Silver Castings

[Hamfg]

Hi,

I have a project I am getting into for making small silver cross castings for wearing around the neck. My plan is to use my CNC mill to make a mold out of steel, I plan on making about as many crosses as I can get for 2-4 oz at a time...

My question is, what equipment would you recommended to get started? Any brands/styles better than the other? What books if any would you recommend to reference? Any books with examples of Re-useable molds for silver work would be great... What websites do you recommend for purchasing said equipment?

A little background on my company,

I have a very large/accurate Kitamura 5 axis CNC mill, another smaller CNC vertical 3 axis, 1 CNC lathe, and 2 CNC Swiss machines.. I want to slowly grow into gaining a casting capability as well as a few other capabilities... But this is my way to tip toe into castings. We have other equipment as well such as a hydraulic press, large band saw, and of course lots of air...

So with knowing this, are there any processes that would be easier than others that I should think about designing the molds around?

I read that some molds use air pressure to help the metal fill voids better, but this is better for smaller thinner parts... I also have seen castings that use a hydraulic press to press 2 molds together.... How should I be thinking about this?


Thank you for any insight you can offer,

Sean Porter

[Harold_V]

I'm not convinced you're on the right track. The reason I say so is the fact that molten silver readily adheres to steel (think silver solder).

While I have no experience with casting sterling (which I assume you'd be using), I do have considerable experience with casting silver, as I used to refine precious metals for a living. In order for me to pour silver to an iron mold and not experience soldering, the mold had to be well blackened with either a sooty torch or mold blackening. I used mold blackening. Even when using the blackening, if I didn't move the stream of metal around while pouring, I experienced some minor soldering of the silver (anode, in preparation for parting the silver for purification). I admit that my circumstances were far different, as the volume of molten metal being poured was much larger. That would make a difference.

That said, you most likely would achieve acceptable results if you preheated your mold and blackened it for each pour. A slow process.

I would encourage you to explore investment casting, which is the common method of producing such items. By tumbling with burnishing media, the end result is quite good, assuming you start with sound castings. That was the process of choice by one of my customers, who used to produce sterling silver rings in quantity. By treeing the patterns, multiple crosses would be poured with each cycle, limited by the size of flask you'd choose to use, which, in turn, would be limited by the motorized centrifugal casting machine you would use. I should also note that such items can be cast with vacuum assist instead of the use of a centrifuge.

If that doesn't suit your desires, then I'd suggest that you explore a die, so you can die strike the crosses.

H

[Bill Shields]

A while back I worked for a company that provided fine detailed 3d printing services to the jewelry business.

We would print a part, and the customer would then make molds from that model (not sure of the process exactly) but it did involve making one rubber and one ceramic.

Sorry, but I cannot remember more details than that,,,but pretty darn sure nobody was pouring metal directly into a metal mold.

Does "lost wax" ring a bell for anyone?

[Rich_Carlstedt]

I did silver investment casting years ago and can recommend you get this book

Centrifugal or Lost Wax Jewelry Casting
by Murray Bovin
SBN 0-910280-05-3

I can see with your CNC equipment why you want to make molds , but there is a lot to learn and experience in making jewelry
Whether you do centrifugal,vacuum,dies ,molds investment processes will be determined by your expected volume of production and time.
For my part and I have no experience with this method, but If you do it yourself and want multiple items ,
you may want to consider machining multiple items in carbon blocks ( Like EDM Graphite ) for permanent mold work

All my work was done with investment material (it's like plaster) and that is labor intensive and my permanent machined patterns made rubber
molds which made waxes which made investment molds to cast - lots of work
Rich

[Harold_V]

Does "lost wax" ring a bell for anyone?

Yes. That's what investment casting is all about.

H

[Bill Shields]

Ah .. memory not totally gone...

[Howard Gorin]

Silver likes to oxidize, a friend who investment cast silver made his own machine and melted and poured silver in an inert atmosphere, I think he used Argon gas, not sure. He no longer pours silver, the equipment may be for sale.