HcIT was developed by condition monitoring consultant Paul Varty some ten years ago as a service offered by his then company Midland Preventative Maintenance (MPM) in the UK. Varty specialised in maintenance activities aimed at preventing machinery breakdowns, working 15 years with British Coal prior specialising in condition based maintenance.

 

The service was used throughout UK coal mines for approximately 10 years until British Coal was privatised and became RJB Mining, which retained the use of the service. Further consolidation followed when UK Coal took over the mines and the service was no longer used.

 

The original concept started in 1993 when operational problems were severely affecting the performance of two underground mine roof-bolting machines at British Coal's Asfordby Mine. The machines, imported from the USA, were Fletcher Drill Rigs and were critical to mining operations, each having up to 36 operational cylinders plus seven main control valve-banks.

 

After around 18 months operational service, the drill rigs began to suffer problems with hydraulic cylinder seals. The cylinders developed internal leakage faults, adversely affecting the performance of the machine; and in some cases failing completely, creating unwanted breakdown situations. Varty was asked to find a suitable method for "predicting" internal cylinder seal failure.

 

Several techniques were trial tested for the purpose of monitoring and assessing levels of fluid bypass within the cylinders, including advanced vibration analysis techniques. By far the most successful method was an adaptation of shock-pulse technology (primarily used for evaluating the operational condition of rolling element bearings).

 

The system works through fluid flowing through an orifice which generates a portion of ultrasonic noise. This is detected, converted into audible sound which can be heard and measured. At this stage the detection of ultrasonic noise is an indication of the presence of fluid flow only, and does not relate to the volume of flow or the severity of the problem.

 

Several factors have to be considered when evaluating the noise readings,including fluid operating pressure, fluid operating temperature, orifice shape and size.

 

Exhaustive tests were carried out on a series of hydraulic cylinders, involving introducing seal faults of known shape and size; measuring and recording the bypass flow; recording the fluid temperature; recording the fluid pressure; and recording the measured noise. Each series of tests was conducted with alterations to only one variable per sensitivity setting.

 

The reference level of the monitoring equipment is critical to the reading if meaningful results are to be gained. The sensitivity is adjusted by altering the "initial value" (dBi) of the meter.

 

All tests conducted had to be carried out over a wide range of meter sensitivity in order to establish "norms". These norms were used to set limits of 20dBn and 35dBn (to maintain an analogy with bearing condition evaluation) to aid the evaluation of by-pass fluid flow severity. The normalised shock-pulse value dBn is used to assess the severity of a bypass problem.

 

The technique is equally successful when monitoring hydraulic control valve banks as well as hydraulic cylinders. Such items as faulty relief valves and worn components can easily be detected and quantified - all without the need to strip-down for inspection.

 

The success of the technique resulted in the method being adopted firstly by British Coal and then by RJB Mining for the commissioning, monitoring and pre-salvage testing of powered roof supports, prior to the eventual demise of the UK longwall mining industry.

 

Varty and MPM parted company last year and he has gone on to developing the HcIT technique into state-of-the-art analytical software, particularly suited to longwall mining applications. The software is fully licensed and is security protected.

 

“A further major advantage of the technique is that the user can be totally independent of any manufacturer or repairer of hydraulic machinery or components, therefore being able to assure accurate and impartial information. The technique can be adopted directly by an end user or by an independent service provider,” said Varty.

 

The software is available to longwall mines as stand alone software or as a complete package with an SPM T30 Ex monitoring instrument.

 

To enable the software to calculate the sensitivity setting of the monitoring hardware a few basic parameters have to be inputed including system pressure, system temperature, and hydraulic fluid viscosity index. The software then produces an exception report, detailing all serious problems with requires actions and approximate bypass flows.

 

Varty said RJB’s Asfordby mine saved £50,000 in refurbishment costs as a direct result of inspection of the powered roof supports and the accurate identification of spares requirements.