Patent Publication Number: US-4256165-A

Title: Stirring of molten metal core in a casting as withdrawn from a machine for continuous casting

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to electromagnetically stirring molten metal in a machine for continuous casting. 
     Generally speaking, stirring and-here particularly-electromagnetic stirring of the not yet solidified metal in a casting is a common expedient. Stirring the interior of the casting is used to enhance the cooling and solidification process and to impede organized solidification and formation of unwanted texture in the crystallization. Moreover, upon stirring one can expect reduced liquation of additives and reduced porosity of the core of the casting as it is about to be established. 
     The devices used for stirring the still molten metal in a casting are either placed alongside the casting as withdrawn from a mold, or the stirring devices circumscribe this casting. It will be appreciated that for the purpose of adequate and efficient electrical coupling, one has to place the stirring device, i.e., the electromagnetic energizing means, as close to the surface of the casting as possible. 
     The stirring devices referred to above are, necessarily, part of the equipment and machine to be installed before casting begins. Moreover, the requisite proximity to the casting requires that the position of the stirring device must be rather accurately predetermined and set in relation to the mold cavity. This means that the stirring device as mounted in the machine is directly tied to the format and cross section of the casting. A different mold and, particularly, a differently contoured and dimensioned mold cavity in the same machine requires a completely new installation of the stirring device, particularly if placed alongside the casting. A stirring device that circumscribes the casting is actually designed and rated for one type of casting as far as dimensions are concerned and may not be usable at all for other casting dimensions. 
     DESCRIPTION OF THE INVENTION 
     It is an object of the present invention to provide a new and improved electromagnetic stirring device for continuous casting machines, which device does not have the limitations outlined above. 
     It is a specific object of the present invention to provide a new and improved stirring device for a machine for continuous casting in which machine the casting is withdrawn along a withdrawal path in a particular withdrawal direction of casting. 
     In accordance with the preferred embodiment of the present invention, it is suggested to provide a stationary bed and a carriage means which runs on the bed in a direction transversely to the direction of movement and withdrawal of the casting as per the specific object. 
     The electromagnetic stirring device (or devices) is (or are) mounted on the carriage in overhung relationship to be placed in close proximity to the casting. The carriage means may have additional mounting means, permitting adjustment of the stirring device in a third orthogonal direction. The invention is suitable for placing a single electromagnetic stirring device in close proximity to the casting, but one may also use sectional stirring devices for multiphase operations and circumscribing the casting. The individual device elements are then separately mounted and separately adjustable. 
     It can thus be seen that the stirring device, in accordance with the preferred embodiment, can be adjusted to different size and differently contoured castings, or is even retracted completely if for any reason stirring is not desired. The retractability facilitates greatly maintenance, repair, and exchange of the several parts, even while casting continues. 
     The preferred embodiment of the invention, the objects and features of the invention and further objects, features, and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of an example in accordance with the preferred embodiment, showing also a cross section through a casting; 
     FIGS. 2 and 3 are views similar to FIG. 1, showing modified examples of the preferred embodiment; 
     FIG. 4 is a side view of another device in accordance with the preferred embodiment; and 
     FIG. 5 is a top view similar to FIGS. 1, 2, and 3, but showing an example of a circumscribing stirring device in accordance with the preferred embodiment. 
    
    
     Proceeding now to the detailed description of the drawings, all Figures show a metal casting 1, e.g., steel, resulting in an ingot of square-shaped cross sections. The section is taken in each instance at a location downstream from the mold, but sufficiently close thereto as the interior of the casting is still in the molten state. The center X represents the direction of casting in the plane of the drawing. 
     FIG. 1 shows an electromagnetic structure or element 2 of conventional design which, when placed sufficiently close to casting 1, will cause the molten interior thereof to move, to thereby provide stirring action to and of the not yet solidified metal. 
     The electromagnetic stirrer is mounted on a holder 3 which, in this example, is directly constructed as a carriage. This carriage can be moved on a stationary support constructed as a rail bed 4. Bed 4 may be constructed as a stationary frame with rails or similar guide elements on which holder/carriage 3 can run. 
     The rail or frame 4 does not extend all the way to the area to be occupied by casting 1 because the dimensions of the latter may change. Thus, carriage 3 is of the overhung variety, permitting the stirring element 2 to be placed as close as necessary to casting 1. If the dimensions of the casting change, it may merely be necessary to advance or retreat devices 2 and 3. Also, during startup, mold changes, maintenance, etc., one will retract device 2 on carriage 3 to facilitate access. 
     The stirring device must be electrically insulated from the casting as direct conduction of current is not desired. Since the metal being cast is necessarily in contact with the mold, and since the mold is usually made (at least in parts) from copper, one really has to insulate the stirring device from from the casting machine as a whole. Thus, one may make either bed 4 or carriage/holder 3 from insulating material, or provide at least insulation between them and the foundation. 
     FIG. 2 shows also a casting 1 and a stirring element 2. This electromagnetic element is mounted here on the front end of a spindle 13 by means of which element 2 (possibly without turning, there being suitable bearings) can be advanced towards or retracted from the casting. 
     Spindle 13, holding, carrying, and positioning the stirring element, is held on an arm 16 or a carriage 5 which, in turn, can slide on a bed 14. Thus, and as indicated by the two arrows, stirring element 2 can be laterally displaced and retracted, or otherwise positioned, in the one direction of carriage movement and in an orthogonal direction, towards and away from the casting axis, i.e., the two adjusting positions are both orthogonal or transverse to each other and to the axis and direction of casting. 
     In order to facilitate putting the device into operation, arm 16 may be provided with suitable adjustable stops, cooperating with a stop on element 2 or its immediate holder, so that for any given dimension of the casting, the spindle needs to be adjusted just until the stops engage. 
     FIG. 3 illustrates also a carriage 25 being movable on rails and carrying a pivot arm 23 extending laterally to and from the casting. One end of arm 23 carries a holder 26 which, in turn, holds stirring element 2 in a suitable position in relation to casting 1. Stirring element 2 is thus also in this example moved transversely to the carriage movement. The stops for adjustment and positioning element 2 exactly as required may be provided inside the carriage in this case. 
     FIG. 4 illustrates a positioning device in somewhat greater detail, but following the basic concepts particularly of FIGS. 1 and 2. FIG. 4 shows a rail 34 as stationary base and support on which runs a carriage 35 having rolls 38. An arm 33 extends from carriage 35, pertaining thereto. Arm 33 may be pivoted in carriage 35 by means of a pivot pin or bolt 39. Stirring element 2 is mounted to the one, external, end of that arm which extends beyond rail 34. 
     A spindle 32 is used to place stirring device 2 closer to, or farther from, casting 1 as a fine position adjustment. In addition, loops are mounted on arm 33 to journal guide rollers 36 which engage the casting and thus position device 2 as positive relation to the outer surface of the casting. 
     The rear of carriage 35 carries equipment 37 which will include the requisite drive means such as an electromotor by means of which spindle 32 can be turned, arm 33 be pivoted, and the carriage be moved on the track. Also, equipment 37 will include cooling means to cool down the equipment as the influx of heat from the solidifying ingot and casting is quite significant. 
     Moreover, device 37 serves as a counterweight for the overhung front portions. Device 37 may include additional weights to balance the carriage as a whole. 
     Conveniently, rolls 38 may be made of electrically insulating material, and/or rails 34 may be so constructed or mounted. 
     FIG. 5 illustrates a three-phase stirring equipment having three electromagnetic devices 2a, 2b, and 2c, which together circumscribe the casting but for the requisite gaps. The equipment includes additionally a pair of pivoting arms 43a and 43b, respectively carrying devices 2a and 2b and being pivoted by a hydraulic device 49. A third, relatively short, arm 43c is provided to hold electromagnetic device 2c. 
     Arms 43a and 43b are pivoted on a frame 45 by means of pivots 47a and 47b, respectively. The frame is also constructed as a carriage, having wheels 48 and running on rails 44. Arm 43c is the piston rod for another hydraulic actuator 46 on the frame and carriage 45. 
     It can thus be seen that the hydraulic actuator 9 causes arms 43a and 43b to spread in order to recede from and clear the casting, whereupon carriage 45 can be retracted For positioning, one reverses the movement, and piston drive 46 will fine-position the third energizing element, 2c, for the stirrer. 
     Also in this example, rollers on wheels 48 may be made of insulating material, and/or frame 45 and/or rails 44. 
     This particular example is shown to be provided with hydraulic actuators for positioning and retracting the several electromagnetic stirring elements. Instead, one could use electromagnetic actuators such as servomotors, solenoids, etc. Any one of the adjustment movements described above can be so carried out. One can also use pneumatic or mechanical actuators. 
     The invention is not limited to the embodiments described above, but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.