• Gialanella, Stefano
• Wahlström, Jens
• Leonardi, Mara
• Ma, Jijie
• Olofsson, Ulf
• Lyu, Yezhe

Abstract

A brake pad is usually replaced before it is totally worn off. Some of these pads are re-melted as scarps in electrical arc furnace process, arising some concerns for the potential emissions due to the combustion of the organic component of the friction material and pad underlayer. To a lower extent, the other exhaust pads are taken to the scrap yard as waste. The concept of this study is to recycle the replaced brake pads, by ball milling the residual friction material into powders followed by hot compressing into new brake pads. A pin-on-disc tribometer designed for particle emission measurement is used to test the virgin and recycled friction material against a commercial cast iron brake rotor material in a controlled environment, to assess their tribological properties. Three factors (pressure, sliding speed and material) form a 23 full factorial experiment. Two pressure levels (1.2 MPa and 0.3 MPa), two sliding speed levels (2 m/s and 1m/s) are tested on two materials (virgin and recycled). The contact conditions correspond to typical city traffic conditions. Coefficient of friction (CoF), total wear of the pin and disc sample, particle generation rate are the response variables from the tests. The results show that the recycled brake pad averages a greater CoF and lower total wear than the virgin brake pad under the current test conditions. This is likely due to the more homogenous microstructure distribution of the recycled pins. Under tougher braking condition (1.2 MPa + 2 m/s) and normal braking condition (1.2 MPa + 1 m/s and 0.3 MPa + 2 m/s), the recycled brake pad demonstrates lower particle generation rate than virgin brake pad. When the pressure and sliding speed are both low (0.3 MPa + 1 m/s), the recycled brake pad has greater particle generation rate than virgin brake pad. In this regard, the results confirm the feasibility of the proposed recycling procedure. However, for a full assessment and validation of the process, two main further actions are required. One is to compare the current tribological results with those obtained with pins extracted from real pads, considering also the possible effect of pad scorching, will be conducted. The other is to conduct a complete life cycle analysis, providing reliable indications as concerns the scaling up of the recycling approach to industrial level.

Topics

• impedance spectroscopy
• microstructure
• experiment
• milling
• combustion
• iron
• ball milling
• ball milling
• cast iron
• coefficient of friction