Billet continuous casting machine and casting method

Details Billet continuous casting machine and casting method Billet continuous casting machine and casting method

1999-12-23

2001-11-27

Nguyen, Nam (Department: 1722)

Metal founding

Process

Shaping liquid metal against a forming surface

C164S454000, C164S466000, C164S486000

Reexamination Certificate

active

06321829

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a billet continuous casting machine and casting method which continuously pour molten metal into a tubular mold to solidify the molten metal, thereby continuously producing a cast piece of a square or rectangular cross sectional shape.
FIG. 7
is an explanatory drawing showing an example of a conventional billet continuous casting machine.
As shown in the drawing, molten metal (molten steel) is poured through a molten metal nozzle
101
into a mold
100
. At this time, cooling water is sprayed from a plurality of spray nozzles
102
, arranged outside the mold
100
, to cool the mold
100
. While the molten metal inside the mold
100
is gradually moving downward, its peripheral area is solidified. A cast piece
103
is continuously formed and forced out of the mold
100
.
The cooling water is supplied by a pump or the like (not shown) through a cooling water inlet
104
into a jacket
105
. The water flowing in the jacket
105
cools the surroundings of the mold
100
, or cools the mold
100
by being sprayed from the spray nozzles
102
as mentioned above, and is then discharged through a cooling water outlet
106
.
The mold
100
is in a tubular form having a square cross section, and is provided with a linear taper (inclination) ranging from a molten metal inlet at the top of the mold to a cast piece outlet at the bottom of the mold. The taper value of the mold
100
is 1% of less, and a generally used taper value is 0.6 to 0.8%.
As described above, a conventional billet continuous casting machine has the tapered mold
100
, and cooling means for cooling the mold, and operates while suitably combining a cooling rate with the taper and the cooling means.
In the conventional billet continuous casting machine, the taper of the mold
100
was relatively small, and low speed casting posed few problems. High speed casting (3 m/min or more), however, caused the following insoluble problems: At the corners of a lower part of the mold
100
, air gaps (gaps between the mold and a solid shell which are generated because of the nonuniform growth of the solid shell in the mold; gaps are generated at the corners of the lower part of the mold) appear between the mold
100
and the cast piece
103
. Furthermore, the site of delay in solidification occurs in the cast piece from its corners as far as 10 mm or so apart, thereby deteriorating the quality of the product. That is, the occurrence of the air gaps makes the cooling of the cast piece
103
nonuniform, thus inducing deformation, cracks or structure defects of the cast piece
103
. The occurrence of the site of solidification delay, moreover, causes rhombic deformation or breakout.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention, to provide a billet continuous casting machine and casting method capable of high quality, high speed casting.
To attain this object, the invention provides a billet continuous casting machine comprising cooling means for cooling an outer wall of a tubular mold, electromagnetic brakes disposed outside the mold for decelerating the flow of molten metal poured into the mold, molten metal level detecting means for detecting and controlling the level of molten metal in the mold, notched portions formed at corners of a quadrangular lower part of the mold, and cooling liquid spray means for spraying a cooling liquid directly onto the notched portions; and having elastically pushing means for imparting a pushing force corresponding to the static pressure of the molten metal to unnotched portions of the quadrangular lower part of the mold to push the unnotched portions inwardly of the mold; whereby molten metal is continuously poured into the cooled mold to solidify the molten metal so that a cast piece, quadrangular in cross section, is continuously produced.
Preferably, taper portions are provided in an upper part of the tubular mold.
Preferably, the tubular mold is curved in an arcuate form in the direction to which the cast piece is drawn.
Preferably, the molten metal level detecting means is an X ray- or &ggr; ray-based level sensor which comprises an emitting portion and a receiving portion disposed along nearly diagonal line of the tubular mold and detects the molten metal level at a position unaffected by the flow of molten metal poured through the molten metal nozzle into the mold.
Preferably, controlling means is provided for controlling the speed of cast piece drawn by pinch rolls based on a molten metal level signal from the molten metal level detecting means.
A billet continuous casting method related to the present invention comprises pouring molten metal into a water-cooled tubular mold having notched portions at the corners of a lower part of the mold; pulling out a dummy bar in the mold when a molten metal level signal from molten metal level detecting means has reached a predetermined value of the level in the mold; starting casting while applying electromagnetic brakes to the poured molten metal flow in the mold; decreasing the speed of cast piece drawn by pinch rolls when the molten metal level signal has fallen short of a predetermined value range of the level in the mold; and increasing the drawing speed of cast piece drawing when the molten metal level signal has exceeded the predetermined value range of the level in the mold.


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