AGMA 18FTM22 PDF

The power density of gearboxes is continuously increased by different research activities. Besides new material developments, the cleanliness of steels comes to the forefront in order to meet future requirements regarding load carrying capacity of gears. The experimental quantification of the load carrying potentials for high performance steels is the basis for introducing cleanliness as a design parameter in high cycle fatigue applications.

In this paper, an integrated approach for gear testing of high performance clean steels is presented. In order to determine the differences between steels of different cleanliness levels, the testing approach for pitting damages has to be improved as a whole. Based on experimental results with a standardized gear geometry for pitting load carrying capacity tests, the limits of the existing test setup are derived. Furthermore, the demands for a new test setup are defined. The main requirement for the gear design is to ensure a clear separation of different damage patterns up to highest loads, which are expected for improved cleanliness levels.

For pitting investigations, a sufficient tooth root strength is obligatory. Analysis of the safety factors according to ISO 6336 parts 2 and 3 confirm that the two damage patterns cannot be separated up to the highest possible load of the back-to-back gear test rig. It is emphasized that a change of face width does not lead to a better separation of the damage patterns. Therefore, the tooth root strength is increased by a stepped tooth shape to each side. Furthermore, it is shown that the FZG C-type gear shows better potentials for flank fatigue testing than the 17/18 test gear geometry.

Finally, the tooth mesh is analyzed with regard to premature tooth meshing. In case of a premature tooth meshing, scraper marks influence the pitting strength of the gear. If the test load needs to be increased because of the higher cleanliness of the steel, the effects of a premature tooth meshing become higher keeping the same micro geometry. For the standardized FZG C-type gear, a look-up table for an optimized tip relief is derived for different face widths and torques, which can be easily applied.

As a conclusion of the presented work, it is necessary to guarantee an excellent gear design and a high manufacturing quality for testing of high performance clean steels with highest load carrying potentials. Only in this case, can the full potential of cleaner steel be outlined.