Automatic surface inspection for steel strip with temperatures of more than 800°C

Citation

(1998), "Automatic surface inspection for steel strip with temperatures of more than 800°C", Sensor Review, Vol. 18 No. 4. https://doi.org/10.1108/sr.1998.08718daf.008

Automatic surface inspection for steel strip with temperatures of more than 800°C

Automatic surface inspection for steel strip with temperatures of more than 800°C

Parsytec HTS-2W ­ the first hot strip inspection with automatic defect classificationParsytec HTS-2W is the world's first surface inspection system for hot mills which makes an automatic defect detection and classification over the entire strip surface possible. This has been achieved by the combination of neural software processes with standard PC and CCD camera components, as well as lighting techniques that have been specifically developed for hot mill inspection.

Early in 1998, Parsytec proved the efficiency of its hot strip inspection system in field tests at a leading steel strip manufacturer. Since then, within a two month period, orders for five Parsytec HTS-2W systems have been placed with Parsytec. The systems will be installed in two CSP plants (Compact Strip Production) in Germany and the USA, as well as in three conventional hot mills in Europe.

In addition to the goal of avoiding equipment damage, strip ruptures and further processing of flawed material, the use of the system strives for the optimization of the entire production process thus increasing productivity and product quality.

The detection and classification of surface defects is of great importance already in the early process phase of hot strip production, since defects occurring at the early stage persist during further processing and reduce the strip quality. Furthermore, surface defects such as inclusions or shells occur in this phase which may result in equipment damage or labour-intensive and expensive strip ruptures during subsequent process steps, e.g. at tandem mills.

Because the strip speeds and temperatures in the hot mill area are very high, a visual inspection by the personnel directly at the line cannot be carried out satisfactorily.

Therefore, up to now, inspections were undertaken using special camera and lighting techniques, in which video recordings are made of the strip that can be examined on screen by an inspector, with a long delay. Owing to the high strip speeds (more than 20m/s) however, this method can only be applied at a fraction of the strip surface area and therefore only inexact statements can be made about strip quality.

Parsytec HTS-2W is the world's first system that offers fully-automatic detection and classification of defects of the entire (100 per cent) hot strip surface (top and bottom side). For this purpose, the Parsytec HTS-2 system which has been successfully installed in cold rolling mills, had to be adjusted to the special requirements of hot mill inspection. Because the system is completely based on software with standard PC and camera technology respectively, these adaptations could be accomplished quickly. Therefore, defect detection and the neural networks for the classification could be retrained quickly and adapted to the specific type of hot strip defects.

For illumination of the hot strip, HTS-2W integrates stroboscopic Xenon flashes which has been particularly developed for hot strip inspection by the US company Unilux. The steel surface is homogeneously illuminated and all surface defects are clearly visible for the cameras. In addition, for highest image quality, lighting and camera techniques had to be matched in order to avoid influences on the images resulting from the characteristic radiation of the hot strip (orange up to infrared wave range).

In summary, Parsytec HTS-2W makes inspection with automatic defect classification on the complete strip surface possible. This applies also to the bottom side, even though the distances between the individual rollers are very small in hot mills (between 100 and 150mm). Lighting and CCD-matrix cameras are installed in existing gauge houses at a distance of two to three meters from the strip because of the danger of being damaged by a cobble and the steel's high temperature. Additionally, the image capture equipment is secured by heat protection windows.

Early in 1998 the adaptation of the Parsytec HTS-2W to the hot strip inspection requirements was finalized. Afterwards, an extensive field test was carried out in a hot strip mill of a leading steel strip manufacturer, where the system was installed and tested and its efficiency proved. Since then, within a two month period, orders for five Parsytec HTS-2W systems have been placed. This shows, on the one hand, the technical advantages of this system and, on the other hand, the urgent need for a complete defect detection and classification in hot mills. The system will be installed in two CSP plants in Germany and the USA as well as in three conventional hot mills in Europe.

Using the Parsytec HTS-2W system in this early phase of steel strip production, equipment damage and expensive strip ruptures with long down-times can be avoided. Owing to the exact determination of the strip surface quality, suitable processing of the strip will automatically follow. In addition, the direct integration of the digitally-stored inspection results into the process control offers an optimization of the entire production process. For example, a damaged roll can be detected and exchanged at an early stage, which increases the produced quality and aim of yield management, similar to that of the seminconductor industry.

For additional information contact Parsytec Computer GmbH, Thomas Glodek/Nicole Lotbach, PR and Communications, Auf der Hüls 183, 52068 Aachen, Germany. Tel. +49 241 9696 200/202; Fax: +49 241 9696-500; E-mail: GLO@parsytec.de; http://www.parsytec.de