Coating Selection for Low Load
Sliding Contact with an Abrasive
Product

Many products are abrasive, either as a result of their basic structure and composition or through the action of added fillers or pigments. In low load situations (as defined by the product areas discussed below), the choice of surface treatment can be made primarily on the basis of surface hardness, since even very thin coatings are able to support the contact.

Before continuing with the analysis, you should read the section on low stress abrasion.

The industrial areas covered in this section include textiles, printing, plastics, packaging, food, pharmaceuticals, leather goods, paints, inks, ceramic powders and wood processing. It is assumed that the part in question is in direct contact with the product (a textile guide, a print roller, a wood cutting tool, a food chute, etc.) and not with another engineering component. The applications cover seals where a non-metallic (e.g. a filled polymer or an elastomer) is in sliding contact with a shaft or a thrust pad.

The base material

The substrate will usually be mild steel, low alloy steel, austenitic stainless steel or aluminium alloy. Tool steels will be used for knives or other cutting or trimming tools.

Applications

A) Chipboard and other wood or composite products, and ceramic powder handling.

The content of wood products is always uncertain, with metal and mineral contaminants being common. The only safe solutions are:

1. Thermally sprayed or welded ceramics or cermets for maximum wear and damage resistance. E.g. WC/Co, alumina, chromium oxide, etc

B) Synthetic textiles (nylon, polyester), glossy newsprint, glass-filled plastics (including seals), and pigmented plastics other than black (i.e. specifically white, green and red). 

These share a common degree of abrasiveness, it being caused by oxide pigments (or silica in the case of glass fibres). They require a surface hardness of at least 1,000Hv to ensure acceptable wear rates:

1. Thermally sprayed or welded ceramics or cermets for maximum wear resistance. E.g. WC/Co, alumina, chromium oxide, etc
2. Nitriding using only an austenitic stainless steel substrate to achieve maximum hardness
3. Hard Chrome Plate will provide good wear resistance in applications where the contact is not concentrated on one area of the part. (E.g. can be used on a textile feed roller but not on an eye-guide)
4. PVD Coatings E.g. ceramics like TiN or CrN
5. Thermochemically formed, chromium oxide based composites loaded with ceramic particles

C) Black and white newsprint, natural textiles (cotton, wool), cardboard and packaging, carbon-fibre reinforced plastics, black-pigmented plastics, paints and inks, food products, leather and pharmaceutical products.

These are mildly abrasive and require a surface hardness over 600Hv for effective protection.

1. Thermally sprayed or welded ceramics or cermets for maximum wear resistance. E.g. WC/Co, alumina chromium oxide, etc
2. Nitriding or Nitrocarburising on any alloy steel substrate
3. Hard Chrome Plate will provide good wear resistance in all applications
4. PVD Coatings E.g. ceramics like TiN or CrN
5. Thermochemically formed ceramics, chromium oxide based composites loaded with ceramic particles
6. Carburising (Case-hardening) for low carbon steels to give high hardness and wear resistance
7. Local hardening (Induction) for medium carbon steels
8. Anodising for aluminium alloys, but will provide only limited protection. Best for dry food products under the lightest loads
9. Electro-Ceramic Coatings, will provide excellent abrasive wear protection for aluminium, titanium and magnesium alloys

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