Using Silicone Molds to Make EPS Patterns For Lost Foam

Discussion in 'Pattern making' started by rightbug, Sep 5, 2019.

  1. mytwhyt

    mytwhyt Copper

    Whatever density perlite is, I guess.. No more SS than what it takes it stick it together.. No compression of the perlite, slight packing to fill a mold.. Just like making a popcorn ball, don't over do the syrup.. I rely of the air to set the silica I use.. I think perlite could find a use as a second layer of insulation.. A backup insulation for fiber blanket, and a stable point of attachment for the blanket..
    Last edited: Nov 9, 2021
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    According to the info at the Schundler link, their perlite structures have about the same insulating value as K23 IFB, but only 1/3 the density. The same info says it only has a service temp of 1200F which is about half its melt point. That seems pretty conservative but that references an ASTM spec so it probably loses a lot of mechanical properties with heat, which probably doesn't mean much for insulation unless you're relying on it as a structure.

    So not really sure what the actual service temp would be. IMO 1200F would be very limiting for foundry use but I suspect 1700F would still be safe for insulation use. On the plus side both Perlite and SS are very inexpensive and in most cases readily available which is a good combination for hobbyists. Just be advised, when folks have used perlite for insulation in home made refractory brews, especially for foundry furnace hot face, it often doesn't end well because it melts into a green glass and fluxes everything in contact with it.

  3. mytwhyt

    mytwhyt Copper

    I could run that cup size sample up to 1200-1700 in my electric oven and test for retained strength.. I read somewhere that sodium silicate will act as a flux at temps above it's melting point.. I've built 2 pottery kilns with 2300 ifb and they both will fire to a flat cone 10.. I bought two pickup loads, in cases, stacked high, for $250, 40 years ago.. Had to rent a storage unit until I found a place for them.. Enough for one 35 cubic foot, and one 65 cubic foot kiln.. I've still have a few bricks..
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I do think the ability to make/mold a monolithic refractory structure from something that approximates properties between Moldable Ceramic Fiber & IFB would be very useful, depending upon how difficult it is to produce of course. There is a process for making/molding moldable ceramic fiber. Vacuum forming. Here are some examples.

    If you search "vacuum formed ceramic fiber" you'll get a bunch of hits. It's quite common.

    I concluded it was still a little too involved to make one structure like my furnace so I went the route I did for a one-off but when tube ovens are made, they literally mold the insulting cylinder with the heating elements in place.


    Might be best to start a separate thread (or did you?) to further discuss molding refractory structures.

    Back to molding EPS for lost foam patterns.

    Not trying to discourage you (or maybe I am) from molding EPS patterns but it really depends upon what you're trying to make. Not sure I can add a lot to what I've already said in my previous posts to the thread, but short of already having a pattern for a very complex shape to pull a mold from, or wanting to make a lot of identical copies in a production environment, I think it's impractical for hobbyists. If you view the YouTube videos of the commercial lost foam process manufacturers, half of the content and complexity of the entire factory is controlling the EPS feedstock and molding. Without pattern consistency, you'll have no casting consistency.

    A couple of advantages of making/machining the foam patterns:
    1. There is no mold material cost or labor to make it, or needed place to store it. If molds are large, it gets worse.
    2. You don't have to worry about the consistency of the foam pattern material. It's known. You just buy it and it's cheap.
    3. I made patterns by hand for a long time. I'm about three months into using my CNC router to make patterns, and I have to tell you, it makes patterns fast, very accurately, and all the information needed to ever do it again is stored in a computer file, not a box on the shelf. So if I'm making one or a dozen patterns, it really doesn't matter.....same set up time, same program. But even before my CNC with hand guided router patterns it was still pretty darn good.
    There's not much cross over for me where I would choose lost wax versus lost foam. For small intricate parts like jewelry or statuary/artwork, foam won't produce the detail or finish that wax (or other lost pattern materials like resins and PLA) will. When parts get larger the cost of investment and equipment to burn out and handle a large hot flask weighing a few hundred pounds or more can become quite an obstacle. By comparison, lost foam has almost no mold cost or mold labor........dirt cheap sand vibrated in place, no burn out or mold curing, dump on clean concrete to demold.

    So for a guy like me that makes small quantities of automotive and machine parts, you can see why it's lost foam fort me. Horses for courses.

  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Wow, what score!

  6. Smoking Shoe

    Smoking Shoe Copper Banner Member

    Thanks for the idea. Will do some research.
    << >>
    Lost wax is a proven method for the kind of parts I'd like to make but if I could find a way to make EPS for lost foam that would eliminate a couple of quality control problems. I'm also very aware that there is going to be a steep learning/development curve for a DIY level of practical EPS forms. Not so sure I want to take on that project.
    I'd really like to stay away from silicone aluminum such as 319 and use a copper alloy like 242 for mechanical/thermal reasons.
  7. Smoking Shoe

    Smoking Shoe Copper Banner Member

    Got my little box of polystyrene beads this morning that I ordered from an eBay seller that claims to sell the smallest beads.
    A quick test of a hundred or so beads in a couple of table spoons of water boiled in the microwave produced no expansion of the beads.
    The beads appear to be the same as the beads (size and density) I bought from another source a decade ago that did expand. My conclusion, based on this one limited test, is that these beads are probably all old stock that have lost their expanding agent over time and have made their way into the beanbag market.

    Time to look for a different source.
  8. mytwhyt

    mytwhyt Copper

    You gotta look for expandable polystyrene. This new listing says they are new and available... They said mine was the last one when I ordered.. I expect to get mine by Sat. I'll do a quick test and keep you posted.. Expandable Polystyrene Foam Beads | eBay
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Back when I was looking, I joined a duck decoy site to ID a source. Sorry don't recall which one. But, IIRC, I think a lot of them were using polyurethane because it was so much easier to buy and use. It's not a good option for lost foam patterns.

  10. mytwhyt

    mytwhyt Copper

    Certainly not a good option, not if you have a machine you can tell exactly what to make.. Coming to the realization I can make hard molds, that are not aluminum, opens up a faster path to what's acceptable to me.. Because I want to make it quick and easy only means I want a bigger profit margin.. The quality of my work is judged every time I sell a piece.. What I make has no useful functional purpose... Other than serving the vanity and as an ego booster for the buyer.. Sad but true..
  11. Smoking Shoe

    Smoking Shoe Copper Banner Member

    I took a chance they were the same thing. Forgot how much of a mess they can make if they go free range.
    The ones I had a decade ago I got thru a school supply house. Can't remember the name, but I still have the can with a label. Just won't be able to get to it for a while.
    They expanded as expected in boiling water but didn't stick to each other really well. Never got the chance to try steam in a pressure cooker.

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