TPT July 2016

T E CHNOLOG Y

Millimetre wave technology for measurement during manufacturing of large plastic tubes By Harald Sikora, director, Sikora Holding GmbH & Co KG

Millimetre wave technology for the measurement of large tubes Precise measurement of large tubes independent from environmental or material influences can be assured by the use of millimetre wave technology, introduced in this article. In recent years, enormous success regarding measuring accuracy has been achieved by researching metrological applications with frequencies in the millimetre wave range. Nevertheless, the results could not yet be used for the coating thickness measurement of cylindrical products. The newly developed millimetre wave technology creates the prerequisite for reliable measurement of the nominal size as well as the outer diameter, ovality and wall thickness of all kinds of extruded tubes. Without any knowledge of the properties of the extruded material and its temperatures, the system measures the outer contour as well as the wall thicknesses simultaneously at several positions of the circumference. Also, individual layer thicknesses of multi-layer tubes can be measured precisely. Thus, the system represents a key technology for future-orientated quality assurance in the production of large tubes. Measurement by millimetre wave technology is based on the FMCW runtime method. Several static or rotating transceivers, arranged around the circumference of a tube, continuously send and receive frequency modulated millimetre waves. From the runtime difference, the product dimensions are defined. Boundary layers, as for example each front and back site of a plastic tube, reflect these radio waves. The signals are detected and demodulated by the receiver of the transceiver. The signals contain information regarding the distance between boundary layers of different materials that means the inner and outer diameter, ovality, wall thicknesses and sagging. After an algorithmic processing of the received signals of each sensor, the requested measuring results are ready for visualisation and control of the diverse tube dimensions in real time. A

Introduction During the manufacture of plastic tubes with large diameters and wall thicknesses, product quality and the reduction of material costs have the highest priority. Norms and standards precisely define the minimum and maximum diameter and wall thicknesses of a tube dimension. In addition, the determination of sagging plays an important role. Due to standards and growing demands in tube extrusion, manufacturers use measuring and control devices for quality assurance in production lines. Sikora, in cooperation with the Fraunhofer Research Institute for High-frequency Physics and Radar Technology and the South German Institute for Plastics, has developed a new technology based on millimetre wave technology for precise non-contact online measurement of inner and outer diameter, ovality, wall thicknesses and sagging of large plastic tubes with a diameter larger than 120mm. The innovative concept of the measur- ing system adapts the characteristics of the extruded plastics and does not require any calibration by the operator. This new millimetre wave technology allows for an increase of product quality and ensures significant material and cost savings during extrusion. Dimension measurement of plastic tubes during extrusion Today, there are diverse technologies used for quality assurance during the productionof plastic tubes, suchas optical methods, eg lasers for determination of the diameter, or X-ray for the additional measurement of the concentricity and wall thicknesses. Conventional technologies such as ultrasonic also measure tube dimensions; however, they often reach their functional limits. An additional technology that is used for quality control works with terahertz impulse technique. This method uses a fibre laser that generates terahertz impulses directed at the measured object. From the reflected echoes striking the inner and outer boundary layers, the wall thickness is determined.

System for measuring diameter, ovality, thicknesses and sagging of large tubes

connected processor system takes the measured values and displays them numerically and graphically. It also includes comprehensive trending and statistical information. Millimetre wave technology for optimisation of tube quality, as well as time and cost savings As product temperatures have no influence on the measuring result when using millimetre wave technology, the system is installed for hot measurement as well as at the cold end of the line for final quality control. Directly after the first cooling, the Centerwave 6000 provides precise information about inner and outer diameter, ovality, wall thickness and in particular sagging. The millimetre wave technology selected for the measurement covers the entire range of plastics, such as PE, HDPE, PP, PA6, etc, as well as PVC. If we assume a line where tubes are produced with an outer diameter of 400mm and a wall thickness of 27.5mm, at a line speed of 0.5m/min, the machine operator receives accurate measuring results after around 10 to 30 minutes. In contrast, the measurement of plastic wall thicknesses with high temperatures via ultrasonic technology represents

46

www.read-tpt.com

J uly 2016