JPS59229268A - Descaling method of continuous casting billet - Google Patents

Abstract

PURPOSE:To remove powder and to eliminate a black belt-like stain from a steel plate, etc. by injecting high-pressure water or high-pressure steam under a specific pressure to both surfaces in the transverse direction of a billet drawn from a casting mold in an area disposed with a secondary cooler. CONSTITUTION:The high-pressure water supplied from a device 8 for supplying high-pressure water is controlled to >=50kg/cm<2> pressure and flow rate by a control device 9. A spray header 10 which supports nozzles 5 is held by a header driving device 11 so as to traverse. The position of the nozzles 5 are changed by driving the device 11 to meet the width of a billet 3 and the water is sprayed to the top and bottom surfaces of the billet 3 from the nozzles 5 in the stage of changing the width of said billet.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for descaling continuously cast slabs.

As is well known, in continuous casting equipment (hereinafter referred to as continuous casting equipment), molten steel is injected into a mold to form a predetermined cross-sectional shape, and then it is continuously drawn out by a group of force id rolls arranged following the mold. Continuously cast slabs (hereinafter referred to as slabs) are manufactured. The slab is cooled in the mold to form a solidified shell of a predetermined thickness (usually referred to as primary cooling), and after being pulled out of the mold, a cooling medium is injected onto both sides of the slab. The solidification is promoted by a secondary cooling device,
After the core is completely solidified, it is cut into a predetermined length.

In recent years, direct rolling, in which slabs produced in the continuous casting equipment described above are directly fed to the rolling process without further cooling or after being slightly heated, has been actively carried out.

Therefore, in order to carry out the above-mentioned direct rolling, it is extremely important from the viewpoint of quality and energy saving to maintain the turbidity of the slab discharged from the continuous casting equipment evenly in the cross-sectional direction and at as high a temperature as possible. be. Therefore, cooling control and casting speed control in the secondary cooling device are managed with high precision according to the steel type, size, etc.

However, under such control, there was often a problem in that black band-like stains were formed on the surface of steel sheets that were directly rolled.

Therefore, in order to understand the cause of the black band-like stains described in FITR, the present inventors investigated the slab immediately before the rolling mill (before the rolling mill that first rolls the slab fed from the continuous casting equipment). [Removal of scale that adhered to and formed on the surface of the slab using a well-known descaling device installed, ie, the slab after descaling] The scale remaining status was investigated. As a result, it was found that powder as a lubricant used in the mold was attached to the surface of the slab.

The chisel is V in order to prevent seizure between the mold and slab.
It is supplied to the surface of the molten steel in the C mold to prevent surface cracking of the slab by preventing seizure, and to improve the surface quality of the slab.
Alternatively, it is supplied in the form of granules or powder. The powder adheres to the surface of the slab that is pulled out of the mold. Conventionally, the powder that adheres to the surface of the slab is cooled by a cooling medium, such as cooling water, when passing through a secondary cooling device casting area. It was thought that this was removed by spraying it onto the slab.

However, according to the above investigation results, when the adhesion index of nozzles on the meniscus is set to 100, about 5 to 10 nozoda still adhere and remain almost evenly in the width direction of the slab just before the rolling mill. This was confirmed.

Then, when the slab to which the powder has adhered is rolled and, for example, the rolled hot-rolled steel sheet is pickled, a mixture of the remaining powder and the oxidized scale that is subsequently generated reacts with the acid, and the surface of the steel sheet is It was found that the black band-like stain was produced.

The present invention was made based on the knowledge from the above investigation and as a result of repeated experiments. The purpose of the present invention is to completely eliminate the occurrence of black band-like stains on the surface of steel plates, etc. as finished products, and the gist of the present invention is to prevent the continuous casting mold from cooling in the secondary cooling device installation area following the continuous casting mold. A continuously cast slab characterized by descaling the continuously drawn slab by injecting high aqua regia or high pressure air water of 50 Kf/- or more onto both sides in the width direction and/or both sides in the thickness direction. This is a descaling method.゛Hereinafter, the experimental research that led to the present invention will be explained in detail.

First, it was discovered that it was possible to remove powder by injecting high-pressure water or high-pressure air water with a VC of 50 Kf/ct1 or higher onto the surface of the slab in the area where the secondary cooling device of the continuous casting equipment was installed, and descaling it. We will describe the experiment we conducted.

FIG. 1 is a structural diagram of an example of a well-known continuous casting equipment, in which 1 is a mold, 2 is a guide roll, 3 is a slab, and 4 is a secondary cooling device installation area following the mold 1. .

FIG. 2 is a cross-sectional structural diagram of the descaling device installed in the secondary cooling device 4 for this experiment.

In this descaling device, a plurality of nozzles 5 for injecting high-pressure water are arranged so as to face both sides (upper and lower surfaces in the figure) of the slab 3 in the width direction. A high-pressure water supply device 8 consisting of a Bonzoro, an accumulator 7, etc. is connected to the nozzle 5 via a control device 9 and a spray header 10.

The high pressure water supplied from the high pressure water supply device 8 is controlled by the control device! It is controlled to a predetermined pressure and flow rate by i9, and is supplied to the nozzle 5 via the spray header 10, and is sprayed from the nozzle 5 onto the upper and lower surfaces of the slab 3.

The high pressure water injected through the nozzle 5 is
The pressure is extremely high, Kt/ff1 or higher, and if this high aqua regia is directly injected onto equipment other than the slab 3, such as the guide roll 2 or other equipment, there is a risk of damaging the equipment. Therefore, in the descaling device shown in FIG. 2, the spray header 10 supporting the nozzle 5 is held by a ladder drive device 11 so as to be able to move laterally. The structure is such that the position of the nozzle 5 can be changed by driving the nozzle 5 so that the nozzle 5 can be placed in the slab.

Furthermore, as shown in FIG. 3, each nozzle 5 may be provided with an on-off valve 12, and the on-off valve 1"2 may be controlled to open and close as appropriate in accordance with the width change, or although not shown, The above-mentioned damage to the equipment can also be avoided by configuring the system so that the injection angle can be adjusted.

Using the descaling device shown in FIG. 2, the installation position (distance from the meniscus) in the secondary cooling device casting area 4, the pressure of the high-pressure water to be injected, and the separation distance between the slab 3 and the nozzle 5 are determined. Table 1 shows the results of investigating the descaling situation by varying the parameters.

Table 1 In this table, the casting position of the descaling device is expressed by the time taken for the slab 3 to reach the casting position, with the meniscus as a reference. In addition, the descaling situation is expressed by the powder residual rate just before the rolling mill, and the ○ mark is 0.1 when the adhesion index at the meniscus is 100.
Hereinafter, it is considered that the picks were almost completely descaled, and the surface quality of the steel plate was good, and the Δ mark is '0.
Those with 1 to 5.0 remaining powder, and the ones marked with an x, which are similar to the conventional ones with 5.0 to 10.0 remaining powder.

From Table 1, the distance between the slab 3 and the nozzle 5 is 200□
If it is less than 50 Kyla1, the descaling condition will be significantly improved by setting the pressure of high pressure water to 50~/- or more, and if the descaling device is installed at a position close to mold 1 and the meniscus It has been found that descaling is extremely effective when descaling is performed within as short a time as possible after exiting. The effect becomes extremely high when the mold 1 is exited f1: When the nozzle adhering to the surface of the slab 3 passes through the guide roll 2, it is pressed against the surface of the slab by the guide roll 2. This is thought to be because the smaller the number of guide rolls 2 that pass, the weaker the pressure is and the easier it is to remove the roughness.

Conventionally, in continuous casting equipment that performs direct rolling, the amount of cooling water sprayed in the secondary cooling device 4 is limited in order to prevent overcooling of the slab 3. Due to insufficient removal, there is a large amount of residual adhesion after the powder passes through the secondary cooling device 4, and in addition, since the powder is pressed against the surface of the slab at high temperatures, complete removal cannot be achieved even with descaling immediately before the rolling mill. It is presumed that there was no such thing.

Next, Table 2 shows the results of an experimental investigation of the temperature drop of the slab 3 when the above-mentioned high-pressure water sieve scaling was performed.

In this experiment, the cooling intensity of the secondary cooling device 4 was set to 0.57 to (1,77 (t, /Kq)) in a continuous casting machine with a machine length of 371n, and descaling was performed using the equipment Fj- shown in Fig. 2 above. ,
The temperature of the slab at the end of the machine was investigated. And for comparison,
The temperature of the slab at the machine end when the descaling was not performed (conventional method) was also investigated.

In addition, the above descaling was performed in the secondary cooling device installation area 0.3 m away from the exit side of the mold 1 at a rate of 150 kg/
1 using high pressure water (flow rate 28 (1/”)) and mixing cooling water and compressed air (mixing ratio Δ-0, 15)
Both cases were investigated using 50 KVl- high pressure air water (flow rate 200t/-f).

As is clear from Table 2, it was found that even if the descaling process was carried out as described above, the temperature of the slab 3 was maintained at an extremely high temperature, almost unchanged from that of the conventional method. This is presumed to be because if the descaling is performed at a relatively forward portion of the secondary cooling device 4, the temperature of the slab increases as it approaches the end due to the recuperation phenomenon after descaling.

It was also found that descaling using high-pressure air and water is effective in further alleviating the temperature drop at the end of the slab.

It was also confirmed that by carrying out the present invention, the residual rate of grains immediately before the rolling mill was reduced to zero, and that grains could be completely removed.

The present invention has been made based on the above experimental results, and according to the present invention, the cooling device is placed at a front position as close as possible to the mold 1 in the secondary cooling device installation area, preferably in the secondary cooling device 4 installation area. Since high-pressure water or high-pressure air water of 50 KW/M or more is injected onto both sides of the slab 3 in the width direction that is continuously pulled out from the mold, the deposits on the surface of the slab, especially the powder mentioned above, are completely removed. There was no black band-like stain on the steel plate, etc., which was directly rolled from the slab.

In the above-mentioned experimental example, descaling was performed only in the width direction of the slab 3, that is, on the top and bottom surfaces, but the nozzle also adhered to both sides of the slab in the thickness direction. Because there are
For example, a meandering prevention guide roller is installed in the secondary cooling device installation area 4.

Alternatively, if a widthwise reduction device is installed, high-pressure water or high-pressure air water of 50 Kq/crI or higher is also injected onto both sides of the slab to descale and prevent the occurrence of surface defects. It can be prevented.

In the above experiment, one descaling device was installed, but in actual continuous casting equipment, two or two descaling devices were installed in the direction of progress of the slab.
It is also possible to install multiple stages.

[Brief explanation of drawings]

Figure 1 is a structural diagram of an example of a well-known general continuous casting device;
FIG. 3 is a sectional view of a descaling device used in experiments leading to the method of the present invention, and FIG. 3 is a perspective view showing an example of the structure of a nozzle of the descaling device. 1... Mold, 2... Guide roll, 3... Slab,
4... Secondary cooling device installation area, 5... Nozzle, 6...
... Pump, 7... Akineem t/-ta, 8...
High-pressure water supply device, 9...Control device, 10...Spray header, 11°" header drive device, 12...Opening/closing valve. Agent: Patent attorney Masamitsu Akizawa, and 2 people

Claims (1)

[Claims] (1) In the secondary cooling device installation area following the continuous casting mold, a high pressure of 50 kg/cl or more is applied to both sides in the width direction and/or both sides in the thickness direction of the slab that is continuously drawn from the mold. A descaling method for continuously cast slabs, characterized by descaling by injecting water or high-pressure air and water.