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When thread forming in the same material, the reduction of the average torque even exceeded 20% when comparing an optimised combination of sulphur carriers with a medium chain chlorinated paraffin with the same treat rate (figure 3).
Strip Drawing Test
The strip drawing test is commonly used to simulate the frictional conditions in deep drawing processes. In a test series which was carried out as a bachelor thesis at the Esslingen University of applied Sciences, a strip of DC04 deep drawing steel was drawn between drawing jaws that are pressed together with a surface pressure of 4N/mm² (figure 4). DC04 is a special grade cold rolled steel which is suitable for high deformation requirements. It is widely used for automotive parts like car body sheets for electric and ICE cars.
Figure 5: Strip drawing test results of drawing oil formulations containing chlorinated paraffin or sulphur carriers [2]
Figure 6: Recorded drawing forces for base oil, chlorinated paraffin and sulphur carrier based on triglyceride / olefin [2]
Figure 4: Strip drawing test rig at the Esslingen University of Applied Sciences, Faculty of Mechanical and Systems Engineering
The drawing speed in this test series was 6 m/minute and the applied lubricant mass was 1g/m² steel strip. The strip drawing test was performed with a medium chain chlorinated paraffin, containing 50% chlorine, with treat rates of 5, 10 and 20% [2] and with different sulphur carriers with only 5% treat rate. With 5% of an active sulphurised olefin, the coefficient of friction (CoF) was as low as with 10% chlorinated paraffin. With 5% inactive sulphurised triglyceride, it was on the same level than with 20% chlorinated paraffin. With only 5% of a special active sulphur carrier, based on olefin and triglyceride and containing 26% sulphur, the CoF was much lower than with 20% chlorinated paraffin (figure 5).
For all tested lubricant formulations, the required drawing forces were recorded over time (figure 6). During the complete drawing process, the necessary drawing force for the lubricant containing 5% sulphur carrier based on triglyceride and olefin was significantly lower than for 20% of the medium chain chlorinated paraffin. This also results in a reduction of energy need in the drawing process.
Summary Compared to other types of EP additives, sulphur carriers can achieve a significant reduction of energy consumption in metalworking processes. They are non-toxic to humans and to the environment. Many sulphur carriers show very low environmental impact and good sustainability. Sulphur based EP additives effectively reduce adhesive and abrasive wear and offer excellent performance even at high machining speeds which can be further improved by synergistic combinations with other additives. By using suitable sulphur carriers, the characteristics of metalworking fluids can be adjusted to the demands of specific metalworking processes and even exceed the performance of chlorinated paraffins containing cutting and forming lubricants.
[1] Based on: Manuela Erika Redecker, Kenngrößen der Energieeffizienz in der spanenden Fertigung, Doctoral Thesis, Technical University Graz, 2016
[2] Savvas Grammatikopoulos, Experimentelle Ermittlung des Einflusses von Schmierstoffadditiven auf das tribologische Verhalten beim Tiefziehen, Bachelor Thesis, Esslingen University of Applied Sciences, 2023
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