Comprehensive Corrosion Protection Design and Construction Technology for All Components of the Rail Fastening System
How are the anti-corrosion grades of different components of the track fastening system divided according to the service environment?
The anti-corrosion grades of different components of the track fastening system are divided into three levels according to the corrosion degree of the service environment, and different components need to design anti-corrosion schemes according to the corresponding grades to ensure that the anti-corrosion capacity matches the environment. The coastal high-salt spray environment is a strong corrosion grade, and all components such as elastic strips, bolts and fish plates in this environment need to adopt the highest grade anti-corrosion, and the anti-corrosion layer's salt spray resistance test must reach more than 1000h to prevent the salt spray from corroding metal components quickly. The humid and foggy inland areas are medium corrosion grades, the core components of the fastening system such as bolts and fish plates adopt medium and high grade anti-corrosion, and the auxiliary components such as rail spikes and pressure plates adopt medium anti-corrosion, and the salt spray resistance test must reach 600-800h. The dry and less rainy inland areas are weak corrosion grades, the fastening system only needs to adopt the basic anti-corrosion scheme, the core components' salt spray resistance test reaches 400h, and the auxiliary components can simplify the anti-corrosion process. Different sections of the same line such as bridges and tunnels also need to be divided differently, the bridge section is designed according to the medium corrosion grade due to high humidity, and the tunnel section is designed according to the medium and strong corrosion grade due to poor ventilation, ensuring that the anti-corrosion grade of each component is accurately adapted to the actual service environment.
What mechanical performance requirements should be considered in the anti-corrosion layer design of elastic strips?
The anti-corrosion layer design of elastic strips must ensure the anti-corrosion effect while taking into account the three mechanical properties of elastic deformation, fatigue resistance and wear resistance of elastic strips, avoiding the anti-corrosion layer affecting the normal operation of elastic strips. Elastic strips are elastic components that need to produce repeated elastic deformation during work, so the anti-corrosion layer must have good flexibility with an elongation rate ≥10% to prevent the anti-corrosion layer from cracking and falling off when the elastic strip deforms. Elastic strips are subjected to vibration loads for a long time, and fatigue resistance is the core. The anti-corrosion layer must be firmly combined with the base material of the elastic strip with a bonding strength ≥5MPa to prevent the anti-corrosion layer from peeling due to vibration, which in turn causes base material corrosion. The contact part between the elastic strip and the rail has slight friction, so the anti-corrosion layer must have a certain hardness with a surface hardness ≥HV200 to prevent the anti-corrosion layer from being worn out quickly due to friction and losing anti-corrosion protection. At the same time, the anti-corrosion layer must have good temperature resistance, can adapt to temperature changes from -40℃ to 60℃ without softening and brittle cracking, ensuring the stability of anti-corrosion effect and mechanical properties at different temperatures. In addition, the thickness of the anti-corrosion layer should be controlled at 50-80μm, too thick will affect the elastic deformation of the elastic strip, too thin can not meet the anti-corrosion requirements, balancing anti-corrosion and mechanical properties.
What are the construction points of anti-corrosion sealing on the fitting surface of fish plates and rails?
The anti-corrosion sealing construction on the fitting surface of fish plates and rails is a key link in the anti-corrosion of the fastening system. The construction points focus on the uniform application of the sealing layer, the cleaning treatment of the fitting surface and the compaction and sealing after assembly to ensure that no corrosive medium invades the fitting surface. Before construction, the fitting surface of the fish plate and the rail must be thoroughly cleaned, and the surface derusting grade is reached to Sa2.5 by sandblasting derusting, removing oil, rust and impurities to ensure the bonding force between the sealing layer and the base material. The sealant should be a special track sealant compatible with the anti-corrosion layer, applied by a combination of dot coating and blade coating, the coating thickness is controlled at 0.2-0.3mm to ensure full area coverage of the fitting surface without missing or missing coating parts. The assembly of the fish plate must be completed within 30 minutes after applying the sealant to avoid the pre-curing of the sealant affecting the fitting effect. During assembly, ensure the precise centering of the fish plate and the rail without offset of the fitting surface. After assembly, apply pre-tightening force by tightening the bolts to compact the sealant on the fitting surface, so that the sealant fills the tiny gaps of the fitting surface to form a gap-free sealing layer. The pre-tightening force must reach the design value to ensure the compaction effect. Finally, edge sealing treatment is carried out on the junction between the edge of the fish plate and the rail, and the sealant is applied in an arc shape to prevent rainwater and dust from invading from the edge gaps. All construction steps must be carried out in a dry environment to avoid moisture affecting the curing and bonding effect of the sealant.
What special requirements are there for the anti-corrosion design of the thread part of track bolts?
The thread part of track bolts is a weak link in anti-corrosion, and its anti-corrosion design must take into account anti-corrosion effect, thread meshing accuracy and pre-tightening force transmission, which is different from the general anti-corrosion requirements of other components. The anti-corrosion layer of the thread part must have good lubricity to avoid excessive meshing resistance of the thread caused by too hard anti-corrosion layer, which affects the precise control of pre-tightening force, and at the same time, lubricity can reduce wear during thread meshing. The anti-corrosion layer must be applied in a thin and uniform way, and the thickness of the anti-corrosion layer on the thread crest, thread side and thread root is controlled at 30-50μm to ensure that the thread meshing gap meets the design requirements without poor meshing caused by too thick anti-corrosion layer. The anti-corrosion layer of the thread must be firmly combined with the thread base material, without falling off or peeling during repeated tightening and loosening to ensure the long-term anti-corrosion effect. For high-strength bolts, the anti-corrosion design of the thread part must avoid hydrogen embrittlement, and the anti-corrosion process must adopt hydrogen-free treatment to prevent hydrogen atoms from invading the bolt and causing brittle fracture, balancing anti-corrosion and bolt strength safety. In addition, the thread part can adopt a double anti-corrosion scheme of anti-corrosion adhesive + anti-corrosion coating, the anti-corrosion adhesive fills the thread gap, and the anti-corrosion coating covers the thread surface to form double protection, preventing corrosive medium from invading from the thread gap and improving the anti-corrosion durability.
What are the quality inspection items after the anti-corrosion construction of the fastening system?
The quality inspection after the anti-corrosion construction of the track fastening system needs to cover three categories: anti-corrosion layer performance, sealing effect and assembly accuracy. Multiple index tests are used to ensure that the anti-corrosion construction quality meets the design requirements without potential quality hazards. First, inspect the appearance quality of the anti-corrosion layer, which requires the anti-corrosion layer surface to be flat and smooth without defects such as sagging, pinholes, peeling and cracking, and no warping at the edges. Second, inspect the thickness of the anti-corrosion layer, measure different parts of each component with a magnetic thickness gauge, and the thickness deviation shall be controlled within ±10μm to ensure that the thickness meets the design requirements. Then inspect the bonding force of the anti-corrosion layer, adopt the cross-cut test, and the anti-corrosion layer does not fall off or peel after cross-cutting, and the bonding force reaches the design grade. For the sealed parts, adopt the water tightness test, carry out the water spray test on the fitting surface and thread part, no water seepage or leakage for 30 minutes to ensure the sealing effect. At the same time, inspect the meshing accuracy of the thread, use thread plug gauges and ring gauges for inspection, the meshing gap meets the design requirements without affecting the transmission of pre-tightening force. Finally, inspect the assembly accuracy of the fastening system, the bolt pre-tightening force and fish plate clamping force must reach the design value with a deviation ≤±5% to ensure that the anti-corrosion construction does not affect the stress performance of the fastening system. All unqualified parts in the inspection must be reworked in time until they meet the standards.