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The customer was facing ongoing challenges related to wear and contamination in their mill lubrication system, with no effective means of monitoring the problem in real time. Persistent contamination ingress, stemming from a known and difficult to resolve manufacturing weakness in the unit, led to increased wear, elevated lubrication costs, unplanned downtime, and reduced equipment life.
The existing Condition Monitoring Program consisted of regular vibration analysis conducted by an onsite technician, 12 weekly routine oil sampling, and a legacy laser particle counter displaying oil cleanliness at the machine. Significant limitations were identified with this monitoring approach.
Vibration analysis presented several challenges in this application. The slow-rotating nature of the equipment meant that fault frequencies occurred at lower ranges with reduced impact amplitudes, making detection difficult. Additionally, high background noise from tumbling balls and rods created a large noise floor that masked critical fault frequencies.
The complex gearbox design, comprising numerous moving components, generated a wide range of fault frequencies, making it difficult to isolate and identify specific issues within such a noisy and dynamic environment. Furthermore, limited physical access posed safety and logistical challenges, namely 24/7 operation restricted opportunities for handheld measurements, and no direct sensor access was available to the rotating bull gear.
The existing oil analysis approach had several limitations: laboratory testing turnaround time took up to two weeks due to the site’s remote location. There were inconsistencies in sampling intervals and practices which introduced potential errors, and infrequent sampling often failed to capture contamination or wear events. Additionally, the installed laser particle counter was not fit for purpose; it was rated for lower-viscosity oils and therefore struggled with high-viscosity and aerated lubricants. The counter was a manual check sensor which offered no system integration or alarm functionality.
To effectively monitor this critical asset given the existing limitations, a more advanced and integrated solution was required.
The required system needed to deliver real-time, tangible data without the long delays associated with traditional laboratory analysis. It also had to integrate seamlessly with existing networks and systems, providing automated alarming capabilities to promptly alert operators to developing issues. The system was required to eliminate or heavily reduce the reliance on manual data collection tasks to improve safety and efficiency. Furthermore, it needed to accurately track contamination, wear, and overall machine condition, while recording and storing data for ongoing analysis and trend monitoring to support proactive maintenance and informed decision-making.
To address the customer’s challenges and monitoring requirements, GVS recommended the installation of Atten2 OilWear S120 sensors. This advanced solution provides accurate ISO code measurements and real-time particle shape analysis, enabling deeper insight into both contamination and wear mechanisms. The system is fully equipped with alarm functionality and integration capabilities, allowing seamless communication with existing networks for faster, more informed decision making. Additionally, the inclusion of a bubble eliminator reduces oil aeration, ensuring more stable and reliable data for continuous condition monitoring.
Key Factors In developing an effective implementation strategy, several key areas needed to be considered. These included oil type, oil pressure, system temperatures, and the potential for aeration within the system. Additional considerations included accessibility of sampling points, a thorough review of the equipment’s P&ID while determining the optimal positioning of the Atten2 system.
The final set up consisted of 2x sensors one on the dirty side before the filter monitoring the contaminations and wear debris coming back from the Gearbox, pinion & Bull gear.
The second sensor on the clean side after the filters to monitor the cleanliness of the oil entering the equipment. We needed to add in the Bubble Eliminator System (BES) due to excessive aeration in the return lines.
Problem Intermittent data readings were observed, with low to no oil flow detected through one of the sensors.
Identifying the Issue A thorough inspection was carried out to ensure all taps and lines were correctly installed and the sensors were properly mounted. System pressures were then verified at multiple points, revealing lower than specification pressure at the outlet, which resulted in insufficient flow through the affected sensor.
Solution To resolve the issue, the inlet hose was relocated to a port with higher pressure, restoring proper flow. A manual flow rate check was also conducted at the sensor below the BES to confirm stable and consistent operation.
• Tuesday 6th Iso trend has a dramatic increase in the
>4 & 6 μm slight increase in the 14 μm
• Thursday 8th minor peaks in the >14 μm
• Dips in the trend indicate introduced filtration
• Thursday 15th Significant increase in contamination particles >14 μm
• Thursday 22nd Dramatic increase in all three size categories
• Saturday 31st equipment shutdown for Maintenance
The customer trialled a different brand of filter, which unfortunately performed poorly, becoming blocked within a short period. The filters were replaced with a second set. When the second set of filters also blocked, the system went into bypass mode, circulating contaminated oil directly into the gearbox. An inspection confirmed the filters were in bypass, and the Atten2 system immediately detected abnormalities, alerting the team to the contamination issue.
The situation required active management until it could be resolved. The Atten2 system provided the crucial contamination and wear monitoring information required to monitor and manage the system to the next maintenance opportunity. During this period, the site performed 10 filter changes, eventually shutting down the system to replace the faulty components. 6,000 litres of oil were replaced, and the gearbox scheduled for refurbishment.
The Atten2 system clearly demonstrated the increases in contamination every time the filters went into bypass. The system identified the steady increase in contamination particles, followed by the initiation and progression of wear as contamination started to impact the machine health.
In the following section, we delve into this data in a bit more detail.
• With a number of filter replacements, the system was managed with a certain level of contamination.
• Around the 22nd large increase in contamination and particles above 21 micron.
• Wear particles started developing in the fatigue and sliding categories indicating bearing and gear wear as a result of the contamination.
Particles >21 μm first started to emerge Thursday 15th
• Definite increase from the Thursday 22nd
• Upward trend in large particles
• Presence of both fatigue and sliding wear
• Wear materials start to emerge around Thursday 22nd
• Large spike in fatigue particles around Saturday 24th
• Significant increase in sliding particles Monday 26th
• Overall trending up until shut down
• Sliding particles indicate poor lubrication conditions resulting from sliding contact in the machine parts in machines/ rotating equipment, typically on gear teeth.
• The cause of sliding contact can be due to inadequate lubrication, contamination ingress, or misalignment of sets.
• There is typically a high probability of occurrence of sliding wear in highly dynamic equipment.
• Fatigue particle result from rolling contact fatigue or surface fatigue, typically found in rolling element bearings.
• Rolling contact stresses that cause rolling contact fatigue can be increased by inadequate lubricant viscosity, contamination, or increases in machine load.
• Once rolling contact fatigue particles are present, we know that pitting has occurred in rolling contact surfaces. Once well advanced, it is typically this pitting that can be detected as a bearing fault using vibration analysis.
Oil contamination and wear often occur in sudden, discrete events, which are difficult to capture through manual sampling. By implementing an online oil monitoring system, the customer gained real-time insights into oil quality and equipment health, enabling a proactive, condition-based maintenance approach. Moving from intermittent manual sampling to a continuous, automated monitoring strategy not only reduces errors but also provides earlier warnings than traditional vibration analysis in challenging applications such as slow-speed, high-noise environments poor transmission paths or hydraulics.
Ultimately, online oil monitoring is more than a convenient sampler, it is a critical tool for maintaining equipment reliability and extending asset life.
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