【作者】 高松福；

【导师】 周清跃； 崔成林；

【作者基本信息】 中国铁道科学研究院 ， 载运工具运用工程， 2010， 博士

【摘要】 钢轨铝热焊接是一种填充焊接,该技术具有设备简单,操作简便,接头平顺性好的特点,是目前我国铁路道岔、锁定焊、既有线应力放散、断轨抢修和日常换轨等工作中不可缺少的钢轨焊接方法。铁路运输提速重载的发展,加大了列车对接头的冲击,同时缩短了线路的维修时间,使得钢轨铝热焊接技术必须同时具备接头高性能和作业短流程两个特点。通过分析影响钢轨铝热焊接头性能因素发现,接头金属抗拉强度分布规律为轨腰部最低,轨底次之,轨头最高。焊缝金属轨腰抗拉强度较低的主要因素是疏松缺陷和夹杂物。此外影响接头承载能力的主要因素为焊接缺陷,焊筋形状,以及焊接残余应力。所以提高钢轨铝热焊接头性能的重点是减少或消除接头中可能存在的缺陷,优化金属凝固顺序,优化焊筋结构。焊剂配方研究发现,焊剂反应生成钢液的温度受反应物初始温度,添加物所占比例,氧化铁中FeO所占比例的影响。反应物初始温度每升高1℃,钢液温度升高0.6℃;添加物的加入量每增加1%,钢液温度降低25.7℃;反应物氧化铁中FeO比例增加,铝热钢液温度降低。焊剂反应速率受焊剂反应生成钢液的温度,反应物粒度和添加物粒度的影响。焊剂反应生成钢液温度越高,焊剂反应速率越快;反应物粒度适中时,焊剂反应速率最快,反应物粒度较大或较小时均不能使反应前沿液态生成物充分渗透焊剂颗粒形成的间隙,导致焊剂反应速率降低;添加物粒度为60～80目时,添加物充填焊剂反应物之间的间隙,降低反应速率,延长焊剂反应的固有时间。砂型研究发现,砂型的物理特性由制备砂型的原材料和工艺共同决定。石英砂SiO₂质量分数越高,泥分质量分数越小,砂型的强度和耐火度越高,水玻璃加入量越多,砂型紧实度越高,越有利于获得高耐火度和高强度的砂型。砂型烘干温度和烘干保温时间影响砂型烘干后的强度。砂型最佳烘干工艺可以是采用较低的烘干温度（120℃）进行长时间（120min）保温烘干,也可以是采用较高的烘干温度（300℃）进行短时间（20min）保温烘干,烘干具体工艺还要综合考虑实际生产情况下的能源效率和时间效率。ZTK浇注系统具有良好的焊合能力和接头金属性能,是大轨型钢轨铝热焊接应当选用的一种砂型结构。添加Ni合金的钢轨铝热焊剂和ZTK浇注系统的砂型适合75kg/mPG4钢轨的铝热焊接,焊接接头平均抗拉强度Rm=853MPa,轨头受压静弯破断载荷1759kN,轨头受拉静弯破断载荷1662kN,实物疲劳200万次循环不断,焊缝硬度达334HB,可与PG4热轧钢轨相匹配。更多还原

【Abstract】 Alumino-thermit welding technology has the characters of filling metal welding, simple equipment, easy operation and smooth joints. So it is widely adopted in switches welding, positioned welding, stress relief, broken rail repairing and routine repair work. With the development of speed up and heavy haul transportation, the impact on the joints increased and the repairing time shortened accordingly. So alumino-thermit welding technology should have high joint performance and short operating time.Researches on joint performance show that the tensile strength of joint metal is the lowest in the rail web, higher in the rail foot, and the highest in the rail head. The distribution of tensile strength contributes to the micro porosity in the rail web and inclusions in the rail foot. In addition, the carrying capacities of joints mainly are affected by welding defects, welding collar shapes, as well as the welding residual stress. So the improvement of joint performance should firstly aimed on reducing or eliminating of welding defects that may exist in joints, optimizing solidification sequence of weld metal, optimizing the structure of weld collar.Researches on welding powder formula show that the temperature of liquid steel produced by thermit reaction is affected by the initial temperature of reactants, additives proportion, and FeO proportion in the iron oxide. If the initial reactants temperature increases 1℃, the liquid steel temperature increases 0.6℃. And If the additives proportion increases 1%, the liquid steel temperature decreases 25.7℃. In addition, the increase of FeO proportion in the iron oxide will lead to the decrease of liquid steel temperature. The reaction rate thermit reaction is affected by molten steel temperature, reactants particle size and particle size of additives. The higher the reaction temperature is, the faster the reaction rate is. If reactants particle size is appropriate, the reaction rate is the fastest. Larger or smaller reactants particle size can make the produced liquid substance penetrate the gap formed by welding powder fully, and results in the decrease of reaction rate. If the particle size of additives for 60 ~ 80 mesh, the additives can fill the reactants particle due to reduce the reaction rate and prolong the reaction time.Researches on sand mould show that the physical characteristics of sand mould are affected by raw materials and producing processes. Higher SiO2 mass fraction and lower mud mass fraction can improve the strength and refractoriness of sand mould. And higher amount of sodium silicate and compaction densities can improve the strength and refractoriness of sand mould as well. Drying temperature and holding time affect the strength of sand mould. The optimum drying process can be used for lower drying temperature with long time holding or higher drying temperature with short time holding. The concrete drying process should comprehensively consider the energy efficiency and time efficiency in the actual production situation. ZTK pouring system has good welding capabilities and joints performance, so it is recommended in thermit welding for large scale rails.Alumino-thermit welding powder with Ni and ZTK casting system are suitable for 75kg/mPG4 rail welding. The performance of welded joints as follows: the average tensile strength is 853MPa, static bending breaking load is 1759kN for rail head up and 1662kN for rail head down, physical fatigue is over two million cycles, and the hardness of weld metal is 334HB. So the joints are matched with 75kg/mPG4 hot-rolling rail steel.更多还原