In a past role, I was hired to work on a mine in Southern Africa. The mine was being pushed hard to produce more tonnes and save money. This brought a number of familiar challenges – overspending in the maintenance budget, unplanned downtime, and a management culture that avoided any major change.
During my time at the mine it became necessary to challenge this management culture, in order to improve maintenance processes and enable the mine to save money and increase reliability in the long run.
The culture was very difficult to deal with. I discovered the majority of the fitters were ready to take on any suggestions that made their jobs easier, the supervisors less so and the middle-management appeared to have little interest in improving the way the maintenance was being carried out or making improvements to the process.
Identifying the need for improvement
The site had been struck with a number of issues with their primary crusher, and management had recognised they needed some outside assistance to help solve their mounting maintenance issues.
Once the immediate issue with the crusher was solved, time came to look at issues in and around the plant.
The plant was, on the face of it, running okay. Issues were dealt with proactively as much as possible. As I walked the plant, I started noticing problems which were symptoms of best practice maintenance (and plant operation) not being done to the extent I would have expected.
Close to the maintenance workshop was an area which had a number of pumps installed. None of the pumps had a standby unit, and each pump was a show-stopper in the event of a breakdown.
I was asked to carry out training with the maintenance crew on a newly purchased “vibration pen”. I chose one of these pumps. The motor I had chosen as the subject of the training had a high frequency vibration at the time.
I noticed a nearby pump, now-and-again ejecting slurry out of the top of the casing. On closer inspection, the slurry was leaking out of the top of the rubber liners, but they weren’t holed. The pump also had a cyclic vibration, with the vibration increasing and decreasing as it pumped.
I looked around the area and found another pump, with the same cyclic vibration, this time, however, the vibration was a lot stronger. Its discharge hose shook violently as the vibration got stronger, less violently as the vibration waned.
Yet another pump in the area was also vibrating cyclically, but this one had a motor with a terminal high frequency vibration.
I reported my findings to the local maintenance management, who basically shrugged their shoulders and blamed the issue on operations.
Analysing the vibration
With no one in the maintenance team interested in what I was seeing, I decided to carry out an informal investigation.
I intended to start with the pump I had seen spitting the slurry out of its liners, but when I was positioning myself to get a better look, I became aware of a harder vibration noise coming from the pump, which I had seen shaking its discharge hose.
I walked to the pump and watched as one of its casing bolts (one of the bolts that clamps together the frame plate and cover plate) shook and started to vibrate out of the eyes it was supposed to be tightened into. The bolt had snapped.
I brought this snapped bolt to the attention of the supervisor, who organized its changeout.
All of the pumps were Warmans, from memory 10/8. I had never seen this kind of vibration before.
As I watched the pumps, I realised that they were pumping their feed tanks dry. When the tank emptied, the pump sucked air and started cavitating until enough fluid was in the tank to allow the pump to momentarily pump again, until the tank was once again empty, and the cycle repeated.
The pump spitting slurry from its liners was the same. It was cavitating to the point of sucking its liners, causing a slight gap between the liners, allowing the slurry to escape.
The vibrating motors were also caused by this cavitation.
I spoke to the local maintenance superintendent who, to my amazement, was more than aware of the issue. He also claimed that the 10/8 Warmans were too big for the job they were doing; they were being fed by tanks which were too small.
He also informed me that the pumps were fitted with variable speed drives which the operators had learned to leave locked at 80%, because if the pumps slowed down (as the tank level dropped), the slurry in the tanks settled and caused blockages and overflow.
His attitude was, that despite the component changeouts and unplanned downtime the cavitation was causing, he wasn’t going to do anything.
I spoke to the local mill manager and operations superintendent about my findings, who assured me that they would speak to the operators about the issues.
This cavitation was causing unplanned expenditure on the (already) overspent maintenance budget, a lot of the expenditure would have been unnecessary (motor replacement, the broken clamp bolt and the replacement of otherwise unworn pump liners), and there was avoidable unplanned downtime and increased spares consumption.
The lack of standby pumps in the initial design of the plant (it was impossible to install any new pumps due to the lack of space as the plant stood) and the choice of oversized pumps for the duty could have possibly been alleviated by operating procedures being adhered to.
All in all, the mine’s challenges could have been made more manageable by a shift in culture – had middle management been less reluctant to improve maintenance processes, much of the unplanned cost and shutdowns could have been avoided.
We have written a number of articles regarding the various aspects of maintenance improvement and change management. To explore some of these, follow the links below.