US2815551A

US2815551A - Method of and apparatus for the casting of metal

Info

Publication number: US2815551A
Application number: US516996A
Authority: US
Inventors: Wilfrid C F Hessenberg; Savage John
Original assignee: British Iron and Steel Research Association BISRA
Current assignee: British Iron and Steel Research Association BISRA
Priority date: 1955-06-21
Filing date: 1955-06-21
Publication date: 1957-12-10
Anticipated expiration: 1974-12-10

Description

Dec. 10, 1957 W. C. F. HESSENBERG ETAL METHOD OF AND APPARATUS FOR THE CA STING OF METAL Filed June 21, 1955 FIG.1

17- FIG. 3

izz I 10 \H a FIG.2

28 22 fii I EV Q 31 5 1 27; g 2 H l'w 2 F 10 INVENTORS WILFRID CF. HESSENBERG JOHN SAVAGE ATTORN EY Unied States METHOD OF AND APPARATUS FOR THE CASTING OF METAL Application June 21, 1955, Serial No. 516,996

Claims. (Cl. 22-57.2)

This invention relates to the casting of metals, and more particularly to a method of and apparatus for the continuous casting of high melting temperature metals such as ferrous alloys.

In the continuous casting of metals various systems of casting are used, although all continuous casting involves the delivery of a stream of molten metal to an open ended fluid cooled casting mold in which an embryo casting is formed and from which the casting is withdrawn by a withdrawal mechanism. Many of the continuous casting systems are operated in such a manner as to cause a relative movement between the mold and the casting during one portion of the casting operation while during another portion of the casting operation the casting is maintained stationary relative to the wall of the mold. In one continuous casting system the mold is oscillated in a direction axially of the casting in a predetermined timed pattern, while the casting is withdrawn by the withdrawal mechanism at a substantially uniform rate. In another system of continuous casting the casting is continuously withdrawn and the mold is arranged for axial movement thereof in accordance with the friction between the casting and the wall of the mold. When the frictional forces between the casting and the mold are sufiicient the mold is moved axially with the casting so that no relative movement therebetween occurs. As the mold moves, the forces preventing move ment of the mold gradually increase until this force overcomes the frictional force between the casting and the mold, and the mold is returned to its previous position. In yet another system of continuous casting, the mold is stationary and the withdrawal mechanism is operated in a predetermined timed pattern so that the casting withdrawal is stopped periodically, and then moved so that alternately no relative movement occurs between the casting and the mold.

During the continuous casting of metal there is a atent tendency for the initially solidified metal forming the from the mold and necessitates a stoppage of the casting process.

Each of the above described systems of continuous casting operation has largely overcome the sticking tendency of the casting to the mold wall, or has at least alleviated the rupture tendency of the casting under such conditions. skin on the casting has not altogether been avoided in any of the known continuous casting systems. In this connection it will be understood that if a perfect method of lubricating the mold wall was possible, the casting skin would not stick to the mold wall. However, in actu- However, the rupture of the initially formed al practice perfection of lubrication has not been at tained since at least occassionally there will be a tendency for the casting skin to stick to the mold wall and to rupture the casting.

In accordance with the present invention the rupture of the initially formed casting skin, by reason of its adhesion to the mold wall, has been largely overcome. This is accomplished according to the invention, by applying a compressive force to the billet so as to release the casting before relative movement occurs between the casting and the mold wall so as to prevent the sticking of the skin to the wall of the mold. The compressive force is applied to the casting in a direction opposite to the normal direction of the casting withdrawal from the mold.

The compressive release force may be applied to the casting by the application of a force in a direction opposite to that of the casting withdrawal, or the compressive release force may be applied to the mold. The application of the compressive release force may be governed by the friction of the casting on the mold wall during relative movement therebetween, which is an indication of adhesion between the casting and the mold.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described preferred embodiments of the invention.

Of the drawings:

Fig. 1 is an elevation, in section, of a continuous casting mold which is spring mounted and constructed in accordance with the present invention.

Fig. 2 is an elevation, in section, of a modified application of the invention to a continuous casting mold; and

Fig. 3 is a still further modification of the invention as applied to a stationary continuous casting mold.

The present invention may be applied to any of the continuous casting systems wherein alternative relative movement and no relative movement occurs between the continuous casting mold and the casting therein. In any of the casting systems described, the compressive release concept of the invention is applied to cause a compression of the casting so as to break the adhesion of the casting relative to the mold immediately prior to the occurrence of relative movement between the casting and the mold. The compressive release concept can be applied in a uniform timed cycle to either the mold or the casting or the compressive release impulse can be imposed as required when the friction between mold and casting exceeds a selected value.

Referring first to Fig. l, the continuous casting mold 10 is provided with a cooling jacket 11 through which a cooling liquid, such as water, passes. The cooling liquid enters by an inlet pipe 12 and leaves the mold jacket by an outlet pipe 13. The mold 10 is mounted on a top plate 14 extending beyond the periphery of the cooling jacket 11 and is supported for vertical movement by three compression springs 15 circumferentially equally spaced around the mold. The springs 15 are mounted on the surface 16 of an annular recess 17 of a support member 18. Aligned with the springs 15 and mounted be tween the top of the recess 17 and the upper surface of the plate 14 are three pneumatic rams 20. These rams are of a type which provide a sudden impact on the plate 16 upon the application of compressed air to the inlet pipes 21. The rams may be, for example, of a type frequently employed as pneumatic hammers.v Astream of molten steel, as indicated at 22, is poured into the top of plate.

the mold from suitable molten metal delivery means (not shown). The steel solidifies within the mold and the casting 23 is continuously withdrawn from the bottom of the mold by a withdrawal mechanism, such as the pinch rolls indicated at 24.

Providing that there is no sticking of the casting within the mold 10, the mold will remain in a substantially stationary position, with the casting 23 being continuously withdrawn from the lower end of the mold. When sticking between the casting and the mold occurs, the increase in the frictional force therebetween applies a downwardly moving force to the mold 10 which acts against the springs 15. When the friction between the casting and the mold reaches a predetermined value, compression of the springs by reason of the downward movement of the mold plate 14 engages a contact 25 at a preselected distance below the normal position of the plate 14. The contact 25 controls a solenoid operated pilot valve (not shown) for the delivery of compressed air to the rams 20. The delivery of compressed air to the rams cause an impulse force to be delivered to the mold, which causes the mold to move downwardly at a speed greater than the withdrawal speed of the casting. This downward force on the mold releases the casting from the mold wall, and causes compressive forces to be applied to the casting to release the casting from adhesion to the mold so that the casting can be withdrawn without rupture of the skin of the casting.

The location of the contact 25, the strength of the springs 15, and other design factors of the mold arrangement are determined by the size of the casting and the rate of casting withdrawal from the mold. By way of example, a 4" square casting withdrawn at a rate of 24" per minute, produced in an apparatus of the type disclosed in Fi l, utilized springs 15 having a compressive strength of 45 pounds per inch of spring compression. Under these conditions the control contact 25 was located so as to be actuated after a l downward movement of the mold 10. When supplied with compressed air of 80 pounds per square inch pressure, each of the rams released a downward thrust on the mold 10 equal to approximately 192 pounds which resulted in a downward movement of the mold of approximately /2. After the rams 20 had been actuated the mold returned to its original position, as guided and dampened by the springs 15 which in this instance served as shock absorbers.

In the embodiment of the invention shown in Fig. 1, one purpose of the compressive springs 15 is to regulate the application of the compressive release force by the rams. It will be further understood that other means can be used to actuate the application of forces on the mold for the compressive release of the casting from the mold.

In the modification of the invention shown in Fig. 2, the mold 10 is substantially the same as that shown in Fig. 1 and the casting 23 is continuously withdrawn by the pinch rolls 24 as described in connection with Fig. 1. In the Fig. 2 version of the invention the mold 10 is mounted on a support 26 by three compression springs 27 acting against the top plate 28. In this modification of the invention, the compressive force on the billet is cyclically applied and is not limited to operation only when sticking or adhesion occurs between the casting and the mold wall. In this arrangement, adhesion between the casting and the mold wall is prevented, rather than released after it has occurred as in the arrangement of Fig. 1. As shown, the top plate 28 is provided with a pair of cams 30 having their surfaces bearing on the The cams are continually driven from the driving means of thepinch rolls 24 so that the cams 30 operate in concert with the pinch rolls. The profile of the cam .surfaces is such that during their operation the mold is caused to move downwardly at a speed greater than the I cycle the mold 10 is returned quickly to its initial position under the forces exerted by the compressed springs 27. Thus, over the majority of the time in which the casting is being withdrawn the mold 10 is moving downwardly at a higher rate than the casting, so as to apply a compressive force to the casting, and thus prevent adhesion between the casting and the mold.

The rate and amplitude of the movement of the mold 10 is dependent upon the size of the casting produced and the rate of casting withdrawal. With a 4" square casting, withdrawn at a speed of 24" per minute, the rate of downward movement of the mold should be at least 1% times the speed of the casting withdrawal during the major portion of the camming cycle. During upward movement of the mold 10, the mold speed should be approximately five times the speed of the withdrawal of the casting. The amplitude of movement of the mold should be at least 1", but with higher casting production rates, the amplitude of mold movement should also be increased.

In the form of the invention shown in Fig. 3, the casting mold 10 is stationary and supported in a fixed position by structural members indicated at 31. The mold construction is similar to the construction illustrated in Figs. 1 and 2 and includes a water cooling jacket provided with inlet and outlet pipes for the flow of cooling fluid through the mold. As shown in Fig. 3, the pinch roll withdrawal mechanism 32 is driven at a suitable speed by, for example, a variable speed, reversing motor 33.

In this arrangement, the pinch roll withdrawal mechanism 32 is operated in a cycle of changing speeds, including a period when the casting is stationary in the mold. Thus, the cycle of pinch roll operations includes a withdrawal of the casting for a predetermined period of time, and a stoppage of the withdrawal mechanism. Immediately before the pinch roll operating mechanism 32 is restarted for the downward withdrawal of the casting, the pinch roll mechanism 32 is operated in a reverse direction to cause the casting to move upwardly within the mold 10. This impulse of upward casting movement is immediately followed by the downward withdrawal of the casting. The compressive forces of the upward movement of the casting releases the casting from the mold wall and substantially eliminates rupture of the casting skin during the subsequent withdrawal operation.

To attain the cycle of pinch roll operations described the motor is controlled by a timing mechanism schematically illustrated by the control box 34. The timing mechanism may be of the general type disclosed in United States Patent 2,682,691 with the addition of a control circuit suitable for the reversal of the motor 33 to attain the upward movement of the casting prior to the beginning of the downward removal of the casting from the mold.

While in accordance with the provisions of thestatutes we have illustrated and described herein a preferred embodiment of the invention, those skilled in the art will understand that changes may be made in the method of operation and form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of the invention may sometimes beused to advantage without a corresponding use of other features.

What is claimed is:

l. The method of continuously casting metal in an open ended fluid cooled mold which comprises the steps of delivering molten metal to said mold, withdrawing an at least partially solidified casting from said mold with relative movement therebetween in a first direction, maintaining the casting stationary with respect to the mold during a portion of the casting period, and causing relative movement between said casting and mold in a direction-opposite to said-first direction to compress the casting within saidrnold before relative movement in said first directionoccurs between said casting and said mold.

'2. The method of continuously casting metal according to claim 1, wherein said casting withdrawal is continuous. I

3. The method of continuously casting metal according to claim 2, wherein said fluid cooled mold is moved in a periodic pattern axially of said casting.

4. The method of continuously casting metal in an open ended fluid cooled mold which comprises the steps of delivering molten metal to said mold, at least partially solidifying the molten metal within said mold to forma self sustaining casting, continuously withdrawing said embryo casting from said mold, moving said mold axially of and with said casting a predetermined distance without relative movement therebetween in accordance with an increase in friction between mold and casting, imparting an impulse movement to said mold in the direction and at a speed in excess of said casting withdrawal, and restoring said mold to a selected position by movement axially of said casting and in a direction opposite to said casting withdrawal.

5. The method of continuously casting metal in an open ended fluid cooled mold which comprises the steps of delivering molten metal to said mold, at least partially solidifying the molten metal within said mold to form a self sustaining casting, continuously withdrawing said embryo casting from said mold, moving said mold axially of said casting with no relative movement between said mold and casting, moving said mold axially of said casting in the direction of and in excess of said casting withdrawal to compress the wall of said casting, and moving said mold axially of said casting in a direction opposite to said casting movement immediately after compressing said casting.

6. The method of continuously casting metal according to claim 1, wherein said casting is withdrawn from said mold intermittently, and the casting is driven into said mold prior to the resumption of casting wtihdrawal.

7. Apparatus for the continuous casting of metal comprising an open ended fiuid cooled mold, means for delivering molten metal to one end of said mold, a withdrawal mechanism for withdrawing a casting in a first direction from the opposite end of said mold, means for retaining the casting stationary with respect to said mold during a portion of the casting period, and means for causing relative movement between said moldand casting in a direction opposite to said first direction to compress the casting within said mold before relative movement occurs between said mold and casting in said first direction.

8. Apparatus for the continuous castingof metal comprising an open ended fluid cooled mold, means for delivering molten metal to one end of said mold, a withdrawal mechanism for withdrawing a casting from the opposite end of said mold, means for reciprocating said mold longitudinally of said casting in timed relation therewith so that the casting is stationary with respect to said mold during a portion of the casting period and the mold moves in the opposite direction to said withdrawn casting during another portion of said casting period so that there is relative movement therebetween, and means for compressing the casting within said mold by moving said mold in the same direction as and at a greater rate than said casting before relative movement in said opposite direction occurs between said mold and casting.

9. Apparatus for the continuous casting of metal comprising an open ended fluid cooled mold, compression springs supporting said mold, means for delivering molten metal to one end of said mold, means for withdrawing a casting from the opposite end of said mold, a contact actuated by movement of said mold when the casting adheres to and is stationary with respect to said mold, and means for compressing the casting within said mold before relative movement occurs between said mold and casting including a pneumatic hammer positioned to transmit an impulse to said mold in the direction of said casting withdrawal when said contact is actuated.

10. Apparatus for the continuous casting of metal comprising a stationary open ended fluid cooled mold, means for delivering molten metal to one end of said mold, means for withdrawing an embryo casting from the opposite end of said mold in an intermittent cycle of operation including a timed period when the casting remains stationary with respect to said mold, and means for compressing the casting within said mold before relative movement occurs between said mold and casting, including a timed control to reverse the withdrawal mechanism and to drive the casting into said mold.

References Cited in the file of this patent UNITED STATES PATENTS 1,088,171 Pehrson Feb. 24, 1914 2,284,704 Welblund June 2, 1942 2,597,046 Sondzimir May 20, 1952 FOREIGN PATENTS 3,221 Great Britain Feb. 8, 1912 718,644 Great Britain Nov. 17, 1954 674,136 Germany Apr. 5, 1939 877,940 Germany May 28, 1953 902,433 Germany Jan. 21, 1954