Anchorage Strength Enhancement Technology for Rail Spikes and Adaptation Solutions for Different Types of Rail Sleepers
What are the core influencing factors of the anchoring strength of spikes?
The core influencing factors of the anchoring strength of spikes include anchoring material performance, spike structural design and anchoring process parameters. The anchoring material is the basis for determining the anchoring strength. The sulfur mortar anchoring material commonly used for concrete sleepers should have a compressive strength ≥50MPa and a tensile strength ≥5MPa. The mortar mix ratio (sulfur: cement: sand: paraffin = 4:1:4:0.5) directly affects the anchoring performance. Improper ratio will lead to cracking and falling off of the mortar. In terms of spike structural design, when the thread depth of threaded spikes is ≥3mm and the pitch is ≥5mm, the anchoring force is more than 40% higher than that of smooth spikes, because the thread can enhance the mechanical interlocking force between the spike and the anchoring material. The anchoring temperature and curing time in the anchoring process parameters are also crucial. The melting temperature of sulfur mortar anchoring should be controlled at 140-160℃. Excessively high temperature will cause carbonization of the mortar and reduce the strength; the curing time should be ≥24 hours to ensure the mortar is fully cured and improve anchoring stability. In addition, the cleanliness of the reserved hole of the sleeper will also affect the anchoring strength. Dust and debris in the reserved hole should be cleaned up, otherwise the bonding force between the spike and the anchoring material will be reduced.
What are the key points of the sulfur mortar anchoring process for spikes of concrete sleepers?
The key points of the sulfur mortar anchoring process for spikes of concrete sleepers are to accurately control the material ratio, melting temperature and anchoring operation process. First, prepare materials according to the weight ratio of sulfur: cement: quartz sand: paraffin = 4:1:4:0.5. The quartz sand should be sieved with a particle size ≤2mm to remove impurities and prevent pores inside the mortar. When melting sulfur mortar, adopt the double-layer pot melting method. The inner pot melts the materials, and the outer pot is filled with water. The temperature is controlled at 140-160℃ through water bath heating to avoid sulfur combustion and carbonization caused by direct heating. Before anchoring, carry out cleaning and drying treatment on the reserved hole of the sleeper. Blow off the dust in the hole with a high-pressure air gun and dry the water in the hole with a blowtorch to ensure the hole is dry and clean. During anchoring, fix the spike on the positioning frame to keep the spike perpendicular to the sleeper surface, then inject the melted sulfur mortar, which should fill the reserved hole to avoid cavities. After anchoring, let it stand for curing ≥24 hours. Do not disturb the spike during curing. After the mortar is fully cured, the fastener system can be installed. In addition, after anchoring, spot check the anchoring force with a sampling ratio of 5 spikes per kilometer of the line. An anchoring force ≥60kN is qualified.
What are the anti-loosening and anti-corrosion treatment technologies for spikes of wooden sleepers?
The anti-loosening and anti-corrosion treatment technologies for spikes of wooden sleepers are to enhance the interlocking force between the spike and the wooden sleeper and extend the service life of the wooden sleeper. First, select helical spikes. The thread of helical spikes is left-handed, which is opposite to the vibration direction of the train during operation, which can effectively prevent the spike from loosening. The anti-loosening effect of helical spikes with a thread depth of 4mm and a pitch of 6mm is 30% higher than that of ordinary spikes. Secondly, when drilling holes in wooden sleepers, the diameter of the drill hole is 1mm smaller than the diameter of the spike. Drive the spike into the hole by interference fit to enhance the mechanical interlocking force between the spike and the wooden sleeper and prevent the spike from loosening under vibration load. Anti-corrosion treatment is divided into spike anti-corrosion and wooden sleeper hole wall anti-corrosion. The spike is anti-corrosive by hot-dip galvanizing with a zinc layer thickness ≥85μm and a salt spray test corrosion resistance time ≥1000 hours; the wooden sleeper hole wall is coated with anti-corrosion oil, which is a mixture of coal tar and diesel oil with a mixing ratio of 3:1 and a coating thickness ≥0.5mm to prevent the hole wall from being damp and rotten and affecting the anchoring strength. In addition, install an anti-loosening washer between the spike head and the wooden sleeper, which is made of spring steel with a thickness of 2mm. The anti-loosening washer can offset the gap caused by vibration through elastic deformation and further improve the anti-loosening effect.
What are the welding anchoring technology and quality control measures for spikes of steel sleepers?
The welding anchoring technology for spikes of steel sleepers prefers arc stud welding technology. This technology melts the bottom of the spike and the surface of the steel sleeper by arc high temperature to realize the metallurgical bonding between the spike and the steel sleeper. The anchoring strength is more than 50% higher than that of mechanical anchoring. The welding process parameters should be accurately controlled. The welding current is controlled at 800-1000A, the welding time is controlled at 0.5-1 second, and the welding voltage is controlled at 25-30V to ensure that the bottom of the spike and the surface of the steel sleeper are fully melted to form a uniform welding molten pool. Before welding, carry out grinding and derusting treatment on the surface of the steel sleeper with a grinding grade reaching Sa2.5 to remove rust and oil stains on the surface and prevent pores and slag inclusion defects during welding. Quality control measures mainly include visual inspection and anchoring force test. Visual inspection requires that the surface of the welded joint is free of pores, cracks and incomplete fusion defects, and the weld reinforcement is controlled at 1-2mm; the anchoring force test uses a tensile testing machine to apply longitudinal tensile force, and an anchoring force ≥100kN is qualified. In addition, after welding, carry out stress relief treatment, grind the surrounding area of the weld with an angle grinder to eliminate welding stress and prevent cracking of the welded joint. At the same time, apply anti-corrosion paint to the welded part with a thickness ≥50μm to improve corrosion resistance.
What are the detection methods and acceptance standards for the anchoring strength of spikes?
The detection method for the anchoring strength of spikes mainly adopts the pull-out test method in accordance with the industry standard TB/T 1499.3-2018. Use an anchor pull-out tester, fix the fixture of the pull-out tester on the spike head, apply tensile force at a speed of 5kN/min, and record the maximum tensile force when the spike is pulled out or damaged, which is the anchoring strength value. During detection, the differences between different sleeper types should be considered. The pull-out test of spikes for concrete sleepers should be carried out 24 hours after anchoring and curing, that for wooden sleepers should be carried out 48 hours after installation, and that for steel sleepers should be carried out after welding and stress relief treatment. The acceptance standards are divided according to sleeper types. The anchoring strength of spikes for concrete sleepers is ≥60kN, and the anchoring material has no cracking or falling off; the anchoring strength of spikes for wooden sleepers is ≥40kN, and the spikes have no loosening phenomenon; the anchoring strength of spikes for steel sleepers is ≥100kN, and the welded joint has no fracture. The sampling ratio for inspection is 5 spikes per batch or per kilometer of the line. If the anchoring strength of one spike is not up to standard, double sampling shall be conducted. If the double sampling is still unqualified, the anchoring quality of the spikes of the batch or the section of the line shall be judged as unqualified and re-anchoring treatment is required.