Hard chrome plating

Hard chrome plating is an electrolytic method that deposits chrome for engineering applications from a solution composed of chromic acid.

The deposits that are applied can vary from .25 – 1,000 microns thickness for a wide range of applications.
The thinner deposits that are used are done so to substantially increase the life of components in wear applications or corrosive environments, also the thicker deposits would be used for salvaging and repairing damaged or worn components.

High hardness

Electrodeposited chrome is an extremely hard substance with typical values of 850 – 1050 HV (63 – 70 HRc) which relates back to the term ‘hard’ chrome.
Thus making it an extremely durable coating for wear resistant and abrasion resistant applications.

Corrosion resistance

Hard Chrome possesses a high resistance to atmospheric oxidation, and a good resistance to most oxidising and reducing agents, (aside from chlorides and other halides) leading to its wide-spread use in the Food and Chemical Industries.

Applications

– Hydraulic and pneumatic piston rods and cylinders
– Plastic and rubber rolls, moulds, dyes, screws etc.
– Automotive and mechanical components
– Press tools and punches
– Print cylinders and plates
– Food machinery
– Valves, gates and bodies
– Mining equipment
– Timber and paper processing equipment
– Pump shafts and rotors
– Textile components

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What is hard chrome plating?

Did you ever want to know what hard chrome plating was?

Hard chrome plating is an electroplating process in which chromium is deposited from a chromic acid solution.

The thickness of hard chrome plating ranges from 2 – 250 micrometers.
A variety of hard chrome include micro-cracked chromium, micro-porous chromium, porous chromium and crack free chromium.
It is vital that the micro-cracked coatings and porous coatings have a minimum thickness between 80 – 120 micrometers in order confer adequate corrosion resistance.

The formation of micro-porous chromium is achieved by a specialised plating method involving the use of inactive suspended particles.
Porous chrome plating is manufactured by etching electro deposited chromium – these are designed to retain lubricant, for sliding type applications.

Chrome plating is used mostly for resistance against wear and corrosion as opposed to its low friction characteristics.
However, there are environmental concerns associated with disposing the plating solution, which has lead to many users of chrome plating to seek out alternative coating methods.

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Hard Chrome Plating & Decorative Chrome: What’s the difference?

Have you ever wondered what’s the difference between decorative chrome or hard chrome plating?

Chromium is about the same hardness in both decorative chrome and hard chrome plating, about 800 to 1000 VHN (which is incredibly heavy). The main difference is found in the thickness of the deposit.

For the decorative purpose of chrome, it is seated best on nickel, which adheres incredibly well to copper – the combination of all three offers possibly the best corrosion protection resistance available. Decorative chrome thickness can vary from anywhere between a few hundredths of a mil to one mil. The mirror finish will effectively only be as good as the finish that is on the surface before the chrome, so it’s all a very difficult process at times.

Mould Tool Polishing
An example of chrome plating

For the purpose of being functional, or take either take advantage of the extremely low friction that chrome holds or for building surfaces and pistons, hard chrome will be plated with a thickness anywhere between 1 to 50 mills.

When used as a bearing surface, chrome simply must be micro-finished, something which will then provide a level of friction much lower than any other metal when used against the likes of steel, iron, brass, bronze or aluminium alloys. There’s something that you mustn’t do; Do not use chrome against chrome. Chrome is much harder than casehardened steel, so we are then left with a perfect set-up for longwearing working surfaces. Chrome will resist pretty much all organic and inorganic compounds and acids, except hydrochloric acid.

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