Why is the train running so smooth? Understanding the principle and working mode of rail grinding

Before the high-speed railway is opened to traffic, the rail is polished. This polishing strategy is called pre polishing. It is not only for high-speed railways, but also for new lines. Generally, after the completion of the new line, the rail needs to be polished before operation. The purpose is to remove the scars, decarburization layers, welding spots at the rail joints, and improve surface roughness. The ultimate goal is to eliminate adverse traces 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 include 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 defects first. "We all know that high-speed trains, bullet trains, subways, and other locomotives do not have steering wheels, and drivers do not need to operate the direction. They completely guide the vehicle through steel rails, so the steel rails bear enormous pressure and impact from the wheels.".

Under extremely complex working conditions, various damages are inevitable, ranging from defects occurring during the smelting process to damages occurring during transportation, construction, and use. Common damages include rail wear, including vertical wear, side wear, and wavy wear (referred to as wave wear); Contact fatigue damage: including rail head cracks, hidden defects, and peeling; There are also fat edges and rail scratches.

Some rail damages are shown in the following figure:

All these are "diseases" that can increase wheel/rail noise, accelerate the deterioration rate of vehicle and track components, and exacerbate the further expansion of rail defects. 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 silhouette? As shown in the following figure, when the train is running on a straight line or a large radius curve, the wheel tread contacts the rail head area B, which is the state of contact stress and the minimum lateral creep force; When the wheel flange is close to the rail gauge corner, i.e., area C in the figure, conformal contact is formed, and the contact stress is minimal. "If it is a disease, it must be treated, and the method is to undergo a surgical procedure - rail polishing.". Rail polishing actually involves cutting the surface of the rail to remove defects and restore the rail to its optimal profile.

 

From left to right: two point contact, single point contact, conformal contact

The rail head contour is similar to an arc shape, but the actual grinding (grinding wheel type grinding) is to divide the rail head into different areas by angle, that is, the rail head contour is considered to be composed of segments divided by angle, and the position to be polished corresponds to a certain angle.