The Foam’s Been Flyin’

Discussion in 'General foundry chat' started by Al2O3, Jun 17, 2018.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    ………………in the not too distant future there’ll be the smell of burning polystyrene will be in the air. I have enough foam patterns to have the mother of all casting sessions…..or maybe a few.

    Haven’t been posting much lately but I’ve been busy. The water necks you’ve all seen before so I won’t go into those……just another batch…..but am planning to use virgin ingot, grain modifier/refiners, and some additions to molten metal management tweaks to cast them. I’ll have to report back later on how/if they benefitted.

    Besides the water necks there are a couple new foam patterns in there that I’m anxious to pour and also a couple additional parts in the works. I’ll start separate threads for each of those in the lost foam sub forum. I’m planning some new process tweaks to cast these parts.

    Best,
    Kelly

    Foamies 6-17-2018.jpg
     
    Red97, Tobho Mott and Mark's castings like this.
  2. PatJ

    PatJ Silver

    Should be interesting, especially the thin vent one.
    That is some nice foam work.
     
  3. DavidF

    DavidF Administrator Staff Member Banner Member

    Kelly, have you tried the ceramic shell lost foam yet??
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    As a single dip surface coat yes, but not in the traditional manner as a multiple layer self-supporting sanded shell or heated and packed in sand. As a lost foam coating it produced same result as drywall mud but didn't come off as easily. It was a simple part but I don't think it breathes like mud does. If I ever had a casting that needed a preheated shell to cast I may but for now I'm managing without........

    Best,
    Kelly
     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That's actually a big finned heat sink with a few raised pads on the back for mounting solid state relays. It's for my new furnace controller. I'll post up when I cast it.

    Best,
    Kelly
     
  6. Interesting stuff! Ten sets of water necks look like production, nice!

    Have you tried a controlled atmosphere in your furnace like a nitrogen blanket? It shouldn't take much.

    You've indicated remelts get progressively more porosity. I'm not seeing that and wonder if the electric furnace might have a different effect.
     
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I built crucible hats with dense castable refractory for that and use Argon to purge the area above the melt. Takes very little gas that way. N2 would be cheaper but I don't have it on hand. I use the hats with the degassing lance but my primary motivation was to prevent any splashing onto my heating elements as opposed to blanketing.

    http://forums.thehomefoundry.org/index.php?threads/degassing-lance.204/page-2#post-3870

    Do you degas? Lot's of things at play. It's probably there and you just don't notice it.

    Best,
    Kelly
     
  8. I didn't know you were routinely using argon to purge/degas.

    I have tried a little eutectic salt but degassing is not an issue for much that I'm pouring yet.

    Can you degas with CO2? I can make that cheaply so it might be worth trying.

    I always look for porosity and have some microporosity just about all the time I'm sure but don't see it in saw cuts or milling cuts for the most part. I've only pressure tested one part, that's a new burner I made but I only tested it to 30 psi (had the gauge installed and using my finger over the MIG tip). I could see no bubbles in about a minute which was good for propane for outdoor use.

    IMG_3638.JPG
     
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Depends on the part. I would say I usually I don't degas on the majority of castings unless the metal is dirty with many remelts, or if it is a relatively thin walled piece that needs to be an air tight hermetic part....like my water necks, or it is something that is critically stressed and strength is an objective, then I do....unless cast from virgin ingot and then maybe not!

    I would say no, but there are those who maintain that you can. It gets into that old chestnut about use of washing soda to degas.

    Most porosity I've seen folks post is what I'd class as severe. Most porosity is pretty subtle and you actually need to section where the porosity is likely present to see it. Sprues and thick sections are good candidates.

    Best,
    Kelly
     

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