Self-tuning mould level control in continuous casters
Mould level control is of crucial importance for product quality in a continuous caster. The self-tuning controller reduces mould level deviations with as much as 50-75% compared to conventional PID control which in turn means less surface defects on the products.
The mould level is controlled by the stopper rod which determines the melted steel flow in the caster tube. The process is very difficult to control. It is disturbed by e.g. clogging in the caster tube, material build-up on the stopper rod, dimension changes, temperature variations, changes in casting speed. The process behaviour may change drastically during the casting. First Control’s self-tuning regulator has shown to cope with the problems in a very efficient way. see the comparative study below.
Comparative study self-tuning/conventional control
The curve shows the frequency of large mould level disturbances before and after an installation of self-tuning mould level control (thick line). The old control was made by PID control where the regulator gains were changed as a function of measured speed and product dimensions.
There was an immediate improvement of about 40% less large disturbances after the adaptive control was installed. After some protective logics on the stopper rod was added, the total improvement was about 75% less large disturbances.
During some long holiday weekends, the production switched back to conventional PID control, which resulted in considerable degradation in product quality, see the peaks in the performance curve.
Sandvik MT improves production with Self-tuning mould level control
The mould level is controlled by the stopper rod which determines the melted steel flow in the caster tube. The process is very difficult to control. It is disturbed by e.g. clogging in the caster tube, material build-up on the stopper rod, dimension changes, temperature variations, changes in casting speed. The process behaviour may change drastically during the casting. First Control’s self-tuning regulator has shown to cope with the problems in a very efficient way. see the comparative study below.
Quality supervision of casting
SPC measures
Data is assembled in high time resolution and is stored as SPC measures (max, min, mean value and standard deviation) for a each length unit. Each data storage in the SQL server includes four measures of data.The max/min values guarantee that all disturbances are displayed.
Event recording
The first 10-12 minutes after casting start, all measurements are stored in compressed files in high time resolution (50msec). The files are saved in the SQL server for post-analysis of the starting sequence..