Failure and success.

Discussion in 'Sand Casting' started by Ironsides, Oct 15, 2017.

  1. Ironsides

    Ironsides Silver

    Hi everyone.

    I just uploaded another video.

    As I melt a lot of cast iron I can judge by eye if the iron is hot enough to pour. Silicon bronze is something I don’t melt a lot of so I misjudged how cold it was. The result was six out of nine castings did not fill up the molds.

    The camera captures every success and failure. The camera also captured some interesting footage. On youtube there are so many silly videos about melting copper but one video caught my attention. In his opening comments he said that crucible tongs needed to be preheated so it will not crack the crucible when lifting it out of the furnace.

    Have a look at my video at 14.10, it shows the crucible tongs have cooled the crucible where it grips it. You would think that stresses would build up in that spot and induce cracks in the crucible wall. As you can see in the video the crucible survived and I will use that crucible until it is too thin to use. So what does everyone here think, would you reuse that crucible after seeing that footage?

     
    _Jason and Melterskelter like this.
  2. I recently saw a well used silicon carbide crucible get discarded as during the last use it was soft enough for the top lip to be pushed in a bit. In other words at molten bronze temperatures the thin crucible wall was flexible. This leads me to think that the material is less likely to crack when orange hot but there still needs to be enough crucible thickness to support the weight and mechanical loads involved. The A20 crucible with a wall thickness of around 8mm was right on the limits even though it was only half full. I've been told steel crucible gripper we use, loses strength when hot as it gets soft, so it gets used quickly.

    I do like seeing the 1960's vintage Hoover hovercraft vacuum cleaner used for a blower.

    Edit: When I help Peter with the bronze castings, it's always poured as fast as possible with a continuous stream of molten bronze and sometimes with a bit of spillage if we can't ease up in time. Having a larger A20 crucible than your smaller one has got to help reduce heat loss too.
     
    Last edited: Oct 16, 2017
  3. PatJ

    PatJ Silver

    The cooling of the crucible where the tongs gripped it seems to be surface cooling only, and while the surface is dark, it is still plenty hot.
    I think that is well within the range of what a crucible can handle, and indeed, all the crucibles I have ever seen that were lifted experienced the same thing.
    There is so much mis-information on YT these days; I cringe when I watch much of it.

    I think problems occur when the temperature change it too rapid, similar to heating a pyrex dish in the oven to 400 degrees, and then either very slowly pouring a tiny stream of cool water over it, or suddenly pouring a lot of cool water on it.
    Too much shock and pyrex will shatter, and too much shock on a crucible and over time it will create fractures that will cause it to prematurely fail.

    Quality crucibles are pretty durable.
    I think the main thing is don't jam them when first loading them with metal, else the metal will expand and crack the crucible.

    Nice castings; I like those hooks.
     
  4. Tobho Mott

    Tobho Mott Gold Banner Member

    Hooks failing to fill... Sounds familiar, lol. I'll have to try the dogs and light switch cover again, but with separate sprues for each... Great video, thanks.

    Jeff
     
  5. Petee716

    Petee716 Gold Banner Member

    I always check for a "ring" in the crucible and for any physical damage before I use it. That's really the only way I'd know. I've never seen anyone preheat their tongs as a regular practice and don't know of the youtube poster you mentioned. Maybe his thinking is intuitive as opposed to experiential. I saw you quench a crucible before. Did you use that one again successfully?
    Thanks for the molding demonstration. I notice you don't ram very hard yet your flasks don't drop out and your sand performs well while cutting your gating, trimming to the parting line, etc. It looks like petrobond in the video.
    I liked the use of the nut and bolt as a jack in the machining setup. I'm self taught and have minimal experience. I find stable setups to be a real challenge sometimes. This will help.

    Pete
     
  6. cactusdreams

    cactusdreams Copper Banner Member

    It's useful to share what doesn't work as well as what does. Maybe more so. I get the same dark spots on the crucible where the tongs touch but don't worry about it. As Pat mentioned, I think its only on the surface and ambient light effects how it looks a lot. I'm more curious about those weight plates with the triple hole on your molds in the first pour. Are they purpose built?
     
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The Morgan Data Sheet suggests charging the crucible at elevated temperature. In the area of the data sheet that discusses initial tempering of the crucible they suggest this is to minimize the temperature gradient across the crucible wall. In that section they reference an increasing range of pre-heating temperatures in reference to tempering of a new crucible, the highest of which is 1650F. This figure varies by the product line of crucible.

    I surmise this recommendation ignores the possibility of the ingot stock being preheated. My first charge is cold and hot from thereafter. I'm only melting aluminum at furnace temps of a couple thousand degrees F......not too taxing. I have somewhere in the range of 50-60 melts on my A10 and other than appearing dark grey rather than pitch black, it looks like the day I bought it.

    Here's the Morgan excerpt.

    SALAMANDER SUPER Crucibles

    CHARGING

    As soon as the crucible has reached the specified pre-heat temperature, charge and melt immediately. Charge light scrap and returns first in order to form a cushion for heavier material. Use tongs to charge ingots and place large pieces and ingots vertically allowing space for expansion. Only add flux once the metal is molten.

    Best,
    Kelly
     
  8. Ironsides

    Ironsides Silver

    Pete

    All of those crucibles that I have quenched in water have lasted for years. As pat mentioned a good crucible will last a long time. Yes you are right I do not mold very hard and the mold does not fall out. It is petrobond sand. When I tried to drill all the holes the casting kept slipping in the vice so the bolt and nut serves as an adjustable jack and support.

    cactus

    The weight plates are used in every foundry around the world so I made a pattern and cast many copies in iron. A quickie way of making them is to get a flywheel of a car engine. It has only one hole but serves the purpose.

    Kelly

    When I melt cast iron the top of the crucible glows a red color at the beginning of a melt and the bottom is still black. The bottom is the last place to get to melting temperature and yet I have never had a crucible fail because of a lack of preheating it.

    Ewasteben is the youtube channel where he says to preheat the crucible tongs. It is so silly because he uses a butane torch for 3-5 seconds but the temp difference between the crucible and tongs is so great it is not going to make any difference.
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That's another good point from cold start with the crucible sitting on/in contact with the plinth. For me, with aluminum and a resistive electric furnace that I set to 2000F, my entire use schedule is akin to the Morgan preheat process so why bother? It takes about 25 minutes from cold start to melt a full A10 and 15-20min once the furnace is at temp. I'd imagine both the ramp and ultimate temps compared to high energy fuel burners are at least 50% higher temps and half the time. The time to melt is not at all objectionable for me because first thing I do is charge the furnace and then walk away from it and ready the mold and pour, and it gives me very good melt temp control.

    That is pretty silly. Pretty much same thoughts as above. With a lift off furnace I snatch and pour with an open ring shank so the crucible is never out of the furnace for more than a couple minutes. I've never given crucible stress from tool contact a second thought. I guess my whole point is considering your use at iron temps and how well the crucibles manage that type of service, I wouldn't think crucible stresses would be much of a concern other than direct flame impingement.

    I do enjoy your posts and videos. Someday I'll need an iron part and when that day comes, I do have a fuel fired furnace and it'll be time to step up. Until then I'll save the wear and tear and enjoy my equipment.

    Best,
    Kelly
     
  10. _Jason

    _Jason Silver

    I finally got round to watching your video last night. I cannot add anything constructive to the conversation but I did appreciate your thoughts on the original die-cast castings' quality. :D I also liked the bonus footage at the end, as well. It reminded me why I have always lit my propane grill from the bottom and as quickly after the burner was cracked open as possible.
     
  11. Tobho Mott

    Tobho Mott Gold Banner Member

    I am actually really glad the cheap die cast hooks have that weak point, that way I don't still have one stuck in my skull from when my daughter threw a fit and slammed her bedroom door in my face last year at age 8; it just broke off its base and fell to the floor while I writhed there beside it moaning in pain and holding my bleeding scalp.

    She lost the door off her room for a couple days for that. Hasn't slammed a door since. She didn't get a new hook. But if she ever does, it'll be one of those cheapo new weak ones again before it'll be a nice strong one like Ironsides cast, that is for sure! I will also put it up a bit higher.

    Jeff
     
  12. Jason

    Jason Gold

    lol.... My sister had to do that to this troubled girl they adopted years ago. No door for you! After awhile, she ran out of stuff to take away from her.
    Now if only someone would please take my cell phone away from me! What a quiet and peaceful life I could have!:p
     

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