Page 1 of 9 123 ... LastLast
Results 1 to 10 of 84

Thread: Gating Tubular Lost Foam Part

  1. #1

    Gating Tubular Lost Foam Part

    It’s a water neck for an automotive intake manifold, 1 1/2" OD, 1/4" wall. Before I made a pattern and core box, I thought I’d have a go at lost foam because I have some other similar one-off parts I’d like to make. I made a few fixtures for my overarm router so I can pop out copies pretty easily now. The question is how to gate it? It’s going to be a challenge. All suggestions welcome.








    Best,
    Kelly
    Last edited by kcoffield; 04-04-2017 at 10:29 PM. Reason: Restore photos

  2. #2
    Senior Member
    Join Date
    Mar 2014
    Location
    Charleston, West Virginia USA
    Posts
    447
    That is going to be an interesting pour. Can't wait to see how it goes.
    From my limited lost foam tries, I would orient the piece as in image 1 but would gate into the flange.

    foam.jpg

    Before doing the whole piece, I would try just the long gooseneck first and see how it fills.
    Pour hot and good luck!
    Bones

  3. #3
    Honestly, I think the odds for success may be less than even money because of the nature of the part, and also because to be functional it must be dense/water/pressure tight, neither of which seem to bode too well for evaporative foam method. But hey, I figure nothing ventured nothing gained……..and if I could succeed with this part, it would be a great approach for several others.

    FishbonzWVa, I was thinking the gas from the evaporated foam needed some place to go/vent other than back through the gating system and that was the reason for the complexity but I like the simplicity. Being tubular, there is very little metal in the part. The flange is by far the most massive section.

    I figure I may as well just run the part. I have 3 of them now and with the pin router fixtures made, it only takes about 30 minutes a piece to make them now so I’m willing to have a few goes at it. I stuck them together with shellac. The black you see at the coped joint is actually Felt Tip Pen I used to mark the cope joint before I drilled the intersecting hole. The felt tip mildly attacked the foam. The shellac did not. The shellac did make the black marker bleed a bit though. I still need to do a little light filleting with wax.

    I was going to coat with thinned POP and dry at 150-200F fora couple days, then vibrate dry silica sand in place. Do you think it would be better coated or uncoated?

    When you say pour hot? How hot? 1400F?

    As an aside, I’m developing an intense dislike for Photobucket and hugely regret having invested so much in that site. Not only were the links to the pictures in my original post broken, but when I went to my PB account, the photo’s were no longer present in that folder there at all. So I uploaded them again and restore the links to my original post. Any of you Photobucket users ever have that happen? Clearly the number one mission of that site is to advertise to you not host your pictures.

    Best,
    Kelly

  4. #4
    Ill be following this. Not a lot of lost foam experience on complex parts like this, and never tried bottom fed lost foam, but what has worked for me on simple stuff is just pour fast, pour hot, pour on top, so I would probably try orientation 1 first but without the extra bottom fed riser. That said most of my lost foam successes havent been exactly museum worthy lol.

    Most of my failures have been from either the metal freezing before it fills, or not keeping the pouring basin filled with metal. There is a point a few seconds into the pour when the foam seems to disappear and suck up all the metal in the pouring basin and it needs to stay full and not draw in any air.
    The gas can also escape from the sand porosity, unless you coat the part in mud.
    I found the metal loses a lot of energy vaporizing the foam so it can cool down faster than you think, so thats why I would be wondering about the extra bottom fed gating, and would pour into heaviest section first and hope it has enough heat to fill out the rest... But, like I said, not much real experience here just throwing out thoughts.

  5. #5
    Senior Member cactusdreams's Avatar
    Join Date
    Aug 2014
    Location
    Canoga Park, CA
    Posts
    539
    Never did hollow lost foam but thought about it a lot. Aside from that I'd keep the orientation similar to #1 with everything flowing downhill from fat to thin. Loose all the sprues on the left side. Feed a larger area on the outside of the curve where its easy to grind off later and continue the sprue down to a second gate at the outside of the elbow. Got your PM re. coatings. The industrial mix I used is described here in post #12. http://www.alloyavenue.com/vb/showth...foam+cast+iron The big advantage over dry wall mud is resistance to cracking. The downside is it will not stick to toilet ring wax. Needs a thin coat of mud first on the wax to stick. Be sure your seams are smooth inside and out or the coating will seep in the cracks and make cracks or faults on your casting. How are you going to deal with the inside of the tube? Loose sand, SS core sand?
    Last edited by cactusdreams; 04-05-2017 at 08:07 PM.
    People who say it cannot be done should not interrupt those who are doing it.

  6. #6
    Senior Member
    Join Date
    Mar 2014
    Location
    Charleston, West Virginia USA
    Posts
    447
    Whenever I sprue foam, I don't think in terms of how it fills, I think in terms of how will the gas exit.
    It's going to go up and there will be giant aluminum bubbles produced, so my sprue and gate will be extra large to let the metal slide past the escaping gas. The solid foam burns out slower and produces more gas than the beaded type. I use the beaded for the sprue so it will cook out fast.
    Hot to me is 3 minutes after the last piece melts.
    I use the 45 minute powdered drywall mud. It's usually dry enough to cast the next day. I would pack the cavity with fairly dry greensand, that's worked for me on cavities. Dry sand will settle leaving voids when vibrating the bucket.
    One more thing, if you drop the piece in a bucket of water right after shakeout, it will blow the mud off and leave a nice shiny finish.
    Edit:
    Another thing, I've taken a hot coat hanger and melted most of the sprue first. Those pieces never came out as well as one done with the sprue solid. Is it just me? Any one else tried it?
    Last edited by FishbonzWVa; 04-05-2017 at 10:25 PM.
    Bones

  7. #7
    Quote Originally Posted by cactusdreams View Post
    The industrial mix I used is described here in post #12. http://www.alloyavenue.com/vb/showth...foam+cast+iron The big advantage over dry wall mud is resistance to cracking. The downside is it will not stick to toilet ring wax. Needs a thin coat of mud first on the wax to stick. Be sure your seams are smooth inside and out or the coating will seep in the cracks and make cracks or faults on your casting.
    Thanks for the link. I'll have to give some consideration to those recipes. Looks like you may have left out a couple constituents of recipe #2. Was that intentional?

    How are you going to deal with the inside of the tube? Loose sand, SS core sand?
    Loose sand (everywhere) was the plan for initial attempt, coated pattern, or perhaps no coating. I have SS but the foam patterns are pretty fragile and if I have to pack them with something other than loose sand, I figure may as well pack the whole thing in SS bound sand inside and out but I think it would be hard to consistently do without damaging the foam pattern.

    The whole lost foam thing is black magic to me, especially when I see people getting decent results with just loose sand around a raw foam pattern. The only way I can get my head around it is as the foam melts the sand must become supported by the hydrostatic pressure of the molten metal. But it basically needs to be uninterrupted plugged flow through the foam pattern or the sand should collapse........

    A nice finish would be great but a completely filled and dense part is ahead of that on the priority list. Loose sand should provide a lot of venting area but my pea brain still wants to believe it needs support of the shell.....but coatings wont vent as well as loose sand. I guess we'll see. Thanks for the suggestions guys.

    Best,
    K

  8. #8
    Senior Member cactusdreams's Avatar
    Join Date
    Aug 2014
    Location
    Canoga Park, CA
    Posts
    539
    Quote Originally Posted by kcoffield View Post
    Looks like you may have left out a couple constituents of recipe #2. Was that intentional?
    The way I read the recipe was bindal H and CMC were alternates for the bentonite and dextrin respectively. Could be wrong. It's worked well except for iron. Might be the higher temps where my sprues collapsed before filling the mold. The article with the coating recipes has some heavy reading about how the foam acts if you want to dig in about it. When all is said and done just take your best shot and learn from the mistakes. One thing I've learned from this hobby is not to be too disappointed if something doesn't work the first time.
    People who say it cannot be done should not interrupt those who are doing it.

  9. #9
    This may not be the proper place but I'll ask it anyway. Has anyone tried sodium silicate painted on then coated with silica sand... maybe 2 or 3 coats ...investment style?

  10. #10
    Quote Originally Posted by cactusdreams View Post
    The way I read the recipe was bindal H and CMC were alternates for the bentonite and dextrin respectively. Could be wrong.
    I was looking at the other recipes and trying to decide the same myself. The one link in your old thread no longer points at Mullite. The eBay seller must have changed it to Manganese dioxide. Think Mullite is fairly common material though.

    It's worked well except for iron. ....... One thing I've learned from this hobby is not to be too disappointed if something doesn't work the first time.
    Good to know and agree.

    Best,
    K

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •