JP3186646B2 - Rolling method of tapered steel plate - 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 rolling a tapered steel sheet whose thickness gradually changes in the longitudinal direction.

[0002]

2. Description of the Related Art A tapered plate whose thickness gradually changes in the longitudinal direction is given a thickness distribution mainly by a rolling method.
The setting or change of the roll gap in the multi-pass taper rolling is described in JP-B-50-35890. Also, for example, Japanese Patent Publication 5-49361
As described in Japanese Patent Application Publication No. 7-265922 and Japanese Patent Publication No. Hei 7-265922, there is also known a rolling method in which rolling reduction of each pass is considered in order to keep the flatness of the material to be rolled constant.

[0003]

However, when the above-described multi-pass taper rolling is performed by a reverse rolling mill equipped with a hydraulic press-down device of a cylinder lowering type, which is currently the mainstream, when the rolling at the rear end of the plate tip is performed. A big problem of warpage occurs.

[0004] In the case of a hydraulic device of a cylinder lower type, this problem is caused by raising and lowering the lower work roll to change the roll gap.

[0005] In a certain pass, when the sheet thickness on the rolling start side (biting side) is small and the sheet thickness on the rolling end side (tail falling side) is large, the roll gap is gradually increased from the biting of the sheet to the trailing edge. There must be. Therefore,
It is necessary to gradually lower the lower work roll. vice versa,
When the plate thickness on the biting side is thick and the plate thickness on the trailing edge side is thin, the lower work roll must be gradually raised.

Usually, when performing multi-pass taper rolling,
This is performed by reverse rolling from the viewpoint of securing the rolling efficiency. Therefore, a pass in which the lower work roll is lowered and rolled for each pass, and a pass in which the lower work roll is raised and rolled are repeated.

However, the problem here is the height of the lower work roll when the material is caught. As the index of the height of the lower work roll, the pickup amount, that is, the difference between the height of the upper surface of the front and rear tables of the rolling mill and the height of the upper end of the lower work roll is used. The approach angle to the rolling mill is determined, and the tendency of warpage at the material tip changes depending on the magnitude of the approach angle.

FIG. 1 schematically shows this state. As for the material 4 that gets caught on the group of table rollers 3 between the upper work roll 1 and the lower work roll 2, if the entering angle α (based on the horizontal line) of the material 4 is large as shown in FIG. The tip is largely warped downward, and as shown in FIG. 1 (b), the occurrence of the warpage is small when the entering angle α of the material 4 is small. Therefore,
It is understood that it is important to adjust the pickup amount when the material is caught in order to suppress the warpage of the material.

However, an optimal pickup amount at the time of material biting can be set in a pass in which rolling is performed while raising the lower work roll. However, in a pass in which rolling is performed while the lower work roll is lowered, the pickup amount at the time of material biting is set. May not be set. This is a case where, even if rolling is started with an optimal pickup amount at the time of material biting, the pickup amount becomes negative during rolling because the lower work roll movement amount during rolling is large. At this time, if rolling is continued in this state, a large load is applied to the front and rear tables of the rolling mill, which may lead to breakage. Therefore, such setting of the pickup amount must be avoided.

On the other hand, if the pick-up amount at the time of biting is set large so that the pick-up amount does not become negative until the roll bottom comes off, the leading end of the material is greatly warped downward and collides with the table roller on the rolling mill exit side. Then, the table roller may be damaged. Further, even if the table roller is not damaged, the flatness of the material may be lost due to the collision of the tip. In order to avoid this situation, such rolling should be avoided and rolling should always be performed in the upward direction of the lower work roll. However, in this case, a significant reduction in rolling efficiency cannot be avoided.

[0011] Regarding such a problem, the prior art does not pay attention and does not suggest any solution.

Accordingly, a main problem of the present invention is that when a multi-pass taper rolling is performed in a rolling mill equipped with a hydraulic press-down device of a cylinder placing type, the tip is warped to cause damage to the equipment, It is an object of the present invention to provide a method for rolling a tapered steel sheet without breaking the flatness of the material.

[0013]

According to the first aspect of the present invention, there is provided a tapered steel plate whose thickness gradually changes in a longitudinal direction, an upper work roll is fixed, and a lower work roll is fixed. In rolling using a rolling mill to be moved up and down, an approach angle of the steel sheet to the upper surface of the transfer table of the steel plate in each pass is calculated based on a pass schedule, and in a pass where the calculated approach angle is smaller than a reference approach angle. A method of rolling a tapered steel sheet, wherein the lower work roll is rolled in reverse while being raised and lowered, and rolling is performed in a direction in which the lower work roll is raised in a path that does not satisfy the above conditions.

According to a second aspect of the present invention, there is provided the method for rolling a tapered steel sheet according to the first aspect, wherein the approach angle is obtained by the following equation (1). α (i) = sin ⁻¹ {(S ₂ (i) −S ₁ (i)) − (H ₂ (i) −h ₂ (i)) / 2} / l (i) (1) where , Α is the approach angle, i is the pass number, S is the distance between the upper end of the lower work roll at the plate end of each pass with respect to the upper surface of the transfer table, H is the plate thickness before rolling of each pass, and h is the rolling of each pass. The thickness of the sheet after the l is the length of the lower surface of the sheet before rolling in each pass,
The suffix 1 indicates a thin portion, and 2 indicates a thick portion.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to embodiments shown in the drawings.

In the present invention, when rolling is performed in the lower work roll descending direction in each pass based on a predetermined thickness, roll gap, etc. of each pass, that is, the smaller the thickness of the steel plate, The entry angle of the material into the rolling mill when the material is bitten from is calculated by the following equation (1).

Α (i) = sin ⁻¹ {(S ₂ (i) −S ₁ (i)) − (H ₂ (i) −h ₂ (i)) / 2} / l (i) (1) Here, α is the approach angle, i is the pass number, S is the separation distance of the upper end of the lower work roll at the plate end of each pass with respect to the upper surface of the transfer table, H is the plate thickness of each pass before rolling, and h is each Thickness after rolling of the pass, l is the lower surface length of the plate before rolling in each pass,
The suffix 1 indicates a thin portion, and 2 indicates a thick portion.

Next, this approach angle α (i) is compared with the reference approach angle α _lim of each path as shown in the following equation (2) to obtain α (i) ≦ α _lim (2) Record the path i. However, the reference approach angle α _lim is not a common value in all cases, but a different value empirically obtained according to the finished plate thickness, steel type, finishing temperature, mill work roll diameter, and the like.

After that, the rolling direction of each pass is determined. In this case, it is preferable that the rolling direction of the final pass is determined first, and the direction is determined alternately by going upstream from that pass. However, if the pass i does not satisfy the expression (2) in the pass where rolling is performed in the lower work roll descending direction, it is determined that rolling in the lower work roll descending direction in that pass is impossible, and Reverse the rolling direction. FIG. 2 is a flowchart showing a method of determining each pass rolling direction described above.

By determining the rolling direction of each pass in this way, the tip of the material does not warp and adversely affect, and the rolling efficiency does not decrease.

The above equation (1) can be derived as follows. That is, as shown in FIG. 3, H ₁ , H
₂ and h ₁ ,
It is defined as h _2.

Here, the pick-up amount when the material is bitten from the thinner one is a value obtained by adding the moving amount of the lower work roll during rolling to the optimum pick-up amount at the time of the trailing end. Here, the optimum pick-up amount is (H ₂ −h ₂ ) / 2 in a certain pass, similarly to the case of the general rolling shown with reference to FIG. Further, the amount of movement of the lower work roll during rolling is determined by the pressing position S of the biting end of the material.
_This is the difference (S ₂ −S ₁ ) between ₂ and the roll-down position S ₁ at the bottom end.

Accordingly, as shown in FIG. 5, the relationship between the approach angle α and the length l of the lower surface of the sheet before rolling in the i-pass is given by the following equation (3). sin α (i) × l = (S ₂ (i) −S ₁ (i)) − (H ₂ (i) −h ₂ (i)) / 2 (3) 1) Equation is derived.

[0024]

EXAMPLES Next, examples of the present invention will be shown to clarify the effects of the present invention. Rolling a tapered steel sheet under the conditions shown in Table 1 according to a pass schedule determined without particular consideration of the rolling direction (Test Example 1), and rolling a tapered steel sheet always in the same rolling direction to avoid trouble ( Test Example 2) and FIG.
Table 2 shows the results when the rolling was performed by the method of the present invention according to the present invention.

[0025]

[Table 1]

[0026]

[Table 2]

As shown in Table 2, in Test Example 1, in the fourth pass, the warpage of the front end of the material became large, and rolling had to be interrupted. Further, in Test Example 2, although the rolling could be completed, the rolling required about 4 minutes. However, in the method 1 of the present invention, the rolling could be completed in about 3 minutes, and no other problems occurred.

On the other hand, when a tapered steel sheet under different conditions shown in Table 3 is rolled according to a pass schedule determined without particular consideration of the rolling direction (Test Example 3), the same rolling direction is always used to avoid trouble. Table 4 shows the results obtained when rolling was performed by using the method (Test Example 4) and when rolling was performed using the method of the present invention according to FIG.

[0029]

[Table 3]

[0030]

[Table 4]

As shown in Table 4, in Test Example 3, although the warpage was not large enough to stop the rolling, the flatness of the material was largely lost. However, the rolling time was as short as about 3 minutes. Further, in Test Example 4, although there was no failure during rolling and the flatness of the material was not lost, rolling took about 4.5 minutes. However, in the method 2 of the present invention, the rolling could be completed in about 3.5 minutes, and no other problems occurred.

[0032]

According to the present invention, the multi-pass taper rolling can be efficiently performed without causing the tip to be warped and causing damage to the equipment and losing the flatness of the material.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are explanatory diagrams of the relationship between the angle of entry of a material tip into a rolling mill and the warpage of the material tip.

FIG. 2 is a flowchart of a method of determining a path schedule according to the method of the present invention.

FIG. 3 is an explanatory diagram of a derivation process of Expression (1).

FIG. 4 is another explanatory diagram of the process of deriving equation (1).

FIG. 5 is another explanatory diagram of the derivation process of Expression (1).

[Explanation of symbols]

1 upper work roll, 2 lower work roll. 3 ... Table roller, 4 ... Material

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B21B 1/38 B21B 37/00 B21C 51/00

Claims (2)

(57) [Claims] When rolling a tapered steel sheet whose thickness gradually changes in the longitudinal direction using a rolling mill that fixes an upper work roll and raises and lowers a lower work roll, rolling in each pass is performed based on a pass schedule. Calculate the angle of entry of the steel sheet into the machine with respect to the upper surface of the transfer table, and roll in reverse while raising and lowering the lower work roll in a path where the calculated angle of entry is smaller than a certain reference angle of entry. A method for rolling a tapered steel sheet, wherein rolling is performed in a lower work roll ascending direction. 2. The method for rolling a tapered steel sheet according to claim 1, wherein said approach angle is obtained by the following equation (1). α (i) = sin ⁻¹ {(S ₂ (i) −S ₁ (i)) − (H ₂ (i) −h ₂ (i)) / 2} / l (i) (1) where , Α is the approach angle, i is the pass number, S is the distance between the upper end of the lower work roll at the plate end of each pass with respect to the upper surface of the transfer table, H is the plate thickness before rolling of each pass, and h is the rolling of each pass. The thickness of the sheet after the l is the length of the lower surface of the sheet before rolling in each pass,
The suffix 1 indicates a thin portion, and 2 indicates a thick portion.