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首页> 外文会议>Thermosense: thermal infrared applications XXXVI >Center crack detection during continuous casting of aluminum by laser ultrasonic measurements
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Center crack detection during continuous casting of aluminum by laser ultrasonic measurements

机译：通过激光超声测量铝连续铸造过程中的中心裂纹检测

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摘要

Crack detection during continuous direct chill casting of aluminum is a matter of economics. Determining cracks during production process saves money, energy and raw material. Of course, a non-destructive method is required for this evaluation. Because of temperature concerns conventional ultrasound is not applicable. One non-contact alternative is laser ultrasonics. In laser ultrasonics short laser pulses illuminate the sample. The electromagnetic energy gets absorbed at the surface of the sample and results in local heating followed by expansion. Thereby broadband ultrasonic waves are launched which propagate through the sample and get back reflected or scattered at interfaces (cracks, blowholes,...) like conventional ultrasonic waves. Therefore laser ultrasonics is an alternative thermal infrared technology. By using an interferometer also the detection of the ultrasonic waves at the sample surface is done in a remote manner. During preliminary examinations in the lab by scanning different aluminum studs it was able to distinguish between studs with and without cracks. The prediction of the dimension of the crack by evaluation of the damping of the broadband ultrasonic waves was possible. With simple image reconstruction methods one can localize the crack and give an estimation of its extent and even its shape. Subsequent first measurements using this laser ultrasonic setup during the continuous casting of aluminum were carried out and showed the proof of principle in an industrial environment with elevated temperatures, dust, cooling water and vibrations.
机译：连续直接冷铸铝时的裂纹检测是经济问题。在生产过程中确定裂缝可以节省金钱，能源和原材料。当然，此评估需要使用非破坏性方法。由于温度问题，常规超声不适用。一种非接触式替代方法是激光超声。在激光超声中，短脉冲会照亮样品。电磁能在样品表面被吸收并导致局部加热，然后膨胀。因此，发射宽带超声波，该宽带超声波传播通过样品，并像常规超声波一样在界面（裂缝，气孔等）处反射或散射回去。因此，激光超声是替代性的热红外技术。通过使用干涉仪，还可以远程完成对样品表面超声波的检测。在实验室进行初步检查时，通过扫描不同的铝制螺柱，可以区分有无裂纹的螺柱。通过评估宽带超声波的阻尼来预测裂纹的尺寸是可能的。使用简单的图像重建方法，可以定位裂纹并估计其范围甚至形状。随后在铝的连续铸造过程中使用此激光超声装置进行了首次测量，并显示了在工业环境中温度，灰尘，冷却水和振动升高的原理证明。

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