JPS5985368A - Gas cutting method of steel material - Google Patents

Abstract

PURPOSE:To remove efficiently and exactly a cut slag by gas blowing, by driving a two-piece set of torches from both ends, executing gas cutting by making reverse side nozzles correspond to each other, and thereafter, moving one reverse side nozzle faster than the cutting speed. CONSTITUTION:A two-piece set of cutting torches 21, 22 are moved in the direction approaching each other from both ends of a slab cutting intended line. In this case, gas cutting is executed by making reverse side nozzles 51, 52 correspond to each other while blowing gas whose O2 dinsity is >=50%, and removing a cut slag. Also, after the cutting is completed, the gas pressure is increased to one - five times while moving continuously one reverse side nozzle 51 along the cut groove at a speed tow -20 times the cutting speed, by which the cut slag is removed. Thereafter, the gas pressure is decreased to 1/3- one time the blowing gas pressure at the time of cutting, and gas blowing is executed. It can be prevented exactly by this post-blowing treatment that a slag is left around the center part of a steel material whose cutting is ended.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas cutting method for removing slag generated by cutting simultaneously with the progress of cutting.

As shown in Fig. 1, the mechanism of occurrence of slag adhesion is that a steel material (υ) is placed with a cutting torch (
2) When V-shaped gas cutting is performed, a part of the molten metal generated by the cutting enters the cutting groove (4) to the back side and adheres to the state shown in code (3), solidifying and generating slag. There is something that will become.

Such slag adhesion is generally more pronounced as the thickness of the steel material to be cut increases, and is therefore particularly noticeable when cutting slabs, particularly extremely thick slabs produced by continuous casting. Moreover, in the case of slabs, since the downstream process is rolling, the adhesion of slag has a large effect, such as causing rolling defects in the product and roll defects. Therefore, in the case of slabs, it is generally essential to take some measure to prevent slag from being brought into the rolling process. The first possible countermeasure is to remove the slag that adheres to the slab during the post-cutting process. Currently, the most common countermeasure for this problem is to remove the slag by mechanical grinding with a cutting tool or by carving. Slag adhesion during gas cutting generally tends to occur as the thickness of the cut steel increases, the amount of unreacted molten metal increases, and the adhesion strength increases. If the material is extremely thick, the slag will adhere very strongly and in large amounts, which is why biting and scarfing are used.

However, recently, especially from the point of view of energy saving, continuous casting has been adopted (hereinafter abbreviated as CC slab), and the so-called hot slab charging, in which the slab is charged into the furnace as hot slabs, makes effective use of the retained heat. (hot charging) and even non-heat rolling (direct roll) have suddenly attracted attention and are being put into practical use. However, if such a direct method were to be adopted, it would be necessary to eliminate the slag caused by cutting. Although it has to be treated in a separate process, it is a big disadvantage in terms of heat utilization. In hot charge (direct low) L/), it is necessary to prevent the heat retained in the slab from dissipating.
How quickly the slab can be fed into the heating furnace (roll) is also an important point in the operation, but the time required to feed the slab after cutting is also important. This results in a prolonged period of time, which precludes significant heat utilization.

In order to cope with the direct introduction of such a method, a method for removing slag that simultaneously processes the slag as cutting progresses (hereinafter referred to as simultaneous processing) is required.

As for simultaneous processing methods, the following method using gas spraying (hereinafter referred to as "gas spraying method") can be said to be the most advantageous method from all points of view, including effectiveness and practicality. That is, during cutting, as shown in Figure 2, the nozzle (5) faces the back side of the steel material, and as the nozzle (5) moves as the cutting progresses, it removes the slag (
3) Oxygen-based gas is sprayed backwards or diagonally backwards, which oxidizes the slag and increases its fluidity and blows it away.

However, in consideration of efficiency, CC slabs are actually cut using two cutting torches simultaneously. That is, as shown in Fig. 8, a set of two cutting torches (
2/X2J) at both ends of the planned cutting line of the slab (F5
At this time, in order to avoid interference between both torches, one cutting torch (2) is moved at the position (Q) on the verge of interference.
A method of stopping the progress and cutting of the torch, immediately reversing and retracting it, and advancing only one torch (2/) as it is until the cutting is completed (hereinafter referred to as the two-way cutting method). ) is taken.

In the case of such bidirectional cutting, as shown in the figure, the back side nozzle (5/) (
If the above-mentioned gas blowing method is applied in accordance with item 5), sufficient slag removal will not be carried out near the center of the slab where cutting ends, resulting in slag residue being generated there. That is, by law, from the viewpoint of the slag removal effect, the position of gas spraying is set slightly behind the cutting tip position (Q) as shown in the figure. When the last cutting is completed near the center of the slab τj and the cutting torch (21) and the back side nozzle (51) driven by it are stopped, the back side nozzle /l/
(5/) results in leaving an unsprayed part in the center of the slab.

If you think about it normally, the torch on the side in charge of the final cutting (
Instead of stopping the back side nozzle /l/(5/) corresponding to 2/) at the same time as cutting ends, if you continue to advance until the required point and continue blowing gas, it will be possible to cut the center of the slab. It seems that some of the slag residue can be prevented.

However, when such a measure (hereinafter referred to as post-blowing treatment) is actually taken, the removed cutting slag is not completely removed from the central part of the slab, but the removed cutting slag is re-sprayed to the front part of the slab. The inventors' experience has revealed that it is very difficult to put it into practical use because it causes the undesirable phenomenon of adhesion and formation of secondary slag. Moreover, this post-blowing process also poses a problem in terms of cutting efficiency.

The present invention is characterized by the fact that when cutting in both directions, the slag (
The object of the present invention is to provide a gas cutting method that involves gas blowing on the back side, which is capable of completely removing cutting slag (including both cutting slag and secondary slag) and is also efficient.

As mentioned above, the post-blow treatment for bidirectional cutting that involves gas blowing has the following effects: the cutting slag cannot be reliably removed, and the slag that has been removed once is reattached, creating secondary slag. There is a problem.

With the aim of solving this problem, the inventors have conducted detailed experiments on the effects of the conditions for performing the after-blowing process on the slag removal situation.
In other words, spraying is performed under two conditions: gas pressure and nozzle advancement speed. - It was found that there is an appropriate range for cutting slag removal and secondary slag generation, and that the above problem (2) can be solved by optimizing these two conditions.

That is, in the present invention, in bidirectional cutting involving back side gas spraying using gas with a concentration of 50% or more, one back side nozzle is operated at a cutting speed of 2 to 20% even after the cutting is completed.
Continuously moving along the cutting groove at twice the speed, the gas pressure is first increased by 1 to 5 times to remove the cutting slag, and then the gas pressure is increased to 1 to 1 times the gas pressure when cutting. The gist of this invention is a gas cutting method for steel materials, which is characterized by performing a post-blowing process in which the blowing process is continued by lowering the blowing rate to twice the original level. It goes without saying that one of the backside nozzles here refers to the nozzle (51) on the side corresponding to the torch (21) that is responsible for the final cutting in the central portion of the slab.

In the present invention, first, the O concentration of the gas sprayed from the back nozzle (5) during cutting is set to 50% or more.If the concentration is lower than this, the slag oxidizing effect of the gas will be too weak, so it will not be possible to remove sufficient cutting slag. This is because it becomes difficult.

Regarding the post-blowing process after cutting is completed, it is important that the processing speed (progressing speed of the back side nozzle /l/(5/)) be at least twice the cutting speed. If the processing speed 5t is set above this value, cutting slag can be reliably removed after cutting is completed by performing post-blowing at an appropriate level of gas pressure, which will be described later. This can be considered as follows.

In other words, as shown in Fig. 8, when the cutting is completed in both directions, the unblown gas remaining in the center of the steel material is the part (d
) can be said to be the one caused by the torch (2, 2) on the side that was evacuated first, and the one caused by the torch (21) on the opposite side where the last cut was made, superimposed. However, looking at the problem caused by the torch (2J), the after-blowing process was not performed immediately after the slag was generated, as in the case of normal gas spraying, but was carried out after a certain amount of time had elapsed. That will happen. Until this post-blowing is carried out, the cutting slag produced by the torch (22) cools down and increases its adhesion strength, making it more difficult to remove.

However, if the processing speed of the post-blowing treatment is increased to more than twice the cutting speed as described above, the cooling time of the cutting slag will be shortened and the increase in slag adhesion strength due to cooling will be effectively suppressed. As a result, it becomes possible to reliably remove the cutting slag in the portions (, i) by gas blowing. Increasing processing speed is also effective in the sense that it directly leads to improved efficiency.

As described above, the processing speed of the post-blowing process must be at least twice the cutting speed, but if it exceeds 20 times, the speed is too high and complete removal of cutting slag cannot be achieved. In addition, as a current problem, the cutting speed
A high speed that exceeds 0 times, a speed that is difficult to express,
Merit power: None. For these reasons, in the present invention, the processing speed of the post-blowing process is limited to 2 to 20 times the cutting speed.

Gas spraying in this post-blowing process must be performed at a gas pressure that is 1 to 5 times the gas pressure during cutting for the cutting slag shown in FIG. 3(d). In other words, if this is less than 1, the cutting slag cannot be removed sufficiently;
If it exceeds twice that, there is no problem in terms of the cutting slag removal effect, but secondary slag is often generated due to the re-attachment of the removed cutting slag, and it becomes difficult to completely remove the secondary slag under the conditions described below.

Therefore, in the present invention, the gas pressure applied to the cutting slag, that is, the gas pressure immediately after cutting is completed and at the beginning of the post-blowing process, is set to be 1 to 5 times the gas pressure during gas spraying during cutting. More preferably, the gas pressure is such that the above ratio is 1.2 or more in view of the cutting sizing effect.

After the gas is sprayed onto the cutting slag in the above-mentioned side), the gas pressure is lowered to 1 to 1 times the gas pressure during cutting. This is essential because as a result of the gas blowing to the cutting slag, the removal slag is directed against the secondary slag that has reattached to the forward part of the cutting slag. If the gas pressure for this gas blowing is less than the gas pressure during cutting, sufficient removal of secondary slag will not be achieved. Note that even if this value exceeds 1 times, there is no change in the slag removal effect and it is uneconomical, so 1 times is set as the upper limit. The range in which this gas is sprayed is not particularly specified, but preferably both back side nozzles /' (5/) (5/
The gas spraying by
Effectively, it is recommended that the distance be approximately 100n or more.

In the present invention, the type of the back nozzle is not particularly limited. Any basic FCI can be used, such as a round nozzle with a circular nozzle hole, a slit nozzle with a slit-like nozzle hole, and other elliptical nozzles. When using a round nozzle, as shown in the schematic plan view of Fig. 4 (the figure shows the case of unidirectional cutting), the cutting progress direction is set for each of the slag generated on the left and right sides of the cutting groove (4). In view of the slag removal effect, it is preferable to spray gas from one nozzle (5) (5) from diagonally rearward. In the case of a slit nozzle, the width can be secured for wide gas spraying, so there is no need to adopt the above method, and the fifth
As shown in the figure (a figure corresponding to Fig. 4), it is sufficiently effective to use one slag on both sides of the cutting groove (4). From the standpoint of stability in removing slag, it is recommended to use the latter slit nozzle.

Note that the gas spray from the back side nozzle is at the corner (upward corner) and the position of the gas spray is at the corner (the upward corner).
It is appropriate to set the gas spraying position (Ml is a position 20 to 150ff away from the cutting tip point (0) backward in the cutting direction. Also, the gas spraying from this nozzle , it does not matter whether or not a preheating flame is used in combination.

The back side nozzle may be moved by being directly connected to the cutting torch while cutting is in progress, and for movement after cutting is completed, the driving means directly connected to the cutting torch may be used as is. Alternatively, this can be easily accomplished by providing an independent drive device, such as a hook-and-binion or cylinder device.

Next, effects of implementing the present invention will be explained.

2700 thickness x 1200111 width CC Nuwofu: (Temperature:
Bidirectional cutting (cutting in the width direction, cutting 1) at 1000°C:
20 am), when performing slit nozzle /L/(
Nozzle hole size: rl] 110 cod) was used as the back side nozzle (5/X5.2) in Fig. 3. 1. With the positional relationship between the cutting torch (2) and the M material (1) shown in FIG. 6 (only one side is shown), slag was simultaneously treated by the gas blowing method described in FIG. Cutting speed is 8007m
'rn.

Back side] -J The gas sprayed from Nonurire has a purity of 99.7
% oxygen gas, and the spraying was performed at a gas pressure of 1.0% s.

During this cutting, a post-blowing process was performed in which gas was continuously sprayed even after the cutting was completed. The processing speed and the blowing gas pressure for each of the (d) part (cutting slag) and ((3) part (secondary slag) in FIG. 3 were shown in Table 1.

The right column of the same table shows the results of investigating the condition of the back surface of the steel material in each of the above cases, that is, the degree of cutting slag and secondary slag residue. The same table also shows the results of the investigation in the same manner as the conventional example, even in the case where no gas blowing was performed after the cutting was completed.

According to the results in Table 1, the processing speed for post-blowing treatment is 2 to 29 times the cutting speed, the gas pressure for spraying the cutting slag is 1 to 5 times the same pressure during cutting, and the gas pressure for spraying the secondary slag. It is clear that if the conditions of the present invention of pressure: 1 to 1 times the same pressure during cutting are satisfied, sufficient removal of both cutting slag and secondary slag can be achieved. In other words, the secondary slag was not sprayed (li, (4), the same spray was applied twice but the gas pressure was lower than the above range (7), and the gas pressure for the cutting slag was lower than the above range (7). At αO9←[Yes], which was too high than the above range, some secondary slag residue was observed in all cases.

Table 1 Note 2) ○: No slag residue, △: Slag residue or ridge, ×:
Slag residue #) Paper sheet Note 3) A: Comparative example B: As is clear from the description of the examples of the present invention, according to the method of the present invention,
When cutting in both directions with gas blowing on the back side, it is possible to reliably prevent slag residue from being generated near the center of the steel material where cutting is completed by performing post-blowing treatment. Since the processing speed is fast, cutting can be performed in a very short time after completion of cutting, and the present invention enables highly efficient bidirectional cutting of 00771 without slag adhesion. It can be said that this is extremely useful in realizing the effective use of the heat retained in CC Nuhp by introducing a roll.

[Brief explanation of drawings]

Fig. 1 is a front view showing how cutting slag adheres, Fig. 2 is a schematic view showing the method of gas spraying, and Fig. 8 is a front view showing the state of adhesion of cutting slag.
A side view explaining the method for gas spraying in bidirectional cutting. Figures 4 and 5 show two specific examples of the method for gas spraying. Figure 4 uses a round nozzle, and Figure 5 uses a slit nozzle. The cases of use are shown respectively. FIG. 6 is a schematic diagram showing the arrangement of nozzles in an embodiment of the present invention. In the figure, l: wI material, 2: cutting torch, 3: slag, 4: cutting groove, 5: backside nozzle Applicant: Sumitomo Metal Industries, Ltd., Figure 6, Day 3, Figure 4, Figure 5: Tokyo Inside Koike Oxygen Industry Co., Ltd., 3-35-16 Nishikoiwa, Edogawa-ku, Tokyo (Old Inventor: Takiguchiana) Inside Koike Oxygen Industry Co., Ltd., 3-35-16 Nishikoiwa, Edogawa-ku, Tokyo Company 3-35-16 Nishikoiwa, Edogawa-ku, Tokyo

Claims (1)

[Claims] (1) Cutting is performed by moving a set of two cutting torches toward each other from both ends of the planned cutting line of the steel material along the planned cutting line, and at this time, the corresponding cutting torch is moved to follow the progress of cutting. In gas cutting, gas with an OJ concentration of 50% or more is sprayed from behind in the same direction toward a position slightly behind the cutting tip point on the back side of the steel material using the backside nozzle to remove cutting slag, and the cutting is completed. Thereafter, while continuously moving one of the back side nozzles along the cutting groove at a speed of 2 to 20 times the cutting speed, the gas pressure was increased to 1 to 5 times to remove the cutting slag, and then the gas pressure was When cutting, the spraying generates gas pressure.
A gas cutting method for steel material characterized by blowing gas at a rate of 1:1.