Safer, harder coatings

Louise Smyth

For decades hard chromium plating (HCP) has been the engineer’s choice for wear surfaces, tools and parts subject to harsh environments, but health and safety concerns and environmental constraints on the process now demand an alternative.

Heat treatment and hard coatings specialist the Wallwork Group strongly advocates Nitron CA ­ a form of chromium nitride (CrN) that is safer and produces a harder film with heat and chemical resistance that also offers an attractive bright silver finish.

Nitron CA is twice as hard as HCP and forms a good bond to the substrate.

Deposited as an even layer it follows the contours of the part closely and maintains coverage on edges and corners.

It shares many of the characteristics of HCP: it is chemically unreactive and therefore stable and corrosion resistant, the surface is smooth and so highly lubricious, it is heat resistant and can be applied in high thicknesses.

This makes it ideal for wear surfaces such as medical devices subject to frequent harsh cleaning and in engineering applications that could wear softer materials such as bearing surfaces and for tooling, including dies and punches.

Nitron CA is applied by physical vapour deposition (PVD) under vacuum conditions at low process temperature.

Within an electrically charged environment, the donor material is placed in a small crucible inside the coating chamber and bombarded with an electron beam to create a vapour or micro fine particles.

Components, placed on racks, are subject to a negative electrical charge and rotate through the vapour to attract the microscopic droplets, which are drawn to the surface to create an even film that can vary in thickness according to the application.

Manufactures seeking to comply with the requirements of REACH regulations in the EU and OSHA legislation in the USA can be assured that Wallwork PVD processes are environmentally acceptable.

Only solid, non-toxic and fully recyclable source materials are used, along with inert process gasses with no toxic waste products from the process.

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