Patent ID: 7735544

Claim:
A method of electromagnetic stirring of molten metal in an unsolidified portion of a continuously cast strand of an ingot, which comprises the steps of: applying an alternating poly-harmonic current to at least four coils of an in-mold stirrer; supplying the alternating poly-harmonic current with three frequency components, including a first frequency component f 1 =3.0-6.5 Hz, a second frequency component f 2 =13-20 Hz, and a third frequency component f 3 =0.5 f intr , where f intr is an intrinsic frequency of the ingot with a liquid portion inside and having a range 0.9-1.2 Hz; setting a ratio of current amplitudes by equations: (a frequency current amplitude of f 2 )/(a frequency current amplitude of f 1 )=0.5-0.75; (a frequency current amplitude of f 3 )/(the frequency current amplitude of f 1 )=0.2-2.0; wherein a current of the third frequency component f 3 =0.5 f intr creates a pressure pulsation with a frequency equal to the intrinsic frequency of melt oscillation in the liquid portion of the ingot, an oscillating pressure spreads along the ingot as acoustic waves that generate a pulse flow at a solidification front; wherein a current of the first frequency component f 1 is a base current and setting the base current in dependence on a size of an ingot cross section for inducing a stirring torque inside the in-mold stirrer for rotation stirring; and wherein a current of the second frequency f 2 is provided for reducing a meniscus disturbance, for reducing particle entrapment into the ingot through the meniscus, and for decreasing oscillating marks on the ingot.