Vac Assist Castings; A new Bronze Age - myLargescale.com > Community > Forums


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Old 06-12-2017, 03:48 PM   #1 (permalink)
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Default Vac Assist Castings; A new Bronze Age

One of our resident Brass Artists requested a primer in lost wax (or sacrificed plastic) castings.

I'm a long retired Silver/Gold smith from Laguna Beach ...

Last year I had my shop wired for Vacuum Assist casting with the Electromelt furnace. The furnace allows an inert gas cover vs. an oxidizing flame during the melt.

With the advent of cheaper 3D prints and better quality, this should be the new Master patterns. No more rubber molds that distort the wax each time.
An understanding in Fluid dynamics really helps when spruing the Master, so that the wax first and then the metal second, flows in without turbulence.
Also how the metal shrinks as it solidifies is important as the sprues keep feeding in metal during the cooling process.

Wax; An item is carved or pulled from a mold and Sprues are attached and a Tree with branches supporting the objects, is built up then weighed. After weighing, a section of steel pipe goes around the tree. Next Investment is mixed and vacuumed and poured over the wax tree, after it sets, the flask is prepped to be fired in the burnout over.

I can describe making molds, but that's so old fashion! Print.

Everything inside the investment turns to ash. There are modern investments for the plastics which aren't as slippery as the wax, but the results are the same, the plastic is lost and a perfect void awaits ... oops got ahead of myself ... the wax melts and mostly runs out, it and impurities are burnt up.

Firing the investment prepares it for the shock of hot metal rushing in. 1500 degrees and it glows! To cast, the flask temp is brought down to protect the molten metal. Was 600 for the gold and silver, but I'll start at 900ish with the hotter bronze. Will check specs for that.

The Burn out is overnight and early in the cooler morning I start the melt and when the carbon stir rod tells me I move the flask from the oven and set it in the opening and turn on the vacuum, after a quick test of the seal, I lift the crucible out of the furnace and quickly pour the metal into the formed opening. The crucible goes back and after a minute I turn off the vac. and lift out the flask, add a weighed amount of metal to the crucible and repeat until all the flasks have been cast.

Hot quenching helps break off the investment, wire brushing and ultrasonic cleaners will take it to a pale color, a run through the magnetic tumbler finishes the cleaning with a shine.

Sprues are trimmed and ground/sanded flat.

Bronze is copper and tin. Brass is copper and zinc.


Questions?

Happy Rails,
John
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Old 06-12-2017, 10:40 PM   #2 (permalink)
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Thank you for starting this thread.... I'm sure many will find it interesting.... I have often thought about learning lost was casting... so far I've only done green sand casting at home.... but with the level of detail I'd like to achieve in my castings sand casting is not as practical as I'd like.
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Old 06-14-2017, 01:49 PM   #3 (permalink)
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I've had mixed feelings about this thread, it is not in my interest to teach you how to cast, but rather to drum up interest in having your parts cast, by me ;-)

I have the skills and quality tools to do it from my home for less than a foundry, but not for free. I don't seek to cover my expenses so far. I purchased the casting shop for my own use. Then I got lung cancer, 5 years later my doc got as close as she could to the other C word, cured. Now with my insurance doomed, I must work.

Last year several modelers were quite interested, but cheap and after I bought more of the tools required, my friends apparently weren't satisfied with the good friend discount ... and wouldn't cover the cost of production. I wasn't asking for tool rental, just material and the electricity ... I'm on a fixed income and I need to supplement my income.

With 3D prints getting better, we can cast your designs directly by my using your prints. Costs will be determined by weight and 50% recycled metal and the other half new.

I left out details in my previous description, but if some one asks I will share more of what I know...

John
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His friend Jerry Dillon looked up at the hillside and said; There is a big ledge, and the whole damned hill is a total wreck with quartz boulders of ore.

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Old 06-15-2017, 12:17 PM   #4 (permalink)
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Doing my homework ... one of these will be added and besides cleaning, they work harden our castings... win win
https://www.riogrande.com/Product/Ra...-System/202183

Well there goes the new R/C ...

John
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Old 06-17-2017, 06:10 PM   #5 (permalink)
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I would like to take advantage of your services as a customer to cast drivers and other small parts. If you can send your requirements for drawings, payment methods etc. it will be appreciated. Thanks in advance - John F
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Old 06-17-2017, 09:45 PM   #6 (permalink)
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John F. and all others,
I am setting up a new shop . I've got to run several tests before I'll have a clue with prices.
Last year my prospects also wanted drivers and I suggested Bronze for better wear on brass track. Those running on Stainless Steel, probably should mill steel tires.

Drawings? Sorry I'm not making masters nor molds. I will accept waxes (carving or injected) or plastic 3D prints. I will sprue them and then build the pattern tree for the cast, cast and snip them off and clean them.
I will advise % of shrinkage to expect so you can adjust your models to allow for it. We'll work together until you are happy with the cast and I am with the profit.

John C.
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Old 06-17-2017, 10:02 PM   #7 (permalink)
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I will be happy to work with you. I am in a situation similar to yours health wise so having you do the parts will save a lot of time. Thanks for the quick response. - John f
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