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Process

The component will generally go through these different stages.

Degreasing to remove heavy soiling.

Manual cleaning to remove all residual traces of dirt and surface impurities.

Various pretreatments depending on the substrate.

Placed into the chrome plating vat and allowed to warm to solution temperature.

Plating current applied and component is left for the required time to attain thickness.

There are many variations to this process depending on the type of substrate being plated upon. Different etching solutions are used for different substrates. Hydrochloric, hydrofluoric, and sulfuric acids can be used. Ferric chloride is also popular for the etching of Nimonic alloys. Sometimes the component will enter the chrome plating vat electrically live. Sometimes the component will have a conforming anode either made from lead/tin or platinized titanium. A typical hard chrome vat will plate at about 25 micrometres (0.00098 in) per hour.

The chrome plating chemicals are very toxic. Disposal of chemicals is regulated in most countries.

Process Example

Information provided below is an example of an aluminum metal part being processed. These steps are specific to a number of metal parts, but actual steps will vary according to the design and condition of the workpiece.

Chrome Stripping

Rack part for stripping process

Dip in electrically activated sodium hydroxide

Dip in hot water

Strip off nickel with activated sulfuric acid (taking care that the nickel is not eroded)

Place in Media Blaster for coating preparation

Grinding

Grind off any and all pits/ protrusions/ unwanted metal material

Smooth unwanted edges

As necessary, grind points of contact for future soldering

Cyanide Bath

Rack part with copper wire (some need weights attached to underside to prevent floating giving special attention avoiding the wire to touch the part)

Dip into Electro-cleaner wash

Rinse off soup lather

Dip in non-electrified sulfuric acid

Spray rinse with water

Place in cyanide

Place in cyanide rinse tank

Touching Up

Solder pits and fill in undercuts (with attention to avoiding a detrimental cut through part)

If applicable, attach broken metal pieces and filler metal with solder

Grind off extra solder to smooth finish

Acid Copper Bath

Place in cyanide to cover solder

Again dip in cyanide rinse

Spray wash with water

Cycle following steps for (1) hour intervals until acceptable appearance is seen:

Copper Bath

Sanding

Buffing

Chome Plating

Re-rack part with wire giving attention to sensitive areas (points and sharp curves are corroded without care)

Clean with kerosene and soft-bristled brush

Hand wash with soap and water

Spray rinse with water

Dip in sulfuric acid

Dip in sterile DI (deionized) water

Nickel plated

Dip in DI water

Dip in chrome tank with settings specific to the part

Spray rinse with water

Buff to smooth finish

Industrial chrome

Hard chrome plating

Industrial chromium plating, also known as hard chrome or engineered chrome, is used to reduce friction, add wear resistance, or increase corrosion resistance. It is very hard, measuring between 66 to 70 HRC. Hard chrome tends to be thicker than the decorative treatment, typically ranging from 0.075 to 0.25 millimetres (0.0030 to 0.0098 in), but thinner and thicker layers are not uncommon. Surface defects and roughness are amplified, because hard chrome does not have a leveling effect. Hard chromium plating is subject to different types of quality requirements depending on the application, for instance, the plating on hydraulic piston rods are tested for corrosion resistance with a salt spray test.

There are two types of industrial chrome plating solutions:

Hexavalent chromium baths whose main ingredient is chromic anhydride.

Trivalent chromium baths whose main ingredient is chromium sulfate or chromium chloride. Trivalent chromium baths are not yet common, due to restrictions concerning color, brittleness, and plating thickness.[citation needed]

A typical bath composition of a hexavalent chromium bath is as follows:

Chromic acid (CrO3): 225300 g/l

Sulfuric acid: 2.253.0 g/l, although it is usually measured in molarity or percent concentration

Operating temperature: 45 to 60 C

Plating current: 1.553.10 kiloamperes per square meter DC

Anodes: lead with up to 7% tin or antimony

Maximum superimposed AC ripple allowed is 18%, preferred ripple is 5% to 10%

Chromium may be stripped anodically in an aqueous solution of sodium hydroxide or inhibited hydrochloric acid.

Automotive use

Formerly most decorative items affixed to cars were referred to as “chrome”, by which phrase was actually meant steel that had undergone several plating processes to endure the temperature changes and weather that a car was subject to outdoors. The most expensive and durable process involved plating the steel first with copper, and then nickel, before the chromium plating was applied.

Prior to the application of chrome in the 1920s, nickel was used. In the US for the short production run prior to the entry into the Second World War, plating was banned to save chromium and the decorative pieces were painted in a complementary color. In the last years of the Korean War, the banning of chrome was contemplated and several cheaper processes (such as plating with zinc and then coating with shiny plastic) were considered.

In 2007, a Restriction of Hazardous Substances Directive (RoHS) was issued banning several toxic substances for use in the automotive industry in Europe, including hexavalent chromium, which is used in chrome plating.

Chrome Plating

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