Stacked Plaster mold

Discussion in 'Investment casting Block method' started by magno_grail, Jan 18, 2021.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    You're right. Still just 220F huh? Do you remember all the previous talk about driving off free water vs chemically bound H20?

    Best,
    Kelly
     
  2. rocco

    rocco Silver

    I do indeed remember those discussions,however those discussions were in the context of normal block molds where one often goes to considerable lengths to minimize air entrapment in the plaster. It seems to me this air entrained plaster is a different animal, it says in one of those pdfs, that the hydroperm plaster is sufficiently permeable to dissipate any steam that may be generated during the pour, if all of the free water had been driven off, the only water left to generate steam would be the chemical bound water.
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It's just hard for me to get my head around that and reconcile the differences. Steam and other of gassing is a fact of life in bound sands but if I was going to the trouble of block investment or plaster mold it wouldn't be something I would willing accept and why would one think the steam only goes one way....through the investment? Entrained air in investment is negative mostly because of surface defects. The Hydroperm docs does mention brushing the pattern first to address this....but that is additional labor.

    In any event, it is worth bearing in mind that less sophisticated plasters have been used quite successfully in art casting for a long, long, time. I meant to mention earlier to that the introduction of Ludo is a good thing, because it conserves and recycles material but improves dimensional accuracy, reduces cure time and cracking tendency.....same thing for grog/aggregate in refractory.

    Maybe the OP will decide to do a lost wax cylinder head in Hydroperm if we give him his thread back....LoL!

    Best,
    Kelly
     
  4. rocco

    rocco Silver

    No where in any of that documentation is there any mention of using hydroperm for investment casting. I might be wrong but I can only assume that's not an oversight and that it shouldn't be used for lost wax. As far as this hydroperm stuff goes, I'm intrigued by it but I'm really groping in the dark as I've never used it nor do I know anyone that has. Maybe I'll bow out of this conversation and let the OP take his thread back.
     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It's true, as near as I can tell it doesn't specifically reference any casting process but does infer reusable patterns/molds in several places. Most of the products in the Hydrocal line don't seem to vary significantly from one another in composition. The only thing the Hydroperm lit seems to highlight as the distinguishing feature is the air entraining agent. I must say, 70-100% volume increase is pretty extreme but permeability should make for good investment for the same reason it makes for good conventional molding material....shouldn't it? 220F wouldn't get rid of any residual wax but not sure why it would be limited to 220F.......why not similar to the rest of the Hydrocal line? Suppose a phone call would resolve it....if I was looking to buy a few 50lb bags I'd make it.

    Best,
    Kelly
     
  6. HotRodTractor

    HotRodTractor Copper

    As far as I know, there aren't any investment cast heads in North America in day to day production at this time. Water-cooled heads are either sand cast or permanent mold (both of which need sand cores). Air-cooled heads are mostly high-pressure die-cast.
     
  7. Billy Elmore

    Billy Elmore Silver

    About what I was thinking. Thanks!
     
  8. HotRodTractor

    HotRodTractor Copper

    I had to do a little internet digging to find a public source..... but yes you can stack plaster molds to make a good aluminum casting. It's done quite a bit for low volume production and prototypes. The method in the link and video below uses "rubber" molds (yes I know the video shows wooden molds.....). It would be pretty easy to make your model in sections, cast rubber molds off of it, then cast the plaster molds off the rubber. Assuming your fins have enough strength in the plaster to be pulled from the rubber. You might even be able to get away with some unique geometry.... depending on the rubber you use, it might be capable of flexing enough during removal to achieve some features that would be more difficult to achieve using another technique.

    https://www.armstrongrm.com/pages/rpm.html

     
  9. Billy Elmore

    Billy Elmore Silver

    I have never done it but couldn't you print a plastic one off and then do a plaster mold on it? Seems like that would be so much easier.
     
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    If he wanted to cast one, that would probably be a good first go, but with PLA, it may be difficult to burnout without breakage at the fin roots. I guess we wont know since this was the OP's first post and he hasn't logged on since.
    This is really the key issue for any mold that must be stripped. The OP mentioned the fins are .1" thick at the root. That's ok but the real issue is the length of the fin and draft.

    The other factor besides how many you want to make is what process you are set up to do. If you had no equipment other than a furnace, or first hand casting experience, I'd think a 3D printed pattern in block investment or make a 3D printed a master, pull a silicone mold from that, cast waxes, and try block investment......but even casting waxes would not be certain and you need to make a relatively large investment vacuum chamber.

    Assuming this is a something like a single cylinder motorcycle cylinder head, for me, I have enough experience in lost foam, I think I could make a pattern in a couple hours and successfully cast one piece. I've progressed the process quite a bit since this post, but something like this:

    http://forums.thehomefoundry.org/index.php?threads/chainsaw-cylinder-head.268/

    I think now-a-days, I could make fins half that thickness and spacing, twice as deep, in about any shape.....and although they could be they wouldn't need to be drafted.

    Best,
    Kelly
     
    HotRodTractor and Billy Elmore like this.
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

  12. Sorry, I did not get update notifications so did not see all that was going on.
    The parts are a head and cylinder for a BSA A65 motor. I want to make it a 750cc but the head studs are too close to the bores. Everyone strokes them because of this but then you end up with a way under square motor and lots of vibration. Size wise, a 10.5" x 9" x 3.5" box for the head. Slightly taller for the cylinder.
    The original casting had many pieces and the fins were thin and deep like an air cooled aircraft engine. If I can mold plater plates for each section between fins then stack the plates together to make the mold it would be simpler than making all those mold pieces.
    After the separate pieces are made they would have to be bound together with an outer plaster cast.
    As far a quantity, this one is experimental. Nobody makes a 750cc kit for these motors and people still race them. In any case it would be a low production rate.
    I have a 500mm cube printer but anything this large would take a month to print and any error late in the print would be a big waste of wax wire.
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Spitfire?
    That's too bad. How close are the studs to the bore? How big are they?

    The plates will be very fragile and the tolerance stack up can be a bugger. I think you'll have hard time demolding and placing them without breakage, then they'll need to survive molten metal. Getting them all to register accurately would take some careful thought too.

    Have you ever cast metal or have any foundry equipment? Can you solid model?

    Did you happen to see this one I banged out after you posted?
    http://forums.thehomefoundry.org/index.php?threads/motorcycle-cylinder-sample.1521/

    Best,
    Kelly
     
  14. Thanks, I saw the build-up that you posted. I was going to machine the sections centered around the fins in Plexiglas so controlling the dimensions of each plate will be accurate. One Plexiglas plate above and below the section being molded. It should be easy to pull off the plates. I could use mold release if the plaster sticks to the Plexiglas but I think some wax is all that would be needed.
    The head bolts are 3/8" and a couple millimeters from the bore. Someone in the UK makes an aluminum cylinder and claims it could be machined to 80mm bore but it will have stepped 5/16" studs (5/16" in cylinder, 3/8" through head). The problem with that is the core of a 5/16" - 18 is about 1/4". That is not much metal holding the head on.
    Currently, the head bolts to the iron cylinder and the cylinder flange bolts to the case. I am making the outer four studs go all the way down into the case.
    I have built up the cylinder 3D model already, still working on the head. No problem machining the plates as I have a CNC mill.
    I have never cast anything except clay. I do have a cone 10 kiln big enough to put a head in with room to spare. However, If I can make the mold, a local investment casting shop said they will pour it.
    Another thought that I had was whether anyone has tried casting aluminum with the mold and raw material in the kiln. The crucible would have a hole in the bottom centered over the sprue. When the aluminum melts it would drop straight into the mold.
    Overflow would have to be accounted for (sand box in the bottom of the kiln?).
    Spitfire was a 60's model of the twin carb engine, later called Lightning. I remachined a 90 degree offset Yamaha XS650 crank to go in the cases and added a centre bearing to the crank. I designed a five speed gearbox to replace the four.
     
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The reason I asked is there can still be a pretty steep learning curve in molten metal management. An established casting house removes this. It's more a matter of whether you want casting in you're arsenal of tools.
    Well, with enough will and determination most things are possible. You may succeed with your first attempt but odds are greater you will not and it will take several iteration. With all the above, I still think your best bet for success is to 3D print (or farm it out if needed) an evaporative pattern, make the investment mold, have your shop cast it. Take advice from them on gating, venting, and rigging for their process.

    For a one-off, or a few, I'd do it in lost foam but that's what I'm set up to do and most experienced in. Good luck with it and keep us updated.

    My older brother had a Norton Commando when I was growing up and then a Z1 900 Kaw. My Dad raced tunnel hull hydroplanes. I raced McCulloh powered carts, had Yamaha RD 2-strokes street bikes, and drag raced Kawasaki Triples. Then had big displacement boosted four stroke Japanese sport bikes. If something didn't have an engine on it we figured it was an oversight and installed one. If it had one, it obviously needed a bigger one and more power.....just simple rules to live by ;)

    Best,
    Kelly
     
  16. Michael Moore

    Michael Moore Copper

    Jeff Henise has cast and HT'd some more cylinders for his 175 Kawasaki racer and I'll let him know about the new forum. I saved a copy of his AA thread on doing the 175 parts and can attach it as a 7.5MB PDF file if that fits within the forum guidelines. I'll have to see if I can get him interested in doing some more foundry work together.
     
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Hey Michael, I didn't initially make the connection but remember (you) now. I corresponded with Jeff a bit and he was nice enough to provide me some sodium silicate catalyst.

    Best,
    Kelly
     
  18. DavidF

    DavidF Administrator Staff Member Banner Member

    Cool with me. I remember those castings, very good work....:cool:
     

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