A McLanahan trunnion rollers assembly.
An established iron ore processing facility in WA has advanced the capabilities of its rotary scrubbers with McLanahan’s new trunnion base assembly.
These particular rotary scrubbers had been installed at the Western Australia site in 2009 and were beginning to show the wear of intensive use from over a decade of operation.
Due to its longstanding history as a trusted original equipment manufacturer (OEM), McLanahan was engaged to implement a design upgrade solution.
“We were also aiming to extend the wear life of the barrel, which was previously a large-welded structure with a shrink-fitted ring all the way around,” McLanahan mechanical design manager Ben Freeburn said.
“It had begun to show some cracking, which was not all that surprising considering that these machines do in the order of two million cycles every six months. So we worked with the customer to implement a deep steel forging design that was a lot more durable.”
While the engineering team worked on retrofitting this new support frame, discussions with the customer resulted in the expansion of the project.
The process of manual precise alignment was time-consuming and presented some safety risks, so McLanahan proposed an upgrade to the trunnion base assembly that incorporated self-aligning features to remove risk and reduce maintenance downtime.
The washdown of crushed rock and ore in these suspended cylindrical barrels is a key step in the ore processing cycle but presents challenges relating to the barrel suspension technique.
“We were able to tackle a couple of issues in one go with this project,” Freeburn said. “With rotary equipment, there are two main support methods – hydrostatic bearings and trunnion rollers.
“While the hydrostatic solution has the benefits of high-capacity support and low friction, it does require complexities such as filtration, accumulator banks and complex hydraulics. In particular, it is important to have a robust sealing arrangement at the full barrel diameters to keep water and dust particles out of the main journal. This is nearly impossible to achieve in a mining environment.”
Conversely, trunnion rollers can support heavy loads on a much simpler apparatus, but the downside is that they are sensitive to misalignment, causing the barrel to thrust back and forth.
The mechanical design engineers at McLanahan sought to create a self-aligning system, rendering the trunnion base assembly as the superior option on various-sized rotary machines.
Freeburn likens this mechanism to “a swivelling shopping trolley wheel” that auto-corrects when misaligned due to a vertical axis offset. He said this design was unique in its flexibility, as it had proven success operating on a broad weight and size range.
“It improves the reliability of the machines more than anything,” he said. “On customer sites where these changes have not been implemented yet, we are seeing reoccurring issues because a single component has shifted 2mm and it has ended up costing them in downtime for realignment.”
This project was not only successful in adjusting the trunnion rollers to skew on a horizontal axis, but also incorporated the ability to correct three-dimensionally in any plane of misalignment via a spherical seat.
“Our engineering team conducts frequent site visits, which helps to strengthen our relationship with each customer and deliver them more tailored support,” Freeburn said.
“Whether it is upgrading existing machinery or extending the equipment’s wear life, McLanahan has over 185 years of expertise to back our services. Through that experience, we have a very intimate knowledge on the capacity and design limits of these trunnion rollers.”
Additionally, other upgrades included a park brake, integrated jacking system and a cassette-style trunnion roller changeout frame co-developed with the site maintenance crew to ensure a holistic integration of this equipment upgrade into existing site operations.
“The park brake is an essential safety implementation, as it allows the operators to stop the machine via a hydraulic pump, support the full weight of the barrel, secure it from rotation, and work on it without causing back injuries or slipping,” Freeburn said.
“It is all about working with the customer to understand their plant layout and requirements.
“The key takeaway from this outcome is that if you prioritise a collaborative working relationship with the customer, it will benefit the outcome and final solution.”
This feature appeared in the June issue of Australian Mining.
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