A new high capacity cylindrical-roller bearing, intended for wind energy applications, bridges a gap in bearing performance by combining high-load and high-speed capabilities. The bearings come from NTN Bearing Corp., Mt. Prospect, Ill, which manufactures bearings for turbine OEMs, operations, and maintenance companies.
The input side of a gearbox transmits low-speed torque from the turbine’s rotor to the gearsets. Conventional bearings for this application are full-complement cylindrical roller bearings which have more rollers than caged bearings and are capable of higher static loads in periods of slow, or no rotation. However, because rollers in full-complement bearings contact each other, they generate higher heat and scuff and smear at high speeds.
Conversely, bearings on output shafts run at higher speeds but lower torque. The application usually calls for conventional cylindrical-roller bearings with cages because of high-speed requirements. The cage separates rollers and reduces damage that comes when rollers contact each other. However, these designs have a lower load rating and shorter service life because the cage occupies room in the bearing that otherwise could be used for additional rollers.
NTN says it has developed a bearing that combines the high-load capacity of a full complement bearing with the high rotational speed capabilities of a caged design. The feat is possible by placing resin rolling elements between rollers so they keep the same number of rollers as a full complement design yet still prevents roller contact to reduce friction and heat. Improving the separators’ shape and guidance method allows speeds equivalent to those for bearings with cages.
The patent-pending roller separator is suitable for input and output shafts in gearboxes. Advantages include a:
- Design that tolerates high load and high speed
- Lower operating temperature than a full complement bearing
- Increased service life, 1.5 times that of a conventional caged bearing
- Improved handling characteristics for service because inner and outer rings are assembled separately