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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Silver tube casting.
Hello.
I use silver in my work, mainly I roll plates and draw wire. Often I need to make silver tubes, half an inch in length, 0.314 inch (8 mm) in diam and with a wall thickness of 0.0393701 inch (1mm). So I do the tubing ouf of a silver plate but there are too many operations involved (rolling, shaping, soldering, stretching), and Id like to make my tubing at a large scale. I have made a propane gas burner as in Ron Reil pages and it worked, and I bought a medium sized crusible for centrifugal casting and made a centrifuge but my burner wont heat up the crusible enough for the silver to flow into the mould. The mould I employed was a drilled screw 3/8 and put a piece of 5/16 brass in the centre. Thing is molten silver stuck in the crusible opening. I guess not enough temperature. Since I am beginning to experiment with silver casting and keeping in mind that I will be casting tubing (mainly) I would like to hear your advice. Any of it sans the advice to quit, I must do this myself. I tried to use "Alcohol investment" I picked up at a dental store, it has 2 liquid components and a white powder, but from my first experiment I did not got satisfactory results, the central piece of investment(the one that stands for the hollow part) breaks too easily. But then again I dont have a vibrating equipment required to shake the investment neither I have a vacuum pump to remove air from the investment. Right now it occured to me making a small forge of bricks, stick my burner in it and put my mould vertically in the centre of the 'forge' with some silver on the top hoping it will melt and fill the tube like cavity. I greately apritiate any of your inputs. Konstantin. |
#2
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The brick forge worked out perfectly, tho my casting needs alot of
improvement. Casting in a metal mould result in a welded piece of work using 925 grade silver. Lol. Anyway it seems my problem reduces to : How and what investment to to use for tube (nipple pipe) casting ? |
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#5
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The reason I got a welded piece of work is this.
I drilled 3/4" diameter screw, with a 3/8" 2" deep, then I drilled it with a 5/16 through the rest of the screw, so I could put a 5/16" brass rod to act as a hollow part of the pipe. And I put some silver on the top and put it all in the forge, after seeing the silver on top melting, I turned off the torch. I have to mention that the screw was red hot. I guess hot enough for the brass inside the hollow part of the screw to melt in with the silver and this is how I got this thing soldered and alloed. I guess this is a No-No in casting. Must use a cooler metalic mould to pour molten silver in it. I never heard about making a tube out of a sheet of metal but I dont think it is for me. |
#6
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"Clamdigger" wrote in message ... wrote: Casting in a metal mould result in a welded piece of work using 925 grade silver. Lol. I don't see why "casting in a metal mould (would) result in a welded piece of work" lead and zinc and alluminium are all cast to my knowledge in metal molds. I have often cast lead in molds made of brass. LOL! What is silver solder made from? Trust me - silver sticks. I would not even consider casting these tiddly little tubes. I'd clean up the lathe, install a pristine chip catcher, and machine them. Beautiful finish, precise tolerance, no heat required, no grief. Turn out dozens of them per hour. More, if you jigged up for it. Machining has got to be the way to go. If you don't have stock big enough, then cast some silver "blocks" (mini-ingots) onto open air, fire-scaled steel (or clay) ingot moulds. Works for me. (I've tried the centrifugal casting method - steel moulds, sterling silver - when making (finger) rings, and cursed for ages whilst I tried to cold-chisel the silver out of the mould.) -- Jeff R. |
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#9
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wrote in message oups.com... The reason I got a welded piece of work is this. I drilled 3/4" diameter screw, with a 3/8" 2" deep, then I drilled it with a 5/16 through the rest of the screw, so I could put a 5/16" brass rod to act as a hollow part of the pipe. And I put some silver on the top and put it all in the forge, after seeing the silver on top melting, I turned off the torch. I have to mention that the screw was red hot. I guess hot enough for the brass inside the hollow part of the screw to melt in with the silver and this is how I got this thing soldered and alloed. I guess this is a No-No in casting. Must use a cooler metalic mould to pour molten silver in it. You can't use brass as a mold, or a part of a mold, not for casting silver. It melts at approximately the same temperature as sterling silver, and is more than eager to solder to silver, even if you don't melt it. Further, you shouldn't heat the mold by melting your metal in or on it. Your metal should be heated independently of the mold, using either a small melting dish (jewelry supply houses sell them) or a crucible. You should also exercise care in melting silver, for it's easy to oxidize the base metal (copper in sterling) and create a porous casting. A neutral to reducing torch flame is in your best interest, or a furnace with a neutral or reducing atmosphere if you melt in a crucible. The metal would be poured into the mold when it has achieved a pouring temperature. If you cast by using the investment process, the mold is poured hot, right out of the burnout oven. Silver has a strong affinity for most other metals, so using a metallic mold of any kind is insane in this instance. It's very difficult to prevent the silver from soldering, even when you don't use flux. If you'd like to produce the silver tubes with success, and you have an ongoing demand for them, you should explore *proper* investment casting. Properly done, you can expect to hold .005" with no trouble. A jewelry supply house can provide all the necessary equipment. You won't get set up without spending some money, but it's the fastest and easiest way for you to produce this item without getting involved in equipment to draw them from plate. If you're curious about how it might turn out, ask a jewelry bench man to cast a few for you. You could carve, or otherwise manufacture the wax models for him to see how it works, minimizing the cost of your experiment. . If he has a large centrifuge, he could tree up several of them at one time, reducing the cost per item. Keep that in mind if you explore casting them yourself in the future. Harold |
#10
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If you're tgrying to co z thin wall tube, you ain't gonna do it sithout
pressure casting methods. The surface tension of the silver will keep it out of fine passages. The surface tension will keep it out of even passages 1/8" or larger so you have to force it into such passages. This is why there is sling and centrificugal casting methods and the sprue has to be long enough to provide the pressure to force the metal into the casting. -- Why isn't there an Ozone Hole at the NORTH Pole? |
#11
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Better yet would be to spin them on an arbor.
-- Why isn't there an Ozone Hole at the NORTH Pole? |
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