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Thread: Delft casting - beginner help!

  1. #11
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    Sep 2013
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    Congratulations on your first delft casting!

    It's just a miscast, sounds like the first bit of metal cooled before it got into the mould, get your gate as large as you can get away with so metal gets to the bottom of your casing as soon as possible.

    Get as little distance between the crucible and the casting as you can, pouring in one smooth, fluid motion (I've read it described as pouring milk into coffee) and not fannying around between lifting to pour and tipping.

    It can be a bit tricky, especially with only a few grams of metal, to keep everything as fluid as possible between melting and pouring. It takes practise but every miscast has something to tell you about how to get things (eventually!) right.

    There are no wasted castings as long as you look for what it has to teach you.

    It's all cool in the gang

  2. #12
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    Quote Originally Posted by caroleallen View Post
    I had a go at Delft casting today and failed miserably. The metal was molten and I kept the flame on it whilst I poured but it just formed a plug around the hole.
    Did you hit the superheat stage with the metal spinning in the crucible?

  3. #13
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    I don't know if it was just coincidence, but I was finding it impossible to cast a really small piece so added twice as many vent holes as before and it seemed to make a difference ... does anyone know if venting the mould more would actually affect the flow ?

  4. #14
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    Anything that gets the metal into the mould as fast as possible helps.

    The gasses in the mould, from the metal, the burning oil, ambient moisture and expanding air all expand on contact with the 900 degree metal, the vent holes let this out away from the liquid metal with no hassle.

    Oil bonded sand isn't as porous as some other casting materials (cuttlefish bone, waterbonded sand), so pretty much all your combustion gasses will need manually venting.

    So yes, lots of vents affect the flow by allowing the expanding gasses out and the metal in as smoothly as possible, more are needed in a non-porous medium than in a porous medium.

    Hope this helps.

  5. #15
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    Thank you, that explains it all really well. It's a pretty fiddly job but nice to know that it makes a difference.

  6. #16
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    Dec 2012
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    I'm just wondering if there's any difference between casting with sterling silver (i.e. my melted down scrap) or silver grain? I was going to use my scrap for my first attempts while I practice...

    Thanks for the tips about making more vents...

    V

  7. #17
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    Sep 2013
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    As long as it's nice and clean and you use a bit of borax then it should be ok, personally I'd chuck in a fair proportion of casting grain to be sure. Dirt, grease and foreign matter in your melt can affect a casting, leaving inclusions and causing cracks when you work the metal.

  8. #18
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    Dec 2012
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    Hi again
    I was just wondering what the thing in the attached photo is?! It came as part of the crucible handle but I can't see where it fits once I've got my square crucible fixed in place...
    Puzzled!
    Thanks, V
    Click image for larger version. 

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  9. #19
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    The wire end goes in the hole in the crucible handle, the bent triangle clips onto the edge of the scorifer/crucible to keep it in place.

  10. #20
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    Dec 2012
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    Thanks Peter, though I confess I still don't see how it fits - it's too long so the claw ends up in the middle of the crucible? Surely not right?

    Next question! I've finally got round to actually having a go. I struggled to keep the silver molten & consequently ended up with a plug like Carol! What temperature does casting require & will this torch be enough (once I've had more practice)? http://www.cooksongold.com/Jewellery...rcode-999-955B

    Thanks
    V

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