JPH03155441A - Vertical continuous casting method and apparatus thereof - Google Patents

Abstract

PURPOSE:To deal with severe demand on the quality in a special steel by setting light rolling reduction means just before solidifying completion point in a strand and applying the light rolling reduction of intense to supplement solidified shrinkage to the strand. CONSTITUTION:The strand 5A is formed with a water cooled mold 1 and this is vertically drawn to execute continuous casting. Then, the solidifying completion point in the strand 5A, i.e., the point, where unsolidified part 52 in shell 51 disappears, is inspected and just before that, the light rolling reduction means 4 is set, and the light rolling reduction of intense to supplement the solidified shrinkage, is applied to the strand 5A. The light rolling reduction means 4 is arranged changeable in position and is made of at least one pair of pinch rolls. By this method, the development of center cavity is prevented, and center segregation can be reduced.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an improvement in vertical continuous casting, that is, a casting technique in which a strand formed in a water-cooled mold is pulled downward without bending and cut to obtain a slab. (Conventional technology) Today, continuous casting occupies an extremely important position in steel casting. Among continuous casting methods, horizontal continuous casting has only been attempted in some cases because it has many technical problems. Currently, the most widely used methods are curved and vertical continuous casting methods. , curved continuous casting in which the strands are curved (in reality, the structure is such that the water-cooled mold provides a curved strand) so that they extend laterally, thereby keeping the height of the casting equipment within a certain limit. Strands extending in the horizontal direction are straightened horizontally using pinch rolls and cut into slabs using a flame cutter.Some special steels are cast using this curved casting-horizontal straightening method. There are some types of steel that are unfavorable in terms of quality.For example, there are valve steels and high-speed steels that tend to crack when straightened.This type of steel is made by forming strands that do not bend in a water-cooled mold, and then leaving them as they are. The vertical continuous casting method should be used, in which the slab is cut by dragging downwards.In this vertical continuous casting method, the strand should be cut at the position just before the unsolidified part disappears inside the strand as it comes out of the water-cooled mold. Applying a light reduction in the strand compensates for the shrinkage caused by solidification, prevents the formation of a cavity at the center of the strand, and reduces center segregation, making it possible to obtain a slab of even better quality. Steel types for which such light reduction is effective are often produced in relatively small quantities in a wide range of products, and not only do the strand cross-sectional sizes vary, but the appropriate drawing speed also often varies. , the optimal position for applying light reduction, that is, the point at which the unsolidified portion in the strand disappears, differs between -. [Problems to be Solved by the Invention] The purpose of the present invention is to To provide a continuous casting method that can flexibly respond to often changing casting conditions, always apply light reduction to the strand at the optimum position, and obtain slabs of excellent quality, and equipment used therefor. [Means for Solving the Problems] The vertical continuous casting method of the present invention is a continuous casting method in which a strand formed in a water-cooled mold is vertically handled.
As shown in FIG. 1, just before the solidification of the strand (5A) is completed, that is, the point at which the unsolidified portion (52) inside the shell (51) disappears, a light reduction means (4), typically a pinch roll, is applied. It is characterized by applying a light pressure to the strand with sufficient strength to compensate for solidification shrinkage. As shown in FIG. 2, the vertical continuous casting apparatus of the present invention for carrying out the above-mentioned casting method includes a water-cooled mold (1) and its ancillary equipment, a drawing drive roll (2) provided below the water-cooled mold, and In a vertical continuous casting apparatus consisting essentially of a strand cutter (3) and equipped with means (not shown) for supplying molten metal to a water-cooled mold, a light reduction means (4) is provided below the water-cooled mold in a variable position. ,
It is characterized by being configured so that a light pressure force strong enough to compensate for solidification shrinkage can be applied to the strand just before the solidification completion point of the strand. Reference numeral (5B) is a slab obtained by cutting the strand, which is successively carried away by another device. Although the light reduction means and the method of providing it in a variable position are arbitrary, typical examples include the devices shown in FIGS. 3 to 5. This device consists of three pairs of pinch rolls (41a
, 41b, 41c) are attached to a frame (42), and this frame (42) is configured to be able to move up and down along four vertical guide columns (43). Each pinch roll is slidably attached to the frame.
The strand (
Pinch the drive motor (45a) from both sides of the front
, 45b, 45c) to apply a desired light reduction to the slab. The position of the pinch rolls (41a-C) is
) The four vertical bars (46) at the bottom rotate with the rotation of the motor (6), and move up and down by the engagement between the male screws of the vertical bars and the fixed female screws.
) can be changed. FIG. 6 shows another embodiment in which the position of the light reduction means is made variable. In this device, the structure of the light reduction means, that is, the frame, the pinch rolls attached to it, and other parts is the same as in the above example, but the vertical movement of the frame is controlled by pulleys (8a, 8b, 8c, 8d, and 8e).

[Puta wire (
9) is different in that it is performed by winding and unwinding. [Function] The position of the light reduction device is made variable to match the solidification end point, which varies depending on the conditions such as the type of steel to be continuously cast, the cross-sectional size of the strand, and the drawing speed.
By performing light reduction at the optimal position, the effect can be highly obtained. The solidification end point can be determined, for example, as follows. In other words, since it is known that the thickness (D) of the shell (51) of the strand that exits the water-cooled mold increases as time (1) progresses, D = kJ'T, the value of k If this is determined by, for example, driving a spike into the strand and then cutting the slab to check whether there is an unsolidified portion at that position, the solidification completion point in the strand can be determined using the above equation. can be inferred. Recently, a technique has been established for detecting the i-suspicious solidification completion point by utilizing the phenomenon that the propagation speed of ultrasonic waves is different in a solid and in a melt. Utilizing this, a device for detecting the molten interface using ultrasonic waves is added to the light reduction means (4), and at the start of operation, the point at which solidification is completed in the strand is found and the light reduction means is positioned there. In addition to performing appropriate light reduction, if the solidification completion point changes due to changes in the type of steel targeted for continuous casting or changes in casting conditions, the light reduction means should follow this and change its position. It is preferable to do so. Since the strand is drawn by the above-mentioned centering drive roll, it is not necessary for the light reduction pinch roll itself to have a driving force. However, it is convenient to use light reduction pinch rolls to insert the dummy bar into the water-cooled mold at the start of casting. Since this object can be achieved by providing the light reduction pinch roll with a drive function, the device is equipped with a drive motor. [Effects of the Invention] The present invention makes it possible to always perform light reduction just before the solidification end point in vertical continuous casting of special steel at the optimal position in response to changes in the strand cross-sectional size and casting conditions. Ta. As a result, we are able to provide excellent products that meet strict quality requirements for special steel, such as preventing the formation of center cavities and reducing center segregation.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the internal state of the strand and the position of light reduction during continuous casting. FIG. 2 is a conceptual side view showing the main parts of the overall configuration of the vertical continuous casting apparatus of the present invention. 3 to 5 are detailed views showing an example of a mechanism for variably providing the position of the light reduction means in the apparatus shown in FIG. 2, in which FIG. 3 is a side view and FIG. -I sectional view, and FIG. 5 is a sectional view taken from FIG. FIG. 6 is a side view similar to FIG. 3, showing another example of a mechanism for variably providing the position of the light reduction means in the apparatus of FIG. 2. 1...Water-cooled mold 2...Drawing drive roll 3...Strand cutter 4...Light reduction means 418.41b. 42...Frame 44a, 44b. 45a, 45b. 46... Vertical bar 5A... Strand 5B... Slab 6... Motor 7... Worm jack mechanism 8a, 8b, 8c, 8d, 8e... Slip 9... Wire 41G... Pinch roll 43...Guide column 44C...Hydraulic cylinder 45c...Drive motor

Claims (5)

[Claims] (1) In a continuous casting method in which a strand formed in a water-cooled mold is pulled out vertically, a light reduction means is positioned just before the solidification completion point of the strand is found, and a light reduction strong enough to compensate for solidification shrinkage is applied to the strand. A continuous casting method characterized by adding (2) Consisting essentially of a water-cooled mold (1) and its ancillary equipment, a drawing drive roll (2) and a strand cutter (3) provided below the water-cooled mold, and provided with a means for supplying molten metal to the water-cooled mold. In the vertical continuous casting device, a light reduction means (4) is provided below the water-cooled mold in a variable position, so that a light reduction strong enough to compensate for solidification shrinkage can be applied to the strand just before the solidification completion point of the strand. Continuous casting equipment characterized by: (3) Adding a device to the light rolling down means to detect the molten interface using ultrasonic waves, thereby finding the solidification completion point in the strand and positioning the light rolling down means there, and when the solidification completion point changes, 3. The continuous casting apparatus according to claim 2, wherein the continuous casting apparatus is configured to change the position of the light reduction means accordingly. (4) A claim in which the light rolling means comprises at least a pair of pinch rolls that are slidable relative to a frame that moves up and down along a vertical guide column and that are arranged to pinch the strand from both sides using hydraulic cylinders. 2 continuous casting equipment. (5) The continuous casting apparatus according to claim 4, wherein the pinch roll of the light reduction means is provided with a driving function and is configured to also serve as a dummy bar pinch roll.