DEVICE FOR STIRRING THE MOLTEN PORTION OF A CAST STRAND

Abstract: Device for stirring of the molten portion of a cast strand coming from a continuous casting machine. The device com­ prises at least one stirrer placed at the cast strand in such a way that the stirrer does not surround the entire strand and is movable away from the strand. Further, a sta­ tionary core portion (3) is.arranged at the cast strand, which together with the stirrer, when the latter is in the operating position, completely or partially surrounds the cast strand.

Description: The invention relates to a device for stirring the molten portion of a cast strand according to the introductory part of Claim 1. Such a device is known from the DE-B-28 28 160. Stirring of the molten portion of a cast strand is performed in order to avoid segregations, the formation of cracks, the formation of voids, and the like, in the continuously cast product. To effect stirring of the molten portion of the strand, it is known to use a so-called round stirrer of an asynchronous motor stator type or a straight stirrer comprising one or more partial stirrers surrounding the cast strand (see, e.g., US-A-4,183,395 and the corresponding DE-C-28 03 503). A disadvantage of these types of stirrers is that they are fixedly mounted around the cast strand and therefore are difficult to be rapidly moved in the case of an operational disturbance in the form of, for example, loss of water and a breakthrough in the strand. This problem is overcome by a device disclosed in the DE-B-28 28 160 which allows the stirrer or parts thereof to be moved in relation to the strand. This is achieved by either mounting the entire stirrer or each separate part of the stirrer to one movable means each of which can be moved in relation to the strand by either a rotating or a translatory movement. In the case where the stirrer is composed of different stirrer parts each part consists of a core portion carrying at least one current-supplied winding. These windings are very sensitive to heat and mechanical impact, and each of these core portions are consequently movably arranged which renders the device very costly and complicated. The DE-A-28 34 305 discloses a stirrer the core of which comprises a yoke and several radially oriented legs each provided with a coil. These coils, along with their legs, can be radially displaced towards the strand thereby moving relatively to their associated yoke portion. According to another solution each coil-carrying leg is rigidly connected to a yoke portion, whereby the yoke portions can be moved relative to each other so that the diameter of the circle on which the coils are arranged around the strand may be varied. These known devices allow to adjust the position of the stirrer portions to the diameter of the cast strand. The invention aims at developing a device for stirring the molten portion of a cast strand of the above-mentioned kind with core portions on movable means the construction of which is simple while yielding full protection of all sensitive parts of the stirrer in case of an emergency. To achieve this aim the invention suggests a device according to the introductory part of claim 1, which is characterized by the features of the characterizing part of Claim 1. Further developments of the invention are characterized by the features of the additional claims. According to the invention the stirrer proper, which comprises the electrical winding and the electric connections, only partially surrounds the strand, and this stirrer is mounted in such a way as to be movable in relation to the strand. The displacement of the stirrer entails that the risk of damage to the stirrer in connection with interruptions of the service, for example loss of cooling water or a breakthrough in the strand, is reduced. To enable repair and maintenance work close to the strand to be carried out in a more simple and rapid manner, the stirrer can be moved from the operating position at the cast strand to a position where it is possible, for example for tools and operating staff, to reach the cast strand and its surrounding parts, such as the cooling device, tubes, backing rollers, and the like, of the continuous casting machine. A stationary core portion without a coil is also arranged close to the strand, which core portion completely or partially fills up the space around the strand which is not occupied by the stirrer when the stirrer is positioned in its operating position. The stationary core portion entails an improvement of the rotating magnetic field which produces the movement in the molten portion of the cast strand. An additional advantage with a stirrer which does not completely surround the strand is that the device is adjustable to different sizes of the cast strand from, for example, billets (100 x 100 mm) to blooms (500 x 500 mm), since the stirrer has an open part which may be completely or partially filled up by the stationary core portion. This stationary core portion can either be dimensioned according to the dimensions of the cast strand in question ore/and the stationary core portion can be supplemented with the addition of magnetically conductive material to fill up any gaps in those cases where the stationary core portion only partially fills up the open part of the stirrer. Figure 1 shows a cross section of the stirrer 1 comprising an iron core carrying 4 to 6 coils which form a winding for a two-phase or three-phase current supply. The stirrer 1 is designed so as to partially surround the cast strand 2. Figure 1 shows how the stirrer 1 surrounds three sides of the strand 2. The cast strand 2 consists of a solidified shell and a molten inner portion, which is brought into motion by the action of a two-pole rotating magnetic field. Around the strand 2 there is a framework consisting of, inter alia, tubes and backing rollers (not shown in the Figure). A stationary core part 3 is mounted close to the strand 2. The core part 3 may completely or partially fill up the space around the strand 2 which is not occupied by the stirrer 1 when the stirrer is in the operating position. Figure 2 shows an example of a suspension of the stirrer 1, enabling the stirrer 1 to be moved away from the cast strand 2.

Claims: Device for stirring the molten portion of a cast strand (2) coming from a continuous casting machine comprising movable means carrying a stirrer core portion (1) provided with induction coils, said means enabling the movement of said stirrer core portion into an operating position close to the strand and away from the strand during the casting operation, characterized in that the core of the stirrer is divided into two parts (1,3), that one (1) of these parts is mounted on said movable means and carries an entire two-phase or multi-phase stirrer winding for generating a rotating magnetic field, and that the other core portion (3) is arranged in a fixed position close to the strand and carries no winding.

Inventors: ERIKSSON, JAN ERIK
Applicants: ASEA BROWN BOVERI AB
Application year: 1988
Main classification: B22D11
IPC codes: B22D11