JPS58212866A - Hot gas cutting method of steel ingot - Google Patents

Abstract

PURPOSE:To prevent generation of secondary slag in hot gas cutting of an extra thick steel ingot, by adding spouting holes that a spout gas consisting essentially of oxygen and oxygen containing a specified proportion of incombustible gas to a nozzle for removing primary slag. CONSTITUTION:When cutting an extra thick steel ingot 1 by the nozzle 2 of a gas cutting torch forming a cutting slit 3, primary slag 72 formed by molten metal adheres to the back of the steel ingot. To prevent this adhesion, a pair of nozzles 5 are provided on the back of the steel ingot 1 on both sides of the cutting line X at slanting angles theta of 10-40 deg. to the back of the ingot. Many gas spouting holes 10 are provided on the nozzles 5, and gas containing >=80% oxygen is spouted from a part E of the holes, and mixed gas consisting of <=30% oxygen, the balance incombustible gas such as N, Ar is spouted from the remaining parts F. A reaction with the steel ingot 1 using an oxygen-enriched gas at the time of removal of primary slag is relieved by low oxygen gas, and the generation of secondary slag is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas cutting method that can reliably prevent slag from adhering to a hot steel billet that occurs during gas cutting of a hot steel billet.

The slag adhesion phenomenon that occurs during gas cutting of extremely thick steel pieces such as continuous casting slabs is as shown in the front view of Figure 1.
When a steel piece (1) is cut by a gas flow from a cutting torch nozzle (2) provided on the front side, a part of the flow of molten metal generated by the cutting goes around from the cut end face (4) to the back side, resulting in a sign ( η+', a state as shown in 7.1 is formed, which is caused by solidification.This slag adhesion interferes with the lower process of cutting.

If the material to be cut is a thin steel plate, it is possible to avoid slag adhesion relatively easily by selecting appropriate cutting conditions. It is extremely difficult to prevent slag adhesion by selecting cutting conditions. Furthermore, the adhesive strength of this 70 adhesion increases as the cutting thickness increases, and it is particularly strong in the case of hot materials. Therefore, if rolling is performed in the lower process with the slag still attached, it will lead to the occurrence of rolling defects and rolling roll defects in the steel plate, and furthermore, this will become a factor in reducing the manufacturing yield.

Such strong adhesion of 70 cannot be removed simply by hand, and is usually removed by mechanical grinding with a cutting tool or scarfing. However, in order to carry out this work, a dedicated process is newly added, and this addition of a process reduces the efficiency of a series of manufacturing processes, which poses a problem.

On the other hand, a method for preventing the above-mentioned slag adhesion during cutting has been proposed by the same applicant in Japanese Patent Application No. 119541/1983. This is because the nozzles, which are arranged in pairs symmetrically on the back side with the cutting line Gas is sprayed along the cutting slit (3) so as not to disturb the cutting gas flow, and cutting is performed while being blown away by the gas flow to prevent slag from adhering.

The above proposal is a method that can be sufficiently effective in preventing slag adhesion when cutting relatively low-temperature steel billets below soo'c; However, it is difficult to say that this is an adequate prevention method. The reason is as follows.

(1) First, in order to prevent the gas from disturbing the cutting gas flow when sprayed from the nozzle on the back side, it is necessary to use high-purity oxygen gas as the gas. However, when the material to be cut is a hot-worked steel piece at a temperature of 500°C or higher, the spraying of high-purity oxygen gas from the nozzle causes secondary damage due to the reaction between the gas and the hot-worked steel piece. Generates a flow of molten metal, some of which solidifies, creating secondary slag deposits. Therefore, the gas sprayed from the nozzle may actually worsen the condition of the back surface of the steel billet after cutting. (2) Since it is extremely difficult to perform even slight maintenance on hot steel pieces heated to 500°C or higher after cutting, it is desirable to incorporate them into the next process completely unmaintained. That is,
Conventionally, after gas cutting, for example, before charging into a rolling heating furnace, -
Because it was cooled to room temperature or close to room temperature, it was possible to easily carry out maintenance such as the mechanical grinding mentioned above after cooling, but in hot piece charging, non-heat rolling, etc. that have recently become popular, The cooling process as described above is omitted.

Since it is sent to the rolling process without cooling, it is extremely difficult to clean it before rolling. Similarly, even if the above-mentioned difficulties are avoided and maintenance is carried out forcibly, the maintenance will take time, the slab temperature will drop, performance will vary, and unfavorable results will occur from the point of view of energy saving effect.

The present invention has been made in view of the above.

The purpose of the present invention is to provide a gas cutting method for hot-worked steel pieces that can reliably prevent slag adhesion during gas cutting of hot-worked steel pieces at temperatures of 500'C or higher and that does not require maintenance after cutting.

As mentioned above, when hot-worked steel pieces are gas-cut at temperatures of 500°C or higher, high-purity oxygen gas is sprayed from the nozzle on the back side, and the oxygen gas reacts with the hot-worked steel pieces, causing secondary slag adhesion. It is believed that if the above reaction could be suppressed, the occurrence of secondary slag adhesion could be prevented. The inventors of the present invention have conducted various experiments and research with the intention of developing a method for effectively suppressing the above reaction, and have discovered the following facts.

That is, first, as shown in the bottom view of Figure 2 (→), the nozzle (5) C5) blows out high-purity oxygen gas from the front part E, and blows out Ar with a low oxygen content from the rear part F, Provided to blow out nonflammable gas mainly composed of N2, etc.

Next, this nozzle (S) (5) is moved as the cutting torch advances, and high-purity oxygen is supplied from the front part of the nozzle (S) (5) to the slag that has gone around the back side of the steel piece during cutting. Cutting is performed while blowing gas and non-flammable gas from the rear. When cutting in this way, the nozzle (5
) (5), the cutting gas flow (8)
The code (7p (
As shown at 79, the slag is pushed back into the cutting gas flow 8), and the spray from the nozzle is suppressed due to the above-mentioned reaction between the oxygen gas and the hot steel piece, resulting in secondary slag adhesion. We have discovered four results: the prevention of 70 adhesion is extremely effective and complete prevention of 70 adhesion is achieved.

Nozzle <5) <5) As shown in the bottom view of Figure 2 (B), the reason why no turbulence is caused in the cutting gas flow (8) despite the nonflammable gas being sprayed from the rear is because of the nozzle. (5) (5
) moves toward the cutting tip point <o'ir while blowing gas, so only the preceding high-purity oxygen gas always mixes into the cutting reaction section. In addition, the above reaction between the oxygen gas and the hot steel billet is suppressed by the high purity spraying from the nozzle (5) (5), which is due to the high purity oxygen gas sprayed in advance. The combustion action is
This is because the nonflammable gas subsequently sprayed afterwards immediately calms down the atmosphere and effectively prevents the reaction between the oxygen gas and the hot steel billet from proceeding.

That is, the present invention was made based on such knowledge, and the gist thereof is that in gas cutting of hot steel pieces of soo'c or more, the cutting torch nozzle (2)
The blowout width (J) is 11011 on the back side of the steel piece on the opposite side.
11J, a pair of nozzles (5) (5) that blows out gas containing 80% oxygen or more from the front and nonflammable gas containing 30% oxygen or less from the rear are connected to the back side of the steel billet. The angle formed by the nozzle (5) is within the range of 16 to 46. On each of the left and right sides of ■, the lateral angle ■ made with the cutting line ■ toward the cutting tip point O when viewed in plan is 76 to 11 (within the range of 5,
And while blowing gas with an oxygen content of 80% or more and nonflammable gas with an oxygen content of 30% or less in a direction toward a position (g) that is at least Iotm apart from the cutting edge (a) when viewed from the front, the crater (2) is The cutting is performed while moving as the cutting progresses, and the slag generated on the back side of the steel piece as it is cut is pushed back into the cutting slit (3) and blown away by the cutting gas flow. Gas cutting of hot steel billet, method.

Here, the above-mentioned lateral angle @) refers to the angle taken toward the direction of cutting progress on each of the left and right sides of cutting +1 (X).

Note that the method of the present invention is equally applicable to both straight and curved cutting lines. That is, in the case of curved cutting, the lateral angle @) may be considered as the angle formed at the cutting tip point with respect to the tangential direction of the cutting line.

Next, reasons and conditions for limiting each requirement of the present invention will be explained.

The temperature of the hot steel billet was limited to 500'C or higher.
At temperatures below 0°C, no secondary slag is generated due to the reaction between the high-purity oxygen gas flow from the nozzles (5) (5) and the steel slab, and therefore nozzles (5) (5) cannot be used from the front. This is because there is no need to blow out high-purity oxygen gas and blow out nonflammable gas with a low oxygen content from the rear part.

The nozzle used in the method of the present invention has a nozzle hole with a slit-like long hole (9) as shown in FIG. As shown in the figure, each blow-off hole is divided into two sections, E part at the front and F part at the rear. It is better.

The reason why the blowing width (71) of the above-mentioned nozzle (5) < 5) was limited to 10 cm or more is because the occurrence of 70 is most noticeable at the cutting tip (1) VC, but it also occurs in the vicinity.
This is because if it is less than 1, the slag pushed back into the cutting slit (3) by gas blowing cannot sufficiently cover the entire slag generating area, resulting in slag remaining.

The reason why the type of gas sprayed from the nozzle is limited as mentioned above is because if the gas from the front part (D) contains less than 80% oxygen, if this gas mixes into the cutting reaction part, it will cause turbulence in the cutting gas. This is because the cutting becomes unstable.Also, the rear part (
If the gas or oxygen from E exceeds the I range, the reaction between the high-purity oxygen gas from the front part and the hot steel slab will not be sufficiently calmed down, resulting in secondary] B adhesion. This is because there is a risk of The front part of the nozzle (the rear CF)
) There is no specific regulation regarding the ratio of the gas blowing width to the front part (D4: rear ■l), but it is best to set the ratio to about the same as the front part (D4: rear ■l).Also, when blowing from the nozzle, the gas flow controls the flow of slag. Since the pressure is only 2-3 to 9
A low pressure of about /lyA is sufficient.

The reason why the upward inclination angle of the nozzle (5) (5) is limited to a range of 16 to 46 is because if the nozzle's aim is slightly off when it is less than 16, the value of the electric charge distance (d), which will be described later, will change drastically. This creates a problem in terms of aiming accuracy.

Moreover, when the number exceeds 46, the part of the gas flow from the nozzle (5) that flows outward when it collides with the lower surface of the steel piece increases, increasing the efficiency by 1.
This is because it is not good.

Regarding the gas blowing from the nozzle (5) I'5), first of all, the direction toward the cutting tip point (O) when viewed from above is as follows.
Needless to say, the main slag generation occurs at the tip of the cut during cutting, but the cutting line (the lateral angle (b) between
The reason for limiting the range to 116 is as follows. In other words, if it is larger than 116, the component force of the gas flow to the rear of the cutting progress will be too strong, and the slag will tend to flow backwards, making it insufficient to push the slag back into the cutting slit (3). , leaving a slag residue. Also, if it is less than 76, the nozzle (5
This is because the gas flow from ) is heavily mixed into the cutting gas flow, making cutting unstable, which not only causes new slag generation but also causes deterioration of the condition of the cut surface. Further, the reason why the power from the front in the cutting direction is limited to 19 W or more is because if it is less than 10 W, there is a high risk that slight fluctuations in the spraying position will lead to slag residue, and a stable effect of preventing 70 adhesion cannot be expected.

Regarding the presence or absence of a preheating flame for the cutting torch nozzle and nozzle,
A preheating flame from the cutting torch nozzle is required as usual, but a preheating flame from the nozzle may or may not be present.

Next, examples of the present invention will be described.

A hot steel piece with a thickness of 250 mm was gas cut under the cutting conditions shown in Table 1, using the long hole nozzle (width 3 Qm x height 1.51 fil) shown in FIG. 3 (a) according to the method of the present invention. ,
The front part [F] and the rear part (0) are divided into length ratios of 4:1, and oxygen is blown out from the front part [F], and nonflammable gas of the type shown in Table 1 is blown out from the rear part (0). In addition, as shown in Figure 2 (
Shown in a) and (b)! The width of the nozzle (J), the separation distance (d), and the angle of inclination (in the direction of
Gas was sprayed with each value shown in the table, and the occurrence of slag adhesion was investigated. Gas was blown under the same conditions as above, except that the blowing width (j), separation distance (d), and inclination angle (lateral angle @) were set to values outside the scope of the present invention. We investigated the occurrence of slag adhesion ◇ The results are summarized in the back column of the same table. The occurrence of slag adhesion is indicated by the presence or absence of slag adhesion.

In the above table, the blowout width (g) is 306, and the separation distance (d
) is 20101, the inclination angle ψ) is 36, and the side angle) is in the range of 7C to 1 degree. Oxygen is sprayed from the front [F] and non-flammable gas mainly composed of N or Ar is sprayed from the rear. −
In all of the invention examples (1) to (4), there was no slag adhesion, and the prevention of 70 adhesion was completely achieved, and no maintenance was required at all. On the other hand, in Comparative Example (5), the separation distance (d
) was less than 10 cm, and Comparative Example (6) had an inclination angle of less than 16, both of which were outside the scope of the present invention. Comparative Example (7) Significant slag residue was observed on the surface and on the side corners since the value of )) was less than 76, which was outside the range of the present invention. Comparative example 8)'fi
Since the lateral angle (b) was too large than the range of the present invention, pushing back the slag was insufficient and 70 was left.

In Comparative Example (9), significant slag residue was observed because nonflammable gas was not sprayed from the rear of the nozzle.

As is clear from the above explanation, the method of the present invention can
The slag generated during gas cutting of hot steel pieces at temperatures above 0°C is
High-purity oxygen gas is sprayed from the front and non-flammable gas is sprayed from the rear, pushing the slag back into the cutting gas stream. Since the reaction between oxygen gas and hot steel pieces is suppressed by spraying nonflammable gas to prevent the generation of secondary slag, it is possible to completely prevent slag adhesion, and there is no need for post-cutting maintenance. It has the remarkable effect of making it unnecessary.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the situation of slag generation during gas cutting, Figs. 2 (a) and (b) are front and bottom views showing the nozzle installation state when carrying out the method of the present invention, and Fig. 3 (
A) and (B) are front views showing an example of a nozzle. 1: Steel piece, 2: Cutting torch crater, 3: Cutting slit, 4
: Cut end surface, 4: Cut edge, 5; Nozzle, 6: Gas flow for spraying, 7. ．． 7. : Slag, 8: Cutting gas flow. 9: Two long holes, 10: Porous. 1Jh11! I (I) Second! ! I 3rd! ! I (B) Continued from page 1 0 Author: Takiguchiana 3-35-16 Nishikoiwa, Edogawa-ku, Tokyo Inside Koike Oxygen Industry Co., Ltd. @ Applicant: Koike Oxygen Industry Co., Ltd. 3-chome Nishikoiwa, Edogawa-ku, Tokyo 35 No. 16

Claims (1)

[Claims] (1) In gas cutting of hot steel slabs at temperatures of 500°C or higher, the back side of the steel slab opposite to the cutting torch nozzle (2) has a blowout width CI) of 10- or more, and oxygen is emitted from the front part. 8
A pair of nozzles (5) (5) that blow out gas with a coefficient of 0 or more and a non-flammable gas with an oxygen content of 30 or less from the rear are cut within the range of 16 to 466 on the back side of the steel piece. Cut from the nozzle (5) on each of the left and right sides of the cutting line ■ (viewed from a plane). Tip point (
The lateral angle (b) made with the cutting line 00 towards O is 76~1
Within the range of 16 and when viewed from the front, the cut edge ('4) and 1
The steel piece is moved as the crater (2) advances while blowing a gas with an oxygen content of 80% or more and a nonflammable gas with an oxygen content of 30% or less in the direction toward F5 at a position spaced apart from O11a or more (in the direction toward F5). A gas cutting method for hot-worked steel billets, characterized in that the cutting is performed while the slag generated on the back side is pushed back into the cutting slit (3) by the gas flow and blown away by the cutting gas flow.