Terahertz inline wall thickness monitoring system for plastic pipe extrusion

Journal Article · Thu May 15 00:00:00 EDT 2014 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.4873740· OSTI ID:22271002

Hauck, J., E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail]; Stich, D., E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail]; Heidemeyer, P., E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail]; Bastian, M., E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail]; Hochrein, T., E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail], E-mail: [e-mail] ^[1]

---

1. SKZ - German Plastics Center, Wuerzburg (Germany)

Conventional and commercially available inline wall thickness monitoring systems for pipe extrusion are usually based on ultrasonic or x-ray technology. Disadvantages of ultrasonic systems are the usual need of water as a coupling media and the high damping in thick walled or foamed pipes. For x-ray systems special safety requirements have to be taken into account because of the ionizing radiation. The terahertz (THz) technology offers a novel approach to solve these problems. THz waves have many properties which are suitable for the non-destructive testing of plastics. The absorption of electrical isolators is typically very low and the radiation is non-ionizing in comparison to x-rays. Through the electromagnetic origin of the THz waves they can be used for contact free measurements. Foams show a much lower absorption in contrast to acoustic waves. The developed system uses THz pulses which are generated by stimulating photoconductive switches with femtosecond laser pulses. The time of flight of THz pulses can be determined with a resolution in the magnitude of several ten femtoseconds. Hence the thickness of an object like plastic pipes can be determined with a high accuracy by measuring the time delay between two reflections on materials interfaces e.g. at the pipe's inner and outer surface, similar to the ultrasonic technique. Knowing the refractive index of the sample the absolute layer thickness from the transit time difference can be calculated easily. This method in principle also allows the measurement of multilayer systems and the characterization of foamed pipes.

• OSTI ID: 22271002
• Journal Information: AIP Conference Proceedings, Vol. 1593, Issue 1; Conference: PPS-29: 29. international conference of the Polymer Processing Society, Nuremberg (Germany), 15-19 Jul 2013; Other Information: (c) 2014 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
42 ENGINEERING
COMPARATIVE EVALUATIONS
EXTRUSION
FOAMS
INTERFACES
LASER RADIATION
LAYERS
NONDESTRUCTIVE TESTING
PIPES
PLASTICS
REFRACTIVE INDEX
THICKNESS
THZ RANGE
TIME DELAY
X RADIATION