# building a melting furnace



## dthoreson81 (Aug 21, 2008)

I have come across 36.15 (Exactly) of silver shot/ bbs and would like to melt this down to bars and or rounds. Does ANYMONE have a simple inexpensive way to do this? The sooner I get this done the better. Thanks ot everyone who chips in.

Dan


----------



## Rag and Bone (Aug 21, 2008)

36.15 what (exactly)? grams, ounces, stones, tonnes?


----------



## Noxx (Aug 21, 2008)

What is inexpensive for you ? I built mine for under 350$. It can reach 1200C.


----------



## dthoreson81 (Aug 22, 2008)

400 works. 36.15 OUNCES


----------



## goldsilverpro (Aug 22, 2008)

What is the purity of the silver? Sterling? 999?


----------



## Lou (Aug 22, 2008)

You won't be casting rounds in quantity without pressure and a multiple piece machined graphite mold.

Similarly, your ingot mold should either be well-sooted cast iron or else made of machined graphite. 


As for the furnace: go to http://backyardmetalcasting.com/forums/


----------



## dthoreson81 (Aug 22, 2008)

it is 36.15 Ounces of .999 fine silver.


----------



## MathewW83 (Aug 28, 2010)

Here is something I have been tinkering with. 
http://www.facebook.com/photo.php?pid=30849056&l=a8691e1e38&id=1122128129
http://www.facebook.com/photo.php?pid=30849054&l=6171d5ef72&id=1122128129

Just some old steel I had laying around the shop. You can find this stuff at any metal fab shop and I am sure they will sell you some scrap for very little. I am going to fill up the outter ring with sand as an insulator. Then all you do is shove a propane weed burner in the bottom and go to work. Let me know what you guys think.


----------



## goldsilverpro (Aug 28, 2010)

Maybe


----------



## Anonymous (Aug 28, 2010)

MathewW83 said:


> Here is something I have been tinkering with.
> http://www.facebook.com/photo.php?pid=30849056&l=a8691e1e38&id=1122128129
> http://www.facebook.com/photo.php?pid=30849054&l=6171d5ef72&id=1122128129
> 
> Just some old steel I had laying around the shop. You can find this stuff at any metal fab shop and I am sure they will sell you some scrap for very little. I am going to fill up the outter ring with sand as an insulator. Then all you do is shove a propane weed burner in the bottom and go to work. Let me know what you guys think.



Make a damn good lawn roller.


----------



## Harold_V (Aug 29, 2010)

MathewW83 said:


> I am going to fill up the outter ring with sand as an insulator. Then all you do is shove a propane weed burner in the bottom and go to work. Let me know what you guys think.


I don't like it, and I expect you won't, either, once you figure out that heat bearing on steel will oxidize the steel rapidly, which, in turn, will report in the heat in question. That may not be a serious issue when melting scrap, but if you used the device for melting refined materials, it would be a mistake. You would be FAR better served to explore the use of a refractory material.

There's nothing wrong with using a steel housing, but it should be isolated from the heat source. 

This issue has been visited time and again. You would profit greatly by paying attention to convention, where the pitfalls have already been addressed. 

Harold


----------



## MathewW83 (Aug 29, 2010)

I accept all advise but there is one thing missing in that picture and it is the crucible. I am having one made from a friend of mine that is an artist out some non glazed kilned clay. I am not sure if this will change your opinions but I thought it might be a good idea to throw it in there. Again thank you for the interest. And to the comment as to it would be a good lawn roller that was the other Idea I had for it! LOL


----------



## Harold_V (Aug 29, 2010)

MathewW83 said:


> I accept all advise but there is one thing missing in that picture and it is the crucible. I am having one made from a friend of mine that is an artist out some non glazed kilned clay. I am not sure if this will change your opinions but I thought it might be a good idea to throw it in there.


I expected you'd use a crucible, but that doesn't change much. As the steel inner diameter corrodes, it will tend to shed bits and pieces, which have the potential to end up in your charge. That was my concern. 

One thing to keep in mind---a furnace that is properly constructed will have enough clearance between the inner diameter and crucible to allow for a proper lifting tool. Make certain you make that provision in your design, regardless of what you end up with. 

Also, it is generally considered less than good practice for the flame to impinge directly on the crucible. The vast majority of crucible furnaces have the port tangent to the inner diameter, so the flame swirls around the crucible without impinging on it directly. You might keep that idea in mind. 

I did a huge amount of melting with a clay melting dish, but volumes were generally under ten troy ounces. Properly seasoned, they tend to be fairly reliable. In the case of melting dishes, it was normal for the flame to impinge directly on the dish---so the rule of not impinging directly on the crucible doesn't necessarily translate to dish melting. 

Be very careful about home made crucibles. I'm not implying that your friend isn't capable, but look at it this way. If you have a crucible full of values and it breaks, the loss can be staggering. I'd be especially concerned about one made of just clay, which tends to be subject to cracking very easily. If you do pursue this avenue, be certain to properly season the crucible before putting it in service. Failure to do so is likely to result in cracking. 

A hazard you may not have considered. If you work over a concrete floor and happen to have a spill, you risk a steam explosion from the molten metal making contact with the concrete, which _always_ has residual moisture contained within. Such an explosion isn't likely to be serious, but the thoughts of hot metal being tossed about, plus the loss of values makes this idea less than acceptable. Be careful!

Harold


----------



## MathewW83 (Aug 29, 2010)

Thank you for the advice Harold. My friend uses the same type of crucible and he has be using the same one for about 2 years. I am sure he dose not just use clay but that is one of the compounds he uses as for the rest your guess is as good as mine. I am constructing this crucible to sit just high enough so you can use tongs and the center pipe is hardened and I am sure you know that it is not very easy to damage. The crucible will be made in the shape of a cone so I am hoping that will help the flame move around the crucible. I think I can make this work but you know half of this is trial and error so if it dose not work just have to hop back to the drawing board. But hopefully you are wrong, ya right LOL, and it dose work for the amount I am working with. Thanks again for the advise.


----------



## nickvc (Aug 29, 2010)

Mathew a cheap furnace is easily made with light weight fire bricks, say 20 which allows you to change the size of your furnace, a bullfinch nozzle and a bottle of propane, I'm tight as hell on my furnaces but always buy good crucibles, a crumbling crucible full of molten metal isn't my idea of fun. Whatever you do wear proper protection and warm your mould before pouring your bar , and don't drop cold metal into molten metal I only did it once and was lucky the explosion of molten metal was avoided by my backwards leap as I realised what I had done, but it took forever to recover the values and the burns in my scalp took a while to heel. Be careful and stay safe.


----------



## Harold_V (Aug 29, 2010)

MathewW83 said:


> I am constructing this crucible to sit just high enough so you can use tongs


That implies that you will run the furnace without a cover. Not a good idea. Generally, the cover reflects heat back to the charge, so you can attain higher (and faster) temperatures. 


> the center pipe is hardened and I am sure you know that it is not very easy to damage.


Makes no difference. Once you reach a temperature above 1350°F, assuming the material you speak of is an iron alloy (steel), it is no longer hard. In truth, it starts losing its hardness much cooler, and is dead soft by the time it reaches red heat. Worse yet, it undergoes a decarburization by the prolonged heat, assuming the atmosphere is oxidizing. So then, even if it _was_ heat treated, it no longer will be, plus if it is decarburized by the flame, it no longer can be. In any case, it will shed oxidized iron, as I said previously. Not a good idea. 



> But hopefully you are wrong, ya right LOL, and it dose work for the amount I am working with. Thanks again for the advise.


It isn't important, to me, that I am "right or wrong". What is important is that you gain an education about matters such as this. People have been working with these processes for hundreds of years. We stand on the shoulders of those that have gone before us, taking advantage of the things they learned through trial and error. It's called not reinventing the wheel. 

The point here isn't that what you're trying to do won't work---it will, to some degree. The problem is you are introducing all kinds of potential problems to what should be a simple process. If you continue your quest to re-engineer everything instead of following, at least to some degree, convention, you will spin your wheels endlessly, often on the edge of success, but never really enjoying the sweet taste of total success. I learned that the hard way, ignoring many of the things quoted in Hoke's book, in the process of trying to learn refining. Unlike you, I had no one to quiz----for this was long before the internet, when the refining process was illegal without federal licensing (you likely don't know about that). You, by sharp contrast, are in a unique position. You have at your disposal, a combined total of at least 100 years of refining experience here on this forum. A wise person would pay attention to what they're told. My logic, here, is that there are some things you do not have to experience in order to gain an understanding. This may be one of them.

Harold


----------



## Stevious (Oct 24, 2010)

Ask your library to find this: 

The Hoover melting furnace : the first thoroughly improved jewelers' melting furnace in 40 years / Hoover & Strong, Inc., refiners.
Author: 
Hoover & Strong, Inc. (Buffalo, N.Y.)
Imprint: 
Buffalo, N.Y. : Hoover & Strong, Inc., [19--]
Description: 
[3] p. : ill. ; 28 cm.
Series: 
Bulletin (Hoover & Strong, Inc. (Buffalo, N.Y.)) ; 1046.
Library of Congress Subjects: 
Metallurgical furnaces -- Catalogs.
Metallurgical furnace industry -- New York (State) -- Buffalo.
Jewelers' supplies -- Catalogs.
OCLC Number: 
ocm26477112

Hoover & Strong are in Richmond VA now, but I don't think that they sell their furnace anymore.

I have one....it's dynamite! It runs on Propane and air (it has a fan) and can melt 100 ozs of silver in about 5 minutes if it's warmed up. If you lived near NH I'd melt it for you just for fun. It sounds like a small jet engine.

The furnace is pretty simple but it is made with refactory cement, and has a refractory liner inside which would have to be made and fired in a kiln. Other than to use an induction furnace I'll bet that nobody has ever improved much on this elemental furnace and you might be able to make it using the book. I assume that it is patented also, and you can review the patent. I wonder if ther'd be a market for these today?


----------



## rusty (Oct 24, 2010)

Just because someone holds a patent does not prohibit another from making same - one of, as long as it's for personal use.

For those who would like to read more on this topic, http://www.ciphersbyritter.com/NEWS3/PATENT.HTM

So please post some pictures of your furnace.


----------



## Stevious (Oct 24, 2010)

I'd be glad to.

Unfortunately my workshop is not where I live. It's at my workshop which is in the house I intend to retire to that's about a half hour drive away. It's empty except for some of my old tools.

I do try to check on the place every few weeks and I'm sure that I'll be up there in a week or three. I'll post a slew of photos then.

It would not be difficult to reproduce, the most difficult part would be making and firing or buying a tubular refractory liner. Since it comes up to temperature pretty fast, and can melt 50-100 ounces in less than (if I remember correctly) five minutes the liner must be able to withstand some severe shock. I would imagine that today a zirconium based ceramic surrounded by fiberfrax would work well. I'll take enough photos with a ruler as a scale so that anyone who wants to try can. H&S (HooverAndStrong.com) is a refiner that I trust absolutely. Back in the 70's and 80's I tried many refiners and would "split" a batch, oftentimes melting a lot of silver and pouring it into water to create casting grain. I'd take 1/2 and give it to refiner A and 1/2 would go to refiner B. There were big differences, and H&S came out on top every time. Thereafter I only sent my sweeps, karat gold and silver to them.

They no longer mention their melting furnace, so I imagine it's history. Most likely, fear of litigation is the cause, but who knows.

Were I to try make a melting furnace I'd copy this one and get a burner from someone who makes burners for ceramic kilns. It should not be difficult, nor tremendously expensive. There is a fellow in NH who makes burners for gas-fired ceramic kilns. He is Dudley Gibberson of http://www.joppaglass.com I'm sure that for less than $200 he could make a propane venturi burner for anyone.

What makes the Hoover Furnace work is that the burner creates a forced vortex around a crucible that is only about a half-inch space between the graphite/ceramic crucible and the refractory wall of the furnace.

It is too cold these days, and I'll be away for several months, but next summer if anyone wants to use it to melt a batch, maybe we can have an "ingot" party. If you want to break your ingot into sheet, or wire, we can do that too. I was an oddity in the silver/goldsmithing business and the only person I knew who made his own sheet and wire. Frankly today I would no longer bother.

I'll include in the photos a homemade machined graphite mold to cast a ~4mm x ~40mm x 120mm ingot; a 20-40 ounce variable sized ingot mold used to cast an ingot that is used to break down the ingot into sheet (I used to do this routinely) and if I can find it, a "wire rod" ingot" used to cast rods that can be pulled into wire.

I can't promise "when" but it'll be before Nov 20th. You guys help me out with my questions, and I'll share what I know...


----------



## Stevious (Oct 24, 2010)

Looking closer at Joppa Glass's burners I'd suspect that this would be the best....

See: http://www.joppaglass.com/burner/coup_mix.html

Forget the "less than $200" though *sigh* I guess I was living in the past...today $350.

If it'll melt glass, it'll melt gold!


----------



## goldsilverpro (Oct 24, 2010)

Stevious said:


> Looking closer at Joppa Glass's burners I'd suspect that this would be the best....
> 
> See: http://www.joppaglass.com/burner/coup_mix.html
> 
> ...



That's basically what I've been using for years except the air and gas are switched. I could probably set it up for $40. Just a few pipe fittings.


----------



## Stevious (Oct 24, 2010)

goldsilverpro said:


> Stevious said:
> 
> 
> > Looking closer at Joppa Glass's burners I'd suspect that this would be the best....
> ...



There 'ya go... $40 beats %360 any day. A glass furnace probably needs a ceramic burner outlet, but a gold melting furnace doesn't. Now we know where to buy the gas/air mixers from! Indeed all it really is is an orifice of the right size and a piece of iron pipe connected with another at a T.

Ever though of making a small (~50 oz or less) furnace? Seems like there is a need.


----------



## Harold_V (Oct 25, 2010)

Stevious said:


> Ever though of making a small (~50 oz or less) furnace? Seems like there is a need.


I built a small furnace that accommodated #1 crucibles. It served the intended purpose perfectly well. I even made a lifting and pouring shank that fit the crucibles properly (I am a retired machinist/toolmaker with a shop). Those I still have, along with a number of new crucibles. They were retired when I discovered that a #1 was too small for the business I had at hand. I ended up building a second furnace that accepted a #8 crucible. It turned out to be an excellent fit for my needs in that one needs considerable volume when melting cement silver. I used to pour anodes that ran 200 ounces, ±. 

There's absolutely nothing wrong with a small furnace. In fact, it's wise to size the furnace in keeping with the work you intend to do. Crucibles are much more reasonably priced in small sizes, plus it makes no sense to fire a large furnace when the task at hand can be handled by a small one. It's also a great way to save space, and to minimize the amount of heat you dump in your work area. (I had a dedicated room, equipped with a hood, for running my various furnaces).

Harold


----------



## goldsilverpro (Oct 25, 2010)

Here's basically what I used.


----------



## Harold_V (Oct 26, 2010)

My design was just opposite that of GSP's. Both work. My logic was it was easier for traces of natural gas to make a 90° turn than the large volume of air involved. So long as the blower can deliver more air than is needed, it makes no difference. I used a gate valve to control air flow, as well as natural gas flow in all of my designs. Never a moment's trouble, and all of them fired well. 

Harold


----------



## Stevious (Oct 29, 2010)

Looks perfect to me. Joppa's real cost is the ceramic burner head. Since firing times in a kiln can be maintained up to 2400f for up to 20+ hours, it makes sense that it is the expensive part. Remove that cost, and essentially that is what you have the only problem that I see is sizing the proper orifice and making a rheostaticlly controlled fan to adjust air input. The iron pipe will never be exposed to 2400f except at the very tip, and even there it can be protected by being slightly recessed. I'll post those pics eventually.


----------



## goldsilverpro (Oct 29, 2010)

In the burner sketch above, for a #20 crucible furnace, which was about 20" in dia x 20" tall, the gas pipe was definitely 1/2" and I am almost sure the larger pipe was 1-1/2". The outlet tip of the gas pipe MUST BE at least 2"-3" beyond the air supply tee. I don't remember exactly how I did the pipe reducers, where the gas pipe enters the larger pipe, but it shouldn't be too hard to figure out. I'm thinking that either I had about 6"-8" of the end of the gas pipe threaded or the pipe was in 2 pieces. I used an old upright vacuum cleaner for the air supply - I used the same one almost daily for 3 or 4 years without failure.


----------



## Harold_V (Oct 30, 2010)

Chris, like you, I used a vacuum cleaner for my air supply, in spite of reading that that isn't a good idea (they are not designed for continuous usage). The only failures I had were related to brushes and bearings. Maintenance stuff, really.

In my case, thanks to having a machine shop, I modified the motor and fan housing such that it would mount directly on the furnace feed pipe. Barring the good fortune to find a different blower, I expect I'll use one for the non-ferrous furnace I hope to build in the future. Frankly, they're a great way to get the needed air. I don't recall paying any more than $5 for those I used. 

Harold


----------



## ashir (Sep 30, 2020)

Harold_V said:


> Chris, like you, I used a vacuum cleaner for my air supply, in spite of reading that that isn't a good idea (they are not designed for continuous usage). The only failures I had were related to brushes and bearings. Maintenance stuff, really.
> 
> In my case, thanks to having a machine shop, I modified the motor and fan housing such that it would mount directly on the furnace feed pipe. Barring the good fortune to find a different blower, I expect I'll use one for the non-ferrous furnace I hope to build in the future. Frankly, they're a great way to get the needed air. I don't recall paying any more than $5 for those I used.
> 
> Harold



Any idea on furnance to smelt ore concentrate with ir? While au is present


----------



## Johnny5 (Sep 30, 2020)

I think we have a record for the oldest thread being revived. 9 years 11 months.


----------

