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Hard chrome plating is an electrolytic process used to coat workpieces with a layer of chrome, of variable thickness, giving excellent mechanical properties and very high corrosion resistance to the pieces which can subsequently be polished or rectified.
The main characteristics of hard chrome plating are:
All carbon steels, whether tempered or not; standard chromium, nickel and chromium/nickel steels; fine cast iron; copper and its alloys; aluminium, etc. can all be hard chrome plated.
Generally speaking, all materials which have already undergone a special thermal treatment (such as nitrided steels, cemented steels, high tungsten alloy steels, silicon carbide, graphite cast irons, etc.) are difficult to chrome due to a lack of metal bonding.
The industrial applications of hard chrome plating are essentially unlimited, with this technique normally providing better yields and a higher quality in the workpieces treated.
RECOVERY
To ensure that workpieces produced out of specification due to a manufacturing defect are given the correct dimensions.
To return workpieces which have suffered excessive wear back to their original dimensions.
Chrome plated workpieces can be restored to working conditions at a much lower cost than producing a new part, with equivalent or improved technical specifications compared to the original piece.
The chromium film can be deposited only in those regions that are out of specification, thus reducing the cost of the technique.
Recovered workpieces can be hard chrome plated once again if they become out of specification after long periods of use.
AS A MANUFACTURING PROCESS
Hard chrome plating is increasingly being used to improve initial production quality due to the excellent properties of this coating.
SPECIFIC APPLICATIONS
As a consequence of the unbeatable results obtained with hard chrome plating, certain applications use this treatment almost exclusively. In light of their importance, these applications will be discussed below in greater detail.
PHYSICAL PROPERTIES OF HARD CHROME COATINGS
| Property | Value |
| Density | 7,2 gr/cm3 |
| Melting temperature | 1,800 ºC |
| Hardness | 70 Rc = 1.100 Vickers |
| Electrical conductivity | 20.000 Ohm-1/cm-1 |
| Termal conductivity | 0,165 Cal/cm2 a 20 ºC |
| Coefficient of thermal expansion | 0,8 x 10-5 ºC-1 |
| Elastic modulus | 15.000 kg/mm2 |
| Reflectivity | Up to approx. 90% |
