Dr. Neomy Zaquen, Lapinus, NETHERLANDS

Mr. Arno Kerssemakers, Lapinus, NETHERLANDS

Mr. Fernao Persoon, Lapinus, NETHERLANDS

Global emission – due to pollution and the use of fossil fuels – has risen drastically since the start of the industrial revolution and is at the core of the problems within the current society. Within the automotive industry, not only the exhaust of vehicles is seen as a large contributor to pollution, also wear of the tires and the brake pads of vehicles contribute to pollution in the form of emission. In 2015 it was concluded that PM2.5 as a direct result of disc brakes, contributes to high percentages of the total amount of non-exhaust emission from road transport within the EU. Due to the severe adverse health effects of PM, the EU has defined general emission guidelines for both fine (PM2.5) as well as coarse (PM10) particle matter. We expect these values to be translated to the automotive industry in the (near) future.

Within Lapinus, we actively investigate the reduction of emission as a direct result of wear of disk brake pads. By using our engineered mineral fibre, friction levels are stabilized and both pad as well as disc wear are reduced, due to the formation of a stable third body layer. Previous studies on mineral fibres have shown the friction performance when using different grades and morphologies of fibres in the friction matrix. While shorter fibres act as anchoring point, engineered fibres spheres can collect wear debris during braking, leading to overall reduced wear.

In this study, a closer look into the formation of the tribolayer was taken when using a NAO/non-steel formulation. Mineral fibres of different length as well as engineered fibre spheres were added to the friction matrix to correlate the impact of performance with the tribolayer formation. Dynamometer full scale tests were executed to compare the friction performance, stability of the friction level and wear of the different (non)-spherical materials. The tribolayer formed on the brake pad surface – and related to that disc surface – was studied by means of SEM-EDX and optical microscopy.

This work shows the importance of mineral fibres not only from a performance, but also tribolayer point of view. Especially the use of engineered fibre spheres leads to new insights with respect to the tribolayer. Combined with the excellent friction performance and decreased wear, this work can be considered an important solution towards the reduction of non-exhaust emissions.

Engineered mineral fibres from LAPINUS are used globally in friction applications. They give the friction material a combination of mechanical and tribological properties, in both NAO/nonsteel and low steel formulations. Mineral fibres have a pronounced effect on the micrometric scale at the surface of the brake material. They can act as an anchoring point, which effectively promotes the third body layer formation and development. As a result, friction stability and wear resistance are improved. They also influence friction level due to their chemical composition and their contact and interaction with the counterpart, the metallic disc.

With regard to health and safety aspects, these mineral fibres have the important property that they are certified as bio-soluble, which is determined by the specific chemistry. The chemical tolerance range of bio-solubility can be effectively controlled during the production process. Thanks to this, it is possible to offer two different bio-soluble fibre grades to the friction industry.

The fibre chemistry is one of the key characteristics for the unicity of these mineral fibres. The chemical composition has a significant effect on the production process and therefore on the specific physical properties of the mineral fibres. This directly influences friction performance and pad and disc wear.

This paper describes the effect of fibre properties, such as chemical composition and fibre diameter, on friction performance in disc pad applications. The paper shows test results of a new mineral fibre grade, which has been specially developed to offer an alternative performance to current products with the aim of reducing disc wear. This new product consists of a different chemical composition without compromising the bio-solubility of the fibres. It is shown that overall friction and wear performance are influenced, which opens up new possibilities for friction material formulations.

The study shows the friction performance of NAO copper-free materials with the focus on the specific role of the chemical composition of two different mineral fibres at the surface layer of brake pads. With the development of a new fibre grade, it is possible to promote third body layer formation and stabilisation of the friction level, without this having an aggressive effect on the disc surface. With this development it is foreseen that this newly engineered fibre can complement future formulations in reducing wear, and therefore also dust emissions (e.g. wheel dust).