# Assessment of Uneven Wear of Freight Wagon Brake Pads
## 1 Introduction  
The efficiency of the wagon brake system is one of the key factors that determine the safety of railway traffic and its economic feasibility [1, 2]. Particular attention is drawn to the problem of uneven wear of composite brake pads, which causes significant losses for railway transport and affects the country's economy. When driving at speeds without braking, the brake pads remain inclined and rested with their upper ends on the rolling surface of the wheels, which creates harmful friction. This causes a number of negative consequences that significantly affect the operational efficiency of railway transport [3, 4, 5]. Firstly, the resistance to movement increases, and locomotives waste thousands of kWh of electricity and hundreds of tons of diesel fuel to overcome it. This entails significant financial costs, especially for large rail networks. Secondly, composite brake pads wear unevenly, which significantly reduces their service life. During braking, high-temperature damage to the rolling surfaces of the wheels occurs, which further increases the resistanceto movement. As a result, the service life of wheel sets, which are one of the most expensive elements of rolling stock, is shortened, and the cost of railway track maintenance increases due to destructive dynamic loads (Figure 1). The friction between pads and wheels significantly impairs the braking efficiency, thus increasing braking distances and reducing overall driving safety. This requires a decrease in the route speed of trains, which, in turn, reduces the performance of transportation and increases the excess costs for train traction. In addition, unevenly worn composite pads have to be replaced ahead of schedule, even with large residues of the working body. Such pads are removed to industrial landfills, which increases the volume of non-recyclable rubber-, soot-, and asbestos-containing waste and causes additional environmental damage to the natural environment. Thus, the relevance of the study is caused to the need to solve the problem of uneven wear of composite brake pads, which negatively affects traffic safety, economic efficiency of railway transport and the environmental situation. Experts and scientists from different countries have conducted a significant number of studies, the results of which have contributed to the development of a different brake lever transmission devices and mechanisms aimed at eliminating or slowing down the intense wear of pads, such as wedge-shaped wear. Reference [6] describes the development of a device for the parallel retraction of brake shoes in wagon bogies, which automatically adjusts the position of the brake pad relative to the rolling surface of the wheel. In theory, such a device can effectively solve these problems; however the use of it can significantly complicate the brake lever transmission design, which may cause a need for regular and time-consuming adjustments during operation. Therefore, there is a need to develop more optimized and easier-to-use solutions that would minimize maintenance cost without losing efficiency due to pad wear. During the operation of the mechanical part of the wagon brake system, especially the articulated joints of the rods and levers, bushings significantly wear. This loosens connections and increases gaps, which negatively affects the operation of the automatic regulator and the efficiency of the brake lever transmission. According to [7], this problem is solved by applying innovative materials to manufacture bushings in hinged joints. In particular, the use of double pinned bushings for brake lever transmission elements and special protective brackets to replace traditional cotter pins in the brake beam reduces the impact of mechanical wear on the efficiency of the system, thereby increasing its reliability and durability. Figure 1: Composite brake pads unusable for wagons. In [8] the authors compare the efficiency of rolling stock brake pads made of different materials (gray cast iron, non-magnetic composite and magnetic composite) used in Indonesia.