JPH0620562B2 - Sheet crown control method during hot rolling - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling a plate crown during hot rolling, and in particular, a pair of upper and lower work rolls having a bottle-shaped profile are axially opposed to each other. The present invention relates to a strip crown control method during hot rolling in which the strip crown is shifted to control the strip crown.

(Prior Art) In recent years, sheet crown / shape control has been very important due to the need for higher dimensional accuracy and higher quality of products in hot rolling. On the other hand, in terms of operations, schedule-free operation is aimed at in order to achieve short delivery times and high efficiency. In order to achieve these objects, a hot rolling mill having a large strip crown control capability is required, and new rolling mills having various strip crown / shape control functions have been developed.

For example, as shown in FIG. 1, an intermediate roll 2 of a six-fold rolling mill consisting of a backup roll 1, an intermediate roll 2 and a work roll 3 is indicated by a black arrow in the figure according to the strip width of the rolled material 4. Direction, and a so-called HC mill that controls the plate crown by adjusting the bending force of the work roll bender indicated by the white arrow in the figure, and the upper and lower parts supported by the backup roll 1 as shown in FIG. There is a so-called pair cross (PC) mill that controls the plate crown by crossing the work rolls 3a and 3b with each other in the direction indicated by the black arrow in the figure with respect to the axial direction, but these rolling mills are not only expensive but also existing. When the rolling mill is remodeled, it takes a long period of time for remodeling, which hinders the production of products and may be impossible due to the dimensional restrictions of the existing equipment.

On the other hand, as a method which can be easily remodeled and has a large plate crown control ability with low equipment cost, JP-A-57-91807, JP-A-63-20106, and JP-A-63-20106 are known.
There is a method of controlling the plate crown of the rolled material by relatively moving the bottle-shaped upper and lower work rolls in the axial direction as disclosed in 63-84713 (hereinafter referred to as the CVC method).

As shown in Fig. 3, according to the CVC method, the work roll 3
Has a bottle-shaped cross section, and the upper and lower work rolls are arranged so that the roll gap profile is point-symmetric. The same members in FIGS. 1 and 2 are designated by the same reference numerals.

The existing equipment modification required when applying the CVC method is only the work roll shift device, and if the bottle shape of the work roll is appropriately selected, it is possible to have the plate crown control ability of the above HC mill or PC mill. It has been known.

Fig. 4 shows the plate crown control method using the CVC method.
A description will be given using (a), (b), and (c). As shown in Fig. 4 (a), when the upper and lower rolls are in the neutral position without shifting, the gap profile in the width direction is constant, and the rolling is similar to that of rolling with a flat roll without crown. . On the other hand, when the upper roll is shifted to the right and the lower roll is shifted to the left in this figure, as shown in FIG. 4 (b), the gap profile has a narrow width center and a wide width end, The plate crown becomes smaller as in the case of rolling with an up-and-down convex crown roll. Conversely, when the upper roll is shifted to the left and the lower roll is shifted to the right, as shown in Fig. 4 (c), the gap profile has a wider width center and a narrow width end, The plate crown becomes large as in the case of rolling with a concave crown roll.

In the plate crown control method using a work roll having this bottle shape profile, if the bottle shape given to the work roll is properly selected, a very large plate crown control capacity proportional to the shift amount can be obtained, and it is effective. It is considered to be a plate crown control means.

(Problems to be Solved by the Invention) However, the CVC method has the following problems and has not been considered as an effective plate crown / shape control means until now.

In normal finish rolling of hot rolling that does not use the CVC method, after performing work roll replacement, 100 rolls are made before the next work roll replacement.
A rolling material (total weight of about 2000 tons) is rolled with the same work roll, but the work roll wears due to contact between the work roll and the rolling material, or thermal expansion occurs, so the work roll profile increases as the number of rolling increases. It changes every moment.

In particular, at the boundary between the contact portion and the non-contact portion, a sudden work roll profile change occurs, which adversely affects the rolled material profile. Therefore, at present, each time one rolled material is rolled, the work rolls are shifted by a certain amount to disperse work roll wear and thermal expansion, or as the number of rolling increases,
By rolling with a rolling schedule that narrows the strip width, the adverse effect of changes in the work roll profile on the rolled material profile is eliminated.

However, the CVC method is a rolling method that attempts to control the strip crown and shape by changing the gap profile by shifting the work roll by using the bottle shape profile of the work roll. This is a large disturbance for the crown shape control.
In the CVC method, the shift position must be determined so as to reach the target strip crown after rolling, which naturally cannot be shifted due to wear and thermal expansion dispersion, and rolling that narrows the strip width as the number of strips increases. Even if the rolling is carried out according to the schedule, there is a fatal defect that the work roll portion having a sudden profile change has to be rolled depending on the rolling conditions such as the target strip crown on the delivery side and the rolling load.

In fact, when the conventional CVC method is applied to the hot rolling finishing mill, the bottle shape profile of the work roll is maintained immediately after the roll change, and although the plate crown shape control effect is exhibited, the number of rolling increases. Immediately before the roll change, the plate crown shape control effect disappears at all, or under bad conditions, even if the temporary crown shifts to a smaller direction immediately after the roll change, the plate crown becomes larger on the contrary. There are even cases. Further, due to local wear of the roll, there may be a case where a sharp plate profile change occurs such that the plate thickness locally increases at the plate edge portion. Therefore, it cannot be said that the CVC method can be applied to actual rolling mills unless a rolling method that can maintain the bottle shape profile is developed even if the number of rolling increases.

The object of the present invention is to achieve stable plate crown and shape control from roll change to next roll change, and to prevent abnormal plate profile from occurring, work roll wear and thermal expansion dispersion can be performed even in the CVC method. It is to provide a shape control method.

(Means for Solving the Problems) In the ordinary hot rolling using a conventional flat roll or a work roll having a quadratic curve profile, in order to prevent the adverse effects of wear and thermal expansion on the plate crown shape control, The following method is used.

As the number of rolling increases, the rolling is performed on a schedule in which the strip width is narrowed so that the contact positions of the strip width end portions of the rolls do not excessively overlap.

Whenever one rolled material is rolled, the upper and lower work rolls are cyclically shifted in the axial direction by the specified amounts in opposite directions to disperse wear and thermal expansion, and a sharp roll profile of the strip width edge rolling section. Avoid changes.

As described above, in the CVC method, the shift position is determined by the rolling conditions such as the delivery side target plate crown, so the above method is not possible. Therefore, it is unavoidable to establish a CVC method that is capable of wear and thermal expansion dispersion due to work roll shift similar to this method. That is, in the conventional CVC method,
If the dimensions and the rolling conditions such as the target strip crown are the same, the shift position is the same and the contact area between the rolled material and the roll does not change. However, in order to put the CVC method into practical use, it is possible to perform work roll shift to change the contact area each time one rolled material is rolled, regardless of the plate crown control in the CVC method. Law needs to be developed.

Here, as a means for realizing the above matters, the present inventors
Focusing on the simple and effective method using work roll bending, theoretical and empirical research and development were conducted. Even in the conventional CVC method, a certain amount of work roll bending force is required to compensate for the load fluctuation during rolling and the plate crown shape change due to the thermal expansion of the work roll, but according to the findings of the inventors, When a large work roll bending force is applied and the contact area between the plate and the roll is the same as the previous rolling process with the plate crown control by the CVC method, the target plate crown can be obtained by adjusting this bending force. While maintaining the rolling condition,
It has been found that the work roll can be worn and the thermal expansion can be dispersed by shifting the work roll, and the present invention has been completed.

That is, the gist of the present invention is that (i) a plate crown control mechanism and a work roll bending device by axially shifting paired upper and lower work rolls having a bottle-shaped profile in mutually opposite directions. Using a hot rolling machine provided with, (ii) axially shifting the work roll to mitigate the local wear of the work roll and its heat crown, and (iii) the shift amount of the work roll. A method of controlling a strip crown during hot rolling is characterized in that a reduction condition for obtaining a target strip crown is maintained by adjusting a combination with a bending force by the work roll bending device.

According to a preferred aspect of the present invention, the work roll shift reference position for obtaining the work roll shift amount may be the work roll position at the time of rolling the preceding material of the same steel type.

Further, the relative deviation amount may be set such that the work roll contact position at the end portion of the strip width deviates from the contact position at the time of rolling the preceding material by a predetermined amount or more.

Furthermore, the variable amount of work roll bending force is The above is preferable. here, Is the amount of strip crown after rolling that changes when the work roll shift of the unit length (1 mm) is changed, Represents the amount of rolled plate crown per chock that changes with a change in work roll bending force of a unit load (1 ton).

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings.

First, FIGS. 5 (a), (b), and (c) are diagrams showing the problems of the conventional CVC method. The upper and lower work rolls having a bottle-shaped profile as shown in FIG. 5 (a) are used to continuously roll the same material so as to have the same outlet plate crown so that the same material is continuously rolled so as to have the same outlet plate crown. When a plurality of rolls are continuously rolled, the work roll profile shown in Fig. 5 (b) changes due to wear and thermal expansion. In particular, as has been conventionally known, the plate width end portion has a larger amount of wear than the other contact portions, and a sharp work roll profile change occurs at the plate width end portion. When a work roll having such a profile is rolled under the same rolling conditions under which the rolling load is increased next, if rolling is attempted to obtain the same strip crown, the rolls shown in Fig. 5 (c) are used. As described above, the work rolls must be rolled in the direction in which the plate crown becomes smaller. In such a case, the edge of the strip width must be rolled by the abnormal profile portion of the work roll, and naturally the rolled material is affected by this abnormal profile, and an abnormal profile material with protrusions at the width edge can be formed. I will end up.

By the way, the plate crown control effect by the CVC method as described above is approximately expressed by the amount of change of the quadratic curve roll crown given to the work roll in order to change the plate crown like other plate crown control means. You can That is, the control capability of the CVC method equivalent to the quadratic curve roll crown change amount ΔR per radius at the end of the roll barrel is expressed by the following equation.

ΔS · ΔR _CVC = K · Bl · ΔR (1) ΔS: shift amount (mm) ΔR _CVC : bottle shape crown shown in FIG. 5 (a) K: constant determined by the bottle curve shape of roll (for example, In case of the standard work roll diameter at the center of the work roll barrel and the position corresponding to the end of the backup roll barrel with the cubic curve bottle curve Bl: roll barrel length [Delta] R: roll barrel length middle roll radius difference Generally the roll radius and the roll barrel length end, the side plate crown C _R out in the case of rolling with a roll having a quadratic curve roll crown of [Delta] R is ΔR: quadratic curve roll crown amount ΔR influence coefficient P _J : Work roll bending force P _J impact coefficient , P _J = 0, it is expressed by a function determined by the rolling conditions such as strip width and rolling load. Becomes Here, if ΔR _CVC is constant, It can be seen that the output side plate crown has a linear relationship with the shift amount ΔS. (4) As can be seen from the equation in C _R constant condition, it is possible to vary the ΔS according to P _J.

That is, as shown in FIG. 6 which shows the quantitative relationship between the work roll shift position, that is, the work roll bending amount and the work roll bending amount, the work roll bending force is reduced to the minimum P _J mi.
without changing the side plate crown C _R output by changing to the maximum P _J max from n, the shift position, It is possible to change only the work roll bending force P _J for each rolled material regardless of the plate crown control by changing the work roll shift amount necessary for predetermined wear / heat crown dispersion. Even in the CVC method rolling with the same width and the same rolling condition, the contact area between the rolled material and the work roll can be changed.
It is possible to prevent the abnormal profile as in (b) and (c).

That is, FIG. 7 is a graph showing the relationship when the work roll shift position is changed in accordance with the number of rollings and the work roll bending force is changed accordingly, and a plurality of rollings are continuously performed under the same width and the same rolling condition. Even when it is performed, as shown in FIG. 7, if the work roll bending force is increased or decreased by a certain amount for each number of rollings, the work roll shift position can be changed accordingly. The work roll shift amount of 5 to 50 mm is effective.

In normal rolling, a mild steel material such as low carbon steel and a hard material such as high carbon steel are mixed and rolled, but the rolling load changes significantly between the mild steel material and the hard material and In order to make the crown the target value, the work rolls must be largely shifted, and the contact area between the work rolls and the rolled material inevitably changes greatly. Therefore, wear of the work roll
It is necessary to perform the work roll shift forcibly to disperse the heat crown between the same steel grades where the rolling load and the target strip crown after rolling are almost the same, and the work roll shift position when rolling the preceding material of the same steel grade. The work roll shift position of the next rolled material must be determined with reference to.

In that case, as shown in FIG. 8 (a), a smooth bottle shape profile can be obtained without causing a sudden work roll profile change at the plate width end as shown in FIG. 5 (b). This can be maintained, and even if rolling with the same width and different rolling conditions continues, as shown in FIG. 8 (b), the occurrence of an abnormal profile as shown in FIG. 5 (c) can be prevented.

Further, the bottle-shaped work roll crown ΔR _CVC can be maintained by the method of the present invention, and a stable plate crown control ability by the CVC method can be secured until immediately before roll change.

By the way, the work roll bending force necessary for carrying out the present invention requires a considerably large bending force as compared with the conventional plate crown during rolling and the bending force required for shape control. Because work roll wear,
This is because the work roll shift amount required for thermal expansion dispersion is 100 mm or more, and the work roll bending with the plate crown and shape control capability corresponding to this shift amount is required by the CVC method. This work roll bending force is given by equation (4), where ΔS _S is the work roll shift amount required for work roll wear and thermal expansion dispersion. Can be found at. As a result of various studies conducted by the present inventors, it has been found that ΔS _S should be at least 100 mm. As shown in the examples below, the work roll bending force actually required is 150 ton / chock or more, and the bending force required for controlling the strip crown shape during rolling is the same as the conventional CVC method. It is not effective unless it is more than twice the bending force of the existing rolling mill.

Next, an example in which the present invention is applied to a hot rolling finishing mill will be described more specifically.

(Example) The hot rolling finishing mill used in this example consisted of a 7-stand quadruple rolling mill, and the roll size of the rolling mill was as shown in FIG. In the figure, each reference numeral is the same as that in FIG.

The bottle shape profile of the upper and lower work rolls 3 shown in FIG. 9 had a cubic curve as shown in the following equation, as shown in FIG. The work roll shift amount ΔS is ± 150 mm
(ΔSm = 150 mm).

x ₀ : Bottle shape Off-center amount (mm) Bl _W : Work roll body length a, b: Positive constant a = 0.461, b = 0.365 By the way, in the bottle shape curve of equation (5), ΔR _CVC =
It is 0.25 mm, and when the work roll shift position is changed from −150 mm to +150 mm in this embodiment from the pack-up roll body length Bl = 1780 mm, if there is no change in the work roll profile due to wear and thermal expansion, the quadratic curve A plate crown control effect equivalent to that when the work roll crown is changed by about 330 μ per radius can be obtained. Also, By changing the bending force by about 170ton / chock, the CVC shift position can be changed by about 100mm. By the way, the off-center amount x ₀ shown in the equation (5) is 0
In the case of, as shown in FIG. 4, the gap profile at the shift position 0 becomes the same in the width direction, but when x ₀ > 0, the gap profile at the shift position 0 becomes a plate. When x ₀ <0, it shifts to the small crown side and to the large plate crown side. That is, as can be seen from the equation (1), the difference between the minimum plate crown and the maximum plate crown, that is, the plate crown control amount is determined by ΔR _CVC and ΔS, and x ₀ is the minimum plate crown or the maximum plate crown value, that is, the plate crown. You can decide the control level.

Table 1 is a table collectively showing the rolling results of the present example regarding the strip crown control effect, and is a table showing the work roll profile and the work roll bending force conditions for the purpose of comparative examination between the conventional technique and the present invention.

The work roll crowns of the existing mills in the table show the values per diameter. A negative profile indicates a concave profile, and a positive profile indicates a convex profile. Also, work roll bending is only for increment venters, and the maximum bending value is shown in the table (minimum value is zero ton / chock).

In addition, C of the present invention equipped with a strong work roll bender
In order to clarify the effect of the VC method, the existing mill with only work roll vendors is used here. However, for F5 to F7, work roll shift of ± 200 mm was performed due to wear thermal expansion dispersion. The conventional CVC method used a normal work roll vendor. However, the bottle shape curve was the same as that of the present invention.

FIG. 11 is a diagram showing rolling width schedule conditions after roll change, and a comparative study was carried out on a schedule in which low-carbon materials for cold-rolled base materials and hot-rolled products and high-tensile materials for hot-rolled products were mixed. The low-carbon material for cold-rolled base metal is a type of steel that requires high plate crown finish even under low rolling load from the viewpoints of stripability, strip crown, and shape controllability in cold rolling (currently target finished strip crown). High-tensile steel requires a low plate crown finish to improve dimensional accuracy (target finished plate crown is 30μ or less), but it is a steel type with a high rolling load and it is difficult to reduce the plate crown.

In addition, the plate profile data of the rolled material indicated by the mark in the figure is summarized in Table 2.

If mixed rolling of these two steel types is realized, the strip crown
Since it is possible to achieve almost schedule-free operation considering shape control, it is necessary to finish high plate crown 3.5mm thickness ×
Roll 950mm wide low carbon material to 20th and 70th,
A 2.6 mm thick x 1200 mm wide high-tensile material, which is difficult to finish with a low plate crown, is rolled into 21st and 71st rolls, and the finished plate crowns are compared to clarify the superiority of the present invention. Regarding work roll wear and heat crown dispersion shift, the work roll shift is performed so that the contact position between the width end and the roll is displaced by 10 mm in low carbon same width material rolling. Specifically, the work roll shift positions at the time of rolling the 20th and 70th low carbon materials are determined based on the 18th and 69th work roll shift positions of the preceding low carbon material.

Figures 12 (a) and (b) show the width schedule shown in Figure 11.
It is a figure which shows the work roll shift position in the CVC method. As an example, the case of F5 mil is displayed. Fig. 12 (a) shows the case of the conventional CVC method, in which the work roll shift position is determined so that it can be rolled to the delivery-side target plate crown depending on the rolling conditions such as strip width and rolling load. On the other hand, Fig. 12
(b) shows the CVC method of the present invention. In the present invention, for low carbon materials and high tensile strength materials, when the width is the same, the work roll shift position is shifted by 10 mm or more with respect to the preceding material, and when the board widths are different, The work roll shift position is set up while adjusting the work roll bending force so that the work roll contact position shifts by 10 mm or more. The deviation amount may be changed according to the rolling schedule.

As a result, when continuously rolling low-carbon materials of the same width,
It can be seen that a wear roll expansion work roll shift of approximately 150 mm is performed.

Table 2 collectively shows the plate profile data of the actual finished plate crown of the rolled material indicated by the mark in the figure. In the existing mill,
The plate crown of the low carbon material for cold rolled base metal of the 20th rolling does not reach the target plate crown of 60μ. This is because the work roll crown becomes large due to thermal expansion in the upstream stand of the finishing mill, and the plate crown becomes small.Therefore, if the plate crown is largely rolled at the downstream stand, the shape defect will occur, and the finish plate crown cannot be made large. Is.
Moreover, it is difficult to reduce the crown of a high-tensile steel, and basically, it can be said that the ability to control the crown of a steel sheet is insufficient in the mixed rolling of a low-carbon steel and a high-tensile steel as in the present rolling schedule. Next, with the conventional CVC method, the target plate crown for cold rolling low carbon material is satisfied, and it is possible to reduce the finish plate crown of high-tensile material to about 20 to 30μ. It will be sufficient as a plate crown and shape control ability. However, in the 19th and subsequent high-tensile steel materials, as explained in FIG. 5 (c), an abnormal profile in which the plate thickness changes in a protruding shape near the edge of the plate width is generated.
It is considered that mixed rolling of low-carbon material and high-tensile material is impossible.

However, in contrast to the above-mentioned conventional technique, the CVC method of the present invention can roll the plate crown of the high-tensile material to 10 μm or less without generating an abnormal profile. Especially, compared with the conventional CVC method, the reason why the CVC method of the present invention has a larger sheet crown in the cold-rolled base metal and smaller in the high-tensile steel is that the conventional CVC method uses the finish rolling mills F1 to F6. Since a shape defect due to the abnormal plate profile occurs on the stand,
This is because the original plate crown and shape control capability of the CVC method cannot be fully exerted.

From the results shown in the above examples, it can be seen that according to the present invention, the effects of crown and shape control are very large.

(Effect of the Invention) By using the plate crown control method according to the present invention, it is possible to dramatically improve the plate crown control capability at a low equipment cost, and to obtain a hot rolled steel sheet with high dimensional accuracy without causing an abnormal profile. Not only is it possible to manufacture strips and hot-rolled steel sheets,
Mixed rolling of different steel types with significantly different rolling loads or reverse width rolling from narrow material to wide material is possible, greatly promoting schedule-free operation, improving production efficiency, reducing the number of work rolls possessed, and cost reduction Effectiveness and short delivery time can be achieved.

[Brief description of drawings]

1 and 2 are schematic diagrams of a conventional rolling mill with a high plate crown and shape control function; Fig. 3 is a schematic diagram of roll arrangement of the CVC method; Figs. 4 (a), (b) , (C) are schematic illustrations of the CVC method performed with a work roll having a bottle-shaped profile; Figures 5 (a), (b), and (c) are illustrations of problems with the conventional CVC method; FIG. 6, FIG. 7 and FIG. 8 are explanatory views of the plate crown shape control method and effect by the CVC method of the present invention; and FIG. 9 is of a rolling mill for carrying out the plate crown control method of the present invention. Schematic diagram; FIG. 10 is an explanatory diagram of a bottle shape profile of a work roll used in the present invention; FIG. 11 is an explanatory diagram of a width schedule example after roll change in hot rolling in an example; (A) and (b) are explanatory views of the difference in the work roll shift position between the conventional method and the present invention. 1: Backup roll 2: Intermediate roll 3 (3a, 3b): Work roll 4: Rolled material 5: Work roll bender

Claims (4)

[Claims] 1. A hot rolling mill comprising a work roll bending mechanism and a plate crown control mechanism by axially shifting paired upper and lower work rolls having a bottle-shaped profile in opposite directions. Shifting the upper and lower work rolls axially in opposite directions from each other by a predetermined amount from the work roll shift position at the time of rolling the preceding material in order to mitigate local wear of the work roll and its heat crown, and the work roll. The method of controlling a strip crown at the time of hot rolling is characterized in that a rolling condition for obtaining a target strip crown is maintained by adjusting a combination of the shift amount and the bending force of the work roll bending device. 2. The work roll shift reference position when the shift amount of the work roll is obtained is the work roll position at the time of rolling the preceding material of the same steel type.
(1) The plate crown control method as described above. 3. The work roll shift position is set such that the work roll contact position at the end of the strip width deviates from the contact position at the time of rolling the preceding material by a predetermined amount or more. The plate crown control method according to 1) or 2). 4. The variable amount of the work roll bending force is set within the range defined by the following formula.
The plate crown control method according to any one of (3). ΔP _J : Work roll bending force variable amount (ton) per chock The amount of strip crown after rolling that changes by changing the work roll shift of 1 mm (μ / mm) The amount of strip crown after rolling that changes by changing the work roll bending force of 1 ton per chock (μ / ton)