US3339623A - Thermal bending of continuous castings - Google Patents

Description

Sept. 5, 1967 v F. w. RYs ETAL 3,339,623

lTIERMAL BENDING' OF C-ONTIUOUS CASTINGS Filed July l0, 1964 Il IT III ,slip

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FEEDRICK PV. HYS ,QL/F05 EASTON BWM 6' Mei/"daxt United States Patent O 3,339,623 THERMAL BENDING OF CONTINUOUS CASTINGS Fredrick W. Rys and Rufus Easton, Pittsburgh, Pa., as-

signors to Koppers Company, Inc., a corporation of Delaware Filed July 10, 1964, Ser. No. 381,620 12 Claims. (Cl. 164-83) The present invention relates to metal castings and, more particularly, to improvements in the method and apparatus to produce continuous metal castings.

The continuous casting of metals, and of steel in particular, is usually accomplished by pouring molten metal from a ladle into a tundish from which the molten metal ilows into a vertical casting mold. The mold is usually oscillated vertically to prevent the casting from sticking to the walls of the mold, and thereafter the casting emerges c-ontinuously from the Ibottom of the mold.

It is customary to start the casting in a vertical posi- -tion and then mechanically bend it toward a horizontal position as soon as it is sufficiently a'ble to withstand forming stresses. A thin outer skin forms on the casting'while it is within the mold, and as the casting emerges therefrom the central portion of the billet or casting is not completely solid.

The various apparatus that have been proposed heretofore to change the path of travel of the casting from a vertical to a horizontal attitude, depend upon a mechanical action to force or bend the casting from the vertical to a horizontal position. As mentioned previously, however, the central portion of the billet exists as a semi-solid or as a liquid, and mechanically bending a continuous cast strand of metal too soon causes cracks to form in the solid skin portion of the casting, which has not yet attained complete solidification and which has little or no tensile strength. It follows, therefore, that the liquid metal in the central portion tends to flow outwardly toward these cracks. In any event, there is a distinct tendency for the newly formed casting to develop cracks as it is mechanically worked to change its path of travel from a vertical to a horizontal position.

In accordance with the .present invention, it has lbeen discovered that the path of travel of the billet may be changed from a Vertical to a horizontal position almost entirely by thermal action, thereby dispensing with the mechanical action and its attendant disadvantages, as discussed previously. In accordance with this invention, steel is cast continuously as a billet traveling in a vertical path and the direction of travel changed to a horizontal path by cooling the sides of the billet differentially whereby one side is cooled to a temperature of about at least 500 F. less than the other side.

As explained before, the outside skin of the billet is a .thin solid as it leaves the mold, and the inner core is still in a liquid or semi-solid condition. It has been the conventional practice heretofore to spray or otherwise cool the billet with streams of Water as described, for example, in Patent No. 2,698,467. Once the billet has become sufficiently solid as a result of this spray cooling, it is then bent Iby mechanical action to a horizontal path of travel. Such spray cooling has also been used in an effort to prevent warping of the billet. There is described, for example, in Patent No. 2,726,430 a method and apparatus for detecting a departure from normal, uniform thermal surface conditions, such as would produce warping. When the casting tends to warp in one direction, however, more water is sprayed on the side opposite the curvature to cool the longer side and counteract this warping. In this way the apparatus tries to maintain even surface temperature conditions to prevent warping.

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It has been discovered quite unexpectedly that the path of travel of the billet can be changed from a vertical to a horizontal attitude without using mechanical force. It has also been discovered quite unexpectedly, and contrary to the teaching in the heretofore mentioned Rossi Patent No. 2,726,430, that if the casting is subjected to uneven cooling within the mold or immediately upon emerging therefrom, the casting tends to as-sume a curved shape. That is to say, when opposite sides of the billet are cooled so as to achieve and maintain a substantial temperature differential, the cooler side becomes the longer side, and the billet will curve away from the cooler side. An explanation and rea-son of this action is not entirely known, but it is thought that, because the inner core of the casting is fluid and somewhat transient, the liquid metal flows toward the cooler side at a greater rate than it does toward the hotter side, whereby more metal is actually present at the cooler side than is present at the hotter side. A greater amount of metal on the cooler side causes the casting to bend away from that side, whereby the hotter side becomes the concave side and the cooler side the convex side. It is possible, therefore, in accordance with this invention to change the path of Itravel of cast billet from -a vertical to a horizontal position by the action of forces within the billet without using external mechanical force. Thus, the tendency for cracking, splitting, checking and the like, which have resulted from the use of heretofore known devices, is eliminated.

In accordance with this invention, molten metal is poured into a vertically reciprocable mold in the usual manner, and there emerges from the mold a continuously cast strand which has a cross sectional shape corresponding to the internal configuration of the mold. In one aspeet of the present invention, one surface of the billet is cooled substantially more than its opposite surface. This is accomplished by a casting support structure whose axis is offset with respect to the coplanar axis of the mold, whereby one surface of the casting is urged into contact with the lower portion lof one wall of the mold, so that this surface is cooled additionally. Consequently, the casting thermally bends away from this cooler side and toward the horizontal direction.

In still another aspect of the present invention, one surface of the billet may be cooled by sprays, for example, at a greater rate than its opposite side; the sprays acting upon the casting as it leaves the mold and while the internal core of the billet is still in a liquid or semi-solid condition. An effective temperature differential between the hotter and cooler sides of the billet, depends upon a number of parameters such as, for example, the rate of flow of the metal, the temperature of the metal in the mold, the size of the billet in cross section, the rate of curvature of the billet from a vertical to a horizontal position, and the like. It is desirable that the temperature differential between the -hotter and cooler sides be at least 500 F. Below this temperature differential, there is insufficient inducement for the metal to changeits rate of curvature effectively. On the other hand, the upper temperature limit is determined by the material itself and its characteristics. The hotter side must be cool enough so that the peripheral skin will be thick enough tovprevent a breakout by the fluid core; the cooler side, of course, will have a thicker skin through which lthe fluid core will not break. In any event, it is desirable to cool the cooler side as rapidly and as much as is practicable.

For a further understanding of the present invention and for advantages and features thereof, reference may be made to the following description taken in conjunction with the accompanying ydrawing forming a part of this application; FIG. l shows a schematic elevational view,

A partly in section, of apparatus that is adapted to .practice the present invention in one aspect; and FIG. 2 shows a schematic elevational view, partly in section, of apparatus that is adapted to practice the present invention in another aspect. Referring to FIG. 1, the lower portion of a tundish 11, containing a quantity of molten metal 13 issuing therefrom, is illustrated in one operative position above a vertical casting mold 15, wherein a continuously cast metal strand 17 is being formed. The cast metal strand 17 emerges from the bottom of the mold 15 and is supported upon a conventional type of roller apron structure 19, which includes a plurality of roller members 21, a plurality of spray nozzles 23 alternately disposed between the roller members 21. I

In the continuous metal casting process, it has long been recognized that there is a first zone of close contact of the molten metal with the Wall of the imold. In this first zone of close contact, heat is rapidly transferred from the molten metal, via the cooler walls of the mold, to the mold coolant medium, and there is formed in this zone, a solidified outer shell or skin on the casting. This initial zone of contact, designated in the drawing as zone A, extends downward from the uppermost level of mold wall contact, from where the mold Wall is tangent to the rneniscus of the lmolten metal, to a lower level at which the outer shell or skin of the casting has become cold enough to solidify. At this lower level, the tensile strength of the outer skin is sufficient to withstand the static pressure of the molten rnetal which, heretofore, has held the newly formed skin of the casting against the wall of the mold. And, once the outer surface has cooled enough to produce a skin that has the necessary tensile strength, thermal contraction causes the casting to shrink away from the mold wall. Below the rst zone of contact, there is a zone of separation by shrinkage in which there is no close contact with the wall of the mold. This zone of separation is indicated as zone B on the right hand portion of the drawing and zone D on the left hand portion 0f FIG. 1. The reason why there are two zones of separation will be explained hereinafter. Since the casting is no longer in -contact with the walls of the mold, it is apparent that in zones B and D the rate of heat transfer is greatly reduced, as is the rate of solidication of the casting shell. More'- over, the rate 0f cooling and shrinkage of the casting is.

also reduced.

Referring again to FIG. 1, it should be noticed that arcuate axis 20 of the roller apron structure is not tangent to vertical axis 22 yof the casting mold, as might be expected, because the apron structure 19 is displaced laterally, toward the right hand portion of FIG. 1 so that the arcuate axis 20 intersects the vertical axis 22 at a point 24, which is located below the bottom level of the casting mold. The arcuate axis, then, is displaced toward the right a distance which, in a preferred embodiment, is approximately 2%,2 of an inch, measured at the level of the bottom of the casting mold I5.

Castings which are produced in accordance with the principles of the present invention, using a vertical casting mold and an arcuate roller apron structure displaced laterally as shown in the drawing and described hereinbefore, thermally bend away from the vertical position toward a horizontal attitude.

To understand the principles of the present invention, reference may be made to the drawing. The continuous cast metal billet or strand 17 may be started in the usual manner by inserting a dummy bar, or other suitable apparatus, into the mold and pouring molten metal 13 into the mold 15. The mold may be oscillated vertically in any suitable manner to prevent sticking of the casting to the mold walls, and as soon as the strand commences to form, the dummy bar and strand may be withdrawn in the normal manner. As soon as the strand 17 emerges from the mold, it is supported by the arcuate roller structure 19, but the roller apron structure, in accordance with the principles of the present invention, is moved laterally about 3/32 of an inch toward the right, and t-he axes of the mold and arcuate structure intersect at the point 24, as meutioned previously. The small horizontal, lateral displacement of the apron structure has the effect, therefore, of causing the right hand surface of the strand 17 to contact the inner wall of the mold wit-hin a second contact zone, designated in the drawing as zone C. There is no comparable second contact zone C at the left hand side of the mold, however. That is to say, the zone of separation 0n the right hand side, which is the zone B, exists intermediately between the first upper zone of contact A and the second lower zone of contact C. Thus, the surface of the strand 17, which is brought into contact with the wall of the mold in zone C, is cooled considerably faster than the left hand or opposite wall surface of the casting strand, which is not in contact with the wall of the mold. It has been noticed, that castings, which are produced in accordance with the principles of the present invention, bend away from the cooler side and their initially vertical cast position, toward a horizontal position.

To illustrate the principles of the present invention by way of example, assume that molten metal at about 2700o F. is being poured into a casting mold and that the casting, which has already been formed, emerges from the vertical mold 1S at the rate of about 100 inches per minute; the rate of emergence being measured along the center line of the casting. The molten metal initially is in contact with the walls of the mold and develops an outer solidified skin in zone A. At the lower limit of zone A, the temperature of the surface of the casting may be about 2400 F. Now then, the lower portion of the casting, which has already emerged from the mold, engages the horizontally displaced arcuate roller apron structure 19. The casting 17 is then urged toward the right, and the right hand surface of the casting is urged again into contact with the wall of the mold in zone C. The surface temperature of the casting in zone C is cooled considerably and reduced substantially below the temperature of the opposite wall of the casting. The surface temperature in zone C, for example, may be as low as about 1800" F., while the corresponding temperature of the surface at the left hand side of the casting 17, may be about 2400 F. Thus, a temperature differential of about 600 F. exists between the right hand surface and the left hand surface of the casting. Now then, when molten metal is cast and there is a surface temperature differential of more than about 500 F., it has been noticed that molten metal will ilow toward the cooler side at a faster rate than toward the hotter side. This means that the cooler surface of the casting becomes longer at a faster rate than the hotter side. In the example which we propose, the cooler right hand side of the casting may be emerging from the mold at a rate of about 107 inches per minute, and the hotter left hand side at a rate of about 103 inches per rninute. It will be apparent then, that the right hand -side of the casting is about four inches longer than the left hand side of the casting. The difference of four inches between the length of the right hand and the left hand sides of the casting results in the casting bending in an arc, with the cooler `and longer side further away from the center -of curvature. That is to say, the casting thermally bends toward the hotter left hand surface and away from the relatively cooler right hand surface.

At some level below the bottom of the mold, when the casting is substantially solid throughout, it is convenient to control the amount of spray cooling so that the surface temperature of the faces of the casting are approximately equal.

In another aspect `of the present invention, a roller arcuate apron structure 25 may be positioned, as shown in FIG. 2, so that its axis is tangent to the vertical axis of a mold 27 about at the bottom level thereof. Thus, there is no tendency for the apron structure 25 to urge one surface of the casting against a wall of the mold 27 as described previously and as shown in FIG. 1. In this instance, molten metal 13 is poured into the mold 27 and a continuous casting 29 is made in the normal manner, with an initial zone of contact, zone A1, and zones of separation, D1, will exist on both opposite sides of the casting. Hence, there is no differential cooling within the mold inthis aspect of the invention. However, the volume of Water emitted by a plurality of spray nozzles 31, 33 on the right and left hand sides respectively of FIG. 2, may be regulated and controlled so that the same surface temperature differential of about 600 F. is achieved. Consequently, the casting 29 will thermally bend toward the hotter side and toward the horizontal position for the reasons mentioned previously. Thus, it is possible to achieve thermal bending as a result of surface differential cooling developed entirely exteriorly of the mold.

It should be apparent to those skilled in the art that thermal bending may also be achieved both =by urging one surface of the casting against the wall ofthe mold, as shown in FIG. 1 and described previously, and by regulating the volume of coolant emitted by the spray nozzles, as shown in FIG. 2 and described hereinbefore.

From the foregoing, it should be apparent that the curvature of the apron structure should be practically conformable to the thermal curvature of the castmetal strand so as to avoid unnecessary mechanical bending action on the casting. The thermal curvature may be determined either by experience or by calculation, so

that the cast metal strand will be directed from the vertical toward the horizontal position with a minimum of bending stresses and attendant flaws and defects.

We claim:

1. Apparatus for use in forming a continuous strand of cast metal comprising:

(a) an oscillatable vertical mold having planar surfaces forming a mold cavity and a substantially vertical axis;

(b) means for pouring molten metal into the mold and forming therein a continuous strand of cast metal;

(c) means for continuously withdrawing the strand from the mold; and

(d) strand supporting means having an arcuate axis lying substantially in the plane of the vertical axis and disposed concavely thereto so as to intersect the vertical axis at a point below the bottom of the mold, said strand `supporting means urging one surface of said strand against one wall of the mold whereby said surface is cooled substantially more than another opposite surface and the strand thermally bends away from said cooler surface.

2. A method for forming a continuous strand of cast metal comprising the steps of:

(a) pouring molten metal into an oscillatable vertical mold having planar surfaces forming a mold cavity and a substantially vertical axis, and forming in said mold a continuous strand of metal;

(b) continuously withdrawing the strand from the mold; and

(c) urging said strand laterally toward said mold so that one surface of said strand is cooled upon contacting a cooled wall within said mold whereby said strand thermally bends away from the cooled surface of said strand and away from a Vertical downward direction toward a horizontal attitude.

3. Apparatus for use in forming a continuous strand of cast metal comprising:

(a) an oscillatable vertical mold having vertical planar lsurfaces forming a mold cavity and a substantially vertical axis;

(b) means for pouring molten metal into the mold and forming therein a continuous strand of cast metal;

(c) means for continuously withdrawing the strandv from the mold;

(d) strand supporting means having an arcuate axis lying substantially in the plane of the vertical axis, and disposed concavely thereto so that the arcuate 6 .i axis is substantially tangent to the vertical axis near the bottom of the mold; and (e) means for reducing the temperature of Ione strand surface in a region below said mold and in contact with the arcuate support means to a temperature substantially below the temperature of the opposite strand surface whereby the strand thermally -bends away from the substantially cooler surface toward the horizontal position. 4. A method for forming a continuous strand of cast metal comprising the steps of:

(a) pouring molten metal .into an oscillatable vertical mold having planarsurfaces forming a mold cavity and a substantially vertical axis and forming in said mold a continuous strand of metal;

(b) continuously withdrawing the strand from the mold;

(c)- reducing the temperature of one surface of the strand in a iirst region below said m-old to a temperature substantially below the temperature of an op.

posite surface whereby said strand thermally 'bends away from said cooler surface and the axis of said strand is arcuately directed toward the horizontal; and

(d) supporting said thermally bending strand in such a manner that the arcuate axis of said strand intersects the vertical axis of said mold at a location fbelow the bottom of said mold.

5. A method for forming a continuous strand of cast metal comprising the steps of:

(a) pouring molten metal into a vertical mold and forming therein a continuous strand of cast metal; (b) continuously withdrawing the strand from the mold; and

(c) maintaining a superficial thermal ditferential of at least 500 F. between an opposite pair of surfaces of said strand in a region below said mold whereby said strand thermally bends away from the cooler of saidopposite pair of sides toward the horizontal.

6. A method for thermally bending a Icontinuous strand of metal cast in a vertical mold from which emerges said continuous strand, comprising the steps of:

(a) reducing the temperature of one surface of the casting in a region below the mold to a temperature of at least 500 F. below an yopposite surface; and

(b) maintaining t-his thermal surface dilferential whereby the casting thermally bends away from the cooler side toward the horizontal.

7. Apparatus for thermally bending a continuous strand of cast metal comprising:

(a) ya mold having a casting cavity comprised of vertical planar walls with a vertical axis adapted to receive molten metal and form therein a cast strand of metal;

(b) means for cooling the planar walls of said mold whereby a portion of the molten metal in cont-act with the cooled walls of said mold solidifies and shrinks away from contact with the mold walls in a rst zone; and

(c) means urging said strand laterally toward said mold so that one surface of the strand portion within the mold contacts one cooled wall of the mold and said one strand surface is cooled thereby to a temperature substantially below the temperature of an opposite surface whereby the strand thermally bends away from said one cooled surface and toward the horizontal.

8. The invention of claim 7 wherein: v

(a) said strand urging means maintains .said one surface in contact with said one cooled wall of the mold causing the thermal differential between said one cooled strand surface and an opposite surface to be at least 500 F.

9. The invention of claim 8 including:

7 8 (a) means for applying cooling medium to the sur- (a) urging said strand laterally with respect to'the faces of said strand in a region below said mold to moldso that one surface of the cast strand contacts substantially equalize the temperature of the surfaces a cooled wall lof said mold and is diierentially cooled of said strand. with respect to an opposite surface of said strand; 10. The invention of claim 4 including: 5 and Y (a) equalizing the temperature of the surfaces of said (b) further differentially cooling said one surface in a strand in a second region located below said mold zone below said mold whereby said strand thermally and below rst region. v bends away from the diierentially cooler surface 11. In a continuous metal casting system wherein a towards the horizontal. quantity of molten metal is introduced into an oscillatable 10 mold having a vertical walled mold cavity from which a References Cited metal casting is continually withdrawn, the improvement UNITED STATES PATENTS comprising:

(a) means urging said metal casting laterally toward lsalslllkeet lll'r 'e'r a Wall of `said mold so that one surface of the cast- 15 c n g ing contacts one wall of the mold and is thereby FOREIGN PATENTS differentially cooled with respect to `an opposite surface of Said casting; and 1,353,998 1/1964 France. (b) means for further differentially cooling said one 911,066 5/1954 Germany' surface whereby said casting thermally bends yaway 20 from said differentially cooler surface towards the OrHER REFERENCES horizontaL Scientic American, The Continuous Casting of Steel, 12. In the method for withdrawing a continuous strand December 1963 V01- 209 N0- 6 PP* 8287 TL S5' of metal formed in a mold having cooled planar vertical y walls defining a mold cavity, the improvement compris- 25 I' SPENCER OVERHOLSER Primary Examiner' ing; R. S. ANNEAR, Assistant Examiner.

Claims (2)

1. APPARATUS FOR USE IN FORMING A CONTINUOUS STRAND OF CAST METAL COMPRISING: (A) AN OSCILLATABLE VERTICAL MOLD HAVING PLANAR SURFACES FORMING A MOLD CAVITY AND A SUBSTANTIALLY VERTICAL AXIS; (B) MEANS FOR POURING MOLTEN METAL INTO THE MOLD AND FORMING THEREIN A CONTINUOUS STRAND OF CAST METAL; (C) MEANS FOR CONTINUOUSLY WITHDRAWING THE STRAND FROM THE MOLD; AND (D) STRAND SUPPORTING MEANS HAVING AN ARCUATE AXIS LYING SUBSTANTIALLY IN THE PLANE OF THE VERTICAL AXIS AND DISPOSED CONCAVELY THERETO SO AS TO INTERSECT THE VERTICAL AXIS AT A POINT BELOW THE BOTTOM OF THE MOLD, SAID STRAND SUPPORTING MEANS URGING ONE SURFACE OF SAID STRAND AGAINST ONE WALL OF THE MOLD WHEREBY SAID SURFACE IS COOLED SUBSTANTIALLY MORE THAN ANOTHER OPPOSITE SURFACE AND THE STRAND THERMALLY BENDS AWAY FROM SAID COOLER SURFACE.

2. A METHOD FOR FORMING A CONTINUOUS STRAND OF CAST METAL COMPRISING THE STEPS OF: (A) POURING MOLTEN METAL INTO AN OSCILLATABLE VERTICAL MOLD HAVING PLANAR SURFACES FORMING A MOLD CAVITY AND A SUBSTANTIALLY VERTICAL AXIS, AND FORMING IN SAID MOLD A CONTINUOUS STRAND OF METAL; (B) CONTINUOUSLY WITHDRAWING THE STRAND FROM THE MOLD; AND (C) URGING SAID STRAND LATERALLY TOWARD SAID MOLD SO THAT ONE SURFACE OF SAID STRAND IS COOLED UPON CONTACTING A COOLED WALL WITHIN SAID MOLD WHEREBY SAID STRAND THERMALLY BENDS AWAY FROM THE COOLED SURFACE OF SAID STRAND AND AWAY FROM A VERTICAL DOWN WARD DIRECTION TOWARD A HORIZONTAL ATTITUDE.

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