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Our innovative vision on tribochemistry

Get to know how deep from the pad surface the tribochemistry induced by oxygen takes place. Also answer this question: How does the interaction of metal sulfides and resin affect performance and wear?

Past October 12 and 13 The Brake Colloquium Digital Summit 2020 was held, an SAE Brake initiative in which we were Platinum sponsors. The event brought together some of the most influential professionals within the friction industry.

Gabriela Macias, our Research Technician for the R&D Department, was present as a keynote speaker sharing her vision on tribochemstry induced by oxygen with her two presentations, reinforcing our statement on developing solutions based on innovation.

We share our SAE Technical Papers:

1.- Study of the Interactions Between Phenolic Resin and Metal Sulphides and their Contribution to PAD Performance and Wear:

Abstract:

In order to keep the coefficient of friction stable, some additives such as metal sulphides, are included in the brake pads formulation. Previous work from RIMSA has shown that oxidation temperature range of the metal sulphides can be one of the key properties to explain their contribution to the performance and wear of a PAD.

This new work is a step forward in the interpretation of the mechanism of sulphides as chemically active additives in the brake pads. Phenolic resin is the matrix of the brake pads and starts to decompose around 300 ºC in presence of oxygen and temperature.

In order to establish a connection on between sulphide oxidation and phenolic resin degradation, several studies based on heat treatment of blends of different metal sulphides (Iron sulphide, Tin sulphide and Composite sulphide) with phenolic resin have been done.

Then the material evolution was studied with techniques such as TGA – DSC, XRD, IR and SEM – EDS. The results obtained confirm that there is an interaction between metal sulphides and resin, and the oxidation mechanism of both materials seems to be modified when they were blended. Studying PAD surface cross section after SAE J2522 and J2707, this work then introduces several SEM – EDS evidences that this mechanism can be found in the brake pads, and the results appoint that oxygen is present several tens of microns beneath the PAD surface during braking.

This research will contribute to understanding the tribochemistry of the metal sulphides and phenolic resin that take place during braking and so the pad behaviour.

To view the video and the technical paper, click here

 

 

2.- Determination of Diffusion Capability of Oxygen Through Brake Pads From the Surface Towards the Interior

Abstract:

The oxidation of raw materials, such as phenolic resin, in the pad during the braking depends on the temperature but also on the oxygen diffusion capability through the pad.

Determination of oxygen diffusion is a key point in knowing how deep from the surface tribochemistry can take place. The diffusion of oxygen through the pad is a drawback because it induces the matrix decomposition that contributes to intra-stop CoF instability and consequently worsens NVH.

This study is focused on determining the oxygen diffusion through brake pads using oxidized iron sulphide particles as indicator parameter. Iron sulphide has a rough microstructure when it becomes oxide that can be recognized easily, making it a good marker.

The oxygen diffusion was determined through the pad characterization, after SAE J2522 and J2707 tests, with SEM and EPMA/WDS techniques.

The results show that tribochemistry also takes place beneath the PAD surface during braking due to the oxygen presence and the high temperatures reached. Depending on the testing schedule the temperature profiles on the pad are different and so is the tribochemistry. In pads tested according to SAE J2707, the oxidized particles are found in deeper sections than in pads tested according to SAE J2522.

The results of this research will contribute to understanding where the decomposition of the resin starts, and therefore, how reactive compounds such as iron sulphide that also react with oxygen helps to keep the integrity of the matrix by decreasing the decomposition and contributing to the stability of intra-stop CoF, and so NVH properties.

To view the video and the technical paper, click here