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Purpose - The purpose of this paper is to investigate the role of solid lubricants (graphite, coke, ZnS) on brake performance. Design/methodology/approach - In this study, the tribological and surface characteristic of non-asbestos organic type brake friction materials containing three different solid lubricants (graphite, coke, and ZnS) in different proportions were examined and evaluated experimentally. The coefficient of friction (COF) and wear behavior of the samples were tested on a chase-type friction tester, and particular emphases were given to the effect of temperature and number of braking cycles on the COF. Each of the lubricants was added to the mixtures in different amounts and seven different brake linings were manufactured, provided that the total amount of solid lubricants and other ingredients were not changed. The worn surfaces of the specimens were analyzed using a scanning electron microscope with energy-dispersive X-ray microanalysis. Findings - The experimental results indicate that graphite has a positive effect on the tribological properties of brake linings. However, brake linings containing higher concentrations of ZnS and coke showed an unstable friction coefficient relationship with the temperature and number of braking cycles. The formation of friction layers was detected on the friction surface of these samples, which indicates that an increase in coke and ZnS content increases the discontinuous and unstable friction film areas. Originality/value - This paper fulfils the effects of solid lubricants (graphite, coke, ZnS) in brake friction materials with detailed tests and analysis.

Purpose - The purpose of this paper is to study the effects of the total bearing deformation on the performance of hydrodynamic thrust bearings. Design/methodology/approach - Pressure distribution in the thrust bearing has been obtained using the Reynolds equation for the case of stable lubricant viscosity and isothermal conditions. Then, the deformation is found out by applying the constitutive equations for the linear elastic materials to both pad and runner. For the purpose of the generalization of the results, it is preferred to examine the case using non-dimensional equations. The lubricant film thickness and pressure distribution before and after the deformation, the bearing deformation and the thrust load-carrying capacity have been computed and compared for the steel runner-steel pad and the steel runner-bronze pad material pairs. Findings - It is found that maximum load capacity loss occurs in the steel runner-bronze pad pair as 3.03 per cent. Also, for a fixed load, when bearing dimensions are small, but deformations are large, the capacity loss due to runner deformations is nearly of the same order as those caused by pad deformations. Practical implications - For small bearings heavily loaded, both pad and runner deformations should be taken into account. Originality/value - In the relevant literature, there exist some papers, which consider the deformability of only one part of a thrust bearing. This paper differs from the previous ones in that the effects of the deformations of both pad and runner are taken into account in evaluating the performance of a thrust bearing.