Replacing a six-tonne slewing ring bearing for iron ore loading

In the Norwegian port of Narvik, Swedish mining company LKAB employs a huge loading station to load bulk carriers with iron ore. Any shutdown of the station is enormously costly. Because, in this instance, time really is money, experts from the SKF Solution Factory had to work hard against the clock when replacing a slewing ring bearing.
W   eighing a total of 2500 tonnes, the gigantic loader in the
port of Narvik ensures that iron ore from the LKAB mines in Kiruna, Svappavaara and Malmberget finds its way into the entrails of the ships. “You have to imagine it like this,” explains Max Andersson from the SKF Solution Factory: “This port sees a vast number of bulk oar carriers riding at anchor – lining up rather like a string of pearls. They’re all ‘on standby’, waiting to be loaded.” Andersson goes on to explain the implications: “If the ship-loading does not run like clockwork and suddenly comes to a standstill, things get seriously expensive. Every hour beyond the agreed loading times that the carriers have to hang about out there consumes huge sums of money.”

So in this case time really is money. “That makes it all the more advantageous for the companies involved if the relevant maintenance work can be done within the shortest possible time,” says Andersson, emphasising the point. The resulting time pressures then present considerable challenges in terms of planning and personnel.

The shiploader’s range of movement is based among other things on two huge slewing ring bearings. The Narvik giant has one at the front and one at the back; both were last replaced almost 20 years ago. “So it was time for a replacement if smooth operation was to be maintained into the future as well,” says Andersson. “With this in mind, we were first commissioned to replace the rear slewing ring bearing, weighing 6000 kg, with a new one.”

At the start of the project it was agreed that the SKF team was to perform the changeover within ten days. However, no sooner had the relevant studies been commenced than it became clear that the output of the mines would require leaner ship logistics. So as not to slow down the mining operations and hamper logistics, LKAB and SKF finally agreed on a timetable of seven days. “Eventually the seven days became just four,” admits Andersson. “Now that really is an extremely small window for a replacement job of this type.”

Advance planning

In view of this additional challenge in terms of time pressure, the conscientious planning and thorough preparation of the team from the SKF Solution Factory really paid off. “Right from the start we had basically been looking at all conceivable options,” says Andersson. “To that extent a lot of things had already been prepared down to the last detail. So in a sense, we ‘just’ had to make our advance planning a bit leaner,” says the SKF project manager with a wry smile.

Once Andersson’s team finally began the replacement work, it became clear that their scrupulous preparatory planning had paid dividends. Both the removal of the old bearing and installation of the new one were able to proceed without major problem. “By the end we had only taken two and a half days to complete the actual replacement work, so that the station was able to fully re-enter service after four days.”

The short changeover time brought significant cost reductions for customer LKAB. “The rapid changeover meant a shorter laytime for the bulk carriers waiting in port. And, as a result, LKAB has of course saved a lot of money,” concludes Andersson.

Enormous weights and forces

To ensure the customer could enjoy this “monetary benefit”, the SKF team had to master a very complex task. Replacing the slewing ring bearing of the gigantic shiploader meant that the entire station, including its conveyor belt, had to be lifted. “We had to cast new lifting plates, for instance, and provide enormously powerful winches in order to be able to lift the station. Once the old bearing had been removed we needed a recovery vehicle to pull the bearing out of the structure. And when it came to installing the new bearing, we had to use this recovery vehicle again to position the replacement bearing correctly,” says Andersson.

Quite apart from the purely technical challenges, Andersson’s team also had to deal with the climatic conditions of the far north. Because the bearing was being replaced in March, the Norwegian weather could easily have led to problems. “Luckily, however, the weather gods were on our side. Let me explain the potential problem. The shiploader represents a big area in terms of resistance to wind forces, and at wind speeds of over 12 metres per second – which are quite normal for these parts – it would have been impossible to replace the bearing. As it happened, just a day after we completed the work there were winter gales of that magnitude. If they had caught us in the middle of replacing the bearing, we’d have had to interrupt the work.

The winter temperatures were another complication. “When we were carrying out the replacement work, the temperature was minus ten degrees Celsius. As a result, the grease that we wanted to fill the bearing with solidified. So we had to get hold of a different lubricant and managed to keep it warm using industrial fans,” says the SKF expert.

Thanks to the successful replacement of the swivel ring bearing, LKAB continues to rely on SKF. “After we had managed to replace the rear swivel ring bearing of the shiploader in such a short time, we were entrusted also with dealing with the front one,” says Max Andersson. The SKF team has since successfully completed replacement of this bearing as well. Apart from that, in its mines LKAB also relies increasingly on SKF condition monitoring systems.

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