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Made my first spinn-casting with zinc today. :-))
Helpful audience!
Today, I made my first spinn-casting with zinc. It was just a first test shot to see what I can do wrong and what I did already do wrong. So the mold was just a plaster mold [1] and the zinc was just some scrap zink sheet metal for roofing. That zinc proofed to be good enough and I will use up all the rest before going to the costy zinc I ordered. At least, the spin caster was a success. I had no other motor at hand, so the disk is rotating with nearly 1400 RPM. Direct driven! The disk has a diameter of 12". I thought more g-force = better surface. It seems, that that is right. No problems with vibration, as the frame where all the suff sits in is quite heavy. The first casting was a (partial) success, some detail very good, other bad. But that only where I had bubbles in the plaster. Also a partial failure, because I didn't melt enough zinc. I have to cut the inlet (in the center of the disk, because to much is cooling down there and remains there and doesn't flow down into the mold. So I will make some mods, add a brake to stop the disk spinning and add shielding and paint. Will put pics and explanations to my HP. This time in English, so you don't have to babelguess about what I have written in Kraut-Language. Will take some days, but I will keep you informed. Oh, the silicone is damned expensive! 1kg (2 pounds) about 50 EUR, that are 60$. :-( OK, it withstands 500°C (930 F), zink poring temperature is 400°C (750F). But that stuff is to expensive for playing around. I will think about to put the rubber in some supporting form to save some rubber. [1] that showed to be my newest invention "lost plaster casting". Also, I baked it too long in the oven. It broke in 3 parts over night. Some super glue fixed that. I didn't get the castings out of the mold, so I broke it apart. It was some wothless casting anyhow. Nick -- Motormodelle / Engine Models: http://www.motor-manufaktur.de Ellwe 2FB * VTM 87 * DLM-S3a * cubic more to come ... |
"Nick Müller" wrote in message ... Helpful audience! Today, I made my first spinn-casting with zinc. It was just a first test shot to see what I can do wrong and what I did already do wrong. So the mold was just a plaster mold [1] and the zinc was just some scrap zink sheet metal for roofing. That zinc proofed to be good enough and I will use up all the rest before going to the costy zinc I ordered. At least, the spin caster was a success. I had no other motor at hand, so the disk is rotating with nearly 1400 RPM. Direct driven! The disk has a diameter of 12". I thought more g-force = better surface. But only to a point. As the G forces increase, you risk blowing the mold. It's a problem for jewelers, casting with gold alloy with a much higher specific gravity. If you have problems with that, you'll know you have to slow down. Well done! Harold |
Harold and Susan Vordos wrote:
But only to a point. As the G forces increase, you risk blowing the mold. Yes, I'm aware of that. I will see. Plaster isn't as tight as the silicone. Well done! How do you know that!? :-) You haven't seen the pictures yet. Or do you want to push me? :-) Anyhow, thanks for the input and hints I got there! Nick -- Motormodelle / Engine Models: http://www.motor-manufaktur.de Ellwe 2FB * VTM 87 * DLM-S3a * cubic more to come ... |
"Nick Müller" wrote in message ... Harold and Susan Vordos wrote: But only to a point. As the G forces increase, you risk blowing the mold. Yes, I'm aware of that. I will see. Plaster isn't as tight as the silicone. True, but you could experience distortion, without complete mold failure, likely only on large items, though. Well done! How do you know that!? :-) Chuckle! I have faith in you! After all, you did achieve results of sorts. Harold |
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On Sun, 21 Aug 2005 21:13:42 +0100, "Triker"
wrote: "Don Foreman" wrote in message .. . On Sun, 21 Aug 2005 19:40:10 +0200, (Nick Müller) wrote: Helpful audience! Today, I made my first spinn-casting with zinc. It was just a first test shot to see what I can do wrong and what I did already do wrong. So the mold was just a plaster mold [1] and the zinc was just some scrap zink sheet metal for roofing. That zinc proofed to be good enough and I will use up all the rest before going to the costy zinc I ordered. At least, the spin caster was a success. I had no other motor at hand, so the disk is rotating with nearly 1400 RPM. Direct driven! The disk has a diameter of 12". I thought more g-force = better surface. 334 G's! How do you know that? Google on centripetal acceleration. There are lots of sites. One is http://www.ac.wwu.edu/~vawter/Physic...etalForce.html You do need to keep track of your units. Then, 1 G = 32.2 ft/sec^2 or 9.807 m/sec^2. |
Don Foreman wrote:
334 G's! I did the math with 1000 RPM, and if I remember correctly, it was in the ballpark of 5 g's. Did you forget to divide by 9.81? Oh, you did divide! I'll recheck... I did some research and found that with pressurized zinc casting they use in the range of 80 atm (1200 PSI) and higher. Well, I will see if I do have distortion. Steel molds are harder than rubber, I know. :-) And, if I do get problems, I can move the part nearer to the center or add a rheostat. On the other hand, there was a link (IIRC your hint?) that showed a commercial spinn caster that had 1000 RPM with a bigger disk (judging from the photo) and rubber molds. Nick -- Motormodelle / Engine Models: http://www.motor-manufaktur.de Ellwe 2FB * VTM 87 * DLM-S3a * cubic more to come ... |
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Don Foreman wrote:
I used first principles rather than a formula, and let MathCAD keep track of the units because I'd surely screw it up using a calculator. I only used mumath, and that was long time ago. Also don't have that Apple ][ + Z80 card anymore. So I (have to) stay with formulas. a = w^2 * r w = 2 * pi * f w = 2 * 3.14 * 1400 / 60 w = 146.5 [s^-1] a = w^2 * r a = 146.5^2 * 0.15 a = 3221 [m/s^2] = 328 G Don't know how I screwed this up. Your result is right (difference due to roundings). Sounds a bit frightening. 8-O. OK, lets see what pressure I have: Average a over the whole length of the zinc column is half the a at the end. p = F / A (pressure = force / area) F = m * a (force = mass * accel.) m = V * rho (mass = volume * spec. weight) V = A * h (volume = area * height) assembling... p = m * a / A p = V * rho * a / A p = A * h * rho * a / A p = h * rho * a units: m * kg * m^-3 * m * s^-2 = kg * m^-1 * s^-2 = N / m^2 = Pa (with N = kg m s^-2) with ... rho(zinc) = 7 kg/dm^3 = 7000 kg/m^3 a = 3220 / 2 m/s^2 = 1610 m/s^2 h = 0.15 m .... I get: p = h * rho * a p = 0.15 * 7000 * 1610 p = 1690500 [Pa] = 16.9 bar = 245 PSI This doesn't sound too frightening. Or did I screw this one up too? OK, judging from the numbers, I have to watch out for distortion. Maybe add a metal ring at the outside of the mold or something like this. I also have to watch out how parts of the mold will bend and orient them to the center to minimize bending. Nick -- Motormodelle / Engine Models: http://www.motor-manufaktur.de Ellwe 2FB * VTM 87 * DLM-S3a * cubic more to come ... |
I used to do some pewter casting of jewelry in silicone. One of our artist
friends was a pewter caster he used a two part silicone that wasn't designed as a casting silicone for some of his moulds. It was much cheaper than the casting silicone. It probably didn't last as long but the price difference was worth it. I don't remember the casting temperature of zinc but it might work. So look around for lower cost silicones that might work. Karl ""Nick Müller"" wrote in message ... Helpful audience! Today, I made my first spinn-casting with zinc. It was just a first test shot to see what I can do wrong and what I did already do wrong. So the mold was just a plaster mold [1] and the zinc was just some scrap zink sheet metal for roofing. That zinc proofed to be good enough and I will use up all the rest before going to the costy zinc I ordered. At least, the spin caster was a success. I had no other motor at hand, so the disk is rotating with nearly 1400 RPM. Direct driven! The disk has a diameter of 12". I thought more g-force = better surface. It seems, that that is right. No problems with vibration, as the frame where all the suff sits in is quite heavy. The first casting was a (partial) success, some detail very good, other bad. But that only where I had bubbles in the plaster. Also a partial failure, because I didn't melt enough zinc. I have to cut the inlet (in the center of the disk, because to much is cooling down there and remains there and doesn't flow down into the mold. So I will make some mods, add a brake to stop the disk spinning and add shielding and paint. Will put pics and explanations to my HP. This time in English, so you don't have to babelguess about what I have written in Kraut-Language. Will take some days, but I will keep you informed. Oh, the silicone is damned expensive! 1kg (2 pounds) about 50 EUR, that are 60$. :-( OK, it withstands 500°C (930 F), zink poring temperature is 400°C (750F). But that stuff is to expensive for playing around. I will think about to put the rubber in some supporting form to save some rubber. [1] that showed to be my newest invention "lost plaster casting". Also, I baked it too long in the oven. It broke in 3 parts over night. Some super glue fixed that. I didn't get the castings out of the mold, so I broke it apart. It was some wothless casting anyhow. Nick -- Motormodelle / Engine Models: http://www.motor-manufaktur.de Ellwe 2FB * VTM 87 * DLM-S3a * cubic more to come ... |
Karl Vorwerk wrote:
One of our artist friends was a pewter caster he used a two part silicone that wasn't designed as a casting silicone for some of his moulds. pewter melts at 200°C to 250°C (390°F to 480°F), that's a big difference. They do sell silicone for pewter casting that is about 25% cheaper than the zinc stuff (no max. temp. indicated) But I will shop around and see if I can get something cheaper from the manufacturer. Nick -- Motormodelle / Engine Models: http://www.motor-manufaktur.de Ellwe 2FB * VTM 87 * DLM-S3a * cubic more to come ... |
I new there was a significant difference but was too lazy to look it up.
Hopefully you can find something that will do the job cheaper. Karl ""Nick Müller"" wrote in message ... Karl Vorwerk wrote: One of our artist friends was a pewter caster he used a two part silicone that wasn't designed as a casting silicone for some of his moulds. pewter melts at 200°C to 250°C (390°F to 480°F), that's a big difference. They do sell silicone for pewter casting that is about 25% cheaper than the zinc stuff (no max. temp. indicated) But I will shop around and see if I can get something cheaper from the manufacturer. Nick -- Motormodelle / Engine Models: http://www.motor-manufaktur.de Ellwe 2FB * VTM 87 * DLM-S3a * cubic more to come ... |
On Mon, 22 Aug 2005 10:32:53 +0200, (Nick Müller)
wrote: with ... rho(zinc) = 7 kg/dm^3 = 7000 kg/m^3 a = 3220 / 2 m/s^2 = 1610 m/s^2 h = 0.15 m ... I get: p = h * rho * a p = 0.15 * 7000 * 1610 p = 1690500 [Pa] = 16.9 bar = 245 PSI This doesn't sound too frightening. Or did I screw this one up too? MathCAD agrees. |
Don Foreman wrote:
MathCAD agrees. Thanks for X-checking! Just doing the paint job, but it takes so long to dry (two sides, two times). Guess that there will be photos tomorow... Nick -- Motormodelle / Engine Models: http://www.motor-manufaktur.de Ellwe 2FB * VTM 87 * DLM-S3a * cubic more to come ... |
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