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Thread: Name plate and mystery sand lift!

  1. #21
    Senior Member Tobho Mott's Avatar
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    I spread some foam-stinking sand out on a baking tray and bbq'd it on high stirring occasionally for about an hour, bucketing it once it stopped smoking and putting some more on there to continue... The bucket I put the cooked sand in had zero foam stench afterwards. It was maybe 1/4 of my entire supply of sand. I haven't used it enough since to be able to say if it made a differnence. I used it as 'facing sand' thinking it would help the foam gas off at least a little before I had to worry about more sand float. Pour failed but not because of that, so I can't say if it would have worked. But at least it got some the stink out of a portion of my sand... I think it would have worked, but I could probably pay for another half a bag of clean new super fine glass blasting beads (what I use for lost foam sand) for the price of the propane I burned doing it. Residual furnace heat might be a cheaper way to go as evlwht-guy suggested to me.

    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. #22
    Senior Member evlwht-guy's Avatar
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    Question I think I solved the sand float issue.

    I think I finally solved the mysterious "sand Float Issue" At least I think I know what "best practice" to use to avoid it.!!! I decided to make an aluminum tray to replace the blow molded plastic tray in my "Car toolbox" socket sets. The plastic wore out. These are cheap and nasty harbor freight socket sets but they are small and I like them for in the car for emergencies.

    Photo 1 shows the broken tool kit plastic tray. #2 shows the lost foam pattern I made Photo 3 shows the 2 sets of patterns drying extra good in front of the wood stove. They have the usual 4-5 coats of plaster and sand. Note the position of the risers....made so that they are at an angle. I was hoping that this would avoid the problem with the casting swelling. Well It didn't work!!! see photo 5. 1 swelled a little and the one on the right swelled really badly and in fact leaked out the sides as it cracked the corners of the shell.



    The thing that happened here that was instructive is that I cast 2 identical pieces that came out differently and I remembered pouring each one.

    Mistake ##1 ....I didn't compact the sand by jiggling the metal buckets....I am sure this contributed to the problem.
    Thing I did do right.....I did vent the pattern with a soldering iron cutting a groove all along the back of the pattern...as well as I could, they were thin...and connecting the sprue and the riser.

    What I noticed when I poured was that on the one that swelled the most I poured very fast and filled the pouring cup [a 6 ounce can with the top and bottom out] very fast and the gas in side boiled very hard. The second one did not get poured as fast and did not boil as hard. I think this is the key. You cannot pour as fast on a coated mold. You do have to pour continuously so you don't get a "Short" but don't go crazy!!!
    So...Best Practices
    1. Try to design the pattern so you don't have large horizontal areas. If it is a sign, at least slope the sprue and riser at 45 degrees.
    2. Vent the pattern and the sprue and riser. If the pattern is thin at least use a soldering iron to cut a thin grove and cover it with tape.
    3. A good thick coat of plaster.
    4. Thoroughly dry the plaster.
    5. Jiggle the metal bucket well after pouring in the sand.
    6. Don't pour too fast.

    You do want to make sure that any sign you do is face down or the lettering will not fill well, so these sort of projects are troublesome, but they can be done.

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