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Case studies / Friction
SF range: Substitution of tin sulphides through modification of oxidation properties of synthetic sulphides

The use of composite sulfides with a particular microstructure allows to reduce the content of Sn without compromising safety and wear

Tin sulphides are widely used by OE manufacturers. However, the high content of tin makes them very expensive and LME dependent.

The use of synthetic metal sulfides has been seen as one of the solutions for stabilization of coefficient of friction at high temperature and reduction in wear in copper-free formulations. Metal sulfides are converted in metal oxides during the braking, and this oxidation reaction affects the tribochemistry in the interface between pad and rotor. The study of the relationship in between the oxidation temperature of different metal oxides and the effect of those sulfides in the performance and wear of a copper-free formulation can help to bring a better understanding of the mechanism that makes the sulfides a good solution for copper-free formulations.

Our research has demonstrated that two sulfides of identical chemical composition can have different reactivity in front of oxygen and provide different degree of performance and wear protection. As a result, we developed our SF range of Iron /Tin sulphides Composites, which are not just mechanical mixes of different sulphides. Their unique microstructure allows us to modify the oxidation temperature compared with a mechanical mix of FeS and SnS of the same chemical composition.

With this change, we can get closer to the oxidation temperature of tin-only based sulphides, but reducing the content of tin and so the price level. Phenolic resin is the matrix of the brake pads and starts to decompose around 300ºC, in presence of oxygen and temperature, resulting in the degradation of the PAD surface. Our objective is now to confirm that there is an interaction between metal sulphides and resin, and the oxidation mechanism of both materials seems to be modified when they are blended. 

Comparative AKM test have been done to correlate the differences on oxidation temperature range with the friction performance in a NAO Cu-free friction material. SF series is a new option with improved cost-to-performance ratio. SF05 is recommended to replace SnS based compounds and SF10 and SF13 are recommended to replace SnS2 products. Please, contact us for more information.

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