DETECTING ECCENTRIC TUBES
25 April 2001 - CSIRO

"If a tube has varying thickness then it may not meet the standard and it will have to be scrapped and resmelted."

"Or the tube has to be thicker to account for the variations. Either way this costs manufacturers money."

The Tube Eccentricity Measurement System is one of the technologies that will be on show at Hannover Fair in Germany from April 23 - 28, 2001.

The CSIRO Tube Eccentricity Measurement System can measure, on-line, the minimum wall thickness and its orientation. It is able to make a profile of the wall thickness and eccentricity along the length of each tube.

CSIRO researcher Dr Don Price says that the problem is that the process of extrusion, whereby a billet of hot metal is pierced by a long mandrel and extruded through a circular die, can produce eccentric tubes if the mandrel loses alignment with the cylindrical axis of the extruder and die.

"The inner surface of the tube is then not concentric with the outer surface, and the tube wall no longer has uniform thickness. Consequently, more material is required to maintain a specified minimum wall thickness," Dr Price says.

On-line eccentricity measurement allows extruder performance to be monitored, badly eccentric shells to be removed from the production process at an early stage and, ultimately, an understanding of the mechanisms leading to eccentric shell production to be gained.

"Thus it can lead to savings in material and energy, improved quality control, and a long-term understanding of process requirements," Dr Price says.

The Tube Eccentricity Measurement System allows measurements to be made either immediately following extrusion, or at a later stage of production. The system can be readily built to cater for various materials and sizes.

The system uses high frequency ultrasound to make measurements on a tube as it is moved through the measurement station. The present instrument makes approx. 100 measurements per second, but this rate can be varied.

Other features of the system are:

Fully automatic operation with no operator intervention required. The presence of a tube is detected and measurement started and completed automatically.
Provides a full-length profile of eccentricity, minimum wall thickness and orientation for each tube.
Controlled by LabView software on a standard personal computer. Can be readily adapted for specific measurement requirements.
Adaptable to other materials (metals, plastics, ceramics, composites) and sizes.
All measurements are made from outside the tube.
Ultrasound coupling is via recirculating water. Dry or non-contact coupling arrangements are possible.

http://www.csiro.au

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