JPH1030128A - Method for controlling tension of strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling the tension of a strip which can uniformly control the tension of the strip as much as possible in a continuos heat treatment furnace. SOLUTION: This method for controlling the tension of a strip is to uniformize the tension distribution of the strip 4 by controlling the number of revolutions of a bridle roll at the outlet in the continuous heat treatment furnace so as to coincide with line speed and controlling the number of revolutions of a bridle roll at the inlet of the furnace so that the detected tension of the strip 4 at the inlet of the furnace coincides with the tension preset value, and further, controlling the number of revolutions of hearth rolls 3 in the furnace based on each strip tension detected at the inlet and the outlet of the furnace. In such a case, the number of revolutions of each hearth roll 3 arranged on the furnace is corrected with a speed set value in proportion to the tension difference of the strip 4 at the inlet of furnace and at the outlet of furnace and the output of a driving motor 2 for hearth roll, and also, a cascade control of the speed correction to each hearth roll section is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the tension of a strip moving in, for example, a horizontal continuous annealing furnace in a steel process line as uniformly as possible.

[0002]

2. Description of the Related Art For example, a method for controlling the tension of a strip in a continuous annealing furnace is disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 60-1.
As proposed in Japanese Patent No. 38018, the rotation speed of the hearth roll is controlled so that the difference in tension between the strip at the furnace inlet and the strip at the furnace outlet is reduced. Specifically, when the tension difference is within the allowable range, the rotation speed of the hearth roll is kept as it is, and when the tension difference exceeds the allowable range, the rotation speed of the hearth roll is increased to a predetermined ratio (for example, 2 to 3%). Or the rotation speed of the second hearth roll is gradually increased by a predetermined ratio (for example, 2 to 3%) while keeping the rotation speed of the hearth roll on the entrance side unchanged. Or after increasing the rotation speed of the hearth roll on the inlet side at a predetermined ratio (for example, 2 to 3%), and further increasing the rotation speed of the second and subsequent hearth rolls at a predetermined ratio (for example, 2 to 3%). The speed is gradually increased step by step.

In Japanese Patent Application Laid-Open No. 5-156371, an optimum correction value of a strip is calculated from a catenary sensor and a load cell installed in an annealing furnace, and the rotation speed of the hearth roll is controlled by the correction value, thereby making the inside of the furnace easier. A method for controlling tension is described. Specifically, the catenary sensor measures the distance to the strip, and calculates the strip tension value from the amount of the catenary using a computer. On the other hand, the load cell is used as a tension meter to directly calculate the strip tension value. Then, the calculated value is compared with the strip tension value calculated from the catenary amount by the computer, and the optimum correction value of the strip in the furnace at that time is calculated, and the rotation speed of the hearth roll of each section is calculated based on the correction value. Is controlled.

Further, in Japanese Patent Application Laid-Open No. 5-271789,
The rotation speed of the hearth roll is controlled so that the difference in strip tension between the furnace inlet and the furnace outlet is reduced, and the degree of expansion and contraction of the strip at each hearth roll and the roll diameter difference between the reference roll and each hearth roll are calculated. Thus, there has been proposed a method of calculating the speed of each hearth roll with respect to a reference speed, and further performing a predetermined tension difference correction to control the rotation speed of each hearth roll.

[0005]

However, the tension control method proposed in Japanese Patent Application Laid-Open No. 60-138018 discloses a hearth roll section calculated by a speed correction coefficient calculator 6 in FIG. Ratio (hereinafter,
Although λ _i is simply set by the method described above, it is difficult to correct unevenness in tension between hearth roll sections.

If the speed of each hearth roll 3 is uniformly corrected, as shown in the furnace tension distribution of FIG.
This is because fluctuations in the furnace tension concentrate on the hearth roll 3 on the inlet side. Japanese Patent Application Laid-Open No. 60-138018 does not disclose any method for determining the speed correction when the speed is sequentially increased step by step. However, even if the speed command signal is changed at a predetermined ratio in a stepwise manner, This is because the tension between the hearth roll sections becomes uniform or non-uniform depending on the ratio. 4 and 5, 1 denotes a hearth roll speed control device, 2 denotes a hearth roll drive motor, 4 denotes a strip, and 5 denotes a hearth roll speed calculator.

In the tension control method described in Japanese Patent Application Laid-Open No. 5-156371, a correction amount is determined by using a load cell installed in an annealing furnace and a measurement value from a catenary sensor. And the correction method is also described in Japanese Patent Laid-Open No. 60-138.
Since there is no difference from the method proposed in No. 018, fluctuations in the furnace tension are concentrated on the hearth roll on the inlet side as shown in FIG.

In the control method proposed in Japanese Patent Application Laid-Open No. 5-271789, the correction value of the hearth roll speed is calculated based on the temperature change of the strip, but the hearth roll speed is corrected. In addition, the correction method is not different from the method proposed in the above-mentioned Japanese Patent Application Laid-Open No. 60-138018, so that the variation in the furnace tension concentrates on the hearth roll on the inlet side as shown in FIG.

[0009] Therefore, in the case of low-strength control of the strip, such as ultra-low carbon steel material whose width is problematic in high-temperature annealing, the unevenness of the tension distribution in the annealing furnace cannot be neglected. A control method that can make the tension distribution in the furnace uniform is required, but it is difficult to make the tension distribution uniform with the above-described conventional control method.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. In correcting tension distribution between hearth roll sections using tension detectors at the entrance and exit of an annealing furnace, It is an object of the present invention to provide a method for controlling the tension of a strip which can make the tension distribution as uniform as possible.

[0011]

In order to achieve the above-mentioned object, in the method for controlling the tension of a strip according to the present invention, the rotation speed of each hearth roll installed in a continuous heat treatment furnace is controlled by:
In addition to correcting the difference between the strip tension at the furnace inlet and the furnace outlet and the speed setting value proportional to the output of the hearth roll driving device, the speed correction to each hearth roll section is cascaded. By doing so, the strip tension distribution in the continuous heat treatment furnace can be made as uniform as possible while preventing mutual interference between adjacent hearth roll sections.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The strip tension control method of the present invention controls the rotation speed of a bridle roll at the furnace outlet in a continuous heat treatment furnace so as to match the line speed, and also detects the detected strip tension at the furnace inlet in advance. Controls the rotation speed of the bridle roll at the furnace entrance to match the set tension setting value, and additionally controls the rotation speed of the hearth roll in the furnace based on the respective strip tension detected at the furnace inlet and furnace outlet By doing so, in the strip tension control method for equalizing the tension distribution of the strip, the rotation speed of each hearth roll installed in the furnace, the difference between the strip tension at the furnace inlet and the furnace outlet and the hearth roll drive device Compensates with the speed set value proportional to the output and cascade controls the speed compensation for each hearth roll section It is the gist of the door.

That is, the strip tension control method of the present invention provides a speed correction signal to be applied to each hearth roll section in proportion to the output of a hearth roll speed control device that drives each hearth roll section.
The purpose is to make the tension distribution of the strip in the continuous heat treatment furnace as uniform as possible. Hereinafter, the concept will be described with reference to FIG.

The hearth roll speed control device 1 is provided with a drooping characteristic (droop) of a few percent that can maintain the necessity and stability of the speed controllability. Assuming that the rotation speed of the hearth roll drive motor 2 is N and the torque is τ, the droop amount γ of the rotation speed N of the hearth roll drive motor 2 is defined as in the following Expression 1.

[0015]

Γ = ΔN / Δτ

Accordingly, the relationship between the rotation speed N and the torque τ in the stable region of the hearth roll drive motor 2 is expressed by the following equation (2).
Can be expressed as

[0017]

[Equation 2] N = N ₀ −γ · τ where N _{0 is the} rated speed

Next, hearth rolls section consisting of n _i stand hearth rolls 3 (i) [i = 1, 2, ..., m-
1, the relationship between the rotational speed N _i and the torque tau _i hearth roll driving motor 2 _i in m] can be expressed as Equation 3 below.

[0019]

N _i = N ₀ − (γ / n _i ) τ _i

Further, hearth roll speed control device 1 _i is n _i stand hearth rolls 3 of hearth rolls section (i)
Is given by n when the torque margin is α.
_i · τ (1 + α), the relationship between the rotation speed _Ni and the torque τ _{i in} the hearth roll speed control device 1 _i can be expressed as the following Expression 4.

[0021]

N _i = N ₀ −γ · τ _i / {n _i · (1 + α)}

[0022] Here, diameter D _i of the hearth rolls 3 _i, the gear ratio g _i of the reduction gear, not shown, the speed margin When beta, the circumferential speed v _i of hearth rolls 3 _i, the following equation 5 Can be expressed as

[0023]

[Number 5] _{v i = π · D i ·} g i · N i (1-β)

Here, when Equation 5 is substituted into Equation 4, it can be expressed as Equation 6 below.

[0025]

[6] _{v i = π · D i ·} g i · (1-β) × [N ₀ -
γ · τ _i / {n _i · (1 + α)}]

[0026] Thus, droop amount of circumferential speed v _i of hearth rolls 3 _i in the hearth roll speed control device 1 _i gamma '
_i can be expressed as in the following Expression 7.

[0027]

Equation 7] _{γ 'i = π · D i} · g i · (1-β) γ / {n
_i · (1 + α)｝

By the way, hearth roll section (i)
, The length of the hearth roll section (i)
L _i , assuming that the output of the hearth roll speed control device 1 _i is p _i , the following equation 8 holds for the tension deviation ΔT _i generated in the hearth roll section (i).

[0029]

[Equation 8] _{L i αn i αp i ατ i} αΔT i

Accordingly, the tension deviation ΔT _in the furnace can be expressed by the following equation 9 when the tension of the strip 4 at the furnace inlet is T _in and the tension of the strip 4 at the furnace outlet is T _out .

[0031]

(Equation 9)

Here, from the relationship of Expression 8, Expression 9 can be expressed as Expression 10 below.

[0033]

(Equation 10)

When this equation (10) is converted into a motor torque, it can be expressed as the following equation (11).

[0035]

Δτ _i = (D _i / 2g _i ) ΔT _i

[0036] Therefore, Equation 7 described above, the speed correction amount Delta] v _i on calculation in hearth rolls sections from equations 10 and Equation 11 (i) can be expressed as following Equation 12.

[0037]

(Equation 12)

However, since the speed correction to the hearth roll 3i in the hearth roll section (i) is a disturbance to the adjacent hearth roll sections, it is performed as follows to prevent mutual interference. For example, if the speed correction to the hearth roll 3 is performed from the hearth roll section (m) at the furnace outlet, the actual speed correction amount Δv _i ′ in the hearth roll section (i) is expressed by the following equation (1).
Perform as in 3.

[0039]

[Number 13] _{Δv i '= Δv i + Δv} i + 1 + ... + Δv m

That is, the cascade control as shown in FIG. 1 is performed. By performing such a cascade control, the fluctuation in the furnace tension causes the hearth roll 3 on the inlet side to change.
As shown in FIG. 2, it is possible to obtain a furnace tension distribution as uniform as possible without concentrating on the furnace.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for controlling the tension of a strip according to the present invention will be described below with reference to an embodiment shown in FIGS. FIG. 1 is an explanatory view of a main part of a control block of a method for controlling the tension of a strip according to the present invention when applied to a horizontal annealing furnace, and FIG.
FIG. 3 is a control block diagram of a method for controlling the tension of a strip according to the present invention when applied to a horizontal annealing furnace.

Reference numeral 11 denotes a horizontal annealing furnace which performs continuous annealing in a processing line for a surface-treated strip in order to improve the strip characteristics. The strip 4 guided to the annealing furnace 11 has a furnace outlet bridle roll 14 whose rotation speed is controlled by an outlet speed control device 12 which outputs a control signal to a drive motor 13 in accordance with a line speed reference signal, and a hearth roll. The hearth roll 3 whose rotation speed is controlled by a hearth roll speed control device 1 which outputs a control signal to a hearth roll drive motor 2 according to a speed command signal, and the drive motor 15 which is controlled according to a furnace entrance bridle roll speed command signal Inlet speed control device 16 that issues a signal
Inlet bridle roll 1 whose rotation speed is controlled by
7 transported.

The hearth roll 3 is composed of a plurality of (eight in the embodiment shown in FIG. 3) hearth roll sections. One hearth roll section is composed of a plurality of hearth rolls 3 and one hearth roll. It is controlled by the speed control device 1.

Reference numeral 18 denotes a tension detector disposed at the entrance of the annealing furnace 11, reference numeral 19 denotes a tension detector disposed at the exit of the annealing furnace 11, and the tension detector 18 includes a tension control device 20 and a hearth roll speed calculator. 5 and the tension detector 19 outputs an electric signal to the hearth roll speed calculator 5 in proportion to the detected tension.

That is, first, when the tension detector 18 disposed at the entrance detects the tension of the strip 4, the detection signal is transmitted to the tension controller 20 and the hearth roll speed calculator 5.
Is output to Then, the tension control device 20 outputs the detection signal to the entrance speed control device 16 so as to be equal to the tension command signal, and controls the rotation speed of the furnace entrance bridle roll 17.

More specifically, in the tension control device 20 to which the deviation between the tension detection signal at the furnace inlet and the tension command signal of the strip 4 is input, a speed correction signal based on this difference is added to the speed reference signal to add a speed reference signal. A speed command signal for the bridle roll 17 is created and output to the inlet speed control device 16.
This is controlled so that 7 rotates according to the speed command.

In this state, when a deviation ΔT occurs between the tension of the strip 4 at the furnace entrance and the tension of the strip 4 at the furnace exit, the hearth roll speed calculator 5 calculates the deviation in the section ratio equation in the above-mentioned equation (12). Therefore, it is distributed to the speed correction coefficient calculator 6 of each hearth roll section. At this time, since all the hearth rolls 3 are connected by the strip 4, if the speed of the hearth roll 3 of one hearth roll section is corrected, the hearth roll 3 of another hearth roll section acts as a disturbance. Become.

Therefore, in the present invention, when the speed of the hearth roll 3 in a certain hearth roll section is corrected in order to prevent the above-mentioned mutual interference, the hearth at the upstream side (furnace inlet side) of the hearth roll section is required. All the speeds of the hearth roll 3 in the roll section are to be corrected.

That is, the hearth roll section (8)
Is input to the adder of the hearth roll section (7), and is output from the adder of the hearth roll section (7) to the hearth roll 3 in the hearth roll section (7). A series of additions of inputting the speed correction signal to the adder of the hearth roll section (6) is performed up to the hearth roll section (1) (cascade control).

The speed correction signal of the hearth roll 3 obtained in this manner is added to the line reference signal, and becomes a speed command signal of the hearth roll 3 via the hearth roll speed control device 1. By performing the cascade control as described above, the strip 4 can obtain a furnace tension distribution as uniform as possible without being concentrated on the hearth roll 3 on the inlet side, as shown in FIG.

Incidentally, when the above-described method for controlling the tension of the strip of the present invention was carried out in a thin sheet annealing line, the tension in the furnace was about 70 kg (0.2 kg / m).
Up to about m ² ), stable tension control was possible.
In this case, the difference between the strip tension at the furnace inlet and the strip tension at the furnace outlet was about ± 4 kg at the maximum.

Although omitted in the above description, when a new correction using the furnace temperature in each hearth roll section, the temperature in each hearth roll section of the strip 4, etc. is added to the speed correction signal of the hearth roll 3, These may be input to the hearth roll speed calculator 5 and the hearth roll speed calculator 5 may correct them.

[0053]

As described above, according to the strip tension control method of the present invention, strip tension control in a continuous heat treatment furnace can be controlled as uniformly as possible.
When processing a very low carbon steel material at a high temperature, it is possible to effectively prevent the width cut caused by excessive tension in the furnace. In addition, the strip tension control method of the present invention has a great effect on strips that need to be conveyed in a furnace with extremely low tension and uniform tension, such as electromagnetic strips.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a main part of a control block of a strip tension control method according to the present invention when applied to a horizontal annealing furnace.

FIG. 2 is a diagram showing the tension distribution in the furnace in FIG.

FIG. 3 is a control block diagram of a strip tension control method according to the present invention when applied to a horizontal annealing furnace.

FIG. 4 is an explanatory view of a main part of a control block of a conventional strip tension control method when applied to a horizontal annealing furnace.

5 is a diagram showing the tension distribution in the furnace in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hearth roll speed control device 2 Hearth roll drive motor 3 Hearth roll 4 Strip 5 Hearth roll speed calculator 6 Speed correction coefficient calculator 11 Horizontal annealing furnace 14 Furnace outlet bridle roll 17 Furnace inlet bridle roll

Claims (1)

[Claims] In the continuous heat treatment furnace, the number of revolutions of the bridle roll at the outlet of the furnace is controlled to match the line speed, and the detected tension of the strip at the inlet of the furnace coincides with a preset tension set value. Uniform strip tension distribution by controlling the number of rotations of the bridle roll at the furnace inlet and controlling the number of rotations of the hearth roll in the furnace based on the respective strip tensions detected at the furnace inlet and the furnace outlet. In the method for controlling the tension of the strip, the rotation speed of each hearth roll installed in the furnace is corrected with a speed set value proportional to the difference between the strip tension at the furnace inlet and the furnace outlet and the output of the hearth roll driving device, A tension control method for a strip, comprising: cascading control of speed correction to each hearth roll section.