Relationship of the Transfer Film Formed Under Low Pressure Drag Conditions and Torque Variation

The chemical composition of the transfer film formed on brake rotor surfaces during a 208 second low, pressure drag was investigated by Sputtered Neutral Mass Spectrometry (SNMS)/Depth Profiling. A stiff non-commercial pad was employed and the applied pressure and cooling air flow were adjusted to induce judder. In addition to the usual dynamometer data, capacitive displacement transducers were used to monitor dynamic rotor thickness variations and an eight-channel dual- wavelength pyrometer was employed to measure dynamic surface temperatures.

The time-dependent torque, rotor thickness and rotor surface temperature measurements were transformed to polar coordinates (rotor radius and angle) and provided the rationale for the locus of points on the rotor surfaces to be analyzed. The results clearly show that at any given time, changes in the film's composition and thickness at a given rotor position are mainly determined by the instaneous rotor surface temperature at that position and the average surface temperature of the pad at that radius.