JPS6257698B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the tension of a metal strip called a strip in a cooling zone of a continuous heat treatment furnace.

In order to cool the metal strip by winding it around a cooling roll, that is, a rotating body in which a coolant such as water circulates around the inner peripheral surface of the body, in the furnace or at the furnace outlet of a continuous heat treatment furnace for metal strips, the metal strip is cooled. A generally known method is to control the cooling rate of a metal band by changing the winding length of the metal band and the flow rate and/or temperature of the coolant flowing inside the rotating body.

In the above control method, from the viewpoint of control responsiveness, equipment cost, etc., a plurality of the rotary bodies are arranged in parallel in the metal strip transport direction, and every other rotary body is moved, that is, raised and lowered. It is desirable to change the winding length of the metal band around the rotating body, but when the rotating body is moved, the path length of the metal band between adjacent rotating bodies changes, and the tension applied to the metal band changes. Therefore, the moving speed of the rotating body is limited, and the response speed of cooling control is also limited. Furthermore, if the metal band becomes slack due to a change in tension, the cooling itself becomes unstable, and if the tension becomes large, operational problems such as breakage of the metal band or generation of heat buckles are likely to occur.

The present invention calculates the change in the path length of the metal strip between adjacent rotating bodies due to the movement of the rotating bodies (hereinafter referred to as cooling rolls) based on the positional relationship between the two cooling rolls, and uses the calculated results as follows. By correcting the rotational speed of each roll after the most upstream moving cooling roll, changes in the tension of the metal strip due to the movement of the cooling roll can be absorbed, preventing the above-mentioned operational troubles, and improving the movement of the cooling roll. It is designed to increase the speed, and its feature is that multiple rotating bodies through which refrigerant flows in the body are arranged side by side in the direction of metal transport, and a metal band is wrapped around these rotating bodies. In a method for controlling the tension of a metal band in a cooling zone of a continuous heat treatment furnace, the tension between the adjacent rotating bodies is controlled by moving them relative to each other in a direction perpendicular to the metal band transfer direction. The time change dL′/dt of the path length L′ of the metal strip is
Let dL′/dL be the distance in the direction of relative movement.
It is calculated as the product of dL/dt, and the velocity of each rotating body after the most upstream rotating body that has moved relatively is calculated by the change dL'/dt.
The purpose is to adjust the tension so that constant tension is maintained. Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 shows an embodiment of the invention. The high-temperature metal strip S is introduced into the cooling zone 6 via the hearth roll 7, cooled to a desired temperature, and transferred to the next process via the hearth roll 8. Cooling rolls 1 to 5 are arranged in the cooling zone 6 to circulate a refrigerant (water) on the inner circumferential surface of the body. Here, the cooling rolls 1, 3, and 5 are of a fixed type, and the cooling rolls 2, 4 are of a movable type (elevating type). When the cooling roll 2 is lowered to a position shown at 2' in FIG. 2, the contact area between the roll and the metal strip S decreases, and the degree of cooling that the metal strip S receives from the roll 2 decreases. If it rises, the opposite is true;
The same applies to the other rolls 1, 3 to 5. The temperature of the metal strip S that has undergone such cooling is measured with a thermometer 10 installed at the exit side of the cooling zone 6, and the deviation △t between the measured temperature t of the metal strip S and the set temperature _t0 is The temperature is calculated by the temperature controller 11 and input to the servo valve 12, and the cylinder 9 raises or lowers the cooling rolls 2 and 4 so that the deviation Δt becomes zero, and adjusts the winding length of the metal band. . During this movement of the cooling rolls 2, 4, the path length of the metal strip between each cooling roll changes, causing a change in tension unless the roll speed is properly adjusted.

Now, focusing on the change in tension between the cooling rolls 1 and 2 and considering the rotational speed correction of the cooling roll 2, the change in tension between the cooling rolls 1 and 2 is determined by the vertical distance L between the centers of the cooling rolls 1 and 2. Path length between cooling rolls 1 and 2 due to change L' = L ₀ + L ₁ +
Since this is caused by a change in L ₂ , in order to absorb this tension change by modifying the rotational speed of the cooling roll 2, it is necessary to The rotational speed V ₂ of the cooling roll 2 may be changed with respect to the rotational speed v ₁ of the cooling roll 1 (when the cooling roll 2 is not moving, v ₁ =v ₂ ). That is, the rotational speed of the cooling roll 2 may be corrected so that v ₂ =v ₁ -dL'/dt (1). Equation (1) above indicates that when the cooling roll 2 is rising and the path length L' is increasing, dL'/dt > 0, therefore v ₂ < v ₁ , and the cooling roll 2 is falling and the path length is increasing.
When L′ is decreasing, dL′/dt<0, so
This means that v ₂ > v ₁ . Here the path length
Since it is difficult to directly measure the rate of change of L'dL'/dt, it is calculated by measuring the distance L between the centers of both rolls. The rate of change dL'/dt of the path length L' can be expressed as dL'/dt=dL'/dL・dL/dt (2). dL'/dL in the above formula (2) is the amount of change in path length L' when the distance L between the centers of both rolls changes by a unit length (when the cooling roll 2 moves up or down by a unit length). be.

This path length change amount dL'/dL will be explained with reference to FIG. The winding lengths L ₁ and L ₂ of the metal band S on the cooling rolls 1 and 2 are determined by the lines connecting the centers of the rolls and the points P ₁ and P ₂ where the metal band S leaves the cooling rolls 1 and 2; If the angle between the center of the roll and the perpendicular line is θ, and the radius of the cooling rolls 1 and 2 is R, then L ₁ = L ₂ = R・θ (3), and between the points P ₁ and P ₂ The length of the metal strip S is L ₀
Since there is a relationship L ₀ ² + (2R) ² = a ² + L ² where a is the horizontal distance between rolls 1 and 2, L ₀ =√ ² + ² −4 ² (4). As shown in the figure, the angle between the horizontal line passing through the center of roll 1 and the line connecting the centers of rolls 1 and 2 is α, and the line connecting point P ₁ and the center of roll 1 is connected with the center of rolls 1 and 2. Letting the angle with the line be β, α=tan ^-1 L/a ...(5) β=tan ^-1 L ₀ /2R ...(6) Therefore, θ=π/2+α-β ...(7) From these (3) to (7), the path length L′ is L′=L ₀ +2R・θ =√ ² + ² −4 ² +2R{π/2+tan ⁻¹ L/a −tan ⁻¹ √ ² + ² −4 ² /2R} ...(8). Therefore, the amount of change in path length is It can be expressed as The curve of equation (9) above is shown in Figure 4. That is, L = 0, that is, when cooling rolls 1 and 2 are lined up side by side, dL'/dL becomes 2R/a, and roll 2 further descends, and L = -2R, that is, the bottom of roll 1 and the top of roll 2. When the metal bands S are lined up side by side and the metal strip S becomes horizontal, dL'/dL becomes 0, and during this time it changes almost linearly, and after L=0 it shows a saturation characteristic. Although the value dL'/dL of this curve can be obtained analytically, it is too complicated to use in actual control, so it is better to approximate it using a broken line as shown in FIG.

In FIG. 1, by detecting the displacement amount of the cylinder 9 with the potentiometer 13, the cooling roll 2 is
(The same applies to the cooling roll 4), that is, the vertical distance L between the roll centers is detected, and this is input to the function generator 15 that generates the function shown in FIG. 4 to calculate the path length change amount dL'/dL. At the same time, the differentiator 14 outputs the roll position change speed dL/dt, and these are input to the multiplier 16 to obtain dL'/dL.
By outputting the product of dL/dt, the path length change rate dL'/dt is obtained. By correcting the rotational speed of the cooling roll 2 according to equation (1), the tension between the cooling rolls 1 and 2 can be controlled to be constant. That is, if the rotational speed of the roll 2 is increased or decreased according to the time change in the path length according to equation (1), the tension remains unchanged. The tension control between the cooling rolls 2 and 3, between the cooling rolls 3 and 4, and between the cooling rolls 4 and 5 may be performed in the same manner as between the cooling rolls 1 and 2. However, the rotational speeds v ₃ , v 4 , and v _{5 of the cooling rolls 3, 4, and 5 are} respectively v ₃ = v ₂ −dL′/dt=v ₁ −2dL′/dt ……(10) v ₄ = v ₃ = The speed must be corrected so that dL′/dt=v ₁ −3dL′/dt ……(11) v ₅ =v ₄ −dL′/dt=v ₁ −4dL′/dt ……(12) , the speed correction amount of the cooling rolls 3, 4, and 5 is the cooling roll 2.
The speed correction amount will be twice, three times, or four times the amount of speed correction. 17,
18 and 19 are multipliers (proportional calculators) that perform this
It is. 20 is a controller for motors M ₁ -M 5 , M _{8 .} . . that drive the cooling rolls 1 - ₅ and the hearth roll 8 downstream of these rolls. The power supply for each motor is controlled by a thyristor in this example, and the gate control circuit for this thyristor includes motor voltage, current, and speed control sections, which are indicated by block 21 in the figure.
22 is an adder that provides a speed command to the control section 21, into which the speed command signal V and the outputs of the multipliers 16 to 19 are input. For the cooling roll 1, only the speed command signal V is applied to the adder 22, but for the cooling roll 2, the speed command signal V and the output signal of the multiplier 16 are also applied to the cooling roll 3, 4,
5, the output signals of comparators 17, 18, and 19 that multiply the speed command signal V and the output signal of multiplier 16 by 2, 3, and 4, respectively, are added. As a result, roll 1 is controlled by the speed command signal V, and rolls 2 to 5 are controlled to v ₂ to v ₅ of the equations (1) and (10). The speed of the hearth roll 8 and subsequent rolls is synchronized with that of the cooling roll 5. In addition, the potentiometer 13 in FIG.
may be any other detection means such as inductosin or selsin as long as it can detect the roll position (cylinder position), and the computing units 14 to 16 may also be used.
may be a microcomputer.

According to the method of the present invention described above, when the movable cooling roll is moved to perform cooling control, the tension of the metal strip does not change, so the metal strip can be cooled stably and operational travel can be prevented. The excellent effect of increasing the moving speed of the cooling roll and increasing the responsiveness of the cooling speed can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 to 5 are diagrams illustrating cooling control and calculation procedures for path length change rate. 1-5...Cooling roll, 6...Cooling zone, 7,8
...Hearth roll, 9...Cylinder, 10...
Thermometer, 11... Temperature controller, 12... Servo valve, 13... Potentiometer, 14... Differentiator, 15... Function generator, 16... Multiplier, 17
~19...proportional calculator, 20...speed controller, S...metal band.

Claims (1)

[Claims] 1 A plurality of rotating bodies through which a refrigerant flows through the body are arranged side by side in the metal body transfer direction, and a metal band is cooled by meandering around these rotating bodies, and the adjacent rotating bodies are aligned in the metal band transfer direction. In a method for controlling the tension of a metal strip in a continuous heat treatment furnace cooling zone in which cooling is controlled by relative movement in orthogonal directions, a temporal change in the path length L' of a metal band between adjacent rotating bodies due to the relative movement is described.
dL'/dt is calculated as the product of dL'/dL and dL/dt, where L is the interval in the direction of relative movement, and the speed of each rotating body after the most upstream rotating body that has moved relatively is determined by the change dL'/dt. 1. A method for controlling tension in a metal strip, characterized in that the tension is corrected using a constant tension.