Everyone who has used the services of railway transport at least once in his life noticed that when moving the wheels of the carriage they emit a peculiar sound, reminiscent of a knock. Songs have even been written about this.
So why are the railway wheels knocking? Probably everyone asked himself this question. How can round and even wheels knock on an absolutely flat track? The answer lies in the very structure of the railroad tracks; the railroad bed has never been perfectly flat. Modern technology is not yet able to make and correctly lay a multi-kilometer rail, and even taking into account all the turns and points of the switch points. A railroad is a set of individual rail segments laid end-to-end. And the reason is not only the difficulty of manufacturing and delivering a solid rail of the required length. As you know, bodies expand when heated. This also happens with railway rails, regardless of whether a passenger or a freight train passes on them, a tram, an electric train or a subway train. The knock allows the metal to expand freely in length. It is at these joints, due to the created artificial unevenness, that the knock is formed. Logically, we can assume that the wheels knock less in the summer. However, even the slightest gap between the rails is enough to hear the sound. The second reason why the wheels can knock is the appearance of a slider due to skidding at the wheelset. That is, the wheel just blocked for some reason. However, in modern railway transport, a special electronic control system is installed and completely eliminates this phenomenon. It is worth noting that now a special system of laying rails without joints is increasingly used. This technology significantly reduces energy losses and wear on train wheelsets and rails. In addition, the number of defects that appear in the rail material at the joints when the wheel strikes is reduced. Most often, this innovation is used on tram lines and in the metro.