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Thread: Core box match plate

  1. #1

    Core box match plate

    I'm trying to make a corebox. This is the result of a few weeks of work making a pattern and another flask.
    I still can't figure out why the surface finish is so rough. Is this as good as it gets?

    027.jpg

    A closeup of the rough surface.
    029.jpg

  2. #2
    Pouring into sand??? How's the temperature of your aluminum??
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  3. #3
    This time the melt was 1300F. In all my casting attempts I've had this rough finish whether 1100F or 1400F. There has been a couple occasions where I got a smooth spot or two but I always get a rough surface.

  4. #4
    Senior Member
    Join Date
    Mar 2014
    Location
    Charleston, West Virginia USA
    Posts
    571
    I'm still in the learning phase and have been battling the same thing but here are some things I've learned through trial and error.
    First, you need good facing sand.
    Second, control the pouring temperature, large thick pieces need cooler metal.
    I use 'time after last piece melted', thirty seconds for thick pieces, three minutes for thin pieces, and some in between, depending on the part.
    Third, vent the mould.
    I get sand float if I don't, gives a very rough surface finish. This one was hard to figure out, I went through all the casting defect list and could not find it listed, at least not in my minds eye. I would get one portion of a pattern with the defect and as soon as I added a vent in that area, it went away. Large surface areas were the worst.
    YMMV

    Edit:
    I'm not talking about the coat hanger punch to 1/8" of the pattern. I use a piece of a hunting arrow to cut vent holes at dead ends of the pattern.
    You've got a lot of metal going in quick and the air has to escape just as fast.
    On your pattern, I would put a vent at each far end corner.
    Last edited by FishbonzWVa; 02-08-2017 at 10:29 AM.
    Bones

  5. #5
    Thanks Fishbonz, your suggestions gave me something to go on.
    So, today I poured at a cooler temp as you suggested. I vented at the dead ends with an arrow shaft and I used a smaller sprue. Guess what, no change. Still have the rough finish, slightly frosty looking and the roughness was a tad bit more sharp. Regarding the facing sand, I riddled the same as before.
    Now I'm sad and dejected again.

  6. #6
    al, I dont know if this will help much, but when I try to go for a really fine finish, and have the issues that your having, I tend to put a thin coating over the pattern of baby powder, then facing sand, the baby powder usually packs in with the sand and will act like a super fine facing sand, and will give a really smooth finish. It worked for me, so maybe it'll work ok for you.

    Also, I tend to get a finish like that when I dont ram the sand hard enough, so maybe try ramming it a bit harder if the powder trick above doesnt work. It'll just need a little more venting is all, but thats easy to fix.

  7. #7
    Here's the side by side comparison.
    001.jpg001.jpg

  8. #8
    I had similar surface finish issues when my sand was too wet. Once I let it sit for a bit the finish got better.

  9. #9
    Senior Member
    Join Date
    Mar 2014
    Location
    Charleston, West Virginia USA
    Posts
    571
    Rodney, when I said facing sand, I was referring to fine sand used just for facing.
    I make mine from playsand by winnowing it in front of a fan.

    IMG_2656.JPG

    I'll set this up and hold a board above the fan and pour the sand from a liter pail onto the board to let it splash off into the air stream. The sand gets spread from coarse to fine. Fold the sides in and divide it into piles. The coarse goes into my carrot bed, the middle makes new greensand and the fines become facing sand.

    IMG_2657.JPG

    Takes 5 minutes to do a 50 pound sack.
    Bones

  10. #10
    Are you saying the facing sand has no clay? My greensand was made from Granusil silica sand 4030 and sodium bentonite. Both pass easily through a door screen when dry.

    There seems to be little gradient between damp to the touch where some sand sticks to my hand and too dry where it passes the squeeze test but sand continually rains off the clump as you turn it. So, I've been running on the damp side.

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