CS205094B2 - Method of thermochemical descaling the workpiece and apparatus for executing the same - Google Patents

Abstract

A thermochemical scarfing process and apparatus capable of reducing the amount of smoke discharged to the atmosphere and/or of preventing the formation of "secondary" fins when spot scarfing, comprising: (a) scarfing oxygen is directed against a reaction zone of molten metal on the surface of the workpiece to produce a scarfing reaction, and (b) relative movement is provided between the oxygen stream and the workpiece, said reaction forming a molten puddle in front of the reaction zone that grows larger as the cut progresses, wherein the improvement comprises: (c) directing at least one stream of non-reactive fluid to form a fluid, sheet-like curtain that provides a cover over the reaction zone and at least the rear portion of the molten puddle in such manner that said curtain forms a pocket with the surface of the workpiece.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for thermochemical scarfing of a workpiece, wherein the scarfing oxygen stream is directed to a molten metal reaction zone on the surface of a metal workpiece to produce a thermochemical reaction thereon. to create the desired descaling. the reaction forming a molten pool upstream of the advancing reaction zone, which pool tends to increase as the notch continues and in which a non-reactive fluid is used.

The invention also relates to an apparatus for carrying out this method.

When descaling, it is first necessary to form a molten metal pool or a "hot spot" on the workpiece surface by:. the preheating flames are directed to a relatively small area of the workpiece until it reaches its ignition temperature. An oxygen stream is then obliquely directed to the molten pool to form a thermochemical reaction on the metal surface. Then between the current. of oxygen and the workpiece causes a relative movement that causes the thermochemical reaction to continue along the metal surface, thereby creating the desired surface removal along the metal body. In the descaling reaction, a pool of molten slag formed downstream of the reaction zone proceeds along the advancing reaction zone. of the workpiece surface. This pool of slag preheats the metal surface before it. its temperature rises to the ignition temperature with a descaling oxygen stream. Thus, the oxygen stream has a dual purpose: first of all to carry out a thermochemical reaction with the metal and, moreover, to continuously advance the molten pool of metal and slag to expose fresh metal. descaling reaction.

Conventional de-scaling entails two seemingly unrelated problems, namely burring when cleaning less than the entire surface of the workpiece, and smoke, regardless of whether the entire surface is scaled or less than the entire surface. Yippee . surprisingly, a preferred embodiment of the invention has the advantage of minimizing the adverse effects of both of these problems, these effects being discussed separately.

One problem associated with scaling less than the full width of a metal surface, a process commonly referred to as " spot " 'Local scaling' is the formation of burrs at the edge of the scaling hole.

As used herein, the term " burrs " o thin flashes or 205094

5 0 3 solids of pure or slightly oxygenated parent metal which are firmly attached to the surface of the metal workpiece to delimit the scarfing notch; burrs are undesirable defects on the metal body and must be removed before rolling the body. Burrs can be caused by one or two causes unrelated. The burrs may be formed directly from the primary reaction zone if the molten metal is pushed out of the zone by the force of a scarfing oxygen stream, thereby adhering the molten metal to the edge of the scarfing notch where it solidifies in place. This type of burr formation (hereinafter simply referred to as "primary" burrs) can be eliminated by using a specially shaped outlet for the descaling oxygen stream, which gradually decreases the intensity of the oxygen stream at the ends of the orifice to the point where the stream it cannot maintain the descaling reaction along the boundary of the descaling notch, but can oxidize the molten metal at the boundary before it solidifies. Nozzles having holes of the particular type described above are particularly suitable for spot scaling in single and group configurations as described in U.S. Pat. U.S. Pat. Nos. 4,040,871 and 4,013,486.

Burrs can also arise from the so-called "secondary" effect, which occurs when the molten slag pool gradually increases upstream of the primary reaction zone up to the limit where the oxygen pre-flow can no longer advance the entire pool, so pushing only the central part of the pool. a portion of the molten metal at the edges of the pool to the side beyond the scaling notch where the metal solidifies in the non-oxygenated state. One problem solved by the invention is a method and apparatus for preventing such secondary burrs.

The use of fluid streams to remove slag generated by the scaling reaction is known. For example, in U.S. Pat. U.S. Pat. Nos. 2,873,224 and 3,163,559 disclose solid and hollow streams of high pressure water which are directed transversely to overcoat the workpiece surface just in front of the reaction zone to wash off the slag. In Pat. U.S. Pat. No. 3,354,002 discloses a plurality of high speed water jets located somewhat downstream of the reaction zone perpendicular to the direction of the descaling reaction process to catch the slag spray and wash it from the workpiece surface into the slag trough. Although the use of such water jets located across the workpiece surface and commonly referred to as "flame jets" or "slag water jets" is effective to remove slag from the metal surface, it is unable to prevent burrs. This is primarily due to the fact that the slag water nozzles or the cross-flame nozzles are located on one side of the workpiece to blow molten slag from the proximal side of the notch into a slag vessel located along the opposite side of the workpiece. This has the effect of reducing the burr formation to a minimum on the proximal side of the indentation, while on the far side the burr formation problem becomes more difficult.

The second problem associated with conventional descaling processes is the large amount of smoke, i.e. flue gases or vapors and fine particulate materials formed by the descaling reaction. Previous techniques for collecting and removing smoke from the adjacent scarfing reaction zone are relatively inconvenient as they require a disproportionate amount of auxiliary scrubbers. In descaling machines, where the workpiece moves around a stationary machine, usually smoke is collected in large stationary hatches and removed by ducts that are kept under negative pressure by the fans. The trapped smoke is then sent by scrubbers and precipitation vessels to remove the pollutants before they are released into the atmosphere. In devices where the scarfing machines move around a stationary workpiece, advancing lines are used to collect smoke instead of the stationary smoke hatch. However, in both cases, the equipment required for collecting and cleaning the smoke is relatively large, expensive and difficult to maintain.

In addition to preventing the secondary burr formation and reducing the amount of smoke released into the atmosphere, the invention also gives a third favorable result, namely noise reduction. Indeed, when comparing descaling processes carried out without using the invention and using the invention, it is clear that the use of the invention reduces the amount of noise resulting from the descaling reaction.

It is therefore an object of the present invention to provide a method and apparatus for spot flame cleaning or scaling of a metal workpiece surface so as to prevent secondary burrs along the boundary of the spot scaling notches.

It is further an object of the invention to substantially reduce the amount of smoke escaping into the atmosphere from the descaling reaction in this manner and by the apparatus.

Finally, it is an object of the invention that both the method and the device for spot scaling the surface of a metal workpiece are designed such that secondary burrs along the scarfing cut are avoided while substantially reducing the amount of smoke escaping into the atmosphere from the scaling reaction.

All these and other effects which are described below are achieved by the invention, which is based on the above-described process of thermochemical descaling of a workpiece, characterized in that a liquid sheet is formed above the reaction zone by at least one stream of non-reactive fluid. forming a cover over the reaction zone and over at least the rear. the part of the molten pool that forms a pocket with the surface of the workpiece.

According to a preferred embodiment of the method according to the invention, the stream of non-reactive fluid is directed upwards and in the same direction as the stream of oxygen and downwards at an acute angle to the workpiece surface.

According to another embodiment of the method of the invention, the stream of non-reactive fluid is directed from one side of the oxygen stream and perpendicular to the oxygen stream and at an acute angle to the workpiece surface.

Preferably, the water jet is directed perpendicularly to the direction of the scarfing cut across the workpiece surface in front of the molten pool until the front edge of the fluid orifice intersects.

According to another embodiment, the water jet is directed perpendicularly to the direction of the descaling cut across. the workpiece surface in front of the molten pool until the front edge of the fluid orifice intersects.

In another embodiment, the stream of non-reactive fluid is directed to impact across the entire width of the molten pool past its leading edge.

When the jet or streams forming the fluid orifice are directed downward from the top of the oxygen stream and substantially in the same direction as the oxygen stream, such streams impinge on the molten pool over its entire width and at a sufficient distance beyond the leading edge of the pool and with sufficient intensity, For example, by pelletizing the front of the pool and driving forward in the peeling path, the pool is kept small enough to be easily pushed forward by the peeling oxygen stream without deflecting a portion of the pool to the side beyond the peel cut. In this way, the formation of secondary burrs is prevented.

The invention also relates to an apparatus for carrying out the above method, starting from an apparatus comprising a nozzle with an orifice for discharging an oxygen stream. According to the invention, the apparatus comprises at least one additional nozzle for discharging the stream of non-reactive fluid located above the orifice of the nozzle for discharging the oxygen stream.

According to a preferred embodiment, the orifice of the additional nozzle for discharging the stream of non-reactive fluid is directed in the same direction as the orifice of the oxygen discharging nozzle.

In a preferred embodiment of the invention, the longitudinal axis of the additional nozzle is perpendicular to the longitudinal axis of the nozzle for discharging the oxygen stream.

As used herein, the term "non-reactive fluid" refers to a fluid that does not react rapidly with a metal workpiece. Water is a preferred non-reactive fluid for achieving both objectives, i.e., avoiding secondary burrs and smoke control. However, other non-reactive fluids such as water vapor may be used. mist (i.e., a mixture of water and air) or a mixture of water and an inert gas such as nitrogen or argon.

The invention will now be explained in more detail with reference to the drawings.

Giant. 1 is a schematic front elevation of a conventional scaling point in which molten pool of metal and slag are formed.

Giant. 2 and 3 are top views, optionally in cross-section, respectively. depicting a steel slab or plate which is scaled using a conventional burr-forming nozzle.

Giant. Figures 4 and 5 are top and cross-sectional views, respectively, showing a steel plate with a scaled nozzle capable of preventing the formation of primary burrs but unable to prevent the formation of secondary burrs along the notch boundary.

Giant. 6 and 7 are top and cross-sectional views, respectively. and illustrate a steel plate which has been scaled according to the invention, i.e. which. has a notch that is free from secondary burrs and primary burrs.

Giant. 8 shows an oblique view of a preferred embodiment of the invention according to which the metal plate can be scaled off to create a burr-free cut while reducing the amount of smoke released into the atmosphere.

Giant. 9 is a side view showing the relative orientation of the water stream and the oxygen stream in order to achieve both a reduction in the amount of smoke and the removal of secondary burrs.

Giant. 10 is a side elevational view, and illustrates a fluid-curtain which will reduce the amount of smoke discharged into the atmosphere but may not prevent secondary burr formation.

Giant. 11 is a side view illustrating a fluid stream that is useful for preventing the formation of secondary burrs, but not for reducing smoke discharged into the atmosphere.

Giant. 13 is a side view of one embodiment of the invention and illustrates how a smoke control pocket can be formed by directing the fluid orifice in the direction of the oxygen flow so as to intersect the nozzles or slag water jets directed across the flame.

Giant. 14 is an elevational view of an embodiment of the invention and illustrates how a smoke control pocket can be formed by directing the fluid orifice perpendicular to the oxygen flow so as to intersect the slag water jets across the flame.

The invention is based, in part, on the discovery that secondary burrs along the edges of the scarfing notch can be prevented by directing a stream of non-reactive fluid to the workpiece in order to efficiently control the size of the molten pool before the reaction zone. The stream of non-reactive fluid reaching the molten pool beyond its leading edge keeps the pool below the level beyond which the pool can no longer be pushed forward along the metal surface by the oxygen scavenging stream without deviating portions of the pool beyond the scarfing cut. The term "behind" is used in relation to the scaring oxygen stream. For this reason, with this preposition "after" is meant toward the descaling nozzle. The permissible puddle length may vary depending on the descaling oxygen pressure, the descaling speed and the depth of the notch. For spot scaling on cold steels, it has been shown that a stream of fluid striking the slag pool at a distance of about 35 cm in front of the reaction zone is effective to prevent secondary burr formation. In order to control the formation of burrs, the fluid stream, preferably a water jet, at a pressure of at least 90 kPa located above the descaling oxygen stream and striking the slag pool at an angle of approximately 45 ° to the workpiece surface, is directed in the oxygen flow direction. However, the angle of inclination of the water jet and its location relative to the pool may vary within wide limits, provided that it granulates the front of the slag pool and moves it in the same direction as the descaling zone. The angle between the fluid and the workpiece may therefore vary from 20 ° to 80 ^э and still be effective for preventing formation of burrs.

It has also been found that the fluid shield that covers the reaction zone and at least the back of the molten pool so as to form a pocket with the workpiece surface or transverse beams to remove slag serves as a dam and absorbs large amounts of smoke generated by the descaling reaction. The fluid stream somewhat “scrubs” unwanted vapors and particulate matter and prevents them from escaping into the atmosphere surrounding the descaling reaction. As a result, undesirable smoke contaminants are concentrated in a fluid stream that can be cleaned with much less effort and cost than cleaning relatively large volumes of air containing impurities in the diluted state.

Fig. 1 shows a single spot scaling nozzle N that produces a notch in the direction indicated by arrow A at depth D on the workpiece M. The primary reaction zone R is formed between the scarfing oxygen stream discharged from the scarfing nozzle N and between the workpiece M. by the descaling puncture, the volatile by-products of the descaling reaction (i.e., smoke F) are discharged from the reaction zone R as well as from the back of the slag pool S. The front of the pool S is cooler and produces less smoke. In addition, the front portion is typically removed by transverse water jets 9 (as shown in Figures 13 and 14). A portion of the molten material from pool S is blown out of the reaction zone R to the edge of the scarf cut. If the nozzle N is a conventional round or rectangular orifice, the melt so blown again solidifies and adheres to the workpiece M, as shown in Figures 2 and 3, along the boundary 11 of the scarfing notch 12 to form burrs 13. In addition to the burrs 13 are formed of metal from the deflated primary reaction zone and may be formed independently of a second source, namely a portion of the molten slag pool S upstream of the reaction zone; burrs formed from this section are referred to herein as secondary burrs. In all cases, the burrs 13 must be removed prior to subsequent rolling of the metal body.

Giant. Figures 4 and 5 show how the secondary burrs 20 are formed on the workpiece surface M by spot scaling in the direction of arrow A when a specially shaped nozzle is used which is only capable of preventing the formation of primary burrs. The resulting scarfing notch 22 is burr-free at a distance d from the initial or leading edge 23 of the notches, while the remainder of the notch is characterized by secondary burrs 20 along the notch boundary 24. The burr-free notch 22 reflects the fact that the molten slag pool has been properly pushed forward along the workpiece surface over a distance d by a scarfing oxygen stream exiting the scarfing oxygen nozzle N, and this particular shaped nozzle has prevented the formation of primary burrs. However, when the size of the puddle before the advancing reaction zone becomes disproportionately large, portions of the puddle will deviate to the notch sides by a scarfing oxygen stream and produce secondary burrs.

Giant. 6 and 7 show a notch 39 with smooth contours, free from burrs along its boundary 31 and formed when the workpiece M is scaled using the specially shaped nozzles mentioned above and in accordance with the process of the invention, avoiding the formation of both secondary and primary burrs.

Giant. 8 illustrates the course of a spot scarfing puncture in which a single water nozzle 40 located above the scarfing unit 41 directs, as shown, a high pressure water jet that extends into a water curtain 44 that impinges on the slag pool 46 at a distance e beyond the front edge 42 of the pool. The puddle front section 43 is cooled and granulated with a water curtain 44 and the granulated slag 45 is swept forward substantially in the direction of the descaling path indicated by the arrow A. To reduce the amount of smoke entering the descaling reaction air, the water curtain 44 must be at least equal to the width of the reaction. zone as it passes over it. It can be seen that the oblique water curtain 44 forms a pocket with the workpiece M to trap rising smoke by absorbing it.

To prevent the formation of burrs, the water jet 44 must have at least the width W of the molten pool when on. The pile strikes to ensure that the puddle front portion 43 is granulated over its entire width and flushes forward by the high pressure water curtain 44. The remainder of the pool 46 is thereby kept small enough to be moved forward by an oxygen stream, but again large enough to still sufficiently preheat the workpiece M. In order to prevent the formation of primary burrs, the descaling oxygen unit 41 must be shaped in a special manner according to U.S. Pat. No. 4,040,871 for forming a single shake-free notch or U.S. Pat. No. 4,013,486, if any. a plurality of adjacent notches are provided.

Although a single water nozzle 40 whose jet extends is shown in FIG. 8, it will be apparent to those skilled in the art that a plurality of such nozzles or wide-hole nozzles may be used instead of the nozzle shown. Multiple nozzles may advantageously be used if improved smoke control is desirable or necessary to provide a fluid curtain that perfectly covers the area above the smoke-forming reaction zone, the primary reaction zone, and the hot rear end of the pool of molten slag.

Giant. 9 is an elevational view of an apparatus similar to that of FIG. 8 except that a scaling oxygen burner with a single nozzle N is used instead of the scaling unit 41. The nozzle N directs the scaling oxygen flow. B in the direction of the nozzle axis N to the workpiece M to form a descaling reaction zone R. Reference D represents the notch depth and arrow A the direction in which the peeler notch advances. The water curtain J discharged from the water nozzle 50 impinges on the slag pool S at a distance L in front of the reaction zone R at an angle α to the workpiece M. Obviously, the water curtain J does not interfere with and must not impinge on the reaction zone R, reaction and its complete disabling.

According to the invention, both smoke control and secondary burr prevention can be achieved using the apparatus shown in Figs. 8 or 9 when the following operating conditions are used to descaling cold steel at a speed of approximately 9 meters per minute to a depth of 4.763 mm: the distance L is approximately 35 cm and the angle α formed by the water jet I 'and the workpiece surface is between 39 ° and 45 °. The fluid pressure should be between 820 kPa and 1120 kPa. The preferred fluid is water. It is prevented that the pool S does not increase to more than length L, which is the amount that the scarfing oxygen stream B is able to move forward, since that pool portion 51 that would normally form before the water stream J is granulated and washed away from the peeling notch. Like the apparatus shown in FIG. 8, the apparatus of FIG. 9 can also be used in combination with a means for preventing primary burrs. To do this is like. nozzles. N needed to use. a special nozzle that prevents the formation of primary burrs as described in U.S. Pat. No. 4,040,871 and 4,013,486.

Obviously, water. the orifice J not only prevents secondary burrs, but also covers it. The area above the reaction zone from which the smoke exits also acts as a smoke-absorbing screen, since the smoke tends to move upwards and is thus captured by a water curtain J. The smoke consists of fumes of iron oxide, vaporized metal, fine particles: slag, etc.

Giant. 10 shows the effect of directing the water jet J further backward so that it intersects the workpiece M before the slag pool S. Here, the water curtain created by the stream J will reduce the amount of smoke discharged into the atmosphere, but will not prevent the formation of secondary burrs, since the water curtain J does not strike the descaling slag pool S, thus avoiding secondary burr formation. by keeping the pool size small. However, if the fluid orifice passes through the reaction zone at a width at least equal to the width of the reaction zone, the amount of smoke discharged into the atmosphere will be substantially reduced. The aforementioned angle can vary between 0 ° and 60 ° and still perform effective smoke control, with a preferred one. the angle is 30 °. The water pressure may vary from about. 310 kPa manometric pressure to any practically usable height. Mixtures of water and air can be used at a lower pressure as air tends to spray water and produce a finer mist. water above the reaction zone. Steam or. a mixture of an inert gas such as nitrogen or argon with water will also be effective. capture smoke. Fluid containing trapped smoke. is usually collected together with water from the slag nozzles in the drainage system below the workpiece, from where it is routed through a pipe to the water treatment system.

Giant. 11 is an elevational view of that embodiment of the invention that avoids secondary burring but does not substantially reduce the amount of smoke discharged into the atmosphere. Here, the water nozzle 50 is positioned such that the fluid flow does not pass through the reaction zone R, thereby not achieving effective smoke control. However, as the water jet J impinges on the pool S over its entire width and at a sufficient distance in front of its front part to be granulated and pushed forward, it is achieved. prevention. formation of secondary burrs. To prevent secondary burrs, the angle may be. and varying from about 20 ° to about 80 °, wherein. an angle of 45 ° is most preferred. Most preferably, the fluid pressure is at least 820 kPa manometric pressure.

Giant. 12 shows another embodiment of the invention that is capable of greatly reducing the amount of smoke discharged into the atmosphere but not preventing the formation of secondary abrasion of the soil. The descaling unit 51 performs a spot descaling notch on the workpiece M as shown. Arrow A indicates a descaling cut or path mixture. The water nozzle 60 extends to form a fan-shaped water stream 54 that is wide enough to cover the entire molten pool 56 and the reaction zone R. Although the preferred method of directing the fluid stream is downstream of the descaling oxygen stream at an oblique angle to the workpiece and substantially in the same direction as the descaling oxygen stream, the fluid may emanate from either side of the workpiece as shown in Fig. 12 if it forms a screen covering the reaction zone R and at least the rear of the molten pool 56 so forming a pocket with the workpiece exiting the descaling reaction. Referring to FIG. 12, the fluid stream 54 is directed from the right side of the oxygen stream 61 and perpendicular to the direction of the stream 61. Although only one water tube 60 is shown, several such nozzles may be used.

Giant. 13 shows how a smoke trap pocket can be formed by combining a fluid orifice 11 with transverse water jets 9. Such nozzles and jets are described in more detail, for example, in U.S. Pat. U.S. Pat. Nos. 2,465,297, 3,163,559 and 3,354,002. The descaler unit 5 is one of several such units (of which only one is shown) adjacent to each other to descaler the entire surface of the workpiece. In such cases, it is no problem to create burrs along the edges of the scarfing notch. According to FIG. 13, the descaling units 5 direct a surface descaling oxygen stream 6 to the surface of the metal workpiece M to produce a thermochemical reaction. A molten slag pool 8 is formed in front of the reaction zone R. Three slag water jets 9 that overcoat the workpiece surface M are used to granulate, trap and remove the slag. The collecting tube 10 discharges the fluid orifice 11 over the upper portion of the reaction zone R. The front edge of the orifice 11 intersects the transverse seams 9 of the slag water to form a pocket to capture the smoke.

Claims (9)

A method for thermochemical scarfing of a workpiece, wherein the scarfing oxygen stream is directed to a molten metal reaction zone on the surface of a metal workpiece to produce a thermochemical reaction thereon and causing relative movement between the oxygen stream and the workpiece to continue the reaction along the metal surface to forming a descaling notch, wherein the reaction forms a molten pool in advance of the advancing reaction zone, which pool tends to increase as the notch continues, and Giant. 14 shows another embodiment of the invention. Its function is similar to that of FIG. 13, except that the fluid orifice is formed by a plurality of nozzle-directed jets from the workpiece side M perpendicular to the direction of the oxygen jet 6 by nozzles 12 which are disposed in a plane inclined downward from the top side of the descaler. The front edge of the fluid orifice intersects one of the three transverse beams 9 to form a pocket to trap smoke F. While the drawings generally depict the fluid orifice of the invention as a thin plane, it will be understood by those skilled in the art that the orifice may have any shape that meets the requirements of its function. For example, the orifice plate may be curved down towards the workpiece surface to prevent the escape of small amounts of smoke that normally escape on the open sides of the planar orifice (as shown in Figures 10 and 13). In another embodiment, the orifice may be formed from several, for example, three planar streams, i.e., one above and one on each side of the reaction zone and the slag pool. If smoke control is to be achieved on a quadrilateral scarfing machine as shown in U.S. Pat. No. 2,465,297, where a descaling reaction occurs on all four sides of a workpiece, a fluid curtain will be required on each of the four sides to capture the smoke. To optimally reduce the amount of smoke, the entire peripheral surface of the workpiece surrounding it should be closed with a water curtain. This can be accomplished by a single orifice, for example as a truncated cone, or by a plurality of individual orifices surrounding all four sides of the workpiece. A smaller but sufficient reduction in smoke can be achieved by adjusting a planar fluid orifice on each side of the descaling surface of the workpiece. If only two surfaces are descaled, for example the top side and the side side, then it is sufficient to adjust the fluid orifice only for the two workpieces. wherein a non-reactive fluid is used, characterized in that a liquid sheet is formed above the reaction zone by at least one stream of non-reactive fluid forming a cover over the reaction zone and over at least the back of the molten pool and forming a pocket with the workpiece surface. 2. The method of claim 1, wherein the stream of non-reactive fluid is directed from the top and in the same direction as the stream of oxygen and down at an acute angle to the surface of the workpiece. 3. The method of claim 1, wherein the non-reactive fluid stream is directed from one side of the oxygen stream and perpendicular to the oxygen stream and at an acute angle to the workpiece surface. 4. The method of claim 2, wherein the non-reactive fluid jet is directed perpendicularly to the descaling direction across the workpiece surface in front of the molten pool until the front edge of the fluid orifice intersects. 5. The method of claim 3, wherein the non-reactive fluid jet is directed perpendicularly to the descaling direction across the workpiece surface in front of the molten pool to intersect the front edge of the fluid curtain. 6. The method of claim 1, wherein the stream of non-reactive fluid is directed to impact across the entire width of the molten pool past its leading edge. 7. Apparatus for carrying out the method according to items 1 to 6, comprising a nozzle with an orifice for discharging an oxygen stream, characterized in that it comprises at least one additional nozzle (40, 50) for discharging a stream of non-reactive fluid located above the orifice (N). discharge of oxygen stream. Apparatus according to claim 7, characterized in that the opening of the additional nozzle (40, 50) for discharging the stream of non-reactive fluid is directed in the same direction as the opening of the oxygen discharge nozzle (N). Apparatus according to claim 7, characterized in that the longitudinal axis of the additional nozzle (40, 50) is perpendicular to the longitudinal axis of the nozzle (N) for discharging the oxygen stream.