KR100370578B1 - Cold rolling system to prevent overlapping flaws on wire rod surface - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball rolling system configured to prevent folding defects on the final product surface under a minimum cross-sectional reduction rate in a rough rolling line of a wire rod rolling process. In order to eliminate the overlapping of the surface of the rolled wire during rolling, the rolling rolls of the 1st stand and the 2nd stand are composed of (2-R) Double Radius Oval ball rolls, respectively. It is preferable that the radius of curvature ratio (P ₂ / P ₁ ) of the ball and the no. 2 rolling stand roll is 0.65 to 0.80, and the corner radius ratio (R ₂ / R ₁ ) is 0.9 to 1.0.

According to this invention, generation | occurrence | production of the overlapping flaw of a rolled wire rod can be prevented, and the wire rod product without a surface flaw can be manufactured.

Description

Cold rolling system to prevent overlapping flaws on wire rod surface

The present invention relates to a ball rolling system configured to prevent seizure of the final product surface under a minimum cross-sectional reduction rate in a rough rolling line of a wire rod rolling process.

Wire rod rolling is a continuous rolling process in which a billet is formed into a desired shape while passing through dozens of rolling stands in a hot rolling state.

However, unlike the general plate rolling process, the shape of the rolling roll is not constant for each stand (pass), and the flow of the material is allowed in the width direction during rolling.

Common wire rolling methods that are practiced around the world are oval-round passes, square-diamond passes, diamond-diamond passes, and the like.

The billet exits the furnace and is rolled first in the box-shaped rolling roll of stand 1, then in the oval pass of stand 2, and in the round pass of stand 3. Is rolled, then the elliptical-circular pass is repeated.

1 shows box, oval and round calibers of a rolling roll. For example, all of the 1,2,3 wire rod mills of POSCO Co., Ltd. are producing wire rod products according to this rolling method, so that 120 or 160 angle billets can be rolled in round-oval passes. Through this, it is manufactured as a wire rod product with a round cross-sectional shape.

Fig. 2 shows the overlapping shape of the billet cross section before rolling and the box-shaped ball in the first stand. After passing through the furnace, Billet rolled the box-shaped ball at stand 1 and the oval ball-shaped ball at stand 2. As a result, the end product is produced with the desired cross-sectional size.

In FIG. 3, the cross-section of the material after the box-shaped rolling pass of stand 1 and the (2-R) Double Radius Oval ball cross-section of stand 2 are superimposed by the process. The first step is the stand 1. The material that passed through the box-shaped pass of is the intermediate form before going through the (2-R) elliptical ball pass of the No. 2 stand, and the third step is the final form that passes through the 2-R oval ball path.

While FIG. 3 shows that the material is not deformed during rolling, FIG. 4 shows a state in which the material is deformed during (2-R) elliptical pass rolling of the second stand. The first step of FIG. 4 shows a state in which the material having passed the box-pass of the stand No. 1 is inserted into the (2-R) elliptical ball of the No. 2 stand, and the second step is the roll gap of the ball while the material is being rolled. The free surface of the material is bulging on the (roll gap) side, and the third stage is still bulging at the end of the (2-R) elliptical pass rolling. Is showing. In the third step, the rolled shape enters a round pass of the third stand and is rolled into a round shape.

Figure 5 shows the cross-sectional shape of the material passed through the elliptical pass of the second stand at the time of actual rolling.

Fig. 6 shows the rolling process in the circular pass of stand No. 3, the first step showing the moment when the material passed through the (2-R) elliptical pass of the stand No. 2 is inserted into the circular ball, and the second step is The intermediate process is shown and the third stage shows the appearance of folding defects in the roll area.

This overlap occurs as the edge material of the bulging site flows toward the roll head rather than flowing in the roll gap direction. This overlapping groove can be seen by confirming that cracks are generated on the surface of the material when the part of the product is cut and subjected to compression test after production of the final product.

Therefore, in order to solve the occurrence of such overlapping flaws, the sectional reduction rate can be given a lot in the stand 1 and 2, but due to the limitation of the motor power of the stand 1 and 2, There is a limit as shown in Table 1.

Table 1 shows the cross-sectional reduction ratios of No. 1 and No. 2 stands for each plant.

Rolling stand factory 1 wire rod 2 wire rod 3 wire rod No. 1 stand (box type) 24.9% 18.8% 21.3% No. 2 Stand (Oval) 29.3% 14.6% 26.9%

The present invention has been made in view of the above-described problems of the prior art, and the sectional reduction rate at the stand 1 and 2 is limited, resulting in bulging on the free surface of the material, which is overlapped on the material when rolled in the circular pass of the stand 3. The aim is to provide a ball rolling system that prevents this from happening and ultimately produces wire rod-free products.

1 shows several shapes of balls;

2 is a view showing a box-shaped ball and billet before rolling,

3 is a view showing a rolling process of a (2-R) Double Radius Oval mold based on an undeformed material,

4 is a view showing a rolling process of a (2-R) elliptical ball on the basis of the material to be deformed,

5 is a view showing a cross-sectional shape of the stand No. 2 exit material,

6 is a view showing a rolling process of a circular ball on the basis of the material to be deformed,

FIG. 7 is a diagram showing a rolling process and a stress state of a (2-R) elliptical ball based on a material to be deformed;

8 is a view showing the (2-R) elliptical ball of the first and second rolling mill rolls to which the present invention is applied.

In order to achieve the above object, in the present invention, in order to remove overlapping defects on the surface of the rolled wire rod during the rolling of the billet extracted from the heating furnace, the rolling rolls of the stand 1 and the stand 2 are respectively (2-R) (Double- Radius) Provides a ball rolling system, characterized in that composed of Oval ball roll.

In addition, in the present invention, the radius of curvature ratio (P ₂ / P ₁ ) of the ball of the first stand rolling roll and the ball of the second stand rolling roll is 0.65 to 0.80, and the corner radius ratio (R ₂ / R ₁ ) is 0.9 to It is preferable that it is 1.0.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings showing preferred embodiments.

FIG. 7 illustrates the stress state in the (2-R) elliptical rolling process in order to theoretically analyze the phenomenon in which bulging occurs on the free surface of the material in the (2-R) elliptical rolling pass followed by the box-shaped rolling pass. The rolling process is shown briefly.

In the first step in FIG. 7, from the moment the cross section of the material after the box 1 pass is inserted into the (2-R) elliptical ball of the stand 2, the elements on both sides are compressed in the horizontal and vertical directions. In the central element, the compressive force is applied in the horizontal direction and the tensile force in the vertical direction.

The reason is that, as shown in the drawing, the free surface of the center of the material and the roll head are separated at the beginning of rolling, and because of the gap between the free surface of the center of the material and the roll head, the material cannot spread uniformly on the free surface on both sides of the material. It provides the cause of bulging. Thus, the material shape as shown in the second step of FIG. 7 is generated.

In the second step of FIG. 7, since both the head of the ball and the upper surface of the material are in contact with each other, the compressive force is applied in the vertical direction and the tension force in the horizontal direction at both sides and the center element. In the central element, the direction of stress was changed in the vertical and horizontal directions, and the direction of stress in the horizontal direction was changed in the elements on both sides.

As the rolling continues, the material spreads further from side to side, but the formed bulging is not significantly improved since the vertical compressive stress in the central element is smaller than the vertical compressive stress in the side elements.

The third stage of FIG. 7 shows the rolling state of the final stage of the (2-R) elliptical pass of the second stand. The stress state in the material is similar to that of the second stage, but the compressive and tensile stresses are both increased compared to the second stage.

One thing to note here is that reducing the roll gap eliminates the bulging of free surfaces.

However, considering the limits of the section reduction rate (18.8%) of stand 1 and the stand reduction rate of stand 2 (14.6%) of stand 2 of wire 2 plant, the overlap design cannot be eliminated only by changing the design of the box-ellipse pass. Do not.

Here, a parameter representing the degree of bulging is defined as "δ" and is shown in FIG. 7, where "δ" is close to zero, which is an ideal rolling process, and overlapping flaws occur in the next circular pass. May not occur.

Therefore, the fundamental solution to the overlapping problem is to use a box-ellipse ball roll combination of the stands 1 and 2, as shown in FIG. 8, (2-R) Double Radius Oval-(2-R). The rolling is performed by forming a ball rolling system using a combination of elliptical ball rolls.

Box-The fundamental problem with (2-R) elliptical passes is the fact that the ratio of radius of curvature (= P ₂ / P ₁ ) between box and elliptic balls is a very large value (greater than 100). .

In the case of rolling by the combination of (2-R) ellipse-(2-R) elliptical ball roll proposed in the present invention, the radius of curvature ratio (= P ₂ / P ₁ ) is 0.70, so the (2-R) ellipse of the second stand No bulging occurs in pass rolling.

In the case of rolling by the combination of (2-R) ellipse-(2-R) elliptical ball roll proposed in the present invention, the shape of the cross-section of the material after rolling of the second stand does not cause bulging on both surfaces of the material. to be.

If the radius of curvature ratio is greater than 0.80, bulging starts to occur on the free surface on both sides of the stand after rolling twice when rolling by a combination of (2-R) elliptical- (2-R) elliptical ball rolls. When the radius of curvature ratio is 1.0, a good free surface can be obtained because the contact between the roll and the material is ideal, but in this case, the section reduction ratio of stand 1 should be 25% or more. Therefore, the curvature radius ratio is preferably in the range of 0.65 to 0.80.

On the other hand, the corner radius ratio (R ₂ / R ₁ ) also plays an important role in the formation of bulging in the process of rolling systems of (2-R) elliptical-(2-R) elliptical ball roll combinations (where R ₁ is Corner radius of the (2-R) elliptical ball of the No.1 stand roll, and R ₂ is the corner radius of the (2-R) elliptical ball of the No.2 stand ball roll).

When R ₂ / R ₁ is made larger than 1.0, it is difficult to prevent bulging on the free surface of the raw material after rolling the stand twice by suppressing the flow to the corner portion of the raw material. Moreover, when R <_2> / R <_1> is less than 0.9, there exists a possibility of bulging. Therefore, the corner radius ratio (R ₂ / R ₁ ) is preferably set to 0.9 to 1.0.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

Table 2 shows the results of testing the rolling process in the rolling system consisting of (2-R) Double-Radius Oval ball rolls of the stand 1 and stand 2 of the present invention, respectively.

(2-R) Ellipse type-The test is performed by changing the design parameters of the (2-R) elliptic ball roll combination into several cases to determine the correlation between the curvature radius ratio (P ₂ / P ₁ ) and the bulging parameter (δ). Saved.

division Bending radius ratio (P ₂ / P ₁ ) Bulging Variable (δ) (mm) Comparative Example 1 100.0 5.1 Comparative Example 2 10.0 3.2 Comparative Example 3 1.0 1.5 Inventive Example 0.70 0.4

As a result of the test, it can be seen that the curvature radius ratio (P ₂ / P ₁ ) = 0.70 is most preferable under the condition that the section reduction ratio of the second stand is limited to 15.0% or less.

Therefore, according to the present invention, since the sectional reduction rate at the stand 1 and 2 is limited, bulging occurs on the free surface of the material, which prevents the occurrence of overlapping defects when the material is rolled in the 3 stand circular pass. It is possible to manufacture a wire rod product without surface defects.

Claims (2)

In order to prevent the overlapping of the surface of the rolled wire during the rolling of the billet extracted from the heating furnace, the rolling rolls of the stand 1 and the stand 2 are each composed of (2-R) double radius Oval ball rolls. Ball rolling system. The method according to claim 1, wherein the radius of curvature (P ₂ / P ₁ ) of the ball of the first stand rolling roll and the ball of the second stand rolling roll is 0.65 to 0.80, and the corner radius ratio (R ₂ / R ₁ ) is 0.9. It is -1.0, The ball rolling system characterized by the above-mentioned.