Viewpoint: bearing down on failure

Bearings are fundamental components in engineering, yet in two thirds of cases where they fail prematurely, the causes – incorrect fitting, poor lubrication or contamination – are avoidable.

A variety of tools and techniques that are neither complicated nor expensive can help maintenance staff overcome such risks.

Small and medium-sized bearings are usually cold-mounted. This demands proper installation tools designed to have an interference fit that ensures forces are only applied to the retaining ring of the bearing.

Some favoured methods are too aggressive and can transmit installation forces through the rolling elements rather than the casing – causing damage to the raceways before the bearing has made a single revolution.

A variety of tools and techniques that are neither complicated nor expensive can help maintenance staff overcome the risks of bearing failures

When mounting larger bearings, heat is often used to expand the bearing inner ring. The old method of immersing the bearing in a heated oil bath can introduce contamination. Using dedicated induction heaters will allow the bearing to be heated efficiently, controllably and safely.

At the same time, rotating shafts must be correctly aligned in all three dimensions. Faulty alignment increases friction – driving up energy consumption and shortening the life of bearings and other components.

Lubricant needs

Poor lubrication is the largest single cause of premature bearing failure, so an effective programme is vital to maintenance.

However, delivering the right amount of the right product at the right point is easier said than done. In a real production environment, it requires a detailed plan that encompasses the whole lubricant supply chain – including selection, storage, application and disposal.

Poor lubrication is the largest single cause of premature bearing failure, so an effective programme is vital to maintenance

Modern lubricants are tuned to the needs of different applications and range from ultra-low friction greases for energy-efficient bearings to high load, high temperate, high viscosity products for extreme applications.

There are also non-toxic or biodegradable types for food manufacturing or environmentallysensitive applications. A ‘one size fits all’ approach is never appropriate.

A further refinement is to use automated or centralised systems rather than expecting a technician to deal with every lubrication point in a machine or across the factory.

A key benefit of such systems is that they deliver the exact amount of lubricant necessary for efficient running – and, unlike humans, are not tempted to over-lubricate.

Conditions read

The rise of condition monitoring – in which process conditions are checked constantly – is an advance on the traditional approach of waiting for components to fail.

A ‘preventative maintenance’ approach spots early signs of failure, prompting repairs when they are needed rather than at fixed intervals.

Once reserved for high priority applications, this method is now applied more widely, thanks to the availability of simple, portable systems: temperature sensors, to identify the signs of excess friction; hand-held tachometers, to pick up deviations in operating speeds; and vibration sensors, which spot signs of wear or damage in rotating components.

A ‘preventative maintenance’ approach spots early signs of failure, prompting repairs when they are needed rather than at fixed intervals

Another technique that can extend bearing life is simulation. SKF recently developed a new model that is designed to help engineers calculate bearing rating life more realistically. It separates effects related to surface failure from those related to sub-surface failure.

The aim is to better represent the tribology of rolling bearings in rating life calculations. By using real condition monitoring data, engineers can make more accurate predictions.

Fixing these three fundamentals will not banish problems completely, but should ensure that premature bearing failure is rare rather than commonplace.

• Phil Burge is country communications manager at SKF