Our first foray into mineral processing systems analysis was in the early 1990s when Chris Meimaris was asked to determine the cause of the failure of the Mt Leyshon mill foundations and to model the repair. This work was the first full dynamic system analysis of mill foundations using Finite Element Analysis in Australia. The work led on to foundation analysis work at North Parkes and then Cadia Hill in 1996.
The analysis of the Cadia SAG and ball mill foundations were critical in the resolution of the stator vibration problem that arose during the commissioning of the 40 ft SAG mill in 1998. Although the foundations were initially suspected as a potential cause of the vibrations at Cadia, the detailed analysis and strengthening of the foundations during design coupled with our vibration measurements of the foundations during commissioning were sufficient proof for the GMD vendor to exclude foundation design as a contributory cause for the motor vibrations. (We note that the vibrations issues were resolved without significant loss of production to the mine – see “Special Projects” for more detail.)
The dynamic design of the Cadia foundations led to our engineers being asked by Newcrest to determine the cause and later the solution to the vibrations exhibited by the stator of the 40 ft SAG mill and also the root cause analysis of the girth gear failures for the twin 22 ft ball mills. In later projects at Cadia, we strain gauged the 40 ft SAG mill to determine stress ranges and also the drives of the two ball mills to determine torsional vibration amplitudes as part of a long-term study of the mill drives.
Cadia was undoubtedly the most significant project we have undertaken. Although there have been many other projects that were larger, the opportunity to work on and repair what were then the largest mills and drives in the world was unique. The measurements of the SAG mill stator in particular are unlikely to ever be repeated and they form the benchmark for mill system analysis work for very large mills.
The Cadia work led on to many other projects in which we were asked to model of the foundation dynamics and machine interfaces for large mill installations such as Antamina, Collahuasi, RPM, Boddington, PT Freeport Indonesia. It also led to the failure analyses, measurement and remedial design of many large ring motors in gearless mill drives (GMDs) including the catastrophic failure of the ABB motor at Collahuasi. These projects also offered the opportunity to measure stresses in large SAG and ball mills including those at Collahuasi and Telfer. The data from the failure analyses and the mill strain gauging provides a means of calibrating our mill system analyses to real-world examples that exhibit failure or behaviour modes that must be avoided in new designs.
Services for New Projects
Since 2001, we developed a vertically integrated technical service to our clients for the purchase of grinding mills with gearless and geared drives in new projects. The approach is to provide a complete technical service for the technical management of grinding mill related equipment from pre-award through to commissioning including:
- initial benchmarking and economic evaluation of mill and drive types;
- pre-qualification of vendors and sub-suppliers;
- equipment technical specifications and tender evaluation;
- independent structural integrity audits (mills, ring motors (GMDs), gears, foundations, crushers, HPGRs, winders, mobile equipment);
- complete equipment system analyses (static, dynamic, non-linear vibration and interface analyses);
- design reviews and quality surveillance;
- vendor co-ordination;
- installation documentation and quality surveillance.
Failure and Reliability Analysis
Engineers don’t design for success; they design against failure. For example, the stress range level chosen for a mill weld will be determined from failure data to provide x% probability of failure. The most interesting work we undertake is still in the form failure analyses. Determining the direct (proximal) and root causes of a failure is critical to the development of reliable new equipment and the financial success of mineral processing plants. Our work includes the failure analyses and remedial design of many of the world’s largest mills and drives. The work has led to the development of many improvements in geared and gearless drives as well as in the design of grinding mills. Some of our more recent work includes the failure analyses of the:
- Antamina ball mills;
- Cerro Verde I ball mill;
- ABB ring motor (GMD) stators at Collahuasi and Antamina and the development of many design detail improvements;
- Rotor pole weldments for Siemens GMDs;
- large gear failure and technical arbitratration;
- Foundation analyses – Fimiston, Red Dog Mine.
Our detailed capability statement that provides more information on our company can be downloaded from the following link.