lost foam casting ??

[max_imum2000]

i was reading about this process, each time i see that it should be dipped in a ceramic slurry and then dried .

i need to ask what is the ceramic slurry compostion, and how can i make it dry well.

does the final parts require machining ? and what level of machining?

thanks

[Redline]

This may sound stupid,but I use drywall compound mixed with a little furnace cement. I thin it with water till it's like a melting milk shake.You only want to coat the part about 1/16 thick or so. If your part has little nooks and crannies you may want to paint it on with a brush.



It turns out just as smooth as the finish of the foam.The better the finish is on the foam the better the part will look. Foam is easier to work than aluminum so take your time on the foam plug and your finished part will require little to no machining.

[max_imum2000]

thanks for your advice
actually if it works then its not stupid at all

but do you bake the mixture after you apply it ? or you just let it down to set ?
if you bake it , what temp and duration do you use ?
what mixture composition for cement and compund ?

thanks

[Redline]

I mix it at about an 80 / 20 mix. 80 drywall compound 20 furnace cement. I just let it air dry for a few days.

[Splint]

Give some thaught to using plaster of paris, I've not used it myself but I think it would work ok and it's cheap.

[tool_man]

I have read a lot on the internet about lost foam casting. although I have not used the process myself,most everyone is thinning drywall compound and brushing on a thin layer.Let it dry.Do not bake,it will damage the foam.This is the first time I have heard of mixing furnace cement with the drywall compound.Interesting.May have to try that.

[appicnc]

Hello Group

I use the following process generally with good results, after the part is cut in foam dip into a 20Ltr container of water with small amount of detergent added, this " wets " the surface of the foam and stops small air pockets forming when dipped into plaster, let drain until free water has drained off ( < 30 secs ) then dip into what we in Australia call " finishing cement " ( used as the top coat in gyprock plaster, air dries )

Set aside until dry then either re-coat or use, drying time varies with season now it's Spring I cut a part at 6:00pm yesterday, dipped twice < 10:00pm and cast this morning ) winter it takes two days ( or more ) per coat.

I tried plaster of paris with unuseable results ( the moisture in the mix reacts with the Al - don't waste your time with any chemical reaction setting plasters )

Ed

[orjan_nilsson]

G'day fellow metal hobbyists.

I've been experimenting with lost foam alu-casting for some time now. My main concern is getting a consistent result. Have tried a lot of different shells for foam patterns.

One of the problems is getting the ceramic slurry to stick to the pattern. Thanks appicnc for providing me with a simple solution(thats why I'am posting this). Without lowering surface tension, the slurry is slipping of the pattern. Even droplets of water is sliding of the surface. Anybody have an explanation for this? I'am cutting the foam in my homemade CNC-router.

Tried dry wall mixture, but had some difficulties. After drying foam+coat in oven(with PC-fan circulating the air!) and investing(is this the right term?) into dry loose sand, the casting has some micro bubbles. Shell is hard after drying but crumbles after heating to pouring temp for some time. (gypsum or other lowtemp binder?).

My next step on the learning curve was discovering that ceramic slurry=mud!. OK, the ceramic slurry for high production industry is tailored to ...hm... high production industry. Stiring the slurry tank 24/7 and so on.

Here in Sweden, an old tech for insulating houses is draping the wood with a mixture of clay and straw. This tech is having an renaissance as insulation in houses(by the way, anybody seen large amounts of polystyrene burning?) So I tried this Lermjöl/Clayflour. I think it has about the right properties. Low shrinkage, dirt cheap:-), fire proof, follows contour. What is lacking is porosity for letting gases out, and when diluted to much in water it has a tendency to crack. Stucco with silica sand solves the problem.

Now to my question:
What will happend to industry ceramic slurry if not ”dipped” in Stucco? Just building layer after layer of slurry.

(Sorry about the lengthly post, but I didn't have time to compress the information further, and compressing it further would have made it incomprehendable)

[CJL5585]

http://www.buildyouridea.com

Has everything step by step.

[CJL5585]

Cannot get link to work at this time.

EDIT: Had extra character in web address. It works.

[appicnc]

Hello Group

I don't think the type of plaster used makes a great deal of difference, I think it the primary reason to use plaster is to provide a smooth finish by keeping the sand off the part, the sand generally being courser ( sp ) than the plaster, all of the makes on the cast part were on the foam pattern except the " pimple " at the 7:00 o'clock position under the six, I have had the plaster break, as in the third photo ( along the end closest to the camera ) but this part was cast vertically and the end was down, now when doing that type I would use maybe three coats but more importantly, I would shake and tamp the container holding the part so the sand was more firmly packed around the part.

I haven't used vents on the parts because I use a big sprule so the gas can escape as the metal is being poured in, the vent would need to be clear so the gas can escape which would mean being careful with the part in the sand and clearing the vent, large sprules seem to work ( for me )

The only plaster I would say away from is the type that sets by a chemical reaction - like casting plaster, I tried that to start with and despite drying for days ALLWAYS had failures, the air drying plaster works - again for me.

The " 168 " was cut by a router in dense blue foam, the linear bearing holder was cnc'd hot wire cut.

The last photo is of the ( unfinished ) machine, as can just be seen the burst plaster didn't affect he bearing, just behind the router, the Z axis slide was also cnc hot wire cut blue foam.

Ed

[JerryFlyGuy]

Anyone tried mixing some silica powder w/ the plaster? Something like Cabosil? I wonder if a person mixed the plaster thin then thickened it back up w/ this if it wouldn't stand up a bit better? or is this simply overkill?


Jerry [not casting, yet ]