For example, the iron (Fe) level in a bearing sump may be 25 parts per million (ppm) and shows an increase of 10 ppm from the last reading. The bearing is pulled from service, and the condition is considered excellent. Over time, it is determined that similar scenarios occurred with a few additional bearings of the same type in the same application. Therefore, a reasonable conclusion could be to raise the threshold to 40 ppm and see if any wear is noticed when bearings are disassembled and inspected.

A dial indicator that is carefully positioned on a haul truck steering tie rod pin and lined up to the axis of force ensures an accurate bushing wear reading can be obtained.

Another example might include a measurement of 0.095 inches of slop on a particular pin/bushing connection. The bushing is almost completely worn through, and cracking is observed in the adjacent structure. If similar observations are documented for this same connection, it would be reasonable to lower this slop limit, perhaps to 0.08 inches.

The basic information needed to refine your inspection thresholds fall into two general areas:

• Document the condition observed when the decision was made to pursue corrective action; and

• Document the condition found upon disassembly.

These two basic sets of information allow a correlation to be made between what your threshold is indicating and what the condition actually is.

One note on thresholds or limits: Frequently, condition assessments are not simply good or bad, based on one reading or inspection. A trend is the better indicator. Establishing the baseline and then monitoring the trend sets a foundation for making fully informed decisions about if and when to pull equipment from service.

Continuous improvement

The basic purpose of these examples is to identify issues prior to an operational failure, allowing time to plan the corrective action to minimize production impact. Additional areas that may benefit from a simple, but carefully developed, inspection/assessment/action approach include electrical ground fault monitoring, suspension charge status, and bearing vibration. Each type of machinery, in its particular application, will have its own unique opportunities.

Most industries are shifting focus from maintenance to reliability, and most recently, to equipment optimization. The steps outlined in this article, and those that are appropriate for your specific application, are still critical to operational success.

Of course, with an investment in continuous monitoring technology, a maintenance program can be further improved with little to no downtime required for invasive, risk-introducing, maintenance steps. Until your operation is ready for that next step, however, implementation of these existing systems can yield improved equipment availability. AM

Craig Eller is Liebherr’s manager of maintenance and reliability programs and Kevin Gildea, P.E., is the product manager for its T 282 mining trucks.

The Evolution of Equipment Maintenance

Fix the failures: A 100-percent reactive approach to fix equipment as it breaks.

Preventive maintenance programs: Avoid failures. Disassemble equipment and inspect it for general problems. Replace components based on time or cycles.

Predictive maintenance programs: Avoid failures and minimize maintenance downtime. Conduct precision inspections with thresholds or limits dictating specific corrective actions.

Equipment optimization: A 97-percent-plus proactive approach based on automated condition monitoring. Most recurring manual inspections/samples are eliminated. Analysis determines precise action based on production schedule and empirical failure trends.