Hybrid bearings

Hybrid bearings have rings of bearing steel and rolling elements of bearing grade silicon nitride (Si3N4). In addition to being excellent electric insulators, hybrid bearings have a higher speed capability and will provide longer service life than all-steel bearings in most applications. The very good electrical insulating property is one of the essential features of the silicon nitride. This protects the rings from electric current damage and so-called washboarding, and thus increases bearing service life. The density of silicon nitride is only 40% of the density of bearing steel. Thus the rolling elements weigh less and have lower inertia. This means less cage stresses during rapid starts and stops and also significantly lower friction at high speeds as explained in the section <% bcat(“friction”, “Friction”) %>. Lower friction means cooler running and longer lubricant service life. Hybrid bearings are thus suitable for high rotational speeds. Under insufficient lubrication conditions there is no smearing between silicon nitride and steel. This enables hybrid bearings to last much longer in applications operating under severe dynamic conditions or lubrication conditions with low operating viscosity (? < 1). For hybrid bearings it is common to apply ? = 1 for running conditions with ? < 1 to estimate life under such conditions. Hybrid bearings may perform well, when lubricated with ultra thin film forming media, such as refrigerants, enabling oil-free designs but care needs to be taken in design and material selection. In such cases it is recommended, to consult the SKF applikation engineering service before deciding upon design and ordering. Silicon nitride has a higher hardness and higher modulus of elasticity than steel, resulting in increased bearing stiffness and longer bearing service life in contaminated environments. Silicon nitride rolling elements have a lower thermal expansion than steel rolling elements of similar size. This means less sensitivity to temperature gradients within the bearing and more accurate preload control. When designing bearing arrangements for very low temperature and as to estimate reductions in bearing clearance of hybrid bearings, please contact the SKF application engineering service.