Non-Chemical Lessons learned...

[goldsilverpro]

This is to answer the old post, at the top of this page, about the Kerr Electro-Melt. First off, there are other brands out there besides Kerr. They are all expensive. The last time I looked, they started at about $800.

http://shorinternational.com/MeltFurnace.htm

I owned one of these gadgets about 25 years ago and didn't care for it. It just sat on the shelf. It seemed to take forever to heat up. Like induction furnaces, you couldn't really flux the metal to clean it up, or you would screw the crucible up. I would much prefer a small home-made gas crucible furnace. Cheaper and better.

It all depends on what you use it for. Not too long ago, we had the idea of using one to buy scrap karat gold, etc., from jewelers or pawn shops. We were going to melt the gold, stir it, pin sample it, and pour it into a bar, in front of the jeweler or pawnbroker, in his own shop. We would keep half of the sample, give him the other half, mark or stamp and weigh the bar, and let him keep it. When we finished our assay, we would go back and do the deal. He could have his sample assayed, in the meantime, if he wished. We figured the customer would like this approach because it kept everybody honest. I still think it's a good idea.

This is the only good application I have seen for the Electro-Melt. You could also maybe find one handy for doing some jewelry castings. For the refiner, I don't think so.

 

[Harold_V]

This is to answer the old post, at the top of this page, about the Kerr Electro-Melt. First off, there are other brands out there besides Kerr. They are all expensive. The last time I looked, they started at about $800.

I owned one of these gadgets about 25 years ago and didn't care for it. It just sat on the shelf. It seemed to take forever to heat up. Like induction furnaces, you couldn't really flux the metal to clean it up, or you would screw the crucible up. I would much prefer a small home-made gas crucible furnace. Cheaper and better.

There has been some outstanding information posted on this forum through recent months, but this post is likely one of the most informative.

I heartily endorse it, every word. I owned a similar furnace, a Handy-melt, and found the cost of crucibles prohibitive. Being pure graphite, they had a very short life cycle, self destructing by burning away at the top. As has already been mentioned, fluxing created unending problems.

I do not recommend the use of one of these for refining, and would have considerable trouble coming to terms with the use of one even in jewelry manufacturing. It's just too easy to use a torch, which is faster, cheaper and, in my opinion, far better. The interesting thing is, at the price of one, a person can buy the best of oxy/acetylene torches, including bottles. A torch setup, as described, will far better serve the needs of a refiner. Jewelry supply houses sell a large Hoke torch, which I highly recommend.

Avoiding a furnace of any kind is in your best interest. With rare exception, it is not a requirement, especially if one refines in small volume. A large melting dish will accommodate more than ten troy ounces of silver with no trouble. Only melting larger volumes would I ever consider the use of a furnace of any type.

My recommendation for melting is using natural gas and oxygen. It's the most economical way to approach the problem, and will provide enough heat to melt even platinum.

Regards cupelling, unless you are attempting to eliminate lead, cupelling has no place in the purification of gold. There are other methods to improve gold quality-----none of which include the use of cupels. If you are using one for any other reason, you need to change your method of operation. Cupels do not make good melting dishes.

Harold

 

[goldsilverpro]

I definitely agree about the natural gas and oxygen. I like it much better than propane/O2 or acetylene/O2. Also, acetylene is very dirty. Have you used hydrogen/oxygen? The cleanest of all. I like it but, you can hardly see the flame. I try to stick with natural gas/oxygen

 

[Platdigger]

What if you have no natural gas supply? Will propane do? Guess it will have to huh.
Randy

 

[Harold_V]

I definitely agree about the natural gas and oxygen. I like it much better than propane/O2 or acetylene/O2. Also, acetylene is very dirty. Have you used hydrogen/oxygen? The cleanest of all. I like it but, you can hardly see the flame. I try to stick with natural gas/oxygen

Acetylene, especially for use in melting the platinum group, is not recommended due to the formation of carbides.

By contrast, there is no better method to blacken a gold ingot mold. An acetylene torch has a place in refining, but should be somewhat limited in use.

No, I never had the opportunity to use a hydrogen torch, which is the torch of choice for melting platinum.

I had occasion to have a couple hydrogen fires through the years. My stock pot was always very close to the fume hood, so liberated hydrogen was exhausted, instead of being allowed to accumulate. On a couple occasions, I had ignition due to the use of a torch in near proximity. Nothing serious, but it was interesting to observe the flame, which was not easy to see. It would have been interesting to see a flame from a torch, based on what little I've seen.

Harold

 

[goldsilverpro]

Propane/oxygen works fine. Like Harold (I think I remember him mentioning it), I always preferred a rosebud tip, especially for large melts. However, a regular cheap tip will work fine.

Even with graphite molds, you get a prettier bar if you smoke the mold first with acetylene alone (using no oxygen with it). I would smoke the molds outdoors. Otherwise, you'll have streamers of carbon lying around everywhere.

 

[goldsilverpro]

Harold,

What's the technical difference in a Hoke torch and a regular torch? I know that C.M. Hoke's father developed it for melting platinum. They are still widely sold in the jeweler's supply catalogs. If I remember right, a lime crucible was also used for platinum.

Speaking of Hoke, I've got to break down and part with the money to buy a new copy of her book. Mine went south about 10 years ago. I sure miss it. I did buy a copy of T.K. Rose's, "The Metallurgy of Gold," the other day. I needed to bone up on the Miller Chlorine process.

 

[Irons]

I definitely agree about the natural gas and oxygen. I like it much better than propane/O2 or acetylene/O2. Also, acetylene is very dirty. Have you used hydrogen/oxygen? The cleanest of all. I like it but, you can hardly see the flame. I try to stick with natural gas/oxygen

Acetylene, especially for use in melting the platinum group, is not recommended due to the formation of carbides.

By contrast, there is no better method to blacken a gold ingot mold. An acetylene torch has a place in refining, but should be somewhat limited in use.

No, I never had the opportunity to use a hydrogen torch, which is the torch of choice for melting platinum.

I had occasion to have a couple hydrogen fires through the years. My stock pot was always very close to the fume hood, so liberated hydrogen was exhausted, instead of being allowed to accumulate. On a couple occasions, I had ignition due to the use of a torch in near proximity. Nothing serious, but it was interesting to observe the flame, which was not easy to see. It would have been interesting to see a flame from a torch, based on what little I've seen.

Harold

To expand on what Harold said:

Like Nickel, Platinum group metals form volatile and very toxic Carbonyls when heated in a reducing Acetylene flame. Besides losing valuable metals, it can ruin your day.

Some examples are:

Platinum Carbonyl(Chini cluster) [Pt12(CO)24]2−

Palladium Carbonyl Pd3(CO)n- (n=0-6)

Rhodium Carbonyl Rh4(CO)12

 

[Harold_V]

Harold,

What's the technical difference in a Hoke torch and a regular torch?

I'm not convinced there is a difference. I don't recall the brand I had, but it had a black plastic grip, and was the size of the standard Victor torch. The tip, for all practical purposes, resembled a rosebud for a Victor torch. There may be some differences in port sizes that I didn't recognize, not sure.

I had two (identical) tips for my torch, one of which was used exclusively for melting gold prior to pouring shot-----so I had the opportunity to look at the tips quite often. They were easily changed, being held in place by a threaded collar.

I used a smaller Hoke type torch prior to buying the larger model. While the body was small, it had a rather large orifice in the tip for the torch size. Again, aside from tip diameter, it resembled the typical torch. Makes me wonder----could the welder's torch been patterned after the Hoke torch? Dunno!

If I remember right, a lime crucible was also used for platinum.

By the time I was involved with platinum, such a vessel was not available, at least from my source. They had produced one that will withstand the melting temperature of platinum, although it does melt somewhat as well. I'm not privy to the formulation, but it must certainly be a silicon product. I recall using hydrofluoric acid to pickle the buttons I melted to remove traces of the melting dish, which would stick to the button much like borax does when melting gold.


Damned shame about not having your copy of Hoke any longer. While I found I could operate without a reference, it was always nice to have it to refresh my memory on operations that weren't performed routinely.

By now, readers may well understand that I am very bullish on Hoke's book. I consider it a mandatory part of refining----it is not a luxury. If you can get past her endless recommendation of tossing gasoline on the things you incinerate, the information the book contains is priceless. It likely goes without saying------gasoline has no place in the refinery-----unless your objective it to burn the building.

Harold

 

[aflacglobal]

It likely goes without saying------gasoline has no place in the refinery-----unless your objective it to burn the building.

If gold is a precious metal then gas should be a precious liquid.
Both bring about the same price. lol

 

[goldsilverpro]

Actually, if you cut gasoline with 50% diesel, it really tames it down and makes it burn longer. I used it to burn filter papers and cloth, in a steel tray with a screen on top of it. I did it outside, of course