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The journey of the friction industry – Part 1: Starting line

All machine in movement needs to be stopped at some moment. The brake is responsible of turning this kinetic energy on heat and release it through the interface. This is the everlasting basis of the friction industry.

Let’s put the reverse gear for a moment and go back to the early 70s. The inertia from the 60s, a decade that was essentially a free-for-all as far as big engines and poor fuel economy goes, gave birth to the muscle cars. There, security was mainly reduced to…“The shortest brake distance, the safest”. Friction “rules” were more permissive and environmental considerations were relegated to the background. With the oil crisis the marketplace changed, and the US government started to impose strict regulation as far as fuel economy, emissions, and safety were concerned [1].

 

And brakes and friction materials have been part of this screening since then, with several regulations throughout the years. During these series of brief newsletters we will travel through the PAST, PRESENT AND FUTURE trying to understand the origin of the challenges in this industry and reviewing which solutions have get acceptance from the market.

During a normal braking, the disc is responsible to dissipate around 80 % of the heat generated by friction. The temperature can raise up to 600-700 ºC in rough conditions. As a result of the energy involved in this process, tribo-chemical reactions and erosion always take place. [2]

The chemical composition of the brake PAD then is directly related with the performance of the whole brake system. Every time you stop your vehicle a small amount of material is released in form of PM10 and PM2,5. Those are particles with diameter below 10 and 2,5 microns respectively, small enough to be caught in air turbulence and easily enter human airways. Depending on their composition, can be quite harmful to wildlife as they might contain metals such as copper, chromium, lead, antimony and metal oxides. [3]

Considering that around 21% traffic-related PM10 emissions comes from brake wear, automotive industry, raw material manufacturers and regulatory organizations have a shared responsibility to follow up dust emissions released during braking, and come up with innovative solutions to overcome this environmental threat. [4]

The result of this join effort has brought to a noticeable evolution throughout the years of the friction materials and their compositions.

Up to the 1980s, asbestos linings were used on virtually all vehicles. Asbestos was and still is an excellent fiber for brake linings. It offers good strength, temperature and chemical resistance, and is cheap compared to other materials that are used for the same purpose. But the physical properties that make asbestos such a good fiber also make it a hazardous substance, as it can produce asbestosis. 

Back in early 1980s, the health conscious Scandinavians were the first to ban asbestos containing products, including brake linings, clutch linings and engine gaskets. The arrival of front-wheel drive required semi-metallic front disc brake pads that could withstand higher operating temperatures. Both factors lead to the introduction of non asbestos substitutes [5]. 

Steel fibre-based materials, had their own troubles, such as the increase of noise and vibrations [6], and also the amount of grey/black dust produced. The industry evolved to offer a wide range of additives to equilibrate the formulas depending on the application and reduce these drawbacks. 

Manufacturers started also to develop formulas with lower and even none content of steel (NAO) using alternative reinforcement materials such as rock wool, polymeric fibers and non-ferrous metals like copper/brass/bronze fibres and chips [7].

These latest products became of general use because of their contribution to the performance and wear at high temperature and also because of their good NVH properties [8], and where in the origin of RIMSA as supplier for the friction industry, providing high quality recycled chips of brass and bronze.

On the other side, recyclability regulations in the latest 1990s for vehicles in Europe (End-of-life directive 2000/53/EC) states a maximum content of metals such as Pb, Hg and Cr(VI) <0,1 %. And Cd <0.01 % [9]. Friction materials were a source of Lead. It was common to use lead sulphide as lubricant and lead derivatives were regular contaminants in natural products such as pyrite (natural FeS2), sometimes up to 10%. Also recycled brass and bronze metal chips contained Lead. The limitation of Lead in friction materials and the use of lead-free alternatives made this toxic element no longer present in dust emissions. 

At rimsa we were pioneers on manufacturing lead-free brass and bronze chips 20 years ago. Since then our unique manufacturing process enables us to offer the OE’s choice of lead-free CHIPS with the best value-for-money.

Research efforts focus on finding eco-friendly alternatives to conventional products, which have to keep same performance, but keeping a reasonable cost in mind! This was, is and will be the prevailing challenge in the friction industry.

 →See here more information about our lead-free brass (ecoChip) and lead-free bronze (ecoBronze)

PART: 2 | 3​​​

 

Sources consulted:
[1] Hirsch, R. L., Bezdek, R., & Wendling, R. Driving Climate Change, 2007, 9–27.

[2] Roberto Dante (Woodhead Publishing, 2016), “Handbook of Friction Materials and their Applications”.
[3] G. Straffelini et al. Environmental Pollution. (2015), 207, 211-219.
[4] Vicente Cano (AutoBild nº 588, 2016), “Llegan las pastillas de freno sin cobre”.
[5] LaDou, J., Castleman, B., Frank, A., Gochfeld, M., Greenberg, M., Huff, J., Watterson, A. et al. Environmental Health Perspectives, 2010, 118, 897–901.
[6] Bernard S, S., Jayakumari, L.S. Matéria, 2016, 21, 656 – 665.
[7] Chan. D, Stachowiak, G. W. J. Automobile Engineering. (2004), 218, 953-966.
[8] Lee, J.-J., Lee, J.-A., Kwon, S., & Kim, J.-J. Tribology International, 2018, 120, 70-79.
[9] DIRECTIVE 2000/53/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on end-of-life vehicles.