Contoured mold for horizontal continuous casting

BACKGROUND OF THE INVENTION

In the continuous casting of steel strands and slabs, it has been the practice heretofore, to use water-cooled copper molds, in vertical or nearly vertical positions that required either bending the casting produced and restraightening at ground level, or using a curved mold and restraightening the casting at ground level. In some installations, solidifying and cutting the strand is carried out while the strand is moving downward vertically, and the severed cast product is brought then to ground level. All of these steps involve substantial expenditure for plant and facilities, including buildings, below ground level pits, high lift cranes, heavy machinery capable of withstanding the high-metallostatic forces present within the strand or slab, and the high forces required for straightening a curved cast strand or slab.

It has been evident that a method of casting steel slabs in a horizontal or nearly horizontal direction would offer great savings; requiring much less rugged machinery, and much less costly cranes, buildings, and other facilities, due to the lesser requirement of vertical height. There have been many suggestions for apparatus and method in the prior art that continuously cast a strand or slab in a horizontal direction. Some success has been achieved with nonferrous metal, but up until the present the horizontal continuous casting of steel has not met with great success.

When the closed mold methods of horizontal casting, which have proven satisfactory with nonferrous metals, are applied to the casting of steel, there is usually great difficulty in obtaining satisfactory solidification of the top surface of the casting. This is due to a number of causes. First, the relatively high-heat content of molten steel, and the relatively low-thermal conductivity of steel tend to cause the solidified skin or shell of the cast strand to be quite thin. Second, gravity causes the solidifying skin or shell, as it shrinks, to lie against the bottom of the mold, withdrawing the skin or shell from contact with the top surface of the mold. Thus, in some degree adequate solidification of the top surface of the casting is not achieved. Third, another effect of gravity is to cause any nonmetallic inclusions within the steel to rise to the top surface where they further complicate the removal of heat and the solidification of an adequate skin or shell on the top surface of the casting. In combination, these causes lead to frequent break-outs as the steel casting emerges from the horizontal mold and the break-outs almost always occur on the upper surface of the cast strand or slab.

It has been fairly evident that a means of obviating these difficulties would be to cast in an open mold without a top, wherein the top surface of the casting remains molten for a time and with only the sides and bottom becoming solid initially. One problem of this method has been to control distortion caused by thermal movement of the casting shell which departed almost immediately from the rectangular configuration of the mold, typically producing a casting which tended to be convex about both longitudinal and lateral axes, and which caused the process to fail.

How the present invention overcomes the difficulties experienced in using prior art horizontal continuous casting apparatus, will be apparent to those skilled in the are from the following description of an embodiment and modification of the present invention.

SUMMARY OF THE INVENTION

A horizontal continuous casting mold in accordance with the invention includes a bottom having a curvature in each one of mutually two perpendicular planes, with the center of the curvature in each plane being below the bottom. Sides are connected to the bottom and are arcuate with the center of curvature of the sides being located outside of the mold. Each arcuate side intersects the bottom at an included angle equal to or greater than 90°.

For a further understanding of the invention and for features and advantages thereof, reference may be made to the following description in conjunction with the drawing which shows for purposes for exemplification an embodiment and a modification of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

Fig. 1 is a schematic elevational sectional view through a horizontal continuous casting mold in accordance with the invention;

FIG. 2 is a sectional view along line II—II of FIG. 1;

FIG. 3 is a sectional view along line III—III of FIG. 1;

FIG. 4 is a sectional view along line IV—IV of FIG. 1; and

FIG. 5 is a partial schematic elevational view similar to FIG. 1, of a mold in accordance with a modification of the invention.

DETAILED DESCRIPTION

Referring to FIG. 1, molten metal 11 flows from a tundish 13 through a pouring nozzle 15 that has a lower end 17 submerged in a pool of molten metal in one end of an open topped continuous casting mold 19.

The continuous casting mold 19 has a steel envelope 21 that is lined with any suitable refactory material forming a bottom 23, and end wall 25, and opposed sidewalls 27, 29. Those skilled in the art will recognize also that the mold walls, 23,25, 27, 29 may be made of a suitable metal such as copper, if it is desired t do so.

The bottom 23 has an inner surface 30 that is arcuate in mutually perpendicular planes, as may be noticed from FIGS. 2 and 3. The center of curvature of the bottom 23 in each plane is always below and outside of the bottom of the continuous casting mold 19. Further, the bottom 23 is wider at Section II—II (FIG. 2) than at Section III—III (FIG. 3) for the reason that the molten metal 11 in contact with the bottom 23 and sidewalls 27, 29, between Sections II—II and III —III, becomes solid and would normally shrink away from the sidewalls 27, 29 in a conventional mold. But, the casting mold 19 of the present invention has slightly converging longitudinal sidewalls, as is evidenced by the reduced width of the mold at Section III—III when compared with the width at Section II—II. This convergent sidewall feature results in the cast strand remaining in contact with the mold sidewalls for a longer time.

Further, it will be noted from FIG. 2 that the sidewalls themselves have arcuate inner surfaces with the center of curvature lying always outside of the mold 19. The included angle between tangents to the bottom 23 and to a sidewall 27, at the point A where they intersect, is about 100°. The included angle between tangents to the bottom and to the sidewall 27 at point B of FIG. 3, however, is about 95°. The included angle between the bottom and the sides, as viewed in FIG. 4, is 90°. These included angles also obtain at points of intersection of side 29 and the bottom 23.

The top of the continuous casting mold 19 is open to the atmosphere, and there are two transversely extending dams 31, 33 that are mounted to the sidewalls 27, 29. These dams 31, 33 are located about where shown in FIG. 1; the dam 31 being located close to the pouring nozzle 15, and the dam 33 being located a short distance away from dam 31.

The refactory lining 23, 25 of the mold 19 is cooled by an arrangement of passages 35 within the refactory lining for cooling water or other fluid to flow thereinto and therefrom, as indicated generally by arrows C and D.

Beyond the right-hand end of the casting mold 19, there is a pair of rollers 37, 39, indicative of a runout table, or other conventional cast stand or slab supporting mechanism, and sets of spray nozzles 41 from which sprays of cooling water impinge on the cast strand to accelerate solidification.

It is believed that at some location, P, within the mold 19 itself, the molten metal 11 commences to solidify at first on the

3,628,596 bottom and sidewalls where a skin 43 forms around three sides of the molten metal 11 as the beginning of a cast strand 45. Because there is no top to the mold, the molten metal 11 adjacent the upper surface cools slower under ambient conditions than the molten metal in contact with the internally cooled mold walls and bottom. It is believed, however, that a thin skin 47 forms also at location, P, at the sides 27,29. But, a thin skin 49 forms only at the top just before the cast strand 45 emerges from the mold 19.

It may be desirable in some applications to provide additional spray nozzles in a location near Section III—III which would emit water onto the surface of the molten metal to induce the formation of a thin skin on the top of the cast strand. The velocity of water emitted from such spray nozzles would have to be regulated, of course, so as to preyent penetration of the molten metal by the water.

The cast strand 45 passes between a pair of powered pinch rolls 51 that are remotely located from the mold 19 at a point where the cast strand is practically completely solidified, and these pinch rolls 51 coact on the cast strand 45 to withdraw it continually from the casting mold 19.

FIG. 5 illustrates a modification of a continuous casting mold 53 which receives molten metal 11 from a tundish 55. The casting mold 53 has a downwardly extending pouring nozzle 57 that is partially submerged in a pool of molten metal in one end of the casting mold 53.

The mold 53 has a bottom 59 and an arcuate end wall 61 that are similar to the bottom 23 and end wall 25 of the mold 19. The mold 53 has sidewalls 63, 65 which support a pair of rollers 67, 69 that are journaled in suitable support bearings 71 fastened to the sidewalls 63, 65. One of the rollers 69 (or 67) is driven by a conventional rotary mechanism 73.

Beneath the rollers 67, 69 is mounted an arcuate guide 75 that curves from the vertical toward the horizontal in a direction toward the discharge end of the mold 53. The guide 75 is also mounted to the sidewalls 63, 65. A roll of material 77 is mounted at any convenient location above the powered rolls 67, 69 and the material 77, passing between the rolls 67, 69 is directed by the guide 75 onto the surface of the molten metal 11 in the mold 53. The material 77 may be corrugated cardboard that is either dry or dampened, or such material maybe some inexpensive, expendable cohesive material that will not burn away quickly when contacting the hot molten metal. The material 77 coacts to subdue irregularities of the surface of the molten metal, such as surface waves which frequently develop in the mold when molten metal teems into the mold through the pouring nozzle 57.

In another instance, the material 77 may be perforated along one or both edges, and the one powered roller 69 (or 67) may have one or more end sprockets that engage the perforations to thereby advance the material 77 from the roll onto the molten metal surface.

In operation, the molten metal teems from the tundish through the pouring nozzle into the mold, and the molten metal fills the mold. A starter bar, of course, is used to close the open right-hand end of the mold, and the starter bar is withdrawn as soon as the molten metal adheres to the end of the starter bar to initiate the cast strand.

During the teeming of molten metal the surface of the molten metal is apt to have irregularities and be wavy in the zone around the pouring nozzle. The dams or the material on the surface of the molten metal, however, smooth out the surface irregularities or waves, so that the top surface of the cast strand, when it becomes solid, is as smooth as the three other surfaces. It will thus be seen that a cast product emerging from a mold of the invention will be substantially rectangular inasmuch as the usual thermal distortions caused by a conventional confining type of casting mold are not here present.

The lateral cross section of the casting at Section II—II shows that the sidewalls are disposed at an angle of about 100°at each lower corner, A, but that the angle at B of Section III—III is about 95°, and at Section IV—IV, the angle is 90°.

Thus, the change in the angular relation of the mold sidewalls to the bottom and that the bottom and sidewalls are curved as shown, eliminate such thermal distorting stresses. The curvature of the bottom and the sidewalls is directly related to the thermal changes in the cast strand as it cools during its progression through the mold. Wherefore, the strand which emerges from the mold of the invention is substantially rectangular as shown in FIG. 4.

From the foregoing description one skilled in the art will recognize several significant features and advantages among which are

That a mold in accordance with the invention is adapted to continuously cast steel slabs as well as strands;

That continuous steel slabs and strands cast in such a mold have a more nearly rectangular cross section than have slabs and strands cast in known molds in the prior art; and

That the mold of the invention is simple and effective to produce cast slabs that have smooth surfaces.

Although the invention has been described herein with a certain degree of particularity, it is understood that the disclosure has been made as an example and that the scope of the invention is defined by what is hereinafter claimed.