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Thread: Core box match plate

  1. #11
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    No, I use about 12% clay in the facing sand, smaller grains = more grains to coat so I up the %.
    Door screen is a large mesh when compared to casting sand.
    I agree with the damp sand causing that problem too, especially if you rammed hard.
    Bones

  2. #12
    I had the same problem with either too wet or no green strength. I cast so infrequently it never seemed right, because it would dry out between uses. Gave up and bought some petrobond, worked fine when fresh but now needs mulling. Is it well mulled?
    Do I have to concede to being an adult if it means that I can play with fire?

  3. #13
    Hey guys. I wanted to let you know that I intend to get to the bottom of this surface finish issue. I'm planning to experiment with 6 and 12% clay content and various degrees of moisture. Sprue size may also be my problem.
    However, my dad fell and now my world of reality is changing. It may be quite some time before my attention gets back onto casting.

  4. #14
    Senior Member HT1's Avatar
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    Sprue size should have nothing to do with surface finish. if you are well vented and getting sound casting you probably do not have a large moisture issue to get that really great baby smooth aluminum as cast finish you need to be at the bitter low end of the pouring range,

    to deal with moisture in green sand, you have to vent well, and skin dry the mold just before you close if, you can do this with a plumbers torch. you want to apply just enough heat to vaporize the surface moisture and push the surface moisture away (into the sand ) if the sand is changeing color ( too much heat). close the mold and pour quickly... I know this is a lot to do alone that s why foundries have pouring teams. but is will get the best surface finish possible. now lastly your surface finish is dictated by the surface finish of the sand... Aluminum will sometimes actually overcome this if the pouring temp is low enough but that is not to be counted on.

  5. #15
    Made a little bit of progress. Before, the surface of the casting was frosty looking with a bazillion tiny aluminum mountains sticking out of the surface.
    Now, nothing sticks up. There's a bunch of pits but that's another story.

    The newest try is on the left.

    IMG_0666.jpg

    The correction was to get a muller, up the greensand clay content to 17-20%, and hold my tongue on the other side of my mouth.

    Muller setup
    Attachment 22600

    Four chunks of steel plate alone does a good job of breaking up shake out; add a steel ball and a cylinder chunk to the mix and a pretty good mulling action takes place.
    IMG_0646.jpg
    Attached Images Attached Images

  6. #16
    Senior Member Robert's Avatar
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    If your sand is fine enough and your pouring temp is correct, that leaves water content of the sand and how tightly it is rammed as variables.
    One other thing you might try it to soot the mold with acetylene or MAPP before closing it for the pour. That can really help with the finish on important pieces.
    Robert
    "Whether you think that you can, or that you can't, you are usually right."
    - Henry Ford (1863-1947)

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    Sand Mixer

  7. #17
    Quote Originally Posted by Robert View Post
    If your sand is fine enough and your pouring temp is correct, that leaves water content of the sand and how tightly it is rammed as variables.
    One other thing you might try it to soot the mold with acetylene or MAPP before closing it for the pour. That can really help with the finish on important pieces.
    Robert
    Pretty much what I was thinking. I'm also going to try a bit more talc. I'll also need to get better at making patterns.

  8. #18
    Senior Member HT1's Avatar
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    Quote Originally Posted by AlPuddle View Post
    Pretty much what I was thinking. I'm also going to try a bit more talc. I'll also need to get better at making patterns.
    be careful with the Talc too much will cause you surface finish problems

    we discussed it here http://www.alloyavenue.com/vb/showth...n-cope-or-drag

    V/r HT1

  9. #19
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    With my HF mixer, I found that the sand was best when it just started sticking to the drum. If the whole mess sticks it's way too wet.
    My routine was to throw the dry crust in, mist until you see signs of sticking, then add the flask, and tumble.
    I started getting better castings at that level of moisture.
    Bones

  10. #20
    Quote Originally Posted by FishbonzWVa View Post
    With my HF mixer, I found that the sand was best when it just started sticking to the drum. If the whole mess sticks it's way too wet.
    My routine was to throw the dry crust in, mist until you see signs of sticking, then add the flask, and tumble.
    I started getting better castings at that level of moisture.
    Okay, that sounds like a good procedure. I was still making the greensand too wet.

    Regarding the talc, HT1, I'm using a sock and it does a good job of dusting without lumps. It just doesn't stick well to vertical surfaces. I'm going to try some graphite to see if there's much difference.

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