Abstract
Copper helps to accelerate heat transfer during the braking process, allowing the brake materials to produce a stable coefficient of friction (COF), which in turn reduces wear loss and braking noise. However, its properties are also quite harmful to aquatic organisms. Finding a suitable replacement that fits all functions of copper for brake materials is not an easy feat. In this paper, six different carbonaceous components (coke, carbon black, carbon fiber, artificial graphite, natural graphite and expanded graphite) were substituted for copper in non-asbestos organic (NAO) friction materials. The hardness, thermal conductivity and tribological behaviors of these copper-free NAO friction materials were examined. Experimental results indicate that carbonaceous components improve lubrication and assist the friction composites with generating friction layers on the worn surface. Specimens containing coke, carbon black or carbon fiber exhibit broken friction layers, whereas specimens containing artificial graphite, natural graphite or expanded graphite exhibit quite adherent and smooth friction layers. Among all the copper-free carbon containing specimens, the specimen containing expanded graphite appears to be the best choice. It has the highest thermal conductivity, a relatively low wear loss and a relatively high and stable COF.
Highlights
Non-asbestos organic (NAO) friction materials are vital in automotive brake components such as brake shoes, brake pads, brake linings, etc
NAO friction materials composed of fibrous reinforcement, internal lubricant, and friction modifiers are usually bound by phenolic resins [1,2,3]
Those copper-replaced components which had been used in different copper-free specimens are coke, carbon black, carbon fiber, artificial graphite, natural graphite and expanded graphite
Summary
Non-asbestos organic (NAO) friction materials are vital in automotive brake components such as brake shoes, brake pads, brake linings, etc. Aranganathan et al [21,22,30] concluded that adding thermal graphite in friction materials showed good thermal properties, fade performance, wear resistance, and lubricity in their study and recommended that thermal graphite should be the replacement component for copper. Ertan and Yavuz [31] investigated the role of solid lubricants (graphite, coke, and ZnS) on brake performance They discovered that graphite has a positive effect on the properties of brake linings. Lee et al [34] studied the effects of two types of liquid impregnant-derived carbon (coal-tar pitch and phenolic resin) on tribological behaviors in a high energy automotive brake system. The mechanical, thermal and tribological properties of these copper-free NAO friction materials were examined
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