【作者】 石德全；

【导师】 李大勇；

【作者基本信息】 哈尔滨理工大学 ， 测试计量技术及仪器， 2007， 博士

【摘要】 表面张力是液态合金重要的物性参数,它不仅是研究界面反应动力学的基础,而且在金属凝固过程和铸造合金参数的预测中起着重要作用,因此,研究液态合金表面张力的快速检测方法具有重要的理论价值和实际意义,然而,目前绝大多数方法都不能够真正实现液态合金表面张力的炉前快速检测。本文在研究表面张力快速检测新方法的基础上,研制适合于炉前快速检测的表面张力检测仪,并研究评价液态合金相关质量参数的新方法。研究内容主要包括液态合金表面张力理论分析及快速检测新方法的研究,炉前当量表面张力快速检测仪的研制和求解当量表面张力数学模型的建立,铸铁石墨形态、铝硅合金变质处理效果、液态合金充型潜力等质量参数快速评价的方法研究及相应评价模型的建立。研究结果表明,基于新方法的当量表面张力快速检测仪可在炉前快速测得液态合金的当量表面张力,并实时给出相应质量参数的非浇注性评价。通过分析最大气泡压力法检测表面张力的原理和过程,认为精确测定毛细管插入液面的深度和严格控制吹出气泡的速度是气泡最大压力法检测表面张力的关键,在此基础上,系统研究了检测液态合金表面张力的新方法——气泡幅频当量法实施过程中的具体问题,为实现表面张力的快速检测奠定了技术基础。通过对气泡压力曲线影响因素的分析和试验研究,确定了求解当量表面张力的基本信息参数和基本数学模型,且毛细管内径为1.8-2.2mm、外径3.5-4.0mm、端口磨平、开口向上,出泡速度控制在每秒2-3个气泡,插入液体深度在可10-20mm内变化。基于新方法研制了当量表面张力炉前快速检测仪,它采用电控电动方式工作,可在10秒钟内测得液态合金的当量表面张力和温度值。分析了信息参数的高精度检测方法,由于毛细管探头属一次性消耗品,设计的自动升降和锁紧机构可方便的锁紧/松开探头和驱动探头上下平稳运动。通过大量实验,建立了当量表面张力的求解模型,将该求解模型固化于机内后,表面张力快速检测仪炉前检测液态合金当量表面张力准确度为:绝对误差≤±15.0mN/m,相对误差≤3.0%,温度的准度度为:铸铁≤±2.5℃,铝硅合金≤±1℃。根据晶体生长理论和相间张力理论分析了铸铁凝固过程中石墨形态与表面张力的变化,表明它们之间确实存在着一定的关系,完善了表面张力评价铸铁石墨形态的理论基础。实验室条件下,通过对铸铁大量试验研究,建立了当量表面张力评价铸铁石墨形态的评价模型,即:当量表面张力σe≤990mN/m时,石墨形态为完全的片状;当990≤σe≤1108mN/m时,为片状石墨和蠕虫状石墨共存;当1108≤σe≤1283mN/m时,为大量的蠕虫状石墨和少量的球状石墨共存;当1283≤σe≤1385mN/m时,为大量的球状石墨和少量的蠕虫状石墨共存;当σe≥1385mN/m时,为完全的球状石墨。该模型的准确度高于95%。从理论上分析了表面张力评价铝硅合金变质处理效果的可行性,并从试验上证实:变质剂是引起铝硅合金当量表面张力变化的主要因素,而温度对当量表面张力的影响较小。通过二元共晶铝硅合金的大量炉前实验,建立了当量表面张力快速评价铝硅合金变质处理效果的模型,即:当量表面张力σe≥530mN/m时,变质处理效果为变质不足,包括未变质和部分变质,相当于AFS的1-2级;当400≤σe≤530mN/m时,为变质中等,相当于AFS的3-4级;当σe≤400mN/m时,为变质完全,相当于AFS的5-6级。实验证明,该模型的准确度达到96%以上。通过合金停止流动通用模型的分析可知:表面张力与液态合金充潜力(包括充型长度和充填尖角能力)之间存在着固定的关系,且在铸型条件、浇注条件和铸型(铸件)结构等不变的前提下,可以用液态合金的当量表面张力预测充型潜力的大小。为了测试液态合金的充型潜力,改进了评价液态合金充型长度的装置,保证浇注温度和静压头压力恒定不变;设计了评价液态合金充填尖角能力的新装置,并提出了相应的评价参数和计算方法。分别以HT200和ZL102为例,建立了液态合金当量表面张力与充型长度和充填尖角能力的关系,为了提高测试精度,测试仪采用查表方法来预测液态合金的充型能力,其充型长度预测结果的绝对误差≤±10mm,充填尖角能力≤±3mm-1。更多还原

【Abstract】 Surface tension is one of the important physicochemical features of the molten alloy. Not only is it the foundation of studying the interface reaction dynamics of the molten alloy, but also plays very important roles in metal solidification process and forecasting parameters of the casting alloy, such as fining and inoculating effect, gas isolation, graphite shape, modification effect, filling mould ability and surface roughness of castings and so on. Therefore, it has very important theoretical value and practical significance to study and test surface tension of the molten alloy. Although many methods had been developed, they cannot fit for fast testing surface tension of the molten alloy in front of the furnace. On the basis of studying new method for testing surface tension, a apparatus of fast testing equivalent surface tension in front of furnace has been developed and new methods for evaluating quality parameters of the molten alloy has been put forward. The research includes theoretical analysis of surface tension and experimental studying of the new testing method, the development of the apparatus and establishment of the model of calculating equivalent surface tension, methods and models of evaluating graphite shape, modification effect, mold-filling potential in front of furnace by equivalent surface tension. The investigation results have proved that the apparatus based on the new testing method can fast test equivalent surface tension of the molten alloy in front of furnace and can fast evaluate the quality parameters before casting.Through further analyzing the principle and testing process of maximum bubble pressure method, it can be concluded the dipping depth of capillary must be measured exactly and the rate of gas blowing out must be slow, so, it can not fit for fast testing surface tension. Consequently, a new method, Amplitude and Frequency Equivalent of Bubble Method, for fast testing equivalent surface tension can be studied synthetically by author, which establishes the technology foundation of fast testing equivalent surface tension of the molten alloy in front of furnace. On the basis of analyzing and experimentally studying the affecting factors of bubble pressure curve, information parameters and mathematical model form have been determined and the requirements of capillary are that inner diameter of capillary is 1.8-2.2mm, outer diameter is 3.5-4.0mm, the rate of blowing out bubbles is 2-3 per second and the dipping depth can be alter at 10-20mm.Equivalent surface tension and temperature of the molten alloy can be tested in 10 seconds by the apparatus that had been developed based on the new method and the high precision methods of testing the information parameters ahd been studied by author. Because the capillary is one-off, a special mechanism is designed to carry out the functions of crimpling detector automatically and driving detector forward or backward. By experiments the model calculating equivalent surface tension has been obtained and programmed in the computer, and it has been testified that the absolute error and relative error of testing equivalent surface tension are below±15.0mN/m, 3.0% respectively, and that the absolute errors of testing temperature are cast iron≤±2.5℃, Al-Si alloy≤±1℃.According to crystal growth theory and interfacial tension theory, the relationship between graphite shape and surface tension has been analyzed and it really exists, which supplies the theoretical foundations of evaluating graphite shape by surface tension. The model evaluating graphite shape has been got by many experiments on cast iron, namely,σe≤990mN/m, graphite shape is complete flake; 990≤σe≤1108mN/m, flake and vermicular; 1108≤σe≤1283mN/m, many vermicular and little nodular; 1283≤σe≤1385mN/m, many nodular and little vermicular;σe≥1385mN/m, complete nodular. The accuracy of evaluating results is higher than 95%.Feasibility of evaluating modification effect by surface tension of Al-Si alloy has been analyzed theoretically; experiments have proved that modifier content is the major factor of varying equivalent surface tension and that temperature effect on equivalent surface tension is faint. The model of evaluating modification effect in front of furnace has been achieved through experiments on binary eutectic Al-Si alloys, namely,σe≥530mN/m, under modification, including unmodified and partial modification, equals AFS1-2; 400≤σe≤530mN/m, moderate modification, equals AFS3-4;σe≤400mN/m, perfect modification, equals AFS5-6. The accuracy of evaluating results is higher than 96%. Through analyzing the general model of alloy Cessation flow, the relationship between mold-filling potential, including the length of filling mold and the ability of filling taper angle, and surface tension really exists and when mold conditions, pouring conditions and casting structure kept invariable mold-filling potential can be evaluated by equivalent surface tension. The device measuring the length of filling mold has been improved to keep the pouring temperature and static pressure constant and the new device measuring the ability of filling taper angle has been developed and its parameter has been put forward. Took as examples of HT200 and ZL102, the practical relationship between the length of filling mold, the ability of filling taper angle and equivalent surface tension has been found and mold-filling potential can been evaluated by equivalent surface tension by means of table lookup. The absolute errors oft he length of filling mold and the ability of filling taper angle are below±10mm and±3mm-1 respectively.更多还原