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New seal and bearing rating life model from SKF

17 April 2015

New from SKF is Taconite seal for split block housed bearings located in dusty, wet environments, along with a new rolling bearing rating life model to help improve the field performance of bearings.

Suitable for the most demanding of applications, SKF’s new Taconite seal is price competitive and delivers an increased level of protection to bearings in split block housings that operate in extremely contaminated and wet environments. This greater level of protection from dust, grit and moisture contamination helps achieve maximum bearing service life, while optimising machine performance and uptime.

The compact, multi-stage labyrinth cartridge seal features an internal low friction V-ring that forms an additional barrier to contamination and provides an effective grease purge. The rotating labyrinth ring faces the bearing housing to deflect and fling water away.

It is available for almost all SKF metric and inch split block housings starting from 50mm shaft diameter. The seals are available in both metric and inch shaft diameters and fit, without modification, into the seal groove of SKF split block housings.

Larger Taconite seals (= 340mm shaft diameter) are also available for ‘bolt-on’ mounting to specially prepared SKF split block housings. All the seals feature a circumferential groove on the outer surface that simplifies and speeds up the alignment and assembly process.

Bearing rating life model
SKF has launched a model that will help engineers to calculate a more realistic bearing rating life by considering more influencing factors than before. The new model will enable OEMs and end users to match bearings to application conditions with even greater certainty.

The new SKF Generalised Bearing Life Model now successfully separates surface from sub-surface failure modes. Based on explicit tribological models, it factors in new performance parameters, including those for lubrication, contamination, surface strength and mild-wear resistance.

By understanding and accounting for more potential failure modes, the model is able more realistically to predict bearing behaviour and life under a wide range of operating conditions.

The current bearing rating life model is primarily based on sub-surface fatigue damage accumulation, which is transformed into a bearing survival probability by using the Weibull probability distribution model and then modified with surface stress concentration models for poor lubrication and lubricant contamination.

The model is used to determine a bearing’s unique basic dynamic load rating, also known as C-value; the load for which the calculated rating life of the bearing population with 90 percent reliability is one million revolutions. Nowadays failure is typically the result of surface damage caused by such factors as contamination, inadequate lubrication, or other environmental conditions that lead to surface distress and wear.

C-value is still a relevant performance parameter, but it tells only part of the story because it doesn’t account for the bearing’s rolling contact micro-geometry, material properties and other critical factors.

New steel heat treatments or materials, better surface textures and contact profiles, high-performance coatings, hybrid bearings, better lubricants cannot be reflected with increases of a single sub-surface fatigue performance parameter like C-value. This is why new concepts in bearing life models are required, says SKF.

Another benefit of the new model is that it is flexible enough to allow the integration of new knowledge in the tribology and materials sciences as it is developed. As bearing science evolves, so will the model.

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