Surface grinding, a new rail grinding technology!
In recent years, with the rapid development of China's rail transit, the situation of rail damage has gradually increased. Rail damage not only affects the driving quality, but may even lead to derailment, which seriously affects the stability and safety of driving. Therefore, improving the service life of rail transit rails has become an urgent problem to be solved. Rail grinding is an important method in line maintenance and repair. It is also a means to improve the life and performance of the rail. After a lot of practice and theoretical research, it proves the practicability and reliability of this measure. Rail grinding has been widely used at home and abroad, and can effectively improve the service life of rail transit rails.
In 2018, a new type of grinding technology was introduced to China - surface grinding, also known as tangential grinding. The biggest difference from traditional grinding is the contact position of the grinding wheel and the rail during grinding: the traditional grinding uses the grinding wheel. The axial faces, that is, the planes and the rails are ground (see Figure 1), while the curved surfaces are grounded by the radial faces of the grinding wheels, that is, the circumferential surfaces are in contact with the rails. As shown in Figure 2, the surface of the grinding wheel is tangent to the longitudinal horizontal line of the rail, so it is also called tangent grinding.
Figure 1 Traditional cup grinding
Figure 2 Surface grinding
Because of the huge differences in technical principles, surface grinding has a unique advantage over traditional grinding techniques. The following is based on the MS-12S type (see Figure 3) grinding machine produced by MecnoService of Italy, which describes several typical characteristics of surface grinding.
Figure 3 MS-12S grinding car
First, the superiority of polishing quality
The principle of surface grinding utilizes the “self-sharpening†feature of the grinding wheel. The arc surface formed by grinding with a grinding wheel can completely cover the surface of the rail with only 4-5 grinding wheels. At least two sets of grinding wheels are locked in one position, so the following There are special advantages in each aspect:
1. Lateral profile: the curved surface is full and there is no facet. See Figure 4-1 for the surface after grinding the surface. Figure 4-2 shows the shape of the traditional cup-type grinding.
2. Longitudinal smoothness: There are 2 sets of grinding stones designed in the same longitudinal plane, which is good for the treatment of welding heads and wave grinding. See Figure 5-1 and Figure 5-2 for comparison of the welding head before and after grinding.
3. Roughness: As shown in Figure 6, the surface roughness of the rail after grinding is less than 4μm on average.
Figure 6 Polishing roughness
Second, the variability of work efficiency and ability
The car is designed with a total of 12 grinding wheels, 6 on each side, but as previously described, typically 4-5 wheels can completely cover the rail surface, depending on the thickness of the selected wheel. Another special feature of the car is that it can be used with different hardness and thickness depending on the needs of the rail.
1. Grinding wheel is suitable for local conditions and flexible combination: If you do not need to modify the profile, you can cover the entire rail surface with only two 60mm thick grinding wheels inside and outside, and finish grinding the average amount of 0.2mm. For the disease condition with fat on the inside, a 25mm grinding wheel can be set to effectively remove the disease. In addition, if it is necessary to polish a profile having a large amount of grinding at a gauge angle such as 60N, a grinding wheel having a thickness of 35 mm may be used in this region. In short, according to different working conditions, different thickness combinations of grinding wheels can be set to complete the targeted grinding.
2, grinding the number: in view of the different combinations of grinding wheels, at least one time can achieve the new rail pre-grinding, to achieve the purpose of removing the decarburization layer. The silhouette repair with a large amount of sanding can generally reach the design profile in 6-8 times.
3. Working speed: The average working speed of 1-2km/h can observe the grinding condition in the slow running and adjust the grinding strategy in time. This has obvious advantages for polishing the ballast.
Third, the scope of work for barrier-free design
In view of the curved grinding stone design, the grinding stone does not interfere with the various facilities on both sides of the rail during the operation. Therefore, the grinding car has almost no obstacles affecting the operation, and no additional equipment for removing the rails is needed during the operation.
1. Turnout: Any area where the ballast can be polished, including the tip rail and the center of the heart. However, in order to prevent the grinding of the area from affecting the geometric parameters of the ballast, the amount of sanding is more cautious in this area, while the curved track and the straight track are The basic rail section, the curved base rail, and the straight base rail section can be free from any restrictions.
2. Line: All kinds of facilities in the line, such as axle counting device, automatic lubrication device, guard rail, civil defense door, etc., do not affect the grinding operation.
3. Groove rail: When the ordinary wheel pair passes the slot rail dedicated to the tram, the rim thickness determines the safety factor through the switch. The MecnoService Surface Grinding Car is designed to replace wheel pairs and use thinner rim wheel pairs when grinding grooved rails for safe operation and operation on the grooved rails. In addition, the car's curved surface design can easily avoid the rail groove, thus easily completing the grinding operation.
4, extreme line conditions: the car travel system is mechanical transmission, can work on the slope of 80 ;; in addition, the smaller size of the car (length 13962mm * width 2320mm * height 2700mm) can also let it pass 20 meters Small radius corners are a very important operational capability for urban rails.
Polishing actual effect analysis:
According to the person in charge of Beijing Tonghe Times Technology Co., Ltd., which introduced the grinding technology, in 2018, they used Mecno surface grinding technology to verify the grinding effect in three different occasions:
First, the new rail profile of the ballast and station line was drilled in the Chengpu section of the Sichuan-Tibet line. The Chengpu section is the pilot section of the Sichuan-Tibet Railway. It is designed and operated at a speed of 200km/h. According to the requirements of the railway management department, the two high-speed rails of the section, 60D and 60N, are suitable for profile. The maximum amount of grinding is 1.3mm in the gauge angle area. . The car can reach the 60N design profile 8-10 times, and found in the later operation, the polished profile has a very important role in preventing the early side grinding and fish scales of the ballast. Figure 7 below shows the macroscopic state of the ballast after grinding, and Figure 8 shows the comparison of the sanding profile.
Figure 7 After the ball is polished
Figure 8 Comparison of the silhouette after design and the design profile
The second is to repair the grooved track in the Haizhu test section of the Guangzhou tram. Guangzhou trams are laid on the edge of the Pearl River, passing through two high-end residential communities along the way, causing complaints from residents due to contact and wave grinding. After polishing, the wheel-rail relationship improved significantly, and the train running noise was reduced by a maximum of 5 decibels. Figure 9 is a comparison before and after wave grinding, and Figure 10 shows the results before and after noise grinding.
Figure 9 Data before and after wave grinding (dark blue for sanding, bright blue for sanding)
Figure 10 Noise measurement before and after grinding
The third is to pre-polish the entire line of new rails on the R1 line of Jinan Metro. Relevant research proves that the new rail is pre-polished before opening to remove the surface decarburization layer and the damage caused by partial installation, which can greatly reduce the chance of fatigue damage of the rail in the later operation, especially micro crack, abrasion and welding. The head is not smooth, etc., can play a very good role in eliminating. Figure 11 below shows the macroscopic surface after sanding the line.
Figure 11 Macroscopic shape after grinding in Jinan subway
In addition, the car design can be quickly decomposed and combined, using the car to transport to the grinding site (see Figure 12), which is very convenient for the grinding schedule, especially in the urban subway line, some lines have no tie lines, can not improve the utilization rate of the grinding car The car is designed to solve this problem well.
Figure 12 Fast transport of curved grinding vehicles
Under different occasions and working conditions, the performance of the car is perfect. It can repair the disease of the rail as well as the traditional grinding, prolong the life of the rail, and can take advantage of the traditional sanding restricted area to fill the technical gap. This will be the pioneering force of the future polishing technology, which will contribute to the maintenance of the rail transportation industry.
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