"Cheap as chips".....homemade crucibles.....the story so far....

Discussion in 'Foundry tools and flasks' started by Jimmy Cogg, Oct 12, 2018.

  1. Jimmy Cogg

    Jimmy Cogg Silver

    Here is how I make my home made crucibles. Capacity one litre of metal. Looking to make a bigger one......looking for a suitable pattern/mold......(plant pot????)

    Once properly fired, they are very strong. I retire them early after 3/4 pourings as I am new to this, and am still experimenting. All the retirees have been good. I am going to push this next batch a bit further. I have been very surprised how strong and resilient they are. I have tested a few with a hammer!!!! They ring like a bell once struck and seem to get stronger with each firing. But unglazed (as mine are) they are very rough and the slag sticks very well to the surface of the crucibles.



    I have found that the retired crucibles make great supports for ceramic shells. The shells I have made I just put in the furnace inside a retired crucible. Fire the shell in the retired crucible and remove it in the crucible....it remains very hot due to the thermal mass of the retired crucible and is also in quite a stable position for pouring into.....a win/win situation :-D
     
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Looks good, but yes you really need to endurance test them for longevity.
    I have concerns with the crucible being flexed when pulled from the mold in it's green? state developing cracks later on. Don't know if it is an issue or not, but maybe?
     
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  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks video Jimmy. I've been waiting for this one.

    1. Why do you retire them after only 3-4 pours?
    2. What is your initial drying cabinet? Just low warmth and air flow?
    3. Have you ever considered adding graphite or SiC to improve thermal conductivity. I have heard of people using abrasive blasting media for SiC.
    4. What are the typical glazes? The A10 I just cracked lost it's glaze but over many, many, melts. You are correct, it was much easier to clean while the glaze was in tact. I wonder if it could be re-glazed mid life?

    Best,
    Kelly
     
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  4. I can't see it here in Australia for some reason..... "Video unavailable" . My Chinese made crucible was bought as "30% Silicon Carbide" and arrived with a pencil graphite finish that burned away quickly, however if you file it to give it a tiny pouring spout you can see silicon carbide grains sparkling amongst the graphite clay mix.
     
    Last edited: Oct 15, 2018
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    He had music playing in background. Maybe the copyright thing?

    Best,
    Kelly
     
  6. That would explain it!

    Update: it's playing from Youtube now which it didn't do earlier. I reckon a vibrator might help the packing of that crucible mould.
     
    Last edited: Oct 15, 2018
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  7. Tobho Mott

    Tobho Mott Gold Banner Member

    That is really cool. Like Kelly, I also find myself wondering how well it might work out if you added graphite to help the heat conduct through. Homemade crucibles aren't something I've ever really felt the urge to try making, but i must say this makes it seem a not too unreasonable prospect!

    Jeff
     
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  8. Jimmy Cogg

    Jimmy Cogg Silver

    They will always develop cracks, the heating cooling cycle will do that. If unglazed they are rough and slightly porous too and you get surface damage. That is why I believe it is important to examine any crucible prior to use, for cracking etc. When good, if you tap them, they ring like a bell or a china teacup. If I make one, and am not happy with it, (they are quick to make) I will not use it. I am quite cautious.
     
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  9. Jimmy Cogg

    Jimmy Cogg Silver


    Hi Kelly,
    I will reply using your numbering.
    1. I am very new to this and am feeling my way with regard to the materials and what they will stand. I don't particularly want them breaking on me with a charge of hot metal at a dangerous point or critical manoeuver. They've all degenerated slightly after three or four heating and cooling cycles ie uses (not pours) but have been retired in decent condition. I've "tested" them with a hammer to see what sort of use and abuse they would take after this and was surprised at the toughness. I will give this batch a bit longer use and see how much longer I can use them.
    2. My first crucibles I kept warm in a domestic airing cupboard in the house, drying them out for days. I watched the colour changes of the clay. That worked ok (this is just a cupboard with a domestic hot water cylinder in, in the house). The drying cabinet I've used in the video is a new thing I have made out of a greenhouse air blower piped into the bottom of a box. It is just ambient temperature air flow. Something new I am trying out. I'm also using it to dry my ceramic shells once dipped and stuccoed.
    3. Yes I think that would be a good idea. Graphite looks messy though. That said I have altered the recipe slightly this time, I've added some very fine powdered silica and put a dash of sodium silicate in the water to help the damp "fluidity" of the clay/grog/ silica mix and hopefully aid initial set of the green crucible. It might be a good idea giving the crucible a graphite coating at least inside before each days use. I think I'll get some.
    4. Glazing is something new and that I have not done yet. I've just been excited at making crucibles that work. That is one of my next adaptions and alterations. I have a friend who is a potter. I will ask about the reglazing second time around, but I don't whether it can be done. The glaze is fired and fuses onto the fired clay body. With regard to glazes one that has stuck in my mind is powdered glass, clay and borax. That is what I will try.

    The ideas are not mine I purchased a book called "Making Crucibles" by Vince Gingery.

    Cheers.

    Jim
     
  10. Jimmy Cogg

    Jimmy Cogg Silver


    Yes I agree a vibrator would be a good idea, and make for even faster production with more consistent compaction. I saw someone had a video with a reciprocating saw they adapted with a rod as a vibrator. I thought that was a great idea. I think it was Tobho Mott....I shall be trying that one!
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    A few years ago I considered making my own crucibles and found this fella.



    It's a bit technical and a heck of a mess but quite few views. I decided I had enough other things to build and figured I was better off buying the crucible(s). I just paid $77 delivered to my door for a new Morgan Salamander Super A10. I had somewhere between 100-150 heats on mine before I broke it. No telling how many heats I might have been able to achieve, but aluminum duty is a fairly easy life for such a crucible. That's ~50c-77cents/melt. As the crucible size increases, I'd probably become less inclined to make them.

    You on the other hand are doing so with success and I say all the power to you. It's probably pretty hard to say how thermally conductive they are and how melt times would compare to a commercial crucible but as long as you are satisfied with the results......that's what counts.

    Keep posting !

    Best,
    Kelly
     
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  12. Jimmy Cogg

    Jimmy Cogg Silver

    Yes, me too I watched that. An interesting video but too difficult for me, and messy, and I agree defeats the object, if you can purchase at that price with 100 to 150 duty cycle....that is awesome.

    I'm not sure thermal conductivity is an issue with the crucible. They get hot like a fire brick just like the refractory walls and are a thermal store. Once up to temperature and hot they just do the job which is to hold the metal at the temperatures we are taking it to without melting/breaking. I think the graphite is there to improve the reliability and longevity of the crucible, and to improve the supporting of sudden changes of temperature without cracking. The graphites are far superior to the clay/grogs but require a more demanding process to create them, outside the scope of what I want to do. For me, something a bit more throwaway but easily achievable and cheap like the clay grogs is the better way to go, and I don't care if I ruin it or break it, and it is just for my hobby :-D

    I'm happy with them for aluminium and brass. If it was for iron, which would be a big, big leap for me, I would have second thoughts and would probably plump for a commercial crucible, unless I can devise something where I could lift and pour the crucible a little more remotely and put me at a little more distance from the melt.

    Regards.

    Jim
     
  13. Tobho Mott

    Tobho Mott Gold Banner Member

    All true, but I never used it on video. Maybe it was Myfordboy's sander-vibrator you saw? He's the one I got that great idea from.

    Jeff
     
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  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Folks here know I am a staunch advocate of vibratory placement of refractory mixes. It fluidizes those mixes and makes them easily flow into complex molds, I have a couple videos and examples of such. I was under the impression it does not work well for plastic materials like clay. Is your fireclay mixture more plastic like modeling clay or a dry suspended mix like refractory?

    Best,
    Kelly
     
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  15. DavidF

    DavidF Administrator Staff Member Banner Member

    I wonder if you could make up a clay, graphite, grog slip that could be vibrated?
    Like how ceramic slip casting is done...
     
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Dunno. If you search Crafting Morgan Crucibles on YouTube, I found the overview to be pretty humbling when it comes to making your own crucibles. I have some limited knowledge but chemistry isn't really my field. They talk about green state binders like ceramic, clay, and tar bonded and those convert to other states upon being fired. They infuse various elements during curing process and shortly after that I start chanting I'm not worthy. I applaud Jimmy for his success but if I can buy good molten metal handling for 50c/heat, I'm moving onto bugging out my casting processes and focusing my energy on making good castings.

    Best,
    Kelly
     
  17. Jimmy Cogg

    Jimmy Cogg Silver

    No it was definitely a reciprocating saw with a rod. I'm sure they said that they'd ground or cut the end of the rod like the top of a saw blade and it fitted in the reciprocating saw very well.
     
  18. Jimmy Cogg

    Jimmy Cogg Silver

    No the idea is make the mix dry. But there is a small amount of water to make the clay bind/ stick the particles together, so that there is a set product. In the book I have they advocated well compacting the grog/ clay rather than a slurry pouring or molded clay product. Less water is more. The problem is that clay is moldable and sticky but is prone to cracking/ shrinking. Whereas the grog, being already burnt, refractory and fired is more relatively stable to thermal shock.
     
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That commentary applies for placing castable refractory, concrete, slips etc. I only ask because when you demolded the crucible in the video after ramming it looked very plastic. Castable refractory wouldn't be that pliable. If you get the itch, I'd like to see what vibration would do for your process. With the mass of your concrete mold you'd need to provide a reasonable level of energy. I use pneumatic turbines but an eccentric on a small motor works well too. Suspending it on a spring table would help a lot. This method is really common in brick making and statuary. I do that for my large refractory casts. Here's a couple examples but if you use the search function with "vibration" and me as the user you'll get a lot of hits, and if you're really ambitious, tool around in my original furnace build link in my signature.

    http://forums.thehomefoundry.org/index.php?threads/furnace-fail-reconstruction.209/page-2#post-3383
    http://forums.thehomefoundry.org/index.php?threads/degassing-lance.204/page-2#post-3870

    The other advantage of using vibe to pack media is the molds don't need to be very strong. For simple one time use parts I use foam. Of course, I use vibe extensively for packing loose foam molds too.

    50 Vent Insert.jpg
    Crucible Cap.jpg

    Best,
    Kelly
     
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  20. Tobho Mott

    Tobho Mott Gold Banner Member

    Definitely me, but definitely not on video. Maybe someone else did the same and I just haven't seen yet.

    Anyhow, one thing I did not know at the time is that there can be too much vibration. I had drops of water flying off the top edge of my hot face even though the mix was so stiff and dry I had had a lot of trouble stirring it, and I just kept going with the vibe for a while even after that... Well, the furnace hasn't fallen apart yet so I guess maybe I'm lucky.

    Jeff
     
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