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Abstract:In rare cases rolling bearings fail by WEC (white etching crack) damage before reaching their calculated rating life, if so called additional loads are applied on the bearing in addition to the normal Hertzian stress (p Hz ). A number of additional loads have been identified by means of tests with rolling bearings. These can be small direct currents as a result of electrostatic charge or large alternating currents from inverter-fed drives that unintentionally flow through the bearing. WEC damages can also be initiated by a pure mechanical additional load which is dependent on factors including the bearing kinematics but also on the dynamics of the drive train. The current state of knowledge on this subject is presented and taken as the basis for developing a hypothesis on the WEC damage mechanism. If load situations critical for WEC cannot be avoided, the risk of WEC can be considerably reduced by the selection of suitable materials and coatings as well as, in some cases, of suitable lubricants.

The combined processing of wood and plastics (thermoplastics) to form so-called wood-plastic composites (WPCs) with a content of up to 70% wood advantageously combines the best features of both materials. In recent years such WPC have gained a lot of attention in both industrial and academic circles in particular with regard to their sustainability. This paper highlights the advantages and disadvantages of PVC as a thermoplastic in comparison to PP, discusses the results of mechanical tests and describes weathering properties and fi re behaviour.