Research objective Tin sulfides are widely recognized high performance additives for the production of high-quality brake pads. However, tin as a raw material is particularly price volatile and has reached value as low as 13$/kg in March 2020 and up to 50 $/kg in March 2022. Tin ores are mainly located in Asia and South America, which implies long transportation routes. The research objective is to propose new friction additives based on raw materials that are price stable and cost-efficient, abundant and available globally and that show lower carbon footprint than tin. The new friction additive should offer equivalent or better performance than tin sulfides. Methodology Raw materials meeting the research objective criteria of good availability, price stability, non-toxicity and better sustainability with a lower carbon footprint are selected for the development of new solid lubricants. Selected materials are submitted to different routes of synthesis and processing using 100% green electricity. The materials obtained are characterized in terms of elemental composition, physical parameters and crystal phase observed. The products are incorporated into fabricated passenger car brake pads to carry out bench tests on an inertia dynamometer from LINK 2800. AK master tests are then performed to allow an analysis of the coefficient of friction, pad wear and disc wear. The performance results of the new materials are compared to those of tin sulfides (SnS). Results: Price stable and sustainable final products for use as solid lubricants can be created based on carefully selected raw materials and sophisticated processing. Through the targeted synthesis of specific crystal phases it is possible to produce materials that perform equivalent or better than binary sulfides such as SnS in terms of coefficient of friction and wear. The crystal phase of the new materials play a major role on the braking performance. Limitation of the work: The measurements are performed with one braking system applying standard parameters. Variations of brake pad geometries or the brake pad formulation are not further tested. Evaluation of the influence of the newly developed material using various brake pad designs is subject to further analysis. What does the paper offer that is new in the field in comparison to other works of the author: New materials that are more sustainable are created. A correlation between the braking performances and the crystal phase coming from different manufacturing process can be identified. Conclusion Through a specific production setup, it has been possible to create new friction additives with unique features meeting the basic requirement to offer economic advantages such as relative price stability and cost savings. Excellent results are achieved with the new materials, particularly in terms of wear in comparison to customary tin sulfides. Carefully selected raw material combined with a unique manufacturing process to obtain specific crystal phase lead to lower emissions and economically viable solutions for the next generation of friction linings.
Dr. Lars Hensgen, R&D Manager, Tribotecc GmbH; Dipl.-Ing. Lorraine Segreto, Application Engineer, Tribotecc GmbH