What is seamless line? Literally, there is no seam line, and this “seam” generally refers to the rail seam, also known as the joint.
The rail of the ordinary line is mostly connected by the standard rail length of 12.5m and 25m rail with joints, and a joint must have a rail gap. When a train travels a certain distance, it needs to pass through many joints.
The existence of these joints will have many problems, such as the train often produces “bumps” (poor track smoothness), the train running speed is low, the train passing noise, the rail life is short, the daily maintenance workload is very large and so on.
Seamless line: The standard gauge rail is welded to the long rail and the laid line is locked
Seamless circuit classification
1. Ordinary seamless line: Simply put, the 25m/100m long rail is welded into 200m-500m long rail at the base, and then transported to the site, and then welded into a length of 1000-2000m, laid on the line, it becomes a seamless line.
2. Inter-district seamless line: Simply put, it is to extend the ordinary seamless line to the inbound and outbound signals of the adjacent Lyon station.
3. Inter-district seamless line: that is, on the basis of the inter-district seamless line, the rail length is further extended to connect the long rail section of the inter-district seamless line with the turnout call.
According to temperature stress:
1. Temperature stress seamless line: The seamless line designed with the track structure to withstand the temperature force accumulated by the annual rail temperature change amplitude.
2. Release temperature stress type seamless line: Simply put, the release stress type is that the track structure cannot withstand the temperature force accumulated by the annual rail temperature change amplitude, and the stress release temperature stress must be required in the spring and autumn of each year.
In order to ensure the stability of the track, the release temperature stress seamless line needs to be released twice a year, the maintenance and maintenance workload is large, and limits the length of each rail section, and the line structure is complex, laying and maintenance is very inconvenient.
Therefore, the current temperature stress seamless circuit is widely used.
How to maintain and repair seamless lines?
The first thing to understand is an important concept: the locking orbit temperature. As the name implies, the locking temperature of the seamless line is the rail temperature when the long rail of the seamless line is locked.
What is locking? In simple terms, when the seamless long rail is laid, the rail is fixed by installing fasteners. Of course, the seamless line is fixed, not only need to install the fasteners, but also need to pass enough ballast resistance, enough track frame stiffness (that is, the ability of the frame composed of two rail and sleeper fixed to resist the track heave deformation). Through the track bed, sleeper and fasteners, the temperature force of the rail can be offset, so that the long rail can not move!
How is the locking orbit temperature determined? In fact, the locked rail temperature is the rail temperature under the condition of 0 temperature force. A simple way to determine the temperature of a locked orbit is to use meteorological data to calculate the midpoint between the local record high and low temperatures. Knowing the temperature situation, you can know the local maximum and minimum orbit temperature (according to long-term observation, the minimum orbit temperature is close to the minimum temperature, and the maximum orbit temperature is about equal to the maximum temperature +20℃).
How to maintain and repair?
1. Maintain adequate ballast resistance
(1) The track bed is an important part of the track, it bears the pressure from the sleeper, and the force is evenly spread with the larger subgrade surface.
(2) The clean track bed can smoothly remove the rainwater and surface water on the road to keep the sleeper and the roadbed dry, and prevent the roadbed from being soft and turning and causing the track to sink.
(3) The track bed has a certain elasticity, which can moderate the impact of the train on the line, and slow down the horizontal direction change to maintain the stability of the track.
(4) Full and dense roadbed, which can prevent lateral movement of the track and crawling of the line.
(5) The road bed is a material for tamping the rectification level, and it is also a material for correcting the direction and preventing rebound.
2. Maintain adequate rigidity of track frame
(1) Maintain sufficient torque of the fastener. The fastener is an important part that connects the rail and the sleeper and provides friction for the seamless line fixation. Therefore, in daily life, we must ensure that the torque of the fastener meets the standard.
(2) The daily lifting of the track does not exceed the rail temperature operation requirements. Working rail temperature is very important for long rail, fully constrained seamless rail temperature force and ballast resistance, rail frame rail these binding forces are in a state of equilibrium, when the rail temperature change is relatively large, loosen the fastening, track, track and other maintenance and maintenance railway operations will destroy this balance, stress concentration phenomenon, It even causes the rail to break or expand the rail (internal temperature force > the resistance of the rail frame, a small transverse movement occurs), and the runway (the development of the rail to reach a critical state. If the rail temperature continues to rise, the deformation of the rail increases rapidly in the weakest position, the track frame is bulging, and the displacement from the center of the line is generated.
(3) Maintain sufficient joint resistance, some people want to ask, it is not a seamless line, where the joint comes from? No matter how long the rail is, it also has a limit, and both ends are also connected by joints. The common joint resistance is to use 6 bolts to connect the splint through friction, but at present, the freezing and adhesive technology of our joint (all measures to increase the strength of the joint and increase the friction of the joint) has been very mature, and the strength of the adhesive joint is even higher than the strength of the rail itself.
3. Stress release
Due to train braking, uneven foundation under the rail, uneven pressure of fastenings and other reasons, it will lead to rail crawling, resulting in uneven stress distribution inside the rail and stress concentration, and even some areas of the rail are stretched and compressed. So how do you get rid of it?
Rail expansion = rail expansion coefficient * rail length * rail temperature change value
The linear expansion coefficient of “α”–rail is 0.0118mm/m/℃=11.8* 10-6/℃
l–Rail length, mm
Δt–orbit temperature change amplitude, ℃
For a definite rail, the linear expansion coefficient “α” and the length “l” are both definite, so the length change “Δl” is proportional to the temperature change “Δt”. In other words, in the actual calculation, laying and maintenance of seamless lines, the temperature change value is equal to the length change value. Simple understanding is that the compression of the rail is equivalent to reducing the rail temperature, and the stretching of the rail is equivalent to increasing the rail temperature.
Of course, there is no technology to compress a very long rail, so the stress release mainly uses temperature and length to control the temperature of the locked rail.
How do you control it with temperature? When locking the rail, the working rail temperature is equal to the locking temperature, the rail is supported by the drum, and then the stress inside the rail is evenly hit by the rail collision car, and then the fastener is installed directly.
What if the working track temperature is lower than the locking track temperature? It can also be controlled by length (stretching the rail is equivalent to raising the rail temperature)! The roller is used to prop up the rail, and then the stretching machine is used to stretch the rail, stretch it to the required length, and then the stress inside the rail is evenly hit with the rail collision car, then the rail temperature is the same as the lock rail temperature, and then the fastener is installed.