DE69009102T2 - Multi-roll stand. - Google Patents

Description

The present invention relates to a multi-roll mill of the 12- or 20-roll class with superior flatness control or regulation characteristics

DESCRIPTION OF THE RELEVANT STATE OF THE ART

In recent years, multi-high rolling mills of the 12- or 20-high class have been commonly used for cold rolling of difficult-to-work materials such as stainless steels and silicon steels. This type of multi-high rolling mill offers an advantage in that, since the work rolls can have a reduced diameter, rolling is possible at a large reduction ratio with a smaller rolling load than in conventional vertical rolling mills. On the other hand, this type of mill has a disadvantage in that the cross-sectional shape or flatness of the rolled products may be deteriorated due to the greater tendency for work roll deflection attributable to the reduction in the work roll diameter.

Various countermeasures have already been proposed to overcome this problem.

For example, a method has already been proposed whereby the outermost support rolls are axially divided into a number of segments and the amounts of axial displacement of these roll segments are suitably adjusted to control or regulate the profile of the rolled product. However, the advantage of this method could not be fully utilized when the rolling mill is a multi-roll type with numerous intermediate rolls, such as a twelve- or twenty-high mill, because the effect of controlling the outermost backup rolls is absorbed or nullified by so many intermediate rolls.

To overcome this problem, a method has been proposed, for example in the unexamined JP patent publication 58-50108, in which work rolls and intermediate roll bending devices are used in combination with the control of the displacements of the outermost support roll segments mentioned. However, this method requires a highly complicated control mechanism. In addition, a significant control effect is only achieved at the two width or transverse ends of the rolled material if the roll diameters are reduced and the roll barrel lengths are increased, because in these cases the bending force effect can hardly have an effect on the middle region of the material in the transverse direction.

For example, in JP Unexamined Patent Publication 63-207405, a method has been proposed in which intermediate rolls are tapered (conical in shape) in the axial direction at one end thereof and these tapered intermediate rolls are displaced independently or separately in the axial directions. In this method, the control effect can be achieved only in areas near the tapered areas of these intermediate rolls. In addition, it is difficult to change the intermediate rolls to apply different degrees of taper in accordance with a change in the rolling conditions such as the type of steel to be rolled and the width of the rolled stock to be produced.

For example, a vertical rolling mill (vertical rolling mill) disclosed in unexamined Japanese Patent Publication No. 63-30104 uses axially movable rolls with S-shaped crowns, the size of which can be approximately determined by cubic equations (third degree). However, this rolling mill is not a multi-roll rolling mill. Furthermore, this rolling mill can only exert the control effect at the two transverse ends and the central region of the rolled material or rolled stock, and it cannot satisfactorily prevent defects or faults such as quarter stretching and composite stretching caused by a combination of a central hump and an edge corrugation.

AP-A-0 255 714 discloses a multi-roll mill using counter rolls. However, these rolls are characterized by the configuration at the roll ends. These rolls are namely barrel-shaped rolls which are symmetrical in the middle areas. With these rolls it is almost impossible to adjust the amount of control if the profile control is to be carried out over a wide area, including the quarter areas, because the end areas, the middle areas and the quarter areas cannot be controlled independently of each other. For different steel grades and different strip widths, rolls of different contours must therefore be provided and used.

EP-A-0 294 544 discloses crowned rollers of a configuration that is or will be determined in accordance with higher order functions. Such determination is complicated and difficult.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to create a multi-roll mill of the twelve or twenty roll class which has a superior profile control or regulation performance and is capable of correcting a complicated profile defect such as quarter elongation and edge/center composite stretching, not to mention simple defects such as center hump and edge undulation, as well as correcting any edge drop and thus eliminating the problems of the prior art described above.

This object is achieved with a multi-roll rolling stand, as claimed in claims 1 and 5.

The above and other objects, features and advantages of this invention will become more apparent from the following description of preferred embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show:

Fig. 1a and 1b are a side view and a front view, respectively, of a twenty-high rolling mill to which the present invention is applied,

Fig. 2a to 2d are schematic representations of a change in the roll gap as observed when parallel T-crown rolls arranged in opposite directions are displaced in the direction of the roll axis,

Fig. 3a to 3c are schematic representations of a change in the roll gap as observed when parallel S-crown rolls arranged in opposite directions are displaced in the direction of the roll axis,

Fig. 4a to 4c are schematic representations of a change in the roll gap as observed when parallel W-crown rolls arranged in opposite directions are displaced in the direction of the roll axis,

Fig. 5 is a graphical representation of the profile control performance of the twenty-high rolling mill when two T-crown, two S-crown or two W-crown rolls are used as the first or second intermediate rolls,

Fig. 6 is a graphical representation of a profile control range of the twenty-high rolling mill for the case of using T-crowned rolls as work rolls and W- and S-crowned rolls as first and second intermediate rolls, respectively,

Fig. 7a to 7c representations of tapers in one-sided tapered or conical rollers,

Fig. 8 is a representation of an S-crown, which can be approximated to a period (pitch) of a sine wave curve,

Fig. 9 is a representation of a W-crown that can be approximated by two periods (pitches) of a sine wave curve,

Fig. 10a, 10b, 11a, 11b and 12a, 12b Representation of arrangements of T-, W- and S-crowned rolls in a twenty-high rolling mill as well as of profile control areas and

Fig. 13a, 13b and 14a, 14b Representations of arrangements of T-, W- and S-crowned rolls in a twelve-high rolling mill and of profile control areas.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention are described below with reference to the drawings.

1a and 1b are a side view and a front view of a multi-roll rolling mill according to the present invention. 1 denotes a material or rolling stock to be rolled. The rolling mill comprises work rolls 2, first intermediate rolls 3, second intermediate rolls 4 and split support rolls 5. In particular, upper and lower work rolls 2, 2 are arranged so that they face each other across the rolling stock 1. Behind each work roll 2, two first intermediate rolls 3, 3 are arranged; thus, there are four first intermediate rolls 3 in total. On each side of the rolling stock 1, behind the respective two first intermediate rolls 2, 2, three second intermediate rolls 4, 4, 4 are arranged, so that a total of six second intermediate rolls 4 are provided. The three second intermediate rolls 4, 4, 4 on each side of the rolling stock 1 are supported by four split support rolls 5, thus, a total of eight support rolls 5 are provided. It can be seen that the two work rolls 2, the four first intermediate rolls 3, the six second intermediate rolls 4 and the eight backup rolls 5 together form the twenty-high rolling mill. The work rolls 2, the first intermediate rolls 3 and the second Intermediate rollers 4 can be moved independently (separately) in the axial directions by means of conventional hydraulic or electrical displacement devices (not shown).

The numbers 6 refer to roller bending devices or apparatus.

Figures 2a to 2d illustrate the manner in which the roll gap between parallel, one-sidedly tapered rolls is changed according to the axial displacements of these rolls. These rolls, which are referred to below as "T-crowned rolls", are tapered or conical by grinding only at their respective one, opposite (or opposite to each other) axial end regions.

As can be seen from these figures, any edge drop can be reduced by changing the width (x) of the widthwise or transverse end regions of the material rolled by the tapered sections of the roll by appropriately controlling (adjusting) the axial displacement of the T-crown rolls.

Figs. 3a to 3c show the manner in which the roll gap is changed between two rolls in accordance with the axial displacement thereof, these rolls having a roll crown (or camber) corresponding to a waveform approximating a period (pitch) of a sine wave (hereinafter referred to simply as "S-crowned roll") and arranged facing in opposite directions.

In the state shown in Fig. 3a, the two rollers are aligned perpendicular to each other, so that between them over the length a constant gap is formed across these rolls. In the state according to Fig. 3b, the rolls have been displaced from the positions according to Fig. 3a in opposite directions so that they define a roll gap which is wide in the middle and narrow at the two transverse ends. In the state according to Fig. 3c, the rolls have been displaced in the directions opposite to those according to Fig. 3b so that they define a roll gap which is narrow in the middle and wide at the two transverse ends.

Figs. 4a to 4c show the manner of changing the roll gap between two rolls according to their axial displacements when the rolls have a roll crown approximating two periods (pitches) of a sine wave (hereinafter referred to simply as "W-crowned rolls") and are arranged facing in opposite directions.

In the condition shown in Fig. 4a, the two rolls are aligned perpendicularly to one another so that they define a constant gap between them along their length. In the condition shown in Fig. 4b, the rolls have been displaced from the positions shown in Fig. 4a in opposite directions so that they form a roll gap that is wide in the middle and at the two transverse ends and narrow in the quarter portions. In the condition shown in Fig. 4c, the rolls have been displaced in the opposite directions to the directions shown in Fig. 4b, forming a roll gap that is narrow in the middle and at the two transverse ends and wide in the quarter portions.

A twenty-high rolling mill of the type shown in Fig. 1 was constructed using two T-crowned rolls as first intermediate rolls and pairs of S- or W-crowned rolls as second intermediate rolls. By means of independent A test was carried out to investigate the profile control performance of this mill by shifting these intermediate rolls. The results of this test are shown in Fig. 5 in comparison with the case where backup roll sections are pressed out corresponding to the quarter areas.

The profile control performance can be expressed as a stretch difference ratio ₂ representing the magnitude of the difference between the stretch in the central region and that at the widthwise or transverse (side) ends of the rolled material, and a stretch difference ratio ₄ representing the magnitude of the difference between the stretch in the central region and that at the quarter regions of the rolled material, wherein the ratios ₂ and ₄ can be expressed by the following formulas (equations), respectively.

&sub2; = (l2 - l0)/l0

This means:

l�0 = length (mm) of the product after rolling, measured in the transverse middle area of the product, and

l2 = length (mm) of the product after rolling, measured at the transverse end of the product;

&sub4; = (l₄ - l₀)/l₀

This means:

l₄ = length (mm) of the product after rolling, measured in the breadthwise quarter of the product.

In Fig. 5, the lengths of the straight lines represent the degree of profile control performance, while the gradients of the lines indicate the ratios of the control of the aspect ratios.

For example, large gradients of the lines representing the characteristics obtained when the T- or S-crowned rolls alone are displaced indicate that such displacements are effective in controlling edge curl and center hump, while no significant effect is expected in controlling quarter stretch and edge/center composite stretch.

The control by pressing out the support roll segments is represented by a line with a very small gradient. This option can therefore only have a very small effect on the control of quarter stretch and edge/center composite stretch and no significant effect on the control of edge corrugation and center hump.

Shifting the W-crown rolls alone can have a significant effect on controlling quarter stretch and edge/center composite stretch, but is quite ineffective on controlling edge curl and center hump.

Another twenty-high mill of the type shown in Fig. 1 was built using T-, S- and W-crowned rolls as work rolls, first intermediate rolls and second intermediate rolls, respectively; the profile correction performance of this mill was investigated. The result is shown in Fig. 6 together with the results of the same investigation on a conventional arrangement using T-crowned rolls as first intermediate rolls in combination with roll benders and also with the split backup roll squeezing method.

According to Fig. 6, the rolling mill according to the invention, which uses T, S and W crowned rolls in combination and relies on appropriate axial displacements of these rolls, shows a superior effect in the correction of quarter stretch, compound stretch and edge drop, not to mention simple edge curl and simple center hump. It can thus be seen that the rolling mill according to the invention is able to carry out flatness control over a wide range. This is in contrast to the conventional rolling mill, which is able to ensure certain effects in the control of edge curl and center hump, but no significant effect in the correction of edge/center compound stretch and quarter stretch.

The rolling mill according to the invention therefore combines the advantages of various types of roll crowning while eliminating the disadvantages, thus eliminating the difficulties in flatness control encountered in current rolling mills which use rolls with large length/diameter (L/D) ratios and employ a large number of intermediate and backup rolls.

According to the invention, the roll pairs to be formed T-, S- and W-crowned can be any roll pairs from the roll groups consisting of the work rolls and the first and second intermediate rolls. However, it is preferred that the roll pairs to which the same type of crowning is applied belong to the same roll group, ie the group consisting of the work rolls, the first intermediate rolls and the third (or second) intermediate groups (or salts - AdÜ.). The types and degrees of rolling defects vary depending on the type of steel material to be rolled and also on the rolling conditions. The types of roll crowning and the rolls to which these crownings are given are selected taking into account the types and degrees of such rolling defects. However, it is generally known that a greater control effect is achieved when the T, S or W crowned rolls are arranged closer to the rolled material. In addition, greater, medium and smaller effects are achieved when the two rolls of the same crown type are arranged symmetrically with respect to a point, a horizontal plane and (respectively) a vertical plane.

The invention does not exclude the simultaneous use of roller bending devices. A greater effect with regard to the stretching at the edges, such as edge corrugation, is achieved when roller bending devices are used in combination with the roller arrangement according to the invention.

The waveforms or curves of the crowning to be provided can be a one- or two-period section of a sine curve or curves approximating these curves.

EXAMPLES example 1

A twenty-high rolling mill of the type shown in Fig. 1 was built using one-sided tapered T-crowned rolls as shown in Fig. 7a as work rolls, S-crowned rolls of the type shown in Fig. 8, approximating one period (one-pitch) of a sine curve, for all first intermediate rolls 3 and W-crowned rolls as shown in Fig. 9, approximating a two-period section of a sine wave, as selected second intermediate rolls shown hatched in Fig. 1.

In a rolling test, stainless steel sheet with a width of 1000 mm was rolled from 1.2 mm to 1.0 mm, with the work rolls and the first and second intermediate rolls being axially displaced in different ways.

Fig. 10a shows the roll arrangement indicated above, while Fig. 10b illustrates the range of profile control that can be covered by this rolling stand. Fig. 10b also shows the results of the same test rolling reduction, carried out to investigate the profile control performance on a known rolling mill that uses axially displaceable, unilaterally tapered rolls of the type according to Figs. 7b and 7c as first and second intermediate rolls respectively in conjunction with a control by extrusion of segments from split backup rolls.

According to Fig. 10b, the conventional rolling mill could only perform the profile control within a small range. In particular, its ability to correct compound stretch and quarter stretch is very low. Due to the small range of profile control, this conventional rolling mill requires a change in the taper of the first or second intermediate rolls depending on conditions such as the type and width of the rolled material.

In contrast, the rolling mill of the invention showed an ability to correct all types of stretches, including compound and quarter stretches, over wide ranges, and could ensure good profile control for a variety of types of rolled material without requiring replacement of the intermediate rolls.

Example 2

A twenty-high rolling mill of the type shown in Fig. 1 was approximated to a two-period section of a sine wave curve as shown in Fig. 11a using T-crowned rolls as shown in Fig. 7b as the first intermediate rolls, W-crowned rolls as shown in Fig. 9 as the outer four intermediate rolls, ie, left and right pairs of second intermediate rolls, and S-crown rolls as shown in Fig. 8 approximating a single period portion of a sine wave curve as the central pair of the second intermediate rolls. With this rolling mill, trial rolling was carried out under the same conditions as in Example 1 to examine the profile control capability of this rolling mill; the results are shown in Fig. 11b.

Example 3

A twenty-high rolling mill of the type shown in Fig. 1 was constructed as shown in Fig. 12a using T-crowned rolls as shown in Fig. 7b as the first intermediate rolls and W-crowned rolls as shown in Fig. 9, approximating a two-period portion of a sine wave curve, as the outer four intermediate rolls, i.e., left and right pairs of second intermediate rolls. Trial rolling was carried out on this rolling mill under the same conditions as in Example 1 to examine the profile control capability of this rolling mill, and the results are shown in Fig. 12b.

Example 4

A twelve-high rolling mill was constructed as shown in Fig. 13a using S-crowned rolls as shown in Fig. 8 approximating a one-period portion of a sine wave curve as work rolls, W-crowned rolls as shown in Fig. 9 approximating a two-period portion of a sine wave curve as the rolls of one of the left and right pairs of intermediate rolls, each pair including an upper and a lower roll, and T-crowned rolls as shown in Fig. 7b as the rolls of the other of the left and right pairs of intermediate rolls. With this rolling mill and under Simultaneously applying the split backup roll extrusion control and using roll benders, a trial roll reduction was carried out under the same conditions as in Example 1 to investigate the profile control capability of this mill. The result is shown in Fig. 13b. Fig. 13b also shows the results of the same trial roll reduction carried out to investigate the profile control performance on a known mill using axially displaceable, one-sided tapered rolls of the type shown in Fig. 7b as intermediate rolls in conjunction with control by extrusion of segments of split backup rolls.

Example 5

A twelve-high rolling mill was constructed as shown in Fig. 14a using T-crowned rolls as shown in Fig. 7a as work rolls and W-crowned rolls as shown in Fig. 9, two pitches approximated to a sine wave curve, as intermediate rolls of one of two pairs of intermediate rolls each having two rolls arranged symmetrically with respect to a point on the rolling section of the rolled material. At the same time, control was carried out by pressing out segments of split backup rolls. With this rolling mill, trial rolling was carried out under the same conditions as in Example 4 to examine the profile control capability of this rolling mill; the results are shown in Fig. 14b.

As is apparent from the above description, the multi-high rolling mill according to the invention offers an excellent performance in correcting rolling defects such as quarter and compound stretching and edge drop, not to mention simple deformation such as edge curl and center hump, thus realizing an excellent flatness control effect over a wide range.

Claims (5)

1. Twenty-high rolling mill with two work rolls (2), several first intermediate rolls (3), several second intermediate rolls (4) and several backup rolls (5), each of which is arranged in succession behind each work roll (2), characterized in that the first intermediate rolls (3) comprise at least one pair of rolls which have either a crown in which the diameter of each roll decreases towards one end thereof, or a crown approximating two periods (pitches) of a sine wave curve, and the second intermediate rolls (4) comprise at least one pair of rolls which have a crown different from the crown of the first intermediate rolls (3) and which have either a crown approximating two periods of a sine wave curve or a crown in which the diameter of each roll decreases towards one end thereof, the rolls of each of these pairs are arranged in axially opposite directions to each other, and each roll of the at least one pair of first intermediate rolls (3) and the at least one pair of second intermediate rolls (4) is displaceable independently (from the other) in the axial direction to realize control of the profile of a rolled product with respect to the final stretch difference ratio ₂ given by the following formula (1) and the quarter stretch difference ratio ₄ given by the following formula (2): &sub2; = (l2 - l0)/l0 ... (1) &sub4; = (l₄ - l₀)/l₀ ... (2) where: l0 = length (mm) of the material after rolling, measured at a widthwise or transverse middle area of the material, l₂ = length (mm) of the product after rolling, measured at a transverse end area of the product, l₄ = length (mm) of the material after rolling, measured in the transverse quarter area of the material. 2. Twenty-high rolling mill according to claim 1, characterized in that the at least one pair of first intermediate rolls (3) has the crowning in which the diameter of each roll decreases towards one end of the same and the rolls are arranged in opposite axial directions and the at least one pair of second intermediate rolls (4) has the crowning approximating two periods of a sine wave curve, the rolls of each of these pairs being arranged in axially opposite directions to one another. 3. A twenty-high rolling mill according to claim 1, wherein the at least one pair of first intermediate rolls (3) have the crowning approximate to two periods of a sine wave curve and the at least one pair of second intermediate rolls (4) have the crowning in which the diameter of each roll decreases towards one end thereof and they are arranged in opposite axial directions, the rolls of each of these pairs being arranged in axially opposite directions to each other. 4. A twenty-high rolling mill according to claim 1, wherein the first intermediate rolls (3) comprise at least two rolls having the crowning in which the diameter of each roll increases towards one end thereof reduced in size, and include two additional rollers with a crown approximating two periods of a sine wave curve. 5. Twelve-roll mill stand with two working rolls and several intermediate rolls as well as several backup rolls arranged in succession behind each working roll, characterized in that the working rolls have either a crowning in which the diameter of each roll decreases towards one end of the roll or a crowning approximating two periods (pitches) of a sine wave curve and the intermediate rolls comprise at least two rolls whose crowning is different from that of the working rolls and which have either a crowning approximating two periods of a sine wave curve or a crowning in which the diameter of each roll decreases towards one end thereof, the rolls of each pair being arranged in axially opposite directions to one another, wherein each of the work rolls and the at least two intermediate rolls is independently displaceable in the axial direction to realize control of the profile of a rolled product with respect to the final stretch difference ratio ₂ given by the following formula (1) and the quarter stretch difference ratio ₄ given by the following formula (2): &sub2; = (l₂ - l�0; )/l�0; (1) &sub4; = (l₄ - l₀ )/l₀ (2) where: l0 = length (mm) of the material after rolling, measured at a widthwise or transverse middle area of the material, l₂ = length (mm) of the product after rolling, measured at a transverse end area of the product, l₄ = length (mm) of the material after rolling, measured in the transverse quarter area of the material.