Extrusion Asia Edition 3-2016

于会改变超声波的传播方向，因而也不适于采用超声波进行 检测。超声测量通常通过水浴的方式来实现，因为需要采用 水作为传输声音的耦合介质。由于用于计算偏心率的超声波 的传播速度取决于温度和材料，因而需要进行精确的温度补 偿以获得可靠的测量数值，故该技术的使用过程中校准是必 须的。此外，壁厚的估算通常仅可能通过将超声波测量技术 与称重系统组合来实现。 X 射线测量技术 X射线技术基于影像分析技术，不需要适应材料，并且无需任 何耦合介质。由于不受材料温度的影响，因而该X射线测量装 置可以直接集成到挤出生产线中而无需其他改造，且无需校 准。该系统可以直接安装在挤出机之后（热端测量）或在生 产线末端（最终品质控制）。通过采用4点的在线测量，该装 置就可以得到被测物体的壁厚、偏心率、内径和外径以及椭 圆度的测量值。该系统最多可测量三层不同材料结构的被测 物，能够将测量值以数字化和图形化的形式，以管材横断面 的方式进行实时显示，为用户对挤出模具进行完美调中提供 保障。另外，为能达到最高的效率，该系统还可对生产线速 度或挤出机转速进行自动反馈控制，将厚度参数控制在最小 值。这样，一方面管材的品质得到了保障，而另一方面，对 最小值的控制还能确保材料的最佳消耗。 该X射线测量技术 适用于直径从0.65到270 mm的产品。对X射线设备安全性的 顾虑是不必要的，因为辐射大小并不取决于射线能量高低。 实际上，一个人从纽约飞到法兰克福会受到更多的辐射。 应用于大规格管道的测量技术 以上的大规格管道（如在建筑及服务领域）的尺寸测量，上 述测量技术也可进行应用。然而，在考虑到功能（超声波） 及成本的限制、测量范围及对圆周上的测量点的限制（X 射 线）、或对于激光技术只能受限于进行外径测量等方面的因 素来说，这些技术的应用已经达到它们的极限。目前正在测 试用于管材品质控制的另一种技术，该技术采用了太赫兹脉 冲，用以激发指向材料的大功率光纤激光，并通过来自内、 外边界层的反射回波来确定产品壁厚。然而，用于测量较大 壁厚度和高阻尼材料（如 PVC）的技术的应用是受限的。此 外，所采用的激光器的持久性也是有限的并且成本较高。 typically only possible by combining the ultrasonic technique with an additional gravimetric system. X-ray technology The X-ray technology is based on an imaging principle. The X- ray technology does not require an adaptation to materials and no coupling medium is needed. The technology is independent of the temperature of the material, what makes it possible to integrate an X-ray measuring device directly into an extrusion line without any additional efforts. A calibration is not necessa- ry. The system is either installed directly after the extruder (hot measurement) or at the end of the line (final quality control). With a 4-point online measurement, the measuring values for the wall thickness, the eccentricity, the inner and outer diame- ter and the ovality are determined by one device. The system measures up to three different material layers. These measuring values are visualized numerically and graphically in the form of the tube/pipe cross section in real-time and enable the user to perfectly center the extrusion tool. Important for highest effi- ciency is the automatic control of the line speed or extruder rpm while considering the minimal values. Thus, the quality of the hose is ensured. On the other hand, the control to the mi- nimal values ensures that only the needed material is used. X- ray technology is available for products with a diameter from 0.65 to 270 mm. Concerns on the safety of X-ray devices are arbitrary, as the radiation is because of the low energy of no re- levance. Practically, a human is exposed to a much higher radia- tion on a flight from New York to Frankfurt. Technologies for the measurement of large plastic pipes For the dimension measurement of large plastic pipes starting at a diameter from 120 mm, as they are found in the building and service area, the above-described technologies can be used. Nevertheless, these technologies reach their limits either functionally (ultrasound) as well as regarding the costs, the limi- ted measuring range and number of measuring points on the circumference (X-ray) or the limitation in the measurement of the diameter only (laser). A further technology for the quality control is currently tested. It uses terahertz pulses, which acti- vate a powerful fiber laser that is aimed at the material. The wall thickness is determined by means of the reflected echoes from the inner and outer boundary layers. The usage of this technology for the measurement of larger wall thicknesses and materials with a high damping, as for example PVC, are how- ever limited. Furthermore, the durability of the laser is limited and the costs are very high. Millimeter waves technology An innovative, significantly less expensive technology for the di- mension measurement and recording of the sagging is the ra- dar technology FMCW (Frequency Modulated Continuous Waves). These systems work within the sub-terahertz range and are already used for some time in the automotive techno- logy for distance measurement. They are based on semiconduc- tor technology, are inexpensive and practically not limited re- garding their lifespan. Within the chosen area from 80 to 300 GHz all plastic materials are penetrated with low absorption and thus, the wall thickness is measured. One or two con- 图 4：安装于管材挤出生产线上的X射线测量系统 Image 4: X-ray measuring system installed in a hose extrusi- on line 34 测量 Extrusion Asia Edition 3/2016