Dörner & Helmer Catalog Wheels Castors Page 13
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De ci si on- maki ng sup p o rt Overview 5. Bearing types When selecting the correct bearing, the load capacity, environmental conditions, application purposes, resistances and travel speed must be taken into account. Slide bearings, roller bearings or ball bearings fulfil different requirements. Also see page 18. 6. Environmental influences The wheel and castor functionality and service life are also determined by environmental conditions. D+H offers special solutions for this purpose. For high temperature applications (e.g. racks for bakeries), we have heat-resistant castors in our range. Chemical resistances of different materials are shown in the table on page 20. For applications in high humidity or spray water, we offer a wide range of stainless steel castors. To avoid electrostatic charges, we offer electrically conductive versions. 7. Starting and rolling resistance Starting resistance is understood as the power required to set a resting object into motion. The rolling resistance describes the power required to keep the object moving. Both resistances are a function of the total object weight, the wheel dimension, the tread, the tyres, the bearing type and the floor composition. The larger the wheel diameter, the harder the tread, and the less friction in the wheel bearing (e.g. ball bearing), the lower the starting or rolling resistance. Manoeuvrability depends on product characteristics and area of application. It is determined by the castor arrangement and type. More information can be found on page 19. 8. Spring deflection Objects deform under load. This also applies to tyres. The degree of deformation is referred to as spring deflection. This increases the wheel’s contact area. The degree of spring deflection essentially determines the surface pressure and the starting resistance. It also characterises the driving comfort. See the table on page 17. 9. Surface pressure The pressure exerted by the contact area of the wheel on the floor is referred to as surface pressure. Every floor may only be loaded to a specific pressure per mm². The selection of elastic materials (high spring deflection!), for example, or larger wheel diameters and widths can increase the contact area on sensitive floors, resulting in lower contact pressure. 10. Special features In addition to protecting against moisture, resistance to chemical substances, electrostatic discharge and heat, rotating-assembly and wheel locks, as well as thread protection can also be useful in meeting your requirements. More information is provided in the corresponding chapter pages. 13
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