Optimisation of Electromagnetic Stirring in Steel Billet Caster by Using Image Processing Technique for Improvement in Billet Quality

Abstract

Determination of best combination of current and frequency of an electromagnetic stirrer (EMS) of a billet caster is of prime importance for ensuring good internal, surface as well as subsurface quality of billets. In the present study, this optimization of current and frequency values is achieved very efficiently using image processing techniques. The EMS currents and frequency are varied between 240–300 A and 3–5 Hz respectively during casting and corresponding billet samples are collected. Samples are also collected from beginning, middle and end of casting heats in order to asses the influence of tundish superheat. The samples thus collected are scanned using ultrasonic C-scanner to get the full color image of samples. The grabbed images are processed and analysed using Matlab Image Processing Toolbox in RGB color space. Finally, data of various defects as obtained from image processing, in each grades of steel are compared for determining the best combination of EMS parameters. It has been found that length of equiaxed zone increases significantly with increasing EMS current up to 280 A, almost for all close casting grades. Increasing EMS current beyond 280 A increased the length of equiaxed zone marginally but chances mould powder entrapment at the surface of the billet and erosion of submerged entry nozzle is more. Central shrinkage number of subsurface and central crack also reduced significantly up to 280 A EMS current. Marginal improvement in billet quality is also observed when 3 Hz EMS frequency is used but the improvement in the quality is not significant.