# Tilting Kettle Furnace Under Construction



## lazersteve

I've been working on a new propane fired furnace, not a really big one, just something for melting around the house.

Today a friend of mine and I worked for six and a half hours to construct a tilting kettle furnace I designed from a mixture of ideas I've seen here and elsewhere. Here's what we got done today:

[youtube]http://www.youtube.com/watch?v=ce1Q4VfglxI[/youtube]

It's still in need of a lot of things ( lid needs refractory, propane plumbing, nozzle is in the mail, inlet on furnace, casters, etc.) but the bulk of the work is done. 

My friend did all of the welding and I did most of the fab work and all of the design work. We worked our buts off in his metal shop. He taught me how to use six of his machines to speed things up.

The core of the furnace is an 8" x 10" x 1/4" steel tube with a welded flat bottom. The base is a 18" x 18" square with a cross member, all made of 1-1/4" square tubing x 1/8" thick. The uprights are 10" x 3" x 1/4" steel c-channels with a 1" steel pipe split in two on top for the furnace pivot and supported by some 1-1/4" angle irons. The support rods were made of 3/4" all thread recess welded into the furnace pipe wall at 5-1/2" from the bottom of the furnace. The lid is an 1-1/2" ring of the 8" pipe and a two piece cone with a 3-1/4" vent hole welded together, hinged in the back with a 3/8" pull pin for easy removal and a large round 3/8" steel loop for a handle. The burner support arm is 2" x 1/4" steel bar bent to the curvature of the furnace and welded in place along with supports. A split 1-1/4" pipe serves as an adjustable tie point for the burner tube. The kettle tilt handle is a 12" x 3/4" rod with a decorative ball on the end. There is a small 3/4" x 3" piece of steel welded to the lower left side of the furnace as a stop to keep the furnace from tilting backwards when the lid is opened. On either side of the rim of the furnace is welded a 30 degree angled 1-1/4" x 1/2" x 3/4" steel stock as a lid guide.

This furnace will hold up to a 5" OD x 7-1/2" height fire clay crucible as seen in the slide show. It will of course hold smaller ones as required.

I designed this furnace several years ago and have been taking ideas from various places to get the design just how I wanted it. I was in the post office the other day and saw my welder friend and asked if he would mind welding it up for me. As you can see, we had one hell of a fun day today. I had to work one handed as I'm still not able to use power tools with my right hand, so it was a labor of painful love for me. 

I want to thank Harold for posting the photos of his furnace years ago, which inspired me with the basic idea of a tilting furnace. My tilting furnace is not as large as yours Harold, but I don't see myself ever needing one that big. If I do, now I feel confident enough to tackle the job. 

Steve


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## 4metals

Steve,

You do very nice work, my only question is why do you need to have a tipping furnace for such a small capacity crucible? I'm sure the unit will work fine but to tilt you will have to either cement in the crucible or support it in a way that the flames can still spin around the crucible. With induction you can pack in a ram mix and it is pretty quick, but with a flame that has to spin about the crucible it is more difficult. 

For a crucible the size you're talking a push up device would allow quick interchange of crucibles and raise the crucible to the top of the melter so all you have to do is grab it with tongs, walk it to the edge (a few inches) and tip it into a mold.


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## lazersteve

4metals said:


> You do very nice work, my only question is why do you need to have a tipping furnace for such a small capacity crucible? I'm sure the unit will work fine but to tilt you will have to either cement in the crucible or support it in a way that the flames can still spin around the crucible. With induction you can pack in a ram mix and it is pretty quick, but with a flame that has to spin about the crucible it is more difficult.
> 
> For a crucible the size you're talking a push up device would allow quick interchange of crucibles and raise the crucible to the top of the melter so all you have to do is grab it with tongs, walk it to the edge (a few inches) and tip it into a mold.



4Metals,

Thank you for the reply.

The main reason I built it like this was to see if I could do it and to get away from my electric kilns. I'm thinking I'll use it upright for everyday tasks like melting gold, silver, and such, and eventually line it with a new refractory configuration and other mods that that allows the furnace to be used with the lid closed. One of the things I have not added to the current design is the locking mechanism for the pivot. This was already in my design, but we ran out of time today and I have not hammered out all of, or even the exact details to construct it yet. I want the latching mechanism easy to operate with gloved hands, yet safe and reliable enough not to fail when the unit has a hot charge in it. 

I already have some refractory pucks cast to boost the large crucible up for easy tong access and to allow the flame room to circulate around the larger crucible. I also have designed the lid with enough extra space to allow the taller crucibles to stick up into the lid area for access as you have mentioned. This is why the lid refractory is not in place yet. I waited to get the refractory placement right with the actual boosted crucible height. This also leaves me room to play with adding a spouted crucible and have the crucible top supported but the pressure from the closed lid to keep it from tipping out when pouring. Even when the large crucible is fully recessed it allows for plenty of flames to spin around it since the inner walls of the furnace are parallel to the walls of the furnace and the crucible tapers.

One other use I have for the tilt is to turn it 90 degrees, lock it in that position and do small scorifications and cupellations with it like an oven. 

Do you have any details on the 'push up' device you mentioned? Is it a pivoting lever that elevates the crucible out of the furnace? How does the refractory seal properly around the mechanism and how do the mechanisms stay protected from the heat of the furnace?

I'll post videos of the furnace in operation once it's fully constructed.

Steve


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## Harold_V

lazersteve said:


> My tilting furnace is not as large as yours Harold, but I don't see myself ever needing one that big. If I do, now I feel confident enough to tackle the job.
> 
> Steve


You're making the right decision, Steve. (Nice, by the way!)

My first melting furnace accommodated only a #1 crucible. Like you, I couldn't see the need for anything large. With time and progress, I came to understand how wrong I was, but building the first furnace was an exceptional learning experience. From it, I knew what to do, and what not to do, for future builds. Without that experience, the tilting furnace I built most likely wouldn't have worked well. Yours, too, is likely to be a good learning experience, better preparing you for a future design. It's all good, Steve. 

As far as volume is concerned, there will always be a time when something larger would be to advantage. However, as crucibles get larger, you must use proper handling tools, to avoid the risk of breakage. They are not inexpensive. For that reason, you will likely settle on a size that will suit your needs. If silver is in your future, it may demand something in the #6 or #8 size. Only you can tell. I got by adequately with a #8. 

The most valuable lesson I have learned in my many years is to take it slow. I have never enjoyed exceptional success, but I have also never been at risk. Had my refining venture not turned out to be a business, it would have been a complete success anyway. After all, it was intended to be a hobby only---nothing more. By allowing it to grow as required, I was assured of success. I acquired equipment only when it was a necessity. As they say, a bird in the hand---

Harold


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## 4metals

Most push up furnaces I have seen use a hydraulic cylinder beneath the unit. The top of the cylinder is actually the crucible rest puck made of refractory and it is as tall as the length of the push up so no mechanical seals of the piston are exposed to the heat zone. 

Inductotherm uses a removable (threaded) head for the piston and a catch tray fits over the extended shaft before the head is screwed on. This functions as a spill tray and protects the piston. For larger units these pistons fit into a hole in the floor because they are long. There are push up furnaces made for most crucible sizes up to #20. 

As I said the main benefit of a push up is the quick interchangeability of the crucible. 

Operating the furnace while tilted 90 degrees for scorification in an interesting idea.


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## HAuCl4

Better tilt it a little less than 90 degrees, or the crucible will empty!. :lol:


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## lazersteve

HAuCl4 said:


> Better tilt it a little less than 90 degrees, or the crucible will empty!. :lol:



When operating at 90 degree tilt as a muffle furnace the crucible would not be used. The cupels or dishes would be placed on a bed of bone ash instead inside the furnace. 

I had even considered using a refractory insert to make the 'floor' of the 90 degree tilted furnace flat when operating in this position. This would provide me with a flat work surface and would serve to protect the lining of the furnace at the same time.

Steve


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## Barren Realms 007

I have a small question, on your burner it looks like it goes straight into the side of the unit and will blow the flame directly at the crucible. Most of the desighns I have seen show the burner going in at and angle so that the flame creates more of a swirling motion. Any personal reason you decided to do this?

And I like the idea of a shelf in the post above.


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## lazersteve

Barren Realms 007 said:


> I have a small question, on your burner it looks like it goes straight into the side of the unit and will blow the flame directly at the crucible. Most of the desighns I have seen show the burner going in at and angle so that the flame creates more of a swirling motion. Any personal reason you decided to do this?
> 
> And I like the idea of a shelf in the post above.



You may notice the inlet hole for the burner is not yet cut so the burner entry angle is not determined yet. The mounting bracket for the burner will be fine tuned with a few hammer taps to position the flame exactly where I want it once the 1:12 flared nozzle arrives and I see all the parts aligned together. 

The burner mounting bracket was fabricated so that it's angle would be tangential to the perimeter of the crucible base and offset from the center line of the furnace.

Steve


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## Barren Realms 007

lazersteve said:


> Barren Realms 007 said:
> 
> 
> 
> I have a small question, on your burner it looks like it goes straight into the side of the unit and will blow the flame directly at the crucible. Most of the desighns I have seen show the burner going in at and angle so that the flame creates more of a swirling motion. Any personal reason you decided to do this?
> 
> And I like the idea of a shelf in the post above.
> 
> 
> 
> 
> You may notice the inlet hole for the burner is not yet cut so the burner entry angel is not determined yet. The mounting bracket for the burner will be fine tuned with a few hammer taps to position the flame exactly where I want it once the 1:12 flared nozzle arrives and I see all the parts aligned together.
> 
> The burner mounting bracket was fabricated so that it's angle would be tangential to the perimeter of the crucible base and offset from the center line of the furnace.
> 
> Steve
Click to expand...


Makes good sense.

Fine tune with a hammer.... 

I am leaning towards a desighn like this and want to see how your turns out. I have from a 5 gal to a 100 gal contaiers available. 

Can I ask where you ordered your crucible from or if you have more you can get. That looks like a nice convinent size to work with.


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## lazersteve

The crucible is a 'K' size type. 

I can source them for you if you like.

Steve


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## Barren Realms 007

That would be excellent, when I get ready for one I will let you know. 

What is the round about cost on one of that size?

Any reason you chose that over a graphite? Or is it just your preferance?


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## lazersteve

Barren Realms 007 said:


> What is the round about cost on one of that size?



Depending on the material it's made of between $10 to $20 dollars ballpark.



Barren Realms 007 said:


> Any reason you chose that over a graphite?



Graphite takes longer to heat and decays with use. I have some salamander type crucibles that I plan on trying in the furnace, but I don't know any of the pros and cons of them yet as I have not worked with them to date.


Steve


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## HAuCl4

lazersteve said:


> HAuCl4 said:
> 
> 
> 
> Better tilt it a little less than 90 degrees, or the crucible will empty!. :lol:
> 
> 
> 
> 
> When operating at 90 degree tilt as a muffle furnace the crucible would not be used. The cupels or dishes would be placed on a bed of bone ash instead inside the furnace.
> 
> I had even considered using a refractory insert to make the 'floor' of the 90 degree tilted furnace flat when operating in this position. This would provide me with a flat work surface and would serve to protect the lining of the furnace at the same time.
> 
> Steve
Click to expand...


IMHO the "revolving circular flue" of this type of furnace is very violent. I doubt the flue swirling around the crucible will be the same with the furnace tilted or without crucible. Be prepared for a lot of "experiments". I never tried tilting a gas-fired furnace with the gas on!. Tilting electric furnaces with electricity on is easily done and relatively trouble free if the crucible is well supported, but here you can even cause the furnace to "smother" and then you'd quickly build up a pocket of unburned gas, a recipe for explosion as soon as oxygen contacts re-establishes. Be very cautious!.


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## lazersteve

I can see how the gas may form a pocket and lead to a burst of flames and hot gases. The propane regulator has an adjustable pressure flow control on it and the propane flow will have a cut off valve as well. 

I will be sure to cut the gas flow when tipping the furnace for a pour.

When using the furnace as a muffle I'll be running the gas at a much lower pressure to keep the temperature in check so I'll have to experiment to see if reverse gas pressure build up inside the titled furnace is an issue. I've been toying with the idea of a removable refractory plug along the side of the furnace (the top when tilted) to allow any reverse pressure and off gasses to escape. 

Thank you for the extra advice as all input is crucial to the successful and safe operation of this unit. I'm sure the design will go through several stages of evolution before it's safe and just how I want it to boot. 

Steve


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## HAuCl4

Also an alternative to 4metals "push-up" is a "lift-off", where the furnace walls lift with a lever or crank and the crucible and rest are stationary. This design loses heat fast though when the furnace walls are lifted, and IMHO is good only for medium to small crucibles. (That can be lifted by 1-2 persons).

A design of this type is clearly described in this booklet:

http://www.amazon.com/Building-Gas-Fired-Crucible-Furnace/dp/1878087088/ref=pd_bxgy_b_img_b#_


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## 4metals

I agree with Mr. Aurochloric acid, without a crucible to define the circular flame path the alternate use as a kiln may have problems. When the furnace is upright and the flame enters at an angle the flame swirls clockwise and hugs the wall without a crucible. But the flame is always spiraling upward towards the top of the furnace. 

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. 

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. 

Are you using just propane or propane and forced air?


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## lazersteve

The plan is just propane for now.

What about my idea for a custom cast muffle insert into the tilted furnace cavity that allows the gas to flow around it?

Steve


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## HAuCl4

Steve: Those gas-fired furnaces have to have an exhaust near the top. The gases heat the charge by convection and move from the bottom up. Any attempts to make the hot gases to flow downwards are doomed to create cross-currents and possibly a "smother" (Think plugged-out chimney), where the burnt-out gases kill the flame due to lack of oxygen. (Like a CO2 extinguisher). Then gas accumulates, heats up and when oxygen gets in (because you open the lid to look. :shock: )==> boom.

Here attached is a design for operating the furnace tilted 90 degrees, you simply put the inlets and outlets as removable inserts, then the gases encircle the crucible and exit on the top (several outlets on the top, inlets 1 is OK, 2 better).

You can use a large clay crucible as the muffle, filled with some refractory cast to make it have an horizontal surface inside.

When you want to operate the furnace upright, you simply, plug in the refractory inserts in the holes and use the holes of your original design.

I hope it helps.


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## lazersteve

That's exactly what I was thinking. 

Steve


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## 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.


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## Harold_V

4metals said:


> 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


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## HAuCl4

goldsilverpro said:


> 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.


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## 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.


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## HAuCl4

goldsilverpro said:


> 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.
Click to expand...


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.


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## 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."_


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## 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:


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## goldsilverpro

HAuCl4 said:


> 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.


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## HAuCl4

goldsilverpro said:


> HAuCl4 said:
> 
> 
> 
> 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.
Click to expand...


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.


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## goldsilverpro

HAuCl4 said:


> 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.


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## 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".


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## 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


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## 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:


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## lazersteve

HAuCl4 said:


> 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.



HAuCl4 said:


> 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


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## HAuCl4

Nice. Thanks!. :!:


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## 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:


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## lazersteve

goldenchild said:


> 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


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## 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.


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## lazersteve

HAuCl4 said:


> 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


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## 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.


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## Barren Realms 007

How thick did you pour your refractory?

The ones I have seen operate the main damage to the inside comes from where the flame attacks the refractory at the point of cntact with the flame.

A layer of tile similar to what is used on the space shuttle.

A replaceable piece of fire resistant sheetrock(not much of a good idea but it works as a barrier to an extent).

A ring of stainless at the bottom where most of the flame is.

Fluxes used seem to cause more damage than the heating itself.


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## lazersteve

Here are the specifications of the insulating refractory that I'm using:



Ellis Custom Knife Works Website said:


> Kast-O-lite 30 LI Insulating Castable Refractory:
> 
> This is a 3000 degree F (3000°F = 1649°C), High Alumina Insulating Castable Refractory for making forges. You can cast the entire refractory liner for a forge or just the floor using this material! This material has a very high resistance to flux, if you're doing a lot of forge welding and have a dedicated forge for forge welding in, this is a great material to use!
> 
> This material has a much better thermal conductivity rating than Mizzou castable...a castable forge doesn't have to be expensive to operate!
> 
> - *3000F degree temperature rating*
> - Highly flux resistant
> - Low thermal conductivity = highly insulating compared to Mizzou
> - Density = 90 lb/ft^3
> 
> - This material has a thermal conductivity of 4.54 BTU-in/hr-F-ft^2 at 2000 degrees F and conducts almost 40% less heat through the forge shell at 2000 degrees F!



The floor of my furnace is 2.5" thick and the walls are 1.5" thick.

As you can see from the specifications above the refractory has a low thermal conductivity and a high temperature rating, so the lining should not be degraded at the temperatures I'm operating it at 0 to 2012 F (0 to 1100C ).

I'm thinking that the steel shell is getting heated via two possible routes:

1. The nozzle inlet. The nozzle glows a dull red color during operation and is in close proximity to the steel shell (~1/8"). This may be causing heat to migrate around the lower section of the steel shell and could be resolved by repositioning the nozzle at the inlet.

2. The lid is getting heated almost directly from the flame that exists the top of the furnace. I feel that cutting the steel about 3/4" back around the top lip of the lid will reduce the amount of heat being conducted to the steel shell of the lid. This would also reduce the amount of heat that migrates down to the lower section of the bucket via the steel of the lid in contact with the steel from the lower shell. 

The second problem could also be resolved with a refractory 'bung' inserted into the exit hole that reduces the exit hole diameter and elevates the flame exiting to above the steel of the lid. The bung would be shaped like and inverted top hat with a hole in the center and inserted into the exit hole where the flame escapes. This would provide a layer of insulation between the exiting flame and the outer steel skin of the lid.

Here's a quick sketch:







An outer layer of additional outer insulation may still be required even after the above modifications.

Steve


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## Barren Realms 007

Your refactory is too thin.


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## Noxx

I have to disagree, commercial refractories do not need to be very thick. Why are you suggesting thicker refractory walls ?


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## Barren Realms 007

Noxx said:


> I have to disagree, commercial refractories do not need to be very thick. Why are you suggesting thicker refractory walls ?



Why would you disagree with that NOXX?

Now I will be the first to admit that I have not been around a foundry of the same nature that most here have been around. Running the high temps that are being delt with. 

But I have been around many similar items in my line of work. 

I worked daily with 3 systems that were 1.5 mbtu burners set in a SS ring (wraped in rock wool with SS cover barrier) that blew the flame into of all things a fiberglass stack where water was sprayed in to evaporate the water, we replaced the stacks every 4-6 months, and the spry nozzels lasted 1-2 months. There was a lot of heat transfer thru this setup. 

I maintained a 300' tunnel furnace where they took cotton and treated it with chemical to make it fire resistant for use in furnature, this system had a layer of rock wool to keep heat tranfer down.

Boilers, I don't even want to count!

Pool heater's, even these have a layer of rock wool for protection 1" to 1-1/2" thick if memory serves me right.

Fire resistant sheetrock 3/4" is desighned to last 1 hour at 2,000 F if memory serves me right. 2 laters for a 2 hour protection.

A firwall of brick is minimum 4" thick.

Have you ever seen a chimney stack built of brick? You see the outside brick, but did you know there is another inner chamber with 3 courses of acid resistant brick if I remember right. This is for protection from the acid not the heat. And the mortor joints are super thin.

If I am correct I don't think you will find a furnace running these temps with only an 1-1/2" wall. A brick layed on it's side is 2-1/4"" thick. And I think you will find that a furnace of this type built of brick is going to have a minimum of 3 courses of brick but I would say closer to 4 or 6 courses of brick layed.

These figures are probably a little off and there are others here in construction that can correct them for me. I have been out of this aspect of construction for some time so I don't have to keep the figures in my head. And besides I didn't have to keep up with this information because in my line of work it was not my job, it was the general contractors responsability to keep up with this info.

I was not trying to imply that Steves desighn was wrong. I don't think it is! I love the desighn of it. 

His concern was the 220 F temp of the outer surface of his furnace. As stated in the post below.

This material has a thermal conductivity of 4.54 BTU-in/hr-F-ft^2 at 2000 degrees F 

When you desighn for something like this you desighn for thermal conductivity. Common sense will tell you that if you have too much heat transfer your barrier is too thin.

I don't recall a furnace that I have seen constructed like this with less than 4" walls maybe 3". And all of them degrade with time and use. So your desighn should accomodate for this factor as well.

Check on this web site for info and desighns. 
http://www.backyardmetalcasting.com/index.html


> HAuCl4 wrote:
> 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 ofeach 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



The fastest and easiest fix for his problem would be to weld some small tabs on the bottom side sticking out, or a bottom support ring. Take a piece of 1" fire rated sheetrock, cut it to size, wet it so it will be flexible and put it on the side of the furnace and hold it in place with long SS pipe clamp's. I would assume this would cut his heat transfer down to 120-140F on the outside of his furnace.

But to be honest a 220F temp is not that bad IMHO, just operate the thing outside and watch your clothing.

This is an uneducated guess on my part:
The refractory will possibly last 18 months depending on how much he uses it and how it is stored.
The thinner the refractory the more prone it is to absorb moisture into the interrior of the refractory.
Thus each time it is cranked up there is a possability of damage from expanding moisture..Steam!
The thinner the refractory the more prone it is to crackes and hairline fractures.
The thinner it is makes it more likely for the refactory to crack apart and break up when these fractures appear.


EDIT: You want to think about heat transfer? I have seen on HVAC system's on a run of ductwork less than 15' in an attic change the temp of the air leaving the air handler and coming out of the vent by over 10 deg F.


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## lazersteve

Barren said:


> When you desighn for something like this you desighn for thermal conductivity. Common sense will tell you that if you have too much heat transfer your barrier is too thin.



Not necessarily, I've already pointed out two sources of heat exchange where the energy can migrate around the insulating barrier. I've now begun the mods on the unit to circumnavigate these sources of heat migrating to the shell. 

I have a feeling that once I control the exposure of the steel casing to direct heating from the nozzle and the lid's exposure to the exit flame that the casing temperature will decrease. I've ordered some paint on refractory surface coatings for the inner side of the refractory lining and the inner side of the steel casing and nozzle as well. I think the exterior of the unit will cool down considerably once these changes are all in place.

I'll post my updated design changes as they are completed and testing is run. I will take new temperature readings when I fire it up after the mods.

If anyone else has made a similar sized furnace please post the temperature readings of the exterior of the furnace after one hour of operation. If possible post the specifications of the refractory you used and it's dimensions.

Steve


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## qst42know

Is it possible there is still moisture trapped within your cast-able? It wouldn't take much to efficiently transfer heat.

Does your shell temperature improve with each firing?


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## Barren Realms 007

lazersteve said:


> Barren said:
> 
> 
> 
> When you desighn for something like this you desighn for thermal conductivity. Common sense will tell you that if you have too much heat transfer your barrier is too thin.
> 
> 
> 
> 
> No necessarily, I've already pointed out two sources of heat exchange where the energy can migrate around the insulating barrier. I've now begun the mods on the unit to circumnavigate these sources of heat migrating to the shell.
> 
> I have a feeling that once I control the exposure of the steel casing to direct heating from the nozzle and the lid's exposure to the exit flame that the casing temperature will decrease. I've ordered some paint on refractory surface coatings for the inner side of the refractory lining and the inner side of the steel casing and nozzle as well. I think the exterior of the unit will cool down considerably once these changes are all in place.
> 
> I'll post my updated design changes as they are completed and testing is run. I will take new temperature readings when I fire it up after the mods.
> 
> If anyone else has made a similar sized furnace please post the temperature readings of the exterior of the furnace after one hour of operation. If possible post the specifications of the refractory you used and it's dimensions.
> 
> Steve
Click to expand...


On the top part it has been suggested to recess the steel at the opening 1-1/2"-2" to stop the heat transfer that you are having. But I like your desighn better and would keep it the way you have it.

On the nozzel do you still have it desighned to point straight in? And if so are you having a blow back at the opening? That was the reason for the suggestion on my part for the angled inlet to create a vortx effect of the flame rather than a streight in efffect that can cause blow back.

I am interested in knowing what kind of paint on refractory you have found and what thickes does it say will stop how much heat transfer?


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## qst42know

These come up often on the blacksmith sites.

http://www.budgetcastingsupply.com/ITC.php


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## lazersteve

qst42know said:


> Is it possible there is still moisture trapped within your cast-able? It wouldn't take much to efficiently transfer heat.
> 
> Does your shell temperature improve with each firing?


This is actually the first time the refractory was fired up to operating temperature, so yes that could also contribute to the problem witnessed.

Steve


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## lazersteve

qst42know said:


> These come up often on the blacksmith sites.
> 
> http://www.budgetcastingsupply.com/ITC.php



I purchased two of the ITC line a few days ago. The 100 for the inner surface of the refractory and the 213 for the nozzle and steel casing inner walls.

Steve


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## lazersteve

Barren said:


> On the nozzel do you still have it desighned to point straight in? And if so are you having a blow back at the opening?



The nozzle has never been aligned straight in, it's always been aligned at a tangent since before the project was fabricated. The flame swirls around the inner wall of the furnace up and out as planned. There is zero blow back at the opening when operating. 



Barren said:


> I am interested in knowing what kind of paint on refractory you have found and what thickes does it say will stop how much heat transfer?



See post above and specifications for ITC-100 and ITC-213. 

ITC-100 is a paint on, highly IR reflective, flux resistant, refractory coating for furnace linings.

ITC-213 is a paint on coating for furnace nozzles, parts, tools, and crucibles to extend the components life at high furnace temperatures. 

Steve


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## Barren Realms 007

Cool, I'm looking forward to see how well it works.


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## butcher

Steve, in boilers we use a castable refactory (thick layer) (also the castables are usually a softer more easily damaged refactory) this refactory has air space (pockets) when dried, and then a wash coat refactory like sairset as a thin layer it bakes on to form a silica glass like coating, this coating is stronger and helps protect the softer castable refactory.
I believe the castable refactory with air pockets in its structure actually helps as an insulator, as it will not conduct as well as a solid like firebrick will conduct heat to the metal surface covering, I do not know if I explained this so you might even know what I am saying, I do not know what type of refactory you are using, the castables are usually covered with a mortor wash coat, it would be kind of like using the two types of firebrick furnace, the white easily cut brick will not absorb the heat well and the air pockets will keep conduction of the heat transfer to a minimum, while if you used the heavier clay type firebrick it would absorb and transfer the heat easier through conduction, hope this helps and is not just another of my rambling's on


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## Noxx

Steve, any ITC-100 remaining you wish to sell ?

On the other hand, Barren, I though you was saying that the refractory is too thin and risk cracking. Thermal conductivity of the refractory layer is not critical, as long as you have many layers of ceramic blanket or equivalent.

Commercial refractory might crack a littler over time, but there's nothing to worry about...






HAuCl4 and others, here is another similar type of burner:






The tip is a MIG welding tip, 0.035'' dia.


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## Barren Realms 007

I agree 100% with you NOXX. I was just stateing there is more of a possability of it with thinner refractory. But I think the coating he is going to put on it will stop this and he will be fine and have many years of service out of the furnace.


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## lazersteve

Noxx said:


> Steve, any ITC-100 remaining you wish to sell ?



I'll make sure you get some Noxx, send me a PM and we will work out the details.

Steve


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## HAuCl4

I'm eagerly awaiting to see if these reflecting paints, modifications, etc, would prove satisfactory. My intuition tells me the walls are too thin. This stuff can be properly calculated for a k and a thickness for a given drop of temperature between the inner and outer furnace. I'll try to find the formulas.


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## lazersteve

HAuCl4 said:


> I'm eagerly awaiting to see if these reflecting paints, modifications, etc, would prove satisfactory. My intuition tells me the walls are too thin. This stuff can be properly calculated for a k and a thickness for a given drop of temperature between the inner and outer furnace. I'll try to find the formulas.



I did some looking, but I couldn't find any formulas except for houses. If you can post one that would be awesome.

I'd like to type in the operating furnace temperature, the desired shell temperature, and refractory type then have a resulting thickness provided from the formula.

The ITC-100 is reported to be very good at reflecting IR. A lot of folks are using it directly over koawool in miniature forges from my reading elsewhere.

I'll put it to the test once it arrives. If all else fails I'll work on a larger 10" diameter kettle and make the liner a two layer system instead of one.

I'm very happy to see people getting involved in this as two heads are always better than one. I'm still curious what other peoples casing temperatures are on coffee can furnaces and the like. Of course the refractory specifications on the furnace would also be great.

Steve


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## lazersteve

I did a little more looking and found these:

Thickness Calculations Example

and 

Insulating Refractories

Now I need to do some math.

Steve


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## Barren Realms 007

That first link dosen't seem to work.

You didn't do any calculations on this before you built the furnace?


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## lazersteve

I had no idea of what normal exterior temperatures should be in order to do any calculations and I didn't find the formulas until today. I based the thickness of my wall on the fact that insulating firebricks are 1.5" to 2" thick and they tend to remain relatively cold when melting gold in them. I found today that G-26 firebrick has a k of 2.6 at 2000 F or about half of the refractory I'm using.

I can't seem to find anyone who can post the external temperature of their furnace verses the operating temperature along with their refractory specs. The above links mention a 600F (315C) external temperature in one of the examples. 

I managed to locate the k value of the refractory I using as 4.4 at 2000F ( 1093 C). If push comes to shove I can bore out this furnace 1/2" and add a layer of 1/2" alumina mat (k = 1.65 at ~2100F) to bring the radiated heat under control.

I'm hoping someone will post readings from their furnace before I go through the trouble of making mine run 'cool to the touch' on the outside.

Steve


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## Noxx

It seems some people need formulas 

I did this nice excel sheet for me. Unfortunately, it's in french but might still be able to understand.

There are interesting html links too!


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## Barren Realms 007

I haven't seen any people post what the temperature is on the outside that was taken with any kind of instrument. I'm going to say 99% of the people that build these just throw them together with out any foresight. You might get lucky and have someone send you some data on one.

The fire brick possibly transfers less heat because of the air pockets.

I had to put a piece of sheetrock under my crucible because I cracked 2. The brick it was setting on was transferring too much heat from the crucible and cracked it was my tought. As soon as I finish with the 2 that are cracked I will check to see if I am right about this with a new one.


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## HAuCl4

Sorry can't find my old heat transfer books for the formulas.


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## oldgeek

I was wondering how this project is coming along? Can you give us an update when you get a chance?

I was going to just "throw something together", until i saw your project. It looks so versatile I am considering going the extra miles to use your design. (as long as you don't mind!)

Thanks
Scotty


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