US3542115A - Continuous-casting method - Google Patents

Description

United States Patent 72] Inventor Irving Rossl Morristown, New Jersey [21] Appl. No. 693,430

[22] Filed Dec. 26, 1967 p [45] Patented Nov. 24, I970 [73] Assignee Coocast Incorporated New Yorl New York [54] CONTINUOUS-CASTING METHOD 2 Claims, 1 Drawing Fig.

[52] U.S. Cl. 164/82, 164/282 [51] Int. Cl. 822d 11/12 [50] Field of Search 164/82, 89, 273, 282, 283

[5 6] References Cited UNITED STATES PATENTS 2,698,467 1/1955 Tarquinee etal 164/89 3,257,691 6/1966 Krueger 164/282X 3,346,036 10/1967 Tarmann. l64/282X 3,344,841 10/1967 Rys Primary Examiner-J. Howard Flint, .lr. Assistant Examiner-R. Spencer Annear A trorney Sandoe, Neill, Schottler & Wikstrom ABSTRACT: In a continuous casting method wherein a strand of metal having a solidified skin and a molten core is formed in a chill mold and emerges from the lower end of the mold to be conducted along a curved guide path and is then straightened along a horizontal guide path, the movement of the strand from the mold to the horizontal guide path is controlled by driven rolls engaging the strand at a position close to the mold at the upstream end of the curved path, thereby avoiding Iongitudinal tension on the strand. In addition, the portion of the strand travelling from the mold to the horizontal guide path is maintained in a temperature range such that the core remains molten and the strand is sufficiently pliable to straighten out along the horizontal guide path by its own weight.

Patented Nov. 24, 1970 INVENTOR IRVING ROSSI r CONTINUOUS-CASTING METHOD cooled) which solidifies the periphery of the metal in the mold to form a strand having a solidified skin and a still molten core. The strand emerges from the lower end of the mold and is further cooled to complete solidification after which it is worked and/or cut into desired lengths. Additional molten metal is continuously poured in the upper-end'of the mold to replace the metal withdrawn in the strand during a casting run. During casting, the mold is usually oscillated generally along its axis to facilitate mold release andto increase casting rate.

In conventional continuous casting machines the strand emerges from the lower, exit, end of the mold in a downward direction. It is known to conduct the strand along a'curved guide path from the mold and then straighten the strand to travel in a horizontal path in order to reduce the height of the apparatus required, and to cut, or otherwise work, the strand in a horizontal position, which is more economical and convenient than a vertical position. It is also known to use a curved mold to cast the strand in a curve compatible with the curved path it follows from the mold, and the curved molds are customarily oscillated in an arc corresponding to the radius of curvature of the mold or the path.

In accordance with conventional practice, the strand is withdrawn from the mold by withdrawal rolls engaging aportion of the strand which is completely or almost completely solidified, because it has been felt that considerable pressure must be applied to draw the strand out of the mold and to move it far enough along a curved guide path past a sequence of cooling devices for it to be solidified sufficiently so as not to be distorted by the pressure applied by the withdrawal rolls. It is therefore conventional practice to apply cooling devices,

such as water sprays, to complete solidification of the strand as it travels along the curved guide path so that solidification is complete, or substantially complete, when the strand reaches the desired horizontal guide path. The withdrawal rolls are thus customarily located along the first portion of the horizontal guide path orat the lower end of the curved guide path. With this arrangement, the casting speed is limited to the rate at which the strand can be sufficiently solidified to withstand the pressure of conventional withdrawal rolls, without being distorted by them, when the strand reaches the rolls. In addition, the use of withdrawal rolls in the conventional manner applies tension to the newly formed portion of the strand which is only partially solidified. This tension is thus apt to break the strand or to produce undesired stresses and strains in it.

A further disadvantage of conventional methods and apparatus for withdrawing the strand from the mold isthat solidification of the strand has progressed so far when the su fficient'depending on the degree to which friction is reduced along the-guide path which conducts the strand down and away from the mold--to draw the strand out of the mold, with perhaps the application of some additional moving force. In any event, even if the lubrication on the surfaces of the mold and on the structure of the guide path away from the mold were such that the strand would move out of, and away from, the mold due entirely to gravity, it would still be desirable to apply some external moving force to control the emergence of the strand and stabilize the speed of withdrawal at a uniformrate compatible with the casting operation of the 'mold and with the most effective operating rates for subsequent apparatus performing work on the strand.

It is therefore an object of the present invention to provide a casting method in which the emergence of the strand from the mold is controlled without applying longitudinal tension to the strand thereby avoiding the creation of stresses and strains in the strand as it is conducted from the mold along a curved guide path to a horizontal guide path.

Another object is to provide a method in which the strand is straightened onto a horizontal guide path without having to apply external straightening forces, which would tend to produce undesired stresses and strains in the strand.

Still another object is to provide a method which enables a strand to be cast at higher speeds than by conventional methods or with conventional apparatus.

A further object is to provide a casting method which can be performed with simpler, less expensive apparatus than conventional methods.

In accordance with the method of the present invention a control force, suitably a pair of driven rolls, is applied to the strand close to the point at which it emerges from the mold, to assure the movement of the strand down a curved guide path to a horizontal guide'path. As mentioned above, the force necessary to remove the strand from the mold and conduct it down a curved guide path has been overestimated in the art. Consequently, the pressure of the control force on the strand may be much less than the pressure applied by conventional withdrawal rolls and can be applied to the strand, almost as soon as it emerges from the mold and while the skin around the molten core is relatively thin, without permanently damaging or appreciably distorting the strand.

Further, in accordance with the method of this invention, the strand travelling down the curved guide path to the horizontal guide path is cooled to the extent necessary to keep the skin from being remelted by the core but not enough to solidify the'coreto an extent that the strand becomes rigid. Thus, when the strand reaches the horizontal guide path it is relatively limp and straightens out along the horizontal guide path by its own weight, after which it is further cooled to complete solidification. In this way the sue of expensive As shown, molten metal from a conventional source, in-

dicated by the outlet 10 of a tundish, is poured in the upper end of a conventional continuously cooled, open ended chill mold 11, in which the periphery of the metal iscooled to form a strand 12 having a solidified skin 12a and a molten core 12b. The mold 11 may have either a straight or curved mold cavity and in either case may be oscillated as in known continuous casting apparatus. As indicated in the drawing, the periphery of the metal, forming the skin 12a of the strand in the mold, shrinks away from the walls of the mold. The strand 12 then emerges from the lower, exit, end of the mold, which is suitably provided with guide rolls 13 at opposite edges to guide the strand out the end of the mold.

.In accordance with the invention a control force, suitably providedby a pair .of driven control rolls 14 hearing against opposite sides of the strand 12, is applied at a position close to the exit end of themold and between the exit end and the upper portion of a curved guide path 15 for the strand. As

' mentioned above, the force forwithdrawing the strand from the mold may be considerably less than heretofore believed necessary. Consequently, the control rolls 14 operate with a relatively. light pressure on the strand so as not to distort it, the portion of the strand at the control rolls 14 having a molten core 12b within the solidified skin. The purpose of the control rolls 14 is twofold: one, toapply to the strand 12 whatever slight degree of force may be necessary to assist its movement out of the mold, and two, to ensure that the strand moves out of the mold 11 and down the curved guide path 15 uniformly at a desired rate. Cooling means, such as water sprays (not shown) may be applied to the surface of the strand 12 between the exit end of the mold and the control rolls 14.

The curved guide path 15 conducts the strand 12 from a point below the mold to a horizontal guide path 16. The curved guide path may be formed in any suitable manner for supporting and guiding the strand and for permitting the portion of the strand travelling along it to be cooled to some extent. For example, the guide path 16 may be formed of a sequence of idler rolls with water sprays for cooling arranged between the rolls and at opposite sides of the strand in a known manner for cooling the strand, or by a single or seg-- mented chute having cooling means incorporated therein or having spaces or openings with cooling devices, such as sprays or cooled surfaces, arranged therein. The horizontal guide path 16 may be similarly constituted, or may be formed in any other suitable or conventional manner for guiding, supporting and cooling the strand.

In accordance with the invention, whatever means is applied to cool the portion of the strand travelling from the mold 11 along the curved guide path 15 to the horizontal guide path 16, is applied to a degree to keep the skin 12a from being remelted by the heat of the molten core 12b but not enough to increase the thickness of the solidified skin, and correspondingly reduce the dimensions of the molten core, to an extent that the strand becomes rigid. As indicated in the drawing a liquid core is maintained in the strand (by limited exterior cooling) down to a portion of the strand which is on the horizontal guide path 16. Thus, the strand is maintained in sufficiently limp flexible condition to straighten out by its own weight as it moves onto the horizontal guide path 16, so that no additional, external straightening force is required.

In known apparatus, the strand may travel a considerable distance along a horizontal guide path 16-to'carry the strand in contact with further cooling devices, through annealing or temperature equalizing chambers, through shaping rolls, and/or in contact with cleaning devices, to a cutting station, for exampleso that additional force may have to be applied to continue the movement of the strand. In the drawing,

means for supplying this supplemental moving force is illustrated by driven forwarding roll 17 engaging the strand 12 at a position along the horizontal guide path 16. In this instance the forwarding roll 17 merely serves to continue the movement of the strand further downstream, the movement of the strand from the mold 11 to at least the first portion of the horizontal guide path 16 being produced by a combination of gravity and the force applied by the control rolls 14.

It is to be understood that the embodiment of the invention shown in the drawing and described in detail above is illustrative only and that modifications and variations may be made in the structure and mode of operation thereof without departing from the scope of the invention defined by the following claims.

I claim:

1. In a method of casting a strand of metal wherein molten metal is poured in the upper end of an open ended chill mold which cools the periphery of the metal therein to form a strand having a solidified skin and a still molten core and the strand emerging from the lower end of the mold is conducted along a curved guide path and is then straightened along a horizontal guide path, the improvement comprising, applying drive means to the periphery of the strand at a point between the lower end of the mold and the upstream portion of said curved guide path for controlling the rate at which the strand moves along said paths, pushing the strand along said curved guide path by applying a combination of gravity and of the force applied by said drive thereby to reduce longitudinal tension and lateral'pressure on the strand, and maintainin the periphery of the portion of the strand travelling from t e mold to the horizontal guide path .within a temperature range for maintaining the shell in solidified condition without completely solidifying the core until said portion of the strand is in said horizontal guide path whereby said portion of the strand is sufficiently pliable to substantially straighten out along the horizontal guide path by its own weight.

2. The method of claim 1 in which forwarding means is applied to the periphery of the strand at a position along the horizontal guide path for moving the strand along the horizontal guide path beyond said position without applying appreciable withdrawal force on the portion of the strand travelling from the mold to the horizontal support path, whereby the speed of movement of the strand to the horizontal support path is substantially controlled by said drive means.

Images