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Lost Foam Casting

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vtsteam:
Hi Tom, I've both vented and not vented in the past very few lost foam castings I've done -- just needle pricks. Ideally you shouldn't need to (as far as I know) if the wash is porous enough. The surrounding sand is dry and much more porous than greensand.

Also ideally the foam should not burn, just vaporize and be driven through the porosity of the coating. I am not an expert on lost foam, but those are my understandings. I have not vented this coating, and plan to just pour it.

vtsteam:
Well the part is cast:

First fill -- I just used a section of steel tubing as a pouring cup. I mainly used it to try to keep sand inclusion in the sprue to a minimum so I can re-melt it later without a lot of junk in it.

 

vtsteam:
Here's the first pour out of the sand into another bucket. I was glad to see the mold looked like it filled:

 

And flipping it over also looked good:

 

vtsteam:
After flaking off the coating, this is what the casting looked like:

Top:

 

and bottom:

 

and here's a detail of the corner where the little bit of foam was glued in. Notice the seams and also the difference in textures of the wire cut foam, and the sanded edge fanfold foam. Amazing detail preservation.

 

vtsteam:
The large hole shape in the casting would have been bored out for a press fit on a cast iron cylinder. A facing plate would have sealed off the chamber which would contain water for cooling.

While the casting turned out great, I've already changed my mind about the design specifics, so this one probably will be remelted to cast a somewhat different configuration. It was mainly cast as a test piece to prove out the foam construction method, and the adhesive (Borden's Rubber cement) which I've used many times in building model airplanes.

I just have to draw the new design up, and try again -- with the recent experience of this one under my belt. I'm very glad it came out right the first time, and there's very little I'd change about the method used.

This part also could have been cast from a conventional wooden pattern in greensand with a core piece for the bore hole. The sides would have needed a little draft and therefore a machining allowance. but for something this small, that doesn't really amount to much metal loss. There are no undercuts so it wasn't essential to do it in lost foam.

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