连铸坯表面裂纹缺陷分析

连铸坯质量缺陷中约70%为连铸坯裂纹缺陷。为此,对连铸坯表面裂纹缺陷进行取样分析,明确了连铸坯表面裂纹缺陷的形成原因是一冷水强度大,冷却速度快,冷却不均匀。     

红外热像测温技术对二冷区冷却均匀性的研究

铸坯表面温度是连铸过程中的一个重要参数。通过红外热像仪对某钢厂的连铸二冷区出口处的铸坯表面温度进行了测量,并利用图像处理技术对测温的红外图像进行了处理,得到了铸坯表面温度的三维图像。分析了三维图像与质量统计数据,结果表明:铸坯纵裂纹位置表面横向温差较大,达到120℃;板坯表面温度梯度最大值的位置与实际板坯对应的纵裂纹位置误差10~200 mm。     

2006年中国金属学会轧钢会议计划

俄罗斯NLMK公司在其新利佩茨克钢铁公司2000珊热轧宽带钢轧机上成功安装了1台带钢表面自动检测系统。该系统能对连铸坯缺陷进行准确探测，从而减少了由此产生的轧制缺陷，进而可减少材料损耗，提高成材率。当前该系统与跟踪系统集合在一起并有效用于冷轧带钢生产中。     

基于Ansys的焊缝缺陷电磁激励红外无损检测

应用Ansys大型有限元分析软件建立试件和线圈模型,改变所检测的材料,构建不同形状的线圈,通过红外热像仪捕捉试件表面的温度变化,得到表面温度分布云图,通过该温度分布是否均匀来推断试件(近)表面是否存在缺陷,从而得到缺陷可检测性的判定。着重研究了试件材料、线圈形状与温度分布之间的关系,从而对平板对接焊缝缺陷的电磁激励红外热像无损检测提供了参考依据。     

重钢连铸板坯表面缺陷在线检测技术的开发与应用

<正>北京科技大学与重钢联合开发了连铸板坯表面缺陷在线检测技术,该技术可用于在线检测1 000℃以上高温连铸坯的表面缺陷,对于连铸坯表面质量问题的及时反馈具有重要意义,可为高温坯热装热送工艺提供技术保障。其主要内容与创新点如下:(1)采用机器视觉检测技术,研制了国际上首套应用于高温连铸坯的表面缺陷在线检测系统。系统     

连铸圆坯表面气孔缺陷的分析

国内连铸圆坯大多采用“转炉＋LF炉”或采用生产节奏较快的“电炉＋LF炉”生产．有时发现连铸圆坯存在一种表面气孔缺陷,其形态特征与铸坯常见的表面针孔、皮下气泡和内部气孔有明显的不同。简要分析了这种连铸圆坯表面气孔缺陷产生的机理和表现特征,据此提出了控制连铸圆坯表面气孔缺陷产生的措施。     

中碳结构钢表面纵裂纹产生原因分析与改善措施

介绍了本钢特钢采用235mm×265mm连铸坯生产的40Cr、40CrMn等钢种,生产(100～130)mm过程出现批量纵裂纹缺陷;研究了钢材、连铸坯裂纹形成机制,明确了钢材纵裂纹是由于连铸过程二冷水冷却不均匀,连铸坯产生皮下裂纹,加热后皮下裂纹扩展到表面所致;得出了通过改善水质,防止喷嘴堵塞,加强连铸坯缓冷,降低加热炉预热段温度等技术措施,可有效控制铸坯裂纹,解决了钢材纵裂纹缺陷。     

主动红外热像无损检测技术的研究现状与进展

与渗透、磁粉、射线等传统无损检测技术相比,主动红外热像技术具有非接触、无污染、高效率等优点,已成为一种重要的材料表面和近表面缺陷无损检测技术,该技术包括主动热激励、表面热图采集和图像处理3个步骤。对热灯、超声波、电磁线圈、微波、激光等几种主要热激励手段进行了对比分析,分别总结了其特点、适用范围及研究应用现状;热图采集效果主要取决于红外热像仪的性能高低;图像处理依靠各种图像处理软件进行,当前应用于红外热像检测中的图像处理方法有背景减去、噪声去除、时间平均等。随着热激励技术和图像处理技术的发展,以及红外热像仪性能的提高,主动红外热像无损检测技术也呈现出由人工识别向自动识别、由定性检测向定量检测、由单一手段向复合手段发展的趋势。     

小方坯连铸结晶器横向曲面模拟优化设计

针对实际连铸生产过程中连铸坯偏角部热点区容易产生表面凹陷等缺陷问题,根据连铸过程凝固规律研究与实际漏钢坯壳测量分析建立了小方坯传热数学模型。采用有限元软件ANSYS模拟计算了不同结晶器横向曲面设计下结晶器内坯壳温度场、应力场以及坯壳厚度分布。结果表明:在结晶器偏角部位设置具有部分横向曲面的结晶器,能在有效消除铸坯偏角部表面凹陷的同时不会增加角部裂纹产生机率,为最优设计方案。     

应用Fluent对40Cr管坯水平连铸过程中温度场及传热的研究

以水平连铸40Cr圆坯结晶器内温度场分布为研究对象,采用Fluent数值模拟软件凝固传热模型并结合射钉试验共同研究了管坯在不同拉坯工艺条件下,结晶器内40Cr钢液温度场分布及凝固传热过程,并对不同拉坯参数下铸坯试样进行了检测分析.分析结果表明:水平连铸拉坯工艺参数:拉速V=2.35 m/min,浇注温度T=1540℃,中间包过热度△T=36℃的拉坯参数下,结晶器内的温度场分布均匀稳定,铸坯质量好,产量高.采用Fluent数值模拟软件凝固传热模型并结合射钉试验可以有效地分析在不同拉坯工艺条件下水平连铸结晶器内的温度场分布及凝固传热过程,制定合理的拉坯工艺参数,减少管坯缺陷的发生,提高铸坯质量.     

高温压力管道红外热成像检测技术

建立了大型管道试验装置，并对带有不同几何尺寸内部开孔缺陷的四种不锈钢和20钢管进行了红外热成像检测试验。结果表明，红外热成像技术十分适用于检测高温压力管道内部腐蚀缺陷，检测灵敏度能够满足压力管道安全运行的要求。     

高强度钢压力容器疲劳锻练的热图研究SCIEI

用红外热成像系统实时监测了高强度压力容器在工作压力下的疲劳打压过程．在疲劳循环初始由热图获得的ＩＲＣＥ效应，可以确定压力容器的应力集中区域。打压泄漏的位置证明，由热图测定应力集中区域是可行的。实验发现压力容器疲劳软化和硬化效应，采用Ｇｌｏｇａｌ座标对筒状薄壁压力容器的应力分布计算表明，热图和计算的结果是吻合的。实验证明，在工作压力下的疲劳锻练效应将会延长压力容器的使用寿命。     

红外热波检测中热像信号重建引起的伪缺陷现象

在脉冲热激励红外热波检测中,热像信号重建技术（TSR）常用来分析和处理试验结果。该方法的特色是可以增加热像序列的空间和时间分辨率,提高信噪比,减少数据量。同时,该方法还能消除某些伪缺陷的干扰,比如脉冲闪光灯和热像仪镜头的反射所带来的伪缺陷。但是TSR是基于对温度变化曲线进行多项式曲线拟合的,而多项式曲线拟合中,拟合阶数和数据长度对拟合结果影响较大,在某些情况下可能会产生伪缺陷。阐述了热波数据重建技术原理,并以试件表面处于热不平衡状态和表面不均匀进行试验的结果来分析由于数据重建技术所产生的伪缺陷。     

Infrared thermography for inspecting the adhesion integrity of plastic welded joints

This work aim at developing a non-destructive tool for the evaluation of bonded plastic joints. The paper examines infrared thermographic transmission and reflection mode imaging and validates the feasibility of the thermal NDT approach for this application. Results demonstrate good estimation performance for adhesion integrity, uniformity and bond strength using a transmission mode application of infrared thermography. In addition, results from a pulsed infrared thermographic application using a modified dynamic infrared tomography scheme show good performance for estimating adhesion layer thickness mapping and detecting delaminations.     

Infrared thermography processing based on higher-order statistics

Active thermography has reached a high status as a non-destructive evaluation method due to both ease and speed of inspection. Nevertheless, automatic processing of an infrared (IR) sequence is essential in order to reduce human intervention. Unfortunately, this target is difficult to achieve given the amount of data recorded by the IR camera during a typical inspection process and human participation is absolutely necessary. In this paper, higher-order statistics (HOS) analysis is employed to process IR sequences and to compress the most useful information into a unique image for each inspection. Pulsed infrared thermographic temporal response is well-known with a statistical behaviour. This statistical behaviour is analyzed and the results of its application to carbon fibres reinforced plastic (CFRP) samples are reported.     

Thermography-Based Investigation into Thermally Induced Positioning Errors of Feed Drives By Example of a Ball Screw

The following paper presents a method, based on thermographic measurements, to calculate the thermally induced positioning errors of feed drives in machine tools, here described with the example of a ball screw drive. Especially the effect of an uneven temperature distribution in the components on the total deformation is examined in this method. A transformation between the 3-D object space and the 2-D image space was created by means of digital image processing and photogrammetry as well as defined reference points on the structure of the feed drive with the surrounding machine components. The transformation enables the necessary identification of the defined structure points in the thermographic picture. With the help of the temperature information contained in the thermographic images, the respective thermally induced errors can then be calculated depending on the respective axial position by means of a temperature deformation model.     

Frictional heating model for efficient use of vibrothermography

This paper investigates vibrothermography for the detection of fatigue cracks in steel compact tension specimens using combined experimental and numerical analyses. First, a numerical modal analysis is carried out to predict the optimal excitation parameters. A coupled thermo-mechanical model is then built to simulate the thermographic inspection. The model predicts the detection of cracks as short as 0.1 mm that is also confirmed experimentally using a commercial infrared camera with a maximum error of 2.13% on the temperature distribution. The model reveals that the specimens’ temperature increases at the crack vicinity according to the excitation frequency and is modulated due to the nonlinearity induced by the crack. The model also shows that the stress at the crack tip is lower than the material's yield stress, which makes the test truly non-destructive.     

Defect detection in aircraft composites by using a neural approach in the analysis of thermographic images

Safety in aeronautics could be improved if continuous checks were guaranteed during the in-service inspection of aircraft. However, until now, the maintenance costs of so doing have proved prohibitive. For this reason there is a great interest for the development of low cost non-destructive inspection techniques that can be applied during normal routine tests. The analysis of the internal defects (not detectable by a visual inspection) of the aircraft composite materials is a difficult task unless invasive techniques are applied. In this paper, we have addressed the problem of inspecting composite materials by using automatic analysis of thermographic techniques. The analysis of the time/space variations in a sequence of thermographic images allows the identification of internal defects in composite materials that otherwise could not be detected. A neural network was trained to extract the information that characterises a range of internal defects in different types of composite materials. After the training phase the same neural network was applied to all the points of a sequence of thermographic images. The experimental results demonstrate the ability of the method to recognize regions containing defects but also to identify the contour regions that cannot be associated either with a defective or with a sound region.     

蜂窝夹层结构胶接面树脂堆积的红外热像检测

为了研究树脂堆积的红外热像检测问题,文章进行了一维模型建模分析、蜂窝夹层结构样件试验验证和解剖分析。研究发现树脂堆积区域在脉冲加热后的原始热图中表现为"暗区"或"暗斑",并且这些区域的表面温度低于正常胶层厚度区域的表面温度,得出了树脂堆积可以在红外热像检测中被检出的结论。通常树脂堆积不是一种缺陷,但是对蜂窝夹层结构胶接面树脂堆积进行检测却具有重要的现实意义。判断树脂堆积区域的位置、形状和面积,将有助于改进生产工艺。对这些区域进行识别、记录和存档,可以为原位检测蜂窝积水问题提供评定的依据。     

缺陷深度脉冲热像检测新方法

介绍脉冲热像检测中由峰值时间求缺陷深度的方法，对热传导性能好的材料，从红外热像时间序列难以捕捉到峰值时间。为此提出了一个既能避开峰值时间又能被红外热像仪探测和记录的新参数，从而达到测量缺陷深度的目的。