CA1147990A

CA1147990A - Rolling mill using variable crown roll

Info

Publication number: CA1147990A
Application number: CA000348781A
Authority: CA
Inventors: Tetsuya Mukai; Kazuo Kondo; Chihiro Hayashi; Takeshi Masui
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 1979-05-24
Filing date: 1980-03-27
Publication date: 1983-06-14
Also published as: JPS5926365B2; EP0019737B1; AU5690380A; AU537257B2; DE3063658D1; JPS55156606A; EP0019737A1

Abstract

ROLLING MILL USING VARIABLE CROWN ROLL

Abstract of the Invention A multi-high rolling mill comprising work rolls and back-up rolls, in which at least one of said rolls is a variable crown roll having the extent of crowning controlled by a pressure-medium.

Description

' Background of the Invention The present invention relates to a multi-high xolling mill using at least one variable crown roll The rolling mill to which.the principle of the present invention applies comprises at least a pair of work rolls and a back-up roll arranged in at least a three-high (mainly four-high) arrangement and in a single stand or tandem stands, for either hot or cold rolling and preferably comprises further roll benders as additional equipmen-t.
The term "work roll" as used herein and in the claims is to be understood to mean a roll in direct contact with a material to be rolled and the term "back-up roll" is to be understood to mean a roll directly or indirectly supporting the work roll.
The variable crown roll is so constructed as to.make it possible to control the extent ofcrowning of the roll by introducing a fl.uid or a viscous material under pressure into a predetermined cavity defined between an arbor and a sleeve.
The variable crown roll has been heretofore used in

2~ two-high rolling mills but never in three- or more high rolling mills. For example, United States Patents Nos.

3,604,086 and 3,457,617 disclose variable crown rolls which were, however, all used in two-high rolling mills only. The two-high rolling mills using conventional variable crown rolls had several disadvantages, such that the work rolls were unable tc withstand high rolling load, it was difficult to manufacture roll sleeves having a high hardness, the toughness of the sleeve decreased because of the requirement for higher surface hardness of the rolls, and shape defects were easily caused in the s-trip in the neighborhood of the pressure receiving 99o sleeve end. Accordingly, such rolling mills, while found to be suitable for light load rolling such, for example, as temper rolling, were not found to be suitable for heavy load rolling such as common hot or cold rolling.
Heretofore, the variable crown roll has not been used in multi-high rolling mills (particularly for back-up rolls) probably for the following reasons:
(1) In view of the fact that the material is rolled by work rolls usually having a diameter as large as 500 - 600 mm, mere application of the variable crown roll (hereinafter referred to simply a VC roll) to the back-up rolls cannot be expected to provide any particular effect.
(2) It is doubtful that pipe-shaped rolls such as the VC rolls can achieve satisfactory rolling.
(3) The diametrically expanded VC rolls may actually be depressed by a high rolling load thus failing to pr~vide any eEfect.
(4j The sleeve holding force may be insufficient, thereby causing roll bending.
(5) The VC rolls may be dangerous from the view point of fatigue safety factor.
Based on many years' experience and theoretical and experimental support, the inventors have the following views of the above-described reasons: -(1) The crowning effect of the back-up roll can be provided to the rolled material through the work rolls. In fact, a change of approximately 1/2 - 1/5 of the diametrical expansion in the outer diameter of the rolls appears in the rolled material. The efficiency of this expansion is ~ufficient for controlling the crown and the shape.

99o (2) Since the VC roll is p~oyided with a small cavity only in the pressure receiving s~leeve portion of the rGll, the mill rigidity thereof is substantially the same as that of solid rolls.
(3) The diametrical expansion of the VC roll can be made larger than the depression thereof by the high rolling load.
t4) When the back-up roll is a VC roll, a large sleeve holding force can be provided since the length of the pressure receiving sleeve part of the back-up roll need not be larger than the width of the material to be rolled. Generally in rolling mills, since the work rolls are driven, the torque exerted on the back-up rolls is smaller than that exerted on the work rolls.
(5) It is possible to design VC rolls having a fatigue safety factor of 1.5 - 3.
Accordingly, the inventors have sufficient reason to believe that a VC roll can be satisfactorily used in multi-high rolling mills.
Therefore, an object of the present invention is to provide an arrangement in which VC rolls are used in a multi-high rolling mill to thereby make extensive and manifold rolling practicable.
Summary of the Invention The basic concept of the present invention is to provide a multi-high (mainly four-high) rolling mill comprising a pair of work rolls and at least one back-up roll, and in which at least one of the rolls is a VC roll.
Having this construction as a basis, the present invention provides the following modifications:

~7~9~
(a) ~ ~our-high rolling mill ip wh~ch at least one of a pair of back-up rolls is a VC ~oll ~r at least Qne ~f a pair of work rolls is a VC roll;
(b) A four-high rolling mill in which the back-up rolls are VC rolls having a different construction from each other, or-the work rolls are VC rolls having different construction from each other; and (c) A detection signal indicating the shape or the crowning, or both, of the material being rolled are utilized to control the extend of the crowning of the VC rolls.

The invention will be better understood from the following description taken in connection with the accompanying drawings.
Brief Description of the Drawings Fig. 1 is a schematic sectional view of a VC roll;
Figs. 2A to 2F are schematic illustrations of typical roll arrangements of rolling mills to which the present invention can be applied;

Figs. 3A and 3B are schematic illustrations of roll stand arrangements of a rolling mill to wh~ch the present invention is applicable;
Fig. 4 is a diagrammatic illustration of the function of roll benders;
Figs. 5A-5G, 6A-6C, 7A-7C, 8A and 8B are illustrations of rol:L arrangements for different embodiments of the present invention;
Figs. 9A, 9B, lOA and lOB are schematic cross sectional views of a four-high rolling mill according to another embodiment of the present invention;

1~7~90 Fig. 11 is a diagram of contxol means for cont~ol of the shape and the crowning of the matexial being rolled by the rolling mill according to the present invention;
Figs. 12 to 17 are graphs showing the results of various tests using rolling m~lls according to the present inven-tion;
Fig. 18 is a schematic cross sectional view showing a construction in which the roll benders are assembled in the - four-high rolling mill according to the present invention; and Figs. 19 to 21 are graphs showing the results of various tests using the rolling mill of Fig. 18.
Description of-the Preferred Embodiments .. . .. . _ Several preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Before describing the present invention in detail, - the construction and the function of the VC roll used in the present invention will be described briefly with reference to Fig. 1.

In the basic construction of the VC roll, as shown in Fig. 1, an annular cavity 3 is defined between an arbor 1 and a sleeve 2 into which a pressure medium (for example, water, oil, grease or the like) under high pressure is applied from a medium pressurizing unit 4 through a conduit- lI provided in the arbor 1 so as to control the extent of crowning of the roll (that is, the extent of the diametrical expansion of the outer diameter of the roll) by regulating the pressure of the medium by means of the unit 4.

The rolling mills to which the present invention is applicable are of the types, for example, as shown in Figs.
2A to 4. In the roll arrangements, the rolling mills have, in ~7~90 principle, multi-high stands ~ainly from three-high to six high stands as shown in Figs. 2A to 2F and most suitably four-high stands as shown in Fig. 2C. Accordingly, the present invention will be described hereinunder as being applied to the four-high rolling mill for the sake of simplicity but it must he understood that application of the present invention is not limited thereto. The rolling mill may have either a single stand as shown in Fig. 3A or tandem stands as shown in Pig. 3s. With respect to additional equipment, the rolling mill is preferably provided with a roll bender JW or JB for the work roll W or back-up roll B thereof.
The basic construction of the rolling mill according to the present invention resides in, as shown with reference to the three-high mill for convenience' sake in Figs. 5A to 5G, a multi-high rolling mill in which at least one of the rolls i5 the VC roll (hatched in the drawing). Accordingly, the three-high rolling mill according to the present invention may have any of the roll combinatlons shown in Figs. 5A to 5G. Special effects achieved by this construction will become clear from the ensuing description.

In an embodiment of the present invention, the four-hiyh rolling mill has, as shown in Figs. 6A to 6C, at least one VC roll (hatched as a drawing) in the back-up roll.
In this embodiment, the extend of crowning of the back-up rolls is first changed. The change then exerts an influence on the work rolls to bend the entire shaft of the corresponding work roll or rolls to thereby cause a substantially predetermined extent of change in the crown of the work roller rolls.

:~L4799~
Sheet crown (thickness distribution across the strip width) and shape tests were performed in the four-high test rolling mill in which, as shown in Fig. 6A, the upper back-up roll is a VC roll having a 200 ~m outer diameter and is 460 mm long while the work roll has an 80 ~m outer diameter and is 460 mm long.
Fig. 12 shows the results of the sheet crown tests performed on an aluminum plate 4 mm thick and 350 mm wide under a rolling load of 20 tons using the four-high rolling mill 10 described above. In Fig. 12, the marks 0, ~,~ and ~' denote: -the oil pressure Pi (~g/cm2) in the VC roll of 0, 165, 340, and 510, respectively. As seen from Fig. 12, as the oil pressure in the VC roll increases, the deflection of the work rolls changes.
The sheet crown changes with the change in the deflection of the work rolls. Thus, the sheet crown control by the present invention was confirmed.
Fig. 13 shows the results of the shape tests performed on a cold rolled coil 0.4 mm thick and ~00 mm long under a fixed draft using the same four-high rolling mill described above. In Fig. 13, the marks 0, ~, ~, indicates a reduction (%) of 0.5, 1.0! and 14.5, respec~ively. As seen from Fig. 13, as the oil pressure in the VC roll increases,the shape of the rolled material changes from wavy edges to center buckle and, at a predetermined reduction good flatness is o~tained at a specified oil pressure. By including a bender it becomes possible to correct quarter buckle shape defect. Thus the shape control effect according to the present invention was confirmed.
The use of the VC roll as the back-up roll provides the following advantages:
(1) Since the roll diameter and the sleeve thickness can ~7~90 be larger than in the work roll, the stress generated in the roll can be reauced.
~2) Sinc~ the rolling is performed through the work rolls, the length of the pr~ssure receiving slee~e part of the back-up roll can be determined independent of the width of the material.
(3) Since the hardness of the surface of the roll can be low, selection of the sleeve material is easy.

(4) Since the rotational frequency is smaller than that of the work rolls for a given rolling speed, the design of the rotary joint is easy.
(~) Since the sleeve thickness is large, the size of the con-cavity is smaller than the amount of expansion in the outer dia-me-ter.
(6) Consequently, rolling at a higher speed, at a larger load, and with a larger width is made possible.
In another embod~ment of the present invention, the four-high rolling mill has, as shown in Figs. 7A to 7C, at least one VC roll (hatched as the drawing) in the work rolls.
In this embodiment, the extent ofcrowning of the work-~0 rolls is directly changed and the change is strengthened by the reaction of the back-up rolls.
Sheet crown and shape tests were performed in the four-high test rolling mills shown schematically in Figs. 7A - 7C, the work rolls and the back-up rolls of which have the same size as those of Fig. 6A.
Fig. 14 shows the results of the sheet crown tests performed on an aluminum plate 4 mm thick and 250 mm wide under a rolling load of 20 tons using the four-high rolling mill described above. In Fig. 14, the marks Q, ~, ~and X denote the 30 oil pressure P' (Kg/cm2) in the VC roll of 0, 200, and 400, ~7~0 respectively. The curves of Fig. 14 show a similar tendency to those of Fig. 12.
Fig. 15 shows the results of the shape tests performed on a cold rolled coil 0.4 ~m thick and 300 mm wide at a reduction of 1% using the same rour-high rolling mill with the oil pressure P' (Kg/cm2) of the VC roll changed. The curves of Fig. 15 show a similar tendency to those of Fig. 13.
The use of the VC roll as the work rolls of the four-high rolling mill provides the following advantages over the use of the VC roll as the work rolls of the two-high rolling mill:
(1) In the four-high rolling mill, since the deflection in the work rolls is received by the back-up rolls, the crowning effect of the VC roll is larger than in the two-high rolling mill.
(2) In the four-high rolling mill, the combination of the diametrical expansion of the VC roll with a work roll bender or with a back-up roll bender to be described hereinafter can correct complicated shape defects such, for example, as quarter buckle.
It will be readily understood that said effect can be doubled by the use of a VC roll for both the upper and the lower back-up rolls or both the upper and the lower work rolls.
Figs. 16 and 17 show the results of the sheet crown and the shape tests, respectively, performed with a further embodiment of the present invention in which the VC roll is use~ as one of each of the back-up and the work rolls as shown in Figs. 8A and 8B. The sizes of the rolls of the mills and the sizes and the quality of the specimens used in the tests of Figs. 16 and 17 are the same as those~ used in the tests of Fig. 14.
In Fig. 16, the marks O, ~, and X denQte the oil pres-sure P' (Kg/cm2) in the VC roll of 0, 100, and 200, respectively.

~7990 In the bar crown tests of Fig. 16, the rolling load was 25 tons.
In Fig. 17, the marks O and ~ , denotes a reduction (%) of 3 and 15, respectively.
As seen from Figs. 16 and 17, the sheet crown and shape control effects show a similar tendency to those described above and as the number-of the ~C rolls used increases~ the effect thereof also increases. It was confirmed that the embodi-ment shown in Figs. 8A and 8B is effective for control of the shape and particularly for correction of the shape defects such as quarter buckle which was heretofore difficult to be overcome in conventional rolling mills.
The foregoing description assumes that the ~C rolls used pairs have of the same internal construction. As shown in Figs. 9 and 10, however, by intentionally making one of the VC rolls in a pair different from the other with respect to variable crown construction (primarily the size of the cavity which is ~illed by the pressure medium), it is made possible to roll eff:iciently materials differing radically in width with-out changing the rolls. That is, a material having a large width can be rolled by rolls having a large width variable crown construction, a material of small width can be rolled by rolls having a small width variable crown construction, and a material of intermediate width can be rolled only by rolls having a large width variable crown construction or in combination with the rolls having a small width variable crown construction.
It was confirmed that the sheet crown correction an~
the shape correction effects are obtained by using the VC rolls properly as described above. Accordingly, the sheet crown and shape control system can be constructed by combining the VC
rolls with a detector.

. .. ..

~7~90 For example, as shown in Fig. 11, a rolling mill 21 is provided at the exit/entry end thereof with a sheet crown and shape detector 22, the detection signal from which is transmitted to a control unit 23 in which the detection signal is compared with a set value, to control the mediu~ pressurizing unit 4 (see Fig. 1) of the VC roll provided in the rolling mill 21.
The detector is preferably a non-contact type.
Various instruments such as an X-ray thickness meter, a ~-ray thickness meter, a flying micrometer and the like can be used as the sheet crown detector. There are various types of shape detectors such as the optical type, the electromagnetic type, the displacement-type, the vibration-type, and the like.
The relation between the sheet crown and the shape will now be briefly described. With respect to the sheet thick-ness distribution of the material to be rolled, if the sheet crown ratio on the entrance side of the mill is Cri and the ; sheet crown ratio on the exit side of the mill is Cro, and if Cri = Cro, there is no shape defect caused because the width-wise distribution with respect to the longitudinal elongation is uniform. If Cri ~ Cro, the sheet is elongated more in the center of the width than in the edges resulting in the shape defect of center buckle. On the contrary, if Cri < Cro, the sheet is elongated more in the edges than in the center of the width resulting in the shape defect of wavy edges. Accordingly, the sheet crown is closely related to the shape.
Generally, since a small change in the sheet crown causes a large change in the shape, rolling is performed (particularly in cold rolling) while paying-attention mainly to the shape. Howe~er, in the case, such as in hot rolling, where the sheet thickness is large and metal flow occurs readily, 1~7~90 1 no extreme shape defect is caused since the material readily flows widthwise when the sheet crown changes.
Accordingly, the crown control is easily effected in hot rolling.
In this way, in multi-pass rolling the sheet crown control is performed within a range of the shape defect that is not disadvantageous to the rolling operation and the shape control is performed at the final pass. In tandem rolling, the sheet crown control is performed at the upstream stand and the shape control is performed at the final stand.
In the conventional rolling mill, the shape correction is performed by a work roll bender or a back-up roll bender. As an application of the present invention, a combination cf a roll bender with the VC roll is possible. The results of nurnerous experiments show that this construction provides un-expected multiplication effects as described below.
'rhe rolling mill used in the experiments was, as shown in Fig. 18, a four-high mill in which the upper back-up roll B was a VC rolland a roll bender was provided between the work rolls W. Table 1 shows the sizes of this rolling mill and the rolling conditions.

, ~

799~
. ., Table 1 Item MarkTemper ~old Tendem llot Tandem .. _ _ . _ _ Db 900 953.9 781.1 Roll Size (mm) DW 585 585 713 ~ Dw 342.9 342.9 457 Rolled Bar Width ~mm) RLl 1200 1000 1000 .. ___ ... .... . .. . _ Mill Size (mm) RL4 600 508 546 .__.___ ... .. .__ .
Rolling Load P 500 900 900 20B-nd ng Force JW 0 - 80 0 - 100 0 - 180 (Initial Crown: 0) Figs. 19 to 21 show the results of tests performed to obtain the relation between the work roll bending force JW (ton~
and the bar cro~n when the oil pressure P' (Kg/cm2) applied to the VC roll in this rolling mill is varied stepwise.
Fig. 19 shows the results of cold temper rolling of a material 1200 mm wide under the rolling load of 500 tons.

In Fig. 19, the horizontal axis indicates the bending force JW

, .

~ 7990 (ton) on the work rolls and the Yertical axis indicates the sheet crown ~c (cm) at a position at 1/~ of width. In Fig. 19, A
denotes the conventional bending effect (19.2~), B denotes the effects of change in oil pressure in the VC roll only t31-3~), and C denotes the multiplication effect (51.6~) from the use of both the VC roll and the bender.
Fig. 20 shows the results of cold tandem rolling of a material 1000 mm wide under a rolling load of 900 tons. In Fig. 20, the horizontal and vertical axes and the reference characters A, B and C, respectively, denote the same items as in Fig. 19, and wherein A = 14.8~, B = 21.8~, and C = 36.5~.
Fig. 21 shows the results of hot tandem rolling of a material of 1000 mm wide under a rolling load of 900 tons.
In Fig. 21, the horizontal axis JW' the vertical axis ~c, and the reference characters A, ~ and C, respectively, denote the sa~e items as in Fig. 19 and wherein ~c indicates the sheet crown at a point 50 mm from the edge and A = 27.2~, B = 39.7~, and C = 66.9~.
As clearly seen from Fig3.19 to 21, in the case where a single VC roll is used, the change in oil pressure from 0 - 300 Xg~cm2 provides the equivalent or better effect than the conven-tional roll bender and the combination of the VC roll with theroll bender provides 2 to 4 times the sheet crown control effect than the conventional roll bender, While the present invention has been heretofore described with~respect to its application to a single - 14 ~

~7~90 rolling mill, it will be obYious to those skilled in the art that the present invention is applicable to a continuous hot or cold rolling stand (Fig. 3B). In this case, it is desirable that the VC roll be used in all the stands. However, even where the VC roll is used only in a limited number of stands for reduction in cost, sufficient effects are obtained therefrom as shown in Tables 2 and 3.
Table 2 Examples in Continuous Cold Mill . ... ........
Stand No. Sheet Crown Shape Edge Drop Control Control Decreasing 1 2 3 _ 5 Effect Effect Effect _ . .
O ~ O
O O ~) O
__ _' ~ O O O

Table 3 Examples in Continuous Hot Mill .

Stand No. Sheet Crown Shape Edge Drop Control Control Decreasing 2 3 4 5 6 Effect I-eceElfect ~ ~ ~ ~ ~ O (~) (~)(~) O ~ O ~ O ~ . O
__ O ~ O O r ~

Where: ~ - VC roll used ~ - very effective 0 - effective X - less ef~ective ,, .

799C~
While Table 3 shows examples of use of the VC roll in a continuous finishing mill, use in a roughing mill is likewise effective. Particularly, its use in a roughing mill for a semi-continuous hot strip mill is effective not only for crown control but also for improvement in the crop loss at the top or bottom of the strip.
In the continuous mill, the combination of the VC
roll with the conventional roll bender proYides an enlarged range of control.

..,

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A multi-high rolling mill for rolling metallic materials for substantially reducing and shaping them, comprising a pair of work rolls and at least one pair of back-up rolls con-stituted by an upper back-up roll and a lower back-up roll; the rolls of one of said pairs of rolls each being a variable crown roll having a rotatable arbor and a sleeve fixedly secured thereto with a space between the arbor and the sleeve, the respective variable crown rolls having spaces which extend different lengths along the variable crown roll and a conduit means through said arbor for admitting pressure medium to said space for controlling the extent of crowning of the sleeve.

2. A rolling mill as claimed in claim 1 in which said back-up rolls are the variable crown rolls.

3. A rolling mill as claimed in claim 1 in which said work rolls are the variable crown rolls.

4. A rolling mill as claimed in claim 1 and further com-prising means for supplying pressure medium to the variable crown roll, means for sensing at least one characteristic of the material being rolled from among the shape of the sheet crown, and control means connected between said sensing means and said supply means for controlling the supply of pressure medium in response to the sensed characteristic for controlling the extent of crowning of the material being rolled.

5. A rolling mill as claimed in claim 1 further comprising a roll bender connected to at least one of said rolls, and means

Claim 5 continued ...

for controlling the extent of crowning of the variable crown roll and the roll bending force exerted by said roll bender for con-trolling the sheet crown and shape of the material being rolled.