KR20050017995A - Method for Manufacturing Steel Plate Using Pair Cross Rolling Mill - Google Patents

Abstract

PURPOSE: To provide a plate manufacturing method for controlling crown generation of work to reduce thickness deviation of the work by preestimating a crown generation amount and changing a pair cross angle, thereby adjusting a roll gap at a lateral side part of work rolls. CONSTITUTION: In a method for manufacturing a plate by rough rolling, widthwise rolling and lengthwise rolling the heated steel slab by a pair cross rolling mill after heating a steel slab, the method comprises a step of respectively obtaining a target work crown amount after lengthwise rolling and a target work crown amount per each pass after lengthwise rolling by rolling force; a step of obtaining a crown control amount by a pair cross angle using the obtained target work crown amount after lengthwise rolling and the target work crown amount per each pass after lengthwise rolling by rolling force; a step of obtaining a pair cross angle during lengthwise rolling using the obtained crown control amount by the pair cross angle; and a step of performing lengthwise rolling on the steel by controlling the pair cross angle according to the obtained pair cross angle.

Description

Method for Manufacturing Steel Plate Using Pair Cross Rolling Mill}

The present invention relates to a method for manufacturing a thick steel plate using a pair cross mill, and more specifically, to adjust the roll gap in the width direction side portion of the work roll by changing the pair cross angle by predicting the amount of crown generation in advance. The present invention relates to a method for manufacturing a thick steel sheet using a fair cross rolling machine, which can reduce the thickness deviation by controlling the generation of crowns.

As shown in Fig. 1, the rolling method of the thick steel sheet is performed in a rough rolling process under low pressure to rotate the material 90 ° to reach a target width in order to even the surface of the slab heated at 1000 to 1300 ° C. in a heating furnace. It is composed of a width rolling process that spreads out until it is rotated, and a length rolling process that increases the length while rotating again by 90 ° and continuously working to the final product thickness.

 In the rolling method of the thick steel sheet, in the length rolling process, cross the upper and lower working rolls and the supporting rolls in pairs, respectively, to change only the roll gap of both side portions (fixing the roll gap in the width center portion) to control the material crown, thereby causing width deviation in the width direction Can be reduced.

The crown represents the difference between the average value of the thickness of the center portion and the thickness of both ends in the material width direction, and can be simply referred to as the width direction thickness difference.

In the width direction, the thickness difference is generally applied to both ends of the work roll in order to give the rolling force to the material between the upper and lower work rolls when rolling the thick steel plate. The thickness deviation in the width direction is large and the thickness of both ends is small.

If the thickness difference in width is large, more thickness margin should be given when setting rolling target thickness to prevent defects caused by lack of thickness, which causes economic loss by causing real error rate which means yield of product in material. It is very important to reduce the thickness difference as much as possible.

Conventionally, in order to reduce the thickness difference in the rolling direction, the rolling process is initially performed in the rolling process, and then the rolling is gradually reduced from 3-4 passes before the end of the rolling process to reduce the bending of the upper and lower work rolls. .

However, the width difference in thickness is mainly caused by bending of upper and lower work rolls, but wear and tear of work rolls due to many rolling works and thermal expansion of work rolls due to temperature transition of materials also change depending on the rolling work environment. Since there is a possibility to be applied, it is difficult to set the rolling pass schedule according to the rolling force pattern which gradually reduces the amount of rolling reduction to improve rolling workability. There is a problem that it is difficult to control the width direction difference.

MEANS TO SOLVE THE PROBLEM This inventor carried out research and experiment in order to solve the problem of the said prior art, and based on the result, this invention was proposed, The present invention is a method for manufacturing a thick steel plate using a pair cross rolling mill. By cross-working the lower work roll and the support roll in pairs, the roll gap is fixed at the center part of the width, and the roll gap is changed to control the material crown by changing only the roll gap at both side parts. , Its purpose is.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is a method for manufacturing a thick steel sheet by heating the steel slab, and then rough rolling, width rolling, and length rolling using a pair cross rolling machine,

Obtaining the material target crown amount [Ch (i)] after length rolling and the material target crown amount [Cmec (i)] for each pass after length rolling by rolling load by following formula (1) and formula (2), respectively ;

Where i is the number of length rolling passes (1 to N passes)

           Ch (i-1): Crown before rolling (crown measurement)

     h (i): material thickness after rolling

          h (i-1): material thickness before rolling]

Where i is the number of length rolling passes (1 to N passes)

          Ch (i): Material target crown amount after rolling

          Ch (i-1): Crown before rolling (crown measurement value) (constant value at initial pass)

          ζ (i): material crown transfer rate

          η (i): Crown ratio dielectric coefficient (= 1-ζ (i))]

Using the material target crown amount [Ch (i)] for each pass after length rolling obtained above and the material target crown amount [Cmec (i)] for each pass after length rolling by rolling load, Obtaining a crown control amount Cθ (i) based on the fair cross angle;

[Where i: number of length rolling process passes (1 to N passes)

          Ch (i-1): Crown amount before rolling (Crown measurement value) (Constant value at initial pass)

          Cθ (i): Crown control amount by pair cross angle

          Cmec (i): material target crown amount for each pass after length rolling

    ζ (i): material crown transfer rate

    η (i): Crown ratio dielectric factor]

Obtaining the pair cross angle [theta] (i) at the time of length rolling by following formula (5) using the crown control amount [C (theta) (i)] based on the pair cross angle obtained as described above; And

[Where Cθ (i): crown control amount by pair cross angle

         Dw: Average work roll diameter

         B: material width

         a: material crown definition point]

It relates to a method for manufacturing a thick steel sheet using a pair cross rolling mill comprising the step of controlling the length of the pair cross angle according to the pair cross angle (θ (i)) obtained above, and rolling lengthwise.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is applied to a method of manufacturing a thick steel plate by heating the steel slab, and then rough rolling, width rolling, and length rolling using a pair cross rolling machine, the upper and lower work rolls and support rolls in the thick steel plate rolling By crossing in pairs, the roll gap of the width center part is fixed, and only the roll gap of both side parts is changed to control the material crown to reduce the thickness variation in the width direction.

As shown in FIG. 2, the pair cross rolling machine is a rolling mill comprising an upper work roll and a support roll as one pair and a lower work roll and the support roll as another pair.

In Fig. 2, B is the material width, θ is the pair cross angle, δc is the cross header travel distance, and Dw is the working roll diameter.

Since the upper and lower rolls of the fair cross rolling mill cross each other in the opposite direction with respect to the center of the material width, only the roll gap of both side parts can be increased without affecting the roll gap change in the center of the width. Can be controlled appropriately.

The crown control through the pair cross of the upper and lower rolls of the pair cross rolling machine is performed in the length rolling process, since the length rolling is performed after the width rolling and the rolls are rolled 90 degrees to the final target thickness. This is because the crown control of is not meaningful.

In order to manufacture a thick steel sheet according to the present invention, it is necessary to first obtain a target crown amount for each pass, which will be described below.

In order to stabilize the rolling workability and shape in the general rolling process, it is necessary to keep the crown ratio constant.

By keeping the crown ratio constant, rolling can be performed while preventing generation of waves and the like due to the difference in elongation of the center and both ends in the longitudinal direction of the raw material. Therefore, in the present invention, it is necessary to set the material target crown amount for each pass according to the crown ratio in order to achieve a smooth rolling operation, in which case the target crown amount tends to gradually decrease as the rolling progresses, that is, the thickness becomes thinner. .

In the present invention, the target crown value [Ch (i)] for each pass after length rolling can be obtained by the following equation (1).

(Equation 1)

Where i is the number of length rolling passes (1 to N passes)

           Ch (i-1): Crown before rolling (crown measurement)

     h (i): material thickness after rolling

          h (i-1): material thickness before rolling]

In addition, in this invention, it is necessary to calculate | require the material target crown amount [Cmec (i)] for each path | pass after length rolling by rolling load by Formula (2).

(Equation 2)

Where i is the number of length rolling passes (1 to N passes)

          Ch (i): Material target crown value after rolling

          Ch (i-1): Crown value before rolling (crown measurement value) (constant value at initial pass)

           ζ (i): material crown transfer rate

          η (i): Crown ratio dielectric constant (= 1-ζ (i))]

The material target crown amount Cmec (i) for each pass after the length rolling includes heat, wear and initial roll crowns.

The initial material crown value of the length rolling process has a constant value, preferably about 300 μm.

The material target crown amount [Ch (i)] for each pass after length rolling is the material target crown amount [Cmec (i)] for each pass after length rolling by the rolling load and the crown control amount [Cθ (i) based on the fair cross angle. ] Is to be taken into consideration, it is expressed as the following equation (4).

The pair of material target crowns [Ch (i)] for each pass after length rolling and the number of target crown amounts [Cmec (i)] for each pass after length rolling by rolling load are obtained according to the following equation (4). The crown control amount Cθ (i) based on the cross angle is obtained.

(Equation 4)

[Where i: number of length rolling process passes (1 to N passes)

          Ch (i-1): Crown amount before rolling (crown measurement)

          Cθ (i): Crown control amount by pair cross angle

          Cmec (i): material target crown amount for each pass after length rolling

    ζ (i): material crown transfer rate

    η (i): Crown ratio dielectric factor]

In the formula (4), the amount of the crown before rolling [Ch (i-1)] is a constant value at the time of initial pass, but is preferably about 300 μm.

The crown control amount Cθ (i) by the pair cross angle may be expressed as in Equation (3) below.

[Wherein, Dw: average working roll diameter (WR) diameter

          B: material width

          a: material crown definition point

When the material crown is obtained using the thickness of both ends, since the thickness tendency of both ends is unstable, it is desirable to define the material crown by using the point moved from the both ends to the center of the portion, thereby providing stability of the crown value. Can be.

In the above formula (3), the material crown defining point (a) is preferably set to 100 mm from both ends of the material.

Equation (3) may be converted as shown in Equation (5).

(Equation 5)

[Where Cθ (i): crown control amount by pair cross angle

         Dw: Average work roll diameter

         B: material width

         a: material crown definition point]

The pair cross angle [theta] (i) at the time of length rolling is calculated | required by said Formula (5) using crown control amount C (theta) (i) by the pair cross angle calculated | required as mentioned above.

Next, the crown of the steel sheet can be controlled by manufacturing the thick steel plate by lengthwise rolling by controlling the pair cross angle according to the pair cross angle [theta] (i) obtained above.

As described above, the present invention can further reduce the thickness margin in the design of the rolling target thickness by more appropriately controlling the material crown, which is the thickness difference in the width direction, and thereby not only improves the error rate, which means the yield of the product in the material. In the case where the rolling load distribution is carried out more economically, it is possible to appropriately cope with it.

Figure 1 is a schematic diagram schematically showing the production equipment for thick steel plate using a conventional pair cross rolling mill

Figure 2 is a schematic diagram showing the control principle of a pair-cruise rolling mill

Claims (1)

In the method of manufacturing a thick steel sheet by heating the steel slab, and then rough rolling, width rolling, and length rolling using a pair cross rolling machine, Obtaining the material target crown amount [Ch (i)] after length rolling and the material target crown amount [Cmec (i)] for each pass after length rolling by rolling load by following formula (1) and formula (2), respectively ; (Equation 1) Where i is the number of length rolling passes (1 to N passes)            Ch (i): Target crown after rolling            Ch (i-1): Crown before rolling (crown measurement)      h (i): material thickness after rolling           h (i-1): material thickness before rolling] (Equation 2) Where i is the number of length rolling passes (1 to N passes)           Ch (i): Material target crown value after rolling           Ch (i-1): Crown before rolling           ζ (i): material crown transfer rate          η (i): Crown ratio dielectric constant (= 1-ζ (i))] Pair cross angle by the following formula (4) using the material target crown amount [Ch (i)] after length rolling obtained above and the material target crown amount [Cmec (i)] for each pass after length rolling by rolling load. Obtaining the crown control amount Cθ (i) by; (Equation 4) [Where i: number of length rolling process passes (1 to N passes)           Ch (i-1): Crown amount before rolling           Cθ (i): Crown control amount by pair cross angle           Cmec (i): material target crown amount for each pass after length rolling     ζ (i): material crown transfer rate     η (i): Crown ratio dielectric factor] Obtaining the pair cross angle [theta] (i) at the time of length rolling by following formula (5) using the crown control amount [C (theta) (i)] based on the pair cross angle obtained as described above; And (Equation 5) [Where Cθ (i): crown control amount by pair cross angle          Dw: Average work roll diameter          B: material width          a: material crown definition point] A method of manufacturing a thick steel plate using a fair cross rolling mill comprising the step of controlling the length of the fair cross angle according to the fair cross angle [θ (i)] obtained as described above and rolling it in length.