The versatility and strength of steel makes it a material of choice in a wide variety of applications throughout the manufacturing world. Nevertheless, steel producers are challenged to differentiate their products in a market where conditions are less than ideal. According to the World Steel Association, world crude steel production for the 65 countries reporting to them was 135 million tons in April 2015, a -1.7% decrease compared to April 2014.
Consistent mill processes are necessary for efficiently producing the highest quality steel. Optimizing mill operations requires analyzing volumes of data from a number of process variables. If there are any questions regarding the final quality of the supplied product, modern data archiving allows producers to review recorded process parameters starting from its origins in the liquid phase to its final pass in the cold mill. Any dimensional abnormalities in the rolling process can be traced upstream ultimately to the hot strip mill. The hot strip steel mill is universally considered one of the harshest environments for process instrumentation and sensors but as the material speed and temperature increases, so does the importance of the measurement values.
Stereoscopic x-ray profile gauges have the ability to determine both the cross-thickness profile and the physical position of the strip in space. By using a narrow x-ray fan beam to measure the strip, the system can record the height of each point of the strip in the time domain, and the flatness, or shape, of the strip can be calculated. Recording these values every five milliseconds presents unique challenges to the data archiving hardware and software. Millions of data points can be recorded for each strip produced. Cataloguing terabytes of data for easy retrieval and analysis requires an application that is both robust and user-friendly.
Process Variables in the Hot Strip Mill
There are many derivatives of the modern hot strip mill, from multi-stand to reversing Steckel mills to direct casting, but the end goal is always to produce a coil with uniform mechanical and dimensional properties from head to tail and edge to edge. Advanced process control algorithms use hundreds of variables from various sensors and drives to maximize the prime quality yield from each ton rolled. Starting with the mechanical properties of the steel grade, strip tensions and temperatures are measured between every stand, pressure transducers measure reduction force, and laser-based velocimeters provide line speeds that monitor mass flow for use in feed-back and feed-forward control loops. At the end of the mill prior to strip coiler, a simultaneous profile gauge is used to validate that the strip produced meets the tight dimensional tolerances demanded in the marketplace.
While each sensor contributes to the overall strip quality, the operator and mill computer are responsible for digesting those inputs and producing the desired product. The profile gauge has the ultimate responsibility for validating that the specifications are achieved. In the past, if coil quality was questioned, the chart recording of the gauge output might be the only archived data to review. Today, with high speed data archiving, all of the previously mentioned variables and measurements can be recorded and reviewed by quality assurance personnel, process engineers, and plant management. Each discipline is able to mine the data for information critical to their areas of responsibility.
Read High Speed Archiving of Thickness and Profile Data in the Hot Strip Mill to learn more about how a high speed simultaneous profile gauge can provide critical dimensional information in real time for profile and shape control.