Sensoteq’s proactive vibration monitoring system saved up to £90K in daily losses, ensuring this client avoided catastrophic mixer bearing failure. The following data provided by JPS Reliability demonstrates that, without intervention, this bearing would have resulted in a costly breakdown. Previous breakdowns from hardened grease and intense heat were detected early thanks to Sensoteq's real-time vibration alerts, enabling precise, proactive action and reducing machine failure.
Machinery and Operations
The bearing in focus is part of a mixer in operation for nearly four years. As a critical component in the manufacturing process, any downtime with this mixer significantly impacts production. Due to previous unexpected problems, the client required a solution to detect when the bearing is nearing failure. This would enable bearing removal and investigation to determine the root cause of past failures. The bearing costs upwards of £35K and is not kept in stock due to its high expense, as the raceway is an integral part of the pulley sheave. The mixer operates at speeds between 20-100 RPM, depending on the recipe. An unexpected failure of this asset could result in daily lost production revenues of £90K per day and reputational damage due to unfulfilled orders.
Implementation
The client decided to trial Sensoteq’s wireless monitoring system on this slow-speed application to closely monitor vibration and determine when a new bearing may be required. By implementing this advanced technology, the client aims to prevent costly catastrophic failures, enabling timely and proactive bearing replacement. This approach not only minimises the risk of unexpected breakdowns but also provides valuable data to investigate and identify the root cause of recurring issues, allowing for more effective long-term solutions.
The Problem
The Sensoteq system detected shock events on the mixer, with a recent surge specifically from the main head bearing. The root cause of the bearing failure was lubrication deterioration, which often leads to cake lock failures.
Cake Lock Failures
A cake-lock failure is similar to a microscopic logjam. As the thickener dries out, it becomes immobile and jams the flow path and even mechanical motion. Oil may flow through the thickener (hydrostatic extrusion), but the thickener goes nowhere. As more grease enters and oil exits, the more the logjam builds. Eventually, a rigid binding condition develops from the stiff, high-density cake. The cake-lock condition leads to thermal excursion and bearing failure. To prevent cake lock, select a suitable low-risk grease formulation and ensure the grease flow is sufficiently high to avoid static conditions that give rise to separation and blockage. Some long-fibre grease thickeners, for example: simple sodium soap, are particularly prone to grease-flow stability problems. Frequent movement of grease can also keep the flow path fresh and inhibit blockage; however, there may still be some unavoidable zones of dry grease that build up in adjacent side cavities.
The Analysis
Figure 1 is the initial Acceleration spectrum provided by JPS Reliability with the mixer rotating at 52 RPM. This displayed a rolling element signal side banded by a bearing cage. On inspection of the bearing, this was due to the grease degradation and the start of heat generation.
Figure 2 is the waterfall spectra from November 2023 to March 2024. This showed that the amplitude of the bearing signal remained steady with a few fluctuations.
Figure 3 is the Acceleration Trend for December to January, before bearing replacement. There was a significant increase in the acceleration levels on the 2nd January. The acceleration levels remained elevated between the 8th and 11th January, then reverted to lower levels.
Figure 4 is the Acceleration trend from November 2023 to August 2024, before the bearing replacement. The largest impacts were recorded before the bearing change on January 2nd at 19 G’s Pk-Pk & February 26th at 25.8 G’s Pk-Pk. The client expected a bearing at 100rpm to be less than 2 G’s.
Figure 5 is the overall Acceleration trend since the bearing replacement. The base levels have dropped by over 87% from 8 G’s to less than 1 G Pk-Pk. However, the levels displayed particularly high impacts on the following dates and times: 8th September 13:36, 11th September 14:04 & 22:38, 14th September 14:58, 15th September 00:56.
An investigation into the production process during these times is essential to identify the root cause of these impacts, as they can significantly reduce the lifespan of the bearing.
The Result
The bearing was removed for an RCA by JPS Reliability.
Rolling Elements
Upon initial inspection, the rolling elements were found to be tight in the cage pockets due to grease degradation. The presence of many hardened particles likely caused the rolling elements to skid rather than rotate smoothly, preventing the formation of the correct lubrication film.
During the clean-up of the cage pockets, signs of initial heat generation are observed, characterised by carbonised and embedded grease damage on the cage surface.
Grease
The grease has experienced base oil separation from the thickener (soap/additives), causing it to dry out and harden, resulting in a complete loss of lubrication properties. This indicates high heat degradation, with oil bleeding, oxidation, and a breakdown in the grease's consistency. There is also a slight possibility of grease incompatibility, where different types of grease may have been mixed, contributing to the degradation. This should be investigated to determine if it was a contributing factor.
Outer Raceway (Fixed Ring)
The outer raceway has clear visual signs of false brinelling, where the bearing is subjected to a shock loading while stationary. This results in permanent depressions at rolling element pitch into raceways caused by vibration-induced micromovement of the rolling elements, whilst the bearing is static.
Inner Raceway (Drive Pulley)
The inner raceway contains a significant amount of hardened grease with no remaining lubrication properties. Additionally, on the main grease channel of the bearing, there is evidence of burring caused by the rolling elements skidding and impacting the surface rather than rolling smoothly with the proper lubrication film. This condition would have eventually led to deeper burring, increased frictional heat, and rapid failure, leaving little opportunity to plan for a controlled bearing replacement.
Through Sensoteq’s advanced wireless monitoring solution, the client minimised costly machine downtime by identifying potential bearing failures before they could disrupt production. This technology allowed the client to replace critical components at the ideal time, preventing a repeat of prior breakdowns and saving them from potential revenue losses of up to £90K per day.
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