JPS632684B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for controlling plate thickness in a cold tandem mill (cold continuous rolling mill), and in particular proposes a rolling speed setting method that enables the coil top and coil bottom to have a target plate thickness. In the production of cold-rolled steel sheets, plate thickness accuracy is the most important control item, and for this reason automatic plate thickness control technology, so-called AGC technology, is adopted in cold tandem mills. By the way, when the rolling process using a tandem mill is classified by rolling speed, it generally ranges from a low rolling speed to a higher rolling speed during the rolling process, during which the tip of the coil of the hot-rolled steel sheet that is the raw material is bitten by the rolling mill. During acceleration, the rolling speed is increased to a steady rolling speed of It is classified into five periods when the bottom is removed from the rolling mill. Since most of the coil is rolled at a steady speed, most of the AGC technologies mentioned above are aimed at the above-mentioned steady rolling. The current situation is that there are almost no products that target the time and butt removal time, and nothing that is sufficiently effective has yet been developed. Therefore, during strip threading, bottom removal, and acceleration/deceleration, the operator must manually control the strip thickness while the rolling speed is lower than several percent to 20% of the steady rolling speed (the speed at which normal AGC is turned on). However, the part that does not meet the target plate thickness, that is, the part that is off-gauge tends to be long, and an effective countermeasure against the decrease in yield due to truncation of this off-gauge part has been desired. In order to achieve the target plate thickness, the rotation speed of the mill motor that drives the rolling mill rolls is set before rolling based on the rolling schedule. There is a problem in that the target plate thickness is not necessarily achieved by the set value of the rotation speed of the mill motor in front of the plate. A major factor in this control error is the drooping characteristic of the motor, the details of which will be described later. The present invention proposes a method for controlling the rotational speed of a mill motor, which solves this problem and improves yield by shortening the off-gauge portions of the top and bottom of the coil. A mill motor rotation speed control method for a cold tandem mill according to the present invention is provided for controlling the rotation speed of a mill motor that drives rolling mill rolls, and includes drooping characteristic control that reduces the rotation speed in response to an increase in mill motor current. In a cold tandem mill equipped with a speed control device configured to perform this function, while detecting the inter-stand tension, a control signal for controlling drooping characteristics is also detected, and a signal to cancel the control signal is sent to the stand-to-stand tension. The detection value is provided to the speed control device when the detected value is within a predetermined tolerance range. The present invention will be specifically explained below using a five-stand tandem mill as an example. Figure 1 shows ST ₁ ,
ST ₂ ... ST ₅ shows a tandem mill with 5 stands, where X-ray thickness gauges X ₁ and X ₅ are respectively on the first stand.
It is installed on the exit side of ST ₁ and the fifth stand ST ₅ . The lowering position is controlled by an electric motor for each stand, but the first stand ST ₁ uses a thyristor type lowering position setting device SCR ₁ , and the second to fifth stands ST ₁
~ _ST5 is equipped with a motor/generator set type lowering position control system _MG2 ~ _MG5 (thyristor type may also be used). Each stand ST ₁ ~ _{ST 5}
The speed of the mill motors MM ₁ to MM ₅ is controlled by automatic speed control devices ASR ₁ to ASR ₅ using signals from tachogenerators (analog speed detectors) TG ₁ to TG ₅ and the like. In the following explanation, hi: first stand STi exit side plate thickness (i = 1, 2...5
The same applies hereafter) Si: Lowering position Ti, i+1 of the first stand STi: Inter-stand tension between the stand STi and the (i+1)th stand STi+1 Ni: Rotational speed of the mill motor MMi of the i-th stand STi ho: First stand ST It is defined as the entry side plate thickness of ₁ . Now, in order to subject the hot-rolled coil to this tandem mill and roll it into a cold-rolled steel plate of the target thickness, the rolling position Si of each stand and the mill motor rotation speed Ni are set in order to realize this. These Si and Ni are calculated using the following well-known formulas (1) and (2). Si=hi-Pi/Mi-Soi...(1) Ni=K/hi(1+fi)...(2) Here, hi is the target value of the exit side thickness of each stand,
That is, a plate thickness schedule is used, and this plate thickness schedule may be calculated based on h ₀ and h ₅ (finishing target value), or may be directly set. Also
Pi is the rolling load of the i-th stand STi, and the above hi
and the inter-stand tension Ti, i+1 (a target value is also used for this tension).
Furthermore, Mi is the mill stiffness coefficient of the i-th stand STi, Soi
is the zero point of the rolling position of the i-th stand STi, fi is the advance rate of the i-th stand STi, and K is a constant. Now, here, the rolling position S ₁ of the first stand ST ₁ is manually set before sheet threading, and after the tip of the hot-rolled coil is bitten into the first stand ST ₁ , absolute value AGC is performed. Note that if there is an error in the rolling position _S1 of the first stand, it will affect the plate thickness _h1 on the exit side and the plate thicknesses of all the stands on the downstream side, resulting in an error in the finished plate thickness _h5 . Absolute value AGC detects the rolling position and rolling load, calculates the exit plate thickness, and controls it to match the target value.It does not require accurate prediction of the rolling load and can be used in large-scale processes. There is no need to use a control computer (hereinafter referred to as a pro-computer). However, it is necessary to accurately detect the zero point So ₁ at the rolling position, and during rolling, an X-ray thickness gauge X ₁ is used to trace the exact zero point So ₁ , and the mill stop time is long. If roll heat-up is a problem, perform zero adjustment to accurately detect So ₁ by bringing the upper and lower rolls into contact while the rolls are idling. Next, for the second to fifth stands, the rolling down positions S ₂ to _{S 5} before threading are manually set as in the first stand. Note that the error in the rolling down positions S ₂ to _{S 5} affects the rear tension of each stand, but has little effect on the finished plate thickness h ₅ . During sheet threading, the tension between the stands Ti,i+
1 deviates from the upper and lower limits of a predetermined allowable range (control target range), control is performed so that the lowered position of the downstream stand is corrected to keep the inter-stand tension Ti, i+1 within the target value. This is based on the knowledge that when the mill motor rotational speed is controlled to a target value, the deviation of the inter-stand tension from the target value is caused by the deviation of the rolling position from the target value. Next, we will explain how to control the rotation speed of the mill motor, starting with the method used during setup. Figure 2 shows the rotation speed control system during setup. In the figure, SRHi is an arithmetic unit that issues a speed command to the automatic speed control device ASRi, and PGi is a pulse generator that issues pulses proportional to the rotation speed of the mill motor MMi. Nerator, FCi is a speed fine adjustment device, and DS is
A draft schedule setting device for setting the plate thickness schedule hi etc. required for calculation of formula (2),
SP is a calculator that calculates the rotation speed ratio of each stand.
MRH is the speed reference value generator for this tandem mill. First, set the plate thickness schedule hi in the draft schedule setting device DS. Here, if the system configuration is such that the draft schedule is calculated based on h ₀ and h ₅ as described above, the draft schedule setting device has a plurality of representative h ₀ ,
A memory is provided that stores representative plate thickness schedules for each combination of h ₅ , and when h ₀ and h ₅ are input, representative h ₀ and _h that correspond to or approximate the combination of h 0 and h ₅ are set. Read out the plate thickness schedule for the combination of ₅ from the memory and use it as the required plate thickness schedule, or use the plate thickness schedule obtained by approximate calculation using a plurality of read-out plate thickness schedules as the required plate thickness schedule, This is a calculator
Output to SP. Arithmetic unit SP calculates the rotation speed of each mill motor MMi. This calculation is basically based on equation (2), but is actually performed using equation (3) below, which represents equation (2) in more detail. Ni=k/hi・(1+fi)・Rwi・gi…(3) However, K=k/Rwi・gi Rwi: Roll diameter gi: Gear ratio between mill motor MMi of the i-th stand STi and the roll Rwi is Each time the roll is changed, the diameter of the roll installed in the i-th stand is set in the calculator SP using a setting device (not shown). The advance rate fi is the rolling schedule of the i-th stand, that is, the inlet side plate thickness hi-l, the outlet side plate thickness
Calculator SP based on hi, board width, rolling reduction ratio of the i-th stand, total rolling ratio up to the i-th stand, material, etc.
The prediction calculation is performed by storing a fi table corresponding to the rolling schedule.
The adaptive value may be calculated by interpolation or extrapolation, or a simple linear equation regarding fi using the rolling schedule may be prepared and calculated using this. After calculating the rotation speed Ni of each stand as described above, the calculator SP calculates the rotation speed ratio (or rotation speed ratio) SSRHi of the mill motor of each stand based on this with respect to the maximum value of Ni. Calculate as follows. The ratio of the rotation speed of the mill motor calculated in this way is output to the calculator SRHi for each stand and set here, as well as the speed fine adjustment device.
Also output to FCi. The speed reference value generator MRH is operated when accelerating and decelerating all stands, and its output value, that is, the speed reference value, is generated by the calculator SRHi of each stand.
Output to the nominal speed fine adjuster FCi, and the calculation unit SRHi
multiplies the input value from the speed reference value generator MRH by the input value SSRHi from the calculator SP, and outputs the product as a speed command to the automatic speed control device ASRi. The configuration of the automatic speed control device ASRi will be explained in detail later, but this device is
The rotational speed of MMi is detected in an analog manner by a tachogenerator, and the rotational speed is controlled to match the speed command value. In addition, Mai in the figure
indicates the manual operation signal given to the computing unit SRHi, allowing manual intervention by the operator. On the other hand, the number of output pulses of the pulse generator PGi, which emits a number of pulses proportional to the number of rotations of the mill motor MMi, is calculated by the speed fine adjustment device FCi for a predetermined time, thereby detecting the actual number of rotations of the mill motor MMi. The fine adjustment device FCi calculates the product of the rotation speed ratio SSRHi inputted from the calculator SP and the speed reference value inputted from the speed reference value generator MRH, that is, the speed command value (target value) of the mill motor.
This is compared with the actual rotation speed, and if the two differ, the amount of change ΔSSRHi in the rotation speed ratio SSRHi required to realize the target value is calculated, and this is output to the calculator SRHi. Calculating ΔSSRHi can be done by correcting the error signal proportional to the absolute rotational speed when detecting the rotational speed, or by preparing a calibration curve for the analog speed detector of the automatic speed controller ASRi in advance and calculating the total rotation at that time. A method may be adopted in which the amount of correction is calculated based on the speed and the error signal. In this way, by providing a means to digitally detect the rotation speed of the mill motor and using the detection result for rotation speed control, a decrease in control accuracy due to detection errors of the analog speed detection means of the automatic speed control device can be avoided. This can be improved by supplementing. As described above, the mill motor rotation speed before sheet threading is accurately set. In addition, when calculating the above equation (2) or (3), Ni
It is conceivable that the prediction accuracy of the advanced rate fi affects the calculation accuracy of . However, the absolute value of the advance rate fi is less than 10% in normal rolling, and fi is used in the form (1+fi) in both formulas. Therefore, it is easy to reduce the calculation error of (1+fi) to a few percent or less. In other words, if fi is obtained as described above without using a large-scale processor, the mill motor rotation speed Ni can be obtained with the required accuracy. Now, if we look at the relationship between the rotation speed of the mill motor and the plate thickness, we can see that the rotation speed is accurately controlled and N ₁・h ₄・(1
+f ₁ )=N ₂・h ₂・(1+f ₂ )…=N ₅・h ₅・(1+f ₅ )
If hi (in the example, the X-ray thickness meter
Even if h ₁ ) measured at X ₁ is controlled so as to fall within the target value, the finished plate thickness h ₅ will not fall within the target value. Therefore, as mentioned above, the exact rotational speed Ni
By setting , the above-mentioned relationship is established and the control accuracy of the finished plate thickness _h5 is improved, but there is a factor that disturbs this relationship when the coil tip is bitten and reduces the control accuracy. This is the drooping characteristic of the automatic speed controller ASRi. The droop characteristic refers to a control characteristic in which the rotation speed of the mill motor should be reduced in proportion to the increase in the mill motor current, with the aim of stabilizing the tension between the stands, and is essential for motors with automatic speed control. Even in motors without automatic speed control, there is a phenomenon called IR drop, which is essential for stabilizing the motor speed. However, while the current of the mill motor set as described above and rotating before threading is minute,
When the tip of the coil gets caught in the roll during sheet passing, the current increases rapidly and the rotational speed decreases. In other words, even if the settings before threading are made correctly, during threading,
Furthermore, such a situation occurs during subsequent acceleration, or conversely, during deceleration, resulting in off-gauge. The gist of the present invention is to eliminate this inconvenience,
This will be explained in detail below. FIG. 3 shows the rotation speed control system of the mill motor during sheet threading. In the figure, T ₁ , T ₂ , T ₄ are inter-stand tensions T ₁ , ₂ ,
This is a tension meter for detecting T ₂ , ₃ , T ₃ , ₄ , T ₄ , ₅ respectively, and the detected tension values are given to the lowering position control system of stands ST ₂ to ST ₅ and MG ₂ to _{MG 5} , respectively. , and also the rotation speed control circuit for stands ST ₂ to ST ₅ SC ₂ to _{SC 5}
I am trying to give it to each person. The output of the load meter P ₁ for detecting the rolling load of stand ST ₁ is given to the absolute value gauge meter GM, and this gauge meter GM also receives information from the rolling position S ₁ of stand ST ₁ and the X-ray thickness meter X ₁ . The stand ST ₁ exit side plate thickness h ₁ of the stand ST 1 is given, and furthermore, the stand ST ₁ exit side plate thickness 1 is given a target value ₁ , and based on these input data, the reduction position setting device SCR ₁ of the stand ST ₁ is controlled to set h ₁ to ₁ . . X
The output of the wire thickness gauge X ₁ is further provided to the automatic speed control device ASR ₁ for feedforward control, and is also provided to the reduction position control system MG ₂ of the stand ST ₂ . Further, the output of the X-ray thickness gauge _X5 is provided to the reduction position control system _MG5 and automatic speed control system _ASR5 of the stand _ST5 for feedback control. Further, the output of the pulse generator PGi is supplied to the rotation speed control circuit SCi. Instead of the pulse generator PGi, the output of an analog speed detection means such as a tachometer may be applied to the rotation speed control circuit SCi. FIG. 4 is a block diagram showing the main parts of the automatic speed control device ASRi and the rotation speed control circuit SCi. The speed command value Qa from the above-mentioned arithmetic unit SRHi (see Figure 2) is given as an addition element (or minuend element) to the addition circuit ADD of this device ASRi, and from the tachogenerator TGi connected to the mill motor MMi. The detected speed value Qb is given as a subtraction element (or subtraction element), basically Qa－Qb
is given to the proportional-integral control circuit PI, the control circuit PI controls the drive of the DC generator DCG, and its output drives the mill motor MMi, so that Qa-Qb=0
However, we are trying to perform the necessary control,
A droop characteristic block Droop is provided, and the current of the generator DCG, that is, the current of the mill motor MMi, is given as control information, and the output Qc, which changes in size depending on the magnitude of this current value, is given as a subtraction element to the adder circuit ADD. . Therefore, when carrying out the method of the present invention, the rotation speed control circuit SCi is provided,
This circuit SCi is the output Qc of the droop characteristic block Droop.
and the inter-stand tension Ti-1,i are used as input data. Then, the rotation speed control circuit SCi outputs a control signal Qd (=-Qc) to cancel Qc to the addition circuit ADD of the automatic speed control device ASRi. That is, in this invention, the output Qc of the droop characteristic block Droop is given to the adder circuit ADD, thereby stabilizing the speed of the mill motor MMi. Then, the rotation speed control circuit given the output Qc of the droop characteristic block Droop gives a control signal Qd (=-Qc) to the automatic speed control device ASRi, and after stabilizing the speed described above, the mill motor
It adjusts the MMi's rotation speed to the set value.
Next, we will explain in detail the functions of Qc and Qd.
The output Qc of the droop characteristic block Droop responds immediately when the load (for example, tension) changes suddenly and activates the droop characteristic to prevent material breakage. this
If Qc is output steadily, plate thickness fluctuations will remain constant, so the rotation speed control circuit SCi outputs Qd in order to gradually offset Qc. As a result, no steady plate thickness deviation remains. In other words, the above-mentioned control is realized such that the drooping characteristic operates in response to sudden load fluctuations, and the motor speed control does not generate the drooping characteristic in steady state. In this example, the inter-stand tension Ti−1,
This Qd is output only when i does not deviate from the upper and lower limits of the allowable range. That is, when the tension exceeds the upper limit, the tension is increased further, and conversely, when the tension falls below the lower limit, the tension is not controlled to be reduced any further. In addition, the control of this rotation speed control circuit SCi is not limited to the time of sheet threading, but it goes without saying that the same function can be achieved even when the tension between the stands changes to the extent that it deviates from the upper and lower limit values, such as during acceleration and deceleration. . If the tension between the stands deviates from the upper or lower limit of the allowable range, the lowering position will be adjusted, but if it exceeds the upper limit, the lowering motor will be driven for a certain period of time to lower the downstream stand lowering position. On the other hand, if the value falls below the lower limit, the lowering motor is driven for a certain period of time in order to raise the lowering position of the upstream stand. When the speed setting method described above is used, abnormal tension normally occurs due to a setting error in the reduction position, so this control can deal with the abnormality in the reduction setting. FIG. 5 shows the variation in the thickness of the coil top section (actual value of the thickness _h5 at the exit side of the mill using an X-ray thickness meter _X5 ) when the sheet is threaded by the method of the present invention as described above.
The rolling conditions are shown in Table 1. As is clear from FIG. 5, in the case of the present invention, the off-gauge part of the coil top can be shortened, and the conventional off-gauge part, which was approximately 50 m, is shortened to 10 m or less, and the yield is improved accordingly. become. In this way, when using the method of the present invention, the control of the rotation speed of the mill motor is related to the drooping characteristics of the motor.

[Table] As a result, it is possible to improve the accuracy of sheet thickness control in acceleration and deceleration during sheet threading, shorten the off-gauge parts at the top and bottom of the coil, and improve yield.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a row of cold tandem mills to which the method of the present invention is applied, Fig. 2 is a block diagram showing the rotation control system during setup of this cold tandem mill, and Fig. 3 is a diagram showing the rotation control system during sheet passing. Fig. 4 is a block diagram showing the rotation control system, Fig. 4 is a block diagram of the rotation speed control circuit and the main parts of the automatic speed control device, and Fig. 5 is a longitudinal plate thickness distribution diagram of the coil top portion showing the effect of the method of the present invention. . ASRi...automatic speed control device, SCi...rotation speed control circuit, Ti...tension meter, PGi...pulse generator,
SRHi…Arithmetic unit.

Claims (1)

[Claims] 1. In a cold tandem mill equipped with a speed control device that is provided to control the rotation speed of a mill motor that drives rolling mill rolls and performs droop characteristic control that reduces the rotation speed in response to an increase in mill motor current. , while detecting the inter-stand tension, detects a control signal for controlling drooping characteristics, and outputs a signal to cancel the control signal when the detected value of the inter-stand tension is within a predetermined tolerance range. A mill motor rotation speed control method characterized in that the rotation speed is applied to a speed control device.