Tuesday, February 28, 2012
No-bake ComposiCast Low Temperature Metal Casting System
A very special thank you to Greg (eBay name Chevi-shop) for sharing this very cool method of using ComposiCast urethane resin with fine sand as a molding material for low melt metals such as zinc alloys (ZA), pewter, and others. This is a summary of Greg’s work in Greg’s words:
I found a new use for your Composicast urethane. If you mix 10% fine sand to ComposiCast, you get a perfect no bake core making compound. I cast antique auto parts and needed a good core making system that didn't use plaster. Your ComposiCast works great for casting my ZA (zinc alloy) alloys.
I use the ComposiCast for the pattern from the original part. Then I make a urethane mold over that with about 60 hardness, Then using 10% ComposiCast and fine sand, make the core. I insert the core into a frame where the original part, Close the mold and pour 750 degree ZA alloy. The metal sets up before the Composicast melts just a bit. Makes really nice parts as there is no gassing like with a plaster mold.
Some limitations include:
• The surface of the core does get soft but holds its shape until the ZA alloy sets up.
• It seems that the core hardens after cooling and they are very hard to remove! Pop out all you can while they are hot. If you let them lay overnight and then try to remove them, you need a CEMENT drill bit to try to get them out!
• With the Composicast, it is a one shot deal. The surface gets soft and mushy and stays on the casting, but is easily removed when warm, either with an air hose or hand wire brush.
Here are some pictures of the part and the parts to make it. The first is a 1937 Packard license stem. The large red part is a Packard tail lamp stand that I make using ComposiMold for the mold to make the sand cores.
I am using it for the entire mold for a 1917 Maxwell distributor holder. Rare part and the customer needs 2 of them. The detail is just great.
Here are the results:
I checked some of the dimensions with a dial caliper and there is not much shrinkage. .020 was the largest, on the widest part. Not bad.
Here is a picture of the largest casting that I have made with ComposiCast no-bake. It is a 3 1/2lb casting and the largest yet for my new system.
Normally I can't cast things this big, but it worked well for the first attempt. The nameplate is very thin (3/16") and over 14" long. I used the no-bake for the detailed front side and a piece of REM board for the back. I didn't get it packed around the letters as well as I should have but still got it to run the full length and fill all the letters.
The flash around the letters would be eliminated if I were to use the no-bake on the back as well. This was just an experiment to see 1. if the detail would be good enough to plate, and 2. would the no-bake let the metal run the full length of a very thin mold.
Here are some pics:
Thank you Greg!!!!
ComposiCast can be found at http://compositherm.com/courre.html