In the metallurgical and metal processing industries, Micro-Epsilon Messtechnik GmbH in Ortenburg is recognised for using a wide range of different measurement principles for determining thickness, width, profile or length.
Indeed, it is true that for process measurement techniques the conditions in rolling mills are quite harsh. Target temperatures of up to 550°C, temperature drift, dirt, vibrations and fast processing speeds make a simple solution seem impossible.
The measurement unit developed for AluNorf, which operates according to a non-contact capacitive measurement principle, is based on a closed high rigidity O-frame. This unit can be seamlessly integrated to the existing V-shaped roller track.
After the reversing rolling stand, while the plate is being transported on the roller track to the cropping shear and is held motionless for a short time to enable cutting, above and below the plate capacitive sensors traverse perpendicular to the plate and synchronously in the opposite direction to the direction of travel. These sensors were developed specifically for this sensitive measurement task. From the known distance of the sensors from one another and their measured distances from the plate, precise thickness information can be calculated. By traversing the sensors, a profile of the complete width of the plate can be calculated from the local thickness signals. The system also enables the sensors to be moved to any desired transverse position over the plate, in order to obtain a dynamic longitudinal profile of the plate as it moves past. Even a combination of forward plate movement and traversing sensors is possible, to obtain maximum information about the overall plate geometry.
In addition, besides capacitive sensors, a laser sensor can be integrated in the sensor arm, which determines the width of the plate during motion.
Here, the system provides information for optimising the adjustment settings for each individual plate. Particularly after width changes or rolling break intervals, the measured plate profile can be used to improve the profile and flatness of the final hot-rolled strip. Accurate knowledge of the plate width and of the existence across the plate’s width of any wedge-shaped regions also enables more stable guiding of the strip in the finishing line.
The standard system for profile measurement of aluminium plates is actually used for plate widths of up to 4m and a maximum thickness of 200mm. For a traversing process, the system only needs four seconds and achieves a thickness accuracy of ±20 μm and ±500 μm on width.