Paul Wilson

25 October 2016

Conveyor Idler Bearing Wear Detection

Using Fibre Optic Acoustic Technology

For Mining3

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Formation of Mining3

• CRCMining was established in 1991 within the Australian Government’s Cooperative Research Centre initiative.

• Generally regarded as the most successful entity to emerge from the program, CRCMining is a fully industry funded organisation.

• In 2016, CRCMining and CSIRO Mineral Resources division joined forces to become Mining3.

• The new entity encompasses all of CRCMining’s capabilities and CSIRO’s mining extraction-related research activities.

• Mining3’s combined research expertise significantly boosts its ability to rapidly develop new technologies, critical to the mining industry.

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Conveyor maintenance issues1

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Previous attempts to detect failures

Fibre optic distributed acoustic sensing

Early results and interpretation

Agenda

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Section 1Conveyor maintenance issues

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Conveyor maintenance is expensive

Metso belt in the desert (courtesy Metso)

1 km of belt contains about 6,700 bearings

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Rollers fail in several ways

• Casing failure

• Pizza-cutter failure

• Bearing failure Total bearing collapse

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Section 2Previous attempts to detect failures

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Methods of monitoring rollers

1. Visual and auditory inspection – walking the belt

2. Acoustic sound recording and analysis

3. Thermal imaging cameras

4. Smart-idler technology: radio connected sensors on

each idler

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Limitations of current methods

Visual and auditory inspection – walking the belt

Time consuming; tedious; requires personnel in constant attendance;

subjective

Acoustic sound recording and analysis

Insufficient time at each line stand to generate clear enough acoustic

signals;

Contamination by extraneous noise; frequently misses roller faults

Thermal imaging cameras

Heat is unreliable as an indicator; early stage forewarnings not visible in

infra-red

Smart-idler technology: radio connected sensors on each idler

Expensive; roller-mounted sensors get damaged; the sensor is throw-

away

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Section 3Fibre optic distributed acoustic sensing

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The fibre-optic cable is a chain of microphones

The concept is to receive acoustic signals every metre along the entire

belt. Each metre section is treated as an independent microphone.

Fastening the fibre to the conveyor frame

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Interrogator units – OptaSense and FFT units

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Underground fibre installation – a few challenges

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How the technology works

Glass fibre contains microscopic imperfections which scatter the light.

The imperfections cause “Rayleigh Scattering”, the same effect that

renders the sky blue.

Vibrations and temperature variations in the fibre cause refractive

index changes inducing readable signals into the reflected light.

High intensity, short pulse lasers are used coupled with sensitive

reflection detectors and fast analogue-to-digital converters.

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Single and dual pulse methodsSingle pulse methods

• Single pulse technology is the simplest approach. The return signal is amplitude de-modulated.

• It suffers from poor frequency response from 100 Hz upwards and temperature variations in signal quality.

• Spatial resolution < 1 metre

Dual pulse methods

• Depends on Moiré fringes generated by pulses of different frequencies. It is phase demodulated using a proprietary technology.

• It suffers from phase drift causing an overwhelming DC frequency component which must be removed.

• Spatial resolution about 8 metres but interpolated to 1 metre

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Section 4Early results and interpretation approaches

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Waterfall plots for viewing the entire belt

Bearing parameters & frequencies

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Early stage wear in ball races – spalling of surfaces

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Early stage wear in ball races – spalling of surfaces

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Using the equations, we can calculate the frequencies we expect to see in the frequency plots.

This was a frequency plot from Dawson Mine using single-pulse technology, before and after a roller change.

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Processing algorithm development – first attempts

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Improvements in signal processing methods

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When it’s time to change the roller

Your questions are welcomemining3.com

Supporters of the project, financially, in kind and supportive

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