NDTnet 1998 Aug, Vol.3 No.8

Abstract

Based on experience from our previous development of a tube inspection system a project was formulated from an aluminum tube manufacturer (HYDRO ALUMINUM) to investigate the possibility for on-line measurement and presentation of eccentricity values of aluminum tubes during the drawing process at drawing velocities up to 60 km per hour. The diameter was 4 to 25 mm and the wall thickness 0.2 to 4 mm.

Results.
Ultrasonic pulse echo scanning technique was selected for the job. The accuracy in ultrasonic dimension measurement (Time Of Flight) is reasonable for the demands, but the measuring conditions demanded evaluation work for optimizing the technique and measuring conditions. The eccentricity is calculated from 4 wall thickness' measured simultaneously 90° apart. The main optimization problems, that had to be solved, are listed in the following.

Coupling media and transducer frequency. To avoid water on the tubes different other coupling fluids (oil, petrol, alcohol) were tested, but the wanted measuring accuracy (5 pm for the wall thickness) demanded rather high transducer frequency, and therefore water was chosen due to the lower damping of the ultrasonic signal.

Guidance (positioning and vibration) and water jet coupling. Precise guidance of the transducer relative to the tube are necessary for wall thickness measurement on small diameter tubes. A special water chamber with the 4 transducers were developed. The water chamber also comprise a water jet system, which proved necessary to ovoid oil contamination of the transducer surface.

Evaluation and calibration. A computer program was made for collecting, showing, storing and evaluating of the results both directly during manufacturing and a statistical afterwards for the whole coil. Calibration procedures inclusive hard- and software were suggested for both static and dynamic calibration of the wall thickness measurements.

Conclusion.
The project demonstrated that it is possible to measure and evaluate eccentricity of aluminum tubes at drawing velocities around 25 km per hour comparable with the normally used drawing velocities. Not all demands regarding small diameter tubes and thin wall were tested, and the calibration procedures were not finalized, when the project was stopped due to other demands in the aluminum tube marked, but hopefully our results could be valuable for others.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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