Casting Foam?

[Rico55]

Has anyone tried casting or injecting foam into molds for lost foam casting?
I would like to be able to model in clay, create a mold from the model, and then use expandable foam or ? to make the pattern for lost foam casing. Just an idea to allow repeatable casting of complex parts.

[schemo]

i think it will leave to many pores

[JerryFlyGuy]

This is how the 'Big boys' do it. I've got a foam pattern of a meat grinder in my office. It's a full size replica of the thing, just add some sand and melted Ally and you'd have a meat grinder. You need a steel mold and some foam bead powder [for lack of the proper name]. You measure some of the powder out and add it to the steel mold and then hit it w/ live steam. The beads expand and fill the mold and after it cools a bit [ less than a minute I think] you can split the mold and pull the 'part'. The 'beading' of the foam part isn't so bad as it expands against the mold and gives a decent finished surface. It's not the same as when you cut into that beaded foam and its full of voids in the center. [Well, it is like that in the center, just not around the molded surface]

I've seen websites which supply the stuff for making duck decoy's and they sell the molds as well. Didn't find the site w/ just a quick search. I'll have to check into it at home. I might have the site in my favorites.

HTH
Jerry

[schemo]

are you refering to polystyrene. yes they use foamed polystyrene pellets (styrofoam is the trademarked name) and introduce a large amount of steam to their surface. within a mold they will expand when introduced to steam and expand to the point of saturation filling the mold completely. the surface is just as those foam products that are in items that are boxed new from the store, not that good as compared to a foam cut with hot wire cutter. it will work just won't be pretty. becareful though acetone, crazy glue, and some paints will melt it like there's no tomorrow.

[JerryFlyGuy]

Yup Schemo, thats exactly what I looks like. You can see the beading in the part surface but generally thats not an issue. I've seen a alum. head on a car w/ an exterior finish like that.. If you want a better finish, then either hot wire or the 'DOW' type blue foam is needed. I think the hot wire kinda melts off the surface and kinda smooth's it doesn't it? Sanding that junk [ the beaded stuff] doesn't seem to really work, its better w/ the Blue/pink stuff but.. whatever floats your boat I guess..

Jerry

[schemo]

yes, it will work just won't be as pretty. alot of car manufacturers use polystyrene since it's easy to work with.

blue or pink installation foam works best for a hot wire cutter. and regarding the hot wire cutter (cnc) one thing to remember is to take into account how much the wire will vaporize and adjust your design accordanly. the cut from a wire cutter is perfect. and well worth it.

[darde]

The blue or pink will not evaporate and disipate in the sand as it is casted. The eps styro is better for this. The blue does do some neet things when melting. I have seen the top of the part beeing cast have an almost leather look to it because the styro. puddled at the top oif the mold and didn't evaporate.

[schemo]

Originally Posted by darde The blue or pink will not evaporate and disipate in the sand as it is casted. The eps styro is better for this. The blue does do some neet things when melting. I have seen the top of the part beeing cast have an almost leather look to it because the styro. puddled at the top oif the mold and didn't evaporate.

was there proper ventalation? i never heard of that before, from my experience that foam always melts, stange

[JerryFlyGuy]

How hot was your pour? Typically for foam you have to pour hotter than for a green sand setup, correct?

Jerry

[darde]

This was at a large foundary .I have not done it by myself. I was cnc cutting there runners they used to make the drive wheels for the case IH tractors that have the rubber tracks on all four wheels. While they said the blue foam would work it could have some of these problems. They had a vacumn set up on there vats and would burn the air as it came out during the pour.I had done some small things that they cast for me in blue foam and it had some of the leather look to it.

[The AAtrain]

Hunters expand polystyrene in duck molds for decoys. They use closed and clamped molds and boil them in 55 gal drums...
Check it out:
http://ca.geocities.com/nbcc2@rogers.../epsdecoys.htm
You could use a lost wax process to make your molds,then do like the duck hunters to produce your foam positives. Seems like a lot of work, though, (when you could repeat your patterns in wax and use a lost wax / shell casting...)

[Eurisko]

There is quite a difference in the way that expanded polystyrene (eps) and extruded polystyrene (xeps) are manufactured.

http://www.dyplastproducts.com/newsl...ore_xpseps.htm

I've had mixed results in casting aluminum with both types. Can't conclusively blame the foam, though. Seems like everything has to be 'just right' when casting. Temperature, pour rate, proper venting, etc.

The extruded polystyrene does have a much smaller cell structure and will leave a better finish ( if everything else goes right) .