Life Cycle of a Stainless Steel Crucible

Discussion in 'Foundry tools and flasks' started by oldironfarmer, Mar 5, 2019.

  1. When I started casting I read that stainless steel would not hold up in aluminum service. My first few pours were in a carbon steel crucible and I didn't like the iron contamination potential so I rounded up a piece of 304 SS, 4" sch 40 (4.5" OD, 0.237" wt). Used a piece of 304 1/4" plate for the bottom. Welded with E-309. March 6, 2017.


    I used it for a year, then built my new furnace and fired it March 17, 2018. Here's the crucible that week


    I noticed the bottom was cracked when I went to replace the deteriorated ears on August 7, 2018


    I welded up the crack and replaced the ears and kept melting.

    I have 260 melts in the new furnace (I'm keeping a log now), and probably ten of them are brass and aluminum bronze in salamander crucibles. I'm sure I have well over 300 melts in this crucible. The bottom is cracked again and bowed out.


    It's been rocking on the plinth for a long time. Cleaning it out I see some deep pits inside.


    The correspond to blisters outside, and when I filled it with water five blisters started seeping.

    The 0.237" wall is generally down to 0.169"


    The spout was forged in, it's not bent.

    All in all I think the 304 SS performed very well. I also think it started deteriorating more rapidly after I started burning used motor oil, but I can't be certain. The little crucible has just been a workhorse which I have pretty much ignored for two ears.
  2. PatJ

    PatJ Silver

    I used steel crucibles made from schedule 40 pipe for several years, and they worked pretty well for aluminum all things considered.
    As I read more about how the steel and aluminum could react, I decided to switch to Morgan clay graphite crucibles, and I have been very happy with them.
    They perform well with iron and the "Salamander Super" Morgan clay graphite crucibles are ferrous-metal-rated at iron temperatures, which many crucibles are not.
    I use the same brand/model crucibles for aluminum too, and they work well with that too.

    And I did not want the wall of my steel crucibles to give out one day without warning like I have seen it do with others.

  3. DavidF

    DavidF Administrator Staff Member Banner Member

    I pulled a SS can out of a sump pump that was less than .030" thick and used it for a crucible for many years... I wish I knew what grade SS it was....
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    What percentage of full would you say you averaged for each melt?

  5. 95%, brim full. I'm melting scrap and ignoring admonishments to not remelt so regardless of what I'm pouring I fill the crucible. It has save my bacon a few times when I spill or have a breakout and still have plenty of metal in the crucible. I have made several pours at 102%, the meniscus being above the brim. Never had it break over and spill but I now realize I'm making more oxides that way. The picture above in the furnace with all the slag typically will get some clean scrap to top it off. I've developed a fetish about full crucibles that I have to fight.


    I call that full but it's hard to see, there is no rim showing inside.

    While we're talking about fetishes, here's my ingot storage, about 600# including four buckets of muffins. If there's ever an aluminum shortage I'm fixed. It's a disease, since I don't see an opportunity to melt ingots as long as there is raw scrap needing to be melted. Free fuel only adds to the disability.

    OMM and Jason like this.
  6. Me too, that would be interesting. Part of my problem is overheating using the waste oil burner. Using the propane burner was a little easier on the crucible, but regardless, 300 melts is acceptable to me for free materials.

    The Morgan crucibles are what I'm using for brass and bronze. I don't think the stainless steel is contaminating the aluminum very much. I've not worn out a Salamander yet but I read guys talking about pretty short life, like 50 melts. Is that true? I also don't want to mix crucible use between Al/Cu/Fe. I can't see an issue having trace tin in my brass.
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    Lost of variables on that one. Flux has been a real killer on crucibles from what I have seen....
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I guestimated the height of your crucible at 6". 100% brimful, that would be about 7.5 lbs/melt of aluminum. 300 melts would be 2250lb. If half of the inner surface of your crucible dissolved that would be about 12 in3 or 3.4lbs dissolved into your melt. 3.4/2250=.0015 or .15% . This means you increased the Fe content in your melts by approximately that percentage. Published data will vary but in most aluminum alloys Fe is usually listed as <.1-.2% by weight. I believe it's generally considered a contaminate and held below those levels because at greater percentages it significantly reduces strength. Cr is undesirable as well. Point being, even the minute amount of crucible loss over those melts introduced something comparable to the generally accepted threshold maximum composition level of Fe. If mechanical properties aren't important this is of no concern. If they are....

    Rotarysmp likes this.
  9. Yeah, and I don't know how to melt brass without using a flux. Although charcoal is a pretty good cover flux which I assume is benign to a crucible.

    I think most of my material loss is to the exterior. There is a lot of exterior erosion due to excessive temperatures. I don't usually clean the inside of my crucible when cold, just scrape it good and shake out loose stuff when hot. It usually has a good layer of oxides inside, and there is at least an inch of hard crap in the bottom which does not want to come out. I cleaned it good to inspect it found the deep pits, then identified them as matching the blisters on the outside. I suspect they originated from small defects in the original pipe wall. I'm doing good to get a 5# melt including crap inside the crucible. I really believe my melts are protected by not cleaning the crucible, as well as the crucible being protected.
  10. DavidF

    DavidF Administrator Staff Member Banner Member

    My crucible gave up the ghost right where the burner impinged on it...

    I never flux yellow brass, although i have thrown in a tea spoon of pure aluminum from time to time. Red brass, yea i flux that crap...
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I think that's probably wishful thinking Andy. Molten metals are solvents to other metals. Fe contamination is a well known and understood problem and why ladle liners and Boron Nitride coatings are so common to protect melts from metal tool contact.....but like I said, if material properties aren't important and the composition of source metal is unknown, it's not much to be concerned about, but that said, I don't think it's fair to state it doesn't happen or affect the melt. At 5lbs/melt (instead of 7.5lbs/melt) the contamination is higher or if you assume some loss from both the interior and exterior....maybe about the same.

  12. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    Quick side-topic: Please be careful filling up your crucible right to the top like that! It's so easy to accidentally let some slosh over the edge like that while carrying it to the mold. When a splash like that hits the ground, it sort of bursts, sending drops of molten metal everywhere, and feet can get 3rd degree burns that take 8 weeks to heal in the brief time it takes a drop or two of bronze to bounce off of shoe leather.

    I found an online video showing how this happened to one fool (who need not be named:oops:) last summer. They say a pic is worth 1000 words, but I say a video is worth 1000 pix!

  13. It's good to repeat that, Jeff. But rest assured I have remembered that video and the burns on your, err, his foot. Did the guy ever heal up or does he have a permanent disability?

    What I intend to do but have not is make a steel outer shoe to strap over my shoes when I pour.

    There may be hazards in this hobby.

    By the way, pouring from that high at the end of the video is not a bifilm friendly practice.:eek:
  14. I measured my crucible this morning, it is 6-1/4" outside and 5" inside, so an inch of hard trash inside.
  15. Jason

    Jason Gold

    OMG look at that stack of buckets and ingots.:eek: You have a problem buddy!
  16. What? Me? Who you talking to? The old crucible made two more heats today, no leaks.:confused:

    I poured three castings with the first heat and made 1-1/2 ingots, then one casting with the second heat and had three ingots loft over. So four more for the stack!:p

    So do I need more wheels to melt?


    I've got four or five more if that's not enough. I've got some of my engine parts cut up.

    Tobho Mott likes this.
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    What is your preferred way to break down the wheels?

  18. Jason

    Jason Gold

    wtf, you trying to corner the market on aluminium? You should start selling it on fleabay while the yt idiots casting swords is still a trend. Take their money!
    Tobho Mott likes this.
  19. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    The foot is fine, just a couple small scars, no pain and I can wiggle my little piggies just fine.

    Nice wheelium stash! I'm now thinking my stack melter for wheels probably isn't very bifilm friendly either...

  20. I have tried a bandsaw, plasma torch, bulk melter, portable bandsaw, and tablesaw. I think I got the tablesaw idea from MyfordBoy.

    The tablesaw works the best for me, but it is hard duty. I have a good aluminum cutting blade and wear respirator, goggles, face shield, hearing protection, jacket, and gloves. The chips go everywhere but I get a great clean cut with good control. I use it to cut up heavy structural which is too big for my crucible.

    Vertical bandsaw would wander and bind. Plasma made a mess and fouled the tip. It was fine on the rim but not in the spider area. The bulk melter was more work to sort the nuggets and each nugget is covered with a thick layer of oxide so it creates a lot of dross. Portable bandsaw works OK but mine is too small to make the cuts required.

    Haven't you heard of the aluminium shortage coming? Sell is a four letter word, I always feel degraded after I sell something so I avoid it. Plus most of it is given to me, it's really hard to sell what has been given to you. I'd rather cast a javelin than a sword.

    Thanks, I'm always on the lookout for more wheels, and think I've found five more. Four on a disabled Suburban abandoned on my property. It may have an aluminum manifold too! I gave up on my bulk melter because of all the dross. It turned out to be more labor for me than just cutting stuff up, but it is fun to watch a whole Brigg & Stratton engine disappear into the drum. I got real tired of sorting charcoal from aluminum and trying to stop picking pinhead size nuggets. But I have a nice stash of charcoal I'm using for flux.

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