Making a casting under vacuum?

[Mike Cirelli]

I was reading Chris's thread about the casting that goes with his DVD. It's said it is cast under vacuum. I would like to know how to do that. I have a vacuum caster and was wondering if that would work and at what stage and how long is the casting vacuumed. Does the catalist have to be reduced to slow it down? The resin goes so fast it doesn't seam possible to vacuum. I'm using Alumilite.

 

[Kevin P.]

Mike, You can use your vacuum caster to vacuum your mold.
I use a two part compound from Zero-D Products in Ohio.
First is to mix the two parts together according to formula by weight. Then vacuum briefly to void the air. Next pour the mixture slowly down one side of mold container to let it flow over what is being molded (prevents air bubbles). Vacuum once more and allow to cure for 24 hours.

This is what I do when molding jewelry things. It's a clear product so it's easy to see where to cut the mold to release the object that was molded.
Hope this is helpful.
Kevin P.
These people are helpful and will answer any questions.

 

[Mike Cirelli]

Thanks Kevin but that part I'm not having any problems. It's the casting resin not the rubber mold. The resin sets up in about 90 seconds. Way not enough time to vacuum.

 

[Christian DeCamillis]

Mike, I'm using a resign that has about a nine minute working time. There is also some that have a twenty minute working time. Also with most of the molding rubber. after you vacum it, you can heat it in an oven at 200 degrees and cure it in one hour instead of overnight. That is as long as your oiece will take the heat. Chris

 

[Mike Cirelli]

Thanks Chris so it's not Alumilite resin, it's another kind. I don't seem to have any problems with the rubber. The tan Alumilite is really bad because you have to shake it before use. The white isn't to bad, but I still get some air bubbles. I'll have to start looking for another product.

Chris what is oiece?

 

[rfattig]

you can also pressure cure with a paint pot and about 50 lbs pressure. Collapses all the bubbles and takes less equipment.
Roger

 

[jerrywh]

When I do precision casting. I make my mold in a pressure cooker. I installed a tire valve on the lid. I use polytek silicone rubber and after vacuuming the silicone and pouring the mold I put it in the pressure cooker and put heat lamps on the outside to speed up the hardening process. I also pump up the pressure to about 25 lbs psi. When making the epoxy casting the epoxy is poured into the mold and the mold is placed in the pressure cooker and then pumped up to 25 lbs psi. Like the man said, this collapses all the air bubbles and forces the epoxy into every available crevice. this process is so precise that it will reproduce your finger prints if they are on the mold or the pattern when making the mold.

 

[rfattig]

I use a pressure cooker w/vacuum to de-gas silicone, but a paint pot is built for up to 100 lbs. pressure

 

[Mike Cirelli]

Thanks guys. I called Alumilite today and they said to heat the rubber mold and dust it with powder. Well that didn't work very well. I got very fine bubbles but more than ever, and the powder didn't seem to do much but give a different finish to the surface. I tried vacuuming the the two part resin before mixing with no success. Maybe what I was getting before is about the best I'm going to get with this stuff.

It seems like you guys have more success with pressure than I am with vacuum.

 

[rfattig]

Mike - powder will give it a paintable surface, but not much else. gases are produced from mixing the pur, you have to vacuum quickly after mixing if you have a short pot life resin, and my experience is it has to be pretty high vacuum. With pressure all you really have to worry about is making sure you have plenty of resin after the bubbles are compressed.

 

[jerrywh]

The alumilite stuff sets too fast for vacuming. That is why the pressure works better.
Like was said before, the pressure compresses the air bubbles to nothing until the aluminite sets up. You can pick up an old pressure cooker at the goodwill for almost nothing. Make sure the seal on the lid is good. 100 lbs is good but I never needed that much.

 

[D.DOUGLAS]

Mike, Sorry to here your having problems with this alumilite. I just ordered some of the white and i am glad you brought it up because i am sure i would have had the same problems. Looks like i will be looking for a pressure pot. We should not have to go to this much trouble. I will keep you posted on my findings with the product.

 

[Mike Cirelli]

Ha D
I'm not having big problems just little annoying ones. As I said the white isn't so bad but the tan I don't like. That pressure pot makes sense to me also. I just don't think I can fit one more thing in my shop. Pretty soon I'll have the tools to do everything but no shop to do it in

 

[rfattig]

Try Smooth-On for longer pot life resin and colorings. Also, I wonder if aluminum fill wouldnt give the castings a metallic appearance to better replicate the original

 

[Andrew Biggs]

I did some castings ages ago and had success with the aluminite by making sure that there was no moisture in the air....it was winter here.......I simply did this by having a small cheap fan heater blow warm air over the work area.

Plus spraying the mould with a laquer fast/instant dry from a spray bomb, then pouring the aluminite. This sort of acts like a coating. I used white but I guess you could use colour if you wanted to although I havn't tried it.

You can also get brass and silver powder (an aluminite product) if you want to colour them. You dust the inside of the mould with it and then pour it.

It's one of those deals that can drive you insane if it's not working............but when it works it all runs smoothley.

Cheers
Andrew

 

[Tom Curran]

Mike, you need to find a resin that has a longer pot life. Alumilite sets up way too fast to get it vacuumed and poured, and then pressurized. You might want more like a 20 min set up time.

The downside of a longer working time is that it will take you all day to make six castings.

Look into Smooth-on products( http://www.smooth-on.com/ ), or PolyTek ( http://www.polytek.com/ ) for starters. Both companies have great tech support teams, and I would not hesitate to call them if you can't find what you need on their sites.

Tom

 

[Mike Cirelli]

Thanks guys I have been looking at those companies. They just have so many different products. I'll have to give them a call.
Andrew I tried dusting I have a pure talcum I use for another type of jewelry mold making, but it didn't improve the quality. I didn't try paint. I would be afraid I would lose detail. It could be moisture we're getting warmer and more humid here now (finally).

 

[D.DOUGLAS]

I looked at a couple videos on you tube and decided to try another product called easy flow 60 casting resin. Cure time is about ten minutes and no pressure or vacuum needed. As Andrew stated you can brush the silicone molds with a metallic powder to give it a more realalistic color. I Also seen were you can ad a little black pigment to the resin and when it cures it will be gray in color. Doug