Teknis: Wheel Condition Monitor

Wheel Condition Monitor (WCM)

The early detection of wheel flats and other defects has become of increased importance to freight and mass transit operators because of economic pressures to raise productivity, usually through longer or more frequent trains and higher axle loads. As a result, the increased likelihood of serious damage to rails, track structure and rolling stock is of major concern to the operator for maintenance and safety reasons.

In addition, the increased use of concrete sleepers has resulted in track structures having a much lower compliance, or higher stiffness. This, in turn, exacerbates the effects of impact loading on rails, sleepers and fasteners.

The Teknis Wheel Condition Monitoring System (WCM) derives an energy related criterion from the real-time processing of the rail vertical vibration data in the relevant frequency domain. The vibration rating due to any given wheel is normalized against a standard vibration reference, being the smooth wheel tread of a new or freshly machined wheel. It has been repeatedly shown that this process results in the consistent and repeatable grading of a range of wheel tread irregularities ranging from impact flats, skids, built-up treads, spalls, shells, subsurface defects, out-of-round and multiple defects on the same wheel[1-8].

WCM is unique in its ability to characterize wheel tread defects using track frequency response criteria which are highly dependent on the track structure. Track response is influenced by rail section, sleeper and support type etc. This is factored into the Teknis system by way of user configured parameters.

This represents one of the main strengths of the Teknis approach, since competing systems have neither utilized or apparently recognized this important fact. It also implies that other systems would be limited to the detection of gross defects only, resulting from a lack of sensitivity to the range of tread irregularities noted above.

Continued development of the Teknis system has refined the resolution of the system to the point where previously hidden long term trends in wheel defect progression have become apparent. This information raises serious questions about the true cost savings of deferring wheel maintenance until the condemn point. For example, it is not uncommon to see the following occur when reviewing archives generated by Teknis' system.

The vast majority of wheel defects increase in severity over time until they reach the alarm limit.
At that point much more material must be removed from the wheel to salvage it than if it had been attended to earlier. This shortens the overall life of the wheel and places a wheel that has been subjected to extreme stress back into operation. Recent research suggests that such wheels are at higher risk of developing catastrophic sub-surface defects at a later time.
Wheelsets adjacent to seriously defective ones have a high probability of developing defects. It is not uncommon for an adjacent wheelset to show minor impacts just before the condemned one beside it is serviced, only to see it too cause an alarm and require exception based service three to six months later.