The separation or cutting of steel rail due to friction or abnormal heavy load is called steel rail wear. Generally, there are three types of rail wear, that is, side wear, vertical wear, corrugation wear.
Side wear is the wear that occurs at the side of head of rails. As the name implies, the side of head of rails wears with the train wheels because of the interaction, which causes the profile change of the rails.
Vertical wear is the wear that occurs at the top of head of rails. The top of head of rails is worn out and damaged in the vertical direction.
The combination of side wear and vertical wear is called the total wear of rails, the formula is as follows:
Total wear= vertical wear+side wear×0.5
On the top surface of rails (or the surface of conjunction part of between top surface and side surface), there occurs uneven but regular corrugation shape of wear, which can be generally divided into long corrugation wear and short corrugation wear.
What are the reasons of various types of steel rail wears? They are basically caused by the followings.
<> The reasons of the side wear are mainly linked with the curve radius, super high setting and the other several factors. Next, we will make further explanation.
The side wear almost occurs exclusively on small radius curves. On straight lines this phenomenon is almost negligible by us. As we know, the train is running on the rails and the main role of the rails is bearing load and guiding the direction. On the curves the guiding role is more obvious and the wheel rim of the train will move in the method of tightly pressing to the outer rails of track curves. The movement will form two-point contact of wheel and rail and cause the increasing of rail wear.
In addition, the train vehicles’ running on the rails is not straight line or curve line of movement in a stricter sense. We can say that it is a snake movement more accurately.
The snake movement is caused by the reason that the distance between the two rails (i.e. gauge) is longer than the distance between the rim distance of two wheels. Objectively, within a certain range this case is beneficial for us, but beyond the range it is harmful. The snake movement possibly leads to form an impact angle at the contact positions between train wheel and rail. On the curves, the angle is one of the main reasons of causing side wear. The smaller curve radius is, the bigger the impact angle is.
For curve rails, the fairness is the most important because it represents that the train wheel can move more smoothly through the curves. Conversely, the unfairness will lead to unsmooth running. It is very easy to understand.
When the train is running on the curves, it will bring about the outward centrifugal force (here F stands for it), the formula:
By formula, we can know that the centrifugal force depends on the train speed and curve radius. The higher the speed is and the smaller the radius is, the greater the centrifugal force is. The centrifugal force makes the outer rail of the curve afford a lot of squeezed pressure, which not only accelerates the outer rail wear and but also may cause serious derailment or train overturning. In order to balance the centrifugal force, we should set the curve superelevation on the outside track of the curve and balance the horizontal component of vehicle gravity to counteract the centrifugal force to achieve roughly equal vertical pressures on the inside and outside two rails of the curve, which will make rail wear uniform and increase the comfort of passengers.
The reason of vertical wear is relatively clear, mainly due to the excessive load of the track. Of course, there are some special reasons, too.
After the rails are put into operation, they will stand the continuous pressure and load. The total weight of all the trains is the total load. When the train passes it, the top surface of the rail will be impacted by machining effect. This effect includes the downward crush and the vertical wear. Two kinds of impacts result in the vertical wear. When the total load reaches a certain limit, the crush impact begins to appear, whose feature is that the top surface of rail is flattened and worn.
The curve superelevation is generally set on the small radius curve in order to train’s smooth pass but not for its parking. When the train is parked there, the unbalanced force will be applied on the rail. So this will result in rail wear.
In the rail corrugation wear is a worldwide technology problem. It is very difficult to solve, and the specific reason what causes it is still in divergent opinions. Basically two believable reasons can be used to explain it. One is elastic sliding, the other is vibration.
On small radius curve, two wheels of the train on the same shaft are relatively fixed. As passing through the curve, they run different rail lengths. But due to they are connected on one shaft and their rotation numbers are also the absolute same. So this will cause a contradiction. In order to pace up the train running, one of two wheels naturally appears the phenomenon of the elastic sliding. This may be the reason leading to the rail corrugation wear.
But corrugation wear appears not only on small radius curve, but also does on straight line. Thus, the elastic sliding cannot completely explain the problem.
The vibration opinion thinks that the reason corrugation wear appears is that the contact force between the rail and the wheel is changed periodically due to reduced stiffness of the rail that makes the vibration amplitude increase. At the same time, as for coincidence resonance caused by the running speed of the train and sleeper gauge, it is another reason. Of these factors, the stiffness is the main factor.
Adjusting the curve means improving the fairness of the curve.
As reasonable curve superelevation has been set up, we shall control each train’s passing at the same speed.
Applying the lubrication between wheels is the most effective method to reduce rail wear. It is to form a layer of oil film between the wheels and rails to reduce mechanical contact and reduce wear through applying the lubrication.
For corrugation wear, it is different from side wear and vertical wear and can be eliminated. The method is rail grinding. The corrugation depth is generally small, and 0.2-0.4mm of depth is suitable for grinding. This will cause too big harm for rail.
When rail wear reaches its limit, we can only replace it. If we want to avoid frequent rail replacement, we can use the heat treatment wear resistance rail whose surface stiffness is increased.