The importance of consistent materials quality for brake – and car – manufacturers

The second in a series of blogs highlighting the most important trends facing car, brake system and brake pad manufacturers.

Brake pads are a complex mix of 20 or more different raw materials, typically divided into abrasives, lubricants, binders, fillers and reinforcing fibres (see my colleague Mark Segeren’s ‘Trends in automotive braking’ article). Car manufacturers are increasingly demanding that brake pads will last the lifetime of the car. Compounders are therefore having to make pads that last longer, while also facing stricter quality and environmental requirements.

Reinforcing fibres like those produced by Lapinus (part of Rockwool) gives mechanical strength to the brake pad, and contributes to the plateau formed on the pad surface during braking. Fibre anchor points contribute to third body layer formation (loose debris between pad and rotor while braking). The fibres improve porosity and compressibility, and the formation of fibre nests improves wear and damping. Different fibre lengths can adjust performance and mechanical strength depending on the requirements. Bound together with the other brake pad constituents, the fibres ensure a stable friction film under all braking conditions.

Lapinus uses an online and offline quality check programme to validate product quality and performance. Shot content and fibre length, diameter and chemical composition (Figure 2) are always checked and matched against product specifications. The chemistry is also checked by independent external parties.

^{Figure 2: Key mineral fibre properties must be tightly controlled during manufacture.}

High shot content influences coefficient of friction, wear and NVH (noise, vibration and harshness). Figure 4 shows the impact of shot content on these brake pad parameters. The blue stacks show the shot content of five Lapinus fibres. Between low and medium shot content, the parameters are fairly constant. Outside that, a small difference in shot content in the raw material can have a large influence on brake parameters.

The two stacks on the left show Extra Low Shot (ELS) products. These are known in the market for excellent friction coefficient, wear and NVH. High shot in the raw material typically degrades wear and NVH.

^{Figure 4: Brake parameters for different shot content.}

For consistent performance of brake pads, the raw materials in mineral fibre products must be carefully selected for high performance and biosolubility (Lapinus has RAL & EUCEB certified biosolubility). The resulting product must be highly stable and resistant in a wide variety of environments, even with extreme brake temperatures (600°C or even higher). Producing fibres with specific and consistent fibre properties like length, diameter, and purity (low shot content) requires years of experience in engineering fibres. That is the only way to guarantee performance in different applications.  

Comprehensive quality evaluations must ensure that product performance always fits the specific requirements. That allows continuous improvement of products and processes.

Lapinus derives its core technology for fibre production from the Rockwool R&D department, which concentrates fundamental research for fibre technology. A strong technical department is needed for application development, and customer needs must drive the development of new or improved fibres and products.

Friction test equipment at Lapinus includes an NVH dynamometer and a Krauss machine for testing brake components and friction materials. These give the detailed information needed to select the most suitable materials.