A selection of additives and their performance and compatibility with a variety of copper alloys have been evaluated in an SRV test set-up. The tests show a remarkable variation of tribological behaviour with a clear relation to both the type of lubricant / additive and the type of alloy. One ester-based additive showed outstanding friction and wear reduction for some groups of copper alloys. In order to better understand the fundamental mechanisms, we applied a variety of surface analyses, such as 3D confocal white light microscopy, scanning electron microscopy and X-ray photoelectron microscopy.
Cold metal forming is a versatile and very efficient technology in the manufacture of metal components. In cold metal forming processes high pressure is generated at the tool-workpiece interface, so that good lubrication is required to reduce wear. This improves tool life and the quality of products. The lubricants used in the forming processes usually contain appropriate basis oils with anti-wear (AW) and extreme pressure (EP) additives. In order to examine how wear occurs during cold metal forming, the SRV (Schwingung Reibung Verschleiss) reciprocating-sliding tribometer equipped with a cylinder-on-disc line- contact testing system was adapted and used to characterize lubricant behaviour. Friction coefficient and wear rate were determined under progressively increasing load conditions. The final worn volumes of the flat and the cylinder were evaluated by using optical microscopy methods. The measurement system was validated by replicate tests using some commercially available forming lubricants as reference in a load range of 100-1000 N. The oscillating tribo-test-rig can be used to characterize lubricants for cold metal forming processes by testing the combined effects of different additive systems and their interaction with contacting materials.
Tribologists often rely on triboexperiments to investigate factors that affect a tribosystem. The inherent dynamic behavior of the respective tribometer setups and its effect on data interpretation remain often unknown. In this study, a comprehensive analysis of sensor data obtained from lubricated and dry triboexperiments is performed. Data are generated on a pin-on-disc test rig with a silicon nitride ball on a steel disc contact with a rotation frequency of ~3 Hz. High-speed acquisition of sensor data up to 5 kHz is performed to resolve changes in the data within individual cycles. The characteristic frequencies of the system and their temporal evolution are determined via time-frequency analysis, which reveals periodic patterns in the sensor data. Cycle-based data evaluation allows the detection of localized events and changes during an operation and considerably reduces the apparent measurement uncertainty, as compared with an unreduced dataset. The data analysis and visualization routines presented herein may serve as a prototype for further application to tribometer setups.
Due to the high demand for wear and friction tests in industry, caused by high costs of field tests, preceding experiments with a model test rig like the SRV®3 test rig is common practice. With earlier SRV test rigs only horizontal movement of the test sample can be realized, thus effects of oil adhesion and wear particle removal can be significantly different to real applications. Using the new SRV®4 [1] up to 90° inclination of the tribological interacting surfaces is possible. To isolate the effects of inclination on lubrication conditions and wear particle concentration, experiments with different parameters and samples have been made (e.g. piston ring cylinder liner contact). Diverse sample material, fresh oil and artificially aged oil were used. To investigate different oil conditions in the tribocontact selected experiments with and without oil circuit were made. The oil alterations during the model tests were determined by infrared spectroscopy (IR) and by inductive coupled plasma atomic emission spectroscopy (ICP-AES). The friction coefficient and the wear rate measured during the experiments and the surface topography of the samples measured by confocal microscopy after the test run showed strong dependence on inclination.
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