Non-Chemical Need some advice on Melting Gold _gasmeltfurnace_

Good day to everyone! First I want to thank this forum for letting me learn so many things about gold refining. The members here are so helpful and accommodating. Thank you everyone!

I started buying gold from the miners here in our place (Benguet Province, Philippines) for about 3 months now. I sell them to a buyer also and gives me little profit for every transaction. After reading things here in the forum, I learned many things (especially the refining part). I am planning to purify the gold that I am buying and find someone that will buy this high purity gold for me to have a better profit. I read Hoke's book already and many topics here about the process.

I have low budget for now that's why I will do the process done by kadriver which only involve the use of nitric acid and not aqua regia. The process involves inquarting and boiling of nitric acid then rinsing. My question for now is the type of torch/fire that I will use for melting. Oxy-acetylene is a bit hard for me to use because of it's hard to transport those heavy tanks here in our place. I am left with the available options here: 1. Air compressor- gasoline combination. This method is used here in our place. 2. Air compressor- LPG( Liquefied Petroleum Gas). Some use this and told me it is more economical and produce more heat.

Please help me choose which method will I use for melting.I also want to ask the type of air compressor that is best for this task. I will appreciate any suggestion/comment/criticism. I will continue to read and learn from this forum and from you guys. Thank you so much!

Mohammed

You can look at set called a B-tank that is an oxygen tank with a regulator. Or you can look at using MAPP gas.

Here is a MAPP gas setup.
[youtube]http://www.youtube.com/watch?v=tWkxtwIebLw[/youtube]

Here is a B-tank set up just showing melting some copper tubing for a demonstration.
[youtube]http://www.youtube.com/watch?v=cDI3pP1suLA[/youtube]

Melting gold with a MAPP gas set up
[youtube]http://www.youtube.com/watch?v=e4jjOmUrWpo[/youtube]

I think you need to build your own gas melting furnace. A hand held torch will work fine if you're buying a few pieces at a time and melting a few ounces. But considering the fuels you have available from what you said;

1. Air compressor- gasoline combination. This method is used here in our place. 2. Air compressor- LPG( Liquefied Petroleum Gas). Some use this and told me it is more economical and produce more heat.

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In my opinion a gas fired pot furnace with a propane (LPG) fuel and a blower will serve you well. The trouble is you cannot afford to go out and buy one. We get that a lot here at GRF.

So to build your own furnace, I would start out with one which holds up to a #3 crucible. That should suffice from a few ounces to a few hundred ounces. Once you see how easy it is to cast one of these and make a good functional furnace capable of melting gold and silver all day long, you will realize that scaling up to larger and larger models is pretty simple so you can really melt whatever quantity of gold you can lift to pour and customize your melt furnace to accommodate your needs.

You will need to form your furnace from either refractory cement or a much lighter insulating fabric which I will give you a link to later. For longevity, I would be using refractory cement. Then you will need some pipe to deliver the gas to your burner and a valve to control the gas flow and a valve to control the output from your blower. Last you need a blower. You can buy a blower made for this purpose but they are pricey at about $500 US for the 27 CFM you need for the small unit I am suggesting. Pricey but they do last. Then there is the good old affordable route which is to use a vacuum cleaner blower. This is the $500 blower I dug out of my barn to show you.



The burner is just the length of pipe, you can see where the gas feed tee's in with a shut off valve (blue handle) and the airflow is controlled with a gate valve (Red handle) for a small furnace there is no need for a mixing chamber. For larger furnaces a mixing chamber blends the gas and air coming into the piping before the jets. This is a pearl I picked up at an auction for $10. AGF made equipment that was essentially bullet proof and lasted forever. Shame they're gone.

I built a gas manifold for this melter, added a refractory melt chamber and can melt Pt by adding pure O2 to the mix. This is the mixing valve.


So to start you need to make yourself the melting chamber. In Loewens excellent book "Small Scale Refining of Jewelers Waste" he gives details to build a furnace body. This image is from that book which you can purchase from a link in the library (worthwhile investment)

The dimensions for the small furnace which refer to the drawing are as follows;
OD 11 1/4" (A metal 5 gallon pail is excellent for this form and makes a nice finished outside to the furnace.)
H 11"
B 4"
L 1 1/2"
O 2 3/4"
The wall thickness is approximately 2" and the crucible rest height (this is made like a puck to be removed) is such that the height of the crucible plus the height of the crucible rest leaves about 1/2" clearance at the top (C in the drawing)

Two things to note; The gas comes in tangent to the inside diameter so it swirls around without hitting the crucible rest. And 2, the crucible rest should be tall enough so the flame is just below the bottom of the crucible. If the flame hits too high you can have solid unmelted metal in the bottom and a liquid top.

Samuel-A a valuable contributing member of GRF posted this thread which shows his melt furnace made with the insulating wool fabric. http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=20501 The burner described above will work in his unit as well.

Another home made furnace can be seen operating in the video in the link posted here; http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=21967&hilit=melting

I think with a little research you can build a nice effective air blower and LPG fueled melt furnace that will serve your needs for years to come.

Good luck

Well what can I say, brilliant Chris, if that doesn't make sense try reading some more.

If you want to go that way 4metals is talking about here is a picture of one and it will hold a #6 crucible. This is a propane furnace.

This is the American Gas Furnace melt furnace catalog page. Starting price $110. How old is that picture??????

This thread is brilliant.

4metals, you are a golden god!

I am building one of these right now, and you have shed a wonderful ray of light in the dark corners of my mind, and noe, my roadblock will easily be overcome!

To say i am appreciative of everything you have contributed to the forum, is an understatement (BEYOND, an understatement)

A Gingery Furnace is the same concept but I'm guessing it wouldn't take the heat very well.

Another quick, non-permanent option is acetlyene-air. Not sure how available that is in your neck of the woods, though.

A Gingery furnace as shown in the link I posted made with the right refractory will take the heat.

nickvc said:

Well what can I say, brilliant Chris, if that doesn't make sense try reading some more.

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Nick my old mate are you getting 4metals confused with GSP?

Brilliant post though 4metals- I like it a lot. Thank you.

Jon

Great thread. Now I know what will happen to the nearly new (old) pottery kiln I was given a couple months ago. Just a bit more studying over it and oh yeah.

Thank you 4metals, you are a man amongst men, and absolutely one of my favorite "authors to search."

spaceships said:

nickvc said:

Well what can I say, brilliant Chris, if that doesn't make sense try reading some more.

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Nick my old mate are you getting 4metals confused with GSP?

Brilliant post though 4metals- I like it a lot. Thank you.

Jon

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Darn need to change my glasses again :lol:
Sorry 4metals my bad.

Nick my old mate are you getting 4metals confused with GSP?

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Darn need to change my glasses again :lol:
Sorry 4metals my bad.

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Being mistaken for Chris is more a compliment in my book.

I looked up the burner type used on the propane furnace Barren posted, this is what the unit looks like.



I do not know if this will generate the heat required to melt gold. There does not seem to be a way to control the gas flow and the air mix. This will limit your ability to generate either a reducing flame or an oxidizing flame.

The up side is it does not require a blower, the down side is what I said about types of flame. I would like to hear from members using this type of burner for melting in a crucible to get some feedback as to its versatility. I see Barren is using it to incinerate e-scrap. I am interested in its ability to do crucible melts.

I use that exact same burn design. I bought both mine from a guy on ebay a couple of years ago who made them ($40/piece). I use one of them out on the farm to melt silver 5 lbs at a time. I now have a butter fly valve on the back to regulate air flow. I can jack the gas up and adjust the air and it will definitely put out some heat. From my previous work with furnaces i have learned that not only burner output is important, but more important is refractory. All I've use mine for is melting silver. I'm happy !

4metals said:

I looked up the burner type used on the propane furnace Barren posted, this is what the unit looks like.

View attachment 3

I do not know if this will generate the heat required to melt gold. There does not seem to be a way to control the gas flow and the air mix. This will limit your ability to generate either a reducing flame or an oxidizing flame.

The up side is it does not require a blower, the down side is what I said about types of flame. I would like to hear from members using this type of burner for melting in a crucible to get some feedback as to its versatility. I see Barren is using it to incinerate e-scrap. I am interested in its ability to do crucible melts.

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That is pretty much close to the way mine is set up. It doesn't have the flared end on the end of the burner like the one you are showing, but from what I have seen on videos I feel it will generate more heat with the flared end. Mine is just a straight 3/4" pipe set into the refractory of the furnace. If I remember right I think on other builds of similar furnaces it calls for a #64 bit to drill out the orifice hole in the nipple running through the reducer for the gas flow. This site will help if anyone wants to build their own furnace. http://backyardmetalcasting.com/

I have watched a number of video's on people that have taken the burners and veined them to burn hotter and get better air flow but IMHO it is a waste of time. The flared end it supposed to help to some degree but I really don't see the necessity of it unless you are running one the size that Ralph has and you are trying to max out the size crucible that you can put into it. My furnace will hold up to a #6 and if I m correct it looks like Ralph's will hold up to a #12 crucible.

Ralph's furnace looks a little bit bigger than the one I have. He should not have any problem maxing out the crucible size for the furnace for melting silver. And I think he would be ok melting gold and copper in it if he wanted to, but I do have some reservations about saying that, and if I were building one that size I would probably upsize the burner to a 1" pipe just for the added capacity.

Kurt uses one that is the same size as mine and he doesn't seem to have any problems with it as far as I know. He was having some heat retention problems with it and had mentioned about building a new one and I suggested to him to close the hole in the top up to retain more of his heat but I haven't asked him if he tried it and if so if it helped him any.

The furnace I have came from Legend's. They do not carry or build the same furnace any longer as far as I know. What they carry now has the same bottom made from refractory cement but the sides and top are made from refractory fiber from the looks of it. It will probably hold up but if I had my way I would stick with the refractory cement for the whole unit. It will last longer and can take more abuse. My guess is they changed the design to save on shipping charges to customers.



When I was doing a lot of silver with the furnace I have I was using the clay crucibles that Steve sold.



I could top the crucible off with cemented silver and it took about 30-45 minutes for the 1 round to melt, I could generally top the crucible off about 3 times with additions of silver then make a pour into my 2 Lb. mold. After the first round it only took about 10-15 minutes to melt a topped out crucible once the furnace got up to operating temperature. I could generally get 8 melts from a full crucible before it would start to fail and develop holes in the sides. There was only enough borax used to coat the sides of the crucible.

As for melting copper or gold. My furnace has no problem handling the melting of them. Most of what I have done with it has been copper using a #4 crucible. It takes about 45 minutes for the furnace to make the first melt and reach operating temperature then after that your looking at about 20 minutes for the melt for full crucibles. If you are going to go up to this size change to a salamander graphite crucible. I tried with the clay crucible and got 2 melts from one and didn't even get a complete melt from another one before they failed. I don't use any flux when working with this material.



The first copper run that I did I was making shot from the copper as shown in the picture above. I was pouring into a 2 gallon stainless pot. At the end of the pour I must have let a large glob go into the bucket. When it did it exploded on me. There was about 3 Lbs' of copper in the pour. When it exploded it was equal to some of the pipe bombs I have made. You think to yourself that you will have time to react when something like that happens to you. But I will tell you that you don't, it happens in a split second. The pot held together, but it made the bottom conform to the contour of the surface it was setting on. The only thing that was left in the pot was maybe 50g of copper and just a little bit of water. Water and copper shot rained down all around me in a 60' circle with me in the middle. It was a stroke of God's fate that I didn't get injured. I was wearing a zip up hoodie coat at the time and when I stood up I could see the back of it glowing in a window payne. I took it off and got the burning stopped and there are holes bigger than my fist in the hood part, and it is missing about 1/3 of the hood that burnt away. After that I went and got a 30 gal steel trash can to pour into.

Hope this information helps and it is not too long winded.

Barren Realms 007 said:

Hope this information helps and it is not too long winded.

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On the contrary, I would especially like to thank you for sharing the story about exploding copper. I don't have a melting furnace yet but I can see myself building one in the future. Copper would be one thing I would use it for. By sharing your story that's one potential accident that I will not have in the future.

Thanks for the shared wisdom!

Göran

Wow! So much information. It will take me a while to digest all. I will take time to read and understand all information by you guys. Thanks you so much!
Forgive me for not replying fast because internet connection here is still a problem.
I hope I can do these furnaces that you guys showed. For the mean time because of my limited budget, i will be using a compressor gasoline set up. This will do the job for now. I am buying small pieces (100 grams is my biggest piece as of the moment). I will try to post pics/vids for you guys to comment/suggest/critisize.
Again thank you so much!

Mohammed

Barren Realms 007 said:

Kurt uses one that is the same size as mine and he doesn't seem to have any problems with it as far as I know. He was having some heat retention problems with it and had mentioned about building a new one and I suggested to him to close the hole in the top up to retain more of his heat but I haven't asked him if he tried it and if so if it helped him any.

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Correct per the underlined above --- the heat retention problem is due to the fact that my furnace (my small one) has done soooo much work for me (including smelting - so we are talking "aggressive" flux involved) so the center hole in the lid has eroded & become "much" larger then it was when new so a lot of heat is being lost out the hole --- I am waiting for warmer temps so I can knock out the old refractory of the lid & re-pour a new lid --- I was considering just doing a repair (drill & pin around the inside of the hole & then do a refractory patch) but am afraid the patch wont really hold up well - so decided to wait & do a complete new pour of refractory

The heat retention problem is only a problem if I am trying to melt copper (with out adding air) - it still melts silver no problem

You will notice that my burner is set up so you can add compressed air (at the back of the burner) so I am actually able to over come the heat retention problem by increasing the burner heat out put by mixing 3 - 5 psi of compressed air --- so I am getting by with it as is until weather warms up enough so I can pour a new lid with a smaller center hole

Kurt

Barren Realms 007 said:

The first copper run that I did I was making shot from the copper as shown in the picture above. I was pouring into a 2 gallon stainless pot. At the end of the pour I must have let a large glob go into the bucket. When it did it exploded on me. There was about 3 Lbs' of copper in the pour. When it exploded it was equal to some of the pipe bombs I have made. You think to yourself that you will have time to react when something like that happens to you. But I will tell you that you don't, it happens in a split second. The pot held together, but it made the bottom conform to the contour of the surface it was setting on. The only thing that was left in the pot was maybe 50g of copper and just a little bit of water. Water and copper shot rained down all around me in a 60' circle with me in the middle. It was a stroke of God's fate that I didn't get injured. I was wearing a zip up hoodie coat at the time and when I stood up I could see the back of it glowing in a window payne. I took it off and got the burning stopped and there are holes bigger than my fist in the hood part, and it is missing about 1/3 of the hood that burnt away. After that I went and got a 30 gal steel trash can to pour into.

Hope this information helps and it is not too long winded.

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:shock: I will bet you never let that happen again :lol:

I had a similar thing happen the "first" time I was doing a smelt on some bonding wire from chip ash concentrates --- I mixed my concentrates with my flux & some silver cement as my collector, loaded the crucible & put it in the furnace --- when it all got molten I remembered that I had a couple sterling chains & a couple sterling rings & I thought - what the heck - I might as well add that in & it should give me a nice size silver anode to run in my silver cell - the problem was I didn't preheat the sterling - so when I dumped the cold sterling in on top of the hot molten smelt - KA-BOOM --- it blow "everything" out of the crucible, busted the crucible & hot slag/metal came raining down on me - it wasn't hot enough to burn me but it did burn holes in the top layer of my insulated jack & made burn marks on my hat --- I think I was able to pick up like 1 - 1.5 oz metal of what should have been more like 2 lbs metal

I learned two things --- you can't duck fast enough - & - don't EVER add large pieces of "cold" metal to a molten melt/smelt :lol:

Kurt