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EuroBrake 2022: Coatings and other developments in brake components update session overview

The Coatings and other developments in brake components session will take place on Tuesday May 17th and will be chaired by Jaroslaw Grochowicz of Ford Werke GmbH and Rick Kaatz of KBAA.

Topics and speakers for the session include:

Energy efficient and resource saving anticorrosion coatings for brake systems

Eduard Rybka, Magni Europe GmbH & Co KG

We have been active in the field of brake system coatings for decades. These primarily concern applications on brake disks and drums, but also on brake calipers and additional attachments. In this context we would like to show the development of the requirements over the last decades until today.

Careful use of energy and resources is playing an increasingly important role and here we would like to present the latest developments in anti-corrosion coatings using examples. Brake discs / drums Initially, the use of coatings was at best of a cosmetic nature, but this has changed over the last few decades and the usefulness of coatings is now also recognized. Therefore, the requirement profiles also increased, which meanwhile also include requirements for temperature resistance and chemical resistance.

For this purpose, quite complex coating processes were used in the past, which require temperatures of over 300 ° C for crosslinking. This leads to a considerable use of energy. The aim of our developments in recent years was to meet the increasing requirements with products whose energy consumption is reduced. Specifically, this means 60 ° C instead of the previously usual 320 ° C. These products are already being used successfully by some OEMs and thus lead to considerable energy savings without having to reduce the requirements for corrosion protection. This was achieved using specific titanium-based binders, which also allow the components to be crosslinked below room temperature by incorporating the oxygen contained in the air, which previously required a much higher energy input. However, this currently extends the networking time.

The influence of the particle size contained in the zinc components is another decisive factor that influences the crosslinking kinetics. In the area of the brake caliper screw connection, we worked with Porsche and Brembo to develop a special coating for the screw connection of the brake calipers, which in this very exposed area meets the highest requirements for chemical resistance. This also enables resistance to very strong acidic cleaning agents over a very long exposure range. This was made possible by the specific chemical composition of the coating on organic components of polyurethanes, which were applied in a layer thickness range of approx. 10 µm. It is possible to use this coating directly on the brake calipers and would extend the service life of galvanized or zinc-nickel coated surfaces many times over. These are just two examples in brakes / add-on parts that we would like to provide in the technical details and from which the participants of the event would certainly benefit.

Brake fluids and corrosion resistance of aluminium alloys: a fundamental investigation

Marco Bandiera, Brembo S.p.A

Top-notch disc brake systems typically include components which are designed using aluminium/silicon alloys. The corrosion resistance of such materials, while immersed in brake fluids, is only barely investigated in the literature, and regards only very few and case-specific examples.

Following this, the manuscript investigates the corrosion resistance of a 42200 aluminium/silicon alloy in different brake fluids (BFs). In particular, five brake fluids comprising an increasing amount of water are investigated. Results are discussed in terms of corrosion potential (Ecorr) and corrosion current (Icorr) values of the alloy, as obtained from linear sweep voltammetry measurements. The suggested lab-scale approach is aimed at: a) proposing a preliminary investigation regarding the corrosivity of different BFs; and b) simulating the effect of the brake fluid ageing (e.g., increasing amount of water) on the corrosion resistance of the investigated 42200 alloy.

It is demonstrated that the corrosion resistance of 42200 is strongly modulated by: a) the nature of the brake fluid in which it is immersed; and b) the amount of water comprised in each BF. Insights regarding the minimum amount of water which is necessary to modulate the electrochemical performance of each BF are proposed as well.

Tribological properties of low wear ceramic matrix composite friction pairings compared to standard friction pairings

Thorsten Opel, University of Bayreuth

The environmental impact of the braking systems of different vehicles has become a topic of interest for the public. With Euro 6 emission limits the particulate matter emissions of standard brake systems are comparable to the particle matter emissions of internal combustion engines which further expedites the public attention. Therefore, the reduction of the particle matter emissions of brake systems is vital not only for electric vehicles.

Three different brake pads were tested on four different brake discs (grey cast iron, carbon ceramic, Al-MMC, metal-ceramic hybrid). A LowMet brake pad was used as a benchmark, state of the art brake pad material. Furthermore, a short fibre reinforced C/SiC brake pad which was modified with petrol coke and SiC powder and manufactured using the liquid silicon infiltration process as well as a fabric reinforced C/C brake pad manufactured using chemical vapour infiltration were investigated.

The tribological tests were conducted using an adapted Auto-Motor-Sport-Test. All friction pairings were characterized using 10 consecutive stop brakings (each ≈ 0.5 MJ) and three different braking pressures (1, 2, 3 MPa). The corresponding friction coefficients were recorded as well as the wear rates of the brake pads. For a deeper understanding of the measured tribological characteristics of the friction pairings, the friction surfaces of the used brake pads were characterized using secondary electron microscopy.

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