JPH11189885A - Method for pickling hot rolled steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suitably set the sheet passing rate in a pickling tank in a pickling method for a hot rolled steel strip and to execute sufficient pickling to be required in accordance with the thickness of scales. SOLUTION: A scale thickness measuring device 3 is set on a prescribed position on the stream side upper than a pickling tank 6, and the thickness of scales formed on the surface and back faces of a steel strip S is detected. A control device 11 detects the maximum value in the prescribed length range of the steel strip from the detected value, and the sheet passing rate in the pickling tank 6 is set per the range from the maximum value of the detected scale thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hot-rolled steel strip which is continuously rewound and passed through a pickling tank.
The present invention relates to a method for pickling a hot-rolled steel strip for removing scale generated on the surface of the hot-rolled steel strip.

[0002]

2. Description of the Related Art Generally, continuous pickling of a hot-rolled steel strip is carried out by passing the strip through a pickling tank containing hydrochloric acid, sulfuric acid, etc., a rinsing tank, a drying device, etc. while rewinding the steel strip with a pay-off reel. It is done by facilities. The pickling step of the hot-rolled steel strip is a step of removing scale (oxide) generated on the surface of the steel strip by reacting with hydrochloric acid, sulfuric acid, or the like. If the scale of the surface is thick, the pickling property is poor. Become. Further, when the temperature of the pickling solution and the concentration of the acid are the same, the pickling effect is enhanced by reducing the plate passing speed and lengthening the dipping time.

Here, the scale thickness greatly fluctuates in the longitudinal direction of the steel strip. However, conventionally, in order to prevent quality deterioration due to insufficient scale removal, pickling is performed in accordance with the assumed maximum value of the scale thickness. The temperature and the acid concentration of the liquid are set to be high, and the pickling plate speed is set to be low.

[0004]

However, according to the conventional method, when a portion having a relatively small scale thickness is passed through the pickling tank, it is pickled with excessive specifications. In other words, the pickling liquid and heat energy (generally, steam energy) are wasted. Further, since the pickling time is longer than necessary, the time is wasted.

The present invention has been made in view of such problems of the prior art, and it is necessary to appropriately set a passing speed in a pickling tank to pick up a necessary and sufficient pickling according to the scale thickness. Is to be performed.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a hot-rolled steel strip which is continuously rewound and passed through a pickling tank while being unwound. In the pickling method of a hot-rolled steel strip for removing scale generated in the pickling tank, a scale thickness is detected at a predetermined position upstream of the pickling tank, and a predetermined length of the steel strip of the scale thickness detection value is detected. Pickling of a hot-rolled steel strip characterized by detecting a maximum value in a range, and setting a passing speed of the steel strip in a pickling tank for each range from the detected scale thickness maximum value. It provides a method.

[0007] The predetermined position (scale thickness detection position)
Is set at a position on the upstream side of the pickling tank by at least the above-mentioned predetermined length (the length of the steel strip in the range where the maximum scale thickness is detected).

[0008]

Embodiments of the present invention will be described below. FIG. 1 is a schematic configuration diagram showing a facility row to which an embodiment of the method of the present invention can be applied. This equipment row includes payoff reels 1A and 1 for rewinding the steel strip S in order from the entry side.
B, a welder 2 for welding the tail end of the preceding steel strip and the tip of the following steel strip, a scale thickness measuring device 3 for measuring the scale thickness of the steel strip S, an entry-side looper 4, and an entry-side looper 4. Variable speed roll 5, pretreatment devices 61 and 62, pickling tank 6
, A post-processing device 63, an exit-side variable speed roll 7, an exit-side looper 8, a run-in shear 9, and a take-up reel 10.
A, 10B and the control device 11.

The scale thickness measuring device 3 is a device for measuring the total thickness of the scale adhering to the front and back surfaces of the steel strip S in a non-contact manner, and outputs the detected scale thickness value T to the control device 11. Here, the length of the pickling layer 6 is 100 m,
The scale thickness measuring device 3 is approximately 50 mm from the entrance of the pickling layer 6.
It is arranged immediately before the entrance looper 4 which is 0 m upstream.

A pulse generator 52 for detecting the rotation speed of the electric motor 51 is connected to the electric motor 51 for driving the variable speed roll 5 on the input side. Is output. A pulse generator 72 for detecting the rotation speed of the electric motor 71 is connected to the electric motor 71 that drives the output-side variable speed roll 7, and a detected speed value V 2 from the pulse generator 72 is output to the control device 11. .

The control device 11 sets the passing speed in the pickling tank 6 based on the scale thickness detection value T input from the scale thickness measuring device 3 and sets the speed so that the speed setting value is achieved. The motor current values A1 and A2 corresponding to the difference between the speed set value and the speed detection values V1 and V2 are respectively expressed by the motor 5
1, 71. That is, the passing speed of the steel strip S in the pickling tank 6 is the same as that of the variable speed roll 5 installed immediately before the pretreatment device 61 and the variable speed roll 7 installed immediately after the post-treatment device 63. By rotating at a speed that achieves the speed set value, the speed set value is controlled.

Here, the curve in FIG. 2 shows the relationship between the scale thickness and the upper limit value of the pickling speed at which the pickling failure does not occur, and the speed set value is set in advance using this curve. The length is set for each length range of the steel strip.
That is, the control device 11 detects the maximum value of the scale thickness in each range from the scale thickness detection value T, and sets the upper limit value of the pickling speed at which the pickling failure does not occur at the maximum scale thickness from the curve in FIG. Then, the sheet passing speed according to the set pickling speed is calculated as the speed set value. Here, the length range of the steel strip as a unit for setting the above-mentioned speed setting value is, for example, 100 m.

Further, the control device 11 has storage means for storing the speed set value calculated for each range by the above method,
Immediately before the corresponding area of the steel strip is introduced into the pickling tank 6,
A corresponding speed set value is called from the storage means, and control is performed to achieve the called speed set value.

Therefore, according to this equipment, the passing speed of the steel strip S in the pickling tank 6 is set at the maximum scale thickness according to the actually measured scale thickness for each predetermined length range of the steel strip S. Is controlled so that the pickling rate does not cause poor pickling even in the portion of the steel strip S, so that the necessary and sufficient pickling according to the scale thickness is performed over the entire length of the steel strip S.

Further, according to the method of this embodiment, since the passing speed is controlled based on the maximum value of the scale thickness for each predetermined length range of the steel strip, the scale thickness alternates in the increasing direction and the decreasing direction. It is not necessary to frequently change the passing speed even if the speed changes frequently. This makes it possible to reduce the load on the equipment while performing appropriate control.

On the other hand, in the control method for changing the passing speed in the pickling tank in accordance with the change in the scale thickness,
For example, when the scale thickness alternately and frequently changes in the increasing direction and the decreasing direction, the passing speed changes frequently and the load on the equipment increases.

In this embodiment, the scale thickness measuring device is installed at a position upstream of the pickling tank from the entrance of the pickling layer. Before entering the pickling layer, the speed setpoint for that range is reliably set. Therefore, a delay in control response hardly occurs, and reliable speed control is performed.

In the above-mentioned equipment, the slack or elongation of the steel strip S caused by changing the passing speed by the variable speed rolls 5 and 7 is allowed by the entrance looper 4 and the exit looper 8. ing.

FIG. 3 shows an example (solid line A) and a conventional example (dashed-dotted line B) of the change in the stripping speed in the length direction of the steel strip in the pickling tank when the method of the present invention is adopted. Show. As can be seen from this figure, conventionally, the passing speed in the pickling tank is constant (sufficient passing speed for surely removing the assumed maximum scale thickness). In the method, the passing speed is set according to the actual scale thickness (the maximum value in the predetermined length range). Therefore, according to the method of the present invention, for example, the average speed can be increased by about 20% as compared with the related art.

[0020]

As described above, according to the method of the present invention, a necessary and sufficient pickling according to the scale thickness can be performed by appropriately setting the passing speed in the pickling tank. . As a result, while obtaining sufficient pickling properties, improve productivity,
The pickling cost can also be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an equipment row to which an embodiment of the method of the present invention can be applied.

FIG. 2 is a graph showing the relationship between the scale thickness and the upper limit of the pickling rate at which no pickling failure occurs.

FIG. 3 is a graph showing an example (solid line A) of a change in a sheet passing speed in a length direction of a steel strip in a pickling tank in a case where the method of the present invention is adopted (solid line A) and a conventional example (dashed line B) It is.

[Explanation of symbols]

 S Steel strip 1A Payoff reel 1B Payoff reel 2 Welder 3 Scale thickness measuring device 4 Inlet looper 5 Variable speed roll 6 Pickling tank 61 Pretreatment device 62 Pretreatment device 63 Posttreatment device 7 Variable speed roll 8 Exit looper 9 Run Intermediate shear 10A Take-up reel 10B Take-up reel 11 Controller 51 Motor 52 Pulse generator 71 Motor 72 Pulse generator

Claims (1)

[Claims] 1. A hot-rolled steel strip which is continuously rolled through an pickling tank while being unwound to remove the scale formed on the surface of the hot-rolled steel strip. In the washing method, the scale thickness is detected at a predetermined position on the upstream side of the pickling tank, and the maximum value of the scale thickness detection value within a predetermined length range of the steel strip is detected. A pickling method for a hot-rolled steel strip, comprising setting a sheet passing speed in a pickling tank of the steel strip for each of the ranges from the values.