Friction materials play a crucial role in the safe movement of automobiles and the protection of human life. As the pad slides against its mating partner, the kinetic energy is transferred into frictional heat. The developed friction at the interface causes the vehicle to slow down as its momentum is dissipated as heat in the pads and rotors. Further, it causes the degradation of the binder and thus the stability of the friction coefficient becomes questionable. Therefore, the role of solid lubricants comes to the scenario which tends to mitigate the abrasion. It is noticed that the sulfide mix composites delay the thermal degradation of the binder by increasing its oxidation resistance. Some researchers have achieved this by blending various resins. Further, solid lubricants have a good third body and secondary film-forming ability and thus they reduced the wear, due to their excellent adhesion properties to the metal substrate. Hence, this review focused on the role of different solid lubricants and sulfide mix/sulfide blend in the stabilization of friction coefficient and controlling the wear.

The purpose of friction material is to decelerate a vehicle by transforming the kinetic energy of the vehicle into heat, via friction, and dissipating that heat to the surroundings. A lot of heat is generated at the contact plateaus formed by the reinforcing fibers. Therefore, inorder to dissipate the heat, steel fibers were coated with FeS and SnS and accordingly brake pads were made and termed as DBF and DBS. Another brake pad with similar formulation but with a mixture of steel fiber, FeS and SnS was made (designated as DBO) for comparison. All three brake pads were tested in an inertia brake dynamometer with a typical schedule. The speed spread (100/50 Kmph) 0.6g and effectiveness variation of all the pads are fallen in the required range. The fade I of DBO is observed 32.8% lesser whereas for DBS and DBF, it is observed10% and 15.7% more than the standard values, respectively. DBF and DBO have shown 25.4% and 39.6% more wear than DBS, respectively. Further, it is observed a more consistent µ during single braking to identify fade during stops in the second effectiveness test. It is evidenced for the increase in the life of the friction film formed by the sulfide coated fibers in DBS which has increased its wear resistance (Max Δµ = 0.10 for DBS, 0.29 for DBF, and 0.30 for DBO). It is also noticed that the radial wear of all three brake pads was greater than the tangential wear and their ratios are 1.36, 1.40 and 1.55, respectively for DBS, DBF and DBO. Moreover, the optimization has revealed the DBS as best performer friction materials formulation.

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The sintered brake pads have been the most commonly utilized brake pads in wind turbines, as it stalls the rotor after shutdown or in case of emergencies. It is a mixture of metallic particles that are pressed together. But it has been noticed that the friction at interface generates the spark in adverse conditions, which cause a fire in nacelle. Due to this a compact unit for fire suppression is used, which adds the additional cost in brake system. Therefore, it is necessary to address the spark issues coming from brake pads under adverse conditions through developing a brake pad using alternate route. Hence, a composite brake button was developed through a compression moulding route, that is, cost economic route. Despite the different compositions and manufacturing routes of materials, a similar frictional behaviour is observed after testing using friction test rig. Further, it is observed a marginally higher friction values for sintered pads. Moreover, the physical and mechanical properties like density, hardness, porosity, shear strength, compression strength, etc., are also found to be similar. In fact, the density of a composite pad is observed 34.7% lesser than sintered pad. Both the developed brake pads have a mean dynamic friction coefficient (∼0.4–0.5) with a mean static friction coefficient of approximately 0.45. In spite of more hardness, the wear resistance is found poorer in sintered pads as compared with composite pads. Hence, it can be concluded that the developed composite pad shows better tribomechanical performance and suitable for application without spark issues.

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