Arc alignment is a key process link in the production process of continuous casting machine. Its accuracy directly affects the quality of ingot, equipment operation stability and production efficiency. It is of irreplaceable importance in continuous casting production. The following is a detailed description from many aspects:
The impact of arc alignment accuracy on ingot quality
Surface quality control
Arc alignment deviation will cause scratches, indentations and cracks on the surface of the ingot. For example, when the arc alignment of the fan-shaped segment roller is not accurate, the ingot will contact the roller surface unevenly during operation, and excessive local pressure will easily cause surface scratches; if the arc alignment of the straightening section is deviated, the ingot will be unevenly stressed during the straightening process, and transverse or longitudinal cracks will form on the surface. Insufficient arc alignment accuracy will increase the depth of vibration marks on the surface of the ingot, resulting in an increase in the incidence of corner cracks and an increase in the scrap rate of about 0.8%.
In addition, poor arc alignment will cause the surface of the ingot to appear “bulging” or “depression”, affecting the subsequent rolling process. For example, due to slag accumulation and arc alignment errors in the fan-shaped sections of Laigang’s No. 6 continuous casting machine, the surface indentation defect rate of the ingot reached 3.2%. After optimizing the arc alignment accuracy, the defect rate dropped to below 0.5%.
Internal quality control
Arc alignment accuracy affects the uniformity of the internal structure of the billet. When the arc line of the roller array does not match the theoretical curve, the billet is subjected to uneven force during the solidification process, which may lead to internal cracks, center segregation and other problems. For example, the arc deviation in the multi-point straightening zone will cause excessive strain in the solid-liquid two-phase zone of the billet, exceeding the high-temperature strength of the material and causing internal cracks. In addition, poor arc alignment will affect the secondary cooling effect, resulting in uneven cooling of the billet and aggravating internal structural defects. Due to the arc alignment deviation of the secondary cooling section of a steel plant’s billet continuous casting machine, the center looseness level of the billet increased from level 1.0 to level 2.0, and after adjusting the arc alignment accuracy, it returned to the standard range.
The impact of arc alignment accuracy on equipment operation
Equipment life and maintenance cost
Arc alignment deviation will aggravate roller wear and equipment failure. For example, when the arc alignment of the fan-shaped segment roller array is not accurate, sliding friction occurs between the roller and the billet, resulting in aggravated roller surface wear, and the replacement cycle is shortened from the normal 120 days to 60 days, and the spare parts cost increases by about 30%. In addition, poor arc alignment can lead to unbalanced force on the equipment, causing bearing damage, frame vibration and other faults.
Production efficiency and stability
Insufficient arc alignment accuracy will increase the risk of production interruption. For example, the deviation of the dummy rod in arc alignment may lead to failure of dummy rod feeding and forced to stop casting. Baosteel’s No. 3 continuous casting machine had arc connection error between the 0# section and the 1# section, and the dummy rod deviation failure occurred 3 times a month, affecting production for 2 hours each time. After adjustment, the fault was eliminated.
Industry standards and management requirements for arc accuracy control
Accuracy indicators and specifications
The industry has clear requirements for the arc alignment accuracy of different types of continuous casting machines: the arc alignment error between sections of slab continuous casting machines is ≤±0.5mm, square billets are ≤±0.3mm, and round billets are ≤±0.2mm. In addition, the arc alignment accuracy needs to be adjusted in combination with the characteristics of the steel grade. High crack sensitivity steel grades (such as peritectic steel) require arc alignment error ≤±0.2mm, and ordinary steel grades can be relaxed to ±0.5mm.
Process control and management system
Arc alignment accuracy control needs to be included in the equipment management system. For example, the roll gap instrument is used regularly to detect the arc state and establish a closed-loop management process of “detection-analysis-adjustment-verification”. After a steel plant formulated a weekly inspection system for arc accuracy, the accuracy rate of equipment failure warning reached more than 90%.
In addition, personnel training is the key to precision control.
