Non-Ferrous Casting

Can I ask has anyone had experience (good or bad) of producing non-ferrous castings from styrene patterns using green sand? I haven't tried it my self but I was wondering if the styrene patterns could produce gas enough to disrupt a green sand mould.

Guy

I regularly make lost foam castings by just burying the foam in loose dry sand with a foam riser protruding above the surface. No need for greensand or venting.

Mike

Guy

I have made a number of bronze castings using the lost foam method in green sand with no problems. I used the rigid blue close cell foam used for insulation (not the white bead board) and used normal risers and venting. Just stand upwind and don't breath the smoke from the burning styrofoam !

John

When our factory (Willans& Robinson/English Electric/GEC/Alstom Victoria Works, Rugby) still had a foundry and made castings for EE and Ruston's Diesel engines up to the early '90s, they were all made from lost polystyrene foam into green sand. That was with SG cast iron.

Thanks Gentlemen, I shall have a try with a polystyrene pattern and report back. Mike's success with dry sand is also food for thought.

Guy

Guy,

Like Michael, I have also made many lost-foam castings in dry sand, with no problems. I used the smallest grain sand I could find - almost like dust. I also used some quartz sand such as is sold for swimming bath filters. Make sure the pattern is well covered by the sand - if it is too close to the surface, then odd things happen. I assume the that as the foam evaporates in the heat, either the resulting gases 'explode' through the sand, or the sand collapses into the void. If it is buried a few centimetres under the sand, this doesn't happen.

I also use the rigid closed cell foam as mentioned by John Purdy. This stuff can be cut with a fine saw or hot wire, and can be sanded to a smooth finish. The white bead type foam is useless. You can make complex patterns by gluing together pieces of foam using hot-melt glue. No draft is necessary on the pattern.

The principle is described in many places online. This site gives a good description of commercial application: **LINK**, It mentions using a ceramic coating to form a sort of 'skin' to reduce the roughness caused by the granularity of the sand. Since I couldn't get hold of any kind of ceramic dip, I tried a suggestion I found online that coating the pattern with a thin coat of latex paint also gave satisfactory result - it does seem to work.

As John says - don't breath the fumes !