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Discussion Starter #1
I read an article a while back about a fellow that turned plastic parts into metal parts. I can't seem to find my reference for that. It seemed like he put the part in something and then the metal literally vaporized the plastic part and filled the void with metal.

Has anyone done this or something similar? I know folks can machine a part from a diagram, but for single parts the cost would be prohibitive for me.
 

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I've heard that one requires the sorcerers stone in order to turn lead in to gold,,, I suppose it would work for plastic.
 

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I suppose you could use the plastic part the same way lost-wax casting are made, namely encasing the part in casting clay with tubes in such a way to drain away the plastic when its heated and it melts the plastic away, you would probably have to raise the heat slowely as not to cause the plastic to burn, once the casting is free of the plastic just plug the drain holes and fill with molten metal, then break away the casting clay once the metal has set.

Persoanlly I think it would be easier to make a latex mold of the plastic part, cast that in wax then repeat the above prodess, be less messy in the melting part, and you would have a master mold in the latex to make multiple castings.
 

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I was going to suggest Alchemy, but rkapuaala beat me to it.
 

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Victor,
I've done lost wax castings before, and don't think that would work. For one, the wax used actually evaporates and leaves no residue. Plastic would not evaporate at those tempratures, you would need some sort of chemical reaction (not to be confused with Alchemy ;). I would guess that its something like nickle plating, but where is the metal is only electro plated the chemical would bond the inert metals to the excited plastic molicules?
 

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Sir,
Given the caveats that it has been 23 years or more since I have made any jewelery, and casting was not my primary interest, I recall that you could sprue up a plastic (or plant) thing with wax rods just like a wax and invest it in plaster. After the plaster has cured and dried it is put in a burn out oven that heats it to relatively close to the tempeture of the metal. The original wax or plastic should be totally consumed. The metal is injecting into the mold while the mold is still very hot, in fact we were taught to direct the flame of the torch across the metal in the crucible and into the opening of the mold to keep it hot. The fun part was releasing the spring loaded centrifuge and hoping it all stayed were it belonged. To get the part out of the plaster the mold flask was dropped in a bucket of water. Instant plaster chunks. If the first one turns out good it could be used to make a rubber injection mold to turn out wax copies. 


Phillip 
 

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Phillip,
I defer to your knowled since mine is 38 years ago since last doing wax casting. It was also for jewelry, but since we did the pasters in wax blanks and wax rods and didn't use centerfugal methods, I think we did it more primitively and the instructor didn't tell us about plastic.
We did do something that was interesting though, in stead of centerfugal forces we used steam pressure to inject the mold. Supposedly this was a process that the Egyptians used. The plaster mold was first placed in a kiln so that all the wax was evaporated. Next the cooled down mold was placed on a stone, and metal ingots (gold or silver) were placed in a bowl on top of the mold and melted. The mold was made in an old tin can (I'm sure the Egyptians didn't use those) and prior to melting the ingots a peanut butter jar lid had a wooden handle screwed to it and an absorbant fire retardant material was placed inside the lid (Don't think the Egyptians had those either) the whole lid was set in a bowl of cold water while the ingots were being melted. Once the ingots were heated the lid was slammed down on the mold and held firmly in place. The resulting steam forced the molten silver/gold into the mold instantly.
We had two choices for removing the piece, dunk in water and let it melt, or simple remove the plaster from the can and crack it open. I did about a dozen rings using this method and a couple of pendants and charms. I got pretty good at it, but like I said that was 38 years ago.
 

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Saw that steam casting method demonstrated a few years ago. Was pretty slick. I was going to say cool, but that didn't seem right.
 

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Discussion Starter #11
I appreciate all the info, thanks to every one. Very interesting discussion. I'll have to check into wax and steam casting.

Richard J., that is the link I was referring to but couldn't remember it. Thanks!
 

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Thanks for the link Richard that was a very interesting read. So it looks like its limited to styrene and delrin, but still that is pretty amazing to know :)
 

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Dental labs have been using a form of plastic to make metal dentures for years. They mix a resin like material and pour into a rubber mold then take that part and put it into casting plaster. Burn out the master in a burnout oven then cast back with molten metal. A dentist and I tried it with epoxy masters one time for some HO stuff. Ran everyone out the dental clinic with the odor. Never did it again. The Colonel kept trying to find out what had gone on but no one was talking. Precision scale uses lost plastic casting techniques as did ?? (cannot remember the mfgr) to make brass Porter engines from Grandt line plastic parts.
N
 

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Having been an active jeweler for the past 40 some years, I guess I can say a few things here. Anything that can be burnt out in an oven, a kiln, can be used for a casting. The trick, of course, is to have enough heat to vaporize the object. As a testament to that I have a belt buckle I have worn since I was in my 20's that I cast a salamander in silver. (I froze him first) I have done pine cones, bumble bees, you name it. There are many ways to cast and you have not said what kind of metal you want to cast in. Tell us what you want to do, and it is possible you could only need to sand cast or even work in cuttle bone. Depends on what you are casting. Does it have undercuts or a lot of detail? If it doesn't there are ways of making the part without the necessity of lost wax techniques. Give me some info and I can get back to you.
 

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Discussion Starter #17
Bob, I was hoping for something like brass, copper or something I could solder. The first part I'm looking at casting (or having cast) is an I-beam for a G scale bridge - about 12.5" long by 3/4" wide. Plastruct makes one in black ABS plastic but I wanted one (well several) in brass or some metal I could solder. Other parts I've made from styrene are smaller but I would like them in metal for soldering.
 

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Hate to say this you, as experienced as I am I would not even consider casting a 12.5" I-beam. Not doable without some serious equipment that is generally beyond home craftsman capabilities. The biggest crisis that you would faace is that the metal would cool and solidify long before you could fill the cavity of the mold. Not to mention that you would need a flask, the device that holds the mold to be plus fourteen inches long! Way too specialized to do in a home workshop. If I wanted to build I-beams, I would construct them by soldering them together with hard solder, but that would require that you make some sort of jig to hold the pieces together as you solder them. I have a bridge on my layout that I built the beams out of steel and welded them together, worked fine. Here is a pic of the belt buckle. The "lizard" is cast and the rest of the buckle is fabricated out of heavy silver sheet.
 

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