The rail is not the end of the laying, the operation process has to be polished rail! Today we will learn how the steel rail is polished.
The rail is polished before the train is run. This grinding strategy is called pre-grinding. Not only the high-speed railway, but also the rail is polished before the operation after the completion of the new line. The purpose is to remove rail rolling scars, decarbonization layer, solder joints at rail joints and improve surface roughness, and the ultimate purpose is to eliminate the bad marks on the rail surface. Prevent the further development of these defects and improve the service life of the rail.
In addition to pre-grinding, rail grinding strategies are also divided into preventive grinding, maintenance grinding (also known as maintenance grinding) and repair grinding (also known as corrective grinding).
When it comes to rail grinding, we have to talk about rail disease first. We all know that high-speed rail, bullet train, subway and other locomotives have no steering wheel, the driver does not need to operate the direction, completely through the rail to guide the vehicle to run, so the rail carries the huge pressure and impact force from the wheel.
In extremely complex working conditions, there will inevitably be a variety of damage, there are defects in the smelting process, but also in the transportation, construction and use of the process of damage. Common damage is rail wear: including vertical wear, side wear, wavy wear (referred to as wave wear); Contact fatigue damage: including rail head crack, hidden injury, stripping; There are fat edges and rail bruises.
All these diseases, they will increase wheel-rail noise, accelerate the deterioration rate of vehicle components and track components, and aggravate the further expansion of rail diseases. The main reason is that they destroy the optimal contour shape of the rail and change the wheel-rail contact state.
What is the best profile? When the train is running on a straight line or a large radius curve, the tread of the wheel is in contact with the rail head area B, and the contact stress and the creep force are the least in this state. When the rim is close to the Angle of the rail gauge, that is, the area C in the figure, the conformal contact is formed, and the contact stress is minimum.
the best profile
Rail grinding is actually to cut the surface of the rail, remove the disease, and restore the rail to the best profile.
The outline of the rail head is similar to an arc shape, but the actual grinding (grinding wheel) is to divide the rail head into different areas according to the Angle, that is, the outline of the rail head is regarded as composed of line segments divided by angles, and the position that needs to be polished corresponds to a certain Angle.
Therefore, the grinding equipment controls the deflection angle of the grinding head to specify different parts of the rail for grinding.
Obviously, the more serious the damage to the rail, the greater the amount of grinding and cutting, the greater the workload, the greater the difficulty, and the reduced rail life. Therefore, restorative grinding and repair grinding are like “treating diseases”, and the best way is to prevent rail “sickness”, that is, regular preventive grinding to completely eliminate damage in the bud.
The thickness of the plastic flow layer is generally 0.2㎜. Therefore, preventive grinding does not require a large amount of rail cutting, generally between 0.1-0.2mm. This does not require too much cutting can play a role in extending the life of the rail, is the most economical and effective way.
According to the information, the regular preventive grinding of the rail can extend the life of 5-8 years, improve the operation of the train, maintain passenger comfort, reduce the serpentine movement, reduce noise, reduce energy consumption, reduce the maintenance cost of locomotive parts and tracks, and bring economic and social benefits.
The following figure shows the impact of preventive grinding and repair grinding on the rail life. The yellow line indicates preventive grinding. Each grinding will delay the speed of damage development and increase the rail life.
There are three main ways to achieve rail grinding: boot grinding, grinding wheel and milling.
Sliding boot grinding is to grind the surface layer of the rail by pressing the grinding stone on the rail for reciprocating movement. This grinding method can only grind the rail head lengthwise, but cannot adjust the rail profile or grind the switch. Therefore, this grinding method has been gradually phased out, and the grinding speed is low.
Grinding wheel grinding is usually the use of motor or hydraulic motor driven high-speed rotating grinding wheel to grind the rail, this is a kind of active grinding, is the main grinding method, through the longitudinal and transverse grinding rail.
There is another kind of passive grinding, in which the position of the grinding wheel is tilted at a certain Angle to the direction of the train, and the high-speed operation of the power tractor drives the grinding wheel to rotate at a high speed on the rail. The relative movement between the grinding wheel and the rail reaches the required material grinding speed, and the entire rail head from the running edge of the rail to the running surface is polished. It is therefore called high-speed rail grinding.
Milling is a new type of rail profile repair operation mode, the milling cutter is installed on the radial surface of the milling wheel, each milling section is installed with several milling cutters, and the milling wheel has several milling sections in one circle, so that all the milling cutters form a rail head profile to be completed.