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USE OF NATIONAL INSTRUMENTS PRODUCTS FOR SOLVING MOLD BREAKOUT PROBLEM IN A CONTINUOUS STEEL SLAB CASTER
Challenge: Bethlehem Steel manufactures steel slabs from molten steel using a continuous casting process. The mold is a copper cooled tube-like structure with a rectangular cross-section. The mold is open at the top and the bottom. Molten steel is poured into the mold from the top, and the steel slab exits through the bottom. As the slab emerges from the mold, its outside walls are solid, but the interior is still in liquid state. The walls of the slab therefore form a shell in which the molten steel is contained. As the slab passes along the production line it is cooled to a completely solid structure. Mold breakout problem occurs when the steel shell of the slab is not thick enough as it exits from the bottom of the mold. This causes the shell to break and spill hot molten steel down the machine. The mold breakout is catastrophic and causes several hours of down time and damage to the caster.
Solution: Using National Instruments DAQ, SCXI, and LabVIEW, and a Bethlehem Steel's proprietary Fortran Mold Breakout Prediction Model, we created a PC based system for acquiring signals from the mold, displaying data, predicting mold breakout, and taking preventive action to avoid mold breakout.
Products Used: List of all National Instruments products, computers, and proprietary software.
Description of System: The Mold Breakout Prevention System (MBPS) is intended to monitor the copper molds continuously to detect anomalous temperature distributions. The molds are instrumented with thermocouples for this purpose. Data acquisition was performed using National Instruments DAQ and SCXI hardware. Two LabVIEW programs, one for performing data acquisition (DAQ) and another for operator panel (MMI) were developed. A proprietary FORTRAN program was developed by Bethlehem Steel staff for predicting mold breakout (MODEL). The DAQ program acquires data from thermocouples continuously, formats the acquired data into a specified data structure, and then transfers it to the MODEL program via a dll. The MODEL program is the mold breakout prediction algorithm and it runs continuously. It analyses the thermocouple data to detect the anomalous temperature distributions. When an impending mold breakout is predicted, the MODEL program sends signals to the DAQ program via the dll. The DAQ program then sends a signal to an external PLC which activates the mold breakout prevention sequence for the caster and sets off an alarm. The MMI program is used as an operator information panel. It obtains thermcouple data via the dll and displays trend charts on the screen. The operator can turn off defective thermocouples from the MMI program, so that spurious alarms can be avoided. The operator can also attach comments, enable/disable the alarm. The MMI program sends the operator inputs back to the MODEL progam via the dll.
(Note: This section will be elaborated more in the final version of the paper)
Figure 1: (Include Screens for MMI here)
Figure 2: (Include Screens for DAQ here)
Conclusions: The MBPS system is a very effective application of National Instruments products and virtual instrumentation approach in an Industrial environment. It has helped Bethlehem Steel to reduce number of sticker breakout occurrences while reducing number of spurious type 1 and type 2 alarms, and resulted in significant savings.
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