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Thread: Name plate and mystery sand lift!

  1. #11
    Senior Member Tobho Mott's Avatar
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    Sand float, I hate that! Bummer, but a nice save indeed. I had to do the same thing with just a hacksaw on my very first casting (pictures linked in post 7). Not fun! It was buried horizontally instead of vertically due to the shape of the bucket I had available. Since then it has been my experience that you can bury foam this way and get away with it as long as the sand above it is heavy enough to keep it from floating up. I agree that vertical would be ideal, but as you say there can be other considerations that may result in a decision to bury a foam pattern horizontally. I think having a bit of length to the sprue can help prevent sand float, if only indirectly, in that a pattern that is buried deeper has a heavier mass of sand on top of it to offset the hydraulic jack factor. Sometimes I'll set a couple of bricks on top of the sand for a little extra a weight too. Since I normally don't use coatings on my foam, I find things like plaques are sometimes easier to do face up rather than face down as Evl prefers, since I don't have to worry about air pockets being trapped between letters, etc. I know there are a few tricks you can use to avoid this and I do my best to shake my bucket up and get the sand packed in nicely, but I don't have an air float machine like sandcrab is talking about or anything...

    Here is where I first came across the notion that too much polystyrene vapour residue buildup in one's sand could be a contributing factor in sand float. I think Nevin is onto something there. Evl's theory that it forms a barrier that pushes the sand up makes sense to me. My sand is pretty stinky from multiple uncoated, unvented lost foam pours and I recently experienced sand float. It was a horizontally buried pattern, but I am convinced I had enough weight on it that it should have worked if some new factor was not in play. I have already melted it back down and don't seem the have a pic of that one though.

    Here's another sand floated casting of mine that is sort of interesting, it actually floated in a few different stages as best I can tell. My sand was still nice and clean then and I'm sure it would have worked if it had been buried deeper. The front of the face was just too close to the top of the sprue to be buried deep enough. A couple of bricks on top of the sand might have saved it...

    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. #12
    Senior Member evlwht-guy's Avatar
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    Well , got it completely finished. Here it is on the car with Haeley standing next to it....now the legions of Koreans in the State of North Carolina will know her name when she drives down the road. I did go in and make a nice fillet of Bondo on the inside of the frame, and used a die grinder to clean up some of the bumps and irregularities on the surface. I then painted and sanded the letters with my belt sander.


  3. #13
    Senior Member cactusdreams's Avatar
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    Looks good! How did you solve the float problem? New sand? Different pattern setup in the sand?
    People who say it cannot be done should not interrupt those who are doing it.

  4. #14
    Senior Member evlwht-guy's Avatar
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    I didn't solve this and float problem with this particular project, I just salvaged it. If you look at post number 7 and post number 10 you'll see a discussion on some best practices that I think will help avoid this problem in the future.

  5. #15
    Senior Member metalbynevin's Avatar
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    I have had this problem. I tried a lot of different things, none of which worked, until I changed my sand. Once I did this the problem went away. You can burn off the polystyrene residual and other organic condensates from the sand, but I have not figured that out quite yet. I just replace my sand as soon as i see this problem developing.here are some pictures from my last pour (likely the last sculpture I will ever make here as I am moving in less then a month). I used no coating and no vents or straws. I pull my can after I pour so I can reuse it, makes for an ugly button but does not matter.

    20150709_204418.jpg20150709_204546.jpg20150709_204655.jpg20150709_205514.jpg
    Last edited by metalbynevin; 07-20-2015 at 05:04 AM. Reason: add stuff
    "Nothing is foolproof to a sufficiently talented fool!"

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  6. #16
    Senior Member metalbynevin's Avatar
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    Quote Originally Posted by evlwht-guy View Post
    Soooo. Why the mystery lift phenomena. the aluminum is not heavier than the sand like Iron is so what is going on. In my case I think the boiling action of the foam burning up, caused a crack around the perimeter of this plate and it sort of "ratcheted" its way up. The pulsing of the bubbling gas being momentarily strong enough to overcome the weight of the sand above it. Note in my pattern the high end is more pushed upwards than the low end as there was less sand there. I believe that every pulse raised the mold shell above it and sand flows in and then supports the new height of the top of the pattern. I believe that this phenomena is worse the wider and flatter the pattern is. I saw recently a report that someone else had seen this but with un-coated patterns in "Stinky" sand....IE sand that had been used with un-coated patterns a lot and had much plastic residue in it. What I think may be happening here is that the sand does not let the gas out well and acts as an impermeable layer. I really believe that this phenomena is aided by low head pressure and not enough weight on top. The lifting occurs well before the sprue fills and causes head pressure.

    Another solution is to place a board in the sand just above the pattern. This will provide solid pressure above the pattern and hopefully stop the "Ratcheting" action of the boiling and sand filling in. This will also prevent the sand from crushing down as the mold fills and the pattern is consumed and no longer supports the weight of the sand above it. I had this problem in casting the bumper step project for my truck several years ago. It was buried very deeply and was in the mold horizontally rather than tilted so the metal flowed in and took away all the support for the shell and it partially collapsed....fortunately leaving me with a usable part.

    Another solution is to wrap the pattern in fiberglass drywall tape. I used this on my Towel drying hanger years ago. If I was to do another one of these I would do all these things to insure a good outcome.

    When I get the part painted and installed I will post another picture.
    I tried everything to weigh down my sand. I filled my flask full, placed a board with a hole cut out for the head pressure can and added many pounds of metal and heavy things as I could on top of the board. All to no avail. I think even when using coated, vented patterns the sand still absorbs polystyrene residual. I found that as soon as I notice any "extra" metal going into my pattern, i replace my sand. pretty inexpensive and cleared up that particular problem for me.
    "Nothing is foolproof to a sufficiently talented fool!"

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  7. #17
    Senior Member metalbynevin's Avatar
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    FYI

    Here is what I found on reclaiming lost foam used sand. It is about how Saturn (the car company) deals with it in their manufacturing process.

    http://www.thefreelibrary.com/System...ly.-a065021016
    "Nothing is foolproof to a sufficiently talented fool!"

    Lost foam cast aluminium - http://www.alloyavenue.com/vb/album.php?albumid=104

    https://www.facebook.com/pages/Metal...07510932833900

  8. #18
    Hmm.. should be able to buy their setup for about 2cents on the dollar. Poor Saturn, a car company that lost their way and ultimately their butts.
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  9. #19
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    Yeah, sorry to see their demise. They looked promising and there's still a lot of them on the road.

    Pete

  10. #20
    Senior Member cactusdreams's Avatar
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    Quote Originally Posted by metalbynevin View Post
    FYI

    Here is what I found on reclaiming lost foam used sand. It is about how Saturn (the car company) deals with it in their manufacturing process.

    http://www.thefreelibrary.com/System...ly.-a065021016
    Interesting! Tried to find a picture on the manufacturer's site but no luck. So basically about 1400F for an hour with an air bubbler. Sounds like a more daunting build than a muller. But no doubt the clever minds here could come up with a simple and elegant DIY solution. Maybe a small scale proof of concept.
    People who say it cannot be done should not interrupt those who are doing it.

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