Fritec Rail System Brake Solutions
Train braking is a very complex process, specific to rail vehicles and of great importance by the essential contribution on the safety of the traffic. This complexity results from the fact that during braking occur numerous phenomena of different kinds - mechanical, thermal, pneumatic, electrical, etc. The actions of these processes take place in various points of the vehicles and act on different parts of the train, with varying intensities. The major problem is that all must favorably interact for the intended scope, to provide efficient, correct and safe braking actions.
The purpose of braking action is to perform controlled reduction in velocity of the train, either to reach a certain lower speed or to stop to a fixed point. In general terms, this happens by converting the kinetic energy of the train and the potential one - in case of circulation on slopes - into mechanical work of braking forces which usually turns into heat, which dissipates into the environment.
At first, the rather low locomotives power and traction force allowed braking using quite simple handbrakes that equipped locomotives and eventually other vehicles of the train. As the development of rail transport and according to increasing traffic speeds, tonnages and length of trains, it was found that braking has to be centralized, operated from a single location - usually the locomotive driver's cabin and commands have to be correctly transmitted along the entire length of the train.
As a consequence, along the time, for railway vehicles have been developed various brake systems, whose construction, design and operation depend on many factors such as running speed, axle load, type, construction and technical characteristics of vehicles, traffic conditions, etc.
Among various principles and constructive solutions that were developed, following the studies and especially the results of numerous tests, the indirect compressed air brake system proved to have the most important advantages. Therefore, it was generalized and remains even nowadays the basic and compulsory system for rail vehicles.
It is still to notice that, regarding the classical systems used for railway vehicles, there are also several major challenges that may affect the braking capacity. These aspects must be very well known and understood, so as to find appropriate solutions in such a manner that the problems to be overcome by applying different constructive, functional, operational and other kinds of measures.
For example, one of these issues is the basic braking systems dependency on the adhesion between wheel and rail, which can lead to wheel blocking during braking. This determines not only the lengthen of the stopping distance, but also the development of flat places on the rolling surface of wheels, generating strong shocks transmitted both to the way and to the vehicle, with damage to traffic safety and comfort of passengers or goods transported integrity. This has generated particular concerns regarding the design and implementation of more efficient wheel slip prevention devices capable to avoid the above-mentioned phenomena with as small as possible reduction of braking capacity.
Another major problem is the friction between wheel and brake shoes, brake pads and disc respectively, which leads to severe thermal regimes and special thermal fatigue nature efforts, requiring specific constructive and operating standards.
More than that, due to the air compressibility and to the length of trains, the pneumatic commands propagates with limited speed in the brake pipe and, as a result, there always is a delay in the braking of neighboring vehicles. As a consequence, the rear vehicles are running into the front ones, producing large dynamic longitudinal reactions in buffers and couplers. The induced compression and tensile forces can reach significant levels, affecting both the rolling stock and the track, even conducting to deteriorations of safety operation of the trains.
Railway high speed operations also determined more severe requirements for braking systems, given to the necessity to develop higher braking forces and to dissipate larger amounts of energy in a short time, not to mention the problem of wear in the case friction brakes. In that case, complementary systems whose performance and reliability are safety relevant were developed to enhance the braking capacity.
These several issues, even briefly presented, reveal not only the importance and complexity of braking systems used for rail vehicles, but also the necessity of knowledge and understanding the problems in order to develop equipments increasingly more efficient and reliable.