Method for designing dry coating layer of tundish, and method for forming the same

Abstract

To provide a technique which enables structural design of a dry coating layer of a tundish in an appropriate manner.SOLUTION: A method for designing a dry coating layer that covers an inner wall surface of a tundish trough includes: a step of defining a maximum allowable warpage amount δmax of the dry coating layer; and a step of acquiring, as a designed thickness ht of the dry coating layer, a thickness h obtained with respect to the maximum allowable warpage amount δmax, based on a relationship that uniquely associates a warpage amount δ and the thickness h of the dry coating layer, which are derived from the following formulas (1) and (2): Warpage amount δ=(load F×height L3) / (3×Young's modulus E×I) (1). Second moment of area I=width b×thickness h3 / 12 (2).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a design method and a forming method of a dry coat layer of a tundish.

Background Art

[0002] For example, in casting techniques such as continuous casting of metals, it is common for a molten metal, which is a molten metal, to be poured from a ladle into a mold via a tundish. By passing through the tundish, inclusions such as oxides can be separated from the molten metal and then supplied to the mold. Also, by passing through the tundish, the supply amount and supply rate of the molten metal from the ladle to the mold can be adjusted, and it becomes easy to branch and flow the molten metal in the ladle into a plurality of molds. Thus, the tundish functions as a buffer vessel for adjusting the supply state of the molten metal to the mold.

[0003] Normally, in a tundish, in order to enhance the durability against a high-temperature molten metal, an inner refractory layer lined with a refractory is formed on the inner wall surface of the iron skin that constitutes the container wall of the tank into which the molten metal is supplied. Also, when the tundish is in use, in many cases, a coating layer is formed on the surface layer of the refractory layer by a dry coat material or a spraying material. The dry coat layer, which is a coating layer by a dry coat material, is disclosed in, for example, Patent Documents 1 and 2 below.

[0004] The dry coat layer is removed from the tundish after casting is completed. At this time, since residues such as ingots and slag generated in the tundish during casting can be removed together with the dry coat layer, the work of removing the residues in the tundish after casting can be facilitated.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] The dry coat layer of the tundish may expand when receiving the heat of the molten metal. On the other hand, for example, when replacing the ladle, etc., when the amount of molten metal in the tundish decreases and the surface of the molten metal drops, the dry coat may also contract due to the temperature drop on the surface of the dry coat. The dry coat layer may peel off from the container wall of the tundish due to the stress generated by such expansion and contraction caused by the heat of the molten metal.

[0007] The dry coat material peeled off from the container wall of the tundish due to the peeling may be mixed into the molten metal as inclusions. Further, when the dry coat layer peels off, at the missing portion of the dry coat layer caused by the peeling, there is a risk that the refractory is exposed to the molten metal and damaged, or that the steel shell melts due to the molten metal reaching the steel shell and steel leakage occurs.

[0008] As described above, conventionally, in some cases, instead of the dry coat layer, a coating layer of a spraying material is formed on the surface layer of the refractory layer of the tundish. In the case of the coating layer of the spraying material, generally, it is easy to form, and has higher adhesion to the refractory layer than the dry coat layer and is less likely to fall off. However, since the coating layer of the spraying material is formed using moisture, hydrogen atoms remaining inside the coating layer of the spraying material may be mixed into the molten metal, causing so-called hydrogen pickup and deteriorating the quality of the casting.

[0009] Further, conventionally, as disclosed in Patent Documents 1 and 2 above, the strength of the dry coat layer is adjusted by adjusting the binder component contained in the dry coat material, and the peeling of the dry coat layer may be suppressed. However, it could not be said that only the adjustment of the binder component was sufficient to sufficiently suppress the peeling of the dry coat layer.

[0010] In order to more effectively suppress the peeling of the dry coat layer, it is preferable that the dry coat layer is appropriately designed structurally. However, generally, the vessel wall of the tundish on which the dry coat layer is formed is finely designed individually for each product to be cast in consideration of a number of factors such as heat insulation when the molten metal flows in, heat resistance, and fluidity of the molten metal for removing inclusions. Therefore, it has not been easy to model the mechanism of the peeling of the dry coat layer while considering the structure of such a vessel wall and appropriately design the structure of the dry coat layer.

[0011] Here, if only the strength of the dry coat layer is simply increased, increasing the thickness of the dry coat layer is simple and effective. However, an increase in the thickness of the dry coat layer may increase the volume of the dry coat layer, leading to a decrease in the capacity of the tundish. In addition, an increase in the thickness of the dry coat layer may lead to an increase in running costs due to an increase in the amount of dry coat material used, and may also adversely affect the response to design changes of the tundish for each product to be cast. Therefore, it is preferable that the thickness of the dry coat layer is determined to be the minimum value that can ensure a thickness capable of suppressing the peeling of the dry coat material.

[0012] As described above, heretofore, sufficient contrivance has not been made for appropriately designing the structure of the dry coat layer in the tundish. An object of the present invention is to provide a technique capable of more appropriately designing the structure of the dry coat layer of the tundish by a simple method.

Means for Solving the Problem

[0013] The present invention can be realized, for example, in the following forms.

[0014] [First Embodiment] The first embodiment of the present invention is provided as a method for designing a dry coat layer that covers the inner wall surface of the ladle tank. In the method of the first embodiment, when the dry coat layer formed on the side wall portion of the tank deflects inward of the tank due to thermal deformation, and the lateral movement distance from the initial position of the upper end of the dry coat layer is defined as the deflection amount δ, the limit deflection amount δ, which is the maximum value of the allowable range of the deflection amount δ that suppresses the occurrence of collapse, is determined. max A step of determining δ, and in a relationship uniquely associating the deflection amount δ and the thickness h of the dry coat layer obtained from the following mathematical formulas (1) and (2), the thickness h obtained for the limit deflection amount δ max is obtained as the designed value ht of the thickness of the dry coat layer, and the method includes the step. [Equation 1] Deflection amount δ = (F × L 3 ) / (3 × E × I) … (1) F: Load applied in the lateral direction when the dry coat layer deflects inward of the tank L: Height of the dry coat layer E: Young's modulus of the dry coat layer I: Second moment of area of the dry coat layer, which is a value obtained by the following formula (2) [Equation 2] I = b × h 3 / 12 … (2) b: Width of the dry coat layer h: Thickness of the dry coat layer

[0015] [Second Embodiment] In the method of the first embodiment, the limit deflection amount δ max may be determined for the inclination angle θ in the initial state using a previously prepared relationship that uniquely associates the inclination angle θ outside the tank with the limit deflection amount δ max in the direction along the bottom wall portion of the tank of the dry coat layer in the initial state.

[0016] [Third Embodiment] In the method described in the first embodiment or the second embodiment, the limit deflection amount δ maxIt may be the amount of warpage δ when the inclination angle θ when the dry coat layer warps inward of the ladle due to thermal deformation is 90° or more.

[0017] [Fourth Embodiment] The fourth embodiment is provided as a method for forming a dry coat layer that covers the inner wall surface of the ladle in a tundish. The method of the fourth embodiment includes a step of determining a design value ht of the thickness of the dry coat layer by the method described in any one of the first, second, and third embodiments, and a step of forming the dry coat layer so as to have the thickness of the design value ht.

Advantages of the Invention

[0018] According to the method of the present invention, by applying a mathematical formula used for analyzing the warping deformation of a cantilever beam in material mechanics, it is possible to easily obtain an appropriate thickness of the dry coat layer that can suppress the collapse of the dry coat layer due to the occurrence of warping caused by thermal deformation such as expansion and contraction of the dry coat layer.

[0019] The present invention can be realized in various forms other than the design method of the dry coat layer and the formation method of the dry coat layer in the tundish. The present invention can be realized, for example, in the form of a method for manufacturing a tundish, a casting method using a tundish, a program for realizing these methods on a computer, and a steel material manufactured using these methods.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0021] 1. Embodiment: Hereinafter, embodiments of a method for designing a dry coat layer and a method for forming the same according to the present invention will be described with reference to the drawings.

[0022] First, with reference to FIG. 1, a tundish 10 and a dry coat layer 25 formed in the tundish 10 will be described. FIG. 1 is a schematic cross-sectional view showing a simplified configuration of the tundish 10.

[0023] The tundish 10 is used, for example, in a metal casting process such as continuous casting. The tundish 10 has a ladle 11 that receives and temporarily stores a molten metal, which is a molten metal. In continuous casting, the molten metal is supplied from a ladle (not shown) through the ladle 11 of the tundish 10 to a mold (not shown).

[0024] The tundish 10 is configured such that when the molten metal is supplied into the ladle 11 from the ladle, a flow is generated in which inclusions, which are impurities in the molten metal, float and separate. Further, the tundish 10 is configured such that the molten metal in the ladle 11 of the tundish 10 is supplied to the mold in a state where the floating inclusions are removed.

[0025] Although illustration and detailed description are omitted, the ladle 11 of the tundish 10 may be partitioned into a molten metal receiving chamber that receives the molten metal and a molten metal outflow chamber into which the molten metal flows from the receiving chamber. The tundish 10 may have a sleeve that constitutes a flow path for the molten metal and a pair of trunnions provided on the outer surface.

[0026] The tundish 10 includes a container wall 20 that partitions the internal space of a tank 11 in which molten metal is stored. The container wall 20 includes a bottom wall portion 21 that constitutes the bottom surface of the tank 11 and a side wall portion 22 that extends upward from the bottom wall portion 21. The container wall 20 has a multilayer structure and includes an iron skin layer 23 that constitutes the outer surface of the tundish 10 and a refractory layer 24 lined with a refractory so as to cover the inner wall surface of the iron skin 23.

[0027] As the refractory that constitutes the refractory layer 24, one that can withstand the temperature of the molten metal supplied to the tundish 10 is adopted. The refractory is mainly composed of, for example, alumina (Al2O3), magnesia (MgO), or calcia (CaO). The refractory has a form such as a sheet, brick, or block and is spread over the inner wall surface of the iron skin. A heat insulating material may be disposed between the iron skin 23 and the refractory layer 24.

[0028] When the tundish 10 is used, the inner wall surface of the container wall 20, that is, the surface layer of the refractory layer 24, is covered by a dry coat layer 25. The dry coat layer 25 is composed of a dry coat material. The dry coat material is composed of, for example, about 90 to 95% by mass of MgO, an organic binder, and an inorganic binder.

[0029] The dry coat layer 25 is formed by filling a dry coat material into the gap between a formwork (not shown) disposed in the tank 11 of the tundish 10 and the refractory layer 24 and heating and firing the dry coat material. Note that the dry coat layer 25 is formed before casting is performed and is removed together with the residue after casting after casting is completed.

[0030] Hereinafter, with reference to FIGS. 2 to 5, a method for forming the dry coat layer 25 for the tundish 10 will be described.

[0031] FIG. 2 is a flowchart showing the procedure of the forming process of the dry coat layer 25. In step P1, the tundish 10 to which the dry coat layer 25 is to be formed is prepared. This tundish 10 has a refractory layer 24 formed on the iron skin 23, and the dry coat layer 25 has not yet been formed on the outer surface of the refractory layer 24.

[0032] In steps P2 to P3, the design value ht of the thickness of the dry coat layer 25 to be formed is determined. In the present embodiment, the design value ht of the thickness of the dry coat layer 25 is determined based on the warpage amount δ of the dry coat layer 25 by applying the concept of the mechanical model of the bending deformation of a cantilever in material mechanics. Hereinafter, first, the warpage amount δ of the dry coat layer 25 will be described with reference to FIG. 3, and then the contents of steps P2 to P3 will be described with reference to FIGS. 4 and 5 in order.

[0033] FIG. 3 illustrates a schematic cross section of the side wall portion 22 that constitutes an arbitrary side surface of the tundish 10. The side wall portion 22 of the tundish 10 is inclined outward of the tank 11 with respect to the bottom wall portion 21. Therefore, the inclination angle θ in the initial state of the dry coat layer 25 formed on the side wall portion 22 is less than 90°. The "initial state" means the state before the tundish 10 is used. Note that the inclination angle θ of the dry coat layer 25 is the angle outside the tank 11 among the angles between the virtual straight line connecting the upper end and the lower end of the dry coat layer 25 and the direction along the bottom wall portion 21.

[0034] When the tundish 10 is in use, when the molten metal is supplied to the ladle 11 of the tundish 10, the dry coat layer 25 expands due to the heat received from the molten metal. Further, when the amount of the molten metal in the tundish 10 decreases, the surface level of the molten metal drops, and the dry coat layer 25 contracts due to the decrease in the surface temperature of the dry coat layer 25. The dry coat layer 25 is constrained by the container wall 20 with its upper end open. Therefore, in the mechanical model of the dry coat layer 25 during thermal deformation such as the above-described expansion and contraction caused by the heat of the molten metal, as shown by the dashed-dotted line in FIG. 3, with the lower end connected to the bottom wall portion 21 as a fulcrum, the warping deformation that bends in the direction toward the inside of the ladle 11 becomes dominant.

[0035] Hereinafter, the lateral movement distance of the upper end of the dry coat layer 25 from the initial position P0 in the lateral direction when the dry coat layer 25 warps inward of the ladle 11 with its lower end as a fulcrum due to thermal deformation is referred to as the "warping amount δ". The "initial position P0" means the position in the tundish 10 before use. The "lateral direction" corresponds to the direction along the bottom wall portion 21.

[0036] In step P2 of FIG. 2, first, the limit warping amount δ max is determined. The "limit warping amount δ max " is the maximum value of the allowable range of the warping amount δ that suppresses the occurrence of the collapse of the dry coat layer 25, that is, corresponds to the limit value of the warping amount δ at which the collapse of the dry coat layer 25 is likely to start. The method of determining the limit warping amount δ max will be described later with reference to FIG. 5.

[0037] In the subsequent step P3, using the limit warping amount δ max determined in step P2, the design value ht of the thickness of the dry coat layer 25 is determined.

[0038] Refer to FIG. 4. FIG. 4 shows an example of a graph Gs showing the relationship in which the thickness h of the dry coat layer 25 and the warping amount δ are uniquely associated with each other. The graph Gs is derived from the following equations (1) and (2).

[0039] [Number 1] The amount of warpage δ = (F × L 3 ) / (3 × E × I) …(1) F: The load applied horizontally when the dry coat layer 25 warps inside the tank 11 L: The height of the dry coat layer 25 E: The Young's modulus of the dry coat layer 25 I: The second moment of area of the dry coat layer 25, which is the value obtained by the following formula (2)

[0040] [Number 2] I = b × h 3 / 12 …(2) b: The width of the dry coat layer 25 h: The thickness of the dry coat layer 25

[0041] The load F in the above formula (1) corresponds to the load that causes warpage in the dry coat layer 25. Here, for the sake of simplicity of calculation, the load F is obtained as a concentrated load at the upper end of the dry coat layer 25. In this case, the load F can be obtained as the difference between the load F1 acting towards the inside of the tank 11 caused by the warpage due to thermal deformation and the self-weight of the dry coat layer 25 shown in Fig. 3, and the load F2 acting towards the inside of the tank 11 caused by the self-weight of the dry coat layer 25 and acting in the direction to suppress warpage. In actual calculation, the load F may be replaced by a constant determined in advance based on experimental results, etc.

[0042] The height L of the dry coat layer 25 in the above formula (1) corresponds to the length in the direction of the inclination angle θ from the lower end to the upper end. The Young's modulus E of the dry coat layer 25 is a value representing the material strength of the dry coat layer 25. In actual calculation, the Young's modulus E may use a constant obtained in advance by experiments, etc. for each material forming the dry coat layer 25. The second moment of area I is the value obtained by the above formula (2).

[0043] In the above formula (2), the width b of the dry coat layer 25 corresponds to the lateral length of the dry coat layer 25. The lateral length of the dry coat layer 25 corresponds to the width of the surface of the container wall 20 on which the dry coat layer 25 is formed. The surface of the container wall 20 is demarcated by the corners of the container wall 20.

[0044] Here, the above formulas (1) and (2) correspond to the formulas used for mechanically analyzing the bending deformation of a cantilever beam in mechanics of materials. As described above, in the mechanical model when the dry coat layer 25 expands and contracts due to heat, the bending deformation that deflects in the direction toward the inside of the ladle 11 with the lower end connected to the bottom wall portion 21 as the fulcrum becomes dominant. Since the inventor of the present invention found that this mechanical model approximates the bending deformation of a cantilever beam, he obtained an unprecedented unique idea that the dry coat layer 25 can be regarded as a cantilever beam and the concept of a cantilever beam in mechanics of materials can be applied to the dry coat layer 25.

[0045] The graph Gs in FIG. 4 is obtained from the function representing the amount of warpage δ of the dry coat layer 25 in terms of the thickness h of the dry coat layer 25, which is derived from the above formulas (1) and (2). In the relationship represented by this graph Gs, the thickness h obtained for the limit warpage amount δ max corresponds to the minimum value of the thickness that can suppress the collapse of the dry coat layer 25. In step P3, in the relationship represented by this graph Gs, the thickness h of the dry coat layer obtained for the limit warpage amount δ max is acquired as the design value ht.

[0046] If the dry coat layer 25 is formed with the design value ht obtained in step P3, it is possible to suppress an increase in the volume of the dry coat layer 25 while suppressing the occurrence of collapse due to thermal deformation of the dry coat layer 25. Therefore, it is possible to suppress a reduction in the capacity of the tundish 10 due to the dry coat layer 25. Further, it is possible to suppress an increase in the running cost due to an increase in the usage fee of the dry coat material for forming the dry coat layer 25.

[0047] The graph in Fig. 4 plots the experimental results obtained by the present inventor. In this experiment, in a tundish where the graph Gs in Fig. 4 was applicable, various dry coat layers with different thicknesses h were formed, and it was verified whether the dry coat layer would collapse when the tundish was used under predetermined conditions. The black circle (●) plots indicate that the dry coat layer did not collapse, and the cross (×) plots indicate that the dry coat layer collapsed. From these results, it can be seen that the occurrence of collapse is suppressed for a dry coat layer formed with a thickness greater than the thickness ht determined based on the graph Gs.

[0048] Referring to Fig. 5, the limit warpage amount δ in step P2 max An example of how to define it will be described.

[0049] Fig. 5 shows an example of a graph representing the relationship that uniquely associates the inclination angle θ of the side wall portion 22 of the tundish 10 with the limit warpage amount δ max An example of a graph representing the relationship that uniquely associates the inclination angle θ of the side wall portion 22 of the tundish 10 with the limit warpage amount δ max The inclination angle θ and the limit warpage amount δ max have a linear relationship such that as the inclination angle θ increases, the limit warpage amount δ max decreases. In step P2, using this relationship prepared in advance, the limit warpage amount δ

[0050] The collapse of the dry coat layer 25 is likely to occur when the inclination angle θ of the dry coat layer 25 reaches a certain limit angle due to warpage caused by thermal expansion and contraction. The limit angle is a value obtained through experiments and the like. The limit warpage amount δ max corresponds to the warpage amount δ when the inclination angle θ of the dry coat layer 25 reaches that limit angle.

[0051] The limit angle may be a value of 90° or more. This is because when the inclination angle θ of the dry coat layer 25 exceeds 90° due to warpage, the action of the self-weight acting in the direction in which the dry coat layer 25 falls inside the tank 11 becomes larger, increasing the possibility of collapse of the dry coat layer 25.

[0052] Refer to FIG. 2. In step P4, a dry coat layer 25 having a thickness of the design value ht determined in step P3 is formed. In step P4, first, a formwork is prepared in which a gap corresponding to the thickness of the design value ht is formed between the refractory layer 24. Next, the formwork is placed in the ladle 10 in the tank 11, and the dry coat material is filled in the gap between the refractory layer 24 and heated and fired. Thereby, the dry coat layer 25 is formed.

[0053] As described above, when designing the dry coat layer 25 of the ladle, if the concept of the deflection deformation of the cantilever beam is applied, the thickness of the dry coat layer 25 can be easily designed to an appropriate value that can suppress the collapse of the dry coat layer 25 and does not become too large. Therefore, a high-strength dry coat layer 25 with suppressed occurrence of collapse can be efficiently formed.

[0054] The present invention is not limited to the configuration of the above-described embodiment, and can be modified without impairing the technical significance. For example, in step P2 described in the above embodiment, the limit deflection amount δ max may be determined as a constant obtained experimentally.

Explanation of reference numerals

[0055] 10... ladle, 11... tank, 20... container wall, 21... bottom wall portion, 22... side wall portion, 23... iron skin, 24... refractory layer, 25... dry coat layer,

Claims

1. A method for designing a dry coat layer that covers the inner wall surface of the tundish tank, comprising: When the dry coat layer formed on the side wall portion of the tank warps inward of the tank due to thermal deformation, and the lateral movement distance from the initial position of the upper end of the dry coat layer is defined as the warping amount δ, The limit warpage amount δ, which is the maximum value of the allowable range of the warpage amount δ for which the occurrence of chipping is suppressed ｍａｘ a step of determining; In the relationship that uniquely associates the warpage amount δ and the thickness h of the dry coat layer obtained from the following mathematical formulas (1) and (2), the thickness h obtained for the critical warpage amount δ ｍａｘ is obtained as the design value ht of the thickness of the dry coat layer, and the process of The method comprising: [Equation 1] The amount of warp δ = (F × L ３ ) / (3 × E × I) … (1) F: The load applied in the lateral direction when the dry coat layer warps inward of the tank L: The height of the dry coat layer E: The Young's modulus of the dry coat layer I: The second moment of area of the cross section of the dry coat layer, which is a value obtained by the following formula (2) [Equation 2] I = b × h ３ / 12…(2) b: The width of the dry coat layer h: The thickness of the dry coat layer

2. The method according to claim 1, comprising: The limit warpage amount δ ｍａｘ is determined for the inclination angle θ in the initial state using a previously prepared relationship that uniquely associates the inclination angle θ outside the tank with respect to the direction along the bottom wall portion of the tank of the dry coat layer in the initial state and the limit warpage amount δ ｍａｘ and the method is defined for the inclination angle θ in the initial state using the relationship prepared in advance that uniquely associates the inclination angle θ outside the tank with respect to the direction along the bottom wall portion of the tank of the dry coat layer in the initial state and the limit warpage amount δ

3. The method according to claim 2, comprising: The limit warping amount δ ｍａｘ is the warping amount δ when the inclination angle θ becomes 90° or more when the dry coat layer warps inward of the tank due to thermal deformation, method.

4. A method for forming a dry coat layer that covers the inner wall surface of the tundish tank, comprising: Determining a design value ht of the thickness of the dry coat layer by the method according to any one of claims 1 to 3; and Forming the dry coat layer to have a thickness of the design value ht. The method comprising:

Images