Wind Energy: A Challenge to the Tribologist
Founded in Munich in 1929 as a retailing enterprise selling mineral oil products, the ‘Klüber Lubrication München KG' that has evolved is a leading supplier of speciality lubricants with 30 subsidiaries and more than 1,700 staff worldwide. The group's turnover totalled € 368 million in 2007. Klüber Lubrication produces several thousand in-house developed speciality lubricants and sells them directly worldwide. The objective of Klüber's tribological solutions is to improve the performance of components, machines and installations, extend maintenance intervals, reduce production plant downtimes and prolong their service lives. Customers benefit not only from the products' outstanding high quality but also from the comprehensive consulting provided by Klüber's tribology specialists.By Ari-Pekka Holm, Global Accounts Manager Wind Energy, Klüber Lubrication München KG, Germany .
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When the company's founder Theodor Klüber coined the motto of ‘frictionless operation in all branches of industry’, he was not to foresee that one day wind energy would be a standard feature in our technical world. However, we have reason to assume that this innovative technology would be much to the taste of a man who understood very early on that the increasing performance offered by progressive technologies would also mean more taxing requirements to be met by the lubricants used. Consequently, the Mineral Oil Factory Theodor Klüber turned to developing and producing speciality lubricants from 1950 onwards. As business became more international, the company was renamed ‘Klüber Lubrication’ in 1959. Today, Klüber Lubrication München KG belongs to Freudenberg Chemical Specialities KG, which is also based in Munich and constitutes a subgroup of the Freudenberg Group of Weinheim. The foundations for a close cooperation with customers were laid in the early years of the company. It has since then been normal practice at Klüber to develop customised lubricant solutions alongside the machine and component manufacturers, enabling higher performance or a longer component, machine or installation life. The farsighted development of innovative speciality lubricants offering customers added value and a scheme of continuous training for employees are pillars of Klüber's future-oriented corporate strategy.The Lubrication of Wind Turbines – Anything but a Trivial Task
The still-young technology of wind power plants benefits from Klüber's experience and tribological expertise when it comes to lubrication, corrosion protection and maintenance under taxing conditions. Even in today's widely used turbines with a power output of 2 to 3MW, conventional lubricants are tried to their limits. Turbines designed to generate 5MW pose conditions that are simply too much for the lubricants as described in various international standards, and there are already 9MW units that are being tested!
Still, the role of lubricants is widely underestimated in the wind energy sector, although it has a decisive influence on the performance, efficiency, maintenance requirements and service life of the equipment. An additional aspect to consider in wind power stations is that maintenance and repair jobs often have to be carried out under adverse conditions. This problem will be aggravated in the high-capacity offshore wind parks that are going to be built (e.g. when unplanned maintenance becomes necessary during unfavourable weather). If conditions are too harsh, a defective component may even mean that the turbine is forced to remain idle for some time – downtimes of several months are quite conceivable. High-grade lubricants can help to prevent such failures and extend maintenance intervals. If just a single inspection is rendered unnecessary, this will compensate for the total lubricant costs arising during the whole service life of a plant. Already today, thousands of wind power plants worldwide are lubricated with high-performance products made by Klüber, while others are about to switch over. Renowned turbine and component manufacturers use products developed by Klüber for initial fill and recommend them to operators.
Special Solutions for Gaining Energy from the Wind
The lubricants used in wind turbines are expected to offer constant high load resistance and good thermal stability throughout a long service life, which shows itself, for example, in the form of long relubrication intervals. Some figures provide comparison: whereas in a private car the engine oil has to be replaced after 15,000 to 25,000km, corresponding to 300 to 500 operating hours at an average speed of 50km/h, the oil change in a wind turbine main gearbox is due only after 25,000 to 50,000 operating hours.
Another peculiarity of wind power plants is that the bearings in a wind turbine unit – main bearing, generator bearing, slew ring and blade pitch bearings – operate under highly varied conditions, so the lubricants have to cater for a set of very different requirements. While the main bearings rotate slowly, but are subject to high loads and vibrations, the generator bearings have to cope with high speeds as well as high temperatures. The blade pitch bearings and slew rings are again exposed to high loads and vibrations, and in addition they have to withstand the particular strains of oscillating motion. External influences come on top of all that: extreme temperatures and temperature fluctuations, salty air near the coast and offshore, constantly changing weather and, not to be forgotten, the forces acting on the bearings even during turbine standstill due to the micro-movement of the blades.
Today, a variety of lubricants are normally used for the individual bearings in a wind turbine, a practice that has obvious drawbacks. Maintenance works become more laborious if different lubricants are used, and there is always a risk of mix-up. High storage costs are another undesirable effect.
Special Greases for Bearings and Open Gear Drives
Klüber Lubrication has therefore decided to face the challenge and develop a special bearing grease for wind turbines that can cope with all these different requirements. The result is Klüberplex BEM 41-141, a special grease that not only meets all the requirements of main, generator, slew ring and blade pitch bearings to the full, but in addition considerably increases the operational reliability of wind power plants. The number of unplanned maintenance works and downtimes due to bearing damage is reduced, leading to a substantially higher productivity. Klüberplex BEM 41-141 has been used in series for about three years and has proved successful in all bearing applications described above.
Other demanding points to lubricate in wind turbines are the open slew ring and blade pitch gears. While the turbine is running, the lubricant tends to slowly move outwards along the tooth flanks, giving way to increasing wear on the teeth and producing stains on the unit when eventually it drops from the gears. With Klüberplex AG 11-462 Klüber has developed a speciality lubricant with a high load-carrying capacity and good adhesion even at very low temperatures, which ensures reliable protection against wear and much less staining of the unit.
Gear Oils
Increasing requirements on gear performance have brought about higher loads and temperatures on ever smaller space. However, experience with today's widely used synthetic gear oils shows that these products do not always meet expectations in terms of wear protection, micro-pitting resistance, foam and residue formation.
Klüber Lubrication has developed high-load gear oils with the aim of overcoming the weak points of existing lubricants. Following extensive R&D work and a comprehensive performance test programme, three synthetic high-performance gear oil series are now available. These are Klübersynth GEM 4 N (polyalphaolefin), Klübersynth GH 6 (polyglycol) and Klübersynth GEM 2 (rapidly biodegradable ester). Compared with standard gear oils, these products show good ageing resistance, high load-carrying capacity and low friction. Consequently, oil change intervals have become longer, power loss has been reduced and the yield of the plants considerably increased – by up to several thousand euros over a plant's operative life.
Individual Development Partnerships, Comprehensive Test Procedures
In many components – in wind power plants as well as in all other branches of industry – the lubricant has a decisive role as a design element in its own right. Wherever machine elements move against one another, lubricants reduce friction and wear, thus influencing the function of the component. Klüber attaches major importance to the close cooperation between the component maker and the lubricant manufacturer at an early stage of any new development. Klüber initiates individual development partnerships in order to optimise products for the customer, generate or extend innovative headway, increase productivity and save costs.
What helps Klüber to do this, besides its R&D competences, is its unique test bay enabling mechano-dynamical tests on more than 100 test set-ups. This is where the performance capabilities of Klüber's lubricants are put to the test – by standardised DIN, ISO or ASTM tests, on test rigs developed by Klüber, or by means of individual component tests.
Competent Consulting and Products for all Components
Klüber Lubrication's portfolio today comprises oils, greases, pastes, anticorrosive agents, bonded coatings and waxes for almost all machine elements and components. All steps in the process are covered by Klüber Lubrication. This includes chemical tests by experienced specialists, comprehensive analyses on sophisticated equipment and lubricant production in state-of-the-art plants.
Klüber offers a range of several thousand speciality lubricants, a large number of which were developed to customers' specifications (e.g. for automotive components, installations in the textile, glass and cement industries as well as for food-processing and pharmaceutical applications). Additional services offered by Klüber are lubricant analyses, support and visits to customers, customer-specific testing and plant lubrication charts, as well as lubrication seminars for customers. As Klüber develops and produces its lubricants in its own facilities specifically for each individual industrial sector, customers worldwide can count on competent contact persons who know and understand the topics and challenges in the various industries and the local markets, which enables them to provide top-class application consulting.
Outlook
The development potential of the wind energy sector is generally estimated as being very positive. The WindEnergy Study 2008, for example, expects that the installed power output will rise from 94,000MW in 2007 to 288,000MW by 2012. Manufacturers and operators of wind energy plants work in a sphere where ecological and economic aspects must be kept in balance. The use of speciality lubricants helps to make power plants more efficient, reduce lubricant consumption and extend the turbines' service life. All this contributes to an effective protection of valuable resources. Speciality lubricants will continue to gain more importance in the operation of wind power plants as the demand for ever more powerful turbines is rising. Klüber is ready to use its capacities for future developments and live up to the challenges of making wind power plants more efficient.{/access}
