JPS6141643B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for use in finishing mill rows that can properly control the plate crown and obtain hot strips with a good plate shape when rolling metal materials such as steel. Concerning rolling method.

For example, in rolling a metal material such as steel, a large rolling load is applied, which causes deflection of the rolling roll and makes the roll surface flat. In addition, plate materials during hot rolling tend to expand in width. The thus rolled hot strip has a cross-sectional profile that is thickest at the center in the width direction and becomes thinner toward the side edges. In particular, at the edge portions of the strip, a sharp decrease in thickness occurs called edge drop.

Such a cross-sectional profile of the rolled product, called plate crown, in conventional rolling is unfavorable in terms of quality and yield. In addition, if a plate crown is produced in the rolled material in the intermediate process of rolling, and if the crown is large, if an attempt is made to reduce the crown in the subsequent rolling process, the longitudinal This difference in stretching causes a wavy shape E (medium elongation: the center is elongated to form a wavy shape) as shown in FIG. 1 in the strip after rolling. The occurrence of such corrugations in the strip not only makes the rolling operation difficult, but also makes it undesirable as a product.

Methods for reducing or controlling the plate crown in finish rolling of hot strip using a conventional four-high rolling mill include providing a barrel-shaped crown on the roll body in advance, and adding a convex crown to the upper and lower rolls using a hydraulic cylinder or the like. Alternatively, a method using a so-called roll bending effect that gives concave bending, a method combining the above methods, etc. are generally put into practical use. However, these conventional plate crown reduction and control methods have various problems.

In this method, the deformation resistance of the rolled material changes depending on the temperature of chemical components, etc., the width of the sheet changes, and the shape of the roll changes due to thermal expansion and wear of the roll. It is practically impossible to provide a roll with an appropriate crown in advance for the rolling conditions. Furthermore, it is extremely difficult to change and reduce the plate crown without creating a wave shape in the strip, that is, while maintaining a good plate shape (flatness).

In the case of the method of applying deflection to the roll using a roll bending device to change the plate crown, it is not possible to apply a very strong bending force with current rolling mills due to the strength of the roll neck, the life of the bearings, etc. In addition, the work roll is in contact with the reinforcing roll over almost the entire roll body length, and the work roll is subjected to an extra bending moment by the reinforcing roll outside the width of the material to be rolled, resulting in bending of the work roll. The effect will be reduced accordingly. For the above-mentioned reasons, the work roll bending effect appears near the edge of the plate, but cannot be obtained up to the center of the width of the plate.

Similar to the above-mentioned method, even the combined method does not provide an effect of reducing the plate crown to the extent that it can absorb variations in the deformation resistance of the rolled material, variations in the plate width, and plate crown changes due to thermal expansion and wear of the rolls.

The present invention solves the above-mentioned problems in the prior art and provides a rolling method in a finishing mill row for obtaining a hot strip having a desired plate crown and good plate shape (flatness). It was done with the purpose of

The feature is that the rough rolled plate material is rolled into hot strips by a row of finishing mills, and includes a final stage of the rolling mill in which at least one pair of rolls is movable in the axial direction. Rolling is performed to change the plate crown by a rolling mill including a rolling mill that is capable of moving the at least one pair of rolls upstream or midstream in the axial direction using two or more finishing mill rows arranged; A final stage rolling mill in which at least one pair of rolls is movable in the axial direction,
Shape control is performed by changing either or both of the work roll bending force and the amount of axial movement of the rolls in response to the rolling direction stretching ratio distribution in the width direction of the input side plate material of the final rolling mill. It's what I did. This invention will be explained in detail below.

As shown in Fig. 4, this invention is based on the fact that in hot rolling, there is a metal flow in the width direction in the upstream region in the middle rolling process even in a gauge such as 6 mm in the finishing rolling process. Therefore, even if rolling is performed to change the cross-sectional profile of the strip, the deterioration of the plate shape (flatness) due to non-uniform longitudinal elongation in the strip width direction (creation of wavy shape) will not be noticeable. The inventors' new finding as shown in Figure 6 is that the sheet shape is determined by the rolling conditions of a single rolling mill, regardless of the rolling history up to that point. is based on.

The finishing rolling mill row when carrying out this invention includes:
Two or more rolling mills of the new type disclosed in Japanese Patent Publication No. 50-19510, Japanese Patent Application Publication No. 48-65153, and Japanese Patent Application Publication No. 49-29263 are installed.

This new type of rolling mill has the following features: the work rolls are not affected by the moment from the backing rolls, the roll bending force can be applied sufficiently and effectively to the work rolls, and the rolling load width is adjusted according to the width of the plate material to be rolled. This rolling mill solves the problems of the conventional method of controlling plate crown reduction in a four-high rolling mill in that it can change the plate crown reduction in plate rolling.

This new type of rolling mill includes the type disclosed in Japanese Patent Publication No. 50-19510 in which intermediate rolls are moved in the axial direction, as well as the type disclosed in Japanese Patent Application Publication No. 1977-19510.
65153, which moves the work roll in the axial direction, and
There is a type in which a backing roll (reinforcing roll) is moved in the axial direction, as disclosed in Japanese Patent No. 26263.

The mechanism of this new type of rolling mill was developed in the 1970s.
To briefly explain the rolling mill disclosed in Japanese Patent No. 19510 as an example, as shown in FIG. 2, in addition to known work roll benders 5, 5', a pair of axially movable intermediate rolls 3, ', and each roll of the pair of intermediate rolls is moved by a moving device 6, 6'.
(The position of the intermediate roll after movement is indicated by the value of δ shown in FIG. 2. The same applies hereinafter.) By moving the work roll 2, It is possible to greatly change the roll deflection given to 2′, and therefore the rolled material 1
It is characterized by the ability to control the plate crown and plate shape to vary widely. Note that 4 and 4' are reinforcing rolls, and L is the amount of overlap between rolls 3 and 3'.

Figure 3 shows that using this new type of rolling mill, the plate width B is
The thickness distribution in the width direction of rolled materials of 900 mm, 1500 mm, and 2100 mm is shown when a roll bending force of 0 ton/chock and 50 ton/chock is applied, respectively, with the intermediate roll position at δ = 0. The solid line curve shows the case of 0 ton/chock, and the dashed line curve shows the case of 50 ton/chock. It can be seen from this that the effect of controlling the plate crown by roll bending force is extremely large for each level of plate width. Although not shown, the plate crown can also be controlled by changing the intermediate roll position δ, and by combining the intermediate roll position δ and the roll bending action, a wide plate crown control effect can be achieved. can.

Such plate crown control function is as described above.
Needless to say, this method also exists in rolling mills in which work rolls are moved in the axial direction and in rolling mills in which backing rolls (reinforcing rolls) are moved in the axial direction.

The above-mentioned rolling mill in which the rolls are moved in the axial direction is used to control the shape (flatness) of the metal strip during cold rolling, as disclosed in JP-A-50-47863. It is applied.

In this invention, the new knowledge mentioned above,
In other words, in hot rolling, the upstream region in the finish rolling process is the middle rolling process, for example, due to the metal flow in the width direction of the rolled material even in a gauge such as 6 mm, the cross section of the strip is Even when rolling is performed to change the profile, that is, to control the plate crown, the deterioration of the plate shape (flatness) (creation of wavy shapes) due to the non-uniformity of the amount of stretching in the longitudinal direction in the width direction of the strip is noticeable. The process of this invention is based on the knowledge that the plate shape (flatness) is determined by the rolling conditions in a single rolling mill, regardless of the rolling history up to that point. When configuring the rolling mill, the powerful roll profile control function of the new type of rolling mill described above is applied to the shape control performed in the final rolling mill of the finishing mill row when rolling is performed to control the plate crown. Used for rolling.

Conventionally, when rolling plate materials such as steel strips, when rolling is performed that changes the plate crown (cross-sectional profile), the shape (flatness) deteriorates due to uneven longitudinal stretching in the width direction of the strip. Therefore, it is believed that the plate crown cannot be changed significantly, and this idea has been followed even in the field of hot rolling, as disclosed in Japanese Patent Publication No. 49-20868. Rolling has been carried out to reduce the thickness while maintaining a constant crown-to-thickness ratio. In such prior art, it was undesirable to modify the plate crown during the rolling process by the finishing mill row.

In the present invention, plate crown control is performed at one or more stands of the upstream and midstream stands of the rolling mill row,
Each stand is arranged so that shape control is performed at the final stand, but this means that even if the plate crown is corrected at the midstream stand in the upstream area of the finishing mill row, the shape (flatness) will not be disturbed much. This is based on the findings of the present inventors that the sheet size is not large and that the sheet shape is determined by the rolling conditions of a single stand, with almost no dependence on the flatness of the sheet on the entry side of the rolling mill. In other words, to obtain a flat product shape, it is sufficient to perform shape control only at the final stand, and sufficient plate crown control at the upstream and midstream stands.

This point will be considered in detail below. Fourth
The figure is a chart showing the relationship between changes in the plate crown and changes in the plate shape, and shows actual values obtained through experiments by the inventors. The horizontal axis of the figure is the difference in elongation in the longitudinal direction (△εcr) between the center part of the plate and the edge of the plate, which was determined from changes in the plate crown assuming that there is no metal flow in the width direction of the plate, and is divided into edge elongation and middle elongation. The axis represents the elongation difference (Δεs) determined from the plate shape as edge elongation and middle elongation, with edge elongation shown as positive and middle elongation shown as negative. Normally, when the plate crown is changed in order to reduce the plate crown, the plate shape naturally changes accordingly, but according to the inventor's experiment shown in Fig. 4, changes in the plate crown affect the plate shape. It can be seen that the influence varies depending on the plate thickness and plate width. That is, when the plate thickness h is 3 mm, although there is a difference depending on the plate width B, a change in the plate crown has a relatively large influence on a change in the plate shape. However, when the plate thickness h is 6 mm, even if the plate crown is changed significantly, the resulting change in shape is smaller than when the plate thickness h is 3 mm. This is thought to be because when the plate is thick, there is material flow (metal flow) in the width direction of the plate, which cancels out changes in shape.

Therefore, first of all, when the plate thickness is relatively thick, it is extremely advantageous to control the reduction of the plate crown at the upstream stand and midstream stand in the finishing rolling mill row, considering the effect on the shape change. It becomes clear that That is, by controlling the reduction of the plate crown at this stage, the resulting shape disturbance is not so large, and therefore, the amount of correction of the plate crown is set large within the allowable range of shape disturbance. That is possible.

On the other hand, since the plate material rolled at the final stand is used as a finished product or as a material for the next process, it is necessary to make the plate shape flat in this rolling process, and the final stand requires more work than correction of the plate crown. , it is necessary to mainly control the plate shape.
This point will be explained below.

First, the new type of rolling mill used in the present invention has a large roll bending effect as described above, and the relationship between the roll bending force variation ΔF and the shape variation ΔS is shown in Figure 5. . From Figure 5, it can be seen that the amount of change in roll bending force is proportional to the amount of change in shape, and even if the sheet width B is the same, the shape change in response to roll bending changes is larger when the sheet thickness h is thinner. Recognize.

Furthermore, FIG. 6 is an explanatory diagram based on experimental results showing that the plate shape is determined by the rolling conditions of a single stand, regardless of its previous history.
Figure a shows the stretching difference in the width direction, that is, the shape, of the plate material rolled by the front stand, and Figure b shows the shape of the sheet material rolled by the front stand, and Figure b shows the shape of the rolled material from the front stand, which is rolled under certain rolling conditions. The shape of the obtained plate material is shown. As is clear from this figure, regardless of whether the plate shape on the inlet side is medium elongated or edge elongated, the outlet side shapes all exhibit edge elongation with approximately the same distribution. This shows that by changing the rolling conditions (particularly by changing the roll bending force), it is possible to make the sheet shape on the exit side good and flat, and if the shape is controlled only at the final stand. It will be a good thing. Therefore, as shown in Figs. 5 and 6 above, if a new type of rolling mill is installed in the final stand that is capable of moving the intermediate roll in the axial direction and has a roll bending device, the shape of the plate on the entry side can be changed. It can also be seen that complete shape control can be achieved by setting the rolling conditions of the final stand to appropriate values.

Based on the above, in the present invention, each stand is arranged so that the upstream stand and midstream stand in the finishing rolling mill row consisting of a new type of rolling mill control the plate crown, and the final stand controls the shape. It's a good thing. A rolling mill capable of controlling the plate crown may be disposed in all of the upstream and midstream stands, or a rolling mill capable of controlling the plate crown may be disposed in any plurality or single stand. FIG. 7 shows an embodiment of a finishing rolling mill row when carrying out the present invention.

In the figure, the #7 stand at the final stage and one or more stands other than the #7 stand are equipped with a mechanism capable of moving the rolls in the axial direction and a work roll bending device as shown in Figure 2. The machine is installed. As a result, the plate crown is changed to a desired crown in the stands other than the final stand, and the roll bending device is operated to correct the shape of the plate in order to improve the plate shape at the final stand.

According to the present invention described above, it is possible to construct a pass schedule that achieves both crown correction and obtaining a good shape, and its practical value is extremely great.

[Brief explanation of the drawing]

Figure 1 is a diagram showing shape defects (occurrence of wave shapes) that occur in rolled products, Figure 2 is an explanatory diagram showing a new type of rolling mill used in the present invention, and Figure 3 is an illustration of the rolling mill shown in Figure 2. Figure 4 shows the relationship between plate crown change and plate shape change during plate rolling for each plate width and plate thickness. Figures and tables, No. 5
The figure is a chart showing the relationship between roll bending force change and shape change in the rolling mill used in the present invention for each strip width and thickness. FIG. 7 is an explanatory diagram showing a change in shape of the side and exit side, and FIG. 7 is an explanatory diagram showing an embodiment of the rolling mill row according to the present invention. In the figure, 1 is the material to be rolled, 2 and 2' are work rolls,
3, 3' are intermediate rolls, 4, 4' are reinforcing rolls,
5 and 5' are roll bending devices, and 6 and 6' are intermediate roll displacement devices.

Claims (1)

[Claims] 1. A method of rolling rough rolled plate material into hot strips using a row of finishing rolling mills, in which two or more rolling mills, including the final stage, are provided with at least one pair of rolls movable in the axial direction. Using a finishing mill row, rolling is performed to change the plate crown by a rolling mill including a rolling mill in which the at least one pair of rolls located upstream or midstream are movable in the axial direction; In a final stage rolling mill that is movable in the direction, either the work roll bending force or the amount of axial movement of the rolls is applied in accordance with the rolling direction stretching ratio distribution in the width direction of the entrance plate material of the final stage rolling mill. or a rolling method in a finishing rolling mill train, characterized in that shape control is performed to change both.