During the appearance of the first steam locomotives, they caused delight. But you just have to think about how he rides on smooth rails and does not skid, as a lot of questions immediately arise.
How do railway wheels?
Each production has its own subtleties of wheel manufacturing, but the main stages of work are unchanged. At the heart of one wheel is approximately 500 kg of steel. The workpiece is subjected to gradual heating in furnaces, heated to 1000 degrees, then immediately to 1300. Then it is treated with water under pressure to remove scale. The next stage is the press-rolling line. The workpiece is compacted by 40-60%, after which it takes the form of a disk - the outlines of the future wheel appear.
At the next stage, the skating circle is finally formed - the part of the wheel that directly contacts the rail, as well as the flange (protruding part). After applying all the necessary markings, the wheel is subjected to isothermal aging in stress relieving furnaces. In the future, it will again be heated and treated with water for quenching, as well as strengthened using a shot blasting machine. After all the procedures, the wheel is turned to the desired parameters. Each stage of production is accompanied by quality control.
Interesting fact: the inventors of the first steam locomotives were afraid that the wheels would not go on smooth rails, so they were equipped with gears, and the rails with teeth. But this method was too expensive, and the movement of the engine slowed down.
Why don't the train wheels slip?
It would seem that the answer is obvious: the train moves due to the operation of the engine and rotation of the wheels. In fact, driving requires another factor - the driving force in the form of traction of wheels with rails. At first glance, the rails and wheels seem absolutely smooth. In fact, there are roughnesses on the surface of the wheels that provide traction.
The wheels slide on the surface of the rail, and this indicates the presence of sliding friction. The stronger the rails and wheels are in contact, the higher this indicator. According to the laws of physics, the body (train) exerts pressure on the surface (rails) in accordance with its mass. But in response, the surface directs the same force with respect to the body, which is called the reaction force of the support.
The train has traction weight. All the wheels in it are mobile, so the grip weight is the mass of the train, which it acts on the rails through the wheels. It is he who makes the wheels spin, starting from the rail. The driving force of adhesion is also called the traction force of the train on the adhesion.
The train moves smoothly. He evenly begins to move, increasing speed, and also stops evenly. This is due to grip. It is strong enough to hold the entire train on rails. The coefficient of adhesion between wheels and rails is about 0.14. The maximum tilt angle that the train can withstand is 8 °. For comparison, the coefficient of adhesion of car tires on dry asphalt is much higher - from 0.50 to 0.70.Therefore, road vehicles can abruptly begin and end traffic, as well as enter into steeper turns.
Interesting fact: to ensure safe turn of the train, its wheels are made asymmetrical in shape. Thus, on the inside, the diameter of the wheel is larger (959 mm), and on the outside, smaller (953 mm). The difference is insignificant, but it allowed to completely solve the problem of turning.
Skidding trains and ways to deal with it
In railway terminology, there is the concept of “slipping” or “boxing” (two variants of use in different dictionaries). It indicates a breakdown of the clutch between the rails and the wheels. Skidding can occur both at the beginning of the train and during it. In this case, the wheels begin to spin much faster. This is due to too high traction gain at a certain point.
If the slipping process has begun, it cannot be arbitrarily terminated. Traction between rails and wheels is greatly reduced. To stop slipping, it is necessary to use friction modifiers, as well as adjust the traction moment.
Reasons for slipping:
- wet rails after rain;
- pollution of rails of various origin;
- large rental on a pair of wheels;
- the entry of the train into a turn (due to the fact that the inner and outer wheels pass a different path), etc.
Skidding negatively affects the condition of the rail, as well as the train itself. First of all, there is a strong load on the engine, which can disable it.Rails can be deformed - due to strong friction, the metal warms up and the rail loses its shape, "spreading" to the sides. Subsequently, they are either repaired by grinding or replaced.
To stop slipping, sand or other abrasive material is fed into the area where the rail is in contact with the wheel. They also reduce the traction that is realized by the engine. Another method is prohibited according to the Rules of technical operation. This method involves the use of a direct brake of a locomotive. It is fraught with cranking the wheelset, and this, in turn, creates a dangerous situation for rail transport.
Train wheels and rails only outwardly seem perfectly smooth. On the wheels themselves there are roughnesses that contribute to the adhesion of two surfaces. Between them there is a friction force with a coefficient of 0.14, which is much less than, for example, the friction of tires on asphalt (0.50-0.70). At the same time, the train starts to move smoothly and also brakes smoothly. Due to its weight, as well as the resistance of the surface of the rail, the clutch of the wheels occurs, due to which the train travels on rails.
