JPH042793A - Method for removing scale on steel strip - Google Patents

Abstract

PURPOSE:To satisfactorily remove scale on a steel strip and to increase work efficiency by establishing relation between the transfer speed of the strip and the flow rate of spray every time and material or coiling temp. of the strip varies from that of the preceding strip and controlling the flow rate of spray in accordance with the measured transfer speed. CONSTITUTION:A flowmeter 12 is fixed in an acid soln. feeding pipe 9 and measured flow rate is outputted to a flow rate controller 13. This controller 13 outputs a signal to a pump controller 15 on the basis of the flow rate and a signal outputted from a device 14 for setting the flow rate of spray so that the flow rate of spray from spray nozzles 4-6 is made optimum. The setting device 14 calculates the optimum flow rate of spray from various tables with inputted data on the basis of a signal from a speed sensor 16 for measuring the speed of a steel strip S and signals from a host computer 17 with the inputted material, width, thickness and coiling temp. of the strip S. The optimum flow rate is outputted to the flow rate controller 13.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for removing scale from a steel strip, and in particular, a method for removing scale from a continuously conveyed steel strip using a spray pickling tank with high efficiency. This article relates to a method for removing such substances.

(Prior art) Immersion-type and spray-type pickling equipment are generally used to remove scale from continuously transported steel strips, but in recent years, pickling equipment has become more popular than these pickling equipment. A highly efficient spray pickling tank has been developed and is now in use.

This method using a spray-type pickling tank sprays acid solution in the width direction of the steel strip from the inlet and outlet sides of the pickling line tank, and at the same time, the acid solution is sprayed in the width direction of the steel strip from the inlet and outlet sides of the pickling line tank. is also a method of removing scale.

At that time, since there was a large amount of scale adhering to the plate joints, the conveyance speed of the steel strip at these parts was reduced and the time taken for the steel strip to pass through the pickling line tank was lengthened.

(Problem to be solved by the invention) However, in the scale removal method using the spray pickling tank, the spray flow rate is kept constant and the steel strip is used to remove the scale.
After changing the temperature and concentration of the acid solution, scale was removed by changing only the steel strip conveyance speed.

Therefore, if the steel strip conveyance speed fluctuates due to factors such as insufficient cycle time of the input/output equipment in the pickling equipment or passing through plate connections, the passage time of the pickling line tank will change.
There was a problem in that uneven pickling, over-pickling, etc. occurred, resulting in product defects.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a scale removal method that makes it possible to manufacture products of good quality with high efficiency.

(Means for Solving the Problems) In order to achieve the above object, the first scale removal method according to the present invention is such that a steel strip that is continuously conveyed is faced to the steel strip at a required interval. In this method, scale is removed by spraying an acid solution across the width of the steel strip and causing convection of the acid solution that immerses the steel strip. The relationship between the steel strip conveyance speed and the spray flow rate per unit area of the steel strip is determined in advance and tabulated, and the spray flow rate is controlled based on the detected value of the conveyance speed and this tabulated relationship.

A second scale removal method is the first method in which, in addition to the table, the line deceleration amount at the plate connection part is input in advance, and the plate connection part is detected in the conveyance line before scale removal. However, when the bottom part of the preceding material is carried into the scale removal line, the line speed is reduced, and the spray flow rate is selected whichever is larger from the tabulated relationship between the preceding material and the following material. It is.

(Example) The method of the present invention will be explained below based on an example shown in the attached drawings.

FIG. 1 is a drawing showing an apparatus for carrying out the method of the present invention and its control system, and in the figure, 1 is a pickling line tank provided on the conveyance path of the steel strip S to be pickled. Pinch rolls 2 for conveying the steel strip S are provided on the inlet and outlet sides of the pickling line tank 1, respectively, and a weir plate 3 is provided directly below the pinch rolls 2. There is.

In addition, acid liquid spray nozzles 4.5 are disposed inside these pinch rolls 2 to face the conveyance line, and remove 0.8 to 3.0 kg of scale formed and adhered to the front and back surfaces of the steel strip S.
It is designed to be removed with an injected acid solution injected at a pressure of cj. Reference numeral 6 denotes a side injection nozzle that causes convection in the acid solution 7 supplied to immerse the steel strip S between the re-injection nozzles 4.5, and this convection acid solution also removes scale.

Reference numeral 8 denotes a circulation pump that sends the acid solution 7 in the circulation tank 10 to the injection nozzles 4.5 and 6 via the acid solution supply pipe 9, and excess acid solution 7 is sent to the circulation tank 10 via the return pipe 11. It is set to be returned to .

Reference numeral 12 denotes a flow meter interposed in the middle of the acid liquid supply pipe 9, and the flow rate detected by these flow meters 12 is determined by the flow rate control device 1.
3 is output. In this flow rate control device 13, the injection flow rates from the injection nozzles 4.5 and 6 are set to optimal values based on the flow rate value from the flow meter 12 and the output signal from the spray flow rate setting device 14.

A signal is output to the pump control device 15 so that

By the way, the spray flow rate setting device 14 uses the output signal from the speed detection device 16 of the steel strip S, the material of the steel strip S, the strip width,
Based on the current output signal of each value from the host computer 17 into which the plate thickness and winding temperature are input, the optimal spray flow rate is determined from various tables input in advance and output to the flow rate control device 13. It is.

Next, various tables that are input in advance to the spray flow rate setting device 14 will be explained.

The amount of scale formed and adhered to the front and back surfaces of the steel strip per unit area varies depending on the material of the steel strip and the coiling temperature on the hot rolling line. FIG. 2 shows the relationship between the winding temperature and the pickling time, and since the length of the pickling time is proportional to the amount of scale attached, it can be said that it indirectly represents the amount of scale attached. FIG. 2 shows data for different plate thicknesses made of the same material, and it can be seen that the thicker the plate and the higher the winding temperature, the greater the amount of scale adhesion. Furthermore, it has been empirically confirmed that this characteristic shifts in the vertical direction when the material changes. Therefore, from the characteristics of scale adhesion shown in Figure 2, the scale adhesion amount depends on the steel strip material, strip width, plate thickness,
It can be seen that it is determined by the winding temperature.

By the way, the scale that forms and adheres to the front and back surfaces of the steel strip is the third scale.
As shown in the figure, Fe0 layer 18, Fe50 . It has a three-layer structure of layer 19, Fe layer, and 03 layer 20, and if this layer is pickled, the scale will be removed as shown in the chemical formula below.

Therefore, it is theoretically possible to determine the spray flow rate from this scale removal mechanism, but since the amount of scale adhesion is not uniform from a microscopic perspective, the theoretical spray flow rate and actual scale removal may differ. Does not match required spray flow rate.

Therefore, in the present invention, steel types as shown in FIGS. 4 to 7,
Various tables are created in advance for the relationship between winding temperature, spray flow rate, and line speed for each sheet thickness, and the optimal spray flow rate is output based on these tables.

That is, Fig. 4 shows 550CH as a high carbon material, Fig. 5 shows 5CPH2 as a general material, Fig. 6 shows 50A 700 as an electromagnetic steel sheet material, and Fig. 7 shows IILc (ultra-low carbon material) as other materials. ) are shown respectively.

In addition, 21 in FIG. 1 is a thermometer that measures the temperature of the acid solution 7 in the circulation tank 10, and 22 is a concentration meter that measures the concentration of the same acid solution 7. These measured values are also sent to the flow rate control device 13. It is being output.

The above is the first method of the present invention, but in the second method of the present invention, in addition to the first method of the present invention, the spray flow rate at the plate connection portion is also controlled. At plate connections, the steel type, plate width, etc. change, and the amount of scale generated also changes.
This is because it is necessary to appropriately control the spray flow rate in accordance with this change.

Therefore, in order to carry out the second method of the present invention, it is necessary to separately provide a detection device 23 for the plate connection portion, and this detection signal is transmitted to the spray flow rate setting device 14 and the line speed control device (not shown). It outputs to . Then, based on this detection signal, the line speed control device issues a line speed deceleration command when the bottom portion of the preceding material is carried into the pickling line tank 1.

On the other hand, the spray flow rate setting device 14 compares the tables for the preceding material and the following material (different tables from the table of the first invention) based on the detection signal, and sets the spray flow rate to be the larger one. It is output to the flow rate control device 13 at the same time as the deceleration command.

The top part of the trailing material is scaled at the above line speed and spray flow rate, and when the top part of the trailing material is carried out from the pickling line tank l, the line speed is returned to the original value, while the spray flow rate is It is also controlled to be suitable for removing scale from trailing materials.

Note that the lengths of the top portion and the bottom portion are set in advance to arbitrary lengths from the connection point. Further, in this embodiment, one pickling line tank 1 has been described, but several pickling in-tanks are arranged in series. Furthermore, 2 in Figure 1
4 is a sliding skid for immersing the strip S to minimize the amount of acid solution spilling out, and 25 is a dipping cover.

(Effects of the Invention) Since the present invention is a method as described above, it is possible to achieve good scale removal, a reduction in energy consumption, and an improvement in work efficiency.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the apparatus and its control system for carrying out the method of the present invention, Fig. 2 is a diagram showing the relationship between winding temperature and pickling time, and Fig. 3 is a diagram showing the relationship between the winding temperature and the pickling time. The explanatory diagrams of attached scales, FIGS. 4 to 7, are diagrams showing an example of a table inputted in advance to the spray flow rate setting device. S is a steel strip, 1 is a pickling line tank, 4 to 6 are injection nozzles, 7 is an acid solution, 13 is a flow rate control device, 14 is a spray flow rate setting device, 16 is a speed detection device, 23 is a detection of plate connection part Device. Figure 3 Lie: It degree (~-R)

Claims (2)

[Claims] (1) An acid solution is sprayed across the width of the continuously conveyed steel strip in opposing directions at a required interval, and the acid solution that immerses the steel strip is caused to circulate. In the method of removing scale by contact, the relationship between the steel strip conveyance speed and the spray flow rate per unit area of the steel strip is determined in advance for each steel strip material, thickness, and coiling temperature, and a table is prepared. A method for removing scale from a steel strip, characterized in that the spray flow rate is controlled based on the detected value and this tabled relationship. (2) In the method according to claim 1, in addition to the table, the line deceleration amount at the plate joint is inputted in advance, and the plate joint is detected in the conveyance line before scale removal, and the line deceleration amount at the plate joint is detected. A steel strip characterized in that when the bottom part is carried into a scale removal line, the line speed is reduced and the spray flow rate is selected whichever is larger from the tabulated relationship between the leading material and the trailing material. How to remove scale.