Fishplate Joint Vibration Damping Structure Design and Rail End Face Close Fit Technology
What are the core design forms of the joint damping structure of fish plates?
The core design forms of the joint damping structure of fish plates mainly include damping grooves on the fitting surface, inlaid elastic buffer pads, hollowed-out damping of the plate body and arc damping at the edges. Each form has a different damping principle and can be used alone or in combination to adapt to the damping requirements of different lines. Damping grooves on the fitting surface are the most basic design form. Several arc-shaped damping grooves with a depth of 2-3mm and a width of 5-6mm are evenly designed on the fitting surface of the fish plate and the rail. When wheel-rail vibration is transmitted to the joint, the grooves can produce slight elastic deformation to absorb part of the vibration energy, and at the same time reduce the contact area between the fish plate and the rail to lower the vibration transmission efficiency. Inlaid elastic buffer pads are a high-efficiency damping form. Nitrile rubber elastic buffer pads with a Shore hardness of A40-50° are inlaid in the grooves on the fitting surface of the fish plate, which are closely in contact with the rail end face. The buffer pads absorb vibration energy through their own elastic deformation during vibration, and the damping effect is more than 3 times higher than that of simple grooves, suitable for high-speed, urban rail and other lines with high damping requirements. Hollowed-out damping of the plate body is a lightweight damping form. Several circular hollowed-out holes with a diameter of 10-12mm are designed in the non-stressed areas of the fish plate, which can not only reduce the self-weight of the fish plate but also make the plate body produce slight bending deformation during vibration to absorb vibration, adapting to the lightweight requirements of ordinary-speed railways. Arc damping at the edges is an auxiliary damping form. The two end edges of the fish plate are designed with an arc transition of R15-R20 to avoid stress concentration caused by right-angle edges, and at the same time reduce the reflection and amplification of vibration at the edges. It is used in conjunction with other damping forms to improve the overall damping effect. All these design forms are carried out on the premise of ensuring the strength of the fish plate without affecting its connection performance.
How do the elastic buffer pads on the fitting surface of fish plates achieve precise adaptation to rails?
The precise adaptation of the elastic buffer pads on the fitting surface of fish plates to rails is achieved through the precise control of four aspects: size design, hardness matching, structural shaping and installation positioning of the buffer pads, ensuring the all-round fitting of the buffer pads with the rail end face and the fish plate grooves. In terms of size design, the external dimensions of the buffer pad are precisely matched with the damping grooves on the fitting surface of the fish plate, with the length and width exactly the same as the grooves, and the thickness 0.5-1mm larger than the groove depth. After installation, the buffer pad is extruded by the fish plate and the rail to produce slight elastic deformation, realizing seamless fitting with the grooves and the rail end face. In terms of hardness matching, buffer pads with different hardness are selected according to the vibration intensity of the line. Soft buffer pads with Shore A40-45° are used for high-speed lines to improve the damping effect; hard buffer pads with Shore A40-50° are used for heavy-haul lines to ensure the bearing capacity while damping and avoid excessive deformation of the buffer pads. In terms of structural shaping, the surface of the buffer pad is designed with slightly raised anti-slip lines with a height of 0.3-0.5mm, which can increase the friction between the buffer pad and the rail end face, prevent the buffer pad from slipping due to vibration during train operation, and the lines can break the continuity of the water film to avoid water corrosion between the buffer pad and the rail. In terms of installation positioning, positioning bumps are designed on both sides of the buffer pad, and positioning concave holes are designed at the corresponding positions of the fish plate grooves. During installation, the bumps are clamped into the concave holes to realize rapid and precise positioning of the buffer pad and avoid poor fitting caused by installation deviation. In addition, the buffer pad is manufactured by compression molding process with a dimensional accuracy of ±0.1mm, which can ensure the adaptability to different rail end faces and greatly improve the fitting degree of the joint.
What is the impact of the precision grinding process of rail end faces on close fitting adaptation?
The precision grinding process of rail end faces is the foundation for ensuring the close fitting adaptation of fish plates and rail end faces, which directly affects the fitting degree, vibration transmission and service life of the joint. The precision of the ground end face is much higher than that of the ordinary cut end face. The rail end face processed by ordinary cutting has processing lines, perpendicularity deviation and dimensional error, with a perpendicularity deviation of up to 0.5mm/m. When fitting with the fish plate, multiple gaps will be generated, and the wheel-rail vibration will be amplified through the gaps, leading to intensified joint impact. At the same time, water and impurities are easy to enter the gaps, causing corrosion of the rail end face. The precision grinding process of rail end faces is carried out by CNC precision grinding machine. First, rough grinding is performed on the end face to remove burrs and processing lines from cutting, then finish grinding is carried out to control the perpendicularity deviation of the end face within ≤0.1mm/m, the flatness deviation ≤0.05mm, and the surface roughness Ra ≤1.6μm. The ground end face is flat and smooth, and the contact area with the fish plate can reach more than 95% when fitting, realizing close fitting. The precision ground end face can effectively reduce the joint gap, avoid vibration amplification, reduce the impact load of the wheel and rail on the joint, and at the same time reduce the intrusion of water and impurities to prevent corrosion of the rail end face. In addition, the precision grinding process can ensure the consistency of the end face dimensions of the same batch of rails, make the adaptability of the fish plate and the rail more uniform, avoid uneven stress on the fish plate caused by the difference in end face dimensions, and improve the connection stability of the joint. If the rail end face is not precision ground, even the most precise design of the fish plate cannot achieve real close fitting adaptation.
What are the gap control criteria for rail joints in different temperature environments?
The gap control of rail joints in different temperature environments follows the core principle of thermal expansion and contraction compensation, and the gap value is accurately set according to the local annual extreme temperature, rail linear expansion coefficient and rail type characteristics to avoid rail deformation or joint damage caused by temperature stress. The linear expansion coefficient of national standard 50kg/m and 60kg/m rails is 1.18×10^-5/℃, which is the core parameter for gap calculation. The basic gap value is determined in combination with the temperature range of the line where the rail is located. The general basic gap is 2-4mm at room temperature (20-25℃), which reserves basic compensation space for temperature deformation. High-temperature areas (annual extreme high temperature ≥38℃) need to adopt the large gap criterion, setting the joint gap to 3-4mm. Because the rail will expand significantly when heated, sufficient gap can avoid axial compressive stress generated after the rail elongates, preventing rail arching, fish plate deformation and even bolt fracture at the joint. Alpine areas (annual extreme low temperature ≤-25℃) need to adopt the small gap criterion, controlling the gap to 2-3mm. The rail will contract when cooled at low temperature, which will increase the gap. A small gap can avoid excessive gap of the joint after cold contraction, prevent intensified wheel-rail impact when the train passes, and at the same time avoid the intrusion of impurities and water into the joint due to excessive gap. Areas with large temperature fluctuations (annual temperature difference ≥60℃) need to adopt the dynamic adjustment criterion. Install according to the basic gap when the temperature is moderate in spring and autumn, check and appropriately expand the gap in the high-temperature period in summer, and timely investigate the problem of excessive gap in the low-temperature period in winter. Replace the adjusting gaskets if necessary to ensure that the gap is always adapted to the real-time temperature. In addition, due to the difference in cross-section of international standard rails (UIC60, BS113A), the gap value needs to be fine-tuned on the basis of the national standard. The overall gap of UIC60 rails is 0.5mm smaller than that of national standard 60kg/m rails, adapting to the smoothness requirements of its high-speed lines. All gap control must be detected with a special feeler gauge, with a deviation ≤±0.5mm to ensure precise gap.
How does the stress compensation design of fish plates improve the fitting degree with rails?
The stress compensation design of fish plates is a key means to improve the fitting degree with rails. It offsets the stress deformation during installation and service through three methods: pre-bending forming, elastic groove design and gradient distribution of bolt pre-tightening force, ensuring that the fish plate and the rail end face are always closely fitted. Pre-bending forming is the basic stress compensation design. The fish plate is slightly pre-bent by CNC bending process during production, and the pre-bending radian is determined according to the rail type and bolt pre-tightening force. The pre-bending value of the fish plate adapted to 60kg/m rails is 0.3-0.5mm. When the bolts are tightened, the pre-bent fish plate returns to flat under the action of pre-tightening force, and at the same time generates continuous fitting pressure on the rail end face, avoiding the fitting gap caused by the own rigidity of the fish plate, and increasing the contact area to more than 95%. Elastic groove design is a local stress compensation design. Arc-shaped elastic grooves with a width of 3-4mm and a depth of 2-3mm are designed on both sides of the bolt holes of the fish plate. When the bolts are pre-tightened or the rail deforms under temperature stress, the elastic grooves can produce slight elastic deformation to offset local stress concentration, avoid the gap between the fish plate and the rail caused by stress warping of the fish plate. At the same time, the elastic grooves can make the stress on the fish plate more uniform and reduce the risk of cracking around the bolt holes. Gradient distribution of bolt pre-tightening force is a dynamic stress compensation design. According to the stress characteristics of the fish plate, the pre-tightening force of the middle bolt is set to the maximum value (450-500N·m for 60kg/m rails), and gradually decreases to the end bolts (350-400N·m for the end bolts). This gradient distribution can make the fish plate fit the rail evenly from the middle to the ends, avoid the warping of the two ends of the fish plate caused by excessive pre-tightening force at the two ends, and at the same time offset the bending stress at the rail joint to ensure that the fitting degree does not attenuate during service. In addition, the stress compensation design of the fish plate is combined with the precision grinding of the rail end face and the control of the joint gap to form a full-process close fitting guarantee of "design-processing-installation". Even under the working conditions of repeated train vibration and temperature changes, a good close fitting state can be maintained to reduce vibration and noise.