Author Topic: Chrome: The process explained:  (Read 3501 times)

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Offline Richard Clark BS parts

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Chrome: The process explained:
« on: April 28, 2010, 12:35:11 PM »
What is chrome:

Chrome is slang for Chromium, one of the 91 naturally occurring chemical elements. Chrome is a metal, but it is not useful as a solid, pure substance. Things are never made of solid chrome. Rather, when you hear that something is chrome, what is really meant is that there is a thin layer of chrome, a plating of chrome, on the object (the bulk of the object usually being steel, but occasionally aluminum, brass, copper, plastic, or stainless steel).

What you call what?

"Show chrome" probably means chrome that is good enough to be on a winning entry in a car show. Although most OEMs rely on the "self-leveling" property of nickel plating to give sufficient reflectivity to roughly polished steel, chrome-lovers believe that the key to "show chrome" is to copper plate the item first and then buff the copper to a full luster before starting the nickel plating. Bridgestone never used "show chrome" just basic cheap chrome, over new smooth metal, this last statement is important, "New smooth metal"  not rusty.

Whether you start with bare steel or buffed copper, at least two layers of plating follow -- a layer of nickel and a layer of chrome. But high quality plating requires either very thick nickel or a minimum of two layers of nickel.

Salespeople are always looking for advantage, and they will use any good-sounding terms they can get away with! There are no laws that define what triple chrome plating actually means, so salespeople will be prone to call their service "triple chrome plating" if there are a total of 3 layers of any kind of plating, or "quadruple chrome plating" if there are 4. So those terms mean little.

The most important issue for durable chrome plating for outdoor exposure such as on a vehicle is that it should have at least two layers of nickel plating before the chrome: namely semi-bright nickel followed by bright nickel. The reason for this involves galvanic corrosion issues. The bright nickel is anodic to the semi-bright nickel, and sacrificially protects it, spreading the corrosion forces laterally instead of allowing them to penetrate through to the steel. Careful control of this issue is probably the principal reason that today's chrome plating greatly outlasts the chrome plating of earlier times. If a restoration shop offers only single layer nickel plating, they must apply it really really heavy if corrosion resistance is to be guaranteed.
Experts argue whether copper plating provides any additional corrosion resistance at all, but with or without copper plating, chrome on top of a single thin layer of nickel will not hold up to the severe exposure of a vehicle! Industry professionals call the two layers of nickel "duplex nickel plating", and that would be a much better term to use than "triple chrome" and such.

Restoring of parts back to "CHROME"

Chrome plating is hardly a matter of dipping an article into a tank, it is a long involved process that often starts with tedious polishing and buffing, then cleaning and acid dipping, zincating (if the part is aluminum), and copper plating. For top reflectivity "Show Chrome", this will be followed by buffing of the copper for perfect smoothness, cleaning and acid dipping again, and plating more copper, then two or three different types of nickel plating, all before the chrome plating is done. Rinsing is required between every step.
When an item needs "rechroming", understand what is really involved: stripping the chrome, stripping the nickel (and the copper if applicable), then polishing out all of the scratches and blemishes (they can't be plated over and any scratches will show after plating), then plating with copper and "mush buffing" to squash copper into any tiny pits, then starting the whole process described above.
Unfortunately, simply replating an old piece may cost several times what a replacement would cost. It's the old story of labor cost. The new item requires far less prep work, and an operator or machine can handle dozens of identical parts at the same time whereas a mix of old parts cannot be processed simultaneously, but must be processed one item at a time. If a plater has to spend a whole day on your parts, don't expect it to cost less than what a plumber or mechanic would charge you for a day of their time.

Steps involved to "CHROME"

    * Chrome Stripping
          o Rack part for stripping process
          o Dip in electrically activated sodium hydroxide
          o Dip in hot water
          o Strip off nickel with activated sulfuric acid (taking care that the nickel is not eroded)
          o Place in Media Blaster for coating preparation
    * Grinding
          o Grind off any and all pits/ protrusions/ unwanted metal material
          o Corrosion pits in "pot metal" (zinc cast) items, such as those found older vehicles, can be drilled or ground out and filled with silver solder and smoothed off prior to re-plating.
          o Smooth unwanted edges
          o As necessary, grind points of contact for future soldering
    * Cyanide Bath
          o Rack part with copper wire (some need weights attached to underside to prevent floating giving special attention avoiding the wire to touch the part)
          o Dip into Electro-cleaner wash
          o Rinse off soap lather
          o Dip in non-electrified sulfuric acid
          o Spray rinse with water
          o Place in cyanide
          o Place in cyanide rinse tank
    * Touching Up
          o Solder pits and fill in undercuts (with attention to avoiding a detrimental cut through part)
          o If applicable, attach broken metal pieces and filler metal with solder
          o Grind off extra solder to smooth finish
    * Acid Copper Bath
          o Place in cyanide to cover solder
          o Again dip in cyanide rinse
          o Spray wash with water
          o Cycle following steps for (1) hour intervals until acceptable appearance is seen:
                + Copper Bath
                + Sanding
                + Buffing
    * Chrome Plating
          o Re-rack part with wire giving attention to sensitive areas (points and sharp curves are corroded without care)
          o Clean with kerosene and soft-bristled brush
          o Hand wash with soap and water
          o Spray rinse with water
          o Dip in sulfuric acid
          o Dip in sterile DI (deionized) water
          o Nickel plated
          o Dip in DI water
          o Dip in chrome tank with settings specific to the part
          o Spray rinse with water
          o Buff to smooth finish


Perhaps we now better understand the easy word "CHROME" This information was taken from different parts of the web, all material was in "free public domain"
Thanks to The Chrome Industry newsletter, finishing.com, Brownsplating and Wikipedia for giving me some information to work with.

Richard Clark
812-944-1643  8am-6pm EST Weekdays

« Last Edit: June 10, 2010, 10:20:48 AM by Richard Clark BS parts »
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