Metal Casting Zone

Hey Gang,
I have set myself up a small foundry to do bronze parts. I am using the solid investment method. My issue is with air bubbles stuck to my waxes in the investment
stage. I am hoping someone has a better method of getting rid of these bubbles other than vacuming since most of my molds are in the range of 16" tall x 16" diameter. I am not afraid to build a vacume chamber, however the size of the chamber as well as the weight of the flasks could be a PITA to work with. By the way, brushing on the first layer is not practical due to the detail in the parts.
Anybody have any suggestions?
Thanks in advance,
Mike

build a small vibrating table with an air powered vibrator. there is also a dip you can use to keep the bubbles from adhering to the part. ill have to look up the de bubble stuff but contenti sells it.

Hi Uncle Mike

The area of bubbles on the wax patterns is a serious one in lost wax casting. Vacuume is realy only the answer to do the job properly. With flasks 16 inches in size you will need a very large chamber and importantly a vacuume pump big enough to vacuune this size chamber down very quickly.
I expect the investment you are using has a work time of 9 min to mix vacuume pour in to flask then vacuune again all in 9 mins. You would need to have a vacuume chamber capable of vacuuming this volume of investment in 1 to two minutes otherwise your work time will run out. A section of the vacuume chamber should be of a clear perpex for viewing the process.
Vacuume chambers of this size must be available because I have seen huge jewellery casting trees at least this tall.

Aonemarine suggestion is also good. Make a vibrating table or use a hand held power tool like a sander to rapid vibrate the huge flask for a minute or so.

De bubblizer fluids could help from a jewellery tool supplier. Maybe dipping the wax trees into a solution of water and mixed with a little detergent might change the surface tention of the wax patterns and help before investing. JOHNCAST

Thanks for the input guys.
My other research has also come up with the de-bubbler aproach.
I like the idea of a vibrating table aonemarine. Do you have any pictures, drawings, or ideas on how to build one? Although I don't think a "small" one would do. I'm guessing that my investments are well over 50#.
JOHNCAST, I think I have pretty much made up my mind that a vacume table is inevitably
in my future! I have a small vacume pump that I got from a friend who does HVAC. Again any construction ideas would be helpful. Maybe I'll start with a small one first just to get a feel for the process. Getting these large flasks into and out of a vacume chamber (in a hurry!) sounds like an exciting day!

Mike

Hi Uncle mike

I have been thinking of your large flasks size you mentioned. Have you thought of dipping the waxes in the slurry and sprinkle with sand tec as you can see on many videos on the web. Lost wax shell casting I think it is called. The burnout cycle is going to be a long one and need a very big furnace. Johncast

Yes JOHNCAST, I have thought alot about shell casting. There are a few downsides for someone who only casts once in a while. First of all the process is slow. Each coat takes a good day to dry, and in order to build up the required thickness it takes 4-5 coats. The next problem is keeping 40-50 gallons of slurry continuously mixed. Most of the foundries that I used to send my waxes to use this method, however they were making alot of shells per week.
Mike

A vibrating table is easy to make, just a plate with an air powered vibrator mounted to it and have it sitting on some springs for give. Have it tuned on while pouring the investment in and it works well. a vacuum chamber isnt to hard to make either, i made a couple from PVC pipe and just used clay for the seal. Cheap and easy thats my motto.

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