Metal pickup is a phenomenon that can be observed during dynamic braking with automotive disc brakes. Hard metallic particle agglomerations embedded in the friction materials rubbing surface can lead to severe disc scoring, accelerated wear and deterioration of the friction surface of either brake disc or brake pad. Such kind of surface conditions are also suspected for generating brake squeal, even if a direct root cause effect had not been proven so far. Disc scoring effects have been reported for all kinds of applications, reaching from small passenger cars up to commercial vehicles as well as railroad brakes. Although such phenomena are known since long, they still appear causing problems in brake systems of today.
Some recent papers have described the effect and mentioned preferable conditions for the appearance of metal pickup. Specific procedures have been proposed for provocation of the effect to allow a better and more systematic investigation of the influencing parameters. Observations on results of such experiments were described and several working hypotheses put forward with influences going back to the brake rotors metallurgy and surface finish as well as to the friction materials ingredients.
This paper gives an overview to the actual situation of the research and developments about the effect of metal pickup generation. An investigation of a multitude of MPU cases from real car driving is used to cluster and structure the principal phenomena and discuss the various aspects. The discussion of the experimental results and the previous findings, lead to a new experimental set up which is proposed for further investigation and future works. This shall lead to a better way of investigating and understanding the influencing parameters within the brake system, rotor and brake lining for their effect to the phenomena.