SKF Enhances Grinding Mill Reliability with Integrated Trunnion Assembly Solution

Last Updated 2 months ago by Kenya Engineer

Blending innovation with decades of engineering expertise, SKF South Africa recently delivered a comprehensive trunnion assembly replacement project that significantly improved the reliability and efficiency of a horizontal grinding mill for a major construction materials supplier in Johannesburg South.

The intervention not only restored operational stability but also strengthened long-term sustainability and asset performance within the customer’s heavy industry and Mineral Processing & Cement (MMPC) operations.

Diagnosing Persistent Housing Misalignment

The customer had been experiencing frequent housing misalignment within the mill’s trunnion assembly — a recurring issue that led to operational instability and costly production interruptions.

SKF’s Mechanical Field Services (MFS) and Engineering teams conducted a detailed site inspection to identify the root cause.

According to SKF Application Engineer Nthavela Makondo, the misalignment stemmed from incorrectly aligned rockers (also known as “panna”) within the trunnion mill housing. During operation, the housing shifted and came into contact with rotating components such as seals. This resulted in:

• Progressive equipment damage

• Repeated unplanned downtime

• Increased maintenance costs

• Production losses

In horizontal grinding mills, the rocker housing is a critical component of the trunnion bearing assembly. Its controlled rocking motion allows axial movement to accommodate thermal expansion of the trunnion during mill rotation — a necessary function to maintain stable and reliable operation.

However, when misalignment occurs, this design advantage becomes a source of mechanical stress and failure risk.

From Assessment to Complete Replacement

Following technical evaluation, SKF determined that repairing the existing trunnion housing would not be economically viable. A full replacement assembly was recommended to ensure long-term performance and reliability.

The customer approached multiple suppliers for quotations, including SKF Authorised Distributor Citi Bearings. Based on a strong track record of collaboration and trust, the customer proceeded with the SKF-Citi Bearings solution.

SKF supplied a complete rocker base trunnion mill housing assembly, including:

• A Labyrinth (triple) seal system

• A 238/1180 CAK/C3W33 large-size spherical roller bearing

• An additional identical bearing supplied as a strategic spare

SKF also removed the existing bearing for potential remanufacturing and carried out all mechanical field services associated with the replacement. Installation was executed by SKF’s MFS and Engineering teams in collaboration with Citi Bearings.

Respecting Legacy Design While Delivering Modern Performance

Interestingly, the customer opted to retain the original bearing assembly design — a configuration with drawings dating back to 1969 that had consistently delivered reliable performance for decades.

Makondo highlighted that SKF’s ability to manufacture and support specifications from legacy technical drawings demonstrates the depth of its engineering capability.

While SKF continues to innovate with advanced bearing technologies, its expertise in supporting established mill designs remains a critical advantage for heavy industry clients operating long-life equipment.

Tangible Operational and Sustainability Gains

The new trunnion assembly delivered measurable benefits, including:

• Improved mill reliability and resilience

• Enhanced operational efficiency

• Reduced unplanned downtime

• Extended service life

Beyond performance improvements, the solution also supported sustainability objectives.

Bearing remanufacturing reduces raw material consumption, while improved mill stability and efficiency contribute to lower energy use and reduced emissions during operation. Furthermore, eliminating housing misalignment mitigates seal damage and reduces the risk of unexpected mechanical failures — improving both equipment reliability and operator safety.

Strengthening Partnerships in Heavy Industry

The successful project not only restored operational stability but also deepened SKF’s service footprint within the MMPC sector. By combining advanced product technology, engineering diagnostics and field service execution, SKF delivered sustainable value aligned with the customer’s long-term operational goals.

For South Africa’s heavy industry sector — where grinding mills remain mission-critical assets — proactive engineering interventions such as this demonstrate how reliability-centred solutions can directly impact productivity, safety and environmental performance.