Help making crucibles

[Matthew Schneider]

So this subject I've had not much luck getting any straight answers. Even called a refractory company today and they couldn't tell ne if any of their materials could be used to make them. SO I'm going to list the available refractories and hopefully someone is more knowledgeable than I to see if it's possible to make my own from any combination of what I can get not far from where I live.

 

One of the things I believe I've read the traditional(I think) crucibles we're made from is MULLITE. Ive seen bricks made from it that were the highest temp rated I've seen.

Here's the list: 

:MIZZOU PLUS DENSE CASTABLE 3000°F

:MIZZOU PLUS CASTABLE 3000°F

:GREENLITE 45L PLUS INSULATING CASTABLE

:GREENSTRIPE FIRECLAY

:KAST-O-LITE 30 PLUS 3000°

:CALCIUM ALUMINATE CEMENT

:MULCOA MULLITE GROG

:SODIUM SILICATE TYPE N 40% SOLUTION

:SUPER 32 HIGH TEMP MORTAR 3200°F

There's other ingredients at ceramics supply stores too but is it possible to make a crucible that would survive at least one melt with a combination or one of these? My knowledge of clay and ceramics isn't like my knowledge of steel and iron.

I just found 2 different kinds of clay by the river one is almost black with some streaks of what looks like rust and another that is light brown and seems to have formed in pockets in the soil. Both are very fine and moldable, should be easy to refine it further but it's pretty good as it is. Is it at all possible to add a high percentage of alumina to this to use even for one melt? I'm not expecting ones I make to last like a salamander super crucible but if I could mix something up to withstand the heat fir one melt I'd be happy.

 

I plan on experimenting but someone more knowledgeable on this pointing me in the right direction to start would be awesome.

Thanks for your time!

 

OHH all these are from:

HIGH TEMP INC. In Portland, Oregon

[Charles dP]

I think @Daniel Cauble might make his own. Maybe he’ll stop by or try sending him a PM.

[Matthew Schneider]

15 hours ago, Charles dP said:

I think @Daniel Cauble might make his own. Maybe he’ll stop by or try sending him a PM.

Yeah after posting this I actually saw that. Going to test out what I have this coming week. I'd like to make like egg sized crucibles to test out how various additions would come out in larger pucks. That and hand forging one that size is a hell of a lot easier

[Daniel Cauble]

Haha, I've never actually made any. From my understanding over the years, you can spend as much time learning to make the perfect crucible as you would spend making the steel. To me it is just too much of an added variable whilst trying to reduce thr amount of variables possible.

 

silicon carbide crucibles while expensive are a necessary cost. The assurance that it's far less likely to expel its contents so as long as you know when enough is enough with them is well worth it. The cost of making a new furnace kinda outweighs the savings jn crucibles to me. It's also easy. You buy it, you cure it and then you have a good 2 or 3 melts and can focus on the steel and not the container. So much stress already, best to reduce as much as possible 

[Jan Ysselstein]

Daniel is spot on regarding the effort i5 takes to chase the ceramics. I suggest you start with  quality crucible and make good steel....if then you think you want to play with clay go for it.

 

[Matthew Schneider]

I get that but it was made successfully by our ancestors with not nearly the ease of ability to materials we have. I'm sure our modern refractories are quite superior as well. I'm going to experiment with what I can get, just hoping to get a bit of direction from ones who have actually done it.

[MacKINNON]

I experimented with crucible for over three years. I made many a crucible that was tough, could handle thermal shock and was fine for non-ferrous materials and even cast iron. But, steel is a different ball game. Yes, I did make crucibles that could handle a wootz puck, but making a pot that can perform like a commercial clay graphite is very, very tricky. Commercial pots are very sophisticated ceramic engineering. The materials are expensive and manufacture is difficult. Most require firing is Saggers, large cover pots to stop oxidation of the graphite. This means you need access to large, high temp stoneware kilns. I did develop several recipes that could handle steel but none could handle slag penetration at steel melt temps. This means that the pots literally melt to glass at the slag line and make removing the pot tricky. The areas in contact with the steel work fine.

Edited May 17, 2021 by MacKINNON

[Jan Ysselstein]

Mathew , I would start reading about how they were made in the old days. I would also start reading about the science of ceramics. 

 

 

[Daniel Cauble]

41 minutes ago, MacKINNON said:

I experimented with crucible for over three years. I made many a crucible that was tough, could handle thermal shock and was fine for non-ferrous materials and even cast iron. But, steel is a different ball game. Yes, I did make crucibles that could handle a wootz puck, but making a pot that can perform like a commercial clay graphite is very, very tricky. Commercial pots are very sophisticated ceramic engineering. The materials are expensive and manufacture is difficult. Most require firing is Saggers, large cover pots to stop oxidation of the graphite. This means you need access to large, high temp stoneware kilns. I did develop several recipes that could handle steel but none could handle slag penetration at steel melt temps. This means that the pots literally melt to glass at the slag line and make removing the pot tricky. The areas in contact with the steel work fine.

 

In all of my commercial crucibles, the life I dictate by how thin the wall gets at the slagline. That's the failpoint If there will be one for me (I've had it give once when I added lime to the slag).

[MacKINNON]

Graphite ( plumbago) is the main 'ant-wetting' agent in standard pots. In industry, the graphite in aligned using electomagnetism before isostatic forming. With the adition of some quite 'techy' anti-oxidents , these are then fired in atmoshpere controlled kilns. I've made 'Berlin' type traditional clay graphite pots but without using a sagger you lose about 1/2 your surface graphite before the body seals. I've tried low temp, self glassing variants and they made fine non-ferrous pots but degenerated quickly at steel temps. I did make a graphite free, mullite/kyanite ( shrinkage correction) pot with a colloidal silica anti-oxidant that was so rubbery at 1200 C you could drop them and they would bounce. They handled steel pretty well as long as you weren't running basic slags and wanting to cast the contents. Of course , my main issue is P so  have to run basic slags making all my experiment pretty fruitless.

[MacKINNON]

I made a few Silicon carbide pots using a molasses and flour , carbonising binder. Could never get the things to bisque without turning into piles a asphalt in the kiln.

Edited May 17, 2021 by MacKINNON

[Matthew Schneider]

I've got mullite tomorrow, would the really high ceramic coating like 100-HT help prevent the inside being degraded at high temperature? It says specifically it for " refractory erosion due to slags and fluxes" I've got some of that coming tomorrow also. The refractory I bought also said it is one of the most resistant to slag and flux.

[Matthew Schneider]

4 hours ago, MacKINNON said:

I experimented with crucible for over three years. I made many a crucible that was tough, could handle thermal shock and was fine for non-ferrous materials and even cast iron. But, steel is a different ball game. Yes, I did make crucibles that could handle a wootz puck, but making a pot that can perform like a commercial clay graphite is very, very tricky. Commercial pots are very sophisticated ceramic engineering. The materials are expensive and manufacture is difficult. Most require firing is Saggers, large cover pots to stop oxidation of the graphite. This means you need access to large, high temp stoneware kilns. I did develop several recipes that could handle steel but none could handle slag penetration at steel melt temps. This means that the pots literally melt to glass at the slag line and make removing the pot tricky. The areas in contact with the steel work fine.

If it survives one nekt I'd be happy. Would you share your recipe?

[MacKINNON]

I'll have to find my notes from 15 years ago.

Half the issue is that pots need to be thermally transparent as well as slag resistant. If they simply insulate well, then you don't end up melting anything unless you are running induction. I've tied all sorts of glazes, washes etc. and I have found that a simple kaolin/alumina wash will increase the life of pots if used on the inside.

[Daniel Cauble]

6 hours ago, MacKINNON said:

I'll have to find my notes from 15 years ago.

Half the issue is that pots need to be thermally transparent as well as slag resistant. If they simply insulate well, then you don't end up melting anything unless you are running induction. I've tied all sorts of glazes, washes etc. and I have found that a simple kaolin/alumina wash will increase the life of pots if used on the inside.

I just recently did a lot of different mixes and tries with lining the insides to utter failure. Like super kiln washes using Zircopax and Gum. No bueno.

[Alan Longmire]

You could ask the folks at ITC.  Their ITC-148 and ITC-213 sounds promising for lining crucibles.  https://www.itccoatings.com/our-product

 

[MacKINNON]

6 hours ago, Daniel Cauble said:

I just recently did a lot of different mixes and tries with lining the insides to utter failure. Like super kiln washes using Zircopax and Gum. No bueno.

I did similarly with little good effect. Most often the wash simply puts more of the pot into solution at high temps. I tried ITC Turdish liner in the early days and found that it handled slags OK but impacted thermal transfer to he charge so badly as to make the whole exercise pointless. These lining are used on pots used to transfer molten iron and steel, not for melting in a standard crucible fire. As I said previously, there are many things that will handle molten steel slags but they tend to be highly insulatory, making melting in a small crucible furnace very difficult.

[Matthew Schneider]

On 5/18/2021 at 7:06 AM, Alan Longmire said:

You could ask the folks at ITC.  Their ITC-148 and ITC-213 sounds promising for lining crucibles.  https://www.itccoatings.com/our-product

 

I've got  100-HT coming via usps, delay delay delay. They used to be so dang reliable but 3 day priority mail is now at least a week...lame. 

I mixed up a few things and gave it a coat of something else. Going to test it later.

I've heard the kaoline is working well several times now, it's cheap too. I'll probably give it a try with high alumina. I'll talk to some potters as well, maybe visit the ceramics teacher and pick his brain. Our ancestors made reliable crucibles, I know we can too

[Alan Longmire]

I think MacKinnon has effectively shot down the ITC route with his experience.  You definitely don't want ITC-100 in a crucible, it's not designed for that. 

 

I don't have much crucible experience, and all of that is with factory ones.  You may want to look at Vince Gingery's book on crucibles (https://usaknifemaker.com/book-making-crucibles-by-vincent-r-gingery.html), and check with the various backyard casting forums.  Vince and his dad Dave also have a book on a gas-fired crucible furnace, including making the blower, in which the top half of the furnace lifts off the base to let you grab the crucible.  They were not doing wootz, though, they were doing iron, bronze, and aluminum.  As has been pointed out, it's the basic (as in the opposite of acidic, not simple) slags that make steel casting so much more difficult than the other metals.  You have to have that basic chemistry to keep the steel steel, and the slag eats ordinary clay like borax eats pressed kaowool board.  

[MacKINNON]

Giving you a simple recipe isn't that easy. I was not making wootz but was trying to make large, first stage direct reduction pots, similar to the process described by Needham as in use in Shanxia, China in the 19th century.

First, I talked with potters. After numerous clay trials I gave up on potters as being particularly useless and began reading patents. I followed them back through 'patents reference by' until I arrived at formulas I understood. Then I moved forward in the patent search trying out new formulas and recipes. Once I had a reasonable handle on the technology. I was able to talk with Ceramic Enginners without them putting the phone down on me in disgust. They really are very, very knowledgeable people who don't suffer fools gladly. The phrase, 'You're not even wrong' is a fond memory.

As you can see but the pictures of my trial notes, I tried all sorts of patents and variants.  Outside of very sophisticated ingredients and manufacturing methods I found four, basic starting points.

Tradtional clay graphites, like Berlin pots.
Prof. Vasily's bulat pot recipes amd my variants
My own shrinkage adjusted, clay graphite pots. And,
a TiO2/ clay, silicon-carbide recipe I based on a patent for 'Self healing' crucibles.

I tried a lot of different things. I tried powdered aluminium addition to create 'Exothermic, internal drying' of clay bodies. I tried borax addition to create 'self glazing' pots and colloidal silica additions to prevent graphite oxidation ( OK for low temps but at steel ranges the whole pot just went into solution ).
Almost all of the carbon/clay pots will work for standard uses. Flake graphite is what you need and that posed my biggest problem, because of where I am. I was forced to use graphite furnace charge , made from ground electric furnace eletrodes or substitute with graphetised coke. Those I made with good grade graphite flake worked fine but were uneconomical to make.

Shrinkage reduction pots.
I won't go into detail here but clays shrink when they are fired. They shrink at known rates. Kyanite expands as it converts to mullite. It converts at the same temperatures as clay contracts. Hence, you can add kyanite in amounts to ballance this shrinkage making your pots ( in theory) more easier to fire and less susceptible to thermal shock

 

Standard 'Berlin' crucible recipe
fire clay     40%
Graphite    20%
Powdered coke    25%
Grog         15% ( traditonally ground broken crucibles)
I took these % by weight
A 9kg bre would be 3600gm Fire clay, 1800 gm     graphite, 2250 gm powdered coke, 1350 gm #200 grog.

My shrinkage adjusted Berlin
Fire or 'Ball' clay     22%
Kyanite            42%
Grog            20%
Graphite        16%

 

Prfessor Vasily's bulat pot recipe follows a 7.3,1 ( or 2) ratio
7 parts volume Flint clay ( I used chamotte or 'flint grog. This isn't a clay but a hard, fired material)
3 part fire clay
1-2 parts grahite.
This is quite a tricky brew to mold as my chamotte was a a bit coarse. It would probably do well in a rammed mold. If you could find a finer chamotte, this recipe would be worth a second look for small, round wootz pots.
I made a variant that was shrinkage adjusted and used a finer, flint grog. It was much finer in texture and  really quite tough for 'one off' use.
firedc clay     25%
Graphite    6%
Kyanite        47.5%
Mulite        9.5%    
#200 flint grog    15%

 

A brew that was quite promising in A8 size, rammed pots.
This has a TiO2 addition  to create a 'self repairing' crucible as per the patent. A similar patent included 5% metallic aluminium powder. Once made into a wet clay, the water/aluminium reaction is claimed to dry the pots from the inside and result in Al2O3 additions.  I made about 9 variants of this and had to pack up my whole shop and move it before all the trials were done. I did several recipes with alumina additions, but both the alumina and the metallic aluminium didn't seem to make any positive difference to this basic TiO2 recipe. For the test pot , I replaced graphite with graphitized coke, simply because I couldn't afford more graphite. It handled a 2kg cast iron melt but did show scouring at the slag zone. It was also very thermally transparent ( probably because of a porous structure caused by the coke loss) and the iron melted in a record time for my setup. I would definitely try this one again with flake graphite in a rammed mold.

Fire Clay /ball clay    35%
Graphite/G coke    45%
silican Carbude #200    17%
TiO2            3%

 

Glazes
I tried a lot of different 'washes' to try to prevent carbon loss during bisque firing. One turned out fine for high temp pots.
Sil. Carbide powder (fine)    164 gm
Kaolin                36 gm
TiO2                20 gm
Al2O3                20 gm
Silica flour            20 gm
Water to form slurry. Painted on bisque fired pots, dried and furnace fired under use to stoneware + temps. I did some with a anhydrous borax addition and these produced the nice, chocolate colour you fine on commercial Borosilicate i.e. clay graphite pots. Fine for non ferous but degraded badly at steel temps.

 

A simple borax glaze brew I developed for non ferrous pots,
2 heaped teasoons of Kaolin
1 teasoon anhydrous borax powder
4-5 teasoons silicon carbide powder ( 1200#)

I did make several non-graphite pots which worked well at low temps but grapite is the main 'ant-wetting' agent in clay pots that stops slag errosion at iron and steel temperatures.

I'll post a few picture of my notes so you can get some idea of the volume of trials I did between 2004 and 2008. In the end, I decided to bypass crucible refining and allotted to make a small, tilting open hearth furnace for the Basic process. These note are only a fraction of those made over the four years. It might be a quick read but it cost me a lot in time and resources when just putting food on the table was a struggle.

 

Edited May 20, 2021 by MacKINNON

[MacKINNON]

Pots are serious business, and I don't even like clay ;-)

[Alan Longmire]

That is excellent information, sir.  Thank you for sharing that hard-earned knowledge. It is much appreciated.

[Jan Ysselstein]

Mac.  That is a tremendous amount of work and information you have given to a person you have never met.Thank you very much.

[Matthew Schneider]

WOW!! That's pretty damg awesome of you! 

What is graphatized coke though? 

It's a shame we don't have the recipe for the crucibles they used to produce hundreds of thousands of pucks 1000 years ago. My guess is their knowledge of ceramics isn't what it is now involving complex chemical interactions. They found a mix that worked and produced huge amounts of the sterl with it.

Thank you fir sharing McKinnon!!

[Alan Longmire]

Matthew, from what we can tell at sites that produced crucible steel in the old days, the old crucibles were mostly one-shot deals. If they lasted long enough to produce a single good puck that was enough, then they were crushed and used again.  I suspect a lot of the very early development (WAY pre-iron age) of metal casting was luck, in the same way as when the Navaho started casting silver in the 1700s they discovered that old pottery shards from one abandoned pueblo in Canyon de Chelly made decent, if small, crucibles.  Not that the wootz producers were using old potsherds necessarily, but the history of technical ceramics in the old world is quite impressive.  Starting in the chalcolithic age and going into the bronze age, a technical elite figured out what worked over hundreds of years, and they did not share their secrets outside their guilds or tribes.  Archaeologists still don't know how they made some of their crucibles, and bronze isn't nearly as hard on things as iron, much less steel.  Just because they didn't use the modern terminology doesn't mean they didn't know exactly what they were doing.