letter 43876

High-Strength Electroformed Copper Parts  

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I'm interested in electroforming parts to create small, intricate pressure vessels. I've read all about large liquid rocket engines using elecroformed nickel and copper structures to produces parts that would be near-impossible to machine. Obviously these rocket engine structures withstand an incredibly high amount of thermal and mechanical stresses.

My project involves electroforming copper parts that must be able to withstand a fairly high level of stress due to pressurization. Although I've done a bit of research I've never seen anyone directly compare the mechanical properties of electroformed parts to those of raw machined stock. Will I be able to electroform parts capable of taking appreciable loads?

From what I've read in texts and in some of the finishing.com posts, the best mechanical performance sounds like it comes from pure, clean copper sulfate solutions with relatively low current densities. Is that correct?

Can someone recommend a good starting point for me to experiment with the plating solution and current levels? My part has roughly 0.6 ft^2 of area and I'm hoping to deposit roughly 0.120 inch of thickness. There is no need to produce these parts quickly so it is acceptable if it takes a long time to plate on the desired thickness.

Thanks! Finishing.com is an amazing resource!

-Ian

Ian Whittinghill
University of Southern California - Los Angeles, CA, USA

Ed. note: Thank you for the kind words, Ian. As you've already discovered, we at finishing.com personally contribute little of the technical expertise; we rely on the generosity of a good number of regular contributors. When you thank us, we trust that they realize that you are thanking them.

I think you should get a copy of the book "Properties of Electroplated Metals and Alloys", by W. Safranek. It's full of references to the properties of electroplated or electroformed copper (and other metals too) using different electrolytes and conditions. Also, mechanical work hardens copper (all kinds) and makes it more resistant.

Guillermo Marrufo
Monterrey, NL, Mexico

Also get ASTM B832 [link is to spec at TechStreet], 'Standard Guide for Electroforming with Nickel and Copper,' and a freebie, 'INCO NICKEL ELECTROFORMING PROCESSES AND APPLICATIONS,' http://www.inco.com/customercentre/nickelplating/science/pdf/EcopyElectroformingGuide.pdf

The above items together are basically an update of the Electroforming chapter in Electroplating Engineering Handbook, 4th Edn., although omit iron electroforming. The Electroforming chapter in The Canning Handbook, pages 573-590 (23rd Edn.), gives more information on plating Ni-Co alloys. The Electroforming chapter in ASM Handbook, Vol. 5 Surface Engineering, is short but gives more iron plating solutions and mentions periodic current reversal for producing fine-grained copper of excellent mechanical properties in greater thicknesses. One probably can locate additional information by searching on the authors and titles of papers presented at the 1996 AESF & NiDI Electroforming Course & Symposium, http://www.finishing.com/Library/conferences/eform96.html

However, I have some doubt that an electroformed copper pressure vessel is permissible under the ASME Boiler and Pressure Vessel Code. Staying below 10 inches diameter will avoid the regulations.

Also, pure copper isn't very strong and suffers from creep when moderately heated, so normally isn't used for pressure vessels. The wrought Cu alloys typically used are alloyed with Ni, Sn, Al, Fe, Zn, Mn, etc. * and have annealed strengths 1.5 to 4 times that of pure Cu. For higher strengths, Cu can be clad onto steel.** The NASA rocket application requires extremely high thermal conductivity rather than high strength -- an oxygen-hydrogen combustion chamber is cooled by liquid hydrogen -- so the only alternatives to copper are silver & gold.

*ASTM B171/B171M, 'Standard Specification for Copper-Alloy Plate and Sheet for Pressure Vessels, Condensers, and Heat Exchangers,' and ASTM B96/B96M, 'Standard Specification for Copper-Silicon Alloy Plate, Sheet, Strip, and Rolled Bar for General Purposes and Pressure Vessels.'

**ASTM B432, 'Standard Specification for Copper and Copper Alloy Clad Steel Plate.' "The material is generally intended for pressure vessel use but may be used in other structural applications where corrosion resistance or conductivity of the alloy is of prime importance."

Ken Vlach - Goleta, California