JPH0532476B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a pickling control method in a pickling tank for removing scale generated on the surface of a metal strip such as a stainless steel strip by annealing treatment. [Prior Art] For example, when a metal strip such as a stainless steel strip is hot or cold rolled, its crystal grains are deformed and work hardened. Therefore, annealing is performed to recrystallize and soften the crystal grains of such a metal band. At this time, scale is generated on the surface of the metal band due to this annealing, so in order to remove this,
Mechanical and chemical descaling treatments are performed after the annealing treatment. Mechanical treatment methods include shot blasting, which removes scale by hitting steel grains, or a scale breaker, which applies local bending force to a metal strip to remove scale. The chemical treatment method is a method in which, after the above-mentioned mechanical treatment, the material is washed with acid by immersing it in a pickling tank filled with nitric acid, sulfuric acid, or hydrofluoric acid alone or in a mixed acid solution. . By the way, the type of acid used in this pickling tank is generally nitric hydrofluoric acid, which has the best descaling effect and the best surface quality of the metal strip after descaling. An inspector visually inspects the surface condition to determine whether the descaling is good or bad on site. If scale remains, the operator is contacted and instructed to check the passing speed of the metal strip (hereinafter referred to as (referred to as sheet threading speed).
Alternatively, the concentration of nitric hydrofluoric acid was changed. However, when the sheet threading speed is changed, the annealing speed in the annealing furnace in the previous stage changes, so it is necessary to change the annealing conditions as well, which causes quality abnormalities and a decrease in efficiency. In addition, changing the nitric-fluoric acid concentration required a long time until the acid was added. As a result, in the past, pickling could not be properly controlled, and the manufacturing efficiency, work efficiency, cost, quality, etc. of metal strip products were not satisfactory. [Objective of the Invention] The present invention has been made in view of the above-mentioned points, and its purpose is to reduce the immersion length of the metal strip in the acid solution by controlling the immersion length of the metal strip in the pickling tank. A pickling control method that makes it possible to control the immersion time without affecting the threading speed, and to quickly respond to acid deterioration to obtain a good descaling effect. Our goal is to provide the following. [Structure of the Invention] For this purpose, the present invention provides a method for controlling the immersion time in a pickling tank after annealing in a continuous annealing and pickling treatment line for metal strips, the method comprising: of,
The metal strip is fed into the pickling tank by controlling the threading speed of the metal strip, the acid conditions in the pickling tank, and the amount of scale remaining on the surface of the metal strip sent from the pickling tank. It is configured to control the immersion length. [Examples] Examples of the present invention will be described below. 1st
2 and 2 show a pickling tank 2 through which a metal strip 1 passes through a continuous annealing and pickling treatment line, and the pickling tank 2 is filled with an acid solution 3. 4 and 5 are sink rolls installed in the pickling tank 2, and 6 and 7 are deflection rolls installed at the entrance and exit sides of the pickling tank 2, respectively. Reference numeral 8 is a scale detection device that detects the remaining scale on the front and back surfaces of the metal strip 1, and a device that uses a colorimetric method or a laser is used, and if it has a calculation processing section inside, it can detect the detected amount of scale and the remaining amount. The result of comparison with the scale determination reference value can be sent as a detection signal. The sink rolls 4 and 5 are provided so as to be movable up and down in the vertical direction by elevating mechanisms 9 and 10 at both ends thereof, respectively. FIG. 3 shows the elevating mechanism 9 of one of the sink rolls 4 and the sink roll rotation drive mechanism 11. The same applies to the other sink roll 5. The lifting mechanism 9 includes a bearing 12 that supports the shaft 4a of the sink roll 4, a rod 13 that supports the bearing 12 from below, a worm jack 14 attached to the bottom of the rod 13, and a screw 15 that engages with the worm jack 14. The screw 15 is fixed to a rotating shaft 16a of a motor 16, and the rotation of the motor 16 causes the worm jack 1 to be rotated.
4 is raised and lowered, and the sink roll 4 is raised and lowered. 17 is a guide for guiding the bearing 12 up and down. Reference numeral 18 denotes an encoder that detects the rotational speed of the screw 15, that is, the position of the worm jack 14 that moves up and down, that is, the current position (level) of the sink roll 4 in the pickling tank 2. The sink roll drive mechanism 11 includes a motor 19, a reducer 20 that reduces rotation of the motor 19, and a propeller shaft 21 that transmits the rotational output of the reducer 20 to the shaft 4a of the sink roll 4. On the other hand, returning to FIG. 2, 22 and 23 are drive parts that drive the motor 16 of the lifting mechanism 9 of the sink rolls 4 and 5, 24 is a control part that sends control signals to the drive parts 22 and 23, and 25 is a drive part that drives the motor 16 of the lifting mechanism 9 of the sink rolls 4 and 5; This is a calculation unit that inputs signals indicating the state of the pickling tank 2 and other current data signals, performs calculations, and sends the calculation results to the control unit 24. Now, the scale generated on the surface of the metal strip 1 is descaled in the pickling tank 2, but in this embodiment, the remaining state of the scale on the metal strip 1 after pickling is detected by the scale detection device 8. The immersion time of the metal strip 1 in the acid solution 3 in the pickling tank 2 is controlled depending on the amount of scale remaining. This immersion time can be controlled by controlling the immersion length if the passing speed of the metal strip 1 is constant, since this can be replaced by controlling the immersion length. This immersion length is determined by raising and lowering both sink rolls 4 and 5 to change the immersion length of the portion of the metal strip 1 suspended between the sink rolls 4 and 5. Therefore, this is directly achieved by controlling the rise and fall of the sink rolls 4 and 5. In FIG. 2, the calculation unit 25 includes a threading speed signal a, a scale detection device 8
scale remaining amount signal b from, both synchronization rolls 4,
Signals c and d indicating the current position of No. 5 and a signal e indicating pickling conditions (liquid temperature, liquid concentration, type of acid, etc.) are input. Signals c and d serve as control feedback signals. The calculation unit 25 calculates the necessary immersion time, that is, the immersion length, by calculating each of the signals a to e described above.
The motors of the sink roll drive mechanisms 9 and 10 are driven via the control unit 24 and the drive units 22 and 23 to determine appropriate target positions of both sink rolls 4 and 5 that are going up and down. Control is performed until this target position matches the position signal obtained from the encoder. For example, if the descaling of the metal strip 1 is insufficient, the immersion time is increased, but at this time one or both of the sink rolls 4 and 5 is lowered by the required amount. In addition, if the skin becomes rough due to excessive pickling, the soaking time is shortened, but in this case, one or both of the sink rolls 4 and 5 may be raised by the necessary amount. When the acid solution deteriorates, the pickling efficiency decreases, but in this case, descaling becomes insufficient, so the immersion time is increased. As a method of controlling both sink rolls 4 and 5, in order to shorten the immersion time, the sink roll 5 on the outlet side of the metal strip 1 from the pickling tank 2 is fixed, and the sink roll 4 on the input side is raised. Then, the sink roll 5 on the exit side is raised. When increasing the immersion time, the opposite control method is used. By controlling in this way, during the control of both sink rolls 4 and 5, the metal strip 1 is re-dipped (temporarily floats up and then re-dipped, and if this is done, uneven acid burn etc. will occur). The fear of occurrence is eliminated. Incidentally, the lifting speed of the sink rolls 4 and 5 should be determined by the sheet passing speed, and for example, if the sheet passing speed is 100 m/sec, 500 to 1000 mm/sec is appropriate. Next, the specific immersion time will be explained. FIG. 4 shows the experimental results of the required immersion time with respect to the amount of scale remaining under general pickling conditions. The horizontal axis shows the degree of scale remaining after pickling, and ranks from A to E (for example, A rank is 0% and is "0", and B rank is 10%).
% is ``1'', C rank is rated ``2'' at 20%, D rank is rated ``3'' at 30%, and E rank is rated ``4'' at 40%. The permissible rank is A. The immersion time on the vertical axis is the additional immersion time required to obtain A rank relative to the remaining scale rank. According to the experimental results, samples SUS304 and SUS430 show almost the same tendency. Additionally, the additional immersion time for the remaining scale rank is not linear, but changes quadratically as the rank worsens.Approximately, the immersion time T is T=3.33, where the rank is X. Represented by X ² . Furthermore, the conditions and results of experiments conducted by varying the pickling conditions using a mixed acid consisting of nitric acid and hydrofluoric acid as the acid solution are shown in the following table and FIG. 5.

〔Effect of the invention〕

As described above, according to the present invention, the immersion time is controlled by controlling the vertical position of the sink roll based on the detection signal of scale remaining on the surface of the metal strip, the threading speed signal, the pickling condition signal, etc. Washing can be properly controlled, metal strips of improved quality can be obtained, and labor savings in personnel allocation can also be achieved. Moreover, since the immersion time is controlled by the immersion length of the metal strip, the threading speed of the metal strip can be controlled as a constant, and it does not affect the annealing conditions in the previous stage, improving quality and efficiency. will improve.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the side surface of a pickling tank according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the top surface of the pickling tank, and Fig. 3 is an explanatory diagram of the elevating mechanism and drive mechanism of the sink roll. 4 and 5 are characteristic diagrams of required immersion time with respect to scale remaining amount rank showing experimental results. 1...metal band, 2...pickling tank, 3...acid solution,
4, 5...Sink roll, 6,7...Deflect roll, 8...Scale remaining amount detection device, 9,10
... sink roll lifting mechanism, 11 ... sink roll drive mechanism, 12 ... bearing, 13 ... rod, 1
4... Warm Jack, 15... Screw,
16...Motor, 17...Guide, 18...Encoder, 19...Motor, 20...Reducer, 21
...propeller shaft.

Claims (1)

[Scope of Claims] 1. A method for controlling immersion time in a pickling tank after annealing in a continuous annealing and pickling treatment line for metal strips, the method comprising controlling the position of a sink roll that moves up and down in the pickling tank to The immersion length of the metal strip in the pickling tank is controlled according to the strip threading speed, the acid conditions in the pickling tank, and the amount of scale remaining on the surface of the metal strip sent out from the pickling tank. A pickling control method for a metal strip, characterized in that the pickling control method controls the pickling of a metal strip.