Removing Pitting and Rust From an Enclosure

Brent Hilpert bhilpert at shaw.ca
Thu Jul 20 02:02:50 CDT 2017


On 2017-Jul-19, at 11:37 PM, Rob Jarratt via cctalk wrote:
>> -----Original Message-----
>> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Chuck Guzis
>> via cctalk
>> Sent: 20 July 2017 03:34
>> To: Fred Cisin via cctalk <cctalk at classiccmp.org>
>> Subject: Re: Removing Pitting and Rust From an Enclosure
>> 
>> On 07/19/2017 07:13 PM, Fred Cisin via cctalk wrote:
>> 
>>> In most places other than the south and Chicago, Coke and Pepsi are what
>>> is used.   I don't think that SNL (Saturday Night Live) ever did a "No
>>> Coke; RC" skit.
>> 
>> There's also some stuff called "Naval Jelly"
>> 
>> http://www.loctiteproducts.com/p/s_trmt_naval/overview/Loctite-Naval-Jelly-
>> Rust-Dissolver.htm
>> 
>> I was going to suggest leveling with Bondo, but that seemed the cheap way to
>> go.
>> 
>> I've used Bondo many times to fill missing bits of broken plastic
>> faceplates.   A little sanding and a coat of paint and it looks
>> downright presentable.
>> 
>> Machine tools (particularly Chinese ones) that use gray iron castings are often
>> smoothed with a Bondo-like putty before being painted.
>> (They're not very pretty under the putty).
>> 
>> If you were really serious about this, you could plate a generous coat
>> of copper, sand it smooth, then plate a layer of nickel.   But if you've
>> never done electroplating, it's probably not a good idea to start with something
>> valuable.
> 
> 
> Well I could always see if I can get electroplating done professionally without spending a fortune, although trying myself with something unimportant is also an option. But first I would need to know what the finish actually is. There seem to be two common finishes to the metal used in MicroVAXen, DECstations and the like, one is a sort of subtle yellow, the other is a silvery finish. In this case it is a silvery finish. Can anyone tell me what those two finished actually are? I am guessing it is nickel. If that is the case, why the copper plating first?

The yellowish plating is probably chromate conversion:
	https://en.wikipedia.org/wiki/Chromate_conversion_coating

A copper layer can perform some filling and smoothing function in a plating job.
Its perhaps more significant purpose however (as I understand it in my limited experience with having plating done*), is to provide an oxygen barrier for the steel substrate.

(* OT, FWIW: I once went through the trial, albeit educational, of having a chrome Scott radio chassis replated. Longer tale.
A proper chrome plate job is not chrome on steel, it's copper on the steel, then nickel, and finished with a few atoms of chrome.)



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