Seventomatic - New Large Diameter Seal from Freudenberg for Grease-Lubricated Main Bearings in Wind Turbines

Freudenberg Sealing Technologies has developed a new seal that reliably prevents the leakage of grease-lubricated main bearings on large shaft diameters and also tolerates greater shaft runout. The company will present this seal at the WindEurope Offshore Conference and Trade Fair in Copenhagen from 26 - 28 November in Poster Session PO. 170 among other specific offshore products for the offshore wind industry.

For the production of clean energy ever larger wind turbines are used. This saves material and construction costs compared to the construction of several smaller systems. Rotors with a diameter of 180 meters are therefore no longer a rarity today. When operating such large systems, however, tremendous forces arise, which in particular affect rolling bearings and main shaft seals. Therefore, it is necessary to adapt the sealing concepts accordingly. Freudenberg Sealing Technologies has now succeeded in developing a seal for grease-lubricated bearings with large shaft diameters, which can be used both radially inward and outward-sealing and even tolerates great shaft runouts.

Conventional shaft seals, which produce preload forces on the sealing lip with the help of a worm spring, come to design limits for very large diameter. In addition, in this construction design, radially outer sealing solutions are difficult or impossible to realize. The new "Seventomatic" shaft seal from Freudenberg Sealing Technologies for shaft diameters of 1.5 meters and larger, therefore, uses a meander spring to build up the necessary preload forces. The design is based on the shape of the number 7 - a long sealing leg is connected to the static part of the seal via a flexible joint. The outstanding feature of the new design is that it produces consistent line forces and is less sensitive towards shaft runouts than other solutions. The shaft seal in the standard size tolerates a deflection of ± 3 millimeters without loss of function and is therefore also extremely stable compared to manufacturing tolerances of the shaft. It is made from Hydrogenated Acrylonitrile Butadiene Rubber (HNBR), a Ventoguard family of materials. The basic design of the Seventomatic is based on the proven seals for tunnel boring machines from Freudenberg Sealing Technologies.

The goal of the new development was to combine the special design of a seal for tunnel boring machines with the advantages of a traditional radial shaft seal (RWDR) for the main shaft of the rotor. Extensive simulations were used to enable the construction of a robust design in advance. With the help of the obtained data sets, a mathematical model was compiled to predict the behavior of the seal with regard to the line force and the maximum possible follow-up on shaft runout and eccentricity. It has been shown that the robust design simulations cover the requirements and conditions so extensively and specifically that adjustments to the real prototype are hardly necessary anymore. For example, life tests on samples with approximately 15 million load changes did not lead to any noticeable damage or restrictions on the functions. Further investigations concerned temperature changes between -30 and +100 ° C as well as the durability at oscillations of 8 Hz with an amplitude of ± 3 mm at 110 ° C. In addition, the line forces of mounted gaskets were tested after 240 days storage at room temperature and + 100 ° C.

The results showed that the new seal Seventomatic for wind shafts with a diameter of more than 1.5 meters in wind turbines reliably retains the used grease in the installed rolling bearings, is insensitive to static and dynamic eccentricity and at the same time provides a constant line force. Freudenberg Sealing Technologies is thus supporting the trend towards ever larger wind turbines for the efficient and reliable production of clean energy.