Hard chrome plating is used for functional surfaces of engineering parts to improve their wear resistance, mechanical durability and corrosion resistance.
Note: PLEASE NOTE that this is not the same as decorative chrome, used as a decorative and anticorrosive coating for car and motorcycle components.
1. Hard Chrome
A catalytic bath is used to ensure the even layering of the chrome coating over the entire functional surface of a component. Both the internal and external surfaces of components may be chrome plated. The hardness of the coating is 1,000 HV. However, it is normal for microcracks to be found in the structure of the coating, running through the whole layer down to the basic material; aggressive corrosion media may penetrate through these tiny cracks, which may result in corrosion of the component at these spots. This coating is the standard hard-chrome coating used in mechanical engineering.
2. Trivalent Chromium
A catalytic bath is used for the electrodeposition of trivalent chromium. The hardness of the coating is 750 HV. The structure of trivalent chromium differs from that of hard chrome, and it is electrodeposited in overlapping flakes. The corrosion medium therefore cannot penetrate through the layer of trivalent chromium to the basic material. Trivalent chromium plating is used as an anti-corrosion layer.
3. Two-part Chrome
A two-part chrome coating is achieved by combining trivalent chromium electrodeposited to a thickness of 15 microns and hard chrome electrodeposited to a thickness of 35 microns. It has a markedly higher corrosion resistance while maintaining all the desired qualities of hard chrome. This coating is recommended for environments with highly aggressive corrosion.
Qualities of Chrome-Plated Surfaces
With regard to the industrial use of chrome coating for technical purposes, the most widely utilised qualities of chrome coatings are:
- low friction coefficient
- wear resistance
- corrosion resistance
- improved mechanical durability
- up to 30 microns - requires no further machining, polishing may be used depending on the desired dimension tolerance
- up to 60 microns – with subsequent grinding to desired dimension tolerance
- up to 300 microns - with subsequent grinding when restoring worn machine components, chromium is used to compensate for loss of material
Maximum Dimensions of Plated Components
2,000 mm(diagonally up to 2,500 mm)
Maximum Weight of Plated Components