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Letter 1095
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Ted is absolutely correct about using internal anodes. Properly designed, zinc plating coverage can be quite uniform, especially if you can find a plating supplier using a cyanide electrolyte. Even with the extra tooling costs it will cost much less than electroless nickel plating.
Have you considered using precoated sheet steel? Coverage is guaranteed and you can avoid plating costs entirely. Galvanneal and electrogalvanized sheet stock work well in many cases for computer frames and chassis. Many computer manufacturers are now using precoated steels for some or all of their sheet metal parts. Pop the top on your PC and have a look inside. Chances are it's precoated steel inside. In a benign office atmosphere, precoated steels can provide adequate corrosion protection, even on cut edges. It may not work for everyone, but it's well worth considering.
Gary Krech
- Brighton, Colorado
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I am a believer in electroless nickel, but it is probably an overkill for a chassis. New Alkaline nickels work well and are not as expensive as EN.
From a practical point, I would find a plater that would do one for you in Alkaline zinc with a yellow chromate. You can take this unit and use an instrument with a small probe to see what coverage the plater got in the corners.(Well, very near the corner)
Any contract based on the demo part should have very specific thickness in the corners specified.
Quality zinc is the way to go. The cheapest plater is rarely the best and the most expensive is not always the best. Look for a good one that will take the time to understand your problem and offer some guarentees of quality and delivery.
James Watts
- Navarre, Florida
As a very slight clarification of what James said, because it is important to get good coverage in the corners but difficult to measure, the ambiguity is often resolved by specifying the minimum thickness at 'any spot that can be touched by a 3/4" diameter ball' (or some other diameter).
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 Ted Mooney finishing.com Brick, New Jersey |
Many job shop operations throughout the US plate zinc onto computer chassis and alkaline non-cyanide zinc plating is the process of choice for computer chassis. Cyanide zinc plating is no longer an economically viable option in the United States. Commercial alkaline non-cyanide zinc systems have better throw, are brighter, are more efficient, and are cheaper to operate.
Richard Painter
Cleveland, Ohio
Mr. Painter might be right about the advantages of non-cyanide, but as late as last year, I know of at least one plater who was still using cyanide zinc for chassis. He did have a non-cyanide zinc recently added to the line, and the operator preferred the latter, while the owner liked the cyanide zinc better. I can't recall the reasons.
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Tom Pullizzi |
I'll second that, Tom. While it is highly desireable to move from cyanide to alkaline non-cyanide for safety, to minimize hassles over cyanide in the effluent, and because the public is paranoid, I think it may be overstatement to say that cyanide plating is no longer an economically viable option.
If there is a study by Pavco that demonstrates that one of their competitor's non-cyanide baths delivers better brightness, throwing power, and efficiency than cyanide zinc, I'd like to see it. Similarly, if one of their competitors has a study showing that Pavco's system is better than cyanide, I'd like to see that too. Otherwise, with cyanide no longer having a champion with a vested interest, such studies are a bit hard to accept, and only remind me that the scientific literature had a very different cast when DuPont was still championing cyanide.
But, in the end, the fact is that alkaline non-cyanide zinc does work, and that's all that is really necessary considering the disadvantages of cyanide.
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Ted Mooney finishing.com Brick, New Jersey |
Galvanic corrosion should be taken into consideration for the future computer design because computers are not only used in offices but also on production lines where the serious corrosion environment is often encountered. Although plated sheets will be further painted, scratching and partially mechanical damaging are inavoidable during use and transportation. Both nickel-plating and zinc plating have advantages and disadvantages. Of course, zinc plating is cheaper than nickel plating. More importantly, zinc as a sacrificial anode can provide protection for other parts while nickel as a cathode could accelerate the corrosion of other parts in a computer. Using galvanized sheet as computer chassis material is a better choice. As I know, IBM is now thinking about zinc-cobalt alloy plating with blue chromating post-treatment in computer chassis design.
Ling Hao
- Grand Rapids, Michigan
I am currently working for a corporation that has installed a large number of computer systems, ISDN equipment, office LAN equipment, printers, and P.O.S. terminals in Pool supply companies in the Florida area. We currently seem to be experiencing problems with rust and corrosion involving rough edges, screws, I.O. Slots, drives, and print mechanisms. Where would would a company such as ours find more information on the chemicals that could cause this problem (chlorine, acids, etc..)? We are under a near law-suit condition, and withholding of final payment, since we are unable to bring these machines to a near 100% perfection. At least twice a week a CD-ROM, power supply, or motherboard is failing. We see large amounts of rust forming around the power supply, and all screws inside and outside of the cases on more than half the machines, and discoloration covering the copper wiring on some circuit boards.
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We have only been able to find one other case of this happening in a pool supply store, but most supply stores we have examined seem to be well ventilated, and are using older IBM 286/386 machines. The machines we are using are built with cheaper minitower cases, but the parts inside are quality (panasonic, western digital, diamond multimedia, intel etherexpress, intel CPU, US RAM, etc..) components. Could the older IBM machines be less effected by the chemical content of the air? Signed.. Confused.. Alfred Knox Winter Park Studios
Sequent manufactures computer systems which are enclosed in sheet metal housings. We recently began a new project which included some cost-reductions. One of the proposed cost reductions was to change our electroless Ni plated aluminum and steel chassis parts to a pre-plated cold-rolled steel design. The previous design which used the Ni plating was chosen for cosmetic appearance, compatibility with the Au flash plating on the circuit boards, and for the best conductivity with the gaskets used for sealing the enclosure for electromagnetic compatibility (EMC). Anyway, the logistics of the chassis change to pre-plated cold-rolled steel (GALXC material) was such that the proposal included changing only the outside chassis, while the inner chassis parts (brackets, several circuit-board holders, etc) were to remain as Ni plated parts. The 1st test of this in our humidity chamber was a disaster. Several of the newer Zn pre-plated parts were covered in a white residue, which we suspect is galvanic corrosion. The EMC testing showed a significant degradation in sheilding effectiveness. I would appreciate pointers to consultants, testing labs, and other resources which could help us answer the following questions: 1) Is the particular residue we are seeing from our humidity tests a result of galvanic corrosion? 2) Is the proposal of cost-savings by conversion from Ni plate to Zn pre-plated steel salvageable? 3) For galvanic compatibility, do we need to convert the entire chassis from Ni to Zn, and never let the two types of plating touch in any enclosure? 4) For galvanic compatibility, do we need to change the design of the circuit boards or the chassis to ensure that Zn plated steel never touches the Au plating on the circuit board? Pat Chewning
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