JPS6192702A - Hot rolling method - Google Patents

Abstract

PURPOSE:To reduce a sheet crown through a rolling cycle by only setting a proper initial crown on a work roll by changing a shifting pitch during the rolling cycle in work-roll shifting rolling. CONSTITUTION:In case of rolling while cyclically shifting work rolls 1,1' by a hot rolling mill having a function of shifting the work rolls 1,1' in the axial directions, the shifting pitch is changed during the rolling cycle. Here, the distance (x) between the center 0 of a sheet in its width direction and each of the barrel centers of rolls 1,1' at both of a right driving side and the other operation side is defined as the roll shifting quantity. And the stepwise increasing or decreasing increment of a quantity (x) per unit rolling-coil is defined as a shifting pitch in the repeat of a shifting operation for increasing stepwise the quantity (x) at every fixed number of coils till its reaches the maximum 100mm, for instance, and decreasing thereafter.

Description

[Detailed Description of the Invention] (Industrial Application Field) The technical content described in this specification regarding the improvement of the rolling method by cyclically shifting work rolls in hot rolling is aimed at reducing false crowns, as well as This paper proposes the results of research and development to enable continuous rolling of as many coils as possible without causing shape defects such as overstretching.

In recent years, there has been an increasing demand for light plates for crowns.

It goes without saying that when hot rolling is carried out for the purpose of reducing the plate crown, it is necessary to consider the thermal crown of the roll as a factor that affects the temporary crown over time.

However, while the growth of thermal crown is related to rolling pitch, actual rolling time, water cooling conditions, etc., it also depends on the type of rolled steel,
It is also known that the growth behavior changes depending on the plate dimensions and the like, and that the growth behavior differs between the first half and the second half of the rolling cycle.

The results of various studies and experiments regarding work roll shift rolling have revealed that the distribution of thermal crown in the roll barrel direction differs depending on the shift pattern, that is, the dependence of the thermal crown profile on the shift pattern.

The basis of this invention is to utilize this knowledge to reduce the temporary crown by changing the shift pitch during the rolling cycle.

(Prior art) For example, the shift pattern of conventional work rolls is set to -ratio without fear of rolling steel, jt of rolling pitch, front and half of rolling cycle, etc. However, in this case, the growth of thermal crown did not vary in the direction of the roll barrel, so variations in sheet crown throughout the cycle were unavoidable. When the roll diameter difference ΔS is small, the plate crown is large; on the other hand, in the latter half of the roll, ΔS becomes large and the temporary crown decreases, but there is also a tendency for a so-called flared shape to occur.

This is because, although it is effective to increase the amount of roll crown in order to reduce sheet crown, in the latter half of the rolling cycle, as the thermal crown develops, belly elongation occurs and the shape becomes defective. In order to avoid defects, it was necessary to make the initial crown small, and as a result, the plate crown was too large in the first half of the rolling cycle, and the variation in plate crown became significant throughout the rolling cycle.

(Problem to be solved by the invention) An appropriate initial crown for the instep is set on the work roll without the conventionally unavoidable variations in temporary crown due to differences in steel type, rolling pitch, etc. and heat crown. It is an object of this invention to ensure an effective reduction of plate crown only throughout the rolling cycle.

(Means for Solving the Problems) This invention provides a hot rolling mill having a function of shifting the work rolls in the axial direction, and when rolling is performed by shifting the work rolls cyclically, the shift pitch is changed according to the rolling cycle. This is a hot rolling method that consists of changing the temperature between

Now, Fig. 1 shows how to shift the work rolls 1, 1' with respect to the boardwalk center 0, and the drive side on the right side of the figure,
On the other operation side, the roll shift amount is defined by the distance X from the center of the barrel of each roll from the board road center O, and this roll shift lx is set in stages for each fixed number of coils during the rolling cycle up to a maximum of 100 mm. Regarding repetition of a shift operation in which the roll shift is increased and then decreased, that is, a cyclic roll shift, the stepwise increase or decrease of the roll shift m per unit number of rolled coils is defined as a shift pitch.

Fig. 3 shows a comparison of the No.-mark crown profile using the cyclic roll shift method shown in Fig. 2, in which the shift pitch was fixed at 20 mm, 140 mm, and eomm per two coils, respectively. This example is 5PCC
, Obtain a product with a width of 935 mm and a thickness of 2.3 ml, 6
F3. in stand finishing mill. This is the result when simultaneous roll shift operations were performed at each stand F4 and F5.

It can be seen that the larger the shift pitch and the shorter the period, the gentler the profile of the thermal crown, and the smaller the roll diameter difference ΔS between the center and edge in the sheet width direction.

Therefore, it is expected that the thermal crown will be relatively small.
For example, for steel types with low rolling temperatures,
By setting the shift pitch small, the thermal crown in the range corresponding to the plate width can be increased, which can be used to reduce the plate crown.

By the way, in general, cumulative addition of the number of rolled coils exhibits a thermal crown profile behavior as shown in FIG.
The shift pitch is 40ml/l as described in Figure 2.
Figure 5 shows the case of a 1/2 coil.

Significant reduction of ΔS occurs in the first and second half of the rolling cycle, but when rolling is performed by cyclically shifting the work rolls, the thermal crown difference ΔS is controlled in the first and second half of the rolling cycle. The following is effective in reducing plate crown.

That is, in the first half of the cycle where ΔS is small, the shift pitch is made small to increase ΔS, and in the second half of the cycle, the shift pitch is increased to keep ΔS small, thereby making it possible to stabilize ΔS throughout the rolling cycle.

The solid line in FIG. 6 compares the case where the shift pitch is changed with the case where the shift pitch is constant, and the rise of ΔS is compared.

By stabilizing ΔS in this way, it is possible to reduce the plate crown and the variation in the temporary crown throughout the cycle by simply providing the work roll with an appropriate initial curve in advance.

(Example) SPC: C, 935mm width x 2.3mm thick products were made into 6
Stand finish rolling (trowel F3. - Cyclic roll shift operation is applied simultaneously to the work rolls of F4 and F5 stands, especially shift 1 in the first and second half of the cycle.
~The results of work roll shift rolling with changing pitches are shown in Fig. 7 and 8 for the shift pitch pattern.
The figure shows the behavior of ΔS.

The average and dispersion of the plate crown of the product thus obtained were compared with the conventional case of constant shift pitch, and the results shown in the following table were obtained.

(￥i! light effect) In this invention, since the growth of ΔS is rapid in the first half of the cycle, a significant effect of reducing the plate crown in the first half of the cycle is recognized, and in particular, roll crown is reduced early in the first half of the rolling cycle. As the value becomes larger, temporary crowns can be reduced, and since the number of roll crowns remains constant even in the second half, plate crowns can also be reduced without causing shape defects.

In addition, since the thermal crown is stabilized early in the rolling cycle, it is possible to make the convex curve of the initial crown of the work roll larger.If the roll curve is increased using the conventional method, the plate will become stretched in the latter half of the cycle, which is unsuitable. However, in pitch change roll shift,
No disturbance of the shape is observed, and therefore the plate crown can be further reduced by making the initial curve convex.

Furthermore, the difference in thermal crown, which is based on the difference in rolling pitch, or the difference in ΔS, has traditionally been resolved by changing the roll initial curve every time the rolling pitch or steel type changes, but by changing the shift pitch, ΔS Since it is possible to change the Generate benefits.

Although the above explanation was given for a normal work roll, the same applies to the so-called single trapezoidal roll rolling method, which uses a pair of tapered grinding parts on one end and overlapping the tapered parts alternately. Compatible.

[Brief explanation of drawings]

Fig. 1 is a constant Ml diagram of roll shift amount, Fig. 2 is a diagram of various shift pitch patterns, Fig. 3 is a comparison graph of △S at each shift pitch, and Fig. 4 is a graph of ΔS with the number of rolling coils. Figure 5 is a graph showing the dependence, Figure 6 is a graph comparing the effects of shift pitch change on ΔS, Figure 7 is a shift pitch pattern diagram of the example, and Figure 8 is a graph showing the effect of shift pitch change on ΔS. It is a graph showing the growth suppression effect of ΔS due to the pattern. Patent Applicant Kawasaki Steel Corporation Figure 1 Figure 2 Figure 6 Rolling Head Office (Wood Figure 7 Figure 8

Claims (1)

[Claims] 1. When performing rolling by cyclically shifting the work rolls in a hot rolling mill that has a function of shifting the work rolls in the axial direction, the shift pitch is changed during the rolling cycle. Characteristic hot rolling method.