HD mold – Caster Assistance System to Increase Product Quality J. Wans, D. Lieftucht, C. Geerkens, M. Arzberger, M. Reifferscheid SMS Siemag AG, P.O. Box 40237 Duesseldorf, Germany Phone: +49 211 881 5861 Email:
[email protected] Key words: HD mold, Continuous casting, Fiber optics, Breakout avoiding
ABSTRACT The HD mold Operator Assistant assures improved process stability and enhanced product quality. Fiber Bragg Grating based temperature measurements continuously monitor the heat transfer into the mold supporting the operator with in-time feedback on casting actions. In this paper the HD mold system is presented in detail based on cause and action to be taken, e.g.: - LFC - to avoid a longitudinal facial crack formation - Taper - to stabilize heat removal - Adaptive sticker – to avoid breakouts caused by e. g. sticker - Mold level control and wave contour SMS Siemag’s HD mold system - Applicable inside all continuous casting molds - Tenfold higher number of measurement points compared to thermocouple solution - Independent from electromagnetic fields - Helps reducing costs by early defect detection and breakout avoiding - Maintenance free
INTRODUCTION The successful operation of modern continuous casters is defined by the quality of the products, safe and maintenance-free operation, favorable conversion costs and a high level of environmental compatibility. Here, using the latest technologies in connection with metallurgical know-how is an important prerequisite. The increasing provision of plants with mechatronic systems is a main indicator of technological development, creating additional safety in operation and ensuring the reproducibility of quality results. Being the place where the first solidification takes place, the mold is the core component that significantly influences quality and yield. With the HD mold, SMS Siemag offers an "intelligent" mold plate system with integrated optical temperature detection. Thanks to modern optical fiber sensor technology, it is possible for the first time to provide high-resolution insight into the solidification processes inside the mold. The findings thus gained are implemented consequently in the control system of the casters and support the casting process. The HD mold provides reliable, high-quality measured values, thus supporting the creation of highgrade cast products. Furthermore, the HD mold system provides support in the continuous effort to significantly reduce costs incurred due to undesired casting events such as sticker-related breakouts.
Figure 1: CSP® mold
HD mold – HIGH DEFINITION FOR FLAT PRODUCTS Conventionally, process monitoring inside the mold is performed using thermocouples. The thermocouples are plant-specifically integrated into the copper plates of the molds; however, they are limited as regards arrangement, number and signal intensity (quality and quantity). Certain areas inside the mold are not distinctively monitored. Defects occurring in these areas can hardly be detected and lead to quality losses and increased costs. With the HD mold, this situation is optimized. Thanks to the HD mold, temperature measuring sensors can now be arranged in almost any location and in greater numbers than ever before.
45 measuring points
225 measuring points Temperature detection three times faster
Figure 2: Left: conventional thermocouples, right: the new HD mold
The use of optical fibers in the HD mold provides the highest signal density and signal quality in the history of the mold. The recording of measured values, their evaluation and the required actions can take place quicker and with less susceptibility to faults. Thus, the development of defects during casting is counteracted immediately.
The optical fiber technology is not affected by electro-magnetic fields. With the HD mold system the required cabling is reduced significantly, so that maintenance is no longer required here. For this purpose, the sensors remain protected inside the copper plates.
Figure 3: HD mold with 96 measuring positions on one broad face (CSP ® copper plate)
Figure 4: Compact and maintenance-free design of the HD mold plates
The optical fibers in the HD mold intrinsically combine measuring point and the signal transport and are integrated into the mold plates. Broad faces and narrow faces are equipped with sensors. The measuring points are located only a few millimeters below the copper surface. The optical fibers are guided away centrally from the mold plates and connected to the evaluation unit. After the light signals have been converted to location-related temperatures, the new software algorithms of the Mold Monitoring System (MMS Plus) take over the data and supply them to the operator systems. A high signal density and quick measurements make it possible to detect defects as they occur, to classify them and to immediately generate the required countermeasures. It is the signal intensity and the signal speed that hold the solution for reducing the number of critical casting events.
Thanks to the quality and quantity of the measured data, the number of alarms is reduced, thus cutting down on costs. With the HD mold, the reduction of the casting speed to gain additional time for the possibly damaged strand shell to regenerate is reduced to a minimum. These advantages directly contribute to an improvement of the products and an increase in production.
Figure 5: Overview of the HD mold system
FUNCTIONS OF THE HD mold SYSTEM The functions of the HD mold provide numerous advantages for the various events in the casting process: Avoiding of longitudinal cracks Longitudinal cracks (symmetrically arranged in relation to the strand centerline) often occur due to an unsteady mold level. The fluctuation of the meniscus influences the boundary surface system consisting of mold surface, casting flux slag and steel. Unsteady heat transfers reduce the thickness of the strand shell, thus being a potential source of defects, e.g. for longitudinal cracks. The optical fibers in the HD mold allow for the exact detection of the mold level contour as regards the measuring position and the measuring speed and thus enable the operator to initiate countermeasures immediately.
Avoiding of sticker-related defects and breakouts The formation of stickers constitutes a considerable risk for the casting process. Stickers often lead to breakouts and therefore have severe consequences for the casting machine, the product and productivity. Thanks to the number of optical fibers and their positions, the formation of stickers is detected at an early stage. Situations which could not be handled in the past and which in the worst case would lead to breakouts are now safely detected and rectified.
Ensuring the required contact behavior of the narrow faces The quality of continuously cast products in the edge zone between the broad and the narrow faces also depends on the taper. Longitudinal cracks in the edge zone may formed by an excessive mold taper; here, the pressure of the narrow faces on the strand produces a depression at the edge of the broad face. The contact behavior of the narrow faces from the meniscus to the mold outlet defines the heat dissipation and thus the formation of the strand shell. Narrow faces equipped with optical fibers across their entire height facilitate the measurement of heat flux densities. Here, the local heat fluxes across the narrow face height are determined – resolved to the exact location. The measurements immediately provide information on deviations in the contact behavior of the narrow faces and thus form the basis for the readjustment of the narrow faces during the casting process.
Safe filling of the mold at sequence start When casting is started, the volume flow of the steel flowing into the molds is defined by the stopper rod position. Recent measured values of the filling level ensure safe filling of the mold and facilitate controlling the stopper characteristic. Therefore, the risk of overfilling and/or a mold being filled only partially is reduced significantly. Because of the arrangement of the measuring sensors of the HD mold, the filling process can be monitored continuously from the point in time the steel first enters the mold until the nominal filling level is reached.
HD mold SOFTWARE CONCEPT Tailor-made and easily expandable model solutions are also available for the HD mold system. The system architecture ensures flexible connection to the customer interfaces, requiring a limited amount of configuration work. Existing process data and simulation tools are subjected to system tests before delivery. In this way, it will be possible in the future to connect new sensor components such as the temperature measurement system with optical fibers to existing systems without incurring great expenditure. A core process, the HD kernel, provides for configurable scalability in hard and software.
EXAMPLES In the CSP® process, the geometry of the funnel-shaped mold and the high casting speeds place high demands on the measuring sensor technology in the mold plates. With the use of the optical fibers, the HD mold provides advantages as regards arrangement, signal quality and reduced susceptibility to faults. Operating results have proven the success of an early detection of casting defects in the formation phase and their indication on the operator screen. Figure 6 shows the mold filling process enabled by the optical fiber sensors and visualized in the control room. Immediately before the steel enters the mold, the operator is provided with exact information on the steel level across the height and width of the mold. The HD mold thus facilitates early detection of defective volume flows from the tundish into the mold. In particular, overfilling of the mold can be prevented.
Figure 6: HD mold: Visualization of the mold filling
Figure 7 shows the operator screen in a control room: in the sequence of individual images, the formation of a sticker in the meniscus area is shown, which in the right part of the figure has already passed through approx. one third of the mold. The HD mold enables besides sticker related breakouts the possible root causes of other breakout reasons e. g. wrong taper, fins or longitudinal facial cracks. In this way, the high defect detection rate of the HD mold also leads to a significant reduction of the high costs caused by breakouts.
Figure 7: HD mold: Formation of stickers – traceable online
The combination of optical fibers with the evaluation software provides advantages as regards measuring speed and intensity of the signals. Figure 8 shows a direct comparison of the measured results of thermocouples and optical fibers. The evaluation of the signals recorded in parallel shows the previous event message and the intensity of the signals.
Figure 8: Advantage of speed and intensity of the HD mold when compared to thermocouples
With the time of approx. 16 seconds gained here, the required measures can be initiated much earlier. With an average dwell time of the strand shell between the meniscus and the mold outlet of approx. 10 seconds, there now is a chance of assessing the event and implementing countermeasures. Experience has shown that the costs of a single sticker-related breakout are enormous, due to the high production loss in addition to the core maintenance work. These costs as well as those incurred by reducing the casting speed can be avoided thanks to the time gained with the HD mold measurement.
CONCLUSION By using optical fibers, the HD mold system allows for a significantly enhanced and more precise monitoring of the solidification processes inside the mold and especially of the strand shell formation. With the same amount of cabling, the density of measuring points is ten times higher than with conventional thermocouples. The temperature measuring system is three times faster and even works within electro-magnetic fields without any interferences. Thanks to their quality, quantity and immediate availability, the measured data open up new possibilities for efficient process control. The use of optical fibers in the mold also provides for new functions; in addition to the optimized prevention of longitudinal cracks and breakouts, effective statements can be made on the contact behavior of the narrow faces. Furthermore, plant availability and product quality will see a drastic increase. The measured values significantly contribute to an enhanced understanding of the process. The compact and closed design of the HD mold combines the mold plate with sturdy, integrated sensor technology. The HD mold is suitable for all mold formats of continuous casters. The "intelligent" mold developed by SMS Siemag is maintenance-free for the plant owner, the cabling work required in the past as well as the extensive amount of set-up and maintenance work are no longer needed thanks to the HD mold sensor technology. In addition to the technological advantages, the high defect detection rate of the system facilitates a significant reduction of costs, in particular by preventing sticker-related breakouts. In the future, the customer will experience these advantages through the implementation in assistance systems that efficiently support the production process.
