M. Yao

Optimization of Oscillation Model for Slab Continuous Casting Mould Based on Mould Friction Measurements in Plant Trial

Lubrication and friction between the mould and strand are strongly influenced by mould oscillation, and play an important role in slab quality and operating safety during continuous casting processes. Investigation of mould oscillation is therefore essential for getting a better online control of the mould processes. A feasible approach for the development and optimization of mould oscillation was put forward, which combined online measurement of mould friction, design of negative oscillating parameters and evaluation for powder consumption. Three different control models including sinusoidal and non-sinusoidal oscillation for mould oscillations were developed to investigate and evaluate the effects of oscillation on mould friction and powder lubrication. For the purpose of investigating mould friction between mould and strand, online measurement was carried out on a slab continuous caster equipped with a hydraulic oscillator. Also the comparison of the mould friction in sinusoidal and non-sinusoidal mould oscillation was made for subsequent analysis. The industrial experiment result shows that the combination of inverse control model and non-sinusoidal oscillation mode will contribute to the proper powder consumption, leading to a suitable effect of friction force on strand surface, especially for high speed continuous casting. The proposed method provides reliable basis for guiding and optimizing mould oscillation among control models, sinusoidal oscillation and non-sinusoidal oscillation.

Effect of casting parameters on sticker breakout and its propagation behaviour during slab continuous casting

Abstract A sticker breakout is a significant occurrence which not only disturbs steady state casting but also reduces plant productivity and efficiency. Optimising the casting parameters and increasing the accuracy rate of breakout prediction systems are two effective measures for reducing breakouts. In the present paper, plant data were collected and the influence of casting parameters such as slab dimension, casting speed and mould level on sticker breakouts were analysed, especially the effect of heat flux. In addition, sticker propagation behaviour characteristics, including vertical velocity, horizontal velocity and propagation angle, were investigated by measuring the temperature of the mould copper plates. These results provide a reference for optimising the casting parameters and enhancing the accuracy of breakout prevention systems.

Analysis of non-uniform thermal behaviour of special steel during slab continuous casting

A full-scale finite-element model of a slab and its mould was developed to reveal the complex thermal behaviour of special steel in a vertical caster during slab continuous casting. An inverse algorithm was applied to calculate the heat flux and combined with the temperatures measured using thermocouples that were buried in different positions of the mould. The model was validated by comparing the calculated temperature with the measured ones. The temperature distribution of the slab is not symmetric, reflecting the non-uniform nature of heat transfer and hence the necessity of formulating a full-scale model. It will provide a helpful tool for further improving the casting parameters and operations for special steel.

Analysis of Non-uniform Mechanical Behavior for a Continuous Casting Mold Based on Heat Flux from Inverse Problem

The distortion of mold plates plays an important role in the formation of surface cracks on continuously cast steel products. To investigate the non-uniform distortion of a mold, a full-scale stress model of the mold was developed. An inverse algorithm was applied to calculate the heat flux using the temperatures measured by the thermocouples buried inside the mold plates. Based on this, a full-scale, finite-clement stress model, including four copper plates, a nickel layer and water slots in different depths, was built to determine the complex mechanical behavior of the continuous casting mold used to produce steel slabs. The heat flux calculated by the inverse algorithm was applied to the stress model to analyze the non-uniform mechanical behavior. The results showed that the stress and distortion distributions of the four copper plates were not symmetrical, which reflected the non-uniform distortion behaviors of copper plates, water slots, nickel layer and the corner region of the mold. The gap between the mold and the slab was increased because of the corner distortion, which was very important for the heat transfer of initial solidifying shell, and it may be a major reason for the slow cooling of the slab corner.

Mould lubrication and friction behaviour with hydraulic oscillators in slab continuous casting

Abstract It is very important to obtain reliable lubrication from casting powder both at the meniscus and in the gap between strand and mould as it affects slab surface quality and caster productivity. With knowledge of mould friction, a quantitative insight into the behaviour of powder during caster operation is possible. In the present research, the friction was studied based on a slab continuous caster equipped with hydraulic oscillators. The effects of mould oscillation and the abrupt change of casting speed on mould friction force were evaluated, and the characteristics of lubrication behaviour in a casting sequence were investigated. In particular, a comparison between the mould friction force between sinusoidal oscillation mode and non-sinusoidal oscillation mode was made. Finally, the characteristics of friction before a breakout are discussed. The experimental and analytical results may contribute to the development of mould friction online measurement and more clearly learn the lubrication behaviour in different conditions.

Experimental research on effect of control model on lubrication for slab continuous casting mould

Abstract In casting the control model relation between casting speed and frequency plays an important role in the optimisation of process parameters and the improvement of lubrication condition. The mould friction between mould and strand can directly describe the powder lubrication situation in a mould. In the present research, based on the slab continuous caster equipped with hydraulic oscillators, the transient friction forces were obtained by the differences between the monitored driving forces of casting and the calculated driving forces of no casting at same oscillation parameters. According to the trends of friction force with different control models, the characteristics and disadvantages of the traditional positive control model, and the improved positive control model and the inverse control model are discussed. This experimental study contributes to studying the frictional behaviour in mould under different control models, as well as selecting reasonable control model for high speed continuous casing.

Study on the non-uniform slab shrinkage of special steel during slab continuous casting

ABSTRACT A full-scale finite-element stress model of a slab and its mould was developed to analyse the non-uniform slab shrinkage of special steel in a vertical caster during slab continuous casting. The stress model was based on the heat transfer model which was validated by comparing the calculated temperature with the measured ones. According to the shrinkage calculation, the single linear taper is not suitable for the continuous casting of this special steel, and the narrow face taper need to be calculated and optimised. It will provide a helpful tool for further improving the casting parameters and operations for special steel.

Visual detection based on computer vision for sticker breakout in slab continuous casting

Abstract Based on the temperature readings of the mould measured by thermocouples during slab continuous casting, mould temperature and its velocity thermographs were built up, and a visual detection method for the sticker breakout proposed. In the temperature velocity thermograph, the abnormal temperature regions are marked by virtue of the computer image-processing algorithm, such as frame difference, threshold segmentation and eight connected component labelling. The abnormal region features are then extracted and processed as the temperature velocities, geometry characteristics and propagation velocities. In order to distinguish the true and false sticker breakouts, a comparison analysis is made. The results show that the combination of the temperature velocity thermograph and computer vision algorithm is an effective method for the sticker breakout detection. The temperature velocities, geometry characteristics and propagation velocities of the abnormal regions are three important criteria for sticker breakout detection. This method also provides a technology for developing a more visual and intelligent mould monitoring system and is helpful to enhance the accuracy for the breakout prediction system.

Effect of casting process on mould friction during wide, thick slab continuous casting

Abstract Real time detection of the complex friction behaviour and reasonable regulation of lubrication between mould and initial solidified shell are key factors in quality improvement, steady operation and efficient production in continuous casting. In the present work, mould/slab friction was detected based on an online mould friction monitoring system on a wide, thick slab continuous caster equipped with hydraulic oscillators. The influence of the main casting parameters on mould friction is discussed including the casting temperature, slab dimensions and mould level. The response and sensitivity of friction to the changes of steel grade and powder were analysed, as well as the effects of different oscillation modes and oscillation parameters on friction. The results show that the friction is sensitive to variations of casting parameters, and steel grades and powder have significant effect on mould/slab friction behaviour. A reasonable match of oscillation modes and oscillation parameters can significantly optimise the friction behaviour at high casting speed, which also has an important role in improving the slab surface quality. These experimental results provided foundations for further understanding and controlling on the mould/slab friction behaviour.

Optimization Control for Solidification Process of Secondary Cooling in Continuous Casting Steel

In order to predict and control the temperature of continuous casting slab, a mathematical heat transfer model simulating the solidification process of continuous casting slab has been developed based on the realistic roller-layout and spray nozzle distribution. And the accuracy has been verified by comparing with the pin-shooting experiment results. An advanced control strategies are adopted to achieve the optimization of water quantity under different production conditions by the integration of energy saving water distribution module and slab temperature optimization module in the dynamic secondary cooling model. The total water consumption has a trend of dropping off after the utilization of the optimization technique. And the slab surface temperature increases which fits for the down stream direct hot rolling.