Strength Grade and Loosening Prevention Requirements of Rail Bolts/Spittles
What are the core strength grades and adaptation scenarios of rail bolts?
The mainstream strength grades of rail bolts are 8.8, 10.9, 12.9 grades, and there are also 4.8 grade ordinary bolts, suitable for different loads and line grades. Grade 4.8 bolts are made of ordinary carbon steel with a tensile strength of ≥400MPa, suitable for industrial and mining low-speed light rail lines to meet basic fixing needs. Grade 8.8 high-strength bolts have a tensile strength of ≥800MPa and a yield strength of ≥640MPa, which are the main models for ordinary railway main lines and metro lines, suitable for conventional connection of fish plates and pressure plates. Grade 10.9 bolts have a tensile strength of ≥1000MPa and a yield strength of ≥900MPa, suitable for high-speed railways and heavy-haul railways to meet the load transmission needs of high speed and heavy haul. Grade 12.9 bolts are ultra-high strength with a tensile strength of ≥1200MPa, suitable for extreme heavy-haul lifting tracks, with small usage but extremely high strength requirements, and can be selected as needed.
What is the product difference between fish bolts and pressure plate bolts?
Fish bolts, also known as bevel head bolts, have a bevel head design, suitable for the oblique bolt holes of fish plates, preventing bolt rotation and improving joint tightness. Pressure plate bolts have a hexagonal head design with a flat head, suitable for straight hole installation of pressure plates, convenient for torque wrench operation and improving installation efficiency. The rod of the fish bolt is fully threaded, and the thread length is adapted to the thickness of the fish plate to ensure the pressing force after tightening and prevent joint loosening. The pressure plate bolt is semi-threaded, the smooth rod part bears shear force, and the thread part bears tensile force, with more reasonable force and suitable for the rail lateral constraint demand. Fish bolts are suitable for rail joint connection, and pressure plate bolts for rail lateral fixation, the two have completely different structures, functions and installation scenarios and are not interchangeable.
What are the anti-loosening design and installation torque requirements of rail bolts?
The anti-loosening design of rail bolts mainly includes three methods: spring washer anti-loosening, lock nut anti-loosening and torque locking anti-loosening, adapted to different scenarios as needed. Spring washer anti-loosening has low cost, prevents bolt loosening through elastic rebound of the washer, suitable for ordinary railway branch lines and industrial and mining lines. Lock nuts have built-in locking gaskets, which bite the thread after tightening with better anti-loosening effect, suitable for metro and high-speed railway lines. Torque locking anti-loosening prevents loosening by accurately controlling the tightening torque and using thread friction, which is the core anti-loosening method for high-speed railways. The installation torque of grade 8.8 bolts for ordinary railways is controlled at 350-400N·m, and that of grade 10.9 bolts for high-speed railways at 500-550N·m with a torque deviation ≤±5%, over-torque or under-torque installation is strictly prohibited to ensure anti-loosening effect.
What are the types of rail spikes and the core requirements for anchoring installation?
Rail spikes are mainly divided into three categories: screw spikes, sulfur anchored spikes and resin anchored spikes, which are the core anchoring connectors between rails and sleepers. Screw spikes have a thread design, which can be directly screwed into the threaded holes of wooden sleepers or concrete sleepers, with convenient installation and suitable for ballasted tracks of ordinary railways. Sulfur anchored spikes are anchored by pouring sulfur mortar with high anchoring strength, suitable for permanent fixation of concrete sleepers, and are the mainstream model for ordinary railway main lines. Resin anchored spikes are poured with resin anchoring agent, with fast curing speed and uniform anchoring force, suitable for ballastless tracks of high-speed railways and emergency repair scenarios. The core requirement for spike anchoring is that the anchoring depth is ≥150mm, the anchoring verticality deviation ≤1°, and the anchoring agent is fully filled without gaps to prevent spike loosening and ensure the vertical fixing effect of the rail.
What are the anti-corrosion treatment and service life guarantee measures of bolts/spikes?
The core anti-corrosion treatment methods for bolts/spikes include hot-dip galvanizing, dacromet coating and anti-corrosion oil immersion, adapted to different environmental working conditions. Hot-dip galvanizing treatment has a coating thickness of ≥85μm and excellent corrosion resistance, suitable for coastal humid and saline-alkali area lines with a service life of ≥15 years. Dacromet coating has salt spray resistance ≥1000 hours and no hydrogen embrittlement risk, suitable for the anti-corrosion needs of high-strength bolts, and is preferred for high-speed railway lines. Anti-corrosion oil immersion has low cost, suitable for inland dry area lines, and anti-rust oil needs to be re-coated regularly. Service life guarantee also requires regular inspection of the rust and loosening of bolts/spikes, tightening the bolt torque once a quarter, and doing anti-corrosion re-coating once a year. If the bolt rust is ≥2mm or the spike anchoring is loose, it must be replaced in time to avoid potential track safety hazards caused by connector failure.