Continuous casting of steel

In the continuous casting of steel, surface imperfections associated with the use of an oscillating bar for removal of the cast billet from the mold are substantially eliminated by providing a pulsating high intensity magnetic field around the mold to cause flexing of the metal to detach solidified metal from the internal wall of the mold.

FIELD OF INVENTION 
The present invention relates to the continuous casting of steel. 
BACKGROUND TO THE INVENTION 
In the horizontal continuous casting of steel to form steel billets, molten 
steel is passed horizontally through a cooled mold to cause solidification 
of the steel. The steel is oscillated back and forth within the mold by 
the use of an oscillating drive to release cooled solidified steel from 
the mold wall as it passes through the mold and to remove the cast steel 
from the mold. The oscillation procedure necessary to remove the cast 
steel continuously from the mold often leads to surface defects, such as 
cracks and tears, and to a general surface roughness. These defects do not 
permit the product to be readily acceptable by a rolling mill. 
SUMMARY OF INVENTION 
In accordance with the present invention, there is provided an improved 
method of continuous casting of steel, or other molten metal or alloy, 
which does not involve the use of longitudinal oscillation and does not 
result in the formation of surface defects. In the present invention, the 
mold is constructed of electroconductive material and is surrounded by an 
electrical coil and molten metal in the mold is subjected to a pulsating 
magnetic field produced by the passage of a pulsating d.c. current through 
the coil. 
An intense electrical field, lasting typically for approximately 50 
microseconds, is produced by each pulse of electricity passing through the 
coil. The resulting induced eddy currents in the mold interact with the 
magnetic field of the coil to effect a mutual repulsion between the 
magnetic field and the mold, causing the mold to flex inwardly slightly 
and compress the cooling molten metal, so that when the magnetic field 
decays the cooled solidified metal is released from the mold walls. In 
this way, the surface imperfections characteristic of the oscillating 
removal procedure do not form and true continuous flow of metal through 
the mold can be effected. 
Since the cooled steel billets that result from the present invention are 
substantially free from surface defects, they can readily be accepted by 
rolling mills for rolling to finished steel.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to the drawings, a continuous casting mold 10, suitable for the 
continuous casting of molten steel or other molten metal or alloy, 
comprises an elongate cavity 12, having an inlet 14 at one end for 
receiving molten steel to be cast from a tundish (not shown) and an outlet 
16 for cooled solidified steel at the other end. 
The elongate cavity 12 in the illustrated embodiment is of circular cross 
section. Other cross-sectional shapes may be used to form steel rods of 
corresponding shape, such as, a rectangular cross section or a dog-bone 
cross section. The elongate cavity 12 is provided within a tubular mold 
member 18 having an inner cylindrical wall 19. 
The tubular mold member 18 is constructed of any convenient 
electroconductive material in which a magnetic field may be induced and 
which maintains the solid state upon passage of the molten metal 
therethrough. One suitable material of construction is copper, which may 
be alloyed with other metals to increase its toughness. 
In the illustrated embodiment of FIGS. 1 and 2, the mold 10 is arranged 
horizontally, so that the molten metal flows through the mold cavity 12 in 
a horizontal direction. The principles of the invention, as discussed in 
more detail below, are applicable to any orientation of the mold and 
direction of molten metal flow, including vertical orientation with upward 
or downward metal flow and angular orientation with uphill or downhill 
metal flow. 
An annular cooling passage 20 surrounds the outer surface 21 of the tubular 
mold member 18. Adjacent the inlet end 14 of the mold cavity 12, the 
upstream end of the cooling passage 20 communicates with a first annular 
cavity 22 defined by a housing 24 having an inlet passage 26 for the flow 
of fresh cooling water to the cavity 22 and thence to the cooling passage 
20. Adjacent the outlet end 16 of the mold cavity 12, the downstream end 
of the cooling passage 20 communicates with a second annular cavity 28 
defined by a housing 30 having an outlet passage 32 for the flow of used 
cooling water from the cavity 28. If desired, the cooling water may be 
caused to flow in the opposite direction through the cooling passage 20 by 
reversing the flow of water through the passages 26 and 32. 
Surrounding and defining the outer wall of the cooling passage 20 is an 
elongate housing 34 having wire coil windings 36 located in a helical 
groove 37 therein adjacent the radially inner wall of the housing 34. The 
housing 34 may be constructed of any convenient electroconductive material 
in which a magnetic field may be induced, for example, copper. The coil 
windings 36 are insulated from the helical groove 37 to prevent short 
circuiting through the housing 34. 
The coil windings 36 communicate with electrical power inlet and outlet 
wires 38 and 40 respectively, which, in turn, are connected to a source of 
pulsating d.c. power, so as to provide in cyclic manner, short bursts of 
power through the coil windings, thereby producing a short duration 
intense magnetic field. 
OPERATION 
In operation, molten steel, or other molten metal or alloy, is fed to the 
inlet end 14 of the mold cavity 12. Cooling water is flowed through inlet 
pipe 26 to the annular cooling passage 20 and thence to the outlet pipe 
32. The pressure of molten metal in the tundish causes the molten metal to 
flow continuously through the casting cavity 12. The cooling passage 20 
causes metal closest to the internal wall 19 of the casting cavity 12 to 
cool and solidify, while the metal remains molten radially inwardly 
thereof, although ultimately the metal throughout the cross-sectional 
dimension is solidified and a billet of solid metal is removed from the 
outlet 16 from the casting cavity 12. 
In accordance with the present invention, pulses of short duration d.c. 
power are applied cyclically to the wire coil 36 to produce an intense 
magnetic field surrounding the coil 36, at a cyclic rate of generally up 
to about 1,000 cycles per second. This magnetic field is of very short 
duration, usually about 10 to about 100 microseconds, and is of high 
intensity, usually about 5,000 to about 20,000 amps. 
The magnetic field produced by the coil windings 36 produces a multifold 
reaction which results in the cross-sectional dimension of the molten 
metal contracting during the period of application of the magnetic field. 
The magnetic field induces eddy currents in the housing 34, the mold 
chamber 18 and the molten steel. These eddy currents interact with the 
magnetic field to cause mutual repulsion. 
The housing 34 is caused to move slightly radially inwardly, which results 
in pressure on the cooling water in the passage 20 and thereby onto the 
mold member 18. This pressure, combined with the effect of mutual 
repulsion, causes the mold member 18 also to move slightly radially 
inwardly, thereby applying pressure to the mold metal and contracting the 
cross-sectional dimension of the molten metal. This contraction is 
assisted by the mutual repulsion produced by the eddy currents in the 
steel, but this effect is minor compared to the contraction force produced 
by the mold member 18. 
During the periods between the d.c. pulses, the magnetic field and 
resulting eddy currents subside or decay, so that the mold member 18 and 
the housing 34 return to their original position. Since the molten metal 
has a skin of solid metal resulting from the cooling induced by the 
passage of cooling water through the passage 20, the metal does not relax 
to the same extent as the mold member 18 before the next pulse again 
induces radially inward movement of the mold member 18. 
The procedure is repeated as each pulse is applied and the metal flows 
through the mold cavity 12. As the metal flows through the cavity, more of 
the cross-section of the metal solidifies, so that the degree of radial 
flexure of the metal becomes less as the metal progresses downstream in 
the cavity. Effectively, therefore, the metal is detached from the inner 
wall of the mold cavity by the rapid reciprocal radial movement of the 
mold member 18. 
The utilization of longitudinally-reciprocating oscillation, as practised 
in the prior art, therefore, is not required to achieve removal of the 
continuous casting from the mold cavity 12. The metal flows continuously 
in a single direction downstream within the mold cavity and is subjected 
to flexure under the influence of the magnetic field, to permit ready 
withdrawal from the mold cavity 12 without the formation of significant 
surface imperfections or blemishes, thereby overcoming the problems of the 
prior art. The absence of surface defects permits the casting to be 
forwarded directly to a rolling mill. 
SUMMARY OF DISCLOSURE 
In summary of this disclosure, the present invention provides an improved 
method of continuous casting of molten steel which enables surface 
imperfections to be minimized and throughput to be increased. 
Modifications are possible within the scope of this invention.