JPS61154717A - Acid cleaning method of strip steel - Google Patents

Abstract

PURPOSE:To prevent the generation of defective goods due to narrow width and the deterioration in product yield by controlling the elongation percentage of levellers by the estimated value of the width of strip steel of the inlet side a tension leveller in the acid cleaning line of strip steel having a tension roller on the inlet side of an aicd cleaning tank. CONSTITUTION:The plate width of a strip steel 1 is measured continuously by the plate width gage 15 of the inlet side of a tension leveller 2 and with the differential value between the detected signal thereof and the target plate width to be set by a width setter 26 the elongation percentage 8 is calculated by the prescribed equation. It is fed to the motor 19 for adjusting the elongation percentage and the number of revolutions of the main motor 16 to drive the bridle rolls 3a, 3b and 4a, 4b which are for giving tension in the leveller 2 is controlled by the elongation percentage 8. The number of revolutions of the rolls 4a, 4b is subjected to a cascade control according to the 8 because of the motor 19 being connected to the planetary gear type differential gear 17 from which the output of the motor 16 is fed and the number of revolutions of the motor 19 being controlled according to the 8. The generation of a short edge cutting allowance in the plate width of after the width shrinkage of the strip steel in the leveller 2 is thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for pickling a steel strip for removing oxidized scale attached to the surface of the steel strip.

[Conventional technology]

Generally, a hot rolled steel strip is
It is wound into a coil shape at a temperature of 0° C. to 700° C., and then cooled to remove oxide scale generated on the surface in the next step.

A common method for removing scale is a pickling method in which scale is chemically removed by passing the steel strip through a pickling solution such as hydrochloric acid or sulfuric acid.

In the conventional pickling method, as shown in Fig. 4, first, as a pretreatment, a hot rolled steel strip 1 is bent and stretched using a tension leveler 2, and cracks are generated in the scale due to the difference in tensile strength of the base metal surface scale. This is done to enhance the chemical scale removal effect of the subsequent pickling solution. This tension leveler 2 consists of two sets of priddle rolls 3 that apply tension to the hot rolled steel strip 1 by winding the hot rolled steel strip 1 at a predetermined winding angle.
a.

It has a configuration in which a leveling roll 5 that applies a bending force to the hot rolled steel strip l is disposed between 3b, 4a, and 4b.

In this way, the hot rolled steel strip 1 with cracks formed in the oxide scale is immersed in the pickling liquid 7 stored in the pickling tank 6 to chemically remove the oxide scale, and then pickled. Post-processing is carried out in a processing device 8 that includes a rinsing tank for washing the liquid and a dryer for drying it, and then it is sent to an edge cutting device 10 via a looper 9 to cut the edges on both sides of the steel strip. to adjust to the specified width. Note that 1) is a side guide that guides both sides of the steel strip 1.

[Problems to be Solved by the Invention] However, in the conventional pickling method described above, in order to enhance the descaling effect of the tension leveler in the pretreatment stage, it is necessary to increase the elongation rate in the longitudinal direction of the steel strip within the tension leveler. It is necessary to take a large δ, and in this way the elongation rate δ
If the value is large, the length of the steel strip in the width direction decreases (width shrinkage), as shown in FIG. Moreover, the width of the hot rolled steel strip usually varies due to the non-uniformity of the rolling conditions (particularly the tension) in the longitudinal direction during hot rolling.

For this reason, the target rolling width is normally set wider by the width variation (several mm to several tens of mm), as shown in Figure 6.
This is called the margin. In addition, in order to perform stable edge cutting at high speed, an edge cutting allowance of about 10 mm is provided at the edges on both sides of the steel strip, and the width of the plate after edge cutting becomes the finished width on the pickling line.

Therefore, if the amount of width reduction caused by the tension leveler is large, the edge cutting allowance may be insufficient, causing problems during edge cutting, or, as shown in Figure 7, the width may become narrower than the finished width after edge cutting, resulting in an inconvenience. There was a problem that non-defective products were produced.

Also, in order to prevent width shortages, it is possible to increase the extra width, but in this case, if the width reduction by the tension leveler is not constant, the product yield in the pickling line will deteriorate. It's not a good idea.

Therefore, the present invention continuously measures the steel strip width on the entry side of the tension leveler, and controls the elongation rate of the tension leveler according to the difference between the measured value and the target strip width. It is an object of the present invention to provide a pickling method capable of controlling the amount of width shrinkage within a predetermined range, thereby preventing ordering of defective products and deterioration of product yield due to narrow width.

[Means for solving problems]

In order to solve the above problems, this application continuously measures the width of the steel strip at the entrance side of the tension leveler in a steel strip pickling line that has a tension leveler on the entrance side of the pickling tank, The specified invention is to control the elongation rate in a tension leveler according to the difference between the measured value and a preset target width. The steel strip width is continuously measured on the entry side of the leveler, and the elongation rate at the tension leveler is controlled according to the difference between the measured value and a preset target width, and the strip threading speed is controlled according to the elongation rate. The combined invention is to control.

〔Example〕

FIG. 1 is a system diagram showing one embodiment of the present invention.

A plate width gauge 15 for measuring the width of the steel strip 1 is provided on the entry side of the tension leveler 2, and the width of the steel strip 1 is measured from the width gauge 15.
The width of the board is continuously measured and the measured values are output one after another.

In addition, the pre-dol rolls 3a and 3 of the tension leveler 2
b is directly rotationally driven by the main motor 6 through a transmission mechanism such as a bevel gear, and the priddle rolls 4a, 4
b is connected to the main motor 16 via a transmission mechanism such as a bevel gear and a planetary gear type differential device 17, and an elongation rate adjustment drive motor 19 is connected to the planetary gear type differential device 17 via a reduction gear 18. are connected.

Furthermore, in the pickling tank 6, pickling; /i7 stored inside;
An automatic concentration measuring device 21 for measuring the concentration of pickling liquid 7 is installed, and a thermometer 22 for detecting the temperature of the pickling liquid 7 is also installed.

Further, on the outlet side of the pickling tank 6, surface scale automatic detection devices 23a and 23b for measuring the amount of residual scale are disposed facing the front and back surfaces of the steel strip 1, and from these, automatic detection devices 23a and 23b for measuring the amount of residual scale are installed. A detection signal is output.

Further, prydle rolls 24a and 24b are provided downstream of the surface scale automatic detection devices 23a and 23b, and the prydle rolls 24b are rotationally driven by a drive motor 25.

Then, the detection signal of the steel strip width gauge 15 and the setting signal of the width setting device 26 for setting the target width of the steel strip 1 are supplied to the elongation rate calculator 27 . This elongation rate calculator 27 uses the measured value W of the board width gauge 15 and the target width W set by the width setting device 26.
0 (the sum of the board width after edge cutting and the edge cutting allowance), calculate the elongation rate δ by calculating the following formula, and calculate this by the elongation rate adjustment motor 19 and the descaling speed described later. The signal is supplied to the arithmetic unit 29.

δ= f (W-WO) #k (W-WO')...
...(1) Here, k is a proportionality constant.

On the other hand, the descaling ability in the pickling tank 6 is determined by the pickling ability calculator 28 to which the detection signals of the automatic concentration measuring device 21 and the thermometer 22 are supplied, and the material conditions ( Pickling standard speed determined by standards, ingredients, FDT-CT, etc.

(m/n+in) and the pickling speed correction coefficient α1 determined by the pickling solution conditions (for example, temperature, hydrochloric acid concentration, FeCl2 concentration). α2. . . . Using α7, the pickling possible speed V I (m/m1n) is calculated based on the following formula.

■1=α,・α2 ・・・・・・・・・α1 ・Vo・・
(2) Then, the elongation rate δ outputted from the elongation rate calculator 27 and the pickling possible speed ■1 outputted from the pickling ability calculator 28 are supplied to the descaling rate calculator 30. This descaling speed calculator 30 first calculates the following equation based on the elongation rate δ from the elongation rate calculator 27,
Calculate the pickling speed reduction rate β.

βsf'(δ)ik'J ・・・・・・・・・・・・
...(31Here, k' is a proportionality constant.

Next, the following formula is calculated based on the pickling speed reduction rate β calculated by the above formula (3) and the pickling possible speed V, and the pre-dol rolls 3a, 3b; 4a, 4b; 2
The rotational speed control value V of the motor 19.25 that controls the rotational speed of the motors 4a, 24b is calculated and outputted to each motor 19, 25.

V=V+ / (1-β) αI 0α2 °01+0080α? 1-V1) 嬌 □
......(4) 1-'FT] layer = j Liu] In this way, the priddle rolls 3a, 3b and 4a, 4 for applying tension in the tension leveler 2
The rotation speed of the main motor 16 that drives the pickling tank b and the rotation speed of the drive motor 25 of the priddle rolls 24a and 24b provided on the pickling tank exit side are controlled by the elongation rate δ and the pickling capacity VI. , an elongation rate adjustment motor 19 is connected to a planetary gear type differential device 17 to which the output of the main motor 16 is supplied, and the rotational speed of this elongation rate adjustment motor 19 is equal to the elongation rate δ from the elongation rate calculator 27. The rotation is controlled accordingly, so
The rotational speed of the priddle rolls 4a and 4b is controlled in a cascade according to the elongation rate δ, and as shown in FIG. When the width W is larger than the target plate width W0, the elongation rate δ calculated by the elongation rate calculator 27 increases accordingly. Therefore, the rotational speed of the elongation rate adjustment motor 19 is increased, a large tension is applied to the steel strip 1, and the actual elongation rate of the steel strip 1 is set to the upper limit value δmax, and the amount of steel strip shrinkage at the tension leveler 2 is becomes larger, and the width W7 of the steel strip l after passing through the tension leveler 2 is the curve shown by the solid line in FIG. 2(a)! , the value approaches the target width W0 of the tension leveler 2.

From this state, as the width W of the steel strip 1 becomes shorter, the elongation rate δ decreases, and when this becomes equal to the upper limit value δmax,
The width W7 of the steel strip 1 after passing through the tension leveler 2 becomes approximately equal to the target width W0.

After that, when the entrance width W of the steel strip 10 becomes less than or equal to the hot rolling target width and becomes approximately equal to the target width W0, the elongation rate δ becomes approximately zero, and the pre-roll rolls 3a, 3b of the tension leveler 2
The rotation speeds of 4a and 4b are set to be substantially equal, the amount of shrinkage in the tension leveler 2 is suppressed to substantially zero, and the width W7 of the steel strip 1 after passing through the tension leveler 2 becomes substantially equal to the target width W0.

Thereafter, the elongation rate adjustment motor 1 is adjusted so that the elongation rate corresponds to the difference between the entrance width W of the tension leveler 2 and the target width W0.
9 to adjust the amount of shrinkage at tension leveler 2,
A predetermined selvedge allowance can be secured.

Further, the amount of residual scale after the steel strip 1 is immersed in the pickling liquid 7 in the pickling tank 6 is determined by the surface scale detection devices 23a and 23b.
This is constantly detected and supplied to the pickling capacity calculator 28, so if descaling is not reliably performed and there is a large amount of residual scale, the pickling possible speed V1 from this pickling capacity calculator 28 will decrease. will be done.

For this reason, the descaling rate (2) is reduced by the descaling rate calculator 30, and the immersion time during which the steel strip 1 after passing through the tension leveler 2 is immersed in the pickling liquid in the pickling tank 6 becomes longer. It is possible to increase the effect and prevent the occurrence of defective products due to insufficient pickling, and in order to prevent the occurrence of defective products, the descaling rate V is lowered more than necessary to reduce the yield due to overpickling. It is possible to prevent a decrease in efficiency and a decrease in efficiency.

At this time, the pickling capacity calculator 28 stores the relationship between the amount of residual scale, pickling solution concentration, pickling solution temperature, steel type, etc.
Based on these, the pickling standard speed is determined by the learning function. By setting the value to an optimum value, it is possible to perform descaling treatment by pickling treatment with higher precision.

In practice, pickling of general cold-rolled steel strip (SPCC) with a thickness of 3.5 mm and a width of 1200 mm was performed when the bath conditions were an average hydrochloric acid concentration of 5%, a ferrous chloride concentration of 30%, and a temperature of 85°C. Descaling speed using only tank 6 is approximately 200m/m
It is in.

Here, by giving δ-3% as the elongation rate δ of the tension leveler 2 when the surplus width (W-Wo) is 3 mm, it is possible to obtain the effect of setting the pickling speed reduction efficiency β to β#20%,
The descaling speed could be increased to 250 m/min.

In addition, there was a width fluctuation at the center of the coil, and the width of the main slope was narrower by 2 mm compared to the steady portion, so the extra width was 1 mm, so it was set to δ-1%. Here, due to the effect of β#12%, the descaling speed is 227 m/m
In addition to preventing insufficient pickling by slowing down to in, it also prevents excessive width w
We were able to avoid the ear cut problem caused by J4.

〔Effect of the invention〕

As explained above, according to the specific invention of the present invention, the elongation rate of the strip in the tension leveler is controlled according to the difference value between the steel strip width at the entrance side of the tension leveler and the target width. Therefore, it is possible to control the width of the steel strip after the width of the steel strip is reduced in the tension leveler so that insufficient edge cutting allowance occurs, and troubles with the edge cutting device after pickling can be resolved. This effect can be obtained.

Further, according to the combined invention, in addition to the elongation rate control of the specified invention, the threading speed (descaling speed) is controlled according to the elongation rate, so that the amount of residual scale due to insufficient pickling can be reduced. It is possible to prevent the descaling rate from increasing and to maintain the descaling rate at an optimum value, and it is possible to obtain the effect that there is no reduction in yield or efficiency due to overpickling.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing a pickling line applicable to the method of the present invention, Fig. 2 is a graph showing the relationship between elongation rate and descaling time shortening effect in a tension leveler, Fig. 3 (a)
and (b) are explanatory diagrams showing the relationship between each part in the longitudinal direction of the hot steel strip, the plate width, and the elongation rate, respectively, to explain the method of the present invention, and FIG. 4 is a system diagram showing a conventional pickling line. FIG. 5 is a graph showing the relationship between the elongation rate in the tension leveler and the difference between the tension leveler outlet side plate thickness and inlet side plate thickness, FIG. 6 is an explanatory diagram showing width fluctuations at various parts in the longitudinal direction of the hot rolled steel strip, FIG. 7 is an explanatory diagram showing the relationship between each longitudinal portion of a hot steel strip and the plate width in a conventional example. In the figure, 1 is a hot rolled steel strip, 2 is a tension leveler, 3a, 3
b, 4a, 4b are pre-dol rolls, 5 is a leveling roll, 6 is a pickling tank, 7 is a pickling liquid, 8 is a cleaning treatment device, 1
0 is the edge cutting device, 15 is the board width gauge, 16 is the main motor, 17
is a planetary gear type differential device, 19 is a motor for adjusting the elongation rate, 2
1 is an automatic concentration measuring device, 22 is a thermometer, 23a, 23b
2 is a surface scale automatic detection device, 24a and 24b are priddle rolls, 25 is a drive motor, 26 is a width setting device, 27
is an elongation rate calculator, 28 is a pickling capacity calculator, and 30 is a descaling rate calculator.

Claims (2)

[Claims] (1) In a steel strip pickling line having a tension leveler on the inlet side of the pickling tank, on the inlet side of the tension leveler,
A method for pickling a steel strip, characterized in that the width of the steel strip is continuously measured, and the elongation rate in a tension leveler is controlled according to the difference between the measured value and a preset target width. (2) In a steel strip pickling line having a tension leveler on the inlet side of the pickling tank, on the inlet side of the tension leveler,
The steel strip width is continuously measured, the elongation rate in the tension leveler is controlled according to the difference between the measured value and a preset target width, and the strip threading speed is controlled according to the elongation rate. Pickling method for steel strip.