Tilting Kettle Furnace Under Construction

[goldsilverpro]

HAuCl4,

You stole my idea (just joking). For the last 30 years, that exact same muffle furnace (for cupeling) was something I was always going to build but never got around to it. It would have been identical to your concept. I was going to use about a #40 silicon carbide (SiC) crucible, with a refractory floor, as the muffle - just as in your drawing. Probably, pieces of hard firebrick or SiC could be used as the furniture to support the muffle and it could be sealed at the front with mortar between the muffle and the furnace shell. The muffle could be set into refractory that is lining the furnace at the back. A hinged, lined door could be used.

Bico-Braun used to make a gasoline-fired assay furnace similar to that except they used a commercial arched muffle. It was quite popular in the late 1800s - early 1900s and I have seen pictures of it in old mining books. They were still making it in the 1960s, when I got into this business. The bottom of the furnace was flat and it sat on a table. They ran the fusions directly in the fire chambers on the 2 sides. I used to have plans for making this furnace, just using firebrick, but they were lost. I think it would be pretty simple to do, though.

 

[Harold_V]

If the furnace is tilted 90 degrees, the flame will be forced to travel horizontally while hopefully continuing to spiral. Without a crucible in place to give the flame a defined path to follow the flame may have a mind of its own.

That did not appear to be the case with my tilting furnace, which used no crucible at all. The combustion air and fuel were added at a tangent, so the swirling action was not reliant on a crucible, nor is it a good idea to do so. Flame should not inpinge directly on the side of a crucible.

With my furnace, venting occured only at the pour spout, and had a bilge type internal construction. I expect that internal pressure kept proper flame flow.

As far as forming gas pockets I think if the furnace is glowing red before you tip it, the gas will combust completely and not form pockets of gas.

I agree. I expect that only a dead cold furnace would be capable of not self igniting.

Harold

 

[HAuCl4]

HAuCl4,

You stole my idea (just joking). For the last 30 years, that exact same muffle furnace (for cupeling) was something I was always going to build but never got around to it. It would have been identical to your concept. I was going to use about a #40 silicon carbide (SiC) crucible, with a refractory floor, as the muffle - just as in your drawing. Probably, pieces of hard firebrick or SiC could be used as the furniture to support the muffle and it could be sealed at the front with mortar between the muffle and the furnace shell. The muffle could be set into refractory that is lining the furnace at the back. A hinged, lined door could be used.

Bico-Braun used to make a gasoline-fired assay furnace similar to that except they used a commercial arched muffle. It was quite popular in the late 1800s - early 1900s and I have seen pictures of it in old mining books. They were still making it in the 1960s, when I got into this business. The bottom of the furnace was flat and it sat on a table. They ran the fusions directly in the fire chambers on the 2 sides. I used to have plans for making this furnace, just using firebrick, but they were lost. I think it would be pretty simple to do, though.

I'd use a clay crucible/ clay muffle instead of SiC to do cupellations, fire assays, scorifications, etc. Litharge is very nasty with the C of the SiC crucible!. :evil: And you want an oxidizing atmosphere in there, not a reducing one. :idea:

Besides, clay is always cheaper and easier to shape: 8)

http://www.amazon.com/Making-Crucibles-Vincent-R-Gingery/dp/1878087274

http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=7004

And for Steve: IMO, probably a better idea is to make 2 furnaces, one for melting like the one you started and one for cupelling, etc (dirty business!). The materials are relatively cheap, and you could use the injector, etc from one in the other unless you use both furnaces at the same time. Really it can all be made with firebrick, mortar and clay, with metal just to give it structure and to look nice and functional, and of course the injectors. But really no metal is necessary for melting or cupelling, except for the nozzle.

 

[goldsilverpro]

I'd use a clay crucible/ clay muffle instead of SiC to do cupellations, fire assays, scorifications, etc. Litharge is very nasty with the C of the SiC crucible!. :evil: And you want an oxidizing atmosphere in there, not a reducing one.

Besides, clay is always cheaper and easier to shape

I totally disagree. A company I worked for had 2 big gas fired DFC assay furnaces that had SiC muffles. I was there for 4 or 5 years and there was zero visible damage to them. We ran at least 100 fusions and cupellations per day in them. I can't see clay lasting nearly that long.

 

[HAuCl4]

I'd use a clay crucible/ clay muffle instead of SiC to do cupellations, fire assays, scorifications, etc. Litharge is very nasty with the C of the SiC crucible!. :evil: And you want an oxidizing atmosphere in there, not a reducing one.

Besides, clay is always cheaper and easier to shape

I totally disagree. A company I worked for had 2 big gas fired DFC assay furnaces that had SiC muffles. I was there for 4 or 5 years and there was zero visible damage to them. We ran at least 100 fusions and cupellations per day in them. I can't see clay lasting nearly that long.

That's interesting GSP. I always blamed the litharge flux for the pitting of a large SiC crucible used for smelting ore years ago, but maybe there was other "stuff" in the ore that did the damage. After the SiC became unusable, locally made clay crucibles became the norm at much lower cost and decent durability.

 

[goldsilverpro]

HAuCl4,

Here's a SiC muffle used for cupellation:
http://www.avion.co.in/pages/CF.htm

A quote from "Fire Assaying" by Shepherd and Dietrich, 1940, page 256:

"The short life of fire-clay muffles, especially when used for fusions as well as for cupellation, has led to the extensive adoption of muffles made of silicon carbide, known under the trade name of Carbofrax or Crystolon."

 

[HAuCl4]

Thanks GSP. I never stop learning!. Must have been some sulphides or chlorides in that ore then.

But can't beat clay for costs. I'm sure you'll agree!. :lol:

 

[goldsilverpro]

Thanks GSP. I never stop learning!. Must have been some sulphides or chlorides in that ore then.

But can't beat clay for costs. I'm sure you'll agree!. :lol:

In my work, the main things that attacked the SiC crucibles (and about any other type of crucible) was sodium nitrate and when I used soda ash to convert silver chloride to silver metal.

Clay is cheaper but I would think you would have to replace it more often.

 

[HAuCl4]

Thanks GSP. I never stop learning!. Must have been some sulphides or chlorides in that ore then.

But can't beat clay for costs. I'm sure you'll agree!. :lol:

In my work, the main things that attacked the SiC crucibles (and about any other type of crucible) was sodium nitrate and when I used soda ash to convert silver chloride to silver metal.

Clay is cheaper but I would think you would have to replace it more often.

I agree. Obviously for someone making a lot of assays per day, that type of SiC muffle furnace you described makes a lot of economic sense. But if one doesn't mind doing clay casting, the costs can't be beaten for crucibles or anything else made of clay/cement. Even if repairs are more frequent. You could build several clay muffles/furnaces for the price of one of those sophisticated units. I haven't checked the cost, but probably $2-$3k retail?. I'm thinking a lot more disposable/recyclable these days, although I used to think more of permanent/indestructible in my younger years.

 

[goldsilverpro]

Thanks GSP. I never stop learning!. Must have been some sulphides or chlorides in that ore then.

But can't beat clay for costs. I'm sure you'll agree!. :lol:

A great thing about this forum is that everyone learns, no matter how long they have been in the business. I certainly admit that I learn something every day. Many people (myself included), who have done this work for many years, first come on the forum with a know-it-all attitude. When they finally realize that no one knows it all, they can really start learning.

In my work, the main things that attacked the SiC crucibles (and about any other type of crucible) was sodium nitrate and when I used soda ash to convert silver chloride to silver metal.

Clay is cheaper but I would think you would have to replace it more often. Were I to build a muffle furnace, similar to your design, I would first try a used, thinned out SiC crucible, as long as there were no holes in it. Since I always preferred and used SiC crucibles, mainly for their strength and durability, I always had some old ones laying around. Remember that we're talking about making a muffle from a crucible, not buying a high dollar commercially made SiC muffle.

Actually, both will work.

Sorry for the repetition of my last post. I somehow posted it a little early.

 

[HAuCl4]

Yup. Great forum and great contributors for learning, doing things differently, cheaper, faster, less fumes, etc.

I have picked up dozens of useful techniques and tips for doing things that I thought I had "mastered".

 

[lazersteve]

All,

I managed to get the lid refractory cast, the nozzle in place, the inlet cut, and a few other minor mods done to the kettle.

Here's a short video of me curing the refractory lining.

[youtube]http://www.youtube.com/watch?v=3HIwLP2HDb0[/youtube]

I ran the furnace at minimum LPG flow for one hour before filming. I still need to install my pressure gauge so I can monitor the gas flow accurately. Temperatures were measured using a hand held laser type measuring device.

Steve

 

[HAuCl4]

Looks "warm" to the touch!.

The nozzle mixes air with the gas right?. Any chance of a diagram or closer picture of the nozzle inside?. :shock:

 

[lazersteve]

Looks "warm" to the touch!.

Indeed it is. The ball on the handle measured 50C peak, gloves are a must when operating this little kettle.

The nozzle mixes air with the gas right?. Any chance of a diagram or closer picture of the nozzle inside?. :shock:

Not my design, but here it is:

I used the Bordeaux version with a Zoeller flare on the end.

Steve

 

[HAuCl4]

Nice. Thanks!. :!:

 

[goldenchild]

I have a feeling Steve is wanting to melt obscene amounts of silver. Am I right Steve? Or are you going for the gold? :shock:

 

[lazersteve]

I have a feeling Steve is wanting to melt obscene amounts of silver. Am I right Steve? Or are you going for the gold? :shock:

I want to melt silver, copper, gold, and use the furnace tilted to perform various assay functions. My electric furnaces run up my power bill and propane is cheap. I may even set up a propane burner top for doing my dissolving reactions.

Steve

 

[HAuCl4]

May I suggest adding a layer of heat insulation to that furnace?. Having something so hot exposed is an accident waiting to happen. Just my opinon, and a layer "sleeve" made of refractory wool would not be heavy or expensive. Maybe too many modifications are impractical, you be the judge.

 

[lazersteve]

May I suggest adding a layer of heat insulation to that furnace?. Having something so hot exposed is an accident waiting to happen. Just my opinon, and a layer "sleeve" made of refractory wool would not be heavy or expensive. Maybe too many modifications are impractical, you be the judge.

I have actually already considered this and I'm on the fence as to whether or not insulating the exterior would cause the steel to retain more heat and begin to get red hot creating a possible failure condition. After that thought I also considered adding cooling fins to the exterior to provide extra cooling to the casing, but this would also sap heat away from the interior of the furnace. Like I said, I'm still working out the pros and cons of each hoping to find a happy medium.

I'm open to suggestions on both fronts and will incorporate any ideas that prove to be useful and practical, now and in the future.

The furnace project is an experiment that is still in process and is by no means completed. I've already considered replacing the bucket with a 10" version for a thicker interior refractory wall. I've also considered a heat reflective coating inside the bucket walls between the refractory lining and the steel.

Steve

 

[HAuCl4]

Refractory casting is that, refractory, not necessarily insulating. There are some castings that are lighter more insulating and less refractory, etc. Then there is Fiberfrac, which is both refractory and insulating, but it's a wool.

In this design, which is more or less what you have 1, 2 then:

3-Is the Fiberfrac filling the space between brick/refractory casting and steel casing.

4-Is firebrick to give structure between the casing and the inner furnace.

A simpler variation would be to simply increase the thickness of the walls of the furnace by using some insulating casting cement. Note that insulating casting cement crumbles easily, so you definitely want to have the inserts of firebrick 4- in there to give it structure/linkage to the steel casing.

The variations are infinite, but the variables are only 2: Thermal conductivity and thickness. Decrease conductivity and increase thickness for lower outer temperature.

I hope it helps.