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Thread: More Fun With Lost Foam Part 2

  1. #1

    More Fun With Lost Foam Part 2

    OK, so we’ve had intersecting tubular plumbing, small unsupported loose sand cores, how about deep aspect ratio features? So I thought I'd start another thread for this subject. Sing along please:





    It’s 2” bore. The fin thickness and spacing are about 0.1” and cylinder itself about 3/16” wall. The fins are 9/16” deep so between a 5:1 and 6:1 aspect ratio, no draft of course.

    Ah heck, it needs a cylinder head too. Same fin dimensions. I just drilled a shallow hole with a forstener bit, ripped the fins on the table saw while the block was square, then sanded it round and rabbited the bottom with a router bit. -It was quick.




    So now the question is the orientation in the mold and gating. My two favorites are sitting straight up as pictured and bottom gated with a sprue down the center of the cylinder, or laying on its side and just gated into the base. Think packing potential may be best on the latter.

    Are ya with me?

    Best,
    Kelly

  2. #2
    Moderator DavidF's Avatar
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    Pretty sure you have 10k viewers that are with you
    Coating, or no coating.. that is the question.
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  3. #3
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    Cylinder base up, 45 degree tilt, sprue into the flange.
    Head vertical, fins vertical, sprue the edge,
    Bones

  4. #4
    Quote Originally Posted by DavidF View Post
    Pretty sure you have 10k viewers that are with you Coating, or no coating.. that is the question.
    For first go no coating. I think it will be a bugger to get the coating in there and get it to dry once/if you do. I also suspect it will be a real bugger to get out.....probably sand blast it out of there. I could really use some finer media.

    Best,
    Kelly

    - - - Updated - - -

    Quote Originally Posted by FishbonzWVa View Post
    Cylinder base up, 45 degree tilt, sprue into the flange.
    That's sort of splitting the baby between the two Bonz but at least all the fins are still pretty much down hill.

    Head vertical, fins vertical, sprue the edge,
    That one was always a given.

    Ya know, when I started fooling around in the first thread, I had no expectations of success. Now I expect it all to work!

    Best,
    Kelly
    Last edited by kcoffield; 08-07-2017 at 02:40 AM.

  5. #5
    I would TOTALLY ceramic shell that thing. Unless you have endless amounts of time to keep remaking those foam patterns after each failure, IT'S WORTH IT!

    On the BP, I had a thin piece of foam laying under the hanging bp on the bench. Well, that slurry dripped onto the foam about the size of a quarter. After it dried, I hit it with a torch until all the foam burned away. It left me with a white HARD as nails quarter sized piece of slurry. I did first dip, no sands. The stuff dries really fast on foam. Then the nest coats were 2 of fine and 3 coarse. After pouring, I hit it with cold water and the shell broke right off as usual. Getting the slurry out of those slots might not be as bad as you think. I would run 2 coats of just slurry and MAYBE one with slurry and fine silica. That should be enough to basically fill the slots. Then proceed onto slurry and course, do that twice. The slurry lacking silica will pretty much fill in the slots and the shell over it will encase it . Shell doesnt stand a chance against 120psi of flying glass beads in the cabinet. Remember ardor, the guy with admiral chicken commander statute? He hurt his wrists busting shell off that thing. Why he didn't blast that off it, is beyond me.

    My point is, the slurry itself could be enough if given a few coats. HOWEVER, you will need to support all of it in a bed of sand or the weight of the metal, could blow out the sides. Silica added to the last coats will give it the strength it needs and not prevent you from getting it out of the slots. (they are already filled with just slurry) Savvy?
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  6. #6
    Jag, what was the ash/residue like in the aftermath of foam burn out?


    K

  7. #7
    lol.. what ash residue? after 20mins at 1700 degrees, it's spotless inside there. Snow white clean. I blew air in the trial just to see if anything came out... nothing. The shell vitrifies like glass. i preheated it again prior to pouring. it was resting in a bucket of sand during pouring.
    Visit me: WWW.HandcraftedLanterns.com
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  8. #8
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    Thanks for your continued experiments Kelly, and thanks for sharing it with us here in such detail. I've found it to be both interesting and important. It's also led me to do a lot of other reading on the topic. I've done a number of foam castings with reasonable success, often in spite of myself, but they are generally pretty basic forms that don't require great as-cast finish or integrity. So I'm gaining some tools to step up my game.
    As to your current project I think Bonz' suggestion about setting the pattern at an angle, at least some angle, is the only way you'll get good compaction between the radial fins. Distortion may be an issue but that remains to be seen I guess. What really has me interested though is how you'll end up gating. I've been gating from the bottom of my last several patterns. Again, mine have been rough castings so it probably hasn't made much difference in the results one way or the other, but I've done it with the idea of minimizing turbulence and to prevent so much of the vaporization products bubbling up through the incoming metal. Plus most of the research and industrial models I've seen elsewhere are gated that way, albeit they invariably slurry coat theirs as well which you've demonstrated isn't always necessary. You've had great success top gating so far in your experiments but it seems to me that it would create some real chaos in this particular mold. A bottom fill with the pattern mostly upright should give you a more continuous front and consistently hot metal coming up as you come up the column of radial fins, with more of the gas permeating the sand as opposed to bubbling back up through the sprue. It just seems like it would be a lot less turbulent. Just tossing it out there.

    Pete

  9. #9
    Thanks Petee, all good thoughts and that little squirrel cage in my cranium has been to a couple of those places too.

    Quote Originally Posted by Petee716 View Post
    …..As to your current project Ithink Bonz' suggestion about setting the pattern at an angle, at least some angle, is the only way you'll get good compaction between the radial fins.


    Yah it’s pretty compelling and the angled orientation has just worked so well in the tubular parts and mock engine block. The base is a natural place to top gate because it’s a thicker section and will feed the rest of the part very well.

    Distortion may be an issue but that remains to be seen I guess.


    I think the key here may be to fill a quart cup or so at a time while vibrating.

    What really has me interested though is how you'll end up gating. I've been gating from the bottom of my last several patterns. …….You've had great success top gating so far in your experiments but it seems tome that it would create some real chaos in this particular mold. A bottom fill with the pattern mostly upright should give you a more continuous front and consistently hot metal coming up as you come up the column of radial fins, with more of the gas permeating the sand as opposed to bubbling back up through thesprue. It just seems like it would be a lot less turbulent. Just tossing it out there.


    I completely agree and has been another counterintuitive part of the learning process for me. I think the reason you can get away with top gating is the foam slows down the propagation of the metal front. The video of metal propagation speed tests behind glass I did back in the first thread sort shows this to be so. If it were just dropping into a hollow cavity I don’t think the result would be as rewarding. Just the same, I think I would like to experiment with different approaches to gating on this part. Even if they fail,there is likely something to be learned from them.

    Quote Originally Posted by jagboy69 View Post
    I would TOTALLY ceramic shell thatthing. Unless you have endless amounts of time to keep remaking those foampatterns after each failure, IT'S WORTH IT!


    All things that work have their place. You should really try the other process before you knock it though….you might learn something….I know I have. I really wonder what would happen if you didn’t fire it at all, just dipped it, air dried it, vibrated it in sand, and poured it.

    Ya know, I wouldn’t want to dip all parts. That waterjacket for example or the interior of my tubular parts I’d rather have as bare sand. But for speed and parts that have intricate difficult to reach features, dipping would be nice.

    However, please keep in mind that all this fart’n around I’m doing is just the opening act. The main attraction isn’t even in the arena yet. These parts just have the kind of features the real parts will have and I'm exploring the art of the possible. I don’t have any real interest in these parts beyond learning. I have up to 50 lb aluminum parts in mind and I’d much rather learn the ropes on parts that weigh a pound or two rather than pouring, resizing, and re-melting 50lbs at a time. Shelling a part that size would be expensive let alone difficult to handle and imagine how much material you would need to dip a part that was 24”x15”x10”! It would literally be 50c worth of drywall mud and $1 of quarry sand that could go in the ditch after you got tired of the smell. Also yet to be seen is how well it comes off various part features.

    Best,
    Kelly
    Last edited by kcoffield; 08-09-2017 at 10:58 AM. Reason: Because I never get it right the first time

  10. #10
    Since you are experimenting I would pour it vertically with the flange up. And an inverted "Y" shaped riser from the kush head made from either your rolled duct tape or white beaded foam. Then cut one fin to half the thickness to see if you are still feeding hot metal at the lower portion of the mold. Getting the sand to fill the spaces will be the real challenge so a couple of dry runs with the vibrator to determine how much manipulation is needed to fill the space between the fins. Incremental filling like you suggested might be the key.
    If you think you can't do it, you're right!

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