JPH0245938B2 - BERUTOSHIKIRENZOKUCHUZONIOKERUBERUTOHENOYOKOCHOKUGEKIBOSHIHOHO - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for protecting a metal belt in a belt-type continuous casting machine at the start of casting, and in particular, from the start of casting, the injection nozzle outlet is immersed in molten steel and a steady meniscus is formed. This is a technology that can be applied until the metal belt is exposed to steel, and we propose a technology that protects the metal belt by preventing it from being directly hit by molten steel. (Prior Art) Continuous casting machines, or "belt casters", that continuously produce steel plates such as sheet bars directly from molten steel have various configurations, and Figure 1 shows one of the typical ones. It is one. This synchronous belt caster is of a narrowing type, and while maintaining a gap for holding cast materials such as molten steel and solidified shell over a predetermined distance, each of a plurality of guide rolls 3a, 3b, 3c ，
Metal belts 1 and 2 supporting a pair of long side surfaces arranged oppositely and moving circularly via 3a', 3b' and 3c'
and fixed short side walls 4 and 5 for the short sides that are in close contact with each other near the side edges between both metal belts, and have a configuration in which four sides are confined to form a casting space. . Molten steel is injected into the casting space through an injection nozzle (immersion nozzle) 6. In the case of the above-mentioned belt caster, at the start of casting, after pushing the dummy bar 7 up into the casting space, molten steel is supplied from the injection nozzle outlet 6a, and after waiting for the necessary meniscus to be formed, steady operation is performed. Move to. At this time, there was a problem in that the discharged molten steel flow directly hit the metal belts 1 and 2, causing them to melt and shorten their service life. In response to this, several proposals have been made to overcome the above problems and start casting. In other words, (1) a method in which a film such as ZrO ₂ is coated on the molten steel contact side of the metal belt, (2) a method in which a steel plate with a thickness of approximately 1.2 mm is placed on the surface of the metal belt, and (3) a method in which a film of approximately 0.5 mm in thickness is applied. There is a method in which two thin steel plates are overlapped over a portion of a metal belt. In particular, the conventional techniques (2) and (3) above were effective in that the metal belt melting damage at the start of casting was significantly reduced compared to (1). However, casting is also affected by conditions: belt melting occurs mainly due to changes in casting speed, the height of the injection nozzle 6 immersion, or the distance the metal belt travels until the injection nozzle discharge port is immersed. However, it was not possible to reduce belt melting loss. In addition, depending on the shape of the thin steel plate mentioned above, which prevents direct impact from molten steel, thermal deformation of the slab, bulging, leakage from the steel plate for preventing direct impact, poor drawing of the slab, or defective slab shape may occur. A problem arose.
In other words, if the thin steel plate for direct hit prevention is too large or too thick, the molten steel will not circulate between the direct hit prevention steel plate and the metal bell, and the contact between the molten steel and the metal belt will be poor, resulting in insufficient cooling in the casting space. As the process is delayed, it becomes uneven and unsolidified slabs are produced. As a result, leakage, local bulging, and thermal deformation of the molten steel occur after the molten steel leaves the area of the casting space, making it difficult to pull out the slab with rolls and resulting in poor properties of the slab. (Problems to be Solved by the Invention) The present invention solves the above-mentioned various problems. (b) To prevent bulging or thermal deformation due to non-solidification outside the mold even when a thin steel plate is installed to prevent direct impact from injected molten steel; We aim to develop a technology that allows the secondary flow of directly hit molten steel to sufficiently flow into the gap between the metal belt and the direct hit prevention plate, thereby achieving sufficient cooling within the mold and producing a strong solidified shell. In this respect, the conventional methods (2) and (3) above both focus on the above (a), and in order to carry out normal casting operations, it is necessary to also satisfy the function (b). . (Means for Solving the Problems) The present invention provides, as an effective means for overcoming the above-mentioned problems, a pair of long-side metal belts that rotate in synchronization and are arranged opposite to each other, and these metal belts. In a casting space of a belt-type continuous casting machine, which is confined on four sides by a pair of tapered fixed short side walls that are in close contact with each other near both side edges of the metal belt,
Before starting casting of molten steel by injecting molten steel into the casting space from an injection nozzle having a discharge port in the casting space above the inserted and held dummy bar, the width (W) and length (L) shown below are determined. , a thin steel plate for preventing direct hit of molten steel that satisfies the relationship of thickness (H) is attached to the surface of the metal belt that is to receive the molten steel flow from the injection nozzle discharge port. How to prevent direct hit from molten steel. Note: 0.35B≦W≦0.90B 0.5 (l ₀ +l _t )≦L≦2 (l ₀ +l _t ) 0.1≦H≦1.5 In the formula; l ₀ : Setting at the start of casting from the upper end of the dummy bar to the injection nozzle discharge port Distance (mm) l _t : Belt movement distance (mm) from the start of casting until the injection nozzle discharge port becomes immersed B: Width of slab (mm) W: Width of thin steel plate to prevent direct hit of molten steel (mm) L: Length of thin steel plate for preventing direct hit of molten steel (mm) H: Thickness of thin steel plate for preventing direct hit of molten steel (mm) (Function) As a result of various casting experiments, the present inventors found that the following results were obtained. It was confirmed that the method to prevent direct hit of molten steel by preparing a thin steel plate with a similar shape and starting casting was effective. The thin steel plate used to prevent direct hits from molten steel has the following shape. Width (W): 0.35B≦W≦0.90B Thickness (H): 0.1≦H≦1.5 Length (L): 0.5 (l ₀ + l _t ) ≦L≦2 (l ₀ + l _t ) Here B: Slab width (mm) l ₀ : Set distance from the top of the dummy bar to the injection nozzle outlet at the start of casting (mm) l _t : From the start of casting until the injection nozzle outlet becomes immersed Belt movement distance (mm) W: Width of thin steel plate to prevent direct hit of molten steel (mm) L: Length of thin steel plate to prevent direct hit of molten steel (mm) H: Thickness of thin steel plate to prevent direct hit of molten steel (mm) Direct hit of this molten steel The thin steel plate for prevention may have a rectangular shape, but in order to improve the ability of molten steel to wrap around between the thin steel plate and the metal belt, the shape should be 0.35B≦W≦0.90B as shown in Figs. 2 and 3. A part of the width of the thin steel plate within the range that satisfies (the part where molten steel is difficult to wrap around)
You can narrow it down. In addition, the installation position of the thin steel plate for preventing direct hit of molten steel should be such that the center of the injection nozzle in the casting width direction is aligned with the center of the thin steel plate for preventing direct hit of molten steel, and the lower end of the thin steel plate for preventing direct hit of molten steel is in contact with the upper end of the dummy bar. Place it in The reason why such thin steel sheets are limited as described above will be explained below. Regarding the formula, W<0.35B: It is impossible to completely prevent the spread immediately downstream of the injection nozzle in the width direction, and there is a possibility that the belt will be melted and damaged. W>0.90B: The molten steel does not flow well between the thin steel plate for direct hit prevention and the metal belt, and there is a possibility that unsolidified pieces will form outside the mold. Regarding the formula: H < 0.1 mm; the direct hit prevention plate immediately downstream of the injection nozzle may melt instantly, resulting in belt melting and damage. H > 1.5mm: It is complicated to shape the direct hit prevention plate to match the curvature of the metal belt, and because it is thick, it does not deform due to heat, and the flow of hot water between the metal belt and the direct hit prevention plate is poor, resulting in unsolidified slabs. Easy to generate. Regarding the formula, L<0.5 (l ₀ +l _t ); the length of the direct hit prevention plate is insufficient and there is a risk of melting and damage of the metal belt. L>2(l ₀ +l _t ): The length of the direct hit prevention plate is unnecessarily long, and the length of the unsolidified slab becomes long. The formula will be explained in more detail. The damage caused to the metal belt by the flow of molten steel from the injection nozzle outlet is significant during the period from when the molten steel begins to be injected into the casting space until the level of the molten steel rises and the injection nozzle outlet is immersed in the pool ( It is especially large at the beginning of injection when no pool is formed),
After that, the level of the hot water surface (the immersion depth of the discharge port)
Damage will be reduced accordingly. By the way, the dummy bar inserted and held in the casting space comes into close contact with the metal belt and moves in synchronization with the rotation of the metal belt, but the movement of the dummy bar and metal belt takes place after the injection of molten steel starts. , after a certain amount of molten water has formed in the casting space. Therefore, when the injection nozzle outlet is immersed in the pool of hot water, the distance from the injection nozzle outlet to the top of the dummy bar is l ₀ , and the belt movement distance from the start of casting until the injection nozzle outlet becomes immersed is l _t The result is (l ₀ +l _t ). FIG. 4 shows an example of changes over time in the molten steel level and the positions of the dummy bar and the thin steel plate for preventing direct impact from the start of pouring. l _t changes depending on the pattern of the rising curve of the hot water level, the moving speed of the metal belt, or a combination thereof. The same figure shows the cases where the metal belt moving speed is constant and the rising curve of the hot water level has three patterns (a), (b), and (c). In the case of (a), l _t = 0,
In the case of (b) and (c), it becomes l _t1 and l _t2 , respectively. In addition, the length of the thin steel plate to prevent direct hit of molten steel is 0.5×(l ₀ +
The position of the upper end of the thin steel plate in the case of (l _t ) is shown by a dashed line for each case of the rise curve of the hot water level, and the length of the thin steel plate for preventing direct hit of molten steel is 2×(l ₀
The position of the upper end of the thin steel plate in the case of +l _t ) is shown by a chain double-dashed line in the case of (b) of the rise curve of the hot water level. The hatched area in the figure shows an example of the direct hit zone of the molten steel flow. Although the direct hit zone expands depending on the shape of the injection nozzle and the narrowed shape of the casting space, the zone shown in the figure Regardless of these conditions, this area is always directly hit by molten steel at the beginning of injection. Therefore, the length L of the thin steel plate for preventing direct hit of molten steel is L≧0.5×(l ₀ +l _t ) or more. The coefficient of (l ₀ +l _t ) in each case of (a) and (c) in FIG. 4 will be explained. In the case of (b),
Since the molten metal surface reaches the injection nozzle discharge port before the metal belt moves, a thin steel plate for preventing direct hit of molten steel that is longer than the upper end of the direct hit zone, i.e. 0.5l ₀ , is sufficient, and the coefficient is 0.5
(∵l _t = 0), but in the case of (c), it becomes 0.5(l ₀ +l _t )
When using a thin steel plate for preventing direct impact on molten steel with a length of The molten steel will directly hit the belt. In order to prevent this, the thin steel plate for preventing a direct hit of molten steel must be long enough for the upper end of the thin steel plate for preventing a direct hit of molten steel to pass through point b. The coefficient at this time is the distance cd from the intersection point c of the straight line that is parallel to the solid line that indicates the change in the dummy bar tip position over time and passes through point b, and the perpendicular line that indicates the start of pulling out to the dummy bar tip position d, and (l ₀ + l _t2 ), for example, 0.73. Further, as described above, the direct impact zone of the molten steel changes depending on the shape of the injection nozzle, the constriction shape of the casting space, the belt movement speed, and the rate of rise in the molten metal level. For example, when the discharge angle is upward, the area below the vicinity of the discharge port is directly hit by the molten steel. In addition, the thin steel plate for preventing direct hit of molten steel may be damaged by melting due to splashes of molten steel flowing upward or depending on the casting conditions, so in order to ensure sufficient safety of protection of the metal belt, the coefficient must exceed 2. Although the length is not necessary, the length L of the thin steel plate for preventing direct hit of molten steel is 2(l ₀ +l _t ) or less. Furthermore, as a method of promoting the flow of molten steel to the back of the direct hit prevention plate, instead of stacking the direct hit prevention plate in close contact with the metal belt surface, a part of both side edges is Providing the folded piece 9 formed by bending improves hot water circulation and more reliably achieves the desired effect aimed at by the present invention. (Example) Metal belt erosion rate at the start of casting when low carbon aluminum killed steel is cast under the casting conditions shown in Table 1 using a belt-type continuous casting machine with a slab width of 1000 mm shown in Figure 1. The degree of thermal deformation and bulging of the slab in the direct hit prevention plate was tested using each casting method shown in Table 2, and the results are shown in Table 3.

【table】

【table】

[Table] * Index display where 1 indicates the most severe belt melting, slab thermal deformation, and bulging.As is clear from the table above, in the case of method a (comparative example), ZrO ₂ is added before the start of pouring. Casting was started after approximately 400g/ ^m2 of powder was applied to the inner surface of the belt running in parallel, but the application of _ZrO2 powder alone was not able to withstand the direct hit of molten steel at the start of casting, and the belt opened due to melting damage. Holes formed and casting became impossible. In the case of method c (comparative example), one direct impact prevention plate was used, but since the length in the casting direction was short, the direct impact flow could come off the prevention plate and cause the belt to move due to the belt movement after the start of casting. It hit me directly. As a result, the belt was melted and damaged, and holes were formed, although this was less than in method a above, making it impossible to cast. In method b (comparative example), the width (W) and length (L) are within the range of the dimensional limitations of the direct hit prevention plate of the present invention, but
The fact that the thickness (H) is large and that two sheets are used in a stacked manner is outside the scope of the present invention. With this method, there was almost no belt melting damage, but because the cooling inside the mold was slow and uneven, and an unsolidified part was formed, the slab was thermally deformed or bulged after it came out of the mold, and the slab was pulled out. I couldn't do it anymore. Method d' (comparative example) is an example of using a direct hit prevention plate larger than the plate width (W) limited in the present invention,
There is almost no belt erosion due to direct impact flow, but since the plate width (W) is equal to the mold width, molten steel does not spread between the direct impact prevention plate and the metal belt, especially the center of the prevention plate width, and the molten steel and metal belt are The contact deteriorated, and for the same reason as method b, it came out of the mold, resulting in slab bulging. As mentioned above, comparative examples a to d' are characterized by belt melting,
Pouring had to be stopped due to perforation or thermal deformation bulging after exiting the mold. On the other hand, method d (embodiment) is an example in which one direct hit prevention plate having a shape within the scope of the present invention is used. There was almost no belt melting due to direct current. However, since the penetration of the molten steel between the direct hit prevention plate and the metal belt was not complete, the contact between the molten steel and the metal belt was poor, resulting in extremely small thermal deformation for the same reason as mentioned above, and even then, it was difficult to pull out the slab. I was able to cast it completely without any problems. Method e (Example) involves bending one direct hit prevention plate of the present invention by 5 mm on both side edges to form a folded piece as shown in FIG. 5, and creating a gap between the metal belt and the direct hit prevention plate. As a result, the penetration of molten steel was improved. This resulted in good contact between the molten steel and the belt, and it was possible to cast high-quality slabs with almost no thermal deformation or bulging of the slabs, and no belt melting due to direct impact flow. In all of the above embodiments, in order to prevent the direct hit prevention plate from collapsing, the direct hit prevention plate was attached to the metal belt using a small magnet before casting was started. (Effects of the Invention) As described above, the present invention is effective in obtaining high-quality slabs with less occurrence of belt melting and failure to cast due to thermal deformation of slabs at the start of casting.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing a belt-type continuous casting machine showing an example of an embodiment of the method of the present invention, FIG. Figure 3 is a front view of the shape of the direct hit prevention plate, Figure 4 is a graph showing an example of changes over time in the molten steel level from the start of pouring, the position of the dummy bar and the thin steel plate for direct hit prevention, and Figure 5 is a folding diagram. FIG. 3 is a perspective view of a direct hit prevention plate having a raised piece. 1, 2... Metal belt, 3, 3'... Guide roll, 4, 5... Short side wall, 6... Injection nozzle, 6
a...Discharge port, 7...Dummy bar, 8...Direct hit prevention plate, 9...Folded piece.

Claims (1)

[Scope of Claims] 1. A pair of long side metal belts that rotate in synchronization and are arranged opposite to each other, and a tapered shape that is in close contact with the vicinity of both side edges of the metal belt between these metal belts. Molten steel is injected into the casting space of a belt-type continuous casting machine, which is confined on four sides by a pair of fixed short side walls, from an injection nozzle having a discharge port in the casting space above a dummy bar inserted and held. Before starting pouring of molten steel, insert a thin steel plate to prevent direct hit of molten steel that satisfies the width (W), length (L), and thickness (H) relationships shown below from the injection nozzle outlet. A method for preventing direct impact of molten steel on a belt in belt-type continuous casting, characterized in that the metal belt is attached to the surface of the metal belt that is about to receive the molten steel flow. Note: 0.35B≦W≦0.90B 0.5 (l ₀ +l _t )≦L≦2 (l ₀ +l _t ) 0.1≦H≦1.5 In the formula; l ₀ : Setting at the start of casting from the upper end of the dummy bar to the injection nozzle discharge port Distance (mm) l _t : Belt movement distance (mm) from the start of casting until the injection nozzle discharge port becomes immersed B: Width of slab (mm) W: Width of thin steel plate to prevent direct hit of molten steel (mm) L: Length of thin steel plate to prevent direct hit from molten steel (mm) H: Thickness of thin steel plate to prevent direct hit from molten steel (mm)