Surface finish on lost foam castings

4catmom · Post by **4catmom** » Mon Feb 05, 2007 1:47 pm

Has anyone made lost foam castings with some type of "coating" on the foam to improve the finish of the castings? I've tried foam, but the cast surface is kinda "hairy" because of the irregularity of the foam, even when the foam is sanded. Maybe some "cling" plastic wrapping or some type of acrylic paint could be applied to the foam?
Thanks in advance,

pockets · Post by **pockets** » Mon Feb 05, 2007 2:54 pm

Dan, I went looking for the link, but couldn't find it. Give me a little time. It's a guy who uses the lost foam method, but he dips his paterns in drywall texture paint. The photos show very smooth castings.

Greg B.

JohnHudak · Post by **JohnHudak** » Mon Feb 05, 2007 2:59 pm

Greg, Here's one.... http://www.buildyouridea.com Click on "foundry"

4catmom · Post by **4catmom** » Mon Feb 05, 2007 5:37 pm

OK, from John Hudak it's Hamiltons White Line Drywall Texture mix. Off to Home Depot tonight to see if they carry it....
I wonder if this would work for iron too?

JohnHudak · Post by **JohnHudak** » Mon Feb 05, 2007 5:46 pm

Dan, When I asked Dave (from the website I posted), about it, he told me he has only poured aluminum using the drywall mud, he didn't know if it would work on Bronze or iron... John

pockets · Post by **pockets** » Mon Feb 05, 2007 6:27 pm

John,
That's the one I had in mind.

Thanks,
Greg B.

4catmom · Post by **4catmom** » Mon Feb 05, 2007 7:58 pm

John and Greg,

I went to HD and found another brand of this texturing mix. I don't think this is the same stuff as the "mud", or drywall joint compound. Instead, this is a product for "texturing" drywall, which is commonly applied with a roller after the drywall has been "floated". The dry powder is mixed with water into a slurry.

I'll make a small foam "test" mold and try it first with aluminum. If no problems, I'll work my way up to brass and hopefully, to iron.

RONALD · Post by **RONALD** » Mon Feb 05, 2007 8:13 pm

Here is a post I made over a year ago on the same subject.

Posted: Sat Dec 03, 2005 2:19 am Post subject:
I have been working with Lost Foam since the 1970's. You will not get the same surface you would from a wood or metal pattern, but you can come close. The type of foam has a lot to do with how smooth you can make it. I will hand sand the surface using fine sandpaper, and then apply a green pattern wax which I bought from Blehm Plastics in Michigan. It is a waterbased wax. The glue I use is water based rubber cement from the same company. Organics based cement will disolve the foam. It has been a number of years since I purchased from them, I'm not sure if they are still around. The biggest casting I have poured is a (1.5" scale) 60" long tender "water bed", but I've even made headlights out of foam. In the 70's there wasn't much information avalable, but today there is loads of information on "Lost Foam" or EPS on the Internet.

4catmom · Post by **4catmom** » Tue Feb 06, 2007 12:06 am

Ronald, thanks for the tip. I googled Blehm Plastics and found their website, so assume they are still in business. Only problems are that they package the sealer wax in five gallon pails and have a $50 minimum order. I wonder what the difference is between this product and automotive paste wax?

Post by **gwrdriver** » Wed Feb 21, 2007 4:46 pm

RONALD wrote:In the 70's there wasn't much information avalable, but today there is loads of information on "Lost Foam" or EPS on the Internet.

Ronald (and others),
What of EPS vs. XPS? From past experience I know XPS is easier to hand work than EPS, I've wire-cut a lot of it for models, but my understanding is that EPS is preferred for lost-foam foundary patterns. Any comment? I'll soon be working on a couple of patterns fror brass castings and would like to use the best material.

RONALD · Post by **RONALD** » Wed Feb 21, 2007 8:27 pm

GW, you got me on that one. What is XPS? Lost Foam is always a balance between foam density and a better appearing casting. Unless you are doing an investment casting where you burn out the foam before pouring metal, the hot metal has to totally burn up the foam, and you have to pour at a little higher temp. Therefore it's best to use the least dense foam that will do the job. Also, always put the good face of the casting toward the drag, because the crud that may be left will float up into the cope of the mold.

Post by **gwrdriver** » Wed Feb 21, 2007 10:30 pm

RONALD wrote: What is XPS?

Extruded Polystyrene, now mostly used as building insulation and commonly called "blue board" or "pink board." Fairly dense.

Therefore it's best to use the least dense foam that will do the job.

That's the kind of information I've been looking for. It only stands to reason that the denser the foam the more potential there is for residue to be left in the mould after burnout, or meltout. In my particular case the casting would be machined all over, or at least all exposed surfaces would be machined, so surface texture is not a critcal issue although I won't want it looking like a corn cob either.