In 1991, JSE-listed platinum-miner Northam Platinum had commissioned an original-equipment circular stacker reclaimer from global integrated and materials group ThyssenKrupp Materials Handling (TKMH), for the replacement of slew bearings.

However, during 2009, problems with the slew bearings on the stacker became evident and TKMH was requested to conduct an on-site inspection of the equipment with specific reference to the conditions of the slew bearings.

Following the inspection, TKMH product support staff and Northam mine management entered into discussions and deliberations around the refurbishment project. Various issues were finalised, including the final scope of work, as well as a feasible schedule for the execution of the work. TKMH secured the refurbishment contract in December 2009.

When the circular stacker was originally installed and commissioned, TKMH recommended that critical spares such as slew bearings with a long delivery lead time be kept in stock to reduce downtime and simultaneously limit the high cost of alternative interim materials handling options. With the replacement bearings in stock, construction work started in January 2010.

The circular stacker weighs 168 t and is fitted with two slew bearings with diameters of 1,70 m and 2 m weighing 300 kg and 650 kg respectively.

“Before our construction team could proceed with the removal of the slew bearings, we had to engineer and manufacture special jacking trestles to jack and support the machine centre column,” explains TKMH product support engineer Dietmar Pratz.

He was appointed as the project manager for the contract from bid preparation, to scope clarification, final pricing, site construction and the final commissioning and handover.

“The jacking process is significant, as the slightest imbalance can result in the machine toppling over. Accurate load calculations and pressure readings on the calibrated jacks were essential to ensure even lifting. The slew bearings were rigged out onto special steel support frames constructed by TKMH,” he adds.

With the slew bearings removed, structural damage and corrosion fatigue on the boom structure and the centre column became evident, which was to be expected after almost two decades of trouble-free service.

While critical repairs were recommended for the centre column on site, TKMH engineers suggested that the boom structure be transported to a workshop for a more in-depth evaluation with possible repairs under controlled conditions.

It is TKMH’s policy to undertake work on its own original-equipment (OEM) installations but it will consider working on other installations provided the client can obtain consent from other OEMs and for the design considerations, as well as detail design drawings.

“Embarking on large refurbishment projects without access to the original design considerations increases the end-user’s risk in significant ways such as safety. Further, equipment reliability can also be compromised,” he adds.

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