【作者】 刘彦磊；

【导师】 米国发； 张斌；

【作者基本信息】 河南理工大学 ， 材料加工工程， 2009， 硕士

【摘要】 提速和重载是提高我国铁路运输能力的有效措施,并已成为铁路货车发展的趋势。速度和载重的提高对车轮质量提出了更高的要求。车轮是机车车辆的重要走行部件,车轮的可靠性关系到整个列车的运行安全。铸钢车轮因其工艺流程短,工艺简单,成本低廉,铸造精度高等优点,逐渐占据了国内货车市场上的一定空间,并呈增长的趋势。为了提高现有铸钢车轮的质量,满足提速重载的需要,本文利用计算机数值模拟技术,对铸钢车轮的生产过程进行模拟研究。结果表明,铸钢车轮在充型过程中,金属液填充比较平稳,没有出现飞溅和紊流现象。而在凝固过程中由于车轮截面尺寸变化比较大,在轮辋向辐板过渡的地方出现了一些缩松缩孔缺陷。究其原因是辐板上最薄部位的冷却速度较周围快,阻断了冒口处的液态金属向轮辋处补缩的通道。由于没有得到及时有效的补缩,在过渡的部位形成了缩松缩孔缺陷。为了消除这些缺陷,在车轮辐板的最薄部位施加一层保温材料,延缓其冷却速度,待轮辋部位凝固完全后再令其凝固,实现铸件的顺序凝固。结果显示,铸件的缺陷体积大大减少。而由于保温材料的特点,直接和铸件接触会造成铸件表面质量的严重下降,为此在保温材料和铸件之间隔一层5mm的砂,保温材料的厚度也由原来的8mm增加到10mm。铸件的缺陷虽略有增加但比原始工艺改进许多,铸件表面质量较好。对采用优化工艺实际生产的车轮产品进行显微组织和力学性能检验分析,其结果符合铁路行业标准的要求。车轮轮辋中的脆性夹杂物Al₂O₃是萌生轮辋裂纹的主要原因,而接触应力是裂纹扩展的动力。利用Hertz理论和Goodier方程,分析计算了轮轨接触应力和轮辋中夹杂物及空穴的应力集中系数,详细分析了裂纹萌生机制。并根据轮轨接触应力和Murakami公式,对不同深度处萌生裂纹的夹杂物临界尺寸进行了计算。将铸钢车轮的夹杂物状态和分布与辗钢车轮相比较得出:由于生产工艺的不同造成两种车轮夹杂物分布状态不同,铸钢车轮内部夹杂物的特点决定了其抗裂能力要优于辗钢车轮。并对减少车轮辋裂的发生提出几点意见。更多还原

【Abstract】 Speed increase and heavy haul of the railway freight car are the effective measures to raise the transport ability of railway, and they have been the development tendency of the railway freight car. The increase of the speed and axle load brings up more advanced requirement for wheels. Wheel is the important part of the rolling stock. The credibility of the wheel is related with the safety of the rolling stock.Cast-steel wheel for its short process flow, simple technology, low cost and high foundry accuracy, gradually occupied a certain space in the domestic truck market, and showed a growing trend. In order to increase the wheel quality and meet the requirement of speed increase and heavy haul, numerical simulation was employed to study the production process of cast-steel wheel. The results show that during mold filling, the molten metal filled stably and no splashing and turbulent flow. While during solidification process, because of the sectional dimension of wheel changed sharply, there appear some shrinkage defects in the transition location of wheel rim and web. The reason for this is that the cooling velocity of the thinnest part of web was faster than that of the surroundings, which blocked the feeding passage. Due to untimely and non-effectively feed to the transition location, the shrinkage defects was generated. For the purpose of eliminating these defects, insulation materials was used to slow down its cooling velocity and guarantee progressive solidification of casting. The simulation results indicated that the volume of shrinkage defects reduced greatly. It may cause the surface quality declined if the insulation material pasted the wheel web directly. So, a layer of sand with 5mm was appended between insulation material and casting, and the thickness of insulation material was increased from 8mm to 10mm. The defect was something of increase, but still reduced a lot than the original scheme did. Microstructure and mechanical properties inspections were proceeded on cast-steel wheel which produced by new production technology, and the dates are in line with the industry standard requirements.Brittle inclusion Al₂O₃ existed in wheel rim is the prime cause of initiating crack and contact stress is the power of crack propagation. Hertz theory and Goodier equation were used to analyze and calculate the wheel-rail contact stress and the stress concentration factor of inclusion and hole which existed in wheel rim. The crack initiation mechanism was analyzed in detail. According to wheel-rail contact stress and Murakami equation, the critical dimensions of inclusion which located in different depth and generated crack initiation were calculated. Comparing the distribution of inclusion in cast-steel wheel and rolled-steel wheel and conclude that different production technology make different inclusion distribution. The distribution features of inclusion in cast-steel wheel decide that its crack resistance is superior to that of rolled-steel wheel. And a few comments on reducing the occurrence of wheel-rim crack were put forward.更多还原