Crucible Failure

Discussion in 'General foundry chat' started by Petee716, May 31, 2020.

  1. OMM

    OMM Silver

    If you really remove small spillage from refractory.... I have done this successfully. With a Oxy-acetylene torch warm up the refractory locally, then add some sand and, just blow it up onto the sand.

    Just be careful. Warming up locally can cause small cracks.

    This can also be done by adding silica sand to the bottom of your furnace and then getting it up to temperature and scraping for a more easily removed pile. Even adding a small amount of table salt to the sand and pouring it on will roll it. Don't get crazy with the table salt. It melts at about 700°C. It is just a small pick up for the dusty sponge.
     
    Last edited: Jun 8, 2020
  2. Petee716

    Petee716 Gold Banner Member

    That's funny, Fellas. For the 15 years we've been together my sweetheart and I have had a running joke about my habit of burning shiite. "Whatcha going to do today?" "Oh, cut the grass, fix the fence, burn some shit, ..." I'd have my fire pit going 24/7 if I could. She was totally unsurprised when I took up this hobby with my charcoal making, stack melting, furnace/burner development. In fact, nothing personal, but she refers to you guys as my "burnin shit" club.lol.
    I think the fact that I can train the torch (harbor freight weed burner) locally will allow me some ability to reach into the furnace as well, at least to some extent. Because most of the offending metal is right at or under the target area of my bore I may be able to just place the burner into the tuyere. Since it will be naturally aspirated the lack of forced air should allow that area to get hot enough.

    Pete
     
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  3. FishbonzWV

    FishbonzWV Silver Banner Member

    I noticed my comment about the steel plate went over like a lead balloon.
    When you're running your furnace the floor is the coldest part because heat rises. As it rises it draws cooler air in through the drain hole and that's why it solidifies in the drain. That plate will absorb the heat and then it radiates that heat at the floor keeping the hole open. It also radiates 360 degrees around the base giving you a consistent heat instead of a hot spot at the wall where the flame hits.
    It does take a significant chunk of steel though.
     
  4. Peedee

    Peedee Silver

    I can't even get the damn coals on the BBQ to light at the moment (Crap briquettes) My Wife of 25 years tomorrow! wasn't at all surprised by a request for her nail polish remover to soak a rag with.
     
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  5. Petee716

    Petee716 Gold Banner Member

    On the contary. I did consider it in the current context. I just didn't have a useful comment. One of the actions I took while the furnace was laying on its side that fateful day was to reopen the drain hole back up with hammer and chisel from the bottom. There was no flame coming out at that time. When I ran the furnace in the upright position on sunday there was so much flame coming out of the drain hole that I feared my pant cuffs might start on fire. So under those circumstances although the floor region itself may be cooler, the drain hole was certainly quite hot. With the current plan to try using naturally aspirated propane the steel plate idea may very well come into play.

    Pete
     
  6. Jason

    Jason Gold

    Hit the "like" button for renaming the forum to "The burnin' shit club" :D:D:D
     
  7. Peedee

    Peedee Silver

    Acetone smoked piri-piri pork kebabas anyone?

    Does anyone remember a thread where a guy was flipping ceramic shells with a weird gating system, fill the cup with bronze, grab the shell and flip? Seemed like madness, not entirely OT but my mind was wandering and I thought about elasticity in different crucible compositions and how we handle them. More importantly deformation from gripping and then cooling to a deformed state. Hope this isn't derailing too much.

    EDIT: I guess what I'm asking is has anyone experienced a crucible go out of round or deformed.
     
  8. Jason

    Jason Gold

    Yeah, That was the guy living in France. They were small pieces. He was a wealth of information, wish he'd come back. Artospy I think. Very talented.
     
  9. Petee716

    Petee716 Gold Banner Member

    I've never had one go out of round but I've been told that they'll fold up pretty easily if their squeezed.

    On Sunday I fired the furnace as I mentioned in post 30. Prior to firing I put 2 scoops of sand in the bottom of the furnace to hopefully provide a medium to catch the bronze for easy removal since the bottom was basically a moonscape and chances of the molten metal making it to the drain hole was unlikely. This strategy was a mistake. The bronze ran down to the bottom alright but the sandstorm created a bronze/glass/sand mixture that simply doesn't flow. I didn't discover that until after yesterday's burn. This time (yesterday, Tuesday) since all of the metal was at the bottom I had high hopes of getting the bottom hot enough to flow to the hole by utilizing the strategies suggested above. So here's what I did.

    -4"x4" steel plate (1/4" HRS) tapped and threaded with three 1/4-20 bolts for feet, placed over drain hole.

    - 5" high pedestal placed on steel plate with a 1" thick X 8" diameter refractory disk per discussions with Mark. (My bore is 10").

    - propane weed burner inserted into tuyere and aimed at worst built-up area. (No one ever told me the propane bottle would float! I had to tie it down! PITA).

    The area under the disk around the entire bore got red hot almost immediately. I knew that local heating wasn't going to be enough to melt the metal without giving the refractor time to heat up, so I was patient. With the weed burner really roaring I found that I had to keep my lid at least half way open or the furnace would cool right down and go dark. So I ran like that for 40 minutes or so till the tank ran out. Still no shiney. Although it was obviously very hot below the 8" disk, the disk was not red hot all the way through.
    I had the oil burner all ready to go so I pulled the weed burner and turned on the oil. I started with very little oil and very little blower but a bit more atomizing air than normal. I also covered my (4") exhaust hole approximately 50% with a firebrick. I swear to God the entire interior of that furnace was yellow inside of 10 minutes. I ran it that way for 1/2 hour and shut it down.
    There had been absolutely no movement of the material in the bottom of the furnace. Remember the effect of the loose sand on the metal mentioned above. With my best protective casting gloves on I used a rod and was able to roll a substantial glob and delaminated about one third of the residue from off the floor. I figured it to be about 3 or 4 lbs of bronze. It was actually about 8oz and on cooling had the weight and texture of deep fried pork rinds. You know the shit they sell in snack bags. It crushed just as easily. So in spite of my best efforts I had just been milking a mouse- a whole lot of effort with very little to show for it.
    Solution: 30 minutes with an air chisel. Problem solved, next topic please.

    image.jpeg image.jpeg image.jpeg image.jpeg

    While chipping out the floor I stuck my shopvac into the tuyere to keep the dust down and allow for pretty good visibility. Of course the furnace was cold and I wore my respirator. Pictures show the tools used to replace the floor with blu-ram as well as the disk and new pedestal also made of blu-ram. I needed a 1-1/8" dowel for the drain hole but I was able to use one salvaged from my pedestal form so my broom handle was saved from further indignity. I used a piece of scrap bronze runner from a previous casting to press channels into the floor.

    So, I'm back as good as new again. Well almost. The localized heating around the exhaust from covering it with a brick has destroyed the sheetmetal cover. There's raw kaowool under there so it'll need attention. But other than that I'll have some new adventures with the 8" disk in the bore. More to come on that I'm sure. Plus I've learned quite a bit along the way thanks to you guys. Great input, and thank you all. But here's probably the most important takeaway:

    image.jpeg


    Pete
     
  10. Jason

    Jason Gold

    Good Job Pete, I still think we should rename the forum.;)
     
  11. Mister ED

    Mister ED Silver

    Hey now ... I love that shit!!!
     
  12. Sounds like some interesting results with the oil, might be time to come up with a fancy name for the disc-on-plinth precombustion chamber like the "Burnin shit burner":oops::rolleyes:.
     
    Last edited: Jun 11, 2020
    Jason likes this.
  13. OMM

    OMM Silver

    Pete, I'm glad things worked out somewhat OK.

    Before you tie up that trash pail, it would be Nice if you did a little walk around where the crucible failed and if you always placed the crucible in in the same way, did the fail result because of impingement of flame of the burner. Take a hammer to it and analyze with lots of pictures of cross-sections, especially around areas where it failed.
     
  14. Petee716

    Petee716 Gold Banner Member

    Oh, that's not the one that failed. The one in the picture is one that was in current service. That crackled surface is a sign of bad things to come, so out it goes. I know now that that is considered to be damaged. That damage is consistent around the outside of whole crucible and resulted from high heat during an iron melt. I place my crucibles randomly and my plinths hold them above impingement so it's not a direct flame damage issue. I did look the broken one over pretty thoroughly at the time by breaking it up all over and found that the graphite was completely depleted from the top down to about 2" inches all around which is where it split. It had cracked vertically from the top down. The graphite then increased gradually toward the bottom. The actual bottom cross section still had full graphite thickness. That, leads me to believe that the issue is oxidation, mainly up high. As part of a number of discussions with others, I believe my furnace is a lot hotter and quite probably more oxidizing up high. That's why I'm pursuing changes in the furnace dynamics e.g. the "burnin shit disk". One of the basic facts here though is that I've been pretty much using the cheapest crucibles available so a better quality one may render the oxidation damage aspect moot, but the temperature differential within the bore is still one worth pursuing.

    Pete
     
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  15. Silicon carbide crucibles will go soft and deformable while heated when close/past their lifetime. I do mean really thin, like 7mm-5/16" thick wall.
     
  16. HT1

    HT1 Gold Banner Member

    what size crucible have you ran down to 5/16 wall thickness??? in an A10 or bigger, that is just insanely dangerous ... , the Navy recommends replacing an A10 crucible at 5/8 wall thickness my A16 brand new are about 1 inch wall thickness and I get real nervious at 3/4


    V/r HT1
     
  17. It was an emergency job and the crucible suppliers were all out of stock in this country.... an A20 half full of bronze. It worked but I'm never going to do that again, after seeing the crucible wall above the metal level move like it was soft. It was that thin at the lip of the crucible but thicker further down.
     

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