NDTnet 1998 Aug, Vol.3 No.8

Abstract

Various rollers are essential components for roll mills in steel works. It is therefore increasingly important to ensure defect free for their continued use under harsh load conditions. For some years, eddy current and ultrasonic testing have been applied to the detection of stress creaks and changed microstrusture of rollers which caused by service loads, with particular attention to automatic methods. Eddy current technique as an attractive tool is to be used for detection of the creak-like defects and softened points on surface, and ultrasonics as a sensitive method for volumetric inspection is also used to detect cold or hot rollers including subsurface area, integral working region as well as the combined layer with glass inclusions between the high alloying cast iron and the casting pig matrix of centrifugally casted composite roller to be used for hot rolling.

Nowadays, we have developed a series of these equipment to achieve on line inspection for a variety of rollers with emphasis on the following specific features:

1. Using roll grinder as on-site mechanism to detect the rollers during their periodically maintenance grinding. Use of contactless technique and the gap for transducers of both ET & UT can be automatically maintained to an optimum, adopting grinding fluid as couplant for UT.

2. Complete roller can be unfolded and be divided into around five hundred units on surface area, and also be allocated to several sections in deep direction. All acquisitive testing data would be recorded and stored in data bank in real time corresponding to each unit just after inspection scanning unit by unit. Finally, a defect-map can be established showing the location of flaws on X-Y coordinate plane and also in Z deepness.

3. With the development of advanced computer and data processing technologies, inspections and measurements were made under computer control and results can be automatically graded according to predetermined threshold levels in order to quantitatively display the layout of defects and its parameters such as peak value of defect signals, number of flaw points and their locations like "C-Scan" picture for each and every unit. All of these will greatly conduce to dissect the present qualitative status of inspected roller.

4. Some areas having suspicious signals would be manually inspected and applied FFT software package available to analyze the defect nature.

Recent application from these approaches has obtained active results. By means of periodic inspections and predictions the service life of rollers are extended and even some catastrophic failure could be prevented.

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:

Publication Contact:
7th ECNDT, Park Alle 345, DK-2605 Broendby, Denmark, Fax: +45 46 26 70 11, Email: 101373.3414@compuserve.com