Railway wheels is the most important structural elements of any railway vehicle - wagons (freight and passenger) and traction rolling stock (locomotives and electric locomotives). All railway wheels are made from special low alloy carbon steels. They are called that - wheel steels.
Railway wheels for wagons are called wagon wheels, for locomotives and electric locomotives - locomotive and electric locomotive wheels.
Wagon wheels carry the entire weight of the wagon. The peculiarity of wagon wheels is, that in case of their breakage, even one of them, the car has no reserve, which could at least temporarily take over the bearing function of a broken wheel. Therefore, railway wheels are required to be almost absolutely reliable in terms of their overall structural strength..
Never break is the main requirement for a railway wheel. Therefore, for him, strength properties are the most important characteristics.. However, the service life of a railway wheel is also influenced by such characteristics as wear resistance., resistance to thermal cracking and even noise level, which they emit when moving.
For, there are two main ways to improve the quality of wheels - improving wheel steel, by improving its quality and efficiency of heat treatment of wheel steel, as well as improving the design of the wheel.
Railway wheels: solid and bandage
There are two main types of railway wheels: solid and bandage. One-piece wheel is a one-piece piece, which is made from one "piece" of steel - a steel wheel blank. The bandage wheel consists of two parts – wheel center and a bandage worn on it. Most solid wheels are solid rolled, however, solid cast wheels are also used. Bandages are made by hot working methods using forging, stamping and rolling, as well as hardening heat treatment. Wheel centers are usually made by casting.
One Piece Railroad Wheel
The one-piece railroad wheel has three main structural elements (picture ): hub, discs and rim.
The role of the hub is to provide a strong connection between the wheel and the axle. The wheel rim is in direct contact with the rail, and the disc connects the hub and rim to each other. The outer surface of the rim, which is in direct contact with the steel rail, called rolling surface, and its protruding part - with a ridge or flange. In Russia and the near abroad, only solid-rolled wheels: a wheel is made from one steel billet on a large wheel rolling mill. In North America, solid wheels.
Requirements for railway wheels
When improving the design, chemical composition of steel and modes of its heat treatment take into account the following, the most important, factors, which affect the efficiency of the wheel performing its function in the work of the car, service life of the wheel and its operational reliability:
- wheel mass;
- disc fatigue strength;
- rim contact strength;
- residual stresses in the rim;
- thermal cracks in the rim;
- rim wear resistance;
- rolling surface shape;
- noise emission;
- axle bond strength.
1) Railway wheel mass
Wheels are the unsprung part of the car (or other rail vehicle). Therefore, their mass should be as small as possible., to minimize their dynamic impact on the bogie and the uniformity of movement on the rails. This is especially important for high speed trains..
2) Wheel disc fatigue strength
The disc must have sufficient fatigue strength to, to withstand cyclic mechanical stresses, wagon weight.
3) Tread contact strength
The steel of the rolling surface must have sufficient rolling contact strength when interacting with the rail (Hertz voltage), including, high contact fatigue strength.
4) Residual stresses in the rim
When the rim tries to expand due to heat from the brake pads when the car is braking, then significant temperature stresses arise in the disc and rim. They are often so big, which can lead to a redistribution of the residual stress system in the wheel. This leads to, that unfavorable tensile residual stresses arise in the rim near the rolling surface instead of the required compressive. These compressive stresses are created in the rim during the heat treatment of the wheels..
5) Thermal crack resistance and fracture toughness
This applies to thermal cracks, which arise in the rim as a result of its heating when rubbing against the brake pads. These initially very small cracks can propagate deep into the rim and ultimately lead to catastrophic wheel failure..
6) Rim wear resistance
Wear occurs on the rolling surface of the rim in contact with the rail, as well as when the rim friction against the brake shoe, if rim braking is applied. The service life of the wheel directly depends on the wear resistance of the rim.. Sometimes uneven rim wear is a problem.
7) Rolling stability of a wheel on a rail
Stability of the carriage movement, as direct, and curved sections, assessed mainly by the behavior of the bogie as a whole. However, the shape of the rolling surface of the wheel is one of the important factors..
8) Noise from a moving wheel
Reducing noise, which is emitted by the wheel, required in terms of reducing the train's environmental impact on the environment. Several approaches are used for this., such as improvements in bogie design or rail lubrication. Special noise absorption systems are applied to the wheels.
9) Vibration wheel
Vibrations, caused by railroad wheels, mostly classified as those, which arise from damage to the rolling surface and those, which result from wheel imbalance. The first cause is influenced by the contact strength of the rim steel., for the second – precision machining of wheels during their manufacture. The latter is especially important for high-speed trains..
10) Wheel-to-axle bond strength
The strength of the connection of the railway wheel to the axle is ensured by the large thickness of the hub.