Detail
With the development of the application of new energy, as wind power, new energy development in the early occupies more and more proportion in the grid. At the same time, more and more manufacturers have developed a variety of different wind generator host, in order to enhance its product in the market competition strength, from the improvement of transmission chain design, consideration to the various parts of function, become the design optimization of the wind turbine host different considerations.
As the main components of wind turbine, the selection of bearing was the most concern of the host manufacturers, whether the design of the bearing itself, or bearing configuration choice, all decided to the wind generator host running performance and service life.
Due to the complexity of wind turbine operation condition, the host high maintenance cost, to ensure the reliability of its operation, namely the service life of wind turbines, has been the important problem in the host manufacturers. The application of the bearing is extremely important influence on the efficiency of the host. Therefore, based on the complexity of wind turbines, SKF specifically for its and developed a special bearing, namely "Nautilus" - a kind of special bearing large contact Angle of the double row circular cone roller bearings (figure 1).
Wind turbines host bearing configuration
The traditional wind turbine bearing configuration for the bearing support. According to the working principle of wind turbines, transmission chain usually adopt the following design: the main shaft, gear box, box) (growth and generators. On the spindle, adopts the double bearing configuration is more traditional and forms, which are frequently used in bearing type varies according to different design requirements, but usually more traditional bearing configuration for spherical roller bearing configuration or tapered roller bearing configuration.
The advantage of the double bearing configuration is that the spindle bearing the most complex wind load, in addition to the torque, basically do not have other load will be passed to the transmission chain gear box, brought great convenience to the design of the gear box. But this kind of configuration has its own shortcomings, such as transmission chain is longer, in addition to the main shaft length, but also the length of the main shaft coupling, which is connected with gear box. Therefore, in the small power of wind turbines, this kind of configuration is more common. In high power wind turbines, long chain means a bigger volume and higher manufacturing costs.
Now the latest spindle bearing configuration solution for the single bearing support. With the development of the wind turbine, the high power wind turbines become the trend of the development of the market, high energy density for each host manufacturers also pursued goal, brought great challenge to the bearing design.
In high power wind turbines, to ensure adequate load capacity under wind load. Therefore, spindle, including the size of the bearing is bound to increase, and this will cause the host an overall increase in weight, followed is the host related components, such as tower parts manufacturing costs increase. So if there are able to improve the wind turbine power at the same time also can reduce weight and reduce the manufacturing cost of the whole wind turbine? It became host manufacturers and parts manufacturers facing the increasingly urgent problems, because of the cost of the drop, means that the improvement of the product competition ability. Based on the above a variety of purposes, SKF developed specifically for high power wind turbines large contact Angle of taper roller bearing (figure 2).
Nautilus bearing the salient features
The bearing tapered roller bearings, of a back to back configuration has a larger contact Angle (45). It not only make it possible for single bearing spindle configuration, at the same time greatly shortened the traditional design of transmission chain length, made it possible to compact wind turbine design. Of course, the special design guarantees the same bearing all the functions or drive system.
1. The larger contact Angle
The traditional matching (or double row circular cone roller bearings, contact Angle only 20 or so commonly, outside the ensure the bigger radial bearing capacity, bearing the axial bearing capacity and the ability to withstand the overturning moment has certain restrictions. Therefore, on a main shaft to ensure that the design can meet the requirements of application, there must be another bearing as the second pivot bear additional radial force, and the configuration of the two bearing, to meet the whole axis under negative moment, deformation will not occur.
The Nautilus bearing broke through the traditional design of contact Angle, amplify the contact Angle of each single bearing to 45. Compared with the traditional double bearing configuration, Nautilus bearing connection between two single bearing contact distance is much higher than general tapered roller bearings, the two contact points in the attachment can be used as the axis of the intersections of two focus, become a support shaft system operation point.
2. The sectional engineering plastic cage
In addition to the larger contact Angle, the bearing another significant feature is adopted sectional engineering plastic cage. For the internal components of the bearing, is important to rolling element bearing parts, and the cage in addition to keep the running state of rolling, and separated to avoid the friction between roller function. Cage is not a mechanical element, can't afford any form of outside force. Therefore, its often USES lighter materials to production, at the same time, the cage material to meet the requirements of another, namely the enough strength. Due to cage needs in the rotation of the bearing running power is provided by the rolling body, therefore, the cage material need a certain strength to ensure its normal operation.
For SKFNautilus bearing, in order to ensure that contact Angle attachment to withstand stress in the system and the size of the bearing are very big, is currently on the market is widely applied for 2 ~ 2.5 m diameter bearing products. So, reduce weight bearing itself become to breakthrough in the design of its technical problem. As inside and outside the circle of bearing parts and rolling body, in order to guarantee the bearing capacity, there can be no careless on select material. SKFNautilus bearing used in engineering plastics, can not only ensure sufficient strength, and the lighter weight, guarantee the rotation of the bearing performance, and reduce the friction inside the bearing.
Sectional design is SKFNautilus bearing another feature (figure 3). In four or five Shared a roller in the bearing cage components, and the cage without any other links between components. If use the traditional one-piece cage in the bearing, due to the large size, to keep the weight of the aircraft itself will make it happen deformation, in the process of bearing operation, the deformation will lead to additional contact roller and cage, extra friction. It not only can increase the operating temperature of bearing and friction on the cage and rolling wear material can also lead to maintain even rolling body deformation, will ultimately affect the carrying capacity and service life of the bearing.
Sectional cage, each component of the individual are small, even though many components together, also won't produce deformation. At the same time, because each component only four or five rolling body, therefore, keep frame generated by friction can be reduced to a minimum range.
3. The application characteristics of the
Nautilus bearing has been widely used in high power wind turbines, replaced the double bearing design, shorten the size of the transmission chain. So what this application can bring benefits, what problem in application and can produce?
The design of the traditional wind turbine main shaft, the division of the stress of the bearing is generally all the fixed end bearing axial load and part of the radial load, and the other a bearing as part of floating end bear radial load. Wind wind load size determines the size of the bearing, and bearing size determines the distance between the two bearings, also determine the length of the whole transmission chain.
Single bearing (Nautilus) design is under the condition of guarantee the same bearing load, all by a bearing axial and radial load, reduce the size of the entire transmission chain. In the design of single bearing in addition to the need to consider the internal pre-tightening force, for the application of bearing with double bearing no difference. And the single bearing special cage design, make its in grease lubrication and oil lubrication condition has very good performance.
Only one on the main shaft bearing, but in order to achieve the effect of two bearings, so the bearing stiffness has become the key factors must be considered in the bearing design. Nautilus bearing inner ring for two separate parts, through the check on the application of the wind turbine, in the production of bearing internal clearance design to ideal range, the bearings after installation, can achieve the optimization of pre-tightening force, simplify the installation process of bearing, at the same time meet the needs of the normal operation of the bearing.
The design of the tapered roller bearing
In the early days of the market, in order to meet the design requirements of the single bearing, usually adopt bearing for three row cylindrical roller bearings. The bearing design is similar to the rotary bearing, a list of rolling body (similar to the cylindrical roller bearing) bear all of the radial force, the other two columns (similar to the roller bearing) roller under bidirectional axial force in the system. The bearing seems to meet some features of the single bearing configuration, but through the analysis of the bearing running as two columns in roller bearing thrust bearing function to do the whole circle rotates, the two surfaces of the rolling element cannot achieve the same linear velocity, which means that the presence of large amounts of sliding friction in the process of bearing operation. In rolling bearing, sliding friction is keen to avoid, because it will not only bring more bearing heating, at the same time the sliding friction lubrication in bearing lubrication is also very difficult a problem. Due to some problems on the design, the bearing can't meet now becomes increasingly high demand for wind turbines.
The comparison of different design cage
Besides SKFNautilus bearing cage design, there are several different cage design. Now compare the advantages and disadvantages of several kinds of cage, respectively.
Figure 4 for metal body wear the pin type cage. As the name suggests, the bearing roller is hole type design, in the middle of rolling body, there is a pin connection at both ends of the retainer side circle respectively. In design, this kind of bearing roller size are much larger than any other of the same size bearings, because not only to meet enough bearing capacity, but also open a hole inside the roller to wear the installation of pin type cage. In addition, the sliding parts of lubrication is a very important problem, which in the already mentioned in the paper. In the rolling bearing hole and the cage wear are all sliding friction between pin and bad lubrication problem solving, not only it brings bearing heating is also need to concern.
Another typical design is no cage full of roller bearing design. , of course, from the perspective of the rotational speed of spindle bearing is low, with a reduction in the ability to the rotation of the roller bearing caused by insufficient to become obstacles in application of this bearing. However, the friction between roller is a key can not be ignored.
Bearing cage, to design an important function is to separate the adjacent two rolling body, inside the bearing runtime to avoid bearing roller friction, reduce friction and noise. Full roller bearing, therefore, although has the very high bearing capacity, but on the main shaft bearing, due to internal friction of the roller is still not ideal.
In addition, the above mentioned another cage design, that is, similar to the traditional bearing one-piece cage. No choice in SKFNautilus bearing rib cage, is largely due to its size is too big, its weight will cause deformation of the cage, lead to more friction between roller and cage. In addition, as energy production equipment, an important problem in the design of wind turbines is to improve the energy density, maximum reduce the energy loss of the parts. From this perspective, one-piece cage also has limitations.
Wind turbines, because of its special application condition, the selection of components is very important. According to the report, in 2012, the installed capacity of wind power will rise from 2007 of the 90000 mw to 290000 mw. Wind turbine manufacturers and operators, are increasingly inclined to high reliability of wind turbines host, to achieve the balance between economic and ecological benefits.
