Choosing the right surface treatment is key to reducing friction, improving corrosion resistance and achieving longer bearing life

Citation

(2005), "Choosing the right surface treatment is key to reducing friction, improving corrosion resistance and achieving longer bearing life", Industrial Lubrication and Tribology, Vol. 57 No. 5. https://doi.org/10.1108/ilt.2005.01857ead.001

Choosing the right surface treatment is key to reducing friction, improving corrosion resistance and achieving longer bearing life

Choosing the right surface treatment is key to reducing friction, improving corrosion resistance and achieving longer bearing life

Keywords: Coatings technology, Surface treatment, Bearings

The demands of modern manufacturing for longer operating life, increased resistance to aggressive media and reliable operation even in extreme environments, mean that bearings today are served by a large number of coatings and surface treatments to combat friction, corrosion and wear. The problem for the designer is to select the optimum process for a particular application. There may even be a range of options available, all of which offer reasonable solutions – the choice then, is one of cost and availability.

Among bearing suppliers, Barden has considerable experience of this area of technology, due to coatings and surface engineering processes being an integral part of its special design capability. In this field, Barden works together with recognised leaders to provide advanced coatings and surface treatments that combat friction, prevent corrosion and reduce wear, even under the harshest operating conditions. The resulting benefits are improved performance, lower running costs and longer service intervals (Plate 1).

Plate 1 Barden's bearings technology reduces friction and improves corrosion resistance

Perhaps the most common process that limits the effective life of engineering components such as bearings is wear. The fundamental problem is that engineering surfaces are neither flat nor smooth, and when two surfaces (such as a ball and raceway) come into contact, only a very small percentage of the apparent surface area is actually supporting the load. This can often result in high contact stresses, which lead to increased friction and wear of the component.

Because the wear rate of a material is proportional to the load applied to it, and inversely proportional to its hardness, one obvious way of reducing wear on bearing components is to increase the hardness at their surface. This is commonly accomplished using hard coatings such as electroless nickel, hard anodised aluminium and thin dense chrome. In addition, other hard coatings, such as titanium carbide, carburising, and both carbo- and plasma nitriding are also widely used. Barden offers all of these treatments and coatings as an effective means of enhancing the performance of its super- precision bearing systems.

Where the problem is corrosion, rather than wear, the challenge is to produce a surface that is less chemically reactive than the bearing substrate material. This is achieved with a range of processes including

• •

  hard chrome coating;

• •

  galvanised zinc;

• •

  zinc/nickel plating;

• •

  titanium carbide;

• •

  electroless nickel plating;

• •

  titanium nitride; and

• •

  passivation treatments

For applications requiring good anti- corrosion performance, Barden also offers advanced material technologies such as with the revolutionary X-Life Ultra® high nitrogen steel bearings. In controlled salt-spray tests, X-Life Ultra® bearings give superior corrosion protection to those manufactured from industry standard steels such as AISI 440C.

In addition to the hard coatings offered to prevent wear and corrosion, Barden also provides a range of solid lubricant films for use in the most exacting environments (i.e. space and medical applications), where traditional fluid lubricants would be rendered ineffective. Solid films offer the advantages that their friction is independent of temperature (from cryogenic to extreme high temperature applications), and they do not evaporate or creep in terrestrial vacuum or space environments.

The solid soft film lubricant can either be applied directly to the surface or transferred by rubbing contact from a sacrificial source such as a self-lubricating bearing cage. Examples of these two processes include the application of physical vapour deposited MoS2 and Barden's PTFE- based TB polymeric cage material. The processes are complementary and have been used successfully in a variety of extreme aerospace applications.

Surface engineering processes – four key steps in determining which one to use

Because of the large number of coatings and surface treatments that are available to combat friction, corrosion and wear, it is often difficult for designers to select the optimum process for a particular application. To help designers in this respect Barden has produced a four- step guide, which gives a simplified approach to the problem. The four steps are:

1. 1.

   Identify the limiting factor(s) on bearing life – friction, wear, and corrosion.

2. 2.

   Prepare a list of candidate coatings and surface treatments, eliminating those considered unsuitable on grounds of thickness and/or processing requirements (e.g. high temperature).

3. 3.

   Where possible, consult previous case histories of similar applications for verification of process suitability and produce a short-list of preferred candidates.

4. 4.

   Refer to detailed surface engineering specifications to select the optimum process.

As an addition to these guidelines, in all cases, particularly where there is little or no proven record of a process for the application, it is recommended that suitable qualification trials be carried out before a respective process is selected, in order to verify its suitability.

For further information, contact: Trevor Morris at tmorris@barden.co.uk