The Performance Of Semi–Metallic Friction Materials For Passenger Cars

Dalam kajian ini, penilaian haus mekanikal ke atas bahan geseran separa logam untuk kegunaan kereta penumpang dikaji dengan menekan sampel kepada piring yang berpusing diperbuat daripada besi tuang kelabu pearlitik. Bagi setiap ujian, sampel dikenakan empat jangka masa pembrekan (3, 6, 9, dan 12 minit) dan empat beban kenaan (200, 400, 600 dan 800 N) yang berlainan. Kelajuan putaran piring brek dikekalkan malar sepanjang pengujian geseran pada 750 psm. Selepas setiap ujian, perubahan morfologi permukaan dan subpermukaan diperhatikan dengan menggunakan mikroskop elektron imbasan (MEI). Hasil kajian menunjukkan ciri-ciri berikut: (i) suhu permukaan meningkat dengan masa pembrekan dan selepas mencapai nilai maksimum, akhirnya sampai kepada keadaan stabil, (ii) pekali geseran telah meningkat pada permulaan pembrekan, kemudian menurun dengan masa pembrekan, dan seterusnya sampai kepada keadaan stabil, dan (iii) isipadu haus meningkat secara lelurus apabila beban kenaan di bawah 200 N dan/atau masa pembrekan di bawah 3 minit dan kedua-duanya seterusnya meningkat secara eksponen. Pemeriksaan mikrostruktur menunjukkan mekanisme haus beralih dengan peningkatan jangka masa pembrekan dan beban kenaan. Fenomena ini juga menyebabkan perubahan kepada sifat haus. Kata kunci: Pad brek, suhu permukaan, pekali geseran, haus, mekanisme haus In this work, a semi-metallic friction material for passenger cars was evaluated for mechanical wear by pressing the material against a rotating pearlitic gray cast iron brake disc. In each test, the sample was subjected to four different braking times (3, 6, 9, and 12 minutes) and four applied loads (200, 400, 600 and 800 N). The rotating velocity of the disc was kept constant throughout the friction tests at 750 rpm. After each test, the morphological changes on the surface and subsurface of the material were observed using Scanning Electron Microscopy (SEM). The following characteristics were observed: (i) the surface temperature increased with braking time and after reaching a maximum value, eventually arrived at a steady state, (ii) the friction coefficient increased at the early stages of braking, then decreased with braking time and thereafter reached steady state, and (iii) the wear volume increased linearly when the applied load was below 200 N and/or braking time was below 3 minutes or both, thereafter the volume increased exponentially. Microstructural examinations showed that the wear mechanism transisted with increase in braking times as well as applied loads. This phenomenon also resulted in changes of the wear behaviour. Key words: Brake pad, surface temperature, friction coefficient, wear, wear mechanism