JP3148113B2 - Transfer method of steel sheet after annealing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for conveying a steel sheet in a continuous annealing equipment for a steel sheet, a continuous galvanizing equipment, and other continuous steel sheet processing equipment having an in-line annealing furnace. This is a method for transporting a steel sheet after annealing that enables prevention of buckling of the steel sheet.

[0002]

2. Description of the Related Art When a steel sheet immediately after annealing is wound around a roll or the like and conveyed, if a roll having an excessively small outer diameter is used, depending on the type of steel, an axial flaw called waist break may occur. In order to prevent the occurrence of the buckling, it is considered that the larger the diameter of the transport roll is, the better. The longitudinal elastic modulus of the steel sheet is E, the thickness of the steel sheet is t,
Assuming that the yield stress is σ _e and the tension is σ _u , conventionally, the roll outer diameter D

[0003]

(Equation 6)

[0004] It was supposed to be good.

A gas cushion bearing (hereinafter referred to as GCB) which bends and conveys a steel sheet by the action of static pressure of fluid is used as a material other than a roll. C. B. It can also be applied to the selection of the bending radius of the steel sheet when transporting the steel sheet by using.

In Japanese Patent Application Laid-Open No. 3-8514, when the sectional yield ratio β is 0.3 to 0.5,

[0007]

(Equation 7)

It is disclosed that the above condition should be satisfied.

[0009]

However, for example, in a cooling zone after plating in a continuous hot-dip galvanizing facility, even if a roll outer diameter that satisfies the above-mentioned formula (6) is used, hip breakage may still occur. In order to avoid this, the material of the steel plate must be limited. Also,
Similarly, in a cooling zone of a continuous steel sheet processing facility having an in-line annealing furnace, even if a roll outer diameter that satisfies the above-mentioned expression (6) is used, breakage may occur.

An example of such a problem will be described with reference to FIG. FIG. 1 shows a plating section of a continuous hot-dip galvanizing apparatus, and 1 is a steel sheet sent from an annealing furnace (not shown), which advances in the direction of the arrow in the figure. 2 is a molten zinc bath, 3 is a sink roll, and 4 is a plating apparatus. 5
Denotes a cooling device for a steel plate, 6 and 7 deflector rolls having an outer diameter of 1500 mm, and 8 and 9 deflector rolls having an outer diameter of 1200 mm. The temperature of the steel sheet 1 is about 460 ° C. in the molten zinc bath 2, about 300 ° C. in the deflector roll 6, and about 10 ° C. in the deflector rolls 8 and 9.
0 ° C. The tension is 1.0 kgf / mm ² .

In this hot-dip galvanizing equipment, the steel plate having a thickness of 2 mm or more (E = 21,000 kgf / mm ² , yield stress σ _{e at} 100 ° C. = 25 kgf / mm ² ) was bent by the deflector roll 9. However, the deflector roll 9

[0012]

(Equation 8)

Equation (6) was satisfied as described above. Furthermore,
Even though the deflector roll 8 on the entry side had the same outer diameter, the roll 8 did not break, and the roll 9 consistently broke. In addition, the buckling of a steel plate having a thickness of 2 mm on the roll 9 is adjusted such that the outer diameter of the roll 9 is 1500 mm.
And solved it. These facts cannot be explained by the conventional test formula (6).

On the other hand, with respect to the conditional expression disclosed in Japanese Patent Laid-Open Publication No.

[0015]

(Equation 9)

This corresponds to the case of the first formula of (7), but the sectional yield ratio β is

[0017]

(Equation 10)

Substituting this into the right side of the first equation of (7) gives

[0019]

[Equation 11]

## EQU1 ## That is, since the first expression of the conditional expression (7) in JP-A-3-8514 is an identity and has no physical significance, it cannot be used as a condition for preventing a steel plate from breaking. Further, the condition of the second expression of (7) is as follows.
In this case, it is applied when the tension exceeds 10 kgf / mm ² , but it is used in continuous annealing equipment for steel sheets, continuous galvanizing equipment, and other continuous steel sheet processing equipment having an in-line annealing furnace. With the exception of tension levelers and transport rolls on the entrance and exit sides of the scan path mill, it is not realistic to load and transport steel sheets with such a high tension in the rolls for transporting steel sheets. Can not be used.

[0021]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the steel sheet after the annealing is 250 sheets.
The purpose of the present invention is to provide an outer diameter condition of a roll or the like that does not cause buckling of a steel plate when being transported while being wound around a roll or the like in a range from a temperature of not less than ℃ to a normal temperature.
Outer diameter D _{o of a} roll around which a steel plate with a temperature of 50 ° C or more is wound
When (1) is satisfied, the outer diameter D of the roll on which the steel sheet having a temperature of 200 ° C. or lower is continuously wound is set to satisfy (2). If the outer diameter D _o satisfies (3), arguments that will 2
An outer diameter D of a roll around which a steel sheet having a temperature of 00 ° C. or less is wound may satisfy (4) or (5) depending on the bending direction.

[0022]

(Equation 12)

Here, t: thickness of steel sheet E: modulus of longitudinal elasticity of steel sheet D _o ; diameter of bending at a temperature of 250 ° C. or more (outer diameter of roll) β _o ; bending at a temperature of 250 ° C. or more Section yield ratio according to σ _eo ; Yield stress of steel sheet at a temperature of 250 ° C or more D: Bending diameter (outer diameter of roll) at a temperature of 200 ° C or more σ _e ; Steel sheet at a temperature of 200 ° C or less Yield stress.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for conveying an annealed steel sheet according to the present invention will be described in detail.

First, a bending test was performed in order to clarify the mechanical mechanism of occurrence of hip break. As a result, when bending is applied to the annealed steel sheet, the stress of the surface layer becomes m times (m
> 1) deformation must be elastic, m <3/2
For materials such as, plastic deformation starts when bending is further applied, but no plastic collapse occurs. For materials such as m ≧ 3/2, the moment the surface stress reaches m times the descending yield point, It was confirmed that plastic collapse occurred and the surface stress decreased to the falling yield point. From the experimental results, the mechanical mechanism of the occurrence of hip break can be explained as follows.

FIG. 2 shows the stress distribution in the thickness direction when a material having m ≧ 3/2 is subjected to bending. According to experiments, the deformation was elastic until the surface stress σ _A reached m times the falling yield point σ _e of the material. FIG. 2A shows this state. At this time, the bending moment M _A per unit width is given by

[0027]

(Equation 13)

Given by When the surface stress of the plate reaches σ _A , the dislocation of the surface layer starts to slip and the stress of the surface layer decreases to σ _e , but the dislocation in the portion closer to the neutral axis by δ / 2 than the surface layer has not yet slipped. This state is shown in FIG. 2B, and the bending moment M _A ′ is

[0029]

[Equation 14]

## EQU1 ## However, because m ≧ 3/2

[0031]

(Equation 15)

Therefore, M _A ′ decreases as δ increases, and δ
/ T = 1, minimum value

[0033]

(Equation 16)

## EQU1 ## Equation (10) gives the ultimate moment, and this state is shown in FIG. That is, when m ≧ 3/2, when the stress of the surface layer reaches m times the descending yield point, plastic collapse occurs without increasing the bending moment. FIG. 3 shows this process in a bending moment / curvature diagram.
It is.

FIG. 4 shows the stress distribution in the thickness direction when a material having m <3/2 is subjected to bending. Also in this case, the deformation is elastic until the stress σ _{A of} the surface layer reaches m times the falling yield point σ _e of the material, and FIG. 4A shows this state.

When the surface stress of the sheet reaches σ _A = mσ _e , the dislocation of the surface layer starts to slip and the stress of the surface layer decreases to σ _e , but the dislocation in the portion closer to the neutral axis by δ / 2 than the surface layer still slips. Not. This state is indicated by a broken line in FIG.
The bending moment per unit width is

[0037]

[Equation 17]

This moment is given by (8)
Because it is equal to the expression

[0039]

(Equation 18)

Is obtained. Here, y _B represents the distance from the neutral axis to the yield layer, and 0 <y _{B in} the range of 1 ≦ m <3/2.
A ≦ t / 2, y _B becomes finite definite value not zero. FIG. 4C shows that the bending moment is further increased and the curvature 1 / ρ
Shows the state bent to ₁ .

FIG. 5 shows this process as a bending moment / curvature diagram. That is, in FIG. 5, although there is a small amount of discontinuous change between A → A ′ → B, between B → C, the deformation is limited to finite even if the bending moment is increased, and the plastic collapse occurs according to the characteristics of the elastic perfect plastic body. Does not.

From the above, in order to prevent the steel sheet after annealing from being bent, the bending moment M applied to the steel sheet must be changed per unit width.

[0043]

[Equation 19]

It is sufficient that For this purpose, the outer diameter D of the wrapping roll is

[0045]

(Equation 20)

It is sufficient to set Here, E is the longitudinal modulus of elasticity of the steel sheet, and I is the second moment of area per unit width. Therefore, the condition of the outer diameter D of the winding roll that does not cause buckling is not the conventional empirical formula (6) but the formula (6).

[0047]

(Equation 21)

It has been found that must be used.

When the annealed steel sheet is conveyed by being wound around a roll or the like in a range from a temperature of 250 ° C. or more to a normal temperature, the outer diameter of the roll or the like which does not cause the steel sheet to break is provided by the following equation (14). Is not sufficient, and it is necessary to consider the influence of residual strain due to bending at a temperature of 250 ° C. or more. In the bending moment / curvature diagram of FIG. 6, O → A ′ → A indicates a state in which a steel plate at 300 ° C. is wound around a roll having an outer diameter _Do. At this temperature, the yield point of the steel sheet has dropped to a value σ _eo which is considerably lower than the value at normal temperature, and at this temperature the elongation at the yield point of the steel sheet has disappeared, so that the roll outer diameter D
_{Even if o} is small, no break will occur. Now, the bending in this roll is elasto-plastic bending,

[0050]

(Equation 22)

If the steel sheet passes through a roll having an outer diameter _{Do and} the bending moment is unloaded, a residual curvature of K _R is generated. This state is indicated by point B in FIG. Now, when the steel sheet is cooled to a temperature of 200 ° C. or less, the yield point rises to almost the value of normal temperature, and the yield point strain also recovers. Bending moment when bent wrapped around the roll outer diameter D in the same direction as the roll of the steel sheet again outer diameter D _o is per unit width

[0052]

(Equation 23)

Is given by Here, β _o is the cross-sectional yield ratio when a steel sheet at 300 ° C. is wound around a roll having an outer diameter D _o . In order to prevent the steel sheet after cooling from causing breakage in the roll having the outer diameter D, it is necessary to obtain the equation (13) and the equation (15).

[0054]

(Equation 24)

Must be Point C in FIG. 6 is (4)
An example of the roll outer diameter D that satisfies the formula is shown. Next, the bending moment per unit width when the cooled steel sheet is wound around a roll having an outer diameter D in a direction opposite to the roll having an outer diameter D _o is bent.

[0056]

(Equation 25)

In order to prevent the hip from breaking, (1)
From equations 3) and (16)

[0058]

(Equation 26)

Must be As is clear from FIG. 6, since OC ">OD", the steel sheet after cooling
Bending in the direction opposite to the bending at a temperature of 0 ° C. or more causes a roll break with a larger roll outer diameter than bending in the same direction. Bending at temperatures above 250 ° C is elastic bending, ie

[0060]

[Equation 27]

In the case of (1), there is no influence of the residual strain after unbending, and in order to prevent the cooled steel sheet from being wound around the roll having the outer diameter D and causing the hip to break (14), ie,

[0062]

[Equation 28]

It suffices to satisfy the following.

[0064]

【Example】

(1) FIG. 1 shows a plating section of a continuous galvanizing equipment showing one embodiment of the present invention. Roll 6 in the figure
In this case, the temperature of the steel sheet was 300 ° C., the yield stress of the steel sheet at this temperature was σ _eo = 15 kgf / mm ² , and the temperature of the steel sheet was 100 ° C. in the rolls 7, 8, and 9 in the figure. The yield stress of the steel sheet at this temperature is σ _e = 25 kgf / mm ² . At this time satisfy the rolls 6 (1) such D _o
If rolls of 3000 mm were arranged and rolls of D = 1200 mm satisfying the expression (2) were arranged in the rolls 7, 8, and 9, no break in the steel plate having a thickness of t = 2 mm occurred. The result is shown in FIG. The occurrence of hip break was visually determined.

(2) D _o = 1500 m on the roll 6 in FIG.
m, and rolls 7 and 8 which bend the steel sheet in the same direction as the roll 6 have D = 120 satisfying the expression (4).
When the rolls of 0 mm were arranged, the rolls 7 and 8 did not break at the steel plates up to the plate thickness t = 2 mm. The result is shown in FIG.

(3) _Do = 1500 m on the roll 6 in FIG.
m is arranged, and rolls 7 and 8 which are bent in the same direction as the roll 6 have D = 1200 mm which satisfies the expression (4).
D = 1500m such that the roll 9 for arranging the rolls and bending the steel plate in the opposite direction to the roll 6 satisfies the expression (5).
When the rolls of m were arranged, no break in the steel plate having a thickness t = 2 mm occurred. The result is shown in FIG.

FIGS. 7 and 9 show that a hip break occurred under conditions outside the scope of the present invention.

That is, regarding the outer diameter of the rolls for transporting the annealed steel sheet according to the present invention, a limit value of occurrence of hip breakage is found based on a bending test, and a theoretical explanation is given thereto. The outer diameter of the roll is determined in consideration of the case where the roll is conveyed while being wound around the roll or the like in a range from a temperature of 250 ° C. or higher to a normal temperature, thereby completely preventing the steel plate from breaking.

[0069]

The outer diameter of the rolls for transporting the annealed steel sheet according to the present invention is configured as described above, and the occurrence of breakage of the steel sheet is completely prevented, so that excessive equipment is suppressed. In addition, it is not necessary to limit the material of the steel sheet to be passed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a plating section of a continuous galvanizing equipment according to one embodiment of the present invention.

FIGS. 2 ( a ), ( b ), and ( c ) are stress distribution diagrams in the thickness direction due to bending of a material in which hip break occurs.

FIG. 3 is a bending moment / curvature diagram of a material in which hip break occurs.

[4] (a), (b), (c) the stress distribution diagram in the thickness direction due to the bending of the material which does not generate buckling.

FIG. 5 is a bending moment / curvature diagram of a material in which hip break does not occur.

FIG. 6 is a bending moment / curvature diagram for explaining the effect of residual strain due to bending at 300 ° C. on the limit of hip break generation.

FIG. 7 is a view showing the results of an example.

FIG. 8 is a diagram showing the results of an example.

FIG. 9 is a diagram showing the results of an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Steel plate 2 ... Zinc bath 3 ... Sink roll 4 ... Plating apparatus 5 ... Cooling apparatus 6, 7 ... Deflector roll (outer diameter 1500mm) 8, 9 ... Deflector roll (outer diameter 1200mm)

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Wake 46-59 Ohara Nakahara, Tobata-ku, Kitakyushu Nippon Steel Corporation Machinery & Plant Division (56) References JP-A-55-154527 (JP, A) JP-A-55-136510 (JP, A) JP-A-3-8514 (JP, A) JP-A-7-112209 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9 / 56,11 / 00 B21B 39/08 B21C 47/00 C23C 2/00 B65H 23/188

Claims (2)

(57) [Claims] 1. A method for transporting a steel sheet by winding an annealed steel sheet around a roll or the like at a temperature of 250 ° C. or higher,
When passing back through a roll or the like to bend back to a flat plate by tension, t: thickness of steel sheet E: modulus of longitudinal elasticity of steel sheet D _o ; diameter of bending (outer diameter of roll) at a temperature of 250 ° C. or more β _o Sectional yield ratio due to bending at a temperature of 250 ° C. or more σ _eo ; yield stress of steel sheet at a temperature of 250 ° C. or more D: diameter of bending (outer diameter of roll) at a temperature of 200 ° C. or more σ _e When the yield stress of the steel sheet at a temperature of 200 ° C. or less is defined as the bending of the steel sheet at a temperature of 250 ° C. or more within the elastic limit represented by the equation (1), A method for transporting a steel sheet, characterized in that the subsequent bending at a temperature of 200 ° C. or less is set in the range of the expression (2). 2. The bending of a steel sheet at a temperature of 250 ° C. or more is set in the range of the equation (3). And if the degree of bending at a temperature below 200 ° C. is the same as the direction of bending at a temperature above 250 ° C., equation (4): The method according to claim 1, wherein the condition of the expression (5) is satisfied if the direction is opposite to the direction of bending at a temperature of 250 ° C or higher.