Difficulty melting copper

Discussion in 'General foundry chat' started by FKreider, Aug 26, 2019.

  1. FKreider

    FKreider Copper

    Hello All,

    I am looking for some advise on what I might be doing wrong when attempting to melt copper/brass/bronze.

    I have a Pyramid Products No. 10 furnace which will fit up to a number 6 or 8 crucible. It uses a propane burner with blower. These furnaces were sold out of the back of magazines in the 80's.

    The previous owner of my furnace used it to cast brass/bronze bells and cleats for boats so I know it can melt these materials (I saw some of his castings when I purchased the foundry.)

    However I can not seem to get the thing to melt anything more than aluminum efficiently. This evening I ran the furnace for over an hour with coils of copper wire (clean scrap of ebay) and they only got orange and kind of melted.

    I am thinking my air/fuel mixture is off?

    How do I know where to set the "air intake" door on the blower?

    Should I be seeing a few inches of flame shoot out of the exhaust hole in the lid?

    Any advise is appreciated as I am getting frustrated and almost ready to just stick with pattern making and pay a foundry to cast parts for me!
     
  2. Petee716

    Petee716 Silver Banner Member

    How about some pictures of the burner and blower. You've got the firepower, don't give up!

    Pete
     
  3. Melterskelter

    Melterskelter Silver Banner Member

    I think most people shoot for a little orangish flame coming out the vent. Also a trace of smoke. Not sure the size of your furnace. But if say 10 inches diameter and 12 high, then maybe a gallon and a half per hour of oil. too much fuel and too much air chases all the hot part of the flame out of the furnace so that heat is released into the air but the furnace remains relatively cold. It will look like a nice clean burn and it probably is. Just happening in the wrong place.

    I'd think it might be worthwhile to slow down the fuel and blower to what seems too slow for sure and then just ramp it up by small increments over 30 minutes to see if you cna get a clue as to when the furnace is getting hot. The flame should be slightly reducing---it should soot a piece of clean metal parked in the flame for 5 to ten seconds. Too much air==cold furnace.

    To bad there are not better metrics for this as learning this in isolation is challenging for all I think. Was for me and still learning.

    Denis
     
  4. Jason

    Jason Silver Banner Member

    What have you got for a regulator on that thing? I shoot for about 3-4" of flame coming out the top. ;)
     
  5. Peedee

    Peedee Silver

    Copper wire is a bit of a nightmare to melt, it oxidises quickly. The oxides are very insulating and with that much surface area ...... you will often here the term 'heel' where you have a molten pool to press the feed stock into, in any case even with solid copper bars getting a melt can be difficult, it just loves oxygen. Rasper, amongst others has done some alloying so may be able to offer more sage advice.
     
  6. FKreider

    FKreider Copper

    I will take some pictures of the gas regulator and blower assembly when I get home from work this evening. The regulator is a fixed one like on a gas grill and is not adjustable, seems like an easy upgrade?

    Also considering selling this unit since it is old and heavy and purchasing a Devil-Forge unit:

    http://devil-forge.com/gas-furnaces/38-fb1sb.html

    They state that their unit can melt cast iron, that is pretty impressive.
     
  7. oldironfarmer

    oldironfarmer Silver Banner Member

    Don't waste money on a new cheap forge with a high price tag.

    Copper wire is easy to melt. You need a cover flux to help keep the oxygen away.

    As others have said, you don't have enough heat. Get a 15 psi or higher regulator. Adjust the air from rich (not enough air) until you see the flame turn from greenish to bluish. It's easy to see the change. But air adjusted properly does not help if you don't have enough fuel.
     
    Jason likes this.
  8. FKreider

    FKreider Copper

  9. Tobho Mott

    Tobho Mott Silver Banner Member

    Post a lot of close up pictures of your devil forge furnace if you buy one; we have only seen the pix from their ads and a bunch of YouTube footage from guys who got free furnaces for posting. I'd like to get an unbiased look at the build quality of those things...

    That said... Don't buy one! You can build a devil forge clone like I did, and you can do it a lot cheaper and probably better. Even if you decide to make one that looks pretty! It's not difficult to do.

    Here's how I built mine. Mine is not pretty. But it works really well:

    http://forums.thehomefoundry.org/index.php?threads/another-lightweight-fiber-blanket-furnace.726/

    I imagine you could probably melt copper in your existing furnace, if you can get your burner tuned right, assuming it's decently well insulated. In the part 2 video embedded in my build thread, you can see how much flame I had coming out of the vent hole in the furnace lid during a copper melt. I think that sort of tuning is just about right for copper - just a little rich, ie. flames coming up out the vent just a couple inches and not much more. More air or less fuel makes the flames pull back; less air or more fuel pushes the flames farther out. Tuning a propane or oil burner really is just about that easy.

    However, I have never seen a devil forge burner in a YouTube casting video (devil forge furnaces are heavily marketed in such) that wasn't running quite rich (reducing). I don't know if they are even capable of running neutral or oxidizing (lean) at the gas pressures those guys are using. I guess it's possible the guys making those devil forge ads on YT run them that way on purpose, simply because fire = eye candy.

    I would take any claims about their products with a grain of salt; the owner of the company has a history of making unfounded and IMO irresponsible claims such as stating that unsealed ceramic fiber blanket insulation is no longer a respiratory hazard once it has been fired once, which just isn't true; pre-fired blanket still sheds carcinogenic fibers. Think, asbestos.

    Did the devil forge ad promise the furnace would still be usable after an iron melt? :eek:

    Whichever way you choose, you should be able to get the job done once you figure out the burner tuning. Good luck!

    Edit - those regulators both look ok to me.

    Jeff
     
    Jason likes this.
  10. Zapins

    Zapins Silver

    Propane is pretty easy to melt with but you have to make sure the pressure of the propane tank doesn't drop. If you're using a bbq tank then you need to keep it in a warm bath of water to prevent it from icing over and reducing the pressure too much.

    You need a high pressure propane regulator to run a furnace properly. I use up to 80 psi to melt bronze.

    Another thing to keep in mind is the orifice that propane comes out of often clogs up with rust and other debris so you sometimes need to clean out the tiny hole in the tip of the burner.

    Try tune the blower and fuel so it jets out the top 4 inches or so. Fire it at night so you can see properly what the flame is doing. Tune it so it is as loud as possible. The sound gives you an indication of the power/heat output.
     
  11. Jason

    Jason Silver Banner Member

  12. garyhlucas

    garyhlucas Silver

    My Mifco furnace uses 225,000 btu. To get that I need to use 2 20lb tanks each with a 175,000 btu regulator.
     
  13. Jason

    Jason Silver Banner Member

    Gary how do you translate that into PSI for the regulators?
     
  14. garyhlucas

    garyhlucas Silver

    Gas regulators for grills and natural gas like in your house put out very low pressures because you burn at atmospheric pressure. Their BTU rating is the amount of gas at atmospheric pressure they can deliver. In the case of my furnace, the venturi in the bulge on the piping actually creates a vacuum that sucks the gas in.
     
  15. Jason

    Jason Silver Banner Member

    That would make sense. I scratch my head at my home natural gas furnace. It's rated for 400k btus. I'm ripping it out this winter to install a new furnace and coil. Looks like I'll have to put the old one under the microscope. I usually just haul them off to the junk man.
     
  16. Jammer

    Jammer Moderator Staff Member Banner Member

    I would go for the 8 foot hose so it would be easier to put the tank into a water bath. I have to wrassle mine.
     
  17. FKreider

    FKreider Copper

    Thank you all for the advice, I purchased the adjustable 0-40 PSI regulator off amazon and gave it another try. Still wasn't getting the heat I needed, then I put the BBQ tank in a water bath and what a difference! With the new regulator and tank in the water bath I am now easily able to get the needed temps.

    Unfortunately I was a little short on material for the pour, I think the copper wire oxidized way too much (as suggested above), next time I will try with flux to get a better melt. I had a lot of dross and I think a lot of it was actually oxidized copper that did not melt correctly.

    I am confident that next time I will get a usable part!

    thumbnail_IMG_7378.jpg

    45DB504D-DE9A-425C-8277-EFDADB275910.JPG

    The "good side" - alloy mix seems zinc heavy due to copper wire not melting correctly I think:

    thumbnail_IMG_7383.jpg
     
  18. Jason

    Jason Silver Banner Member

    Straight copper sucks to cast with. It helps if you get it started and smash a beer bottle and lay the glass on top of the melt. Add more copper by tucking it under the glass. Before pouring, scrape off the glass and dross. You'll get a cleaner melt this way. What is that thing anyways that requires you to run 100% copper?
     
  19. FKreider

    FKreider Copper

    I am trying to make yellow brass, I weighed out copper and zinc to get what I thought would be the appropriate alloy ratio.

    It is a decorative dome for the top of a 7 1/4" gauge steam locomotive.
     
  20. Jason

    Jason Silver Banner Member

    Then the same thing would apply. Cover that melt with broken glass to keep the copper dross under control.;)
     

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