JP2012183573A - Immersion nozzle for continuous casting, and its designing method - Google Patents

Abstract

An immersion nozzle for continuous casting having a structure for preventing destruction of a rectifying plate nozzle body in the immersion nozzle.
An expansion coefficient of a nozzle body is M _1α [× 10 ⁻⁶ / ° C.], an elastic modulus of the nozzle body is M _1E [MPa], a tube wall thickness of the nozzle body is T _nzl [mm], and a current plate When the elastic modulus is M _2E [MPa], the bending strength of the nozzle body is σ _b [MPa], and the maximum value of the stress intensity ratio index at which the nozzle body does not break is S _est / σ _b , all the partial plates are fixed. The length distance L _span [mm] in the nozzle axis direction between the parts is set to a length within the range defined by the following expression (1a). ^{_{0 <L span ≦ {-b- (}} b 2 -4ac) 1/2} / 2a ··· (1a), however, the _{a = c 18 / σ b,} c 18 = -4.83886 × 10 -5 To do.
[Selection figure] None

Description

  The present invention relates to an immersion nozzle used for continuous casting in which molten steel is poured into a mold, and more particularly, to improve the flow of molten steel in the molten steel mold, the nozzle body has an immersion surface with a height of at least at the outer wall surface of the nozzle body. The present invention relates to a submerged nozzle for continuous casting of molten steel, in which a rectifying plate made of a plate-like refractory that is longer than the length of the portion and whose lateral width is at least wider than the outside width of the nozzle body is fixed symmetrically.

  In continuous casting of molten steel, the immersion nozzle not only immerses in the molten steel mold and injects the molten steel into the mold, but also plays an important role in rectifying the molten steel in the mold. For this rectification (improvement of molten steel flow), various ideas have been made on the shape and structure of the immersion nozzle. As one of the methods for rectification, an attempt has been made to attach a structure (rectifier plate) with a unique structure for forcibly controlling the direction of the molten steel flow to the outer periphery of the nozzle body of the immersion nozzle. Yes.

  For example, Patent Document 1 is characterized in that the horizontal cross-sectional shape of the outer shape of the submerged nozzle or the outer shape of the rectifying plate attached to the submerged nozzle is asymmetric with respect to the center line in the mold longitudinal direction. A continuous casting method is shown.

  Moreover, in patent document 2, in the immersion nozzle for continuous casting which attached the baffle plate for forming a swirl flow on the molten metal surface to the outer peripheral surface, the baffle plate was made into the box-shaped structure which provided the hollow part. A continuous casting immersion nozzle is shown.

  Further, in recent years, a simple plate-like rectifying plate is formed on the outside, specifically, on the outer surface of the nozzle wall of the nozzle body, the height is at least longer than the length of the immersion portion of the nozzle body, and the lateral width is at least outside the tube of the nozzle body. An immersion nozzle has been developed in which a current plate made of a plate-like refractory wider than a width is fixed symmetrically.

  However, the immersion nozzle in which the rectifying plate as in Patent Documents 1 and 2 is attached to the outer peripheral surface of the nozzle body is likely to break due to its unique structure. If these rectifying plates are broken, the purpose of rectification cannot be achieved, the immersion nozzle main body portion may be broken, and the operation may be stopped and other serious troubles may be caused. Patent Documents 1 and 2 do not disclose a solution regarding this point.

JP 2001-286993 A JP-A-8-112657

  The problem to be solved by the present invention is an immersion nozzle in which a simple plate-like rectifying plate is attached to the outside of the nozzle body, and a continuous casting immersion nozzle having a structure for preventing the destruction of the nozzle body as described above. It is to provide the design method.

As a result of the thermal stress analysis of the nozzle body and the current plate of the continuous casting immersion nozzle, the present inventor has obtained the following knowledge.
(1) Damage to the nozzle body is mainly due to thermal stress.
(2) Thermal stress is generated largely in the height direction of the current plate, centering on the connection with the nozzle body.
(3) The thermal stress is the length of the current plate in the vertical direction (height direction), that is, when the current plate is configured by combining several partial plates in the vertical direction, Depends greatly on length.
The present invention has been completed on the basis of these findings, and when attaching a rectifying plate to the nozzle body, the length of the rectifying plate in the vertical direction (height direction) is set to an optimal length, It is configured to relieve the stress generated between them and prevent the immersion nozzle from being broken.

That is, the immersion nozzle for continuous casting according to the present invention is an immersion nozzle used for continuous casting of molten steel,
A plate-like refractory having a length in the direction along the nozzle axis that is at least longer than the length of the immersion portion of the nozzle body of the immersion nozzle and a width in the direction perpendicular to the nozzle axis that is at least wider than the outside width of the nozzle body A rectifying plate is fixed symmetrically to the outer surface of the tube wall of the nozzle body, and the rectifying plate is formed by connecting a plurality of partial plates in the vertical direction,
The expansion coefficient of the nozzle body is M _1α [× 10 ⁻⁶ / ° C.],
The elastic modulus of the nozzle body is M _1E [MPa],
The thickness of the tube wall of the nozzle body is T _nzl [mm],
The elastic modulus of the current plate is M _2E [MPa],
The bending strength of the nozzle body is σ _b [MPa],
The maximum value of the stress intensity ratio index at which the nozzle body does not break is expressed as S _est / σ _b
The length distance L _span [mm] in the nozzle axis direction between the fixed portions of the plates for all the attached partial plates is a length within the range defined by the following equations (1a) to (1d). It is characterized by being.

Further, the method for designing a submerged nozzle for continuous casting according to the present invention is a submerged nozzle used for continuous casting of molten steel, wherein the length in the direction along the nozzle axis is at least a submerged portion of the nozzle body of the submerged nozzle. A rectifying plate made of a plate-like refractory that is longer than the length of the nozzle body and has a width in the direction perpendicular to the nozzle axis that is at least wider than the outer width of the nozzle body is fixed symmetrically to the outer surface of the nozzle wall of the nozzle body, The rectifying plate is a design method of a continuous casting immersion nozzle formed by connecting a plurality of partial plates in the vertical direction,
The expansion coefficient of the nozzle body is M _1α [× 10 ⁻⁶ / ° C.],
The elastic modulus of the nozzle body is M _1E [MPa],
The thickness of the tube wall of the nozzle body is T _nzl [mm],
The elastic modulus of the current plate is M _2E [MPa],
The bending strength of the nozzle body is σ _b [N / mm],
The maximum value of the stress intensity ratio index at which the current plate does not break is expressed as S _est / σ _b
For all attached partial plates, the length L _span [mm] in the nozzle axis direction between the fixed portions of the plates is set to a length within the range defined by the above formulas (1a) to (1d). It is characterized by.

  When the immersion nozzle for continuous casting according to the present invention is configured as described above, it is possible to prevent the current plate from being broken during use in continuous casting.

It is a figure showing the whole structure of the immersion nozzle for continuous casting which concerns on this invention. It is the figure which cut and modeled the partial board of ZG and AG shown in FIG. It is the figure which showed the dimension parameter about the analysis section | slice of Fig.2 (a). It is the result of calculating the sensitivity of each parameter of the immersion nozzle for continuous casting.

  First, the process up to the derivation of the configuration of the continuous casting immersion nozzle according to the present invention will be described.

  FIG. 1 is a diagram illustrating the overall configuration of a continuous casting immersion nozzle according to the present invention. 1A and 1B are longitudinal sectional views, and FIG. 1C is a transverse sectional view. 1 (a) and 1 (b) are cross-sectional views taken along the lines AA and BB shown in FIG. 1 (c), respectively, and FIG. It is sectional drawing at the time of cutting along the CC line of Fig.1 (a).

  In FIG. 1, the continuous casting immersion nozzle 1 is composed of a nozzle body 2 and two rectifying plates 3 and 3. The nozzle body 2 has a substantially cylindrical shape, and the outer diameter is gradually reduced from the base end (upper side) to the front end (lower side). The nozzle body 2 includes a base end portion 2a, a slag in portion 2b, a tip end portion 2c, and an inner cylinder portion 2d. Two discharge ports 4 and 4 are formed in the distal end portion 2c so as to face diagonally downward and opposite to each other. The inner cylinder portion 2d is inserted into the pipe from the middle of the base end portion 2a to the middle of the distal end portion 2c. The central axis of the cylindrical nozzle body 2 is the nozzle axis 5.

  During the continuous casting of the molten steel, the molten steel flowing down in the cylinder of the nozzle body 2 from the base end portion 2a toward the tip end portion 2c is injected into the molten steel reservoir from the discharge ports 4 and 4. At this time, as for the continuous casting immersion nozzle 1, the front-end | tip part 2c is completely immersed in a molten steel reservoir, and the molten metal surface of a molten steel reservoir becomes the middle of the slag in part 2b. The base end portion 2a, the tip end portion 2c, and the inner cylinder portion 2d are usually made of an alumina-graphite refractory or a spinel-graphite refractory. On the other hand, the slag-in part 2b is made of zirconia-graphitic refractory because it is in contact with the mold powder layer existing near the molten steel surface of the molten steel reservoir and is easily consumed.

The rectifying plates 3 and 3 have a length in the direction along the nozzle shaft 5 that is at least a portion that is immersed in the molten steel reservoir of the continuous casting immersion nozzle 1 (portion from the tip portion 2c to the middle of the slag-in portion 2b). It consists of a refractory material in the form of a rectangular plate that is longer than the length and has a width in a direction perpendicular to the nozzle shaft 5 (horizontal direction) that is at least wider than the outside width of the continuous casting immersion nozzle 1. The rectifying plates 3 and 3 are respectively fixed symmetrically to the outer surface of the tube wall of the continuous casting immersion nozzle 1 with the continuous casting immersion nozzle 1 interposed therebetween, and the plate surfaces are the centers of the discharge ports 4 and 4. Parallel to the axes 6 and 6. Each of the rectifying plates 3 and 3 is configured as a composite of partial plates by connecting a plurality of partial plates in the vertical direction. The length in the vertical direction (nozzle axis direction) of the partial plate constituting the rectifying plate 3 is L _span [mm].

FIG. 2 is a diagram in which the ZG and AG partial plates shown in FIG. 1 are cut out and modeled. 2A shows the ZG portion, and FIG. 2B shows the partial plate of the AG portion taken out. In consideration of the symmetry of the continuous casting immersion nozzle 1, 1/4 of the pipe circumference of the nozzle body 2 is cut and modeled. In the present invention, in order to determine the distance L _span between the fixed bosses in the height direction of the rectifying plate 3, thermal stress analysis is performed by the finite element method. It is divided. Hereinafter, these extracted portions are referred to as “analysis sections” below.

  In FIG. 2, bosses 2e are provided on the outer wall surfaces of the slag-in part 2b and the tip part 2c. By fitting the boss holes formed in the rectifying plate 3 into the bosses 2e, the rectifying plate 3 is It is fixed to the slag-in part 2b or the tip part 2c.

  FIG. 3 is a diagram showing dimensional parameters for the analytical intercept in FIG. It should be noted that the dimension parameter of the analysis section in FIG.

_3, (see FIG. 1 (c) also) _T ita [mm] is the thickness of the current plate _{3, L straight} [mm] is the width of the portion where the rectifier plate 3 and the nozzle body 2 is in contact, T _nzl [mm] represents the thickness of the tube wall of the nozzle body, and L _span [mm] represents the distance between the upper and lower bosses 2e, 2e.

For simplification of calculation, it is assumed that the expansion coefficient, elastic modulus, and thermal conductivity of the base end part 2a, the slag in part 2b, and the front end part 2c of the nozzle body 2 are the same, and the expansion coefficient is set to M. _1α [× 10 ⁻⁶ / ° C.], the elastic modulus is denoted as M _1E [MPa], and the thermal conductivity is denoted as M _1λ [W / m · K]. The expansion coefficient, elastic modulus, and thermal conductivity of the rectifying plate 3 are _denoted as M _2α [× 10 ⁻⁶ / ° C.], M _2E [MPa], and M _2λ [W / m · K], respectively. Further, the bending strength of the rectifying plate 3 is denoted as σ _b [N / mm], the maximum value of the thermal stress applied to the rectifying plate 3 is denoted as S _est [N / mm], and the stress intensity ratio index is denoted as S _est / σ _b .

First, out of the above-mentioned parameters, parameters that greatly affect the destruction of the rectifying plate 3 in the hot state are extracted. Therefore, first, a representative value of each parameter is determined as a central value, and when each parameter is varied within a range of ± 5% from the central value, how much thermal stress is generated in the rectifying plate 3 during the heat. We evaluated whether it changed. FIG. 4 shows the calculation result. The center value of each parameter P of interest is P ₀ , the value fluctuated + 5% is P ₊₅ , the value fluctuated -5% is P _−5, and the result of thermal stress analysis by the finite element method for the parameter P is obtained. The maximum value of the thermal stress applied to the rectifying plate 3 is S _est (P) [MPa]. At this time, the sensitivity Se for the parameter P is defined as Se = (S _est (P ₊₅ ) −S _est (P ₋₅ )) / S _est (P ₀ ). FIG. 4 shows the sensitivity of each parameter obtained in this way. A parameter having a large absolute value of the sensitivity Se is considered to be a parameter (an effective parameter) that greatly affects the destruction of the current plate 3 in the hot state. From this result, as effective parameters, the expansion coefficient M _{1α of} the nozzle body 2, the elastic modulus M _{1E of} the nozzle body 2, the tube wall thickness T _{nzl of the} nozzle body 2, the elastic modulus M _2E of the rectifying plate 3, and the upper and lower The distance between the bosses L _span was extracted.

Next, as shown in Table 1, for each of the five extracted parameters, the minimum value and maximum value of the parameter are determined, and each parameter is changed between the maximum and minimum values. Stress analysis was performed, and S _est was obtained as the maximum value of the thermal stress applied to the rectifying plate 3. In addition, the change of each parameter was performed by the division | segmentation Monte Carlo method using the Latin supersquare method (LHS). The minimum and maximum parameter values were set to cover all possible values in actual design.

The thermal stress analysis assumes that the initial temperature is 25 ° C, molten steel is assumed on the nozzle inner surface, the contact temperature is 1550 ° C, the heat transfer rate is 1160W / m ² k, and the nozzle outer peripheral surface is exposed to the surrounding heat. Assuming that the conditions were a contact temperature of 25 ° C. and a heat transfer coefficient of 11.6 W / m ² k, the maximum stress generated in the nozzle body was calculated.

  In addition, about the number of parameters, although the stepwise method and other verification were performed together, the result that the 20 parameters adopted in the present invention were optimum was obtained.

From the relationship between the parameter P = (M _1α , M _1E , M _2E , L _span , T _nzl ) obtained by this piecewise Monte Carlo method and the maximum thermal stress S _est (P), the maximum thermal stress S _est ( P) was approximated by a quadratic expression of parameters (M _1α , M _1E , M _2E , L _span , T _nzl ). The following equation (2) is an approximate expression representing the response surface of the maximum thermal stress S _est (P) with respect to the parameters (M _1α , M _1E , M _2E , L _span , T _nzl ) obtained by this multiple regression analysis. is there.

Dividing both sides of the equation (1) by the bending strength σ _b of the rectifying plate 3, the equation of the stress intensity ratio index S _est / σ _b is obtained. Therefore, the expression for the stress intensity ratio index _{S est} / _{σ b} believe quadratic equation parameters _{L span,} solving equation (1) the parameters _{L span.} Thereby, the length L _span of the partial plate is expressed by the following formula (3a) or formula (3b). Here, the coefficients a, b, and c are expressed by the aforementioned equations (1b) to (1d).

The maximum thermal stress S _est is 7.5 to 22.5 MPa (bending strength of the material is 5 to 15 MPa, stress intensity ratio index S _est / σ _b described later is 1.5, and the range of stress to be evaluated is estimated). The result of calculating the length L _span of the partial plate according to the formulas (3a) and (3b) by shaking each range (M _1α , M _1E , M _2E , T _nzl ) in the parameter range shown in Table 1 The formula (3b) was always 500 mm or more. On the other hand, as shown in Table 1, since the range of the boss distance L _span is 40 to 356.66 mm, the solution of the equation (3b) is not appropriate. Therefore, the formula (3a) was adopted. Since the maximum thermal stress S _est increases as the length L _span of the partial plate increases, if the stress intensity ratio index S _est / σ _{b at} which the rectifying plate 3 breaks is determined, the distance L _span between the fixed portions of the partial plate The maximum value (non-destructive limit value) can be obtained by substituting this stress intensity ratio index S _est / σ _b into the equation (3a). Therefore, it can be seen that the range of the distance L _span between the fixed portions of the partial plate that does not break due to thermal stress is defined by the equation (1a).

Next, the stress intensity ratio index S _est / σ _b will be described. The stress intensity ratio index S _est / σ _b is obtained by dividing the maximum thermal stress S _est applied to the partial plate by the bending strength σ _b of the partial plate, and does not depend on the material of the partial plate and is almost a common value. It is thought that it becomes. Therefore, this maximum thermal stress S _est is employed as a parameter that defines the range of the distance L _span between the fixed portions of the partial plate where no fracture occurs.

The maximum value of the stress intensity ratio index that the rectifying plate 3 does not break is determined by collating the calculation result of the maximum thermal stress S _est by the finite element method with the result of the pouring test for the continuous casting immersion nozzle 1. Tables 2 to 4 show a comparison between the maximum thermal stress estimated by the approximate expression (3b) and the result of the pouring test. In Tables 2 to 4, the unit of each numerical value is as already shown in the above description.

In Tables 2 to 4, the table of “Experiment” at the bottom _indicates the maximum thermal stress S when the parameter (M _1α , M _1E , M _2E , T _nzl ) and the bending strength of the rectifying plate 3 are determined as σ _{b. The} comparison of the calculated value of _est and stress intensity ratio index _Sest / (sigma) _b , and the pouring test result in the same conditions is shown. “◯” in the pouring test result indicates that the current plate 3 and the nozzle body 2 were not broken, and “X” indicates that the current plate 3 or the nozzle body 2 was broken. From the results of Tables 2 to 4, it can be seen that the maximum value of the stress intensity ratio index S _est / σ _{b at which} the current plate 3 and the nozzle body 2 do not break is S _est / σ _b = 1.5.

The upper table of “Calculation” in Tables 2 to 4 shows that S _est / σ _b = 1.5, the parameters (M _1α , M _1E , M _2E , T _nzl ) and the bending strength of the rectifying plate 3 are σ _It is the result of having calculated _| required the estimated value of the distance L _span between the fixed parts of the partial board which does not produce a destruction when _b is determined by Formula (3b). From these results, it is found that the estimated value of the maximum length L _span between the fixed bosses of the partial plate obtained by Equation (3b) with S _est / σ _b = 1.5 is in good agreement with the result of the pouring test. confirmed.

From the above results, by setting the distance L _span between the fixed portions in the nozzle axis direction per piece of the partial plate within the range represented by the formula (1a), it is caused by the thermal stress of the rectifying plate 3 and the nozzle body 2. It becomes possible to prevent destruction.

DESCRIPTION OF SYMBOLS 1 Submerged casting nozzle 2 Nozzle body 2a Base end part 2b Slag in part 2c End part 2d Inner cylinder part 2e Boss 3 Current plate 4 Discharge port 5 Nozzle shaft 6 Center axis of discharge port

Claims (2)

An immersion nozzle used for continuous casting of molten steel,
A plate-like refractory having a length in the direction along the nozzle axis that is at least longer than the length of the immersion portion of the nozzle body of the immersion nozzle and a width in the direction perpendicular to the nozzle axis that is at least wider than the outside width of the nozzle body A rectifying plate is fixed symmetrically to the outer surface of the tube wall of the nozzle body, and the rectifying plate is formed by connecting a plurality of partial plates in the vertical direction,
The expansion coefficient of the nozzle body is M _1α [× 10 ⁻⁶ / ° C.],
The elastic modulus of the nozzle body is M _1E [MPa],
The thickness of the tube wall of the nozzle body is T _nzl [mm],
The elastic modulus of the current plate is M _2E [MPa],
The bending strength of the nozzle body is σ _b [MPa],
The maximum value of the stress intensity ratio index at which the current plate does not break is expressed as S _est / σ _b
In this case, the length L _span [mm] in the nozzle axis direction between the fixed portions of the plates for all the attached partial plates is a length within the range defined by the following equations (1a) to (1d). An immersion nozzle for continuous casting characterized by the above.

An immersion nozzle used for continuous casting of molten steel, wherein the length in the direction along the nozzle axis is at least longer than the length of the immersion portion of the nozzle body of the immersion nozzle, and the lateral width in the direction perpendicular to the nozzle axis is at least A rectifying plate made of a plate-like refractory wider than the outer tube width of the nozzle body is fixed symmetrically to the outer surface of the tube wall of the nozzle body, and the rectifying plate is formed by connecting a plurality of partial plates in the vertical direction. A method for designing an immersion nozzle for continuous casting,
The expansion coefficient of the nozzle body is M _1α [× 10 ⁻⁶ / ° C.],
The elastic modulus of the nozzle body is M _1E [MPa],
The thickness of the tube wall of the nozzle body is T _nzl [mm],
The elastic modulus of the current plate is M _2E [MPa],
The bending strength of the nozzle body is σ _b [MPa],
The maximum value of the stress intensity ratio index at which the current plate does not break is expressed as S _est / σ _b
In this case, the length L _span [mm] in the nozzle axis direction between the fixed portions of the plates for all the attached partial plates is within the range defined by the equations (1a) to (1d) according to claim 1. A method for designing an immersion nozzle for continuous casting, characterized in that the length is as follows.

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