Beginner with a melting furnace: What am I doing wrong?

Discussion in 'Furnaces and their construction' started by Conor, Apr 29, 2024.

  1. Conor

    Conor Lead

    Hi all.
    Just want to share a problem that I've been having since getting my VEVOR propane furnace last summer. Loving this hobby and I'm certain that this is just a small thing I'm doing wrong- I've never seen a proper tutorial re. adjusting air intake/ gas pressure etc and even thoguh I've used it a lot and had good melts, I'm still clueless really as to the proper operation of one of these, especially in the areas detailed above.
    Basically what starts happening is the output from the burner starts to 'sputter' and gurgle, as per the video linked below. This usually starts happening after about 20 minutes of operation. Only thing that solves it is adjusting the choke so that no air is taken in. If I run the furnace like this from the start, i.e with a large orange flame with very little air intake, it doesn't happen, but it takes about an hour to melt a kg of copper which is not ideal.

    • I will up the gas pressure but this only solves it for about a minute.
    • There are no blockages anywhere in the system, it's been taken apart and cleaned multiple times.
    • Gas can is new and full (11 kg can of propane).
    • Gas can doesn't seem to be 'icing up' and have tried insulating it, putting it in water, etc to no avail.
    • No wind and mild temperatures where I live- around 15 degrees Celsius (59 Farenheit).
    Let me tell you how I have been running the furnace since I first got it- maybe there's some clue here:

    Gas pressure roughly 10-15 PSI
    Choke fully open to half closed (strong jet engine sound)
    I always let the furnace heat up for about a minute before closing the lid down.

    Doing it this way I can melt copper in about 25 minutes but the sputtering will start about 10 or 15 minutes in which makes it very hard to keep heat in the furnace.

    My furnace has a cracked firebrick at the bottom (needs replacing) and there have been some odd small spillages at the bottom. Otherwise the furnace seems good, apart from the insulation showing the signs of use (I need to spray it with rigidizer I know). No holes etc in the structure of the furnace.

    Here is the link to the video:

    And here is a guy with the same furnace as me, just for reference as to the type of furnace I have:

    Thanks in advance. Looking forward to your suggestions! Hopefully I can solve this.
  2. mytwhyt

    mytwhyt Silver

    I think closing the air off is a mistake. That type of burner needs the fuel to mix with air in the burner to burn hotter in the furnace. Other than that, it seems to be a pretty good furnace to start with. Coating the blanket also protects it somewhat from damage. If it wasn't needed they wouldn't' have included. it.
  3. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    Try opening the choke on your burner up gradually to add more air to the mixture and the fire ought to climb back just about completely inside your furnace and behave itself. Either that and/or turn down the gas. 10-15 psi for a naturally aspirated burner doesn't sound that high to me though (although mine do all use forced air, different animal) so I'd try more air before trying less gas.

    Good luck,

    Conor likes this.
  4. Tops

    Tops Silver Banner Member

    I have a naturally aspirated one, enclosing pics on how it was set last run and the cone I use to counteract cross breezes. I do not have gauges, I light the furnace with the propane on low and bring up the propane until I like the way it looks and sounds.

  5. Conor

    Conor Lead

    Cheers Jeff, have tried this somewhat but after a while it always starts to sputter, in which case the solution seems to be to decrease air intake for a while
  6. Conor

    Conor Lead

    They didn't include it and I can't get the rigidizer anywhere where I'm from
  7. mytwhyt

    mytwhyt Silver

  8. garyhlucas

    garyhlucas Silver

    I suspect your single tank of propane is not large enough. The gas isn't going from liquid to gas fast enough and you may even be getting droplets of liquid coming out of the tank. I have a little larger furnace and it kept popping and going out until I checked the size of the regulator and realized it couldn't pass the BTUs needed. So now I have two 11Kg tanks each with a regulator teed together and it runs smoothly now. Two tanks also don't freeze up, twice the surface area.
  9. nobodyspecial

    nobodyspecial Copper

    Fumed silica is available as a rigidizer and is sold in places that sell fiberglass and plastics supplies, although it's the kind of thing you should probably use a respirator for when applying. Rigidizer is important for protecting your blanket, but more importantly it's needed for protecting you, otherwise bits of the fiberglass tend to break off and go everywhere, such as in your lungs.

    You may also be able to get commerical rigidizers from pottery supply houses. If they don't carry them, they likely can tell you who does. If you are using a castable refractory, rigidizer also makes it a lot simpler to apply.
  10. Tops

    Tops Silver Banner Member

    @nobodyspecial Would one suspend the fumed silica in another medium to apply to ceramic fiber insulation? I use it in fiber glass work as a thickening/anti-slump agent and it's definitely a fluffy white powder.
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Fumed silicas are most commonly used as thickening agents. Colloidal silica is commonly used as inorganic high temp binder. The various refractory manufacturers market is a rigidizer for fiber insulation.

    Though they may contain some fumed silica as well, the ones I have used have very low viscosity. The ceramic wools will absorb large amounts of the stuff like a sponge if you try to apply with a brush, and it's not cheap (like ~$50-$100/gal). You really just want to stabilize the outer layer of fiber so a simple spray bottle might work best. Satanite is more economical, can be thinned and brushed to stabilize the outer layer, and will be a more durable furnace hotface.

    HT1 and Tops like this.
  12. FishbonzWV

    FishbonzWV Silver Banner Member

    Conor, there is a product that can be bought in the EU called Cement Fondu that can be used as a paint on coating for the wool. According to one of our members, he has used it as a hot face on his furnace and is similar to Satanite.
    Tops likes this.

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