Schaeffler: enhanced performance in wind turbine gearboxes with bearing and system expertise
Resource from: Schaeffler 19 Nov,2015
Highly dynamic forces with extreme peaks and minimum loads, sudden load changes, and strongly varying operating temperatures are the challenges faced by bearing technology in wind turbine gearboxes. With the most up-to-date calculation and simulation programs, Schaeffler offers extensive system expertise in the design of gearboxes and thus bearings with high static safety and safer dynamic design. One current example is the high-capacity bearing, which allows high load ratings with low friction thanks to a newly developed cage geometry.
High-capacity in the gearbox: higher load rating with less friction
Planetary gear bearing supports are extremely challenging bearing positions because of the high radial loads that occur. Only a limited amount of space is available for this bearing support, and the planetary gears, which have comparably thin walls, tend to distort leading to rotation of the bearing outer ring in the planetary gear.
Due to the particularly streamlined design of the cage, the high-capacity cylindrical roller bearing from the FAG brand combines the advantages of full complement bearings with those of cage bearings. Thus, there is room for at least one additional rolling element in the bearing. That increases the load rating. Due to the bearing cage, the high-capacity bearing has significantly less friction than full complement types.
When fitted as a direct bearing support, the FAG high-capacity cylindrical roller bearing in X-life quality allows significantly improved use of the design envelope compared to a comparable standard bearing support. With a direct bearing support, there is no outer ring and the raceway is integrated directly into the planetary gear. Thus the risk of the outer ring moving can also be avoided.
Cylindrical roller bearing with MPAX cage
Cylindrical roller bearings with a single-piece MPAX brass cage are often used in the output or intermediate shaft of a wind turbine gearbox. The bearings in these positions must support very high speeds compared to high-capacity cylindrical roller bearings, which are exposed to high loads and load ratings in the planetary gear stage at comparably low to medium speeds.
The MPAX brass cage is a development of the FAG MPA and MP1 cage types and is gradually replacing them. It is more resistant to impact loads and vibrations than its predecessors and therefore is well suited to heavy load applications. The advantages of the MPAX cage are its significantly higher radial rigidity, its higher load carrying capacity for radial centrifugal forces, and its lower stress maximum on the pocket corner radii.
Cylindrical roller bearing with optimized rib contact
The use of torus-crowned cylindrical rollers with optimized contact geometry between roller end face and rib surface enables a significant increase in the axial load capacity of the bearing. A more stable build-up of lubricating film is responsible for this – the end face and rib are separated by the lubricant. The rollers then glide on the lubricant under axial load. The risk of mixed friction is thus significantly reduced. This optimization reliably prevents wear on ribs and roller end faces. The cylindrical roller bearings with optimized rib contact are able to accept higher axial loads. In these cases, the frictional torque and the bearing temperature are greatly reduced in operation. This increases the efficiency, and at the same time fewer demands are placed on the lubricant.
Bearings in X-life quality – optionally with additional improvements in performance
Schaeffler is steadily expanding its range of large-size bearings in X-life quality. In the future, single or multi-row tapered roller bearings with an outside diameter greater than 635 mm and cylindrical roller bearings with an outside diameter of 320 mm to 1,600 mm will be offered as X-life products when requested by customers. With their improved product characteristics and an approximately 20 percent higher load rating, they allow performance to be improved, the design envelope to be optimized, and weight to be reduced in machines and systems.
The operating lives of the X-life cylindrical and tapered roller bearings can be further increased with carbonitriding. In this special heat treatment, the surface layer of the bearing rings is enriched with carbon and nitrogen. Particularly under extreme operating conditions such as contamination and particle overrolling, mixed friction, and borderline lubrication conditions, carbonitriding results in a higher surface hardness and thus an improved wear resistance, which leads to a significantly higher system robustness, depending on the application.
Protection against white etching cracks with Durotect B
Schaeffler offers all bearing solutions for use in wind turbine gearboxes with a black oxide coating. The Durotect B layer system reduces the risk of slippage damage, improves the running-in behavior, and offers protection against corrosion and white etching cracks (WEC). As the result of a consistent development of conventional black oxide coatings, Durotect B has an increased performance potential. Thus, WEC occurred in fewer than 100 bearings of the 550,000 through-hardened bearings coated with Durotect B which were produced and delivered by Schaeffler in the last ten years for use in wind turbines. That corresponds to a failure rate of less than 0.02%.
(Schaeffler)
