bwhite@oucsace.cs.ohiou.edu (Bill White ) (02/02/91)
I apologize in advance for cross-posting, but I have asked questions along this general theme before and gotten little or no response. Please direct all responses to me, or if you must follow up please do it in sci.electronics. Essentially I am trying to form four (4) 1 meter hemispheres (with a 10 degree "excess", making it slightly more than a hemisphere) for use in a Van de Graaff system. After investigating various technologies such as spun aluminum and explosive forming, I found them either beyond my means financially and/or beyond the abilities of our university. It was suggested I investigate electroplating. Cost for custom-production of the four hemispheres by traditional methods was quoted from $1000 up. This is more than I would like to pay. What I would like to do is take a form, 1 meter diameter, coat it with a conductive material, plate a 1/8 to 1/4 inch (sorry about mixing measurement units) thick layer of copper (yes I know that's awful thick), do some elementary forming, and then coat it with nickel and then chromium. The resulting finish *must* be smooth, though I don't really care what it looks like. The copper *must* be malleable, though if it can be annealed to make it malleable that is fine as well. One idea that popped into my head was to use an aluminized mylar spherical balloon, strike plate it in a cyanide plating solution, then finish plating the copper in an acid solution. Most of my metal plating experience, however, has been with small items using only acid solutions. If I can find a company willing to do this, at a cost I can afford, fine. If not, I would like to undertake this project using the university's facilities. Here are the questions I have: 1. Is it feasible to plate onto an aluminized mylar surface? I know that it is possible to plate onto insulating surfaces *somehow*, so I would assume that plating onto an aluminized surface would be easier from the standpoint of conductivity. 2. Does anyone know where to get spherical aluminized mylar balloons in the range of 750mm to 1m diameter? (if the answer to the above question is yes, of course) 3. Can anyone suggest any references on plating copper to a thickness of 1/8 to 1/4 inch? References on strike-plating onto aluminized surfaces? 4. I assume it would be simpler to have some company finish the nickel and chrome plating (I actually don't know if I need chrome, so long as the nickel won't corrode I could just use nickel alone). Is it practical to do this type of plating myself using University resources, or would it be easier to do this commercially? The thickness does not matter; the surface condition does. I will not be placing the hemispheres in SF6 (I can't afford it; if air breakdown is a problem I may go for dehumidifying or for some other, cheaper gas). Please respond to bwhite@oucsace.cs.ohiou.edu Thank you for your time.
ornitz@kodak.kodak.com (Barry Ornitz) (02/02/91)
In article <2867@oucsace.cs.OHIOU.EDU> Bill White writes: >1. Is it feasible to plate onto an aluminized mylar surface? I know that >it is possible to plate onto insulating surfaces *somehow*, so I would >assume that plating onto an aluminized surface would be easier from the >standpoint of conductivity. Yes, it is feasible. You will need an electroless copper to produce the base layer, followed by a "strike". Conventional acid plating can be used over this. The aluminized surface would be a hindrance and actually interfere with the plating. (Remember the electrochemical series when you consider what can be plated over what.) >2. Does anyone know where to get spherical aluminized mylar balloons in >the range of 750mm to 1m diameter? (if the answer to the above question >is yes, of course) I doubt it would be spherical enough. >3. Can anyone suggest any references on plating copper to a thickness of >1/8 to 1/4 inch? References on strike-plating onto aluminized surfaces? Building up to this thickness will be next to impossible. Grain growth and leveling problems will be the killer. Stress will also develop as the thick- ness grows. You should be able to get more information in something like "Modern Electroplating Handbook". Getting above 10 to 20 mills is going to be quite difficult. See my comments above about aluminized surfaces. >4. I assume it would be simpler to have some company finish the nickel >and chrome plating (I actually don't know if I need chrome, so long as >the nickel won't corrode I could just use nickel alone). Is it practical >to do this type of plating myself using University resources, or would >it be easier to do this commercially? The thickness does not matter; >the surface condition does. You could not do this yourself without lots of specialized equipment, chemicals, and most importantly experience. I really think this technique in general is a poor one. I would look carefully at spun aluminum or spun copper using wooden forms. If you have to go the electroplating route, consider plating over well-sealed wooden forms. Use something like polyester resin to seal the wood. A number of plating houses can start here. If they can bronze baby shoes, they can copper plate this form. Strike solutions tend to be expensive, complex, and very poisonous. Why do you always have such grandiose projects, Bob? ;-) Barry ----------------- | ___ ________ | Dr. Barry L. Ornitz WA4VZQ | | / / | | Eastman Kodak Company | | / / | | Eastman Chemical Company Research Laboratories | |< < K O D A K| | Process Instrumentation Research Laboratory | | \ \ | | P. O. Box 1972, Building 167B | |__\ \________| | Kingsport, TN 37662 615/229-4904 | | INTERNET: ornitz@kodak.com -----------------
ardai@teda.UUCP (Mike Ardai) (02/02/91)
In article <2867@oucsace.cs.OHIOU.EDU> bwhite@oucsace.cs.ohiou.edu (Bill White ) writes:
- Essentially I am trying to form four (4) 1 meter hemispheres (with
-a 10 degree "excess", making it slightly more than a hemisphere) for use
-in a Van de Graaff system.
You might want to look into flagpole finials. I don't know if they come
in this large a size, but it is worth a shot. They use them as the grounded
targets for Van de Graff's generator at the Boston Museum of Science.
/mike
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\|/ Michael L. Ardai Teradyne EDA East
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/|\ ...!sun!teda!ardai (preferred) or ardai@bu-pub.bu.edupetes@sheridan.NCD.COM (Peter C. Simpson) (02/06/91)
Two points - immersion of your gas filled balloon in a plating bath of
higher density will destroy its shericity. You would need to fill it with
something of equal density.
Also, electroless plating is normally used to plate non-conductive surfaces.
It is commonly used to plate plastic computer enclosures, for instance. The
process involves a bath in an etchant to activate the plastic surface,
then a series of plating and rinse baths. Plating thickness is entirely
a function of time, but your thicknesses will be financially impractical to
achieve. 40 millionths of an inch of copper will take about 15 minutes, so
you're talking about one month for 1/8 inch. The standard process is to plate
nickel overthe copper for corrosion protection. Standard plating thicknesses
for shielding applications would be 40 uI copper, 10 uI nickel.
I guess that if I were trying to do this, I would build up a thickwalled hollow
sphere out of ABS or some other platable plastic, and then put a much thinner
coating than your 1/8 inch on. Finally, you might look at the plastic ball/
electroless shielding to generate a thinly coated sphere, then use this
conductive
part for a faster depositing electrolytic process.
I can recommend sources for electroless platers, if you are interested.
Peter Simpson
Network Computing Devices