JPS61246387A - Method for controlling pickling of metallic strip - Google Patents

Abstract

PURPOSE:To obtain a good descaling effect without affecting a passing speed by moving upward or downward the position of sink rolls in a pickling tank according to the remaining amt. of the scale on the surface of a metallic strip on the outlet side of the pickling tank thereby controlling the dipping length of the metallic strip. CONSTITUTION:The metallic strip 1 after continuous annealing is passed continuously through the inside of an acid soln. 3 in the pickling tank 2 via deflecting rolls 6, 7, sink rolls 4, 5, etc. and is thereby descaled in a continuous annealing and pickling treatment line for the metallic strip. The positions of the above- mentioned rolls 4, 5 are adjusted by lifting devices 9, 10 according to the passing speed of the strip 1, the pickling conditions of the acid soln. 3, etc., the remaining amt. of the scale detected by a detector 8 for the strip 1, etc., by which the dipping length of the strip 1 in the tank 2 is controlled. The passing speed is thereby made constant and the dipping time is adequately controlled according to the pickling conditions, by which the quality of the strip 1 is improved without affecting the annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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 strip by this annealing, so in order to remove this, mechanical and chemical descaling treatment is 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 mechanical treatment, the substrate is washed with acid by immersing it in a pickling bath filled with nitric acid, sulfuric acid, or hydrofluoric acid alone or a mixture thereof.

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 determine the passing speed of the metal strip ( (referred to as sheet threading speed), or the concentration of nitric hydrofluoric acid.

However, when the sheet passing speed is changed, the annealing speed in the annealing furnace in the previous stage also changes, and the annealing conditions also need to be changed, resulting in a decrease in quality control and efficiency. Furthermore, changing the nitric-fluoric acid concentration required a long time until the acid was added.

In the end, it was not possible to properly control pickling with conventional methods.
The manufacturing efficiency, work efficiency, cost, quality, etc. of the metal strip products were not satisfactory.

[Purpose of the invention]

The present invention has been made in view of the above points, and its purpose is to control the immersion time of the metal strip in the acid solution by controlling the immersion length of the metal strip in the pickling tank. It is an object of the present invention to provide a pickling control method that does not affect the sheet threading speed, can quickly respond to acid deterioration, and can obtain a good descaling effect.

[Structure of the invention]

To this end, the present invention provides a method for controlling the immersion time in a pickling tank after annealing in a continuous pressure annealing pickling line for metal strips, the position of the sink roll moving up and down in the pickling tank is 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.

〔Example〕

Examples of the present invention will be described below. 1 and 2 show a pickling tank 2 in which a metal strip 1 passes through a continuous annealing pickling treatment line, and the pickling tank 2 is filled with an acid solution 3. 4.5 is a sink roll installed in the pickling tank 2, and 6.7 is a defrifro installed on the exit side of the pickling tank 2! It is one ru. 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 out as a detection signal.

The sink rolls 4.5 are each provided at both ends thereof so as to be vertically movable by a lifting mechanism 9.10.

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 has a bearing 1 that supports the shaft 4a of the sink roll 4.
2. A rod 13 that supports the bearing 12 from below, and a worm jack 1 attached to the bottom of the rod 13.
4. Screw 1 that engages with the worm jack 14
5, the screw 15 of which is connected to the rotating shaft 1 of the motor 16.
6a, the worm jack 14 is raised and lowered by the rotation of the motor 16, and the sink roll 4 is raised and lowered. 17 is a guide for guiding the bearing 12 up and down. 18 is 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 (gibel) 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 reducer 20.
The propeller shaft 21 transmits the rotational output of the sink roll 4 to the shaft 4a of the sink roll 4.

On the other hand, returning to Figure 2, 22.23 is synchronized roll 4.
24 is a control unit that sends a control signal to the drive unit 22 and 23;
Reference numeral 5 denotes an arithmetic unit that inputs signals indicating the state of the pickling tank 2 and other current data signals, performs arithmetic operations, and sends the arithmetic 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.

The immersion time can be controlled by controlling the immersion length if the passing speed of the metal strip 1 is constant. This immersion length is determined by raising and lowering both sink rolls 4.5.
The immersion is carried out by changing the immersion length of the portion of the metal strip 1 suspended between the sink rolls 4.5.

Therefore, this is directly achieved by controlling the rise and fall of the sink rolls 4.5. In FIG. 2, the calculation unit 25 includes a threading speed signal a, a scale remaining amount signal b from the scale detection device 8, signals c and d of the current position of both sink rolls 4.5,
and a signal e indicating pickling conditions (liquid temperature, liquid concentration, type of acid, etc.) is input. Signals c and d serve as control feedback signals.

The calculation unit 25 calculates each of the above-mentioned signals a''-e,
The necessary immersion time, that is, the immersion length is calculated, and the control unit 24
and the sink roll drive mechanism 9 via the drive unit 22.23.
．． Both sink rolls 4 that drive 10 morphs and move up and down
．． 5. Determine the appropriate target position. 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 4.5 is lowered by the required amount.

In addition, when rough skin occurs due to excessive pickling, the soaking time is shortened, but in this case, one or both of the sink rolls 4.5 may be raised by the required amount. When the acid solution deteriorates, the pickling efficiency decreases, but in this case, descaling becomes insufficient, so the immersion time is increased.

As for the control method for both sink rolls 4.5, if the immersion time is to be shortened, 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, both sink rolls 4.
During the control in step 5, there is no possibility that the metal strip 1 will be re-dipped (it floats once and is dipped again, which would otherwise cause uneven acid burns, etc.).

Note that the lifting speed of the sink roll 4.5 should be determined by the sheet passing speed, but for example, if the sheet passing speed is 10
0 m/see, 500 to 1.000 m/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 A-D (for example, A rank is 0% and "
0", B rank is "1" at 10%, C rank is "2" at 20%, D rank is "3" at 30%, and E rank is 40.
It is marked with "4" (%). 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, Material 5US304 and SUS430
shows almost the same tendency. In addition, the additional immersion time for the scale remaining amount rank is not linear, but changes quadratically as the rank worsens.Approximately, the immersion time T is, where the rank is X, T = 3.33X ”.

Furthermore, the conditions and results of experiments conducted by changing 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 in Section 5.
As shown in the figure.

From the experimental results shown in the table above, it has become clear that the immersion time for the remaining scale rank becomes shorter as the nitrate-Ms degree is lower, as the hydrofluoric acid concentration is higher, and as the liquid temperature is higher.

From the above experiments, the present inventor has found that the additional immersion time T (sec) can be reduced to a -film using the following equation.

T=αX! +β However, X Niscale remaining rank α: 8.59X10-5X (400XN -FX
t) β: Correction coefficient N: Nitric acid concentration (g/j, however, 10≦N≦15F Dihydrofluoric acid concentration (g), however, F≦F≦50t: Liquid temperature ('e)
However, 20≦t≦80. The present invention can be applied not only to hot-rolled materials but also to cold-rolled materials.

〔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 arrangement 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 drawings]

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 same pickling tank, and FIG. The explanatory diagrams, FIGS. 4 and 5 are characteristic diagrams of the required immersion time with respect to the scale remaining amount rank, showing the experimental results. 1... Metal band, 2... Pickling tank, 3... Acid solution, 4.
5... Sinking roll, 6.7... Deflecting roll, 8... Scale remaining amount detection device, 9.10... Sinking roll lifting mechanism, 11... Sinking roll drive mechanism,
12... Bearing, 13... Rondo, 14... Worm jack, 15... Screw, 16... Motor, 17... Guide, 18... Encoder, 19...
・Motor, 2o...Reducer, 21...Propeller shaft.

Claims (1)

[Claims] (1) 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 position of a sink roll that moves up and down in the pickling tank is adjusted so that the metal strip passes through the pickling tank. The immersion length of the metal strip in the pickling tank is controlled according to the plate 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 method for controlling pickling of a metal strip, characterized in that: