DIN ISO 20056-1:2018-11

Hybrid bearings are rolling bearings with raceways consisting of commonly used steel rolling bearings and rolling elements made from silicon nitride (for definitions, see ISO 5593). Due to the higher modulus of elasticity of the ceramic rolling elements, hybrid bearings have a noticeably smaller contact ellipse at the same load than rolling bearings with rolling elements made of rolling bearing steel. This will lead theoretically to a reduction of the dynamic load-carrying capacity. In practice, hybrid bearings are used in numerous industrial applications, where these bearings show at least the same service life as conventional rolling bearings with steel rolling elements. Thus for the typical range of application of hybrid bearings, the theoretical reduction of the dynamic load rating is not observed in actual applications. The smaller contact ellipse and the material combination of ceramic-steel will lead to noticeably lower surface shear stress in the rolling contact, which again will lead to a higher load-carrying ability. This is reflected by defining a higher bm factor compared to steel bearings, which compensates for the higher contact stress under the same load. Therefore, the formulae specified in this document give the same dynamic load ratings as defined per ISO 281 for rolling bearings with identical internal geometry and rolling elements made of steel. This document specifies methods of calculating the dynamic load ratings for hybrid bearings with bearing rings made of contemporary, commonly used, high quality hardened bearing steel, in accordance with good manufacturing practice and rolling elements made from silicon nitride in contemporary, commonly used, high material and manufacturing quality and surface finish.