KR820001086B1 - Automatic control method of steel tube thickness - Google Patents

Abstract

In manufacturing the welded steel tube, the strip thickness is continuously measured by the instrument at the entrance of the pinch roll (5, 8) and the heating furnance (11). The thickness signal (49') measured by the instrument is retarded with the line speed from the measuring point to the rolling stand. The number of rotations is sought from the delayed thickness signal, the pre-fixed standard signal, the fixed number of the controlled rolling stand and the standard signal of the rotational frequency. The rate of rotation controls the rotational frequency of all kinds of the controlled rolling stand.

Description

Automatic control of thickness of single welded steel pipe

1 is a schematic view of a continuous production line of cut steel pipe.

2 is a graph showing a change curve of the number of revolutions of each stand.

3 is a schematic diagram of a mill motor speed control system.

4 is a block diagram showing an example of a synchronization delay device for thickness deviation signals.

The present invention relates to a method for automatically controlling the thickness of a single welded steel pipe.

In order to control the product pipe thickness of conventional single-tube steel pipes, it is possible to directly measure by micrometer after rolling, cutting, cooling, ear picking, or by converting the predetermined number to the thickness after rolling and cutting cooling. Based on the obtained product tube thickness information, the operator tried to control product tube thickness uniformly by changing rolling conditions.

However, due to the large time delay between the control point and the measurement point, accurate thickness control was not possible. Moreover, there was a drawback that the change of the thickness occurring in a short time could not be dealt with, and if the rolling conditions were excessively changed, the operation would be incorrect.

SUMMARY OF THE INVENTION In view of this, an object of the present invention is to provide a method of controlling the thickness of a product pipe constantly by automatically reducing or eliminating the effect of strip thickness variation on the thickness fluctuation in the longitudinal direction of the product pipe in a continuous production line of single-piece steel pipe. To provide.

That is, the gist of the present invention continuously measures the thickness of the strip traveling between the inlet to the rolling mill inlet with a pinch installed in the front of the heating furnace in the thickness control method of the single welded steel pipe by a thickness measurement system. The thickness signal measured by this thickness gauge is synchronously delayed from the measuring point to the rolled steel control stand with the line spoid, so that this synchronous delayed thickness signal is changed by the AGC individual with respect to the thickness change of the inlet side of the rolling mill. The ratio is determined, and the compensation ratio of each stand is controlled by maintaining the motor load rate of each stand by the stand distribution gain, and the thickness variation caused by the thickness variation of the thick plate strip is changed during the thickness variation in the longitudinal direction of the tube. The thickness control of the single-piece steel pipe characterized in that the control.

Hereinafter, the present invention will be described in detail with reference to the embodiments illustrated in the drawings.

1 shows an overview of an embodiment of the invention.

The strip coil is unwound by the uncoiler 1, corrects the habit of being wound by the leveler 2, and is a cutter of 3, and after cutting the front and back of the coil, a flash butt welder 4 By connecting the coil end and the rear end by the endless. The strip 35 passes through the first pinch roll 5 and the magnet roll 6 to the roof floor 7, and the front of the furnace 11 whose speed is synchronized with the inlet of the mill 12, which is a rolling mill. It enters into the heating furnace 11 through the 2nd pinch roll 8 installed in the inside. Just before the strip 35 enters the heating furnace 11, a thickness measuring system 10 such as an X-ray type or a capacitive type is provided. The thickness of the traveling coil is continuously measured, and the measurement result is measured by a speed detector. and (9) Therefore, the thickness gauge 10 to a speed signal from a distance of L _m and the rolling mill, the line speed by the synchronization delay sent to a router milmo control system (16). The mill motor control system 16 changes the speed of each stand motor in accordance with the AGC system, which is a preset AGC system and a stand distribution system, which is proportional to the amount of deviation in the reference value of the strip thickness, but will be described later in detail. . In the figure, reference numeral 13 denotes a tube velocity detector, 14 a rotary saw, and 15 a molding machine. Since these configurations are not directly related to the present invention and are conventionally known, detailed descriptions thereof will be omitted. As mentioned above, in order to control the thickness of a pipe | tube, the factor which fluctuates thickness must be considered first. This is because, if these factors are consciously changed, the thickness naturally changes and is controlled accordingly.

Thus, the present inventors obtained the relationship between the stand rotation speed N and the thickness t as described below. Before and after the i-th stand of a continuous rolling mill such as a single-stage steel tube mill, the following equation is established.

Di is the average of the pipe inner diameter and outer diameter

t _i is the pipe thickness

V _i is the pipe velocity

The subscript i stands for the i th entry.

In the case where the thickness change Δt _i-1 of the incoming pipe exists, the pipe velocity Vi may be differentiated as follows in order to maintain a constant foot thickness.

(Except change of Di)

If the pipe velocity V _i is not changed, the change Δt _i of the thickness coming out is given by the following equation.

Moreover, there is the following relationship between the roller rotational speed N _i of the i-th stand and the outgoing pipe speed.

Where R _i is the average of the minimum and maximum diameters of the roll, and a _i is the coefficient between the roll speed and the exit speed.

This coefficient a _i is called the advance rate in general rolling, and is a ratio of the roll circumferential speed and the exit speed, and when the roll speed (roll speed) becomes large, the advance rate decreases, and the roll speed decreases. The rate of advance is large, and the rate of change of the coefficient a _i is smaller than the rate of change of the roller rotational speed N _i .

Differentiating the expression (4)

는 상기의 로울회전 N과 계수 a_i의 관계에서 -1과 0과의 사이값으로 된다.It becomes In this formula (5),

Is a value between -1 and 0 in the relationship between the roll rotation N and the coefficient a _i .

In the single-piece steel tube rolling mill which is the object of the present invention, this value is in the range of -0.15 to -0.9, and becomes substantially constant for each stand under the same rolling conditions.

so

Put it on,

It becomes In (2) and (7),

It becomes In the above formula (8), if there is no speed change of the upstream stand than the i-stand,

(t ₀ is the thickness of the mill inlet)

Is established. Therefore, with respect to the amount of change Δt ₀ of the thickness of the mill inlet side. changing the speed roll in the i stands by to maintain the dukkeeul certain value on the side of coming out of the i stands may be seen that by changing the number of revolutions the roll of the i stands N _i by ΔN _i according to the above (9) formula .

In this case, if the stand rotational speed of the i stand is changed, the tension between each stand on the downstream side of the i stand is changed to affect the final thickness of the mill exiting side. Each stand on the downstream side of the stand must also change the roll speed corresponding to the amount of change in the rotation speed of the i-stand.

The correction amount of the rotational speed of the downstream stand (k stand) for this tension variation correction is calculated as follows.

In the formula (1)

In (7)

If you substitute equation (7) and equation (11) into equation (10),

이므로It becomes In the formula (9)

Because of

It becomes Therefore, by changing the rotational speed of the stand in accordance with the change amount Δt ₀ of the plate thickness of the mill, and modifying the rotational speed of each stand downstream from the i-stand according to the above formula (13), It can be seen that the final thickness of the exit side of the mill can be controlled even if there is a change in the thickness of the entering side.

However, the above-described one main stand can be used when the amount of change in the plate thickness of the mill is small when Δt ₀ is small, but when Δt ₀ is relatively large, the amount of change in the rotational speed of the stand is too large and stable. There is a problem, and it is difficult to absorb the variation in thickness with one stand.

Thus, in the present invention, a plurality of stands are controlled as main controller stands.

The change of the number of revolutions when controlling a plurality of stands as main controller stands is as follows.

For example, the case where the m side stand from the i stand to the (i + m-1) stand in the stand row is used as the main stand will be described. together

Is obtained. By changing the expression (14)

로 하면From here

If

It becomes Where b _j is the ratio of the rate of change of the plate thickness of the entering side of the mill to the rate of change of the plate thickness of the entering side of the _j . It is a value determined by sharing. For example, suppose that m = 3 and compensate one-third of the rate of change Δt ₀ / t ₀ of the side plate thickness entering each of the three stands, i stand, (i + 1) stand, and (i + 2) stand. b _i = 1/3, b _i +1 = 2/3, and b _i +2 = 3/3. In other words, b _j is that the stand on the downstream side of the plurality of main controller stands is always larger than the upstream stand, and is 1 in the lowest stand. Therefore, in the case where a plurality of stands are used as the main controller stands, the compensation rate for each stand is determined, and then the roller rotation speed of each stand may be changed at the same time according to the equation (15). Also in this case, of course, the rotational speed correction for correcting the tension fluctuation of the following stand is made. In practical control, the constant k _j average value of each m stands,

To obtain, using this integer k _m ,

Transform to

은 m개의 스탠드를 주제어 스탠드로 하여서 파이프두께를 제어할 경우에 밀의 들어가는 쪽 판두께 편차에 대하여 m개의 스탠드로서 어느정도의 로울회전수를 변경시키면 될 것인가의 기능을 표시하는 것으로서, 본 발명에 있어서는 이것을 AGC계인이라고 한다.In formula (17),

In the present invention, "m" stands for the function of changing the number of revolutions of the roll as m stands for controlling the pipe thickness by using m stands as main controller stands. It is called AGC seal.

는 m개의 각 스탠드에서 분담하는 보상량의 비율에 상당하는 값이며, 본 발명에 있어서는 이를 스탠드 배분게인 A_j라고 한다.In addition, of (17)

Is a value corresponding to the ratio of the compensation amount shared by each of the m stands, and in the present invention, this is referred to as the stand distribution gain A _j .

By quoting the above formula (17), the thickness of the tube can be controlled as follows.

FIG. 2 shows a change curve of the number of revolutions of each stand in the embodiment of the present invention in which a main stand is the third stand to the fourth stand in a series of stand rows formed of 14 stands.

In this figure, as the series of stands moves from the first stand to the fourteenth stand (of course, the number of these stands can be increased or decreased) in the normal operation state, the roll rotation speed N increases according to the reference curve. Therefore, when there is no fluctuation in the plate thickness of the strip which enters a mill, rolling may be continued according to this reference curve.

In other words, when the delayed thickness deviation signal Δt ₀ / t ₀ is 0, each stand roller revolution curve coincides with the reference curve. However, such a thing rarely occurs, and it is common for a change in the thickness of the strip plate to occur.

That is, the thickness deviation signal Δt ₀ / t ₀ is almost neither positive nor negative, and therefore, thickness control is necessary.

By the way, when the thickness deviation signal is positive (that is, thicker), the roller rotational curve of each stand changes according to the above equation (17) so as to conform to the curve of B ₁ or B ₂ or B ₃ of group B. .

When the thickness deviation signal is negative (that is, thinner), the roller rotation speed is changed in accordance with the equation (17) so as to follow the curve of group A ₁ or A ₂ or A ₃ . If this operation is continued, the thickness of the plate can be constantly controlled.

Next, using the equation (17), the method of actually controlling the thickness of the tube as shown in Fig. 2 will be described in detail.

3 shows a part of the mill motor speed control system 16, which corresponds to one stand motor. Referring to FIG. 3, reference numeral 20 denotes a terminal for inputting a thickness deviation signal Δt ₀ / t ₀ from the thickness gauge 10 of FIG.

이 되며, 이 신호는 승산기(乘算器)(23)로 보내진다.The thickness deviation signal Δt ₀ / t ₀ receives the AGC chain setting from the terminal 20 through the amplifier 21 and the setter 22 which is the AGC chain.

This signal is sent to a multiplier (23).

신호와, 각 스탠드의 스피이드 기준신호 N_j를 곱셈하여

로 하고, 다시 이것은 스탠드 배분계인 설정기(26)로 보낸다. 스탠드 배분계인 설정기(26)는

의 신호에

를 설정하여, 다음의 신호 ΔN_j를 출력한다. 가산점(25)에 있어서는 2개의 신호 N_j와 ΔN_j가 가산된다. 이 가산된 신호 N_j+ΔN_j는 통상의 계자제어(界磁制御)에 의한 속도제어계(27)를 통하여 밀(12)에 설치된 밀모우터(28)에 보내지고, 이것에 의하여 밀모우터(28)의 속도제어를 하게된다.On the other hand, the speed reference signal N _j of each stand enters the terminal 24 through the master leotard (MRH) and the stand speed retarder (SSRH), which are the multipliers 23 and the addition points, respectively. Is sent to (25). Multiplier 23 is input as described above

Signal and the speed reference signal N _j of each stand

This is again sent to the setter 26 which is a stand distribution meter. The setter 26 which is a stand distribution meter

At the signal of

Is set to output the next signal ΔN _j . At the addition point 25, two signals N _j and ΔN _j are added. The added signal N _j + ΔN _j is sent to the mill motor 28 installed in the mill 12 through the speed control system 27 by normal field control, whereby the mill motor 28 Speed control.

Then, the roller rotation speed is changed as shown in FIG. 2 by controlling the speed of the mill motor 28. That is, if ΔN _j is positive, it is changed as B ₁ (or B ₂ , B ₃ ), and if it is negative, it is changed as A ₁ (or A ₂ , A ₃ ).

4 is a block diagram of Embodiment 1 of a synchronization delay device of the thickness deviation signal? T ₀ / t ₀ .

The strip 35 is supplied to the rolling mill 12 through the heating furnace 38 of the preheating furnace 37 (these are collectively referred to as the heating furnace 11 in FIG. 1) to be the product pipe 35. Reference numeral 40 denotes a pass line stabilizing pinch roll provided for the thickness gauge 10 and the pulse generator 43, and 42 denotes a direct current motor for driving the pinch roll 40.

The thickness signal t ₀ + Δt ₀ measured by the thickness gauge 10 becomes the thickness deviation signal Δt ₀ / t ₀ to the Percent converter 45 by the signal t ₀ from the reference thickness setter 44, and then A / It is converted into a digital value in the D converter 46 and supplied to the register 47. Reference numeral 49 denotes a pulse signal of 8 pulses / 2 m supplied from the pulse generator 43.

The calculator 48 stores this signal obtained by dividing the digital thickness deviation signal at a rate of 8 times in 2 m.

Reference numeral 48 denotes an operator, which calculates the average value of the signal read eight times in 2m and sends the operation result to the shift register 50.

The signal 49 'is a pulse signal of 1 pulse / 2m, and shifts the shift register 50 every time the strip 35 advances 2m. The changeover switch 51 is for setting the stand on which the AGC control water of the mill 12 enters, and compensates for the change in the strip length from the measuring point to the operating point. Reference numeral 52 converts a digital signal shifted in the shift register 50 into an analog signal as a D / A converter. The converted analog signal 53 is sent to the terminal 20 of FIG. 3 as a Δt ₀ / t ₀ signal.

Since this invention is comprised as mentioned above, the desired objective of invention was reliably achieved.

In particular, the following two things had a significant effect.

1) The thickness nonuniformity is very small.

Since the whole control is automated and the correction speed is high, in the prior art, even if the thickness nonuniformity of the longitudinal direction of a product pipe | tube became 50 micrometers no matter how much, according to this method, it improved to about 10 micrometers.

2) There is no need for a mill action with respect to thickness.

Since the thickness of the strip while running is continuously measured and synchronized, the number of stand motor rotations of the rolling mill is automatically adjusted, so that no mill action is required. In addition, the operation is automatic, so no operator is required.

By applying the method of the present invention, significant results are obtained in the case where an electrostatic pipe manufacturing process has a stretch reducer, or a stretch reducer in the manufacturing process of a seamless steel pipe.

Claims (1)

In the production process of single welded steel pipe, the thickness of the strip is continuously measured by the thickness gauge between the pinch roll installed at the front of the furnace and the inlet of the furnace, and the thickness signal measured by the thickness gauge is measured from the measuring point to the control rolling stand. The constant of each control rolling stand (AGC) and the angle of the delayed thickness signal, the predetermined reference thickness signal, and the ratio of the speed change on the outgoing side of the pipe to the roll speed change of the control rolling stand. For each control rolling stand that is changed in the control rolling stand and determined by the thickness of the pipe, the number of rotation changes for each control rolling stand is obtained by using the constant (stand distribution) and the reference speed signal of each control rolling stand. The number of rotations of each controlled rolling stand is controlled, and the thickness of the pipe in the longitudinal direction Automatic thickness control method for a steel pipe danjeop, characterized in that to control the thickness variation caused by the thickness variation of the plate strip.

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