JP2713012B2 - Roll cooling method for metal strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cooling a metal strip such as a steel strip in a continuous annealing process by using a cooling roll to cool the metal strip by a cooling roll so that the metal strip can be stably passed without a shape defect such as drawing. About.

[0002]

2. Description of the Related Art Cooling by a cooling roll that circulates a coolant through an internal passage and cools a metal band or the like that comes into contact with the outer surface thereof is faster than a gas cooling method such as a gas jet, thereby improving quality. Since it is effective, it is frequently used in continuous annealing equipment for metal strips.

[0003]

FIG. 10 shows an example of a typical roll cooling equipment, in which 10 is a water-cooled cooling roll,
Reference numeral 20 denotes a steel strip. These # 1 to # 5 cooling rolls
When the steel strip 20 passes through the roll 10, the portions where the steel strip 20 comes into contact with the roll 10 and the portions where the steel strip 20 does not come into contact are in the state indicated by α and β in FIG. Since a temperature difference is generated in the longitudinal direction of the steel strip as shown in (b), FIG.
As shown in (c), thermal stress is generated in the width direction of the steel strip 20.
Due to this thermal stress, the shape of the steel strip 20 is likely to collapse, and in severe cases, vertical wrinkles in the longitudinal direction of the steel strip called "drawing" occur, resulting in product failure and breakage accidents accompanying the meandering of the steel strip 20. There were problems such as causing serious trouble.

[0004] The main cause of the drawing is that the thermal stress of the compression in the width direction generated due to the temperature difference in the longitudinal direction of the steel strip immediately before the entry side where the steel strip comes into contact with the cooling roll is triggered. It is known to cause buckling of the steel strip.

For this reason, various measures have been proposed to reduce the compressive stress in the width direction of the steel strip immediately before the cooling roll entrance side and to increase the resistance to drawing and buckling.

For example, in Japanese Patent Laid-Open Publication No. Sho 59-107031, as shown in FIG. 12A, a portion (within 1 m) of the steel strip 20 immediately before entering the cooling roll 10 is cooled by a cooling nozzle 34 or the like. )
Discloses a method of relaxing the temperature gradient in the longitudinal direction of the steel strip immediately before the entry side and improving the proof stress against drawing. Also, Japanese Patent Application Laid-Open No. 1-268820 discloses a method of detecting an out-of-plane deformation increase portion of a steel strip which causes a drawing and spraying a cooling gas intensively thereat.

However, these techniques are not always effective for wide and thin metal strips, and a more effective roll cooling method for preventing drawing of metal strips such as steel strips has been required.

The present invention has been made in view of the above-mentioned problems of the prior art, and it is an object of the present invention to provide a method of cooling a metal strip roll which enables stable thread passing without a shape defect such as drawing of the metal strip. It is.

[0009]

According to the roll cooling method of the present invention, when cooling a metal strip by a cooling roll, the center of the metal strip immediately before the roll entry side is moved in the width direction by 15 to 15 mm of the sheet width. While cooling in the range of 85%, and in the range of 0.3 to 10 m from just before the entrance side to the upstream side in the longitudinal direction ,
When performing the front cooling, the temperature gradient due to the front cooling
The distribution ΔTf / b is within the range shown in the following equation 3, and
Equation 4 shows the temperature difference ΔTf in the longitudinal direction of the metal strip due to the cooling.
It is characterized in that it is controlled within the range.

[0010]

(Equation 3)

Where ΔTf is the temperature difference in the longitudinal direction of the metal band due to cooling of the front surface.
(° C) b: Front cooling length of metal strip (m) W: Sheet width of metal strip (m) t: Sheet thickness of metal strip (m)

[0012]

数 Tf ≦ 50 ° C.

In the process of inventing the above-described structure, the inventors of the present invention disclosed in the above-mentioned JP-A-59-107031 and JP-A-Hei.
An additional test was conducted to cool the portion immediately before the entrance of the cooling roll as shown in Japanese Patent No. 268820. However, such cooling did not provide a sufficient effect to prevent the drawing of a wide and thin metal band.

The reason for this is that the range for cooling the front surface of the metal strip is limited to the portion Y just before the roll entrance as shown in FIG. 13, and it is not necessarily effective for relaxing the compressive stress in the width direction of this portion. If the compression stress in the width direction is to be relaxed only by cooling this portion, a considerable amount of cooling is required, and on the contrary, new buckling and reduction occur.

In the first place, as shown in FIGS. 10 (b) and 10 (c), the occurrence of the drawing of the metal band due to the roll cooling is caused by the steel band.
As 20 is cooled on the roll 10, it is caused by thermal stresses due to the temperature difference occurring in its longitudinal direction. Due to the temperature difference in the longitudinal direction, the steel strip 20 on the cooling roll 10 is restrained on the roll exit side from a portion having a lower temperature that is not in contact with the roll, whereby a tensile stress acts in the width direction, and conversely. In the steel strip 20 on the roll entry side that is not in contact with the roll, the steel strip 20 on the roll 10 is affected by the heat shrinkage, so that a compressive stress acts in the width direction. This compressive stress reaches a maximum σmin at the center of the metal band 2 on the roll entry side as shown in FIG. 13, and when the buckling limit is reached, out-of-plane deformation of this portion occurs rapidly, and the deformation is generated on the roll 1. The iris is generated by riding and collapsing. The present inventors have paid attention to this compressive stress, and have again examined the configuration effective for relaxing this stress and preventing drawing.

It has been confirmed by the study of the present inventors that the cooling of the front surface which is effective in preventing the occurrence of the drawing does not have a structure in which only one point just before the roll contact is cooled as in the conventional case, but is shown in FIG. Therefore, it is better not to cool with a certain appropriate length b and width w, and the cooling itself is not a matter of blindly increasing the cooling amount, but the temperature gradient ΔTf / b in the longitudinal direction of the metal strip 2. Must be controlled within an appropriate range.

Of these, the compressive stress in the width direction generated at the center of the metal strip 2 on the cooling roll entrance side shown in FIG. 13 by the preliminary experiment is a temperature gradient dT / dx (° C./m) in the longitudinal direction of the metal strip on the cooling roll 1. ) Was first confirmed. Next, when the metal band 2 on the front side of the cooling roll 1 is cooled at a certain temperature gradient, a tensile stress acts on the metal band 2 on the roll entry side in the width direction due to the cooling of this portion. It has been clarified that the maximum compressive stress in the width direction generated along with this is alleviated by this, and drawing is prevented. Furthermore, the findings obtained in these preliminary experiments showed that the cooling of the roll front part was not always effective in all cases, and that in some cases the effect was adverse.

Therefore, the present inventors have predicted that there is a certain appropriate cooling length, cooling width, and front cooling temperature gradient as a method of cooling the front surface which is effective in preventing drawing, and systematic drawing experiments using an actual machine. Was performed.

First, in the case of roll cooling of a steel strip, an index of the drawing prevention effect at the time of cooling the front surface was determined. That is, as shown in FIG. 1, when the cooling roll inlet side temperature Tin (° C.) and the outlet side temperature Tout (° C.) of the steel strip are set,
Limiting temperature difference T _R (° C) when there is no front cooling (T _R =
(Tin-Tout) was taken as the reference temperature difference at the origin, and the increment ΔT _R (° C.) from the reference temperature difference when the drawing limit temperature of the steel strip changed due to front cooling was used as the index.

In order to determine this index, the present inventors have determined that the sheet thickness (t) is 0.66 mm, the sheet width (W) is 1450 mm, and the sheet thickness (t) is 0.5 mm × 1500 mm.
Roll cooling and front cooling were performed on the soft annealed material of each size of 0.5 mm × 1800 mm, and the front cooling width w and the front cooling temperature gradient ΔTf / b (° C./m) were variously changed. An experiment for determining the ΔT _R was performed (however, the front cooling length b was 1 m). The result is shown in FIG. From the figure, if the temperature gradient ΔTf / b of the front cooling is set to a certain appropriate temperature gradient (in the figure, 10.0 ° C./m or less), a wide range of cooling width / plate width (w / W), particularly 0.15 ≦ w / W ≦ 0.85
ΔT _R rises from about 5 ° C. to nearly 12 ° C. in the range, and it can be seen that the effect of preventing drawing is obtained.

On the other hand, when the front cooling temperature gradient ΔTf / b is increased (12.0 ° C./m, 15 ° C./m, 23 ° C./m), as shown in FIG. Even if there is, it can be seen that ΔT _R is lowered and the effect is opposite. This is because excessive front cooling causes buckling of the front side of the steel strip entry side, so that squeezing easily occurs in the cooling roll.

Next, in order to specify an optimum front cooling temperature gradient, the present inventors have determined that a front cooling temperature gradient (ΔTf / b) c which causes buckling of the front portion on the steel strip entrance side which adversely affects the drawing.
Regarding r, for the steel strip of the same size and the same material as those used in the above experiment, the front cooling width / plate width (w / W)
A series of experiments were performed while changing the front cooling length b (0.3 to 10.0 m) (for W / t = 2200, the front cooling length b was set to 0.3 m, 1.0 m, 3. The experiment was carried out by changing to 0 m). As a result, the front cooling temperature gradient (ΔTf / b) cr that causes buckling is not affected by the cooling length b and the cooling width / plate width (w / W) as shown in FIG. It became clear that it depends on the width / thickness (W / t). In other words, in the figure, when W / t is 2200 , even if b is changed to 0.3, 1.0, and 3.0 m, (ΔTf
/ B) cr is substantially unchanged at the same position, and w
Even if / W is changed, the value does not substantially change. On the other hand, W
When / t changed to 2200, 3000, and 3600, (ΔTf / b) cr became a different value.

From the above results, based on these, based on these, W / t and (ΔTf / b) cr when steel strips of many sizes (ie, different W / t) were passed through An experiment was performed to determine the relationship, and the results shown in FIG. 4 were obtained. From the figure, the front cooling temperature gradient Δ within the range shown by the following equation ( 5)
When it was set to Tf / b, it was found that buckling of the cooling roll entrance side front surface due to front surface cooling did not occur, which was effective for preventing the occurrence of drawing of the steel strip.

[0024]

(Equation 5)

Next, from these experimental results, W / t, w /
W as a parameter, was to organize the influence of the ΔT front cooling temperature on the increase in the _R gradient .DELTA.Tf / b, Fig. 5
The result was as shown in the figure. In this figure, W / t is 22
00, the w / W is 0.25, 0.
Even if it changes to 5, 0.75, there is not much change in ΔTf / b. On the other hand, W / t is 2200, 3000, 3600
ΔTf / b changes completely, and accordingly, ΔTf / b
T _R shows a completely different change.

[0026] If it is controlled within a range .DELTA.Tf / b from the figure shown in following equation 6, it is found to be effective in increasing [Delta] T _R.

[0027]

(Equation 6)

Further, in order to specify the optimum range of the front cooling length b, W / t is used as a parameter, and ΔTf / b is calculated by the above equation (1).
A series of experiments were carried out with the values set within the optimum values shown in (4) (4.9, 6.8, 10.0 ° C / m). The result at that time is shown in FIG. It can be seen from the figure that when the front cooling length b is 0.2 m, the increase in ΔT _R has an adverse effect. This ΔT _R
Changes from the front cooling length b to a positive value from less than 0.3m,
Saturates after reaching a maximum near 1 m, then decreases after forming a flat part to 3 to 5 m, and depending on W / t, the effect of increasing ΔT _R when the front cooling length b is 5 to 10 m Is lost.
As the front cooling length b and the temperature gradient ΔTf / b increase, an out-of-plane deformation called an ear wave occurs on both sides of the steel strip, and the temperature difference in the longitudinal direction of the steel strip is particularly reduced in the width direction. If the maximum temperature difference ΔTfmax of a plurality of examinations is 50 ° C. or more, the ear wave becomes very large, and the occurrence of vibration and the failure of the inlet side shape cause the occurrence of ΔT _R even when the front surface is cooled. This is because the effect is lost, and rather, squeezing on the cooling roll is more likely to occur. As can be seen from FIG.
Even when a steel strip having a larger / t is considered, it is difficult to imagine that the optimum range of the front cooling length bm is 10 m or more. On the other hand, it is not realistic because it requires a large facility. . From these experimental results, the front cooling length b
It was found that the range of 0.3 to 10 m was optimal, and that the temperature difference ΔTf in the longitudinal direction of the steel strip due to the front cooling was to be controlled to 50 ° C. or less.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the method of the present invention will be described below in detail.

The present inventors carried out the method of the present invention in a continuous annealing facility for steel strip 20 using a roll cooling facility having the respective configurations shown in FIGS.

In these roll cooling equipment configurations, the steel strip 20
There is provided a front cooling device 3 for injecting a cooling gas to the opposite side of the steel strip 20 just before coming into contact with the cooling roll 10 to perform front cooling. The cooling header of the cooling device 3
Reference numeral 30 denotes a box having a width w of 0.6 m and a length b of 1 m. The gas ejection surface has a large number of gas ejection holes (not shown) having a pitch of about 0.1 m and a diameter of 25 mm. As described above, the steel strip 20 is provided in a portion immediately before coming into contact with the cooling roll 10.

The cooling roll 10 can be moved left and right in the drawing to adjust the contact length with the steel strip 20, so that the cooling header 30 can be prevented from contacting with the steel strip 20, and the front cooling temperature can be reduced. For the purpose of avoiding that the gradient ΔTf / b and the like greatly deviate from the set values, the cooling roll 10
The cooling header 30 can also be moved in the same direction following the movement of the cooling head, and the structures shown in FIGS. That is, in FIG. 7, a rotation fixed shaft 31 of the cooling header 30 is provided near a point where the steel strip 20 is separated from the entry-side deflector roll 11, and a control device (not shown) that detects a movement signal of the cooling roll 10 provides the same. The cooling header 30 is rotated about the shaft 31 by a cylinder 32 whose expansion and contraction is controlled, and the cooling header 30 is always kept parallel or nearly parallel to the surface of the steel strip 20. I am doing it. On the other hand, in FIG. 8, first, the cooling header 30 is disposed immediately before the contact point of the cooling roll 10 of the steel strip 20 in an inclined state, and the cooling
The cooling header is provided by a cylinder 33 whose expansion and contraction is controlled by a control device (not shown) which has detected a movement signal of the cooling roll 10 as described above. Numeral 30 is adapted to be translated so that the cooling header 30 is always kept close to the surface of the steel strip 20.

In the above-described roll cooling facility, 0.9 to
A steel strip 20 having a width of 1.85 m and a width W was passed through (w / W was 32 to 6
7%). At this time, when the cooling by the front cooling device 3 is not performed, and when the cooling by the front device 3 is performed, the temperature gradient ΔTf / b is reduced by ΔTf / b = 2.5 × 10 ⁷ (t / w) ² + 1.1 ×
10 ⁴ (t / w) (all satisfy the conditions of the present invention) and the temperature difference ΔTf in the front-side cooling longitudinal direction is controlled to 30 ° C. or less (also satisfying the conditions of the present invention). FIG. 9 shows the results. As shown in the figure, when the front surface cooling is not performed, the upper left side of the curve without the front surface cooling becomes an area where the steel strip 20 can be stably passed without the occurrence of drawing or the like of the steel strip 20. W / t <3000. On the other hand, when the front cooling according to the present invention is performed, the upper left side of the curve with the front cooling is a region where the steel strip 20 can be stably passed without the occurrence of drawing or the like of the steel strip 20. Compared with this, the stable threading area has been expanded. That is, the present invention has made it possible to stably pass the steel strip 20 having a size up to approximately W / t = 4000. Therefore, compared to the case without front cooling, the area where the sheet can be passed without the occurrence of drawing or meandering is expanded to about 0.10 to 0.15 mm thinner steel strip 20 compared to the case without front cooling,
Significant improvements were seen in productivity and operability.

[0034]

According to the method of the present invention described in detail above, it becomes possible to surely suppress the occurrence of a throttle which could not be prevented even by the front cooling as the width of the metal strip becomes wider and thinner. The area that enables stable threading has expanded. For this reason, the operation rate and productivity have been greatly improved, and it has become possible to cope with the wide and thin CAL designated material of the user.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a cooling range of front cooling according to the present invention.

FIG. 2 shows w / W and ΔT _R when W / t is used as a parameter.
6 is a graph showing the relationship of.

FIG. 3 is a graph showing the relationship between w / W when W / t is used as a parameter and ΔTf / b when buckling the front surface.

FIG. 4 shows buckling of front cooling section and front cooling temperature gradient ΔTf /
It is a graph which shows the relationship of b and W / t.

FIG. 5 shows ΔTf / b and Δ when W / t is used as a parameter.
Is a graph showing the relationship between T _R.

FIG. 6: Front cooling length b when W / t is used as a parameter
6 is a graph showing the relationship between and ΔT _R.

FIG. 7 is an explanatory view showing one embodiment of a roll cooling configuration in equipment for implementing the method of the present invention.

FIG. 8 is an explanatory view showing another embodiment of the roll cooling configuration.

FIG. 9 is a graph showing experimental results of the present example.

FIG. 10 is an explanatory diagram showing a typical roll cooling configuration.

FIG. 11 is an explanatory diagram showing a state of a temperature gradient in a typical roll cooling configuration.

FIG. 12 is an explanatory diagram showing a state of a temperature gradient in the improved roll cooling configuration.

FIG. 13 is a perspective view showing a conventional roll cooling configuration.

[Explanation of symbols]

 1, 10 Cooling roll 2 Metal strip 3 Front cooling unit 20 Steel strip 30 Cooling header

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hidemine Kobayashi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Kazunori Hashimoto 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Incorporated company (56) References JP-B-63-1381 (JP, B2)

Claims (1)

(57) [Claims] When cooling a metal strip by contacting it with a cooling roll, a central portion of the metal strip immediately before the roll entry side is in the width direction within a range of 15 to 85% of the sheet width and immediately before the entry side. Is cooled in the range of 0.3 to 10 m in the upstream side in the longitudinal direction, and the temperature gradient ΔTf / b due to the front surface cooling is calculated by the following equation (1).
Wherein the temperature difference ΔTf in the longitudinal direction of the metal band due to the front surface cooling is controlled within the range represented by the following equation (2). (Equation 1) Where ΔTf: temperature difference in the longitudinal direction of the metal band due to front cooling
(° C) b: Front cooling length of metal band (m) W: Plate width of metal band (m) t: Plate thickness of metal band (m) ΔTf ≦ 50 ° C.