SPECIALIST on-site machining including bespoke developed equipment by Furmanite has enabled downtime of a ball mill at an Australian uranium mine to be minimised by machining a trunnion journal in-situ, avoiding the time and logistical implications of removal to a workshop.
The project was one of a trend that is now seeing this specialist expertise increasingly called upon.
When significant scoring and fretting erosion was discovered on the ball mill’s trunnion journal, work was required to repair the damage and restore the surface to manufacturer specifications.
Replacement or removal to a workshop would have been time-consuming and costly options, so in-situ machining was required.
The requirement exceeded the machining capabilities generally available however, as options such as grinding were not sufficiently accurate and would have left the journal out of true.
Furmanite developed purpose-built equipment to undertake the project. This involved modifying its Mirage 30501 large flange facing machine to incorporate a specially manufactured large right angle arm with a cutter (able to machine a diameter of 1.15 to 1.6 m at a reach of 800 mm), in order to undertake the work required.
An initial survey undertaken by Furmanite revealed the extent of the damage.
Scoring of 15 mm wide and 8mm deep had been identified on the 1.05 m diameter journal, requiring the damage the be machined out and the journal returned to the specified tolerances.
Moreover, further machining was also needed to ensure that the bearing and journal contact (found to be only 10%) was restored to the recommended 90%.
A full size mock-up journal was fabricated by Furmanite to allow workshop trials of the purpose-built machine in advance of application.
Once on site, the machine was mounted on the front of the journal, and set to the front and rear seal areas, to within 0.05mm concentricity, allowing the arm, housing the cutter, to extend across the diameter and machine the journal bearing face and seal areas.
A surface finish of 6.3 thou was required and was successfully achieved, with the diameter within 0.05 mm of parallel.
Flatness was checked using an eight inch steel straight edge and ‘bearing blue’, and multiple tests were carried out around the circumference and along the length of the journal to gain 95% minimum contact, which was successfully achieved.
The project was successfully undertaken in just four days plus set up and dismantling time.
Furmanite national sales manager Michael Pearson pointed out that the cause of the damage had been general wear and tear, and that the need for this machining expertise is widespread in the mining sector.
“Since developing the equipment to machine these large trunnions and undertaking this project we’ve been called upon for this specialist expertise at a number of other mines facing similar problems with trunnion journal and bearing damage,” he said.
“By developing this machine to meet the requirements we were able to undertake the necessary work in-situ to within tight accuracy tolerances, representing substantial time and cost savings for the operator. This is typical of Furmanite’s ability to apply its expertise and develop a solution to help clients keep their assets operating and maximise uptime.”