JPH069685B2 - Cold rolling method for steel strip - Google Patents

Description

TECHNICAL FIELD The present invention relates to a steel strip (strip) cold rolling method in a Zenzimer mill.

[Prior Art] When cold-rolling a strip with a Zenzimer mill,
For brittle materials with high silicon content, such as magnetic steel sheets, the occurrence of edge cracks in the strip during cold rolling and the resulting strip rupture reduces the production efficiency (T / H) and yield in the rolling process. It is a big cause.

In recent years, from the viewpoint of energy saving, in order to reduce power loss in electric equipment, materials with lower iron loss have been required for electrical steel sheets as well, and steel has been used to reduce eddy current loss in iron loss. The tendency toward high Si and thinness with a larger silicon content and thinner plate thickness is particularly remarkable in grain-oriented electrical steel sheets.

This direction of higher Si / thinner is a direction that promotes the occurrence of selvage cracks during rolling and the resulting strip breakage, and the importance of preventing selvage cracking is ever increasing.

FIG. 2 is a view showing an example of a roll configuration of a Zenzimer mill, which is two work rolls 1, four first intermediate rolls 2,
6 second intermediate rolls 3 and 8 support bearings 4
It is configured with. In the figure, 5 indicates a strip being rolled.

Generally, in the Zenzimer mill, the cross-sectional shape of the strip 5 is adjusted by the crown of the work roll 1, the shift of the first intermediate roll 2 having a taper at both ends or one end in the width direction of the strip 5, and the crown of the second intermediate roll 3. ,
Various combinations such as the crown of the support bearing 4 are performed.

As compared with the case where the strip 5 is flat in the plate width direction, the edge crack is more likely to occur in the middle stretched state where the center part of the strip width is extended, even if the tension applied to the entire strip is the same, Since the ratio of is large, it is easy to cause ear crack fracture.

In this way, the middle stretched state of the strip is not preferable from the viewpoint of ear cracking, but on the other hand, from the viewpoint of threadability in the rolling line, the middle stretched state has better threadability, which is the opposite of Further, in the case where the strip ears are extended from the center, the strip tends to be offset in the width direction and the strip is likely to be narrowed down to the rolling roll.

[Problems to be solved by the invention]

As described above, since the strip in the middle stretched state is likely to cause the splitting of the selvages, it is possible to adjust the shape of the strip in the stretched state to adjust the shape of the strip in the stretched state by the adjusting function of the cross-sectional shape that has been used in the conventional Zenzimer mill. However, the effect of preventing selvage cracking was not so great in materials such as grain-oriented electrical steel sheets with high Si content and high brittleness.

The present invention locally strongly depresses the ears of the strip to positively place the ears in a state of ear extension, thereby sufficiently preventing selvage cracking while narrowing the strip into a roll due to deviation of the strip during rolling. It is an object of the present invention to provide a cold rolling method for strips in a Zenzimer mill that also prevents the above.

[Means for solving problems]

The present invention relates to a method of cold rolling a steel strip by a Zenzimer mill, in which a step portion having a roll length of 5 mm or less and a height of 0.5% to 7% of the entry side thickness of the rolled steel strip is provided on both sides of the work roll body length. By using a work roll with the diameter of both ends of the roll larger than the diameter of the center of the roll, the ears of the steel strip to be thickened are localized at both ends of the work roll with a diameter larger than the center of the work roll. It is characterized by preventing the ear splitting and narrowing down by making the ear extension state by strongly pressing down.

The contents of the present invention will be described below.

FIG. 1 is an explanatory view of strip rolling according to the method of the present invention, in which both sides of the work roll 1 ′ in the cylinder length direction have a roll length a of 5 mm or less and a height b of a rolled steel strip. The step portion 6 having a thickness of 0.5% to 7% is provided, and the roll end portions 7 are provided.
Of the strip 5'using a woker roll 1'where the diameter A of the strip is larger than the diameter B of the central portion 8 of the roll.
Only the strips 5'at both ends 7 of the work roll 1 '.
It shows a state in which the pressure is lower than that in the central portion 10.

In the cold rolling of strip, for example, Japanese Patent Publication No.
As shown in Japanese Laid-Open Patent Publication No. 47605, it is usual to try rolling so as to reduce the ear wave, but in the present invention, rather, the ear portion 9 of the strip 5 ′ is positively strongly pressed and the strip 5 is positively pressed. ′ Is placed in the ear extension state to reduce the tension applied to the ears and prevent ear cracking. When the strip 5'is rolled into the edge-stretching state as described above, the work roll 1'used in the present invention is provided with specific step portions 6 on both sides of the roll so that the ears 9 of the strip 5'can be made larger at both ends. The widthwise movement of the strip 5'of which the ears are extended and easily biased is restrained by the stepped portion 6 while the ears 7 are stretched to prevent the ear splitting, and the strip 5'becomes biased. The work roll 1'is also prevented from being narrowed down.

If the height of the stepped portion 6 shown in FIG. 1b is less than 0.5% of the entry side thickness of the strip 5'to be rolled, the selvage cracking prevention effect is insufficient, while if it exceeds 7% of the entry side thickness. The ear extension becomes excessively large, and narrowing is likely to occur, and since the excessively extended ear portion is not a product, it is necessary to remove the slit of the ear portion, which causes a decrease in yield.

In addition, the effect of restraining the movement of the strip 5'in the width direction becomes insufficient at the gently sloping step portion 6 whose length exceeds 5 mm shown in FIG.

In this case, both ends 7 of the work roll 1'shown by c in FIG.
If the width of the ear portion 9 of the strip 5'which is strongly pressed by is too small, the effect of reducing the ear splitting is small, and if it is too large, the range of the ear extension becomes large in the plate width direction, and the level difference in the subsequent pass is accordingly increased. When rolling with a normal work roll 1 having no part 6, the risk of offset of the strip 5 and consequent narrowing of the strip 5 into the work roll 1 increases, so a range of 10 to 60 mm is desirable. .

The rolling method of the present invention using the work roll 1'having the stepped portion 6 may be used in all the passes of rolling in the Zenzimer mill depending on the degree of brittleness of the strip to be rolled. Since the risk of cracking is reduced, rolling is performed by the method of the present invention only in the first and second passes, and in the subsequent pass, a normal work roll having no step 6 is used to perform rolling to the edge extension state. The cross-sectional shape of the strip is made flat so that the entire width of the strip can be used as a product, and the reduction in yield due to the removal of the slits in the ears does not occur.

In the rolling using the work roll 1 ′ having the stepped portion 6 as described above, it is desirable to stop the rolling to the minimum necessary among the rolling of a plurality of passes while observing the situation of the strip 5 ′.
It is possible to maximize its effect in a rolling mill such as Zezimer Mill, which allows extremely easy work roll exchange and can respond flexibly.

[Embodiment] The following (1) to (3) in the two-stage Zenzimer mill shown in FIG.
FIG. 3 shows an example in which the change in the frequency of occurrence of edge cracks when the height b of the stepped portion 6 (see FIG. 1) is changed under the above condition and 100 ton strips are rolled is obtained.

(1) Rolled steel strip Material: Si content (wt%) 3.0 to
3.5% electromagnetic steel plate, entrance side plate thickness, entrance side plate thickness 2.0 mm, plate width 950 to 1000 mm (2) Work roll roll body length 1180 mm, step portion length a (see FIG. 1) 1 mm or less, Diameter of both ends 7 63.5
0 mmφ, the diameter of the central portion 8 is 0 to 140 for the height b of the stepped portion 6.
63.50 mmφ to 63.22 mmφ depending on the value of μ
Use the one changed. Both ends 7 and central part 8 have flat shapes.

(3) Rolling conditions Only the first pass is rolled at a reduction rate of about 30% using the work roll 1'having a step portion 6 used in the present invention, and the step portion 6 is usually not provided after the second pass. Using the work roll of No. 3, the final plate thickness is 0.35 mm to 0.23 mm.

The number of edge cracks shown in FIG. 3 is not the number of cracks in the first pass using the work roll having the step portion 6 used in the present invention, but the number of occurrence of edge cracks in all the passes.
When the height b of the stepped portion 6 is 0.5% of the thickness of the entrance side strip, the number of occurrences of ear cracking is reduced by about half, and a considerable effect can be seen. As the height b of the step 6 increases, the frequency of occurrence of ear cracks decreases, but the ear crack prevention effect tends to be saturated when the height b of the step 6 exceeds 5% of the entrance side plate thickness. The value of b is 7% of the thickness of the entrance side plate, and it is also a limit from the viewpoint of the sheet passing property and the fact that the shape of the strip in the ear extension state can be flattened in the subsequent pass.

Further, in the case of this embodiment, the narrowing due to the offset of the strip 5'has never occurred, and the effect of suppressing the offset of the strip 5'by the step portion 6 has a remarkable effect.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

In a method of cold rolling a steel strip by a Zenzimer mill, a step portion having a roll length of 5 mm or less and a height of 0.5% to 7% of an entrance side thickness of a steel strip to be rolled is provided on both sides of a cylinder length of a work roll. Is used to make the diameter of both ends of the roll larger than the total diameter of the center of the roll.
By performing local strong reduction at 7) in the figure, contrary to the case of normal cold rolling, the tension applied to the ears is positively set in a strip extending state, and ear cracking can be prevented.

At the same time, by constraining the offset action of the strip in the plate width direction by the step portion of the work roll,
It is possible to prevent the strip from being squeezed into the roll due to the one-sided shift that tends to occur in the strip in which the ears are stretched.

The above effect is effective not only for the pass using the work roll 1'used in the present invention, but also for the subsequent pass using the normal work roll having no step portion, the strip has already reached the ear extension. This prevents the occurrence of cracks, and nevertheless the width of the ear extension is limited (c in Fig. 2), so there is less offset of the strip, and there is less tearing and narrowing of the strip. Since both of these can be prevented at the same time, it is possible to improve the production efficiency of the rolling work and the yield.

[Brief description of drawings]

FIG. 1 is an explanatory view of a method for rolling a steel strip according to the method of the present invention,
FIG. 2 is a diagram showing an example of the roll constitution of the Zezimer mill, and FIG. 3 is a diagram showing the relationship between the height a of the stepped portion of the work roll and the frequency of occurrence of selvages in one embodiment. 1 ... Work roll, 1 '... Work roll in the method of the present invention, 2 ... First intermediate roll, 3 ... Second intermediate roll, 4
... Support bearing, 5 ... Strip, 5 '... Strip being rolled by the method of the present invention, 6 ... Step portion of work roll 1', 7 ... Both ends of work roll 1 ', 8 ... Center of work roll 1' Parts, 9 ... ears of strip 5 ', 10 ... central part of strip 5', A ... diameter of both ends 7 of work roll 1 ', B ... diameter of central part 8 of work roll 1', a ... step part 6, the length of b, the height of the step portion 6, and the width of the ear portion 9.

Claims (1)

[Claims] 1. A method of cold-rolling a steel strip by a Zenzimer mill, wherein both sides of the cylinder length of a work roll have a roll length of 5 mm or less and a height of 0.5% to an entrance side thickness of a steel strip to be rolled.
Use a work roll that has a 7% step and the diameter of both sides of the roll is larger than the diameter of the center of the roll. The roll of the steel strip to be rolled has a larger diameter than the center of the work roll. A method for cold rolling a steel strip, characterized in that the edges are extended by locally strongly rolling down at both ends to prevent edge cracking and narrowing.