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SKF has helped Iggesund Paperboard, a European manufacturer of virgin-fibre paperboard, to optimise the productivity of its UK plant through a reduction in vibration levels.

A bespoke dryer cylinder solution, incorporating SKF bearings, housings, seals and shafts, has provided Iggesund with improvements in performance and reliability, while also simplifying essential maintenance.

Before installing the SKF solution, Iggesund was finding it impossible to operate its paperboard mill at the optimum capacity of 600m/min without damaging shafts and bearings.

Ted Hodgson, mechanical engineer at Iggesund, said: ‘We were running the mill at a reduced speed in order to minimise maintenance and downtime.

‘Whenever we tried to increase the speed of the system, we noticed unacceptable levels of vibration, particularly in the drying cylinders.

‘As well as impairing the quality of our paperboard, this led to premature bearing failures.

‘We couldn’t risk damaging the bearings; to replace them, we had to remove the entire shaft, taking a considerable amount of time and bringing production to a standstill.

‘In the case of the idler gears on the dryer cylinders, the bearings were actually spinning in their housings as a result of the high speeds and loads they were frequently subject to.

‘In some cases, this was causing the shafts to snap, costing us up to 15 hours of production time in each instance,’ he added.

According to Hodgson, the company was also experiencing problems with the bearings within the drying cylinders.

‘These bearings were on a rocker system to allow for movement, but when the steam-filled cylinders became hot and expanded, the bearings couldn’t take it and began to vibrate, affecting performance,’ he said.

SKF’s application engineers assessed the situation and came up with a bespoke solution that could be installed without major alterations to the paperboard supplier’s existing equipment.

The solution would be able to cope with much higher speeds and accommodate movement and vibration, allowing production levels to be increased.

The new bearing units, each incorporating a shaft, would be faster and easier to change, with no subsequent need to remove the entire shaft each time, according to SKF.

The idler gear bearing arrangement was made possible partly thanks to the company’s CARB roller bearing design, which combines the self-aligning capability of the spherical roller bearing with the unconstrained axial displacement ability of the cylindrical roller bearing.

The rollers of the CARB bearing are self guiding, meaning that they adopt the position where the load is evenly distributed over the roller length, irrespective of whether the inner ring is axially displaced or misaligned with respect to the outer ring.

Iggesund began to install the bespoke units, which also incorporated shafts, housings, seals and fixings, into the idler gears.

As this new setup could compensate for the angular misalignment and axial displacement that occurred when the idler shaft expanded, the effect was said to be immediate, reducing vibration levels by 120 per cent and providing smoother, more consistent rotation.

Iggesund also asked SKF to develop a system for the bearings inside its drying cylinders.

SKF was able to eliminate the problematic rocker system, suggesting a more stable arrangement.

The company’s CARB bearings again played an integral role as, unlike conventional bearings, they could cope with 5mm to 6mm of expansion and withstand temperatures of up to 200C.

After the installation of the new units, vibration decreased and the speed of rotation could be increased with no damage to components.

‘The new SKF solutions have enabled us to increase machine speed with none of the vibration-related problems we were experiencing previously,’ said Hodgson.

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