect the sand is sucking heat away from the hotface.
    A final side issue is that lighting the dang thing takes forever, suspect that I need to let it run with the lid off for 15m?

    Some solutions off the top of my head...
    • Too much space - uh...? Get bigger crucible?
    • Burner not functioning correctly - uh...? Put in an air valve/flapper to properly set ratio? Get pressure gauge and higher PSI reg? Get thermocouple to help diagnose?
    • Sand is acting as a heat sink, replace w. kaowool?
    If y'all see anything obvious, let me know. Otherwise, I still have to find time to re-read Anon's book & the foundry manual.
     
  2. So it uses loose sand as the insulation behind the hotface?. That may be dense enough to conduct a significant amount of heat away from the combustion chamber, there may not be enough rate of burn vs thermal losses. I'd want some minimal forced air supply for an exhaust hole that relatively small size.


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  3. I wish you would post some pictures of your burner. You should be making a blue flame.

    I don't believe it takes much energy to heat up air. The volume of the furnace is only an issue because you have a larger wall to heat. My furnace is in a 55 gallon drum with two layers of soft firebrick and an inch of ceramic fiber outside that. My crucible is only 4-1/2" in diameter and it heats a charge in 35 minutes. Reheats in 15 minutes and I make six or eight muffins from a charge. Last time I lit my furnace i was able to make a green sand pour and two lost foam pours (same crucible heat) in 65 minutes, start to finish.

    It appears you have two basic problems, the burner is not putting out the heat and your thermal mass is too great.

    You need to get enough air to make the flame blue, don't worry about propane volume until you get to heat with a blue flame.

    Get a piece of ceramic fiber blanket (1" 8# is fine) and form it inside you furnace wall. It's easy to do, do it outside, it cuts with a knife, wear your respirator, and buy some rigidizer to spray on it. That will protect it from degradation from the flame. You will see a dramatic improvement with the blanket.

    Long term buy some soft firebrick and line your new furnace with that. It is cheap, works great, and lasts a very long time. I have 78 heats on my firebrick furnace with no noticeable degradation yet. You can rip it on a table saw, it cuts really easy, to make shapes which will fit inside your furnace shell. The dust is hazardous so cut outside and clean up before your kids come out to play. You only have to do it one time.
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Agree, need to see details on your burner with dimensions and orifice size. Also, approximately how may lbs of dense castable and sand were used in the construction of your furnace?

    Best,
    Kelly
     
  5. Petee716

    Petee716 Gold Banner Member

    OIF hit some great points. My 10" bore furnace heats up on propane reasonably quickly. It has 1" of mizzou backed by 1.5" of 2:1 sand/fireclay. Both have fairly low thermal conductivity whereas your crucible conductivity should be quite high. I stands to reason that your crucible and charge should be getting good use of the heat. Yes your thermal mass isn't helping, but lack of heat is probably the culprit.

    Pete
     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I think one thing is for certain and that is the time initially required to heat is inversely proportional to furnace mass. Low mass = fast heat.

    The temperature eventually achieved is a function of fuel and insulation. I certainly agree with Pete about the crucible being a much better conductor than dense castable but even though dense castable is not a great conductor, it's still many times better than wool, IFB, and insulating castable, in that order, and is no coincidence that density/mass is increasing in that sequence. That's why I asked for the mass of the materials. There's a certain amount of physics that will be quite stubborn in this regard.

    I noticed a marked difference in initial time to temp in my electric when I replaced the IFB with dense castable hot face, each having wool outer. It's easily calculated but all a trade of time to heat and durability. In my case it went from 25-30 minutes for first melt of a full A10 to 45-50 minutes from cold start on a 10" bore furnace. Both are about 15 minutes per recharge to full melt and pour temp.

    For the most part it's only home gamers that care about time to heat as commercial foundries more typically maintain temperature and avoid cycling as it is hard on materials. If time to temperature is the most important factor for you, it will be hard to beat Bonz's approach to Satanite covered wool for the aforementioned reasons.

    Best,
    Kelly
     
  7. PatJ

    PatJ Silver

    I have melted aluminum in my high-mass (600 + lbs) furnace, and aluminum will easily melt in a #10 crucible without bringing the entire furnace up to temperature (using an oil burner).
    I have also melted aluminum in the same furnace using a "Hybrid Burners" propane burner 1.25" foundry burner in reasonable amounts of time, and I consider that burner very much overkill for aluminum melting.

    Seems like your burner is not adjusted/setup correctly.
    You should be melting aluminum in a #10 crucible in 30 minutes max with a propane burner that is working correctly such as a Reil or Hybrid burner, regardless of furnace mass (been there, done that). I have always used a naturally aspirating propane burner; ie: no blower is required.

    For melting iron, you do need to get the entire furnace up to temperature before the iron begins to melt, but no so with aluminum.

    Post photos; we fix it.
     
  8. chris.trotter

    chris.trotter Copper

    Photos inbound, should give you a good idea of crucible size, interior dimensions, hotface thickness, etc.

    The tuyere tube itself has an ID of 1.5", so the burner tube has air around it, but sits mostly flat (angled up at ~10 degrees toward the front) on the bottom of the tuyere tube
    • The burner nozzle tip says .08, and is angled at ~30-40 degrees into the burner tube.
    • Tube itself has an ID of ~1".
    • Hotface is ~0.75"
    • The pic showing the tube into the furnace body is just to give you an idea of tuyere placement. During operation the end of the burner tube is just inside the edge of the hotface ID
    Also included the pic showing hard drive aftermath. I suspect some good alum got caught up in the dross, but the liquid alum below the dross was very liquidy, and it was quite clear what was dross and what was good alum (i.e. I don't think it was too cold).

    Here's a quick video (might still be processing), tried to show the sound of the no-forced-air burner. It was very choppy-sounding. When you put the air onto it, it smoothes out quite a bit, and when the air is fully attached it becomes very smooth sounding and more roar-ey.



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  9. PatJ

    PatJ Silver

    Your first video shows the burner in a straight line, and it looks like at some point you changed it to an angled entry on the propane.

    I would suggest using one of the REIL arrangement shown below or better yet, use the "Sidearm" since I consider it a simpler and better design.


    4576cd784c9dff7a38c9d1d03e716ec4.jpg


    burner.gif






    I were going to build one, I would use this (Sidearm) design:

    Sidearm.jpg


    I would run the burner naturally aspirated. You don't need forced air with propane to melt aluminum.
    Be sure to use some sort of choke assembly so that you can tune the fuel/air mixture, as the burner will not operate properly without this adjustment.

    I use a flair on my propane burner, and that allows me to light the burner outside the furnace, adjust the air damper, and then insert the burner into the tuyere and make final air damper adjustments.
    You really need the jet tip centered in the burner tube (in my opinion), although I know those who run forced air propane burners do not worry about this.
    I would run it naturally aspirated only and center the jet tip in the burner tube. Works great and is simple.
    For the Sidearm burner, you don't have to make a butterfly damper; your damper can be as simple as a piece of tape partially obstructing the intake pipe, or a rotating disk on the end of the intake pipe.

    Here is a video and a picture link to show how the burner should look running either reducing, neutral, or oxidizing.

    I generally run my propane burner neutral; ie: there is no visible flame coming out the top of the furnace lid. I tune my burner with it running in the furnace, and start with a rich mixture with flames coming out the furnace lid, and then lean it out so the flames stop coming out the lid.
    You don't need very much propane pressure to melt aluminum.
    I would use as low a pressure as practical, else I think you are just wasting propane.
    I can't quote an exact propane pressure I use, but I seem to recall using perhaps 10 psi (check me on that).

    With a properly adjusted Sidearm or REIL, you should be able to easily melt a #10 of aluminum in about 20 minutes (or less).




    http://ronreil.abana.org/richtolean.jpg
     
    Last edited: May 12, 2018
  10. Jason

    Jason Gold

    Do you own an air compressor? Build a Kwiky and burn diesel. Problem done! You are just not putting out the BTUs with your current build to overcome the heat loss from that big furnace. Your other option is to tighten the furnace down and that is too much work at this point. Opting for a big oil burner is now the best way to go. I melt about 15lbs of bronze in 20mins from cold.
     
  11. PatJ

    PatJ Silver

    My large furnace is that size, and no problem melting aluminum with the right propane burner.
    I really think he just needs to fix his burner.
     
  12. Jason

    Jason Gold

    Yeah he doesn't have a furnace problem. His burner just sucks.
     
  13. Petee716

    Petee716 Gold Banner Member

    My propane burner doesn't have an orafice. Just an 1/8" fitting that dumps unregulated propane into the side of a 2" pipe.

    Ive since learned that I should be opening my tank valve all the way as I heard from what I believe to be a reliable source that they are designed to be fully opened. I've also changed to the above mentioned 2" pipe.
    Once it's lit and the lid is on I tune it by flame color, keeping the flame mostly inside the furnace. I often use this method to preheat the furnace for oil, but I've melted aluminum with just propane as well. I turn the propane up as high as I can within color and containment limits and although a near empty tank will frost up quickly and I'm probably terribly inefficient, it gets hot fast.

    Pete
     
  14. Jason

    Jason Gold

  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    What kind of blower are you using for forced air? With a 1" ID tube you'll need something that develops some head or that could be (likely) the limiting factor.

    Is 20 psi the limit of your regulator? If so and once you establish you have adequate air supply, you can drill the orifice as long as the regulator itself isn't the limiting factor, which I presume isn't the case if your gauge is downstream and stable at 20 psi. Do you have a video of the furnace in operation posted somewhere?

    Best,
    Kelly
     
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Since there's pressure drop across your tank valve, it's hard to say what the feed pressure is to the 1/8" tube. Ever put a gauge down stream of the tank valve? Or more importantly, measure the lb/hr of propane consumption? 5lb/hr is about ~100kBtu/hr in a reasonably tuned LP burner.

    Best,
    Kelly
     
  17. chris.trotter

    chris.trotter Copper

    Lol, in another thread someone was all 'guy, propane burners are soooo easy, you're overthinking it!', so I made something stupid simple, and is no work!

    You guys are awesome for all these suggestions/ideas, do you know that? :D

    I will try to address in order...
    • PatJ - I will look at those designs. I have a mill and lathe, so I mean we could go nuts here. :)
    • Jason - Kwiky/diesel, huh. I didn't want to get into oil burners because of various notions I had, but if you could relatively cleanly burn diesel...hum... Will read!
    • Petee - Ok, so that's interesting. I have never seen the tanks frost up, or even get cold enough to condensate. So maybe this is a 'not enough propane getting out there' problem?
    • Kelly - It's a low speed squirrel cage (from a dehumidifier) that I ghetto fabricated with aluminum tape and flashing. It puts out air akin to a blow dryer on low, maybe not even that much. 20psi is my regulator max, I have no gauge, just the mechanical limitations of the regulator (i.e. fully open it is spec'd for 20psi) . Check my youtube channel via that video link for videos of it in operation.
    See your answers are part of my confusion - some say 'not enough air!', some say 'no air needed!'. I think whatever is going on, it's definitely a fuel-air mixture issue of one sort or another.

    I will do some reading tomorrow and let you know - totally willing to rebuild the burner if there is some consensus on what actually needs to happen. :D
     
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    First thing is to put a gauge downstream of your regulator. 20 psi will be enough with the right orifice and forced air but the regulator itself may not be able to flow enough gas. Where did your regulator come from? Some will have built in flow limitation. If it can maintain 20 psig down stream, that will eliminate that concern. I would say a hair drier would do better than a the dehumidifier blower which is likely your limiting factor but we're shooting in the dark here with no video and/or gauge pressure. Can you weigh your tank and measure how many lbs are consumed in an hr? Even so the burn must still tuned. When you get the burner set up right you'll be melting aluminum in <30 minutes.

    Best,
    Kelly
     
    Last edited: May 12, 2018
  19. PatJ

    PatJ Silver

    The T-Rex in the video I posted above does not use a blower; it is naturally aspirated, and it is quite a beast with the right fuel flow.
     
  20. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Yes, I'm sure an NA burner would do it to but was just trying to guide Chris on easiest path from where he is at, but I agree with you, I wouldn't see the need to add an electrical cord to the mix unless he wanted to have a very high burn rate.

    Best,
    K
     

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