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Thread: Gearing up for sand casting

  1. #191
    Senior Member Tobho Mott's Avatar
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    Tried to get this done in time for Hallowe'en, but the weather did not co-operate, and it began raining the moment I got finished ramming up the mold. So much for that weekend, and the following one was rainy too...

    Then it snowed and everything froze up. Finally came up above freezing this past weekend and nothing wet was falling out of the sky, woohoo! So I gave it a shot. My sand was pretty cold, verging on frozen, and as a result - not as sticky as I like. Took some extra ramming to get the mold to build up properly.

    I also used chalk line refill for parting instead of baby powder after seeing it suggested here somewhere. Not sure it's an improvement for me; I found that when my sand was nice and sticky, it wanted to stick to my mold more than I'm used to seeing (admittedly this was worse when my sand was just a little wetter than what I try to shoot for, ie., when I rammed it up a couple weeks ago before it go so cold, which is the same mold you see me ram up in the video but not the one I ended up pouring), which may have played a role in some of the surface porosity I am seeing on the parts of the casting that were in the deepest crevices of the drag side where the excess dust wasn't as easy to blow out before closing up the mold, even with halfway frozen sand. And it didn't seem to be quite as finely ground up as the baby powder. That last part might just be down to the (comparatively cheap) brand of chalk I used.

    The casting came out not too bad IMO, other than that bit of porosity and a small amount of flashing (got a great tip from (I believe it was) Porositymaster for avoiding that in the video's comments already - rap the pattern and blow off any loose sand before ramming up the cope, I'll be trying that for sure!), and there are some faint and difficult to photograph streak-like markings on the casting that was in the part of the mold that filled last (deepest part of the ashtray) where I figure the metal must have met in the middle from opposite sides. I guess I could have molded it in the cope to avoid that, but I'm not sure it would be an improvement overall. Actually if I look close I can see the same but to a lesser degree in all the deep sections of the ashtray (his eyes, etc.), but it is mostly visible in his forehead, toward the right side. Hoping it'll buff out somewhat if I hit it with some Mother's polish and a felt wheel. Certainly open to other suggestions though, particularly if they involve avoiding having to conceal such markings... I think I might have overheated the melt a little too actually, I turned around and everything was molten all of a sudden and my hot rod dip pouring temperature test (poor man's wildly inaccurate pyrometer) came back positive on the first try while I was still charging the crucible... maybe that also helped cause these minor defects? Anyhow, at least this time I didn't break off the sand in the little dimple in his jaw-hinge...

    I'll try and add some pictures later if I can get any good ones of the streaky markings I mentioned above. Best still pic I have been able to get of it so far is the video's thumbnail image, which should be visible below already.



    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

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  2. #192
    Senior Member Robert's Avatar
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    That is a beautiful surface finish. Your sand looks much finer than mine. What type of sand are you using and where did you get it?
    Robert
    "Whether you think that you can, or that you can't, you are usually right."
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  3. #193
    Senior Member Tobho Mott's Avatar
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    Thanks Robert!

    I bought my sand (water bonded greensand, not sure what mesh etc. though) freshly mulled from Smelko Foundry Products Ltd. in Milton Ontario. Paid $100CDN at the warehouse for my 100#, which might or might not sound like a bargain, but IMO it's worth not having to do the tarp stomp dance only to get unpredictable results. For me it was more than worth it to get an actual feel for what properly mulled sand really feels like - a picture might be worth a thousand words, but an in-person squeeze test straight out of the muller is worth a thousand pictures!

    I love the stuff, I'm looking into getting more of it since 100# is really only enough for one mold at a time of the size I usually end up making; I'm currently discussing maybe combining an order with a local guy who has an intersting casting project in mind and who reached out to me here via PM recently (handle here is Krusty, keep an eye out for him), so's to split the shipping cost between us. If that happens I will ask for more info about the ingredients. I'm kind of itching to pick all you guys' brains about the project Krusty has in mind, but I said I'd wait and let him introduce himself and his project first. Anyhow, from my place, Milton is about a 5h drive each way, so a road trip is expensive and time consuming and tricky to arrange since I have young kids at home and my wife's work schedule is unpredictable lately, but owner Tim Smelko will happily sell anyone a wheelbarrow full or a dump-truck load of the stuff. I would love to go back there though - he gave me a great and surprisingly long tour of his facility, an amazing place with a fully equipped sand analysis lab and a couple of huge mullers (I truly believe I could park my Grand Caravan inside the bigger one and still have room to get out the front doors on either side AND get the groceries out of the rear hatch), not to mention more steel flasks and crucibles of all sizes and stacks and stacks of bags of refractory and insulated riser sleeves and exothermic riser-topper compound and ceramic foam sprue filters and basically you name it - every fun toy you ever heard of for the foundry, and a bunch you probably haven't. He had just picked up a bunch of really cool old match plates at auction to hang up in the lobby for decoration when I was there a couple years ago.

    Had my young son with me, who would have been 9 at the time, but since there was no X-Box there, all he cared about was the shredding machine in Tim's office, where he opted to spend the whole hour or so I was being showed around, turning almost all of the old magazines in the lobby into confetti. He's 11 now and showing a little more interest in my casting hobby these days, but I think he really just wants me to build him a forge so he can make knives like the guys on Forged in Fire... Seems like progress; makes me both proud and a little nervous!

    Smelko's advertisement video: https://vimeo.com/71518305

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

  4. #194
    Every one I know of that's dealt with Smelko has had nothing but good things to say about them.

  5. #195
    That came out really nice Jeff. I like your steady, un-rushed approach to your projects.

  6. #196
    Senior Member Tobho Mott's Avatar
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    Thanks Neg, if I'm slow and careful, it's in hopes of not having to make the same mold 3 times for one pour... Clearly, it doesn't always work!

    Got a tip from one of our members in the comments that was a new one on me - Clarke suggested I ought to rap the pattern and blow off any loose grains before ramming up the cope when molding flat-backed patterns like the skull ashtray. Supposed to help avoid flashing. I'll have to try that!

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

  7. #197
    Good advice I would say! Thanks.

  8. #198
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    Most of my castings are one piece flat backs. I generally place a piece of smooth 3/4" plywood over the drag and exposed pattern to ram the cope so I'm not banging directly on the pattern and exposed sand. When the drag is initially rammed with the pattern on the moldboard, the sand in contact with the moldboard and face edges of the pattern isn't as tightly compacted as the rest of the sand in the mold, so it's weaker. Remember the guy who couldn't get a smooth bottom on his furnace lid? Same deal. So when the cope is rammed on the drag surface directly, especially if it's rammed harder, the mold shifts, details break off, and pattern edges suffer.

    Pete

  9. #199
    Senior Member Tobho Mott's Avatar
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    Makes sense, thanks for the explanation!

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

  10. #200
    Quote Originally Posted by Petee716 View Post
    Most of my castings are one piece flat backs. I generally place a piece of smooth 3/4" plywood over the drag and exposed pattern to ram the cope so I'm not banging directly on the pattern and exposed sand. When the drag is initially rammed with the pattern on the moldboard, the sand in contact with the moldboard and face edges of the pattern isn't as tightly compacted as the rest of the sand in the mold, so it's weaker. Remember the guy who couldn't get a smooth bottom on his furnace lid? Same deal. So when the cope is rammed on the drag surface directly, especially if it's rammed harder, the mold shifts, details break off, and pattern edges suffer.

    Pete
    This is gold, thanks Pete.

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