JPH0745046B2 - Multi-stage rolling mill - Google Patents

Description

TECHNICAL FIELD The present invention relates to a multi-high rolling mill equivalent to 20 stages having an excellent flatness control function.

(Prior Art) Cold rolling of hard-to-work materials such as stainless steel and silicon steel is often carried out by a multi-high rolling mill having 12 or 20 steps. In such a multi-stage rolling mill, the diameter of the work rolls can be reduced, so that there is an advantage that the rolling load can be reduced under a high pressure as compared with the conventional rolling mill having a vertical arrangement. On the other hand, however, when the work roll has a small diameter, the roll is largely bent, which causes a defect that the rolled material is apt to have a defective shape.

Therefore, various solutions have heretofore been proposed in order to prevent the occurrence of such shape defects.

As one of them, there is a method of controlling the shape of the rolled material by dividing the outermost backup roll into a plurality of parts in the axial direction and adjusting the displacement amount of each divided roll. However, in this method, the more intermediate rolls there are between the backup rolls and the work rolls, the less the effectiveness thereof. Therefore, a multi-stage rolling mill having many intermediate rolls such as 12 or 20 rolls. Then, I was not able to fully demonstrate that ability.

In order to improve this point, a method of using a work roll bender or an intermediate roll bender together with the above-mentioned backup roll displacement amount adjusting method has been proposed in Japanese Patent Publication No. 58-50108. However, this method has the drawback that the equipment becomes complicated, and the thinner the roll, the more
Further, as the roll barrel becomes longer, the bending force does not act on the central portion, so that there is a problem that the control force remains only at the rolled material end portion.

Also, Japanese Patent Publication No. 63-207405 proposes a method in which one end of the intermediate roll has a tapered shape and is independently shifted in the axial direction. However, even in this method, the control force and the range are only around the taper portion, and the taper shape needs to be changed one by one according to the steel type and the plate width.

Further, Japanese Patent Publication No. 63-30104 and the like propose a rolling machine of a vertical type in which an S-crown that can be approximated by a cubic formula is given to a roll and the roll can be shifted in the axial direction. However, even with this method, it is possible to control only the end portion and the central portion of the rolled material, and it is helpless to control the quarter elongation, and further the composite elongation in which belly elongation, ear elongation and the like are mixed.

(Problems to be Solved by the Invention) The present invention advantageously solves the above-mentioned problems, not to mention simple belly stretch and ear stretch, and complicated shape defects such as quarter stretch and ear belly complex stretch. In addition, it has excellent shape control ability that can correct edge drop.
The purpose is to propose a multi-high rolling mill equivalent to 20 high rolling mills.

(Means for Solving the Problems) That is, the present invention provides a multi-stage rolling mill in which a plurality of first intermediate rolls, second intermediate rolls, and backup rolls are sequentially arranged behind a pair of work rolls. , A roll having at least two rolls selected from a roll group consisting of a first intermediate roll and a second intermediate roll is provided with a crown whose one end is tapered, while also selected from the above roll group. On at least another pair of rolls, a roll crown extending over at least one wavelength of the same wavy curve, and on at least another pair of rolls extending over at least two wavelengths of the same wavy curve, , And each of the above crown-providing roll pairs,
This is a multi-stage rolling mill which is arranged such that the roll axis directions are opposite to each other and is incorporated in a mill housing so as to be movable in the roll axis direction.

Further, the present invention is a multi-stage rolling mill in which a roll bending device is incorporated in the above rolling mill.

In the present invention, as the waveform curve for one wavelength or two wavelengths to be given to the roll, one pitch or two pitches are extracted from the sine curve, and one pitch is also obtained from a higher-order function of third or higher order. Alternatively, those obtained by taking out two pitches, and further, their approximate curves are advantageously matched, but among them, one taking out one pitch or two pitches from the sine curve and its approximate curve are particularly preferable.

Hereinafter, the present invention will be specifically described with reference to the drawings.

1 a and b show the roll arrangement of a multi-high rolling mill according to the invention in side and in front.

In the figure, 1 is a rolled material, 2 is a work roll, 3 is a first intermediate roll, 4 is a second intermediate roll, and 5 is a split-type backup roll. Rolls 2 are arranged and these work rolls 2
4 first intermediate rolls, 2 behind each
However, behind the first intermediate roll 3, there are a total of six second intermediate rolls 4 each in the upper and lower three, and the second intermediate roll 4 further.
A total of 8 split back-up rolls 5 are installed behind each of the above and below, forming a 20-high rolling mill.

In addition, 6 is a roll bending apparatus.

Of these, the work roll 2 is provided with a roll crown whose one end is tapered, and the first intermediate roll 3 is provided with a roll crown having a waveform curve that can be approximated by one pitch of a sine curve. It has a structure that can be shifted in any direction. Further, the second shaded area in FIG.
The intermediate roll 4 is provided with a roll crown formed of a waveform curve that can be approximated by two pitches of a sine curve, and has a structure that is also shiftable in the roll axial direction.

The roll to which the one-side taper crown and the waveform curve that can be approximated by one pitch or two pitches of the sine curve are to be added is not limited to the above example, and the work roll 2, the first intermediate roll 3, and the second intermediate roll are provided. All the rolls 4 can be freely selected and combined.

The waveform curve to be given is, in addition to the above-mentioned sine curve and its approximation curve, a waveform curve obtained by extracting two pitches or two pitches with a coordinate origin interposed from a higher-order equation of a third order or higher, and further It may be an approximate curve.

Further, the roll shift device may be either a hydraulic type or an electric type.

(Operation) FIGS. 2A to 2D show changes in the roll gap when a one-sided taper roll whose one end is tapered is installed in the roll axis direction in the opposite direction and the one side roll is axially shifted.

As is clear from the figure, the plate thickness of the plate edge can be adjusted by changing the set value of the length (x) of the edge of the material to be rolled that is rolled on the tapered grinding surface. Control can be performed effectively.

Next, FIGS. 3A to 3C show roll gap changes when a roll pair provided with a corrugated roll crown that can be approximated by one pitch of a sine curve is installed in the roll axial direction in the opposite direction and is shifted in the axial direction. .

FIG. 11A shows a case where the roll pairs are arranged to face each other and the roll gap is constant in the axial direction. FIG. B shows the case where each roll is moved in the direction of the arrow from the state of a,
The roll gap is wide at the center and narrow at the ends. Further, FIG. 6C shows the case where each roll is moved in the opposite direction to that of FIG. B, but the roll gap is narrow at the center and wide at the ends.

Therefore, by appropriately shifting the roll pair provided with the corrugated roll crown that can be approximated by one pitch of the sine curve in the roll axial direction, it is possible to effectively correct the ear stretch and the belly stretch.

Next, FIGS. 4A to 4C show roll gap changes when a roll pair provided with a corrugated roll crown that can be approximated by two pitches of a sine curve is installed in the roll axial direction in the opposite direction and is axially shifted. .

FIG. 11A shows a case where the roll pairs are arranged to face each other and the roll gap is constant in the axial direction. FIG. B shows the case where each roll is moved in the direction of the arrow from the state of a,
The quarter has a narrow roll gap, while the center and both ends have wide roll gaps. Further, FIG. 6C shows the case where each roll is moved in the direction opposite to that in FIG. B, but the quarter portion has a wide roll gap.

Therefore, by appropriately shifting the roll pair provided with the corrugated roll crown that can be approximated by two pitches of such a sine curve in the roll axis direction, it becomes possible to effectively correct the ear-abdominal compound stretch and the quarter stretch. .

Now, referring to FIG. 5, when a roll pair having a one-tapered crown (hereinafter simply referred to as T-crown) is used as the first intermediate roll (1IMR) of the 20-high rolling mill shown in FIG. 1 intermediate roll or 2nd intermediate roll (2IM
As R), a roll pair provided with a corrugated roll crown (hereinafter simply referred to as S crown) that can be approximated by one pitch of a sine curve or a corrugated roll crown (hereinafter simply referred to as W crown) that can be approximated by two pitches of a sine curve.
The results of examination of the shape control ability when the respective roll pairs provided with the numbers are appropriately shifted individually in the roll axial direction are shown in comparison with the case where the split backup roll of the quarter portion is extruded.

The shape control ability was evaluated by the elongation difference ratio Λ2 between the central portion and the end portion and the elongation difference ratio Λ4 between the central portion and the quarter portion of the rolled material.

As is clear from the figure, in the case of the single taper roll shift alone and the S crown shift alone, the ear extension and the belly extension can be controlled to some extent, but the quarter extension and the ear-belly composite extension control can hardly be expected.

It should be noted that the split backup roll extrusion can be expected to slightly control the quarter elongation and the ear-abdominal compound elongation.

On the other hand, in the case of W crown shift alone, a remarkable effect can be expected in controlling the quarter elongation and the ear-abdominal compound elongation control. However, it is hard to say that it is enough to control ear and belly stretch.

Next, referring to FIG. 6, in the above-described 20-high rolling mill, a T-crown roll as a work roll, a W-crown roll as a first intermediate roll, and an S-roll as a second intermediate roll.
The results of examining the shape correction ability when the crown rolls are used at the same time are shown in comparison with the examination results when the single taper roll is used as the first intermediate roll and the roll bender and the split backup roll extrusion are used together.

As is clear from the figure, by combining T crown rolls, S crown rolls, and W crown rolls and appropriately shifting in the roll axial direction, not only ear elongation and belly elongation but also quarter elongation and composite elongation, Further, it is possible to obtain an excellent correction ability for edge drop, and thus it is possible to realize flatness control over a wide range.

In the present invention, the roll pair to which the T-crown, S-crown and W-crown are to be applied is at least two roll pairs selected from a roll group consisting of a work roll, a first intermediate roll and a second intermediate roll. As long as it is any roll, each roll pair is a roll group of the same kind, that is, a work roll pair, a first intermediate roll group,
More preferably, it is selected from the second intermediate roll group. In addition, the control effect increases as the T-crown, S-crown, and W-crown-applied rolls are closer to the material to be rolled, and the arrangement of each roll pair is greater in the order of point symmetry, vertical symmetry, and left-right symmetry with the material to be rolled as the center.

Further, if a roll bending device is also used, the above effect is further enhanced.

When comparing a sine curve as a reference line of a waveform curve to be given to a roll and a higher-order function curve, if the sine curve is followed, the roll crown amount and the waveform pitch can be easily adjusted simply by giving the amplitude and period. It is extremely advantageous in that it can be set, and also has the advantage of good symmetry in the width direction.

On the other hand, in the case of a higher-order function curve, as described below, it may not be possible to arbitrarily set the roll crown amount and the waveform pitch. It has some disadvantages in that it becomes complicated, and that the symmetry across the width is not very good.

That is, for example, considering the case where a waveform curve for two pitches as shown in FIG. 7 is given here, in order to perform shape control at this time, the center of the roll barrel is set as the origin and the waveform curve is set with respect to the origin. Since it is necessary to make point symmetry, the higher-order function is expressed by the following equation (1).

f (x) = a ₁ x + a ₃ x ³ + a ₅ x ⁵ + ... + a _n x ⁿ (1) In order to arbitrarily set the roll crown amount and the pitch using the formula (1), it is shown in Table 1. It is necessary to determine the coefficients a _{1 to} a _n so as to satisfy the six equations.

That is, equation (1) has six unknowns a ₁ , a ₃ , a ₅ , a ₇ , a ₉ ,
It is an 11th-order odd function as in the following equation (1) ′ having a ₁₁ , which is extremely complicated.

_{f (x) = a 1 x} + a 3 x 3 + a 5 x 5 + a 7 x 7 + a 9 x 9 + a 11 x 11 ...
(1) 'Also, if n <11, the roll crown cannot be set arbitrarily. This is because when we try to express it by a fifth-order odd function like the equation (1), there are _three unknowns, a ₁ , a ₃ , and a ₅ ,
This is because only three conditional expressions of the expression (2) shown in Table 1 can be taken into consideration.

f (x) = a ₁ x + a ₃ x ³ + a ₅ x ⁵ (1) ″ For example, in order to define the crown amount, when the formulas (2) -1, (2) -2 shown in the first case are selected, To specify the pitch, the remaining four conditional expressions (2) -3, (2) -4,
Only one conditional expression can be selected from among (2) -5 and (2) -6, and the pitch of the crown is uniquely determined by this, so the crown pitch cannot be changed arbitrarily. .

In this way, when a particular roll crown is represented by a higher-order function curve, the crown cannot be arbitrarily selected when the order is low, whereas when it is represented by a sine curve, on the other hand, when the order is high, it becomes extremely complicated. The disadvantage remains.

(Example) Example 1 In the 20-high rolling mill shown in FIG. 1 above, a work roll having a one-tapered shape (T crown) as shown in FIG. A roll having a crown (S1 crown) that can be approximated by a cubic formula as shown in FIG. 9 is further used as a second intermediate roll 4 shown by hatching in FIG. 1 by a quintic formula as shown in FIG. A roll with an approximate crown (W1 crown) was used.

Then, the work roll, the first intermediate roll, and the second roll
By shifting the intermediate roll in the axial direction, a stainless steel plate having a plate width of 1000 mm was rolled to a plate thickness of 1.2 mm to 1.0 mm.

Shape plan views showing the roll arrangement and the shape correction ability at this time are shown in FIGS. 10A and 10B, respectively.

Further, FIG. 11 shows the case where the conventional device is used, as shown in FIG.
A roll having a single taper shape as shown in a and b is used as the first intermediate roll and the second intermediate roll, these rolls are axially shifted, and the split backup roll extrusion is also used, The results of an investigation of the shape control ability when rolling is also shown.

As is apparent from FIG. 11, the conventional apparatus can obtain the shape control ability only in a narrow range, and the shape ability to follow the composite elongation and the quarter elongation is remarkably small. Moreover, because of the narrow control range, it is necessary to change the taper shape of the first intermediate roll or the second intermediate roll depending on the case depending on the steel seed plate width of the rolled material.

On the other hand, when the device of the present invention is used, it is possible to obtain a wide control range that can sufficiently cope with the composite elongation and the quarter elongation, and moreover, the shape of the intermediate roll can be applied to various rolled materials. It is possible to obtain a plate having a good shape without changing it.

Example 2 Similarly, in a 20-high rolling mill, as shown in FIG. 13a, the first intermediate rolls each have a crown (T crown) as shown in FIG. 12a, and the second intermediate rolls The upper and lower two sets, a total of four rolls, have a crown (W1 crown) that can be approximated by a quintic equation as shown in FIG. 10, and the central upper and lower sets are as shown in FIG. 13b shows the results of an investigation of the shape control ability when the same rolling as in Example 1 was performed by providing each crown (S1 crown) that can be approximated by a cubic equation.

Example 3 Similarly, in a 20-high rolling mill, as shown in FIG. 14a, the first intermediate rolls each have a crown (T crown) as shown in FIG. 12a, and the second intermediate rolls The upper and lower two sets, a total of four rolls, have a crown (W2 crown) that can be approximated by two sinusoidal pitches as shown in Fig.15, while the upper and lower sets located in the center are shown in Fig.16. The crown (S2
Crown) and the shape control ability when rolled in the same manner as in Example 1 was investigated.
Shown in Figure b.

As is clear from the figure, when the S2 crown and W2 crown rolls are used, better shape control ability is obtained than when the S1 crown and W1 crown rolls are used.

Example 4 In the same 20-high rolling mill, as shown in FIG. 17a, the first intermediate rolls were all provided with W2 crowns, and the four rolls located outside the second intermediate rolls were respectively provided with points. The T-crown and S2 crown are given to the pair of rolls at symmetrical positions, and the roll bender is used together,
FIG. 17b shows the results of an examination of the shape control ability when the same rolling as in Example 1 was performed.

Example 5 Similarly, in a 20-high rolling mill, as shown in FIG.
With respect to the first intermediate roll of the book, T-crown and S2 crown are applied to the pair of rolls located at point symmetry positions, and W2 crown is applied to each of the second intermediate rolls, and the same rolling as in Example 1 is performed. Fig. 18b shows the result of the investigation on the shape control ability when the pressure was applied.

Example 6 A stainless steel plate having a plate width of 1000 mm was rolled from a plate thickness of 1.2 mm to 1.0 mm in the 20-high rolling mill shown in FIG. 1 above. At that time, the taper roll shown in FIG. 12a, the S crown roll shown in FIG. 16 and the W crown roll shown in FIG. After the first intermediate roll is installed and rolled, the difference in elongation difference distribution in the width direction of the rolled material when the first intermediate roll is shifted by 50 mm and rolled to the position shown in FIG.
Shown at a, b and c in Figures, 21 and 22. In each figure, “a” indicates the distribution of elongation difference ratio before the shift, and “b” indicates the distribution of the elongation difference ratio after the shift of 50 mm. Further, c indicates a distribution of variation in the elongation difference ratio in the width direction of the rolled material due to the shift of 50 mm (an elongation difference ratio distribution a before the shift minus an elongation difference ratio distribution b after the shift is subtracted).

The elongation difference ratio Λ is defined by the following formula (for example, see "Theory and practice of sheet rolling" edited by The Iron and Steel Institute of Japan, p. 96).

Λ = (1 _i −1 _o ) / 1 _o where 1 _i is the elongation (mm) of the rolled material at each position in the strip width direction, and 1 _o is the elongation (mm) of the center of the rolled material. . When the difference in elongation is positive, that part of the rolled material extends from the center of the rolled material, and when it is negative, it does not extend. That is, if the difference in elongation difference in the width direction is equal, it means that the shape of the rolled material is flat.

The 20th which used the taper roll alone for the 1st intermediate roll
In the case of the figure, the quarter elongation is generated, and even if the first intermediate roll is shifted by 50 mm, only the shape of the end of the rolled material can be changed. Further, in the case of FIG. 21 in which the S crown roll is used alone as the first intermediate roll, only the shapes of the end portion and the central portion of the rolled material can be changed. On the other hand, the second intermediate roll using the W crown roll alone
In the case of the figure, it is possible to mainly change the shape of the quarter portion. Therefore, if the W crown roll is used, the quarter elongation control can be sufficiently performed.

Example 7 Similarly, in a 20-high rolling mill, a W crown roll as shown in FIG. 15 was used in addition to the conventional shape control function, and each roll was shifted to an appropriate position to obtain the best shape. The same rolling as in Example 6 was performed. In addition, a good shape means that the variation of the elongation difference ratio distribution in the width direction is small.

If the W crown roll is not used as the conventional device,
Fig. 23 shows the case where the W crown roll is used for the center second intermediate roll, Fig. 24 shows the case where it is used for the outer second intermediate roll, and Fig. 25 shows the case where it is used for the first intermediate roll.
Each is shown in Figure 26.

As is clear from these figures, in the conventional device, the quarter elongation occurs, and this cannot be suppressed. On the other hand, when the apparatus of the present invention is used, it is possible to control the elongation of the quarter portion and flatten the shape of the rolled material. In this case, the controlled variables are the central second intermediate roll (Fig. 24), the outer second intermediate roll (Fig. 25), the first
It becomes larger in the order of the intermediate rolls (Fig. 26). Therefore,
For example, the elongation of the quarter part of the rolled material on the entry side is large,
If a large amount of control is required in the quarter section, the W crown roll may be applied to a roll located near the rolled material, and conversely, even if there is a quarter elongation of the incoming rolled material, the elongation is small and When the control becomes too sensitive, it is desirable to use it at a position away from the rolled material. As described above, the present invention enables optimum control for various quarter elongations.

Example 8 In the same 20-high rolling mill, as shown in FIG. 14a, the first intermediate roll was the taper roll shown in FIG. 12a, and the central second intermediate roll was the S crown shown in FIG. Using the W crown rolls shown in FIG. 15 for the outer second intermediate rolls, shift these rolls to the proper positions to obtain the best shape and perform the same as in Example 6. It was rolled. At that time, the elongation difference distribution of the rolled material was
Shown in the figure.

By combining W crown rolls, S crown rolls, and taper rolls, the W crown roll controls the quarter portion, the S crown roll controls the end portion and the central portion, and the taper roll controls the end portion, and the elongation difference ratio in the width direction. It was possible to obtain a completely flat rolled material.

It is obvious that the W crown roll is essential in addition to the conventional S crown roll and taper roll in order to obtain this completely flat rolled material.

(Effect of the invention) Thus, according to the multi-high rolling mill according to the present invention,
Not only the belly stretch but also the quarter stretch, the composite stretch, and the edge drop can be excellently corrected, so that the flatness control over a wide range can be realized.

[Brief description of drawings]

1A and 1B are side and front views showing the roll arrangement of a 20-high rolling mill to which the present invention is applied, and FIGS. 2A to 2D are T crown rolls installed in parallel in opposite directions. FIG. 3A to FIG. 3C show roll gap changes in the case of shifting in the roll axis direction, and FIGS. 3A to 3C show roll gap changes in the case of installing S crown rolls in parallel in opposite directions and shifting in the roll axis direction. 4A to 4C are views showing changes in roll gap when W crown rolls are installed in parallel in opposite directions and shifted in the roll axial direction, and FIG. 5 is a 20-high rolling mill. FIG. 6 is a diagram showing the shape control ability when the T crown roll pair, the S crown roll pair, or the W crown roll pair is independently applied to the first intermediate roll or the second intermediate roll of FIG. Work roll FIG. 7 shows a shape control range diagram showing the shape correction ability when the T crown roll and the W crown roll and the S crown roll are simultaneously used as the first intermediate roll and the second intermediate roll, respectively. Fig. 8 is a diagram showing a possible W crown, Fig. 8 is a diagram showing the taper shape of a single taper roll, Fig. 9 is a diagram showing a suitable S crown that can be approximated by a cubic formula, and Fig. 10 is a quintic formula. Fig. 11 is a diagram showing a suitable W crown that can be approximated by Fig. 11, a and b are roll arrangement diagrams and shape control range diagrams showing the arrangements of T crown rolls, W crown rolls and S crown rolls in a 20-high rolling mill, respectively. 12 Figures a and b show the taper shape of a single taper roll, and Figures 13 and 14 a and b show the T-crown roll, W-crown roll and S-crown roll in a 20-high rolling mill, respectively. Fig. 15 shows a suitable W crown that can be approximated by two pitches of a sine curve, and Fig. 16 is a suitable S that can be approximated by one pitch of a sine curve. The figure showing the crown, and FIGS. 17 to 18a are all T in the 20-high rolling mill.
A roll arrangement diagram showing the arrangement of the crown rolls, W crown rolls and S crown rolls, and b in the figure is a shape control range diagram in each roll arrangement of FIG. A, and FIG. 19a and FIG. The figure which shows the roll position before the shift of the 1st intermediate roll in a multi-stage rolling mill, and after shift, FIG. 20 a, b, c respectively shows the shift in the case where a taper roll is independently used for a 1st intermediate roll. The figure showing the distribution of the difference in elongation before and after the shift and the distribution of the amount of change in the difference in the elongation, FIGS. 21a, 21b, 21c, 21c, 21c, 21d, 21c, 21c, 21c, 21c, 21c, 21c, 21c, 21c, 21c, 21c, 21c, 21c, 21c, 21c, 21c and 21d, respectively. , A diagram showing the distribution of the difference in elongation before and after the shift and the distribution of the variation in the ratio of the difference in elongation, FIGS. 22a, 22b, and 22c show the W crown roll used alone as the first intermediate roll. In case of before and after shift And the distribution of the difference in elongation difference and the distribution of change in elongation difference, Figure 23 shows the distribution of elongation difference when a conventional 20-high rolling mill is used, and Figure 24 shows the W crown. Fig. 25 is a diagram showing the difference in elongation distribution when the roll is used as the center second intermediate roll of the 20-high rolling mill. Fig. 25 shows the W crown roll as the second intermediate roll outside the 20-high rolling mill. Fig. 26 is a diagram showing the distribution of elongation difference ratio when used, Fig. 26 is a diagram showing the distribution of elongation difference ratio when the W crown roll is used as the first intermediate roll of the 20-high rolling mill, and Fig. 27 is , The elongation difference distribution when a taper roll was used as the first intermediate roll of the 20-high rolling mill, an S crown roll was used as the central second intermediate roll, and a W crown roll was used as the outer second intermediate roll was shown. It is a figure. DESCRIPTION OF SYMBOLS 1 ... Rolled material, 2 ... Work roll 3, ... 1st intermediate roll, 4 ... 2nd intermediate roll 5 ... Backup roll 6 ... Roll bending apparatus

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-63-30104 (JP, A) JP-A-63-238905 (JP, A) JP-A-2-303606 (JP, A) JP-A-2- 235510 (JP, A)

Claims (2)

[Claims] 1. A multi-stage rolling mill in which a plurality of first intermediate rolls, second intermediate rolls and backup rolls are sequentially arranged behind a pair of work rolls, wherein the work rolls, the first intermediate rolls and the second intermediate rolls are provided. A roll having at least two rolls selected from the roll group is provided with a crown whose one end is tapered, while at least two other rolls selected from the above roll group. The roll is provided with a roll crown having at least one wavelength of the same waveform curve, and at least another pair of rolls is provided with a roll crown having at least two wavelengths of the same waveform curve, and For each crowned roll pair,
A multi-stage rolling mill characterized in that the roll axes are arranged so as to be opposite to each other and are incorporated in a mill housing so as to be movable in the roll axis directions. 2. A multi-stage rolling mill according to claim 1, comprising a roll bending device.