United States Patent Wang 51 June 13, 1972 [54] METHOD AND APPARATUS FOR [56] References Cited CONTINUOUS CASTING WITH UNITED STATES PATENTS GYRATING MOLD 1,010,851 12/1911 Bruckmann ..l64/260 72 Inventor: Chih Chung Wang, Lexington M 2,410,837 1 H1946 Peters ..l64/83 3,528,482 9/1970 Fastert ..l64/260 [73] Assignee: Kennecott Copper Corporation, New

York, Primary Examiner-Robert D. Baldwin AItorneyJohn L. Sniado, Lowell H. McCarter and Kenway, [22] Filed; Dec. 17, I970 Jenney& Hildrelh 211 App]. No.: 99,076 [57] ABSTRACT A method and apparatus for continuous casting of an ingot [52] US. Cl ..164/83, 164/260 f a mohen meta] empbying a mold having a conic opcm [51] Int. Cl. ..B22d 11/02, B22d 27/08 ing passing vertically through it and a mechanism for gyrating [58] Field of Search 164/83, 260 the mold about a point without rotating the mold about a vertical axis. The rate of gyration of the mold is related to the rate of continuous withdrawal of the ingot from the mold.

9 Claims, 3 Drawing Figures PATENTEnJun 13 m2 3.669.182

SHEET 10F 2 INVENTOR CHIH CHUNG WANG BY ATTORN EYS PATENTEnJu'n 13 m2 3. 669. 182 sum 2 [IF 2 MOTOR :41

I, INVENTOR CHIH CHUNIG WANG ATTORNEYS METHOD AND APPARATUS FOR CONTINUOUS CASTING WITH GYRATING MOLD FIELD OF THE INVENTION BACKGROUND OF THE INVENTION The present techniques used for continuous casting of metal ingots does not present an entirely satisfactory result. In a typical continuous casting process, the liquid melt is fed continuously from above into the pool and the cast ingot moves downward in synchronization with the feed rate. The ingot is formed in a generally cylindrical open-ended mold. One problem in the usual process arises from rupturing of the ingot, which allows molten metal to flow through the fissures into gaps which may exist between the ingot and the mold. This escaped metal solidifies and thereby causes defects on the surface of the ingot and increases friction as the ingot is being withdrawn. One method of obviating this difficulty has been to introduce vertical reciprocal motion of the mold as the ingot is being withdrawn. The velocity of reciprocation of the mold is related to the velocity of withdrawal of the ingot. On the downward stroke the mold is moving in the same direction as the ingot and thus there is little or no relative velocity between them and the skin rupture problem is eliminated. On the upward stroke, however, the relative movement between the ingot and the mold may increase to values of three times the ingot withdrawal rate and in this portion of the cycle ruptures may still occur.

SUMMARY OF THE INVENTION In the continuous casting process of this invention a mold having a conical opening through it is employed. The conical mold is disposed generally in a position so that the opening is vertical. The molten metal is fed from above into the mold with the ingot being formed within the mold and withdrawn at a steady rate from the bottom of the mold. A mechanism is provided to gyrate the cone about a gyration point located on the axis of the cone. The mold does not rotate about the cone axis. As the mold gyrates about the gyration point, that side which is aligned with the vertical axis of the ingot moves downward simultaneously with the withdrawal of the ingot. The pitch of the mold opening and the rate of gyration of the mold are selected so that the velocity of this downward vertical movement of the mold is matched to the withdrawal velocity of the ingot and hence there is no relative movement between the two.

On the opposite side of the mold where the mold wall is tilted by the gyration, there is upward movement of the mold. However, because of the conical shape this portion of the mold wall is moving not only upward but also outward from the ingot wall, thereby substantially eliminating friction between the two. Critical factors in this casting arrangement are the rate of gyration and the gyration point of the cone with respect to the position of the melt level in the ingot. If the rate of gyration is too fast, a downward compressing force may be exerted on the ingot skin. On the other hand, if the rate of gyration is too slow in relation to the ingot withdrawal speed, the meniscus of the liquid may become too high to be supported by the surface tension of the melt and thus spill over. The melt level should be held below the gyration point of the cone in order to ensure that the ingot diameter remains constant. However, if the melt level is too far below the gyration point then the rotational sliding of the surface of the mold on the ingot may become excessive.

DESCRIPTION OF THE DRAWINGS In the drawing,

FIG. 1 is an illustration generally in diagrammatic form of a casting apparatus suitable for use in the practice of this invention;

FIG. 2 is an-illustration in vertical cross-sectional view of a continuous casting apparatus suitable for use in the practice of this invention; and

FIG. 3 is a horizontal cross-sectional view taken along the line 3--3 of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS With reference now to FIG. 1, there is illustrated a continuous casting apparatus in accordance with this invention. A cone shaped mold 11, typically formed of copper, is open at either end and, in the casting process, a cast ingot 13 is withdrawn from the lower end of the mold at a constant rate. The ingot is formed by the solidification of a melt portion 15 within it, which melt is being continuously supplied molten metal through a feed 18. The cooling process in the ingot 13 is aided by water jets 23 positioned below the mold. The top of the melt 15 is definedby a meniscus 17 within the mold. The mold 11 is arranged to gyrate about a gyration point 28 located on the cone axis without rotation about the axis of the cone by means of a gyrating mechanism shown illustratively as wheel 20. As the wheel 20 traverses a circular path on the frame surface 12 beneath the peripheral lower edge of the mold 11, it produces the gyration to the mold. Thus one portion of the mold wall, shown generally as 25 is, at one time, aligned vertically with the ingot, while the opposite wall 27 of the mold is tilted away from the ingot.

If the rate of gyration with respect to the rate of withdrawal of the ingot produced by rollers 16 is properly arranged, then the downward motion of the vertical side 25 will match in velocity the downward movement of the ingot 13, so that there is no relative motion between them. On the opposite side 27 of the mold, the upward movement of the mold does not introduce friction between it and the ingot 13 wall because the wall 27, being tilted, does not come in sliding contact with the ingot at this point. The mold illustrated in phantom shows the opposite position during gyration with the wheel 20 located away from its initial position. As the wheel circles under the mold each portion of the mold is raised and lowered in similar fashion to the portions indicated as 25 and 27 in FIG. 1. The relationship between the cone angle, the rate of withdrawal and the rate of gyration can be expressed as follows:

R=2 G D tan 0 where,

R= rate of ingot withdrawal in inches/minute G rate of mold gyration in rpm D= diameter of mold opening in inches 0 cone angle.

In a typical example for a small ingot production, a mold inner diameter of r inch with a cone angle of 2 would be operated with a gyration rate of 200 r m and therefore a rate of ingot withdrawal of 7 inches per minute. In general the cone angles of the mold would be expected to be in the range of from about 1 to 4.

In FIGS. 2 and 3 there is illustrated in cross-sectional views a continuous casting apparatus suitable for use in this invention. The apparatus includes a mold element 30, which normally would be formed of copper and which has a generally cylindrical form, but wherein the bore 30a of the mold has a taper between 1 and 4 to form a generally conical shaped opening through it. The lip 32 at the top of the mold 30 is attached to a retaining flange 31, the latter being supported on a bearing 33. The bearing 33 is itself supported on a flanged collar 35 which includes an upstanding portion 38 retaining the bearing 33, a horizontal ring cam surface 37 and a lower collar 36 which bears against a lower bearing; 39 for rotation with respect to the fixed base 29. The cam surface 37 is tapered so that upon rotation with respect to the base 29 the bearing 33 and hence the supported mold 30 wobble about a point 56 on the cone axis introducing the gyration required. A vertical post 44 attached to the base 29 secures a horizontally extending arm 45 from the flange 31 of the mold to prevent the mold from rotating about an axis.

A motor 57 drives a circular gear 42 which meshes with a ring gear 40 attached to the flanged collar 35 to produce rotation of this flange and its cam surface and hence produce gyration of the mold. A water cooling coil 48 surrounds the bore 30a of the mold 30 to aid in the solidifying process. The ingot 50, cast in the mold, is withdrawn downwardly from the mold 30 through a pair of idler rollers 51 and this withdrawing motion is imparted to the ingot 50 by means of a driving roller 52. The roller 52 is driven by a motor 55 and, as earlier indicated, the relative speeds of the withdrawing roller and the rotating cam are arranged to control the rate of gyration with respect to both the taper of the mold and the rate of withdrawal.

What is claimed is: l. A method of continuous casting of a metal ingot from a Supply of molten metal comprising the steps of,

gyrating about a point a mold having a vertical cone shaped opening through it, said gyration continuously aligning a portion of the mold side with the vertical axis of the ingot,

continuously supplying molten metal into the top of the opening through said mold while withdrawing the solidified ingot from the bottom opening of said mold at a predetermined rate, and

maintaining the downward vertical movement velocity of said portion of the mold side matched to said predetermined withdrawal rate while tilting a portion of the opposite mold side out of sliding contact with said ingot.

2. A method in accordance with claim 1 wherein the conical opening through said mold has a cone angle and wherein the rate of ingot withdrawal is expressed as,

R 2 G D tan 6 where,

R rate of ingot withdrawal in inches/minute G rate of mold gyration in rpm D diameter of mold opening in inches 0 cone angle.

3. A method in accordance with claim 1 wherein said molten metal forms within said ingot a melt having a meniscus level defining its upper surface and wherein the point of gyration of said mold is above said meniscus.

4. Apparatus for continuous casting of metal ingot from molten metal comprising,

a mold element having a conical opening extending through means for gyrating said mold element about a point on the axis of said conical opening, such that a portion of the mold side will be continuously aligned with the vertical axis of the ingot means for continuous supplying said molten metal to one end of the opening through said mold element, and

means for withdrawing continuously at a predetermined rate the solidified ingot from the other end of the opening through said mold element such that said ingot withdrawal velocity is matched to the downward vertical movement velocity of said portion of the mold side.

5. Apparatus in accordance with claim 4 wherein said mold element is formed of copper and is water cooled.

6. Apparatus in accordance with claim 4 wherein said mold element is constrained from rotating about the axis of said conical opening when said element is gyrating.

7. Apparatus in accordance with claim 4 wherein said mold element is positioned so that said conical opening is generally vertical.

8. Apparatus in accordance with claim 4 and further including means controlling the rate of gyration of said mold element to a first velocity and controlling the rate of withdrawal of said ingot, said means for controlling being arranged so that the relationship between the rate of withdrawal of said ingot and the rate of gyration of said mold is R= 2 G D tan 0 where,

R= rate of ingot withdrawal in inches/minute G= rate of mold gyration in rpm D= diameter of mold opening in inches 0= cone angle.

9. Apparatus in accordance with claim 4 and further including a base member, said means for gyrating said mold element comprising a rotatable cam element of varying thickness supporting said mold element upon said base element and, means for rotating said cam thereby producing the gyration of said mold.