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how would I create styrofoam? Answered

I am investigating th' lost foam casting technique and one of th' problems is th' surface texture of carved foam !

I know that large scale mfg's of cast alloy parts make foam patterns by injecting foam into a permanant (female) mold and then use th' foam pattern to cast th' part !  This gives th' cast part a very fine finished surface with no need of  machineing (except for fitting to another component )

I'd like to know how they create and manage th' foam !



I wuz born and raised in East Tennessee ,  fer th' most part I spell it like I speak it !

And I do know how to write the words "properly , I just like to inject a little personality in my posts !

Funny, I thought he was from my part of England - we drop t' rest of t' word "the" too.

Nope ,  jest an east TN smoky mt hillbilly livin' in Scotland with my scots wife I  met while stationed at th' Holy Loch as a US sailor !

And RMS you want to read what scots accent written out is like go to www,hillbillysmc.com and read some of th' posts (if you can)

That is in Ayrshire , where Robert Burns came from !

Try my local accent.

Welcome, Bonny Brid

‘Tha’rt welcome, little bonny brid ,
But shouldn’t ha’ come just when tha did;
Toimes are bad.
We’re short o’ pobbies for eawr Joe,
But that, of course, tha didn’t know,
Did ta, lad?

Aw’ve often yeard mi feyther tell,
‘At when aw coom i’th’ world misel’
Trade wur slack;
And neaw it’s hard wark pooin’ throo-
But aw munno fear thee,- iv aw do
Tha’ll go back.

Th' only accent I ever heard that could not make ANY sense of was that swamp country ,  mushmouth South Carolina mumblin' ! I asked fer directions at a fillin' station in a little town about ten mile south of Charleston S.C.  and after ten minuitse of listenin' I STILL have no clue what that bugger was sayin' 

The foam you're carving and the foam you want aren't the same as far as I can tell. Styrofoam is made of beads of polystyrene which are expanded in a mould by injecting steam.

The injected foams are usually two-part polyurethanes.


Yeah ,  that is what I've been gettin' elswhere as well ,  I just seem to remember seein'  that kind of foam bein' produced by combinin' two chemicals and watchin' it come boilin' out of a beaker !

It was on one of those "science" shows we used to get so much of a good while back ,  aimed at th' kids !

I just cannot remember more that that and it bugs me !   I do recall th' fellow doin' th' demo sayin' that this was "styrofoam"  ( foamed polystyterene )

Th' polyurethane foam is not good for what I want unless I move up to casting iron !

The only two-packs I know are polyurethanes. Why can't you use them ? 

It'll burn away just the same.


Fer th' size of castin' I want to do ( ford flathead V8 60 block ) aluminum alloys arent hot enuff to move all that poly foam before freezin' ,  It would work with iron but I really want to do this in alloy as th' finished engine is gonna be in a motorcycle frame !

And it needs to be a lost foam castin'  'cause th' pattern work for it as a conventional 2 part mold would be a headache I might not recover from ! 

Another thought: PU comes in different densities - or you can mix it in different ratios to make it fluffier inside - Some experimenting might be needed to see if aluminium WILL flash off the foam.

Mill it from polystyrene foam ? You'll get a better surface finish.


AFAIK, the non-bead blue foam used for home insulation is also expanded polystyrene, just processed differently to make the cells smaller.  So theoretically it's possible, but practically it doesn't seem like there are any resources for the DIY'er.
I have been told that if you dissolve a whole bunch of EPS beadboard in Acetone, you can use the resulting sludge to mold polystyrene pieces, but I'm guessing those would be way too dense to burn out of your metal mold, though.