Rio Automatic Melting Furnace w/ graphite crucible

[Harold_V]

Harold, I see you had cone molds in your bag of tricks, great tool for refining, one which I haven't seen discussed much on this forum. Honest refiners use them for collecting every last drop in front of the customer, dishonest ones like it when the beads don't end up in the pool.

Indeed! How would anyone refine successfully without them?

I had three sizes. The ones in the picture were generally used for processing silver, although not exclusively. If I had a large enough batch of scrap gold to melt, especially if it required fluxing, I'd use the furnace, but otherwise it was done with a large Hoke torch.

The cone molds you see were used when melting silver that had been reclaimed from nitrates, using copper, or silver chloride that had been converted to elemental silver using aluminum. I'd flux with borax, which improved the quality of the silver. The cone mold, as you know, made separating the values from the flux a non-issue. I would then re-melt the resulting buttons to cast my anodes. The square mold, standing on edge, is the anode mold that was cast specifically for my application. I made the pattern to insure that the anode would fit the basket as desired.

I also made the pattern for the two cone molds in question. I still have the pattern. Given enough time, I may eventually offer them for sale, although it won't be in the near future. As of now, I'd likely cast them in ductile instead of gray, to insure they had a long lifespan. Ductile is far less likely to experience thermal cracking than gray iron.

Another of the cone molds I relied on was the typical small cone mold used by assayers. How any of these guys get by without one is a mystery to me. I used mine almost daily. One of my favorite tricks was to clean melting dishes for my customers (gratis, which is one of the reasons I had such faithful customers). I always recovered values when doing so, which were collected easily in the cone mold.

The third size I had is pictured below. They were used exclusively with the tilting furnace, where I processed my wastes. Again, how one would deal with such issues without a cone mold is a mystery to me.

I borrowed a large cone mold from a friend and had mine cast from it, using it as the pattern. End results were very satisfactory in that size was not an issue. I didn't want to dedicate the time necessary to make the pattern.

As far as talking about them----I have done so infrequently, but it appears to me that no one listens. They have no idea what they're missing, however.

Thanks for taking note, 4metals. It is obvious to me that you know refining extremely well.

Harold

 

[Harold_V]

Harold,

I also used the #8s for pouring pure silver 10 oz and 100 oz bars in book molds. I used a #16 (usually) or #20 crucibles for pouring silver cell bars. It took 27 bars, about 3" x 9" x 3/8" thick to fill the cell. This would take too long with a #8 crucible. I usually used #4s or #6s for gold.

You clearly dealt with volumes much greater than those I handled. About the only place I could have imagined using a larger crucible than the #8 was when melting my recovered silver. I could easily cast a 200 ounce anode with my #8, which was the upper limit of size for the cell, and larger than I preferred. Incidentally, I mentioned I made the pattern for the two medium sized cone molds in that picture. I made it to work in conjunction with the #8 crucible. I pretty much sized my entire operation around my ability to process. I preferred, by far, to run my silver cell for extended periods, producing without a lot of attention from me. That was important in that it ran 24 hrs/day until I processed all of the anodes I had on hand. I generally had 2,000 ounces of silver to part before I'd make the setup.

I probably shouldn't admit this, because it is against all foundry safety rules, but I didn't even own tongs that gripped the crucible on both sides. <snip balance of interesting information>

I think we all find those little dodges we tend to use, even when they're stupid. Not calling you stupid, but your pouring procedure could have taken a turn that could have proven interesting!

As far as lifting with the charging tongs, I'd be concerned that you'd have a failure out of the furnace, especially with a large crucible. If you've never had anything hit the floor, you may not understand the significance of my concern.

I had three layers of epoxy on the concrete floor in my entire lab. In addition, any openings in the floor (heat registers, for example) had 1¼" thick asbestos risers held in place by epoxy. That insured that should I have an acid spill, or anything molten, it would remain on the floor, not migrate to the superstructure of the castle. I also had the entire perimeter of all rooms coved with quarry tile, also held in place with epoxy. In the course of time, I experienced a spill of nitric acid, as well as a small amount of molten flux that hit the floor. The paint was well burned by the flux, but there was no risk of fire, thanks to the type of construction. To avoid the concrete floor from spalling, I kept kicking the flux around until it had cooled sufficiently. That prevented a steam explosion, which would have been assured otherwise.

The tongs in the picture were a handful when pouring 200 ounces. I shudder to think how difficult it may have been using charging tongs with large crucibles! :lol:

I don't recommend that anyone else do this. Use the recommended tongs that grip both sides of the crucible - see the other photos in the link. Do as I say and not as I do.

I hope readers have the wisdom to understand that it's not really a good idea. One reason I could offer is that if you have been fluxing, it's not uncommon for the base of the crucible to be somewhat stuck to the crucible rest. I used to use a heavy piece of cardboard below the crucible, which helped, but as the rest got more and more covered, it was often sticky enough to be troublesome. Picking up with charging tongs could prove interesting under such conditions, especially if the crucible is ringed from fluxing. Overall, GSP, your success is a tribute to your many years of experience! One does not gain these skills reading a book.

Harold

 

[4metals]

Harold wrote,
One of my favorite tricks was to clean melting dishes for my customers (gratis, which is one of the reasons I had such faithful customers). I always recovered values when doing so, which were collected easily in the cone mold.

That is one brilliant little pearl of wisdom which helps get and keep your customers. It only takes a little time, a few pennies of borax, and a cone mold to do a flux wash and clean up a jewelers melting dish. Then you cool and flip the mold and if there's any metal it will be neatly collected in the point of the mold. And when you gave them back their little button, it made an impression!

Where's the icon for applause? That is a great strategy.

 

[Refiner232121]

Thanks very much for those pictures Harold
Pictures speak a thousand words
That is what I was saying in the previous post but I forgot to type the last part of that sentence

Question 1
referring to picture: Small furnace and accessories-resized
I am assuming that the object in the front part of the picture is a tong
Do they sell this in stores or did you make them yourself


Question 2
referring to picture: Small furnace and accessories-resized
I see 1 big barrel with as furnace
What is the other smaller barrel with cement
Do both work in conjunction with each other or separate.

Question 3
As for buying parts
I wrote to a few companies on was the backyardcasting and the other was a link 4metals posted before
on another thread and no one wrote back
I will eventually find something , probably from a local place

Question 3
cone molds are new to me
I guess to better understand the usefulness of this mold one would have to use it.
I will have to find a supplier

Question 4
Tilt furnace #2-resized.jpg
This is really something this picture
I don't understand anything from it
I see that you are pouring metal that looks like silver into cone molds
I see valves on the right hand side
and a small motor
And and a wheel with a handle attached to a gear for tilting the barrel

Where is the gas coming from

Now you see why I like those pictures
They are full of untold techniques

Thanks very much Harold

Also thanks 4metals for point out those cone molds

 

[lazersteve]

As far as talking about them----I have done so infrequently, but it appears to me that no one listens. They have no idea what they're missing, however.

Harold,

I for one listen to everything you write. Your posts have helped me in many ways. I aspire to accumulate the equipment you mention in my refining operation. My biggest hold up is daily life in general. I don't always have the time or resources to obtain the 'optimal' equipment and therefore have to go with other solutions. Necessity is the mother of all inventions.

Cone molds of several sizes are on my shopping list for the near future and I hope to demonstrate their use on video soon. I'm studying up on assaying and also have a lot of old filter ash to process.

As a side note to everyone, I've had carpal tunnel surgery this week on my dominant hand and have two to four weeks to recover before I can 'get back in the game'. I'm doing well and catching up on my reading and sleep this week. Next week I plan on doing some minor, one handed, cleanup around here. Needless to say I'm typing everything with my off hand so I won't be posting too much for a while.

Keep up the great posts Harold, GSP, and everyone else!

Steve

 

[4metals]

Harold wrote;
if you have been fluxing, it's not uncommon for the base of the crucible to be somewhat stuck to the crucible rest. I used to use a heavy piece of cardboard below the crucible, which helped, but as the rest got more and more covered, it was often sticky enough to be troublesome.

A trick which I have used forever, is one I learned from assaying. Every assayer, let me rephrase that, every experienced assayer I know has a pail of powdered bone ash near the furnace to keep a layer on the bottom of the furnace to soak up flux spills. Applying that to melting I always have a layer of bone ash on the crucible rest and some in the bottom of the melter, it serves to keep the crucible from sticking to the rest and unlike cardboard it doesn't burn up. Plus any spills are easily collected because they don't stick.

Now the caution: if you keep a pail of bone ash near the melter, label it and note it is not for fluxing. I had a worker read part of the label, the ash part, and add it to a melt thinking it was soda ash. What a mess, it will not melt it is a refractory material so NEVER add it to a melt, just use it in the melter to prevent sticking on the outside of the crucible.

 

[teabone]

Using bone ash is a great trick. I knew about using cardboard under the crucible to keep it from sticking , but never thought about bone ash and also to use on your furnace bottom for spills is a great idea. Thanks !

 

[goldsilverpro]

Harold wrote;
if you have been fluxing, it's not uncommon for the base of the crucible to be somewhat stuck to the crucible rest. I used to use a heavy piece of cardboard below the crucible, which helped, but as the rest got more and more covered, it was often sticky enough to be troublesome.

A trick which I have used forever, is one I learned from assaying. Every assayer, let me rephrase that, every experienced assayer I know has a pail of powdered bone ash near the furnace to keep a layer on the bottom of the furnace to soak up flux spills. Applying that to melting I always have a layer of bone ash on the crucible rest and some in the bottom of the melter, it serves to keep the crucible from sticking to the rest and unlike cardboard it doesn't burn up. Plus any spills are easily collected because they don't stick.

I've always preferred the cardboard method (which creates a carbon layer between the crucible and the pedestal) over the bone ash method for the following reason: I always build a sloped drain hole in the furnaces I've made, to periodically clean out the slag that always seems to accumulate - with me, much of it came from throwing in pinches of fluxing chemicals and partially missing the crucible. Sometimes, it occurs when the crucible gets thin and a hole appears in it - sometimes, metal will be in it. It can occur when you don't use anhydrous fluxing chemicals - the water in the chemicals will expand them and some can go over the top.

Occasionally, it gets so deep that it's almost up even with the 2" pedestal - that can cause problems if you don't get it out. The drain hole goes completely through the furnace - from the inside furnace floor to near the outside bottom of the furnace. When I'm not using it, I keep a plug in it. When I want to drain out the slag, I pull out the plug and get the furnace quite hot. The slag slowly creeps through the hole and onto the 1/2" sheet of steel that my furnace sits on. I usually spent a lot of time scraping the slag towards the hole - it would probably work better if I tilted the furnace a bit during the removal.

Anyway, the slag is viscous enough without making it thicker. If I used bone ash, I would never get it out.

When you get a slag spill on the floor of the assay furnace, a liberal coating of bone ash soaks up the slag and prevents the crucibles and cupels from sticking. Works great. I have done this many times.

Now the caution: if you keep a pail of bone ash near the melter, label it and note it is not for fluxing. I had a worker read part of the label, the ash part, and add it to a melt thinking it was soda ash. What a mess, it will not melt it is a refractory material so NEVER add it to a melt, just use it in the melter to prevent sticking on the outside of the crucible.

I would have to disagree with this. Traditionally, bone ash has been sprinkled on a melt to thicken the slag and to prevent it from coming out when pouring the metal. I've seen this in print at least a dozen times and, I think, the US Mint even did it. The trick is to use tiny amounts. The only time I tried it, I overdid it and, like you said, I had a mess.

 

[4metals]

I have discovered over the years that the workers respond best to definite do it, or, don't do it rules, if you make it subjective it is invariably screwed up. I have tried techniques I read about in classic text's that I would never ask someone who has little or no care in the profitability of the corporation to do. Using bone ash to scavenge floating crud off the top of the flux layer (as in if there were pieces of crucible in the flux) does work, sprinkle a little on top and twist a graphite stir rod to collect the solids on the rod much like a honey dipper collects honey in a jar.

I still think the mess resulting from over adding is much worse than the benefit of skimming the top of the slag coating. That's why I would vote for never, but in the interest of learning to refine for our members who care to try it, give it a shot. Then come back and tell us your vote.
By the way if it's floating on the slag in the crucible, it will most likely float to the top of the slag layer in the mold too so it will not contaminate the bar.

As far as 2 inches of molten flux in the bottom of a #16 melter, wow, that's a lot of flux!

 

[Harold_V]

Question 1
referring to picture: Small furnace and accessories-resized
I am assuming that the object in the front part of the picture is a tong
Do they sell this in stores or did you make them yourself

As you assumed, it is a tong, although multi-purpose. Typically, a crucible (of substantial size, not assay crucibles) are pulled from the furnace with one tong, and transferred to a pouring shank. I wanted to avoid the double handling, especially considering the relatively small size of my operation, where I knew I had no need to melt silver in larger quantities. The shank was my own creation. I have never seen one aside from my own. It might interest you to know that the jaws were machined from heavy walled pipe, so they matched the contour of the crucible. That way you don't risk crushing a crucible. Most lifting tongs have stops to prevent over gripping.

Question 2
referring to picture: Small furnace and accessories-resized
I see 1 big barrel with as furnace
What is the other smaller barrel with cement
Do both work in conjunction with each other or separate.

Separate. They are unrelated in application. If you noticed, there is a small retort in the picture, also home built. I used the small furnace to heat the retort to distill mercury from dental amalgam. The pump in the picture was for recirculating water from a large container, which cooled the condenser of the retort.

I also used that small furnace for incinerating eye glass frames, which I processed by the thousands. After breaking the lenses, they were simply tossed in the furnace, which operated under a large hood, removing the fumes from combustion. The eyeglasses were heated to dull redness, where they self destructed, turning them into individual component parts.

Incineration of eye glasses is a very important step, even if all plastic was to be removed manually. It is not uncommon to find them covered in dirt and oil. Incineration eliminates everything that is troublesome. As I keep trying to have readers understand, incineration is a very important step in refining.

Question 3
As for buying parts
I wrote to a few companies on was the backyardcasting and the other was a link 4metals posted before
on another thread and no one wrote back
I will eventually find something , probably from a local place

Welcome to the good ol' USA. Many businesses of today have a total lack of manners. Even back when I was actively machining, I sent an inquiry to six companies concerning an item I was seeking. Three of them failed to respond. I sent my inquiry on my business letterhead.

Question 3
cone molds are new to me
I guess to better understand the usefulness of this mold one would have to use it.
I will have to find a supplier

An assayer's cone mold will serve your small melting deeds very well. I used my small one more than the large ones. If it's not obvious to you why they are important, here's why. when you pour, the values are the heaviest, so they go to the tip of the cone. Unless you have a great deal of metal present, the button will be very small, with a tiny surface area exposed to the flux. It is easy to separate from the flux, which stratifies perfectly, assuming you have fluxed well, and have heated properly. It also cools rapidly, due to the heavy casting, which is generally not used constantly. You won't be sorry for acquiring a cone mold.

Question 4
Tilt furnace #2-resized.jpg
This is really something this picture
I don't understand anything from it
I see that you are pouring metal that looks like silver into cone molds
I see valves on the right hand side
and a small motor
And and a wheel with a handle attached to a gear for tilting the barrel

Where is the gas coming from

The tilting furnace, also shop built, was designed as a tilting reverberatory furnace, whereby the charge is melted directly in the furnace, with no crucible in use. It was built to process my waste materials, which was the source of my retirement income. The blower feeds air and gas through the trunnion, which also has a spark igniter within (a spark plug from an automobile). Gas was provided by a large diameter rubber hose. My lab was supplied with 1# gas pressure, unlike the typical home supply which is generally something like 4 ounces. The furnace surpassed my wildest expectations, by the way!

Of interest. They were widening the entrance to Creek Road, where we had built the castle. I walked down one evening to see how the project was progressing. I saw a jack from a model T Ford, along with the large wheel you see on the furnace. It was from an old coffee grinder. Both the wheel and the jack had been unearthed in the road widening project. It had a chip in one side, so I machined both sides equally to remove the chip and keep the wheel in balance cosmetically. It turned out to be a perfect size for the tilting furnace.

Harold

 

[Harold_V]

Steve,
Sorry to hear about your recent surgery, but I'm sure you're going to be all the better for having undergone the procedure. Get well soon!

4metals,
As far as the cardboard under a crucible goes, as GSP alluded, it doesn't burn away, surprisingly. The atmosphere is such that there isn't a great deal of oxygen present, so it carbonizes, and retains its form, at least where it's in contact with the crucible. It worked perfectly well until the rest got heavily coated. A new rest solved that problem.

My procedure was to use a piece of a laundry soap box. It would be soaked in water prior to placing on the crucible rest. That way you could place one in a hot furnace and still have it function as required. You had to work fast, however, to avoid the cardboard burning away, even wet.

Were I still refining, I'd have appreciated the tip on bone ash. Considering I never tried any assaying, relying, instead, on the local assayers, now long gone. I never had bone ash in my operation, not understanding it's potential use as recommended.

Assaying is the one phase of refining I wanted to pursue, but never got around to it. Too busy refining, as it turns out.

Harold

 

[Refiner232121]

Hi Harold
Thanks for taking the time to help.
I once had a shop and now I don't have one anymore.
I am planning on opening something soon.
The reason I am saying this is because sometimes I ask question that are a bit trivial.
That is because I don't have the means to actually perform those tasks that I am asking about.

I see that the most crucible furnaces have a lid or a cover
It is probably to save on heat.
Any reason why you didn't have a lid for your furnaces
Thanks again

 

[teabone]

Wow , that is a really nice furnace you had , Harold. Makes mine look like crap. I wish I could make something like that , but lack skills for such. I'm sure the lack of lid is for proper exhausting and combustion. Harolds furnace is designed that way by purpose , and no lid required. Big plus being able to pour right from the furnace. A furnace like that is very costly , unless you can make it yourself.

 

[Harold_V]

Wow , that is a really nice furnace you had , Harold. Makes mine look like crap. I wish I could make something like that , but lack skills for such. I'm sure the lack of lid is for proper exhausting and combustion. Harolds furnace is designed that way by purpose , and no lid required. Big plus being able to pour right from the furnace. A furnace like that is very costly , unless you can make it yourself.

I got the idea that his question revolved around the smallest furnace, the one I used with the retort. If that be the case, the retort was placed on top of the furnace, supported by four strips of stainless bar. A lid wouldn't have permitted the use of the retort, plus it was unnecessary for incinerating eyeglasses, which were constantly fed to the furnace.
As they collapsed they made room for more to be added. It happened very quickly, so I was constantly adding glasses until the chamber was full of incinerated glasses, at which time I'd clean it out and go again. I would have built a larger furnace at the outset, but I never expected to process the huge number of eyeglass frames that came along.

The other two furnaces have lids, although the tilting furnace lid was bolted in place. It had to be removable in order to reline the furnace. The medium furnace, which was used with a #8 crucible, had a lifting and turning device, so the lid was very easy to move to the side when removing or placing the crucible. The handle was a slip fit, with a pin welded on the furnace frame, so it had a place to be stored when not being used. That kept it perfectly handy when it was needed.

I hope some of this has been useful for you guys. Building a furnace isn't a big deal, but it can be if you add desirable features. The tilting furnace was a huge project, but I was well rewarded for my efforts.

Here's a picture of the tilting furnace during construction. It clearly shows the form in place for the discharge in the lid.

Harold

 

[Refiner232121]

Hi Harold
How are you
Thanks for surprising us with those pictures

 

[PreciousMexpert]

Hi Harold
I like the way the blower and the burner is assembled in this picture
Can I use this to model for making the large size furnace that you have made in your picture

He has a black pipe blowing air and a quarter-inch propane gas line centered in the pipe

http://img90.imageshack.us/i/34526380.jpg/

I am not clear about this pipe where I wrote Number 1

1" iron pipe with a

That is what I have seen on the web site where I got this
That the pipe for the blower, it does not look like 1 inche


Where I wrote Number 2
Is the pipe held there lossy or is the foundry cast while the pipe is in that position

Where I wrote number 4
That brass items is something that I have to find if anyone knows a place to buy that I would like to have the link
Thanks

 

[Harold_V]

Hi Harold
I like the way the blower and the burner is assembled in this picture
Can I use this to model for making the large size furnace that you have made in your picture

In my experience, you can use almost any combination of things and get a functioning furnace. I would say that you can scale up that design with no issues.

That the pipe for the blower, it does not look like 1 inche

It can be difficult to judge size when there are no objects of known size with which to compare. Do remember that pipe is not measured by the OD unless it is 14" in diameter or greater. Physical pipe size for anything under 14" is measured by the ID, which is still a bit misleading because schedule of pipe size makes the ID vary from one schedule to another. The OD dimension of 1" pipe is 1.315" (a couple thou larger than 1-5/16").

Where I wrote Number 2
Is the pipe held there lossy or is the foundry cast while the pipe is in that position

I cast the pipe in place, so there is a snug fit of the refractory surrounding the pipe. I also made a form, a cone, for lack of better description, to increase the diameter of the discharge as it entered the furnace. By using a form, I eliminated the pipe from entering the chamber, where it would degrade from oxidization. The snug fit also prevents any gasses (along with considerable heat) from escaping through any gaps you may create. I suggest you either ram or pour your refractory tightly around the pipe. It should discharge at the side of the chamber (tangent to the hole) so the combustion gasses swirl around the crucible. It in not desirable to have the flame impinge directly on the crucible, so avoid placing the pipe where it will. It should also be placed such that the pipe enters the chamber approximately at the top of the crucible rest. Make certain you have a support that creates a moat of sorts below the crucible, so if you have any spills they won't back up in the pipe. A drain hole in the bottom of the furnace is desirable, but it can be the source of trouble if too much heat escapes from the hole and it is directed towards the floor. I personally never allowed for draining, but that's a personal choice. You may feel differently.

Where I wrote number 4
That brass items is something that I have to find if anyone knows a place to buy that I would like to have the link

That is a quick connect for airlines. You can usually find them at stores that sell air hoses, or air tools. It can be the source of trouble, however. If you choose to use one, make sure it does not leak at the connection.

An alternative (although more expensive) to the cover on the intake of the blower, to control air flow, is a gate valve. I chose that method over the flap, although you may not care to have the degree of control over the furnace that the gate valve permits. Both systems will work adequately, but it's easier to get fine adjustments with a gate valve.

Harold

edit: removed redundant comment. No change in message content otherwise.

 

[Frankk12]

Hi Harold
Thanks for this valuable info

I was wondering if you remember the materials used for making the refractory.
I was reading up on this subject and it looks like the proportion of materials used is very important
If there is too much of one thing thank the refractory will crack and so on.
Thanks

 

[Harold_V]

I was unwilling to mess with making the refractory, especially for the tilting furnace. It is available in a wide variety of applications and is easy to use, even if you choose a ramable refractory. Therefore, I have nothing I can lend towards the idea of making it yourself. I will suggest that you are highly unlikely to achieve the degree of success that is available if you make your own, however. You'll have to consider how much work you're willing to do to avoid spending the necessary money. It might be wise to investigate buying the refractory before you make any decisions. You may discover that you'll spend as much money making your own as it would cost to use a commercially prepared material.

Remember-----when you're working with high temperatures, the idea of using Portland cement for binding isn't a good one. Just as it is created by heat, it is also destroyed by heat. It also has the nasty quality of exploding when it is heated too rapidly when still damp (steam explosion).

Check your yellow pages for a refractory supply house. Most cities of moderate size have one, or there's usually one in the nearest larger town.

Harold

 

[Frankk12]

Hi Harold
Thanks for taking the time to reply.