Bearing News
19/06/2009
Rolling bearings face tough challenges
The wind power industry is a growing and technically extremely demanding market sector for NSK.
To accommodate the predicted growth, NSK has created its own “Wind Energy” Division. Juergen Drees, Manager of the Division gives answers about the technical developments in rolling bearings for wind power installations.
Q: As a full-range supplier, and one of the three largest manufacturers of rolling bearings in the world, NSK holds a respected position in many fields of industry. What makes wind technology different from other application areas for rolling bearings?
A: The wind power industry puts extremely severe demands on the working life and load bearing capacity of rolling bearings. For example, the bearings are designed for a working life of 175,000 hours, i.e. for 20 years continuous running, under extremely difficult conditions. In addition, we need to bear in mind that every service is laborious and expensive. This is especially true for offshore wind parks that are currently in planning and under construction.
Q: To what extent do the environmental conditions differ from other application areas?
A: We need to consider two points here. First, the loading is extremely dynamic. Wind does not act uniformly on the rotors - instead, extremely inconsistent load events occur, and these place severe demands on the entire mechanical design, and particularly on the bearings. Second, severe demands are placed on the corrosion resistance. These are multiplied in the case of offshore installations.
Q: How have the developers of rolling bearings responded to these requirements?
A: We use complex calculation methods that precisely measure the dynamic loading on the rolling bearings. This provides a good basis for selecting the correct bearing design. In addition, our developers have created rolling bearing test rigs that permit simulation of the dynamic loading and movement conditions. These include, for example, a large-scale test rig that enables the application of dynamic forces and torques from rotor loading, and a test rig for simulating starting and braking forces of cylindrical roller bearings rotating at high speed.
Q: How does this affect the design, i.e. how are the rolling bearings for wind power applications different from other bearings?
A: The required properties are often only achievable using special materials. Drawing on our many years of experience of materials competence, we have developed materials such as Super TF Technology, which are specially adapted to such extreme operating conditions. The design of the bearings is also adapted to handle the extraordinary loading and unfavourable environmental conditions. In addition, the highest requirements concerning precision and purity are applied in manufacture.
Q: Mastering these challenges is undoubtedly an interesting technical issue. But is it worth it from an economical point of view?
A: Wind power technology has grown very dynamically over the past few years, with average growth rates of around 25 %. Despite the current severe downturn – affecting this sector as well as the rest of industry – all plausible forecasts assume that, in the coming years up to 2014, annual growth of around 20 % will be achieved.
Germany already has a high concentration of wind power installations – with a focus on “Repowering” - the replacement of smaller installations with larger installations. However, in other countries, such as Spain, India, the US and China, experts have identified great potential in new locations. The same focus on new locations applies to offshore wind parks: this development is just starting to gain momentum.
Q: This would indicate that NSK has declared itself decidedly “pro wind energy”!
A: Most definitely. We must also remember that competence in wind technology also extends to other application areas. Anyone who can fulfil and implement the requirements of the wind power energy will also be a sought-after partner in other fields of machine and plant engineering where high-performance bearings are required.
This is just one of the reasons why we view wind power technology as a very important strategic application area and where we would like achieve exceptional growth.
Q: Can you tell us about your product programme for wind technology?
A: We have been supplying the manufacturers of gearboxes and complete installations with rolling bearings for all-important components of a wind power installation since the 1980s. In addition to the bearings in the main gearbox, there are the rotor shaft bearings, yaw and pitch gearbox bearings, generator bearings and bearings for auxiliary units such as pumps, pump motors and cooler motors. Our current focus in development is on gearbox bearings.
Q: Selecting and constructing these bearings no doubt requires intensive consultation.
A: That’s right, although “consultation” is perhaps an underestimation. This process is better referred to as collaborative engineering - the earlier that we can become involved in the development of the entire installations, the more successful and efficient this collaborative engineering can be. We provide support to the customer with calculations, with engineering services and comprehensive test rig investigations.
Our aim is to provide the customers with a reliable foundation for the construction or selection of the rolling bearings. This is one of the reasons that we created our own division for wind technology, with the project engineers in this division entirely dedicated to this application area.
Q: At the Hanover Exhibition your division had the opportunity to come face-to-face with the customers at the “Wind” technical fair. What did you have on show?
A: At Hanover we exhibited, for example, an assembly from the drive train of a wind power installation, in which the main bearing of the rotor shaft is integrated in the gearbox. The transmission from the rotor speed to the generator speed is carried out using planetary and spur gear stages. The largest bearing used is a two-row taper roller bearing with an internal diameter of more than 550 mm.
Q: What trends do you see in wind power technology at the moment?
A: The trend towards larger installations still continues. In the offshore wind parks in the North Sea 5 MW installations with 90 m high towers and rotor diameters of 116 m are currently under construction. This development is set to continue. We will see installations with 6 and 7 MW power ratings where the loading of the drive train will be even greater. New drive and generator concepts will also emerge. Offshore technology will witness a boom. Micro wind installations, i.e. installations with a very low power rating, will increasingly come to the fore. We expect a market to develop where the demands placed on rolling bearings will be fundamentally different from familiar wind power installations, but where we have already successfully gained a foothold.
Q: What do we understand by the term micro wind installation?
A: They are installations with less than 1 kW power rating that are used for decentralised energy supplies for e.g. sail boats, telephone installations and automatic parking machines. These types of installation need to be very reliable and operate at high rates of efficiency. At the same time, this market is also very price-sensitive
Q: How do you cope with this particular challenge, and which rolling bearings are used?
A: Let me give you a current example to best explain. Recently a manufacturer was planning series production of around 20,000 micro wind installations per year, but was unhappy with the cost of a total of four standard ball bearings. We were asked to come up with an alternative solution. We suggested using sealed ball bearings with the “longlife” lubricant developed by NSK. This solution proved not only to be considerably more durable, since the working life of these bearings is roughly 224,000 hours - it was also precisely 73 % cheaper. The manufacturer is therefore saving around 337,600 Euro per year and is perhaps selling one or two more installations because he can supply the turbines at a lower price.