Bearings - 2020-12-02
A leading UK bakery was experiencing regular, unexpected stoppages due to the premature failure of pillow-block ball-bearing mounted units fitted to the recirculation fan of a high-temperature oven. However, switching to NSK plummer blocks with high-capacity spherical roller bearings and labyrinth seals increased service life by a factor of 4.5, delivering annual cost savings of €34,907.
Failures of the pillow-block mounted bearing units were causing significant disruption to the bun production line at the bakery, leading to high downtime costs and spoilt product. With bearing failures occurring every 6 weeks, the management team invited NSK’s team of experts to investigate the issue as part of its AIP Added Value Programme.
Upon completion of a full application review and failed bearing analysis, NSK engineers concluded that the bearings were seizing from excessive pre-loading and the use of incorrect lubricant. It was concluded that the existing bearings were inadequate for the operating conditions of the oven fan unit, which is belt-driven in a vertical orientation, and that improved reliability would result from more informed bearing selection/design. Fan reliability is vital as it recirculates air within the oven to ensure uniform temperature and evenly baked products.
NSK proposed the adoption of its SNN series plummer blocks with high-performance standard (HPS) spherical roller bearings and labyrinth seals, and recommended the correct bearing location, radial internal clearance (RIC) and lubrication. This solution would give significantly higher axial and radial load support, aided by a ‘floating’ arrangement to accommodate thermal expansion of the shaft and tolerate any fan imbalance (dynamic misalignment).
A trial was conducted and the solution resulted in an immediate improvement, with bearing life extended from 6 to 27 weeks, thus reducing both machine downtime and maintenance costs.
Modular SNN series plummer blocks have been developed for use in unfavourable application conditions. Maintenance is simple due the precision-engineered split housing that ensures easy bearing replacement. Re-lubrication is possible via two boreholes, while an escape hole means that excessive grease accumulation is avoided.
Additional advantages of SNN series plummer blocks include high rigidity (to minimise deformation of the bearing seat) and good heat dissipation. Mounted units can be supplied for shaft diameters from 20 to 140 mm.
Supplied with a steel or brass cage, features of NSKHPS spherical roller bearings include optimum raceway design and surface finishing, as well as temperature stability up to 200°C. NSKHPS bearings also offer 25% higher dynamic load rating – important in the oven fan application – and up to 20% higher limiting speed.
In combination with the SNN series plummer blocks, NSKHPS bearings enabled the bakery to make large cost savings via fewer bearing replacements, less breakdowns, reduced maintenance technician costs and less spoilt product, ultimately leading to improved production efficiency and better equipment reliability.
Picture 1): A cutaway section showing NSK plummer blocks with high-capacity spherical roller bearings and labyrinth seals
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