连铸凝固坯壳厚度电涡流在线检测方法研究

Solidified shell thichness of continuous casting slab is an important parameter.It reflects the the rationality of continuous casting process， and it can give an important basis for optimization design of secondary coolingschedule. Currently domestic researches centre upon the indirect method which can work out the solidified shell thickness by the calculations of temperature fields . The method which can realize the shell thickness online non-destructive testing is still a problem needed to resolve. When phase transition from solid to liquid state there is sudden change in the magnetic conductivity and electrical conductivity in metal solidification process. This can be useed to research the electromagnetic field theory about thickness measurement of multilayered conductive structures and its application in the solidified shell thickness of continuous casting slab. The main contents are summarized as follows: According to the temperature distribution inside the slab , relationship between metal temperature and its magnetic properties, building the distribution model of magnetic conductivity and electrical conductivity in continuous casting slab by electromagnetic field simulation software .Building the electromagnetic field model of eddy current testing system and the deducing mathematical representation of output impedance by the electromagnetic parameters are highly nonlinea variation, its numerical solution will be given. Building the electromagnetic field model of eddy current testing system and the relationship between sensor's frequency of the excitation, output impedance and solidified shell thickness by the simulation datas and advanced modeling method such as particle swarm optimization, iterative algorithm,support vector machine regression,memory based classification algorithm etc.Doing optimizing design of sensor and validating the model by nail-shooting technique, it can provide an effective online detection means for the study of technological parameters. .

铸坯凝固坯壳厚度是连铸生产中一个重要参数，它反映了连铸工艺的合理性，并为二冷制度的优化设计提供重要依据。目前国内大量研究集中在通过温度场数值计算推算坯壳厚度。研究能够实现坯壳厚度在线无损检测的方法仍然是急需解决的问题。本项目利用金属凝固点及居里点处电磁特性的突变，研究多层导电结构厚度测量电磁场理论及其应用于凝固坯壳厚度测量的方法；根据铸坯内部温度分布及金属温度和电磁特性的关系，利用电磁场仿真软件建立坯内磁导率、电导率分布，推导多层导电结构中电磁参数非线性连续变化情况下的涡流传感器阻抗表达式并给出有限元数值解，基于仿真正问题数据及粒子群等寻优算法与迭代算法相结合、支持向量机回归、基于记忆的分类方法等先进建模方法获得传感器激励频率、阻抗特征与坯壳厚度的关系，实验验证该模型并进行传感优化设计。为研究工艺参数提供有效检测手段。

连铸凝固坯壳的电涡流反射信号特征无损表征了铸坯的表层组织、内部温度和铸坯壳厚度。研究凝固坯壳厚度检测可以有效控制轻压下、二冷配水及拉速，并最终提高铸坯的产品质量。课题组经过4年研究，在以下几个方面取得了研究成果。.1.依据连铸钢坯生产的实际状况，对结晶器内部出口处的凝固坯壳厚度进行了仿真研究。计算结果表明当拉速为2.5m/min、3.5m/min、4.5m/min时,50毫米厚度薄板结晶器出口处坯壳厚度的对应值分别是13.3mm、10.28 mm、8.87 mm。.2.根据液相线、固相线，将被测对象离散化分层，建立涡流探头仿真模型，确定了探头激励频率和内半径，对探头的外半径、厚度和匝数参数完成优化。.3.依据多频多参数检测原理，确定了提离影响最小的双频检测的两个频率；对凝固坯壳及固液两相层厚度的变化与探头阻抗及感应电压之间的关系进行研究；计算了坯壳及固液两相层总厚度20毫米范围内变化引起的输出变化。.4.仿真研究了互感差动探头，对它的脉冲响应进行了时频分析，选择了特征量进行厚度反演计算并给出了非线性拟合公式。利用自制探头、虚拟仪器及采集板卡搭建了脉冲激励及信号采集系统，完成了用铜铝复合板及不同钢叠加复合板替代坯壳的厚度测量冷态实验。.5.委托爱德森公司制作了互感式高温水冷涡流探头，利用单片机设计了一套可以对涡流探头进行混频激励、信号分解、数据采集的硬件系统。在定制加热炉中，惰性气体保护下进行了工件和传感器同时加热实验，由于水冷的影响，炉温1200摄氏度时工件及与其接触的传感器温度达到300摄氏度，传感器长期工作良好。.6.研究了钢坯表面温度800摄氏度的电磁超声洛伦兹力传感机理，优化了脉冲电磁铁及电磁超声横波传感器的参数。给出了800-1300℃横波速度随温度的变化曲线，根据被测对象内部温度场分布，得出坯壳内平均声速，利用回波时间与平均声速计算坯壳厚度。搭建高温连铸坯壳电磁超声测厚试验系统。由于实验环境无法达到实际炼钢条件1450℃以上，选择400℃的相似意义替代实验，用液态锡代替液态钢，验证了电磁超声横波法测连铸坯壳厚度是可行性，带有氧化铁皮的钢坯仍能进行电磁超声厚度测量。