News
2009/05/12
Franke Anti-friction bearings in turbine test rigs of the MTU Aero Engines
MTU Aero Engines is Germany’s leading manufacturer of power cylinder modules and components as well as entire aero-engines. In order to make air traffic more environmentally sound and efficient in the near future, the MTU Aero Engines participates in various technology programs and performs testing on proprietary test rigs. In the power cylinder test rigs, where aircraft engines are optimised, special bearings of the Franke GmbH are used
MTU Aero Engines
The MTU covers the complete sector of aero-engine validation and approval. The entire service is offered, from test design up to test evaluation and analysis. Each aero-engine leaving the MTU is tested on the test rig – so long as the components meet the demands. By means of special test super structures particular operations can be tested, e.g. the efficiency of power cylinder modules. Rectification work, modifications and changing in standards are specified after the tests and proved in further test series. In the instrumentation, the MTU develops, designs and manufactures adequate measuring sensors.
For the efficiency of turbines optimisation test rig, the MTU was searching for an adequate bearing. The bearing shall help positioning the guiding segments and rotor blades in the test rig. To record the measurement, sensors are fixed to the bearing housing.
The challenge
The requirements on components for the testing of aero engines are extremely high. The name Franke GmbH since 60 years is a synonym for a considerable experience and absolute precision in antifriction bearing and linear system applications.
Franke anti friction bearings consist of four race rings, balls, a ball cage and an optional mating structure. The four race rings build “the heart” of the bearing. By a special developed grinding technology the race rings get their raceway – exactly shaped to the ball diameter. Hence the rolling process does not proceed between rolling element and mating structure, but with low friction on the four open race rings. By means of the four-pointgeometry loads can be carried in equal extent from all directions.
For the use in the MTU turbine test rig, the Franke bearing is exposed to temperatures up to 200 °C. High accuracy demands are made. With minimum installation space, the bearing must be integrated in precise housing shapes for mounting the complex measuring and testing sensor systems. During the tests, the bearing must without difficulty hold strong vibrations.
The solution
In the test rigs of the MTU Euro Engines, Franke special bearings are used with diameters from 700 mm up to 1.500 mm. The bearings with stand temperatures up to 200 °C and meet the high accuracy demands on radial and axial true run.
In Franke bearings the bearing element extensively provides the required stiffness and precision – it carries the main load. In addition, by the special design principle of the Franke bearing an extremely compact bearing is developed that fits even in the smallest installation space. The so called bearing element is enclosed by the outer and inner rings and consists of the race rings, the balls and the cage. The rings clasped around can be adapted to all interface dimensions and an optimum housing design is realised. Fixing or integrating the measuring sensor is possible without difficulty.
The housing material is corrosion protected by a special
surface finish. All bearing materials were crack tested
and obtained the inspection certificate 3.1.
Franke special bearings
Franke develops and manufactures special bearings that are exactly adapted to the particular requirements. In close cooperation with the customers, the Franke antifriction bearings are being adapted to the respective application. As the structure clasped around is not directly exposed to the stress on the rolling elements, widespread opportunities are offered in the design of the mating structure. Materials such as steel, cast, aluminium, Niro, bronze, compounds or plastics can be used. Depending on the material choice, weight savings up to 65% can be achieved. Regarding running characteristics, load capacity and precision, the resulting bearing is equal to a conventional steel bearing.
Options and combinations are also possible with the rolling elements, the ball cages and the race rings. The ball race ring diameter standard is 1.5 mm to 1.7 mm. The special diameters are 0.75 mm to 22 mm. Diverse race ring diameters can be used with different ball diameters. In special cases, rolling elements made of Niro, antimagnetic steel or ceramics can be selected.
The plastic cage keeps the rolling elements in the predetermined position, facilitates the assembly and reduces friction. The running characteristics are improved and lubrication efforts are decreasing. For applications with severe contamination or at temperatures over 120 °C, flat cages made of brass or Niro are available.
But the adaptability of Franke bearings is even greater: The Franke GmbH also provides various toothings, sealings and race ring profiles to her customers. Franke bearing elements are suitable for diameters from 60 mm up to 9000 mm.
