JP3651452B2 - Tension control method near the weld zone in cold tandem rolling - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cold tandem rolling method in which a rear end of a preceding strip and a front end of a subsequent strip are sequentially welded at the inlet side of the cold tandem rolling mill and continuously rolled, and in particular, the thickness control of the welded portion is performed. The present invention relates to a tension control method in the vicinity of a welded portion in cold tandem rolling with excellent properties.
[0002]
[Prior art]
Conventionally, in cold tandem rolling, as shown in FIG. 5, the trailing end of the preceding strip 1 </ b> A and the leading end of the trailing strip 1 </ b> B are generally joined by, for example, laser welding and continuously rolled. However, it is not uncommon for welding to be incomplete at the end of the welded portion in the width direction of several mm. If the welded part 2 rolls an incomplete strip, stress concentration occurs due to the notch effect, and it may even break.
[0003]
Therefore, a round notch 3 is formed for the purpose of removing an incomplete portion of the weld.
By the way, in recent years, as shown in Japanese Patent Laid-Open No. 8-174026, so-called AGC (automatic plate thickness control) is also effective in the vicinity of the welded portion, the plate thickness is actively controlled, and the very rear end of the tip coil and The very tip of the trailing coil is also being placed within the required thickness tolerance. However, the tip of the trailing coil, in particular, did not satisfy the required plate thickness accuracy and was discarded as an off-gauge defect. Depending on the required plate thickness accuracy, the off-gauge has reached several tens of meters, leading to a serious decrease in yield.
[0004]
As a result of careful observation of the off-gauge, as shown in FIG. 2, it was found that the film became thin immediately after passing through the welded portion, and thereafter became thick. And it took a considerable time for the over-thickness portion to fall within the required thickness tolerance, and as a result, the off-gage lengthened. As a means for correcting the plate thickness of the welded part, for example, in Japanese Patent Application Laid-Open No. 59-183921, the strip becomes excessively thick immediately after passing through the welded part, and the AGC reacts to this and the strip becomes excessively thin. However, the off-gauge generation tendency is completely opposite to this, and it has not been an effective measure. Also, as disclosed in Japanese Patent Application Laid-Open No. 59-33005, the tension is reduced to 75 to 95% during steady rolling when the rolled material passes through an abnormal part for the purpose of preventing fracture and drawing trouble in the vicinity of the weld. A tension control method is also proposed, but the effect is not sufficient for shortening the off-gauge.
[0005]
[Problems to be solved by the invention]
Now, the notch as described above is formed in the welded portion, and as is clear from FIG. 5, the width of the strip during rolling becomes narrow for a short time when the welded portion passes the rolling stand. It has been speculated that the excessively thick off-gauge generated at the tip of the succeeding coil may be caused by the notch, but the clear reason was unknown. Therefore, no measures were taken, and several tens of meters have been discarded depending on the required thickness accuracy.
[0006]
Therefore, the main problem of the present invention is to clarify the causal relationship between the off-gauge generated at the welded portion of the preceding strip and the succeeding strip, especially the excessively thick off-gauge generated at the tip of the succeeding strip, and the notch formed in the welded portion. Another object of the present invention is to provide a tension control method in the vicinity of the weld in cold tandem rolling that is excellent in sheet thickness controllability in the vicinity of the weld.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention sequentially welds the trailing end of the preceding strip and the leading end of the succeeding strip at the inlet side of the cold tandem rolling mill, and then forms a notch at the strip width end and continuously rolls. A tension control method in the vicinity of a weld in cold tandem rolling, wherein the tension between the i-th rolling stand and the (i-1) -th rolling stand immediately before the notch bites into the i-th rolling stand. The control is substantially “off”, and the tension control is substantially “on” immediately after the notch passes through the i-th rolling stand.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the operation of the present invention will be described in detail.
In cold tandem rolling, it is very important to control the tension in order to secure the necessary thickness accuracy and stabilize the operation. If the tension becomes too high, the strip will break between the rolling stands, and conversely if it becomes too low, the strip will be narrowed down. Therefore, various tension control methods have been proposed, but generally used are ATL (automatic tension limit control) and ATR (automatic tension constant control). In normal operation, these tension controls are often always “on” during rolling.
[0009]
For example, in the case of ATL, as shown in FIG. 3, the strip 1 detected by the tension detector 7 disposed between the i-th rolling stand 5 and the (i−1) -th rolling stand 6 is used. Based on the deviation between the actual tension value that acts and the target tension value that has already been set, when this deviation value exceeds the bandwidth that has been set in advance by the computer 8, the reduction device 9 of the i-th rolling stand. Thus, so-called bandwidth control is performed to control the tension acting between the rolling stands by adjusting the gap between the upper and lower work rolls 5a in real time. The upper and lower limits of tension that may cause operational problems are set in advance, and fluctuations in the actual tension value within the range that does not deviate from the range between the upper and lower limits are acceptable. .
[0010]
Then, as described above, the notch is formed in the welded portion between the rear end of the preceding strip and the front end of the succeeding strip, so that the width of the strip is reduced for a short time when the welded portion is rolled on the rolling stand. Will be reduced. By reducing the width of the strip, at the moment when the notch is engaged with the i-th rolling stand, as shown in FIG. 4, the gap between the i-th rolling stand and the (i-1) -th rolling stand is obtained. The tension will decrease.
[0011]
As described above, the tension between the rolling stands is controlled by, for example, ATL, but the ATL reacts to the decrease in tension caused by the notch. When the ATL responds to the decrease in tension, it attempts to increase the lowered tension, thereby opening the work roll gap of the i-th rolling stand. And when tension | tensile_strength recovers, it will transfer to a stable rolling state again. The point to be noted here is that, as shown in FIG. 4, the tension between the i-th rolling stand and the (i-1) -th rolling stand is due to the opening of the i-th work roll gap. It changes to a slightly higher value than the state before passing through the weld. However, since it does not become so high that it exceeds the upper limit of the ATL, the ATL does not start control based on the above-mentioned reason. Eventually, the work roll gap remains open.
[0012]
Opening the work roll gap transiently increases the thickness of the strip. This was the cause of an excessively thick off-gauge at the trailing strip tip.
In the present invention, the tension control between the i-th rolling stand and the (i-1) -th rolling stand is substantially “cut” immediately before the notch formed in the vicinity of the strip welding position bites into the i-th rolling stand. And the tension control is substantially “ON” immediately after the notch passes through the i-th rolling stand.
[0013]
At the moment when the notch bites into the i-th rolling stand, as shown in FIG. 4, the tension between the i-th rolling stand and the (i-1) -th rolling stand is greatly reduced, Since the tension control reacts to open the work roll gap of the i-th rolling stand, immediately before the notch is engaged with the i-th rolling stand, the tension control is substantially “off” and the i-th rolling stand Avoid opening the work roll gap. A punch hole 4 is formed to recognize the welded portion of the preceding strip and the succeeding strip, and the positions of the punch hole and the notch are always constant. As the strip thickness decreases due to the progress, the length of the strip increases and the product of the thickness and the distance between the punch hole and the notch has a constant relationship. It's easy. Thereafter, immediately after the strip advances and the notch passes through the i-th stand, the tension control is again substantially “on”. Therefore, in the case of the present invention, the tension control reacts to the tension drop between the i-th rolling stand and the (i-1) -th rolling stand while the notch is engaged with the i-th stand. In addition, since the work roll gap of the i-th stand is not separated, the thickness of the strip does not increase as described above, and the influence of the notch can be almost eliminated.
[0014]
Further, the time during which the tension control is “off” is a short time from when the notch starts to bite into the i-th stand until it finishes passing through, so there is no possibility of hindering actual operation.
[0015]
【Example】
Hereinafter, the present invention will be described in detail based on examples. As shown in FIG. 1, a tension detector 7 such as a tension meter roll is disposed between the i-th rolling stand 5 and the (i−1) -th rolling stand 6. The type and specification of the tension detector can be anything. As the tension control method, the ATL described above is used in this example, but there is no problem even in the case of ATR.
[0016]
On the other hand, a punch hole 4 for tracking a welding point is formed in the strip, and the punch hole is optically detected by a WPD (welding point detector) 10. As a method for tracking the punch hole, a method in which the strip speed is integrated by the calculator 11 is used utilizing the fact that the distance between the WPD and the rolling stand is constant. The speed of the strip is the same as the number of pulses generated by the rotation detector such as a rotary encoder (not shown) every time the rolling mill work roll 5a is rotated at a certain angle by the mill motor 12 according to the model advance rate calculated from the rolling state every moment. Multiplied by the constant angle, the circumference ratio, and the diameter of the work roll 5a, and divided by the constant time, multiplied by the work roll peripheral speed of the rolling stand, etc. Ask. In recent years, there are many rolling mills equipped with a speedometer such as a laser speedometer between stands, but it is obvious that the punch speed may be tracked by actually measuring the speed of the strip with these speedometers. . Furthermore, since the product between the punched hole on the strip and the notch is always the same as the product of the strip thickness after each rolling pass, starting from the time of welding, the notch is tracked according to the relationship. This can be done easily.
[0017]
Thus, the tension control is substantially “off” immediately before the start of the notch bites into the i-th rolling stand, and the tension control is substantially “on” immediately after the notch passes through the i-th rolling stand. In this embodiment, since 5 cold tandem rolling mills are used, 2 ≦ i ≦ 5. As long as there are two or more stands, it does not matter. In addition, the terms “cut” and “on” substantially mean that, for example, in the ATL, the band width is greatly increased immediately before the start of the notch engages with the i-th rolling stand so that the influence of the notch is not transmitted to the control system. (Corresponding to “cut”), and then the band width is returned as usual (corresponding to “turn on”) immediately after the notch passes through the i-th rolling stand.
[0018]
In recent years, the number of facilities for connecting the pickling line, which is the process immediately before cold rolling, directly to the inlet side of the cold rolling equipment and welding the trailing end of the preceding strip and the leading end of the trailing strip on the inlet side of the pickling line has increased. However, it goes without saying that the present invention can also be applied to such equipment.
FIG. 6 shows the effect of shortening the off gauge length of the trailing strip tip by the tension control method according to the present invention. Compared to the conventional method, it can be seen that the off-gauge length can be greatly reduced.
[0019]
【The invention's effect】
As described above, according to the present invention, the tension control does not react with the tension drop caused by the notch in the vicinity of the welded portion, and the work roll gap of the i-th rolling stand is not opened. The off-gauge at the end of the strip, which has become thicker, can be significantly shortened. In addition, when the present invention is applied, there is a time during which the tension is in an uncontrolled state for a short period of time, but there is no operational problem due to this.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a tension control method between rolling stands according to the present invention.
FIG. 2 is a diagram showing a state in which a strip becomes excessively thin at a weld and an excessively thick off-gauge is generated immediately afterward.
FIG. 3 is a conceptual diagram of a general tension control mechanism.
FIG. 4 shows that the tension between the i-th rolling stand and the (i-1) -th rolling stand decreases at the weld, and ATL reacts to this, opening the work roll gap of the i-th rolling stand and It is a figure which shows progress which recovers.
FIG. 5 is a schematic view of a welded portion between a rear end of a preceding strip and a front end of a subsequent strip.
FIG. 6 is a diagram showing that the implementation of the present invention improves the excessive thickness off-gauge at the trailing strip tip.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Strip 2 Welding part 3 Notch 4 Punch hole 5 i-th rolling stand 5a Work roll 6 (i-1) -th rolling stand 7 Tension detection device 8 Computer 9 Reduction device
10 WPD (Welding point detector)
11 A calculator that tracks the welding point from the speed of the strip and the position of the punch hole detected by WPD.
12 mil motor

Claims (1)

After welding the trailing end of the preceding strip and the leading end of the succeeding strip sequentially at the inlet side of the cold tandem rolling mill, the tension in the vicinity of the weld in cold tandem rolling is continuously formed by forming a notch at the strip width end. A control method,
Immediately before the notch bites into the i-th rolling stand, the tension control between the i-th rolling stand and the (i-1) -th rolling stand is substantially “off”, and the notch defines the i-th rolling stand. A tension control method in the vicinity of a weld in cold tandem rolling, characterized in that the tension control is substantially “ON” immediately after passing.

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