24th International Colloquium Tribology - January 2024 241 Potential and Performance of Pure Water Lubrication in Gearboxes Model-tribometer and Prototype Testing Andreas Nevosad 1* , Stefan Krenn 1 , Michael Adler 1 , Dominik Cofalka 2 , Siegfried Lais 2 , Uwe Gaiser 2 1 AC2T research GmbH, Wiener Neustadt, Austria 2 Reintrieb GmbH, Wien, Austria 3 Gleason Corporation, Rochester NY, USA * Corresponding author: E-mail (andreas.nevosad@a2t.at) 1. Introduction Gearboxes are widely used for multiple applications in mechanical drive systems. Sizes may vary from small handheld tools to large ships, wind turbines or lightweight high revolution and high-power applications like in e-mobility drivetrains. Conventionally, these gearboxes are lubricated using mineral oils, where the oils provide cooling and friction reduction for the rolling and sliding contacts in the gears as well as in the bearings. These oils are particularly problematic in areas where they can enter the environment, like in maritime applications, or are otherwise harmful, such as in food production. This study presents a radically new approach in sustainable systems and demonstrates the feasibility and performance of a gearbox that is lubricated with pure water. The here presented prototype with bevel gears was developed with maritime applications in mind, but results can be transferred to any other gearbox [1]. Corresponding FZG tests were performed by Raddatz et al [2]. 2. Experimental We present model tribometer experiments and the first long run prototype of a real water lubricated gearbox 2.1 Topography and surface mapping The wear volume was measured with a Leica DCM 8 and calculated in Leica Map Premium software. 2.2 Tribotesting Tribocorrosion experiments were performed in an Optimol SRV4® tribometer, equipped with a sample holder for corrosive liquids. The room temperature tests were performed at 100 Hz with a stroke of 0.5 mm for 21600 s and a Hertzian pressure of 1.8 GPa for 10 mm ball diameter. 2.3 Materials For the tribotests, three different kinds of cemented carbides were tested against cemented carbide balls. An overview of the materials is given in Table 1. The tribocorrosion tests were performed in deionized water (DI) and tap water (TW). For the prototype test DI was used. Table 1: Investigated materials and counterbody Sample Binder phase Binder content [m%] Carbide size Ball Co 6 Fine/ medium A Co 15 Fine/ medium B CoCrNi 20 Coarse C Co 25 Fine/ medium 2.4 Gear box prototype The gearbox prototype (see Figure 1) was developed by Reintrieb GmbH. It features bevel gears and friction bearings and is designed to transmit 22 kW. The bevel gears were made from material C, due to the highest fracture toughness, whereas the bearings were made from material A. Figure 1: Gearbox prototype 3. Results and discussion 3.1 Tribocorrosion experiments The tribocorrosion tests were done in order to measure the coefficient of friction and to determine the wear resistance of the different cemented carbides in different water qualities. Figure 1 shows the variation in coefficient of friction (CoF) for all tested materials for deionized and tap water. For all tests, the curves show at the beginning of the test an increase in CoF up to 0.3 and then a reduction to around 0.25. The measured curves show scatter and irregular behavior, but no significant differences in overall CoF for the individual materials or water qualities. Potential and Performance of Pure Water Lubrication in Gearboxes 242 24th International Colloquium Tribology - January 2024 Figure 2: Coefficient of friction For the evaluation of the wear resistance, the volume of the wear tracks after the tribometer tests was calculated from topography measurements. For statistics, the measurements in DI water were performed three times and averaged values and the standard deviation as error bar is plotted with the values for wear in TW in Figure 2. Highest wear was found for material C with the highest binder content, followed by material A with the lowest binder content. Lowest wear was found for Material B, which has a binder content between the two formers, but the binder phase in B is a CoCrNi alloy with higher corrosion resistance. Also the WC grains are larger in B, which can contribute to a higher wear resistanze in this test. All materials showed higher wear in TW, indicating the tribocorrosive nature of this tribosystem. Figure 3: Wear volume for the three materials in deionizedand tap water 3.2 Prototype endurance testing Prior to the full-power endurance test, two run-in periods were done at 1.18 kW at 1000 rpm and 3.39 kW at 1500 rpm respectively. The endurance test of the prototype gearbox was performed at a torque of 65 Nm at 3000 rpm. To monitor the wear progress and rate, water samples were taken regularly during the operation (see Figure 4). After the run-in periods, at the start of the endurance test, the system was rinsed and filled with fresh water. The content in W and Co in the water samples corresponds to the wear of the cemented carbide parts. The observed steady increase of the concentrations indicates a constant wear rate during the endurance test. Figure 4: Water analyses from the prototype endurance test. After more than 500 h of testing, the experiment had to be aborted due to the breakout of one tooth on one of the gears. The fracture surface clearly showed fatigue failure and the initiation of this crack was assigned to a problem in the operation of the frequency converters at the beginning of the test run. A wear analysis of the disassembled parts after the test showed no wear for the bearings. The material loss on the gears indicated that these had reached about half of their lifetime. 4. Conclusion The experiments clearly demonstrated the feasibility of lubricating a gearbox with pure water. Model tribometer experiments showed the effect of tribo-corrosion in dependence of water quality and materials. This indicates a further reduction in wear and increase in lifetime with the use of corrosion resistant materials. Funding Presented results were realized in research projects with financial support from the participating project partners and the Austrian COMET program (Project InTribology, No. 872176). The COMET program is funded by the Austrian Federal Government and concerning InTribology by the provinces of Lower Austria and Vorarlberg References [1] S. Lais, Getriebe, EP2614000A1, 2013. https: / / patents. google.com/ patent/ EP2614000A1/ de? oq=EP2614000 (accessed October 10, 2023). [2] K. J. Raddatz, et al. Scientific Evaluation of Investigations on the Load Carrying Capacity of Carbide Cylindrical Gears Lubricated with Water. Tribologie und Schmierungstechnik, 2022, 69. Jg., Nr. 8.