JP3493966B2 - Continuous casting mold - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting mold, and more particularly to an advantageous improvement of cooling uniformity in a width direction of a long side of the mold. 2. Description of the Related Art It is well known that molten steel, molten aluminum, and the like are made into a slab as a material of a rolled product by continuous casting. The continuous casting of such a slab is generally performed using a continuous casting mold that forms a rectangular cross-section casting space that is open up and down by a pair of short sides of the mold and a pair of long sides of the mold. This is performed by pouring a metal and solidifying at least its skin to form a cast piece, which is continuously pulled out from below. In such a continuous casting mold, the long side of the mold is usually constituted by a mold copper plate facing the casting space and a back plate provided on the back surface thereof. Usually, a plurality of cooling water grooves are provided on the back plate surface side of the mold copper plate, so that the cooling is performed by cooling water supplied from a water supply / drain port provided on the back plate. The back plate and the copper mold plate are stud bolted on the copper mold plate side for easy maintenance, and are easily attached and detached via the stud bolts. [0004] The surface of the mold copper plate is exposed to a very high temperature in order to come into contact with the molten metal, while the back surface is constantly cooled by the cooling water passing through the cooling water groove, so that a difference in thermal expansion occurs between the front and back surfaces. For this reason, a deformation stress is generated in the mold copper plate so as to protrude toward the casting space. Therefore, it is necessary to strongly tighten the back plate and the mold copper plate to overcome the stress. Therefore, conventionally, the mold copper plate and the back plate have been fastened using stud bolts as thick as possible. FIG. 1 shows a typical fastening structure between a copper mold plate and a back plate. In the figure, reference numeral 1 denotes a copper plate, 2 denotes a back plate, 3 denotes a fastening bolt, and 4 denotes a cooling water groove.
As shown in the figure, the connection between the copper plate 1 and the back plate 2 is made by a fastening bolt 3 screwed from the back plate side to the copper plate side. However, not only the cooling water groove cannot be provided in the place where the tightening bolt is installed, but also a gap is formed between the tip of the tightening bolt and the bolt hole, which creates an air layer with poor thermal conductivity. Therefore, a decrease in cooling capacity was observed at the bolt tip. FIG. 2 shows a temperature distribution on the surface of a copper plate of a conventional mold. As shown in the figure, the heat removal ability is clearly reduced around the bolt screw tip. [0007] Such a phenomenon causes a local rise in the mold surface temperature and locally delays the formation of a solidified slab shell, which not only causes surface defects but also causes thermal strain on the copper plate. For this reason, there have been disadvantages such as a reduction in the life of the mold. In order to solve the above problem, Japanese Patent Laid-Open No. 2-20
Japanese Patent Application Publication No. 0353 proposes a technique in which a cooling water groove is made orthogonal to a casting direction to uniformly cool a slab width direction. Also,
Japanese Utility Model Publication No. 2-11956 proposes a technique of suppressing a decrease in heat removal at the tip of the bolt by increasing the depth of cooling water grooves located on both sides of the bolt. Further, Japanese Patent Application Laid-Open No. Hei 4-251638 discloses that, in the mold copper plate, the vicinity of the meniscus having the largest effect of non-uniform cooling is fastened with a small-diameter bolt, and the cooling water groove intervals in this portion are evenly arranged. A uniform cooling method has been proposed. [0009] However, in the method of making the cooling water grooves orthogonal to the casting direction as disclosed in Japanese Patent Application Laid-Open No. 2-200353, bubbles mixed in the cooling water grooves are stagnant. There was a problem of causing a local cooling failure. Further, in the method disclosed in Japanese Utility Model Publication No. 2-11956, in which the depth of the cooling water groove located on both sides of the bolt is increased, the distance from the molten steel contact surface to the tip of the cooling water groove determines the life of the copper plate. Therefore, not only the cooling water groove cannot be sufficiently deepened, and a sufficient cooling uniformity effect cannot be obtained, but also the cooling water groove depth in a region other than the vicinity of the bolt installation portion. There is a problem that the difference causes uneven cooling in the width direction. Furthermore, in the invention of Japanese Patent Application Laid-Open No. Hei 4-251,638, although the non-uniform cooling in the width direction near the meniscus has been eliminated as desired, a problem remains in that the non-uniform cooling at the lower part of the mold is not eliminated. . The present invention advantageously solves the above-mentioned problem, and it is needless to say that the cooling effect in the vicinity of the tightening bolt, which has conventionally been a concern in the mold, is eliminated. It is also an object of the present invention to propose a continuous casting mold that enables uniform cooling. [0011] The details of the invention will be described below. By the way, in order to achieve the above object, the present inventors provided grooves for cooling water having the same depth on the back surface of the copper plate at the same interval in the casting width direction, and the grooves were uniform in the copper plate width direction. It has been confirmed that an excellent cooling is achieved. However, in order to provide the cooling water grooves at equal intervals, the diameter of the stud bolt must be made smaller than before, which reduces the fastening force between the mold copper plate and the back plate. Therefore, it is difficult to implement in terms of conventional common sense. [0013] Then, the present inventors investigated in detail what form of thermal deformation of the copper plate actually occurred by conducting a number of experiments using a steel slab continuous casting facility. As a result, the following facts became clear. In other words, the thermal deformation behavior when a small-diameter bolt is used, rather than causing the bolt to elongate due to insufficient strength of the bolt itself,
It has been found that the thread portion of the stud bolt hole provided in the mold copper plate is deformed, and in extreme cases, the thread portion undergoes shear failure. Therefore, when only the bolt diameter of the implanted part was increased, stress concentrated at the boundary between the small diameter part and the large diameter part,
This time, the extension and deformation of the bolt occurred. [0014] From the above experimental results, the inventors have conducted intensive studies on a method of alleviating the shear stress applied to the bolt hole without enlarging the bolt shape of the stud portion. The idea of fastening the bolt and the bolt hole via a helical interposer was completed, and the present invention was completed. That is, the present invention is a continuous casting mold that forms a casting space having a rectangular cross section open up and down by a pair of mold short sides and a pair of mold long sides. A mold copper plate facing the casting space and a back plate provided behind the mold copper plate. The mold copper plate has a plurality of cooling water parallel to the casting direction and equidistant from each other on the side facing the back plate. A groove is provided, and the back plate and the mold copper plate are provided with a stud bolt having one end inserted through a helical insertion member into a screw hole provided to avoid a cooling water groove of the mold copper plate. A continuous casting mold, which is fastened through a plurality of through holes provided in a plate. Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 3 shows a preferred arrangement of cooling water grooves provided in a copper plate according to the present invention. As shown in the figure, in order to perform uniform cooling over the slab width direction of the continuous casting mold copper plate, it is most effective to keep the depth of the cooling water grooves constant and to install the grooves at equal intervals. It is. Here, the width of the cooling water groove is 3 to 10 in order to secure a water cooling area of a certain amount or more and to prevent clogging when foreign matter is mixed.
Optimally, it is in the range of mm. Furthermore, for uniform cooling, it is desirable that the spacing between the cooling water grooves is as small as possible.However, in consideration of the bolt fastening force and the bolt diameter,
Optimally, the range is 20 to 32 mm. In order to provide the cooling water grooves at such uniform intervals, the diameter of the stud bolt for fastening the mold copper plate and the back plate is made smaller than the conventional one (about 16 to 24 mm) (about 12 to 14 mm).
mm). However, as described above, when the diameter of the stud bolt is simply reduced, the thread portion of the stud bolt hole provided in the mold copper plate is deformed, and good fastening cannot be expected. Therefore, in the present invention, when the stud bolt is implanted into the mold copper plate, as shown in FIG. 4 (a), the stud bolt is implanted between the screw hole and the bolt via the spiral insertion member 5. The spiral insertion member 5 is preferably made of metal from the viewpoint of securing strength and thermal conductivity, and is preferably made of steel or stainless steel having substantially the same material as the stud bolt. The screw holes in the mold copper plate have a diameter larger than that of the stud bolt (preferably about 1 to 4 mm larger), and a female screw having a pitch equal to the thread pitch of the stud bolt is formed. The helical insertion member is a helical body that fits into the male screw of the stud bolt and the female screw cut in the screw hole of the mold copper plate. By using the helical insertion member, a sufficient fastening strength can be obtained with a small diameter screw hole without increasing the diameter of the stud bolt itself. Thus, the formation of the cooling water grooves at equal intervals in the mold copper plate, which has conventionally been difficult to achieve, has become a reality. When such a structure is adopted, as can be seen from the temperature distribution diagram shown in FIG. 5, cooling not only in the meniscus portion but also in other regions is performed in the bolt portion and the stationary portion having no bolt. It is much more uniform than before, and the various problems of the above-mentioned conventional mold are eliminated. In addition, the distance between the contact surface of the molten steel and the tip of the cooling water groove is always kept constant during remodeling after using a copper plate.
By simply adjusting the amount of cooling water, uniform cooling can always be achieved regardless of changes in the thickness of the copper plate. EXAMPLES In a slab continuous caster having a mold cross section of 260 mm thick × 1200 mm wide, the following mold according to the present invention was used when continuously casting stainless steel. Casting speed is 0.8
~ 1.5 m / min. Copper plate thickness on the long side of the mold: 45 mm. The groove width of the cooling water groove provided on the back surface of the copper plate: 5 mm, groove depth: 20 mm, groove interval: 25 mm. As the stud bolt, an M14 stainless steel bolt was used, the screw hole on the copper plate side was 18 mmφ, and a stainless steel spiral interposed member was inserted between the stud bolt and the screw hole. FIG. 5 shows the results of investigation on the copper plate surface temperature at the meniscus position and the lower end position of the mold during casting. When the mold of the present invention was used, the temperature difference on the copper plate surface in the width direction was small at any position. The mold copper plate was used for 450 charges and was remodeled for wear, but no thermal deformation was observed. Further, inspection of the cast stainless steel slab revealed no defects such as surface cracks. Further, this slab was subjected to hot rolling and cold rolling by a conventional method to form a thin steel sheet, and the surface properties thereof were examined. No difference in quality in the width direction was found. COMPARATIVE EXAMPLE The stud bolts at the position corresponding to the meniscus described in Japanese Patent Laid-Open Publication No. Hei 4-251638 were reduced in diameter only, and the cooling water grooves were provided at equal intervals. At other positions, large diameter bolts were used. The same continuous casting test as described above was performed using a copper mold plate having cooling water grooves provided at irregular intervals so as to bypass the holes. The thickness of the copper plate on the long side of the mold was 45 mm, the groove width of the cooling water groove at the meniscus position was 5 mm, the groove depth was 20 mm, and the groove interval was 25 mm. The meniscus stud bolts were M14 stainless steel bolts, and the other portions were M18 mm stainless steel bolts. FIG. 6 shows the results of investigation on the surface temperature of the copper plate at the meniscus position and the lower end position of the mold during casting. In this mold, the temperature difference in the width direction at the meniscus position was small, but a remarkable temperature difference occurred in the width direction at the lower end of the mold. In addition, this mold was subjected to thermal deformation at the bottom of the mold when 300 charges were used, and the mold was worn,
It had to be refurbished. Furthermore, inspection of the cast stainless steel slab revealed that 5% of the slab had defects such as surface cracks. The slab was hot-rolled and cold-rolled by a conventional method to obtain a thin steel sheet, and the surface properties of the slab were examined. An abnormal surface gloss in the width direction was observed in 10% of the entire length. As described above, according to the present invention, the uniformity of cooling in the width direction of the long side of the mold can be remarkably improved, and the cooling of the slab in the width direction can be made uniform. It is possible not only to improve the quality of the slab, but also to extend the life of the copper plate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a fastening structure between a mold copper plate and a back plate. FIG. 2 is a surface temperature distribution diagram of a copper plate of a conventional mold. FIG. 3 is a diagram showing a preferred arrangement example of cooling water grooves provided in a copper plate according to the present invention. FIG. 4A is a diagram showing a state in which a screw hole and a bolt are fastened via a spiral insertion member, and FIG. 4B is a perspective view of the spiral insertion member. FIG. 5 is a surface temperature distribution diagram of a copper plate when the long side of the mold of the present invention is used. FIG. 6 is a surface temperature distribution diagram of a copper plate when a conventional mold long side is used. [Description of Signs] 1 Copper plate 2 Back plate 3 Tightening bolt 4 Cooling water groove 5 Spiral insertion member

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model 4-447 (JP, U) Japanese Utility Model 62-7745 (JP, U) Japanese Utility Model 62-20747 (JP, U) Japanese Utility Model 6 23651 (JP, U) Japanese Utility Model 1-96245 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/055

Claims (1)

(57) [Claim 1] A continuous casting mold that forms a casting space having a rectangular cross section that is opened up and down by a pair of short sides of the mold and a pair of long sides of the mold, The long side of the mold is composed of a mold copper plate facing the casting space and a back plate provided behind the mold copper plate, and the mold copper plate has an equidistant parallel to the casting direction on the side facing the back plate. A plurality of cooling water grooves are provided, and the back plate and the mold copper plate are implanted with one end into a screw hole provided avoiding the cooling water groove of the mold copper plate via a helical insertion member. A casting mold for continuous casting, wherein stud bolts are fastened through a plurality of through holes provided in the back plate.