Improvement of Billet Surface Quality by Ultra-high-frequency Electromagnetic Casting

Electromagnetic casting using ultra high frequency magnetic field (100 kHz) was investigated. At the initial stage, laboratory experiments have been made, and it is clear that oscillation marks can be totally suppressed and the homogeneity of the initial solidified shell is greatly improved. From these results, EMC has beneficial effects on preventing surface and sub-surface cracks. Furthermore, accumulation of inclusions and pinholes to the surface due to electromagnetic force does not occur, together with the electromagnetic stirring in the mold, when EMC frequency enhances to 100 kHz. Based on these results, plant trials were put into practice. As far as operational conditions are concerned, a new method of meniscus control was developed, and lubrication between the mold and the initial solidified shell is improved as the reason that friction force decreases, and mold powder consumption increases. From an investigation of the quality of rolled bars, it was confirmed that the quality of bars rolled from EMC billet without surface conditioning is the same as that of bars rolled from conventionally cast billets with surface conditioning.