Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1996-04-17
1998-03-03
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164502, B22D 2702, B22D 1107
Patent
active
057224803
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for continuous casting of a molten metal. The present invention relates to a process for continuous casting of a molten metal comprising repeatedly changing a property, such as an amplitude, a frequency or a phase, of an alternating current to be exerted so that an electromagnetic force is applied to the molten metal to separate it from the mold, whereby the instability of the initial solidification is suppressed while imparting an operation for lubrication between the mold and the molten metal and a surface property improvement is effected.
BACKGROUND OF THE INVENTION
In continuous casting, powder is generally added to the upper surface of a molten metal pool within a mold. The powder is melted by heat from the molten metal, and the relative movement of the mold wall oscillating up and down and the solidified shell being drawn at a constant rate causes the molten powder to flow into a gap between the wall and the shell. The meniscus and the tip of the solidified shell are deformed by dynamic pressure generated during the inflow of the molten powder. Since the deformation is repeated at the cycle of the mold oscillation, periodic shrinkages, termed oscillation marks, are formed on the cast metal surface.
The formation of regular oscillation marks having a depth of an ordinary magnitude is known to contribute to the stabilization of casting operation and the cast slab surface quality. However, when the oscillation marks are excessively deep, cast metal surface defects may be formed. Moreover, in addition to the problem that the marks themselves are overly deep, there arise problems in, for example, that positive segregation of Ni is formed in the mark bottom portion and surface grinding the cast slab surface is required when austenitic stainless steel is continuously cast, and that an increase in the number of bubbles and inclusions trapped in the marks is observed as the marks are formed even when common steel is cast. In some cases, even the yield of the cast slab is lowered.
On the other hand, rape seed oil was previously used in place of the powder in continuously casting a metal having a small cross section, for example, a billet. In such continuous casting of metal having a small cross section wherein teeming is conducted without using an immersion nozzle, the powder cannot be used because powder is entrained by the teeming flow. It is known that the rape seed oil burns in the meniscus to form graphite, which prevents the solidified shell from sticking the mold wall. However, it is difficult to obtain regularly formed distinct oscillation marks on the surface of the resultant cast slab. The stability of the casting operation and that of the cast metal quality are inferior compared with the stability in casting using the powder.
As a method for controlling the initial solidification as described above, Japanese Unexamined Patent Publication (Kokai) No. 52-32824 has proposed a method for improving the surface properties of cast slab in a process for continuous casting by teeming a molten metal 2 together with a lubricant 4 into a water-cooled mold 1 which oscillates at a constant cycle and continuously drawing downward, the method comprising continuously applying an alternating current to an electromagnetic coil 5 provided around the periphery of the mold as shown in FIG. 2 so that the electromagnetic force generated by the alternating electromagnetic field makes the molten metal 2 form a convex curve. Moreover, Japanese Unexamined Patent Publication (Kokai) No. 64-83348 proposes a method for further improving the surface properties in powder casting at the time of imparting an electromagnetic force to a molten metal within a mold, using an electromagnetic coil, by intermittently applying an electromagnetic force through imparting the alternate magnetic field in a pulse form as shown in FIG. 3.
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 52-32824, the surface properties of the cast slab have been improved by con
Asai Shigeo
Li Tingju
Sassa Kensuke
Sawada Kenzo
Takeuchi Eiichi
Asai Shigeo
Lin Kuang Y.
Nippon Steel Corporation
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