Process and quality control with ultrasonics
The inline measurement of eccentricity and wall thickness on extrusion lines is standard practice today. Up to now, however, it was necessary to choose whether to focus on process monitoring or on quality control. Thanks to eccentricity and wall thickness testing using ultrasonic and continuous diameter measurement, it is now possible to monitor the production process with maximum accuracy and to inspect for quality at the highest level.
Using ultrasonic measurement systems, it is possible to monitor and adjust the eccentricity from the very first second regardless of the temperature of the material. As soon as the eccentricity is correct, the cable production process then turns to determining the average wall thickness in order to derive the minimum value. Measurements are performed upstream and downstream of the extruder for this. An additional measurement of the outside diameter at the end of the line enables integration of the cold diameter measured value, which allows the shrinkage to be determined.
Similar process challenges are confronted in pipe extrusion. At the start of production, the eccentricity of the pipe must be brought under control as fast as possible in order to be able to then adapt the wall thickness and the outside diameter. The use of ultrasonic and laser measuring technology guarantees cost-effective wall thickness optimisation and outside diameter control.
The control parameters:
• Screw speed (cable and pipe)
• Line speed (cable and pipe)
• Supporting air pressure (pipe)
• Vacuum (pipe)
• Centring of the extrusion head (cable and pipe)
Using the UMAC® ultrasonic measurement solution in combination with ODAC® laser scanners, the data of the collected parameters (eccentricity/concentricity, wall thickness, outside diameter, inside diameter) can be measured with maximum precision. As a result, all parameters relevant for the process and quality inspections are determined.
Ultrasonic Measurement Principle
It is based on the “Pulse-Echo” principle. A piezoelectric crystal is excited by a short electrical pulse. The crystal converts electrical energy into mechanical energy, i.e. sound waves. When the sound waves encounter a difference in the propagation medium (for instance when passing from water to a synthetic material), a part of them is reflected to the crystal (echo).
Main economic benefit of ultrasonic measurement:
• Amortisation within months (20-30% less expensive than X-ray measurement systems)
Main technical benefit of ultrasonic measurement:
• Measurement with up to eight measuring points on the circumference
Measurements of Insulations or Jackets on Cables
For the extrusion of cores or jackets the WALLMASTER system offers many possibilities thanks to its flexibility and ease of configuration. All parameters, thickness, eccentricity, diameter and ovality, can be monitored and controlled.
Wall Thickness and Diameter Control on Tubing and Hoses
Wall Thickness Measurement and Control During the Extrusion of Pipe up to 350mm (13.8 in.)
Scanners are available for measurement at the hot end or the cold end of the line. Optionally, also with integrated diameter.