Metal Casting Zone

Hi there, folks. I've been using home-made, ramshackle equipment for years and it's working OK. But I'm trying to step it up now. I have never used vacuum to remove bubbles from my investment (Small-scale silver/gold jewelry casting), and I think it's time to start. I've had a few bubbles, luckily, not TOO bad over the years, but I don't want ANY. I'm too old for this bubble nonsense anymore.

My options are:

1. Buy a super expensive vacuum pump and bell jar (bah!).

2. Make my own out of a fridge compressor. This sounds pretty good - anybody know if a mini-fridge compressor is strong enough?

3. New idea: I read that you need maybe 25-30 inches of vacuum ("mercury" to get the air out of your investment. Well, there are hand-operated vacuum pumps (for automotive use) available that can pull about 25 inches. Why not? Anybody know if this would work? Might be nice to minimize all the "gear" sitting around in my shop - and these things are only about $35! Anybody ever used one for this?

Like this: www.amazon.com/OEM-25136-Vacuum-Pump/dp/B000CMDPBM/ref=pd_sbs_auto_1

Hello Daverham and welcome to the forums.

I do not have experience with vacuum systems. Some of the folks here do. Just remember the one safety factor if you make your own vacuum chamber. Any explosion results in an explosion. So use very thick plastic.

I can say though in resin and silicone pour applications all the yammering is about how to get their vacuum right and such when 35 psi pressure does the same thing, silent dependable and precise.

I would ask the tech guy where you buy your investment if its a jewelry supply about whether pressure is also an option. CO2 tank, a couple regulators and a paint pressure pot and your in business. I use this set up daily.

Good luck.

Welcome to the forum..

I don't know if those pumps will have the volume you need to evacuate the air and pull enough vacuum in a short time. Plaster investment really bubbles a lot, the first one I did boiled all over inside my chamber. Made a big mess. I picked up a Welch vacuum pump and a Lexan thing at a local surplus store. Got it all for less than $50. I know I was lucky to find it, but I have seen other pumps since. Like Blobber said, anything you use for a chamber would have to stand up to the pressure difference. I think an old pressure cooker would hold up to the vacuum, just put a thick piece of Lexan on top for the lid so you can see what's going on.

Thanks guys. Last night I picked up a used (working) fridge for $20. I'll pull the unit out of that. Those supposedly pull about 27 inches, which seems in line with what I need, according to some reading.

So... pressure is an option for resin, rubber, etc... Does that just flatten the bubbles? Does anybody know if that works for investment? I already have an air compressor that will do 110PSI.

Jammer,
you certainly did luck out at that price; I know one fella that spent $400 for a lesser system. Looks plenty powerful enough. Lucky yes, but of course you had the initiative to find the elements and get it together.

A heavy blanket or carpeting over the plastic tank and peep hole is not a bad idea, just in case it cracks. But you know me; I am a bit of a safety fanatic since I had my favorite nose picking finger smashed to smithereens (Image #2).

Daverham,
Yes indeed pressure works for resin and silicone just fine. Now the majority of small industry that do RTV seem to use vacuum so I am obviously in the wrong. On the other hand the ready built systems for vacuum being marketed are very expensive in comparison to pressure pot systems. So draw your own conclusions.

My way isn't the right way, its just what floats my boat. I just reread your first post and it reminded me of the important fundamental just behind safety, staying within your budget, if that 40 bucks so be it, if its 400 alright it can be done for that too, if its 4,000, I'll meet you at the casino at 2:00 PM.

Here is a picture of my setups minus a simple CO2 bottle, or the cheap small compressor I was using before that. Quality double regulators I buy from a home brewery supply. 35 PSI is plenty to pressure presses the majority of the (lighter) air up and out of the viscous material. The remainder of air is squeezed into bubbles so small they are beyond sight even with a 60x magnification. At that point who gives a rats butt. You have all the strength and clarity you need. Note how Jammer mentioned one instance of it bubbling all over the place making a mess. As I suspect you may already know you have to double or more the vessel area in order to vacuum pull the air out. With pressure there is no need for that. I often work in water clear resin so I bloody well know if there are visible bubbles. The principle works with all the resins and silicones and 281 metal. As for investment, I do not know but would suspect it would work fine as well. I'll pop up a clear casting and a pour pressured mold for you to see. Sorry if I sound rough this morning, got a pinched nerve in my face that hurts like hell.

Here is image 1 of 3
Black ten gallon and gray 2.5 gallon. Harbor Freight 2.5 gallon when on sale goes for about $40.00. The ten gallon is for larger sculpture. There is also a white and silver colored sleeve for fast loading of the ten. Their much more expensive about $400.00 if memory serves. CO2 tanks are often available for rent. I preferred to buy a 20 pound aluminum as I like to make my own soda pop too. Did I mention this system is silent?

Image 2
Here you can see the clarity of the castings. Of course they may be dyed to whatever color I want.

Blobber

Image 3
This RTV is Rebound 25, marketed only for brush on mold applications. BUT it pressure cast beautifully as well. Here is a simply a mold of five duplicate David faces with rough surfaces as that was what I needed for the period.

Note: None of the objects in these images are my sculpture. The David is from a found object, a broken David in a thrift shop. The Beethoven is a life casting while the man was still healthy. The skeletal elements show the scale of the tanks. I sculpt human organ educational models.

The resin stuff looks great. After thinking about it, it is my suspicion that compressing an investment/plaster mold for metal casting, one might collapse the pores in the plaster and ruin the molds permeability. A mold for metal casting has to be permeable for air/gas to escape from, and compressing a wet mold might ruin that it it closes up all the tiny air spaces. Just a thought....

Yes Dave, doOOh...you are right.

That makes perfect sense with investment, it needs its porosity. Gold and Silver will need far greater heat than the 281F and other metals I am working in. So back to vacuum for your application...hmmm.

Dave I would think a call to these two firms might be worth your time. Asking what your options are. There are new materials and methods always coming out.

Bruce - Tech & Sales at Contenti. Very competent and easy to talk to. In general these folks have the better quality materials and direct answers, if not always the best prices.
www.contenti.com/
Phone: 1-401-305-3000

When you get to sales ask who would be best to talk with about investment and vacuum options. In my experience these folks go out of their way to take care of you. But so far I have not received especially insightful information possibly because I was not asking the right questions. They have shipped items not matching descriptions online a couple times and they always made it right and even comped me a free $80.00 Foredom handpiece. I like that a lot of their items are made in the USA.
www.riogrande.com/default.aspx
Phone# 1-800-545-6566

While building your own vacuum solution is most likely the most affordable solution, I would not be surprised if their was an investment sold somewhere that did not require it.

Bye the way that is one great anniversary ring, for a first effort, quite stunning.

Blob

Progress. I don't have a vacuum gauge yet, but so far so good. I got the compressor out of the mini-fridge and hot glued the suck-pipe to a hole in a tupperware tub which contained a smaller container of water and plugged it in...

I was hoping to see if I could get the water to bubble, but the tupperware completely collapsed on itself and split open before that could happen. That's all I needed to see to know that this is worth pursuing further. Within the next day or two I'll have a fully-sealed system in place, made of better materials which (hopefully) won't implode. Then the water test happens again. Next time: photos!