Method for treating metal surface and method for manufacturing steel sheet

Abstract

To provide a metallic surface trimming method and a manufacturing method of a billet which can detect and respond to abnormality occurring in processing in an early stage.SOLUTION: A metallic surface trimming method is operations shaving down the thickness of a metallic surface in which a sound pressure level occurring in processing is measured to adjust a scarfing allowance or a grinding allowance according to the sound pressure level. A manufacturing method of a billet comprises: a carry-in process which carries a billet into a machine scarf; an insertion process which inserts the billet into a processing position in the machine scarf; a scarfing process which performs scarfing of a surface of the billet; a scarfing operation being arbitrarily selectively performed which includes an imaging process that images a surface of the scarfed billet, and a grinding process that automatically grinds a portion of the billet surface requiring trimming obtained from the imaged surface picture as needed by using a grinding truck and an invert traverser; and scarfing allowance adjustment according to a trimming method of the metal surface at the time of scarfing the billet surface in the scarfing process when repeatedly performing the scarfing operation of next billet from the carry-in process after completing the processing of the billet.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method of machining a metal surface by shaving the thickness of the metal surface, and to a method for manufacturing a steel slab to which the method is applied.

Background Art

[0002] As a method of machining a metal surface, particularly the surface of a steel slab, the surface is machined by melting and cutting with a high-temperature combustion gas or oxidation heat, or by grinding with a grindstone or the like. Automatic scarfing by a machine scarf is used for melting and cutting.

[0003] Surface defects such as inclusion entrapment and surface flaws may occur on the surface of a steel slab produced by continuous casting.

[0004] In order to remove the surface defects of this steel slab by machine scarfing, first, a combustible gas is supplied to a scarfer unit and the combustible gas is ignited (ignition step). Next, a part of the steel slab surface is melted by the heat of the burning combustible gas to form a molten pool as a heat source (preheating step). Next, oxygen gas is supplied toward this molten pool, and the surface of the slab is melted to a depth of about 1 to 3 mm by the oxidation reaction heat of the oxygen gas and iron, and the surface defects are removed (scarfing step). The generated scarfing slag is removed by high-pressure jet water.

[0005] As a technique related to machine scarfing, for example, Patent Document 1 discloses an ignition method for a scarfer facility capable of suppressing the generation of noise and vibration during ignition of a combustible gas supplied from a scarfer unit.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, the above prior art has the following problems. That is, in the technique disclosed in Patent Document 1, there is a problem that if an unexpected event occurs and abnormal combustion occurs, braking cannot be applied, that is, there is no criterion for judging it.

[0008] In the past, during machining, abnormal reactions sometimes occurred when the machining chips overcame the high-pressure jet water. And high-temperature machining chips sometimes scattered to peripheral equipment, causing disaster prevention troubles such as ignition of hoses. As a countermeasure, it is conceivable to reduce the machining cost per time and reduce the generated machining chips. However, the criteria for abnormal evaluation were ambiguous, the reduction of the machining cost became excessive, and there was a concern about a decrease in work efficiency.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to propose a method for maintaining a metal surface capable of detecting and dealing with an abnormality generated during processing at an early stage during the operation of shaving the thickness of the metal surface. In addition, a method for manufacturing a steel slab by a machine scarf to which the method is applied is proposed.

Means for Solving the Problems

[0010] The inventors have found that there is a correlation between an abnormal reaction and a noise level during machining of a steel slab by a machine scarf, and have quantitatively evaluated it to complete the present invention.

[0011] The method for maintaining a metal surface according to the present invention that advantageously solves the above problems is an operation of shaving the thickness of a metal surface, measuring a sound pressure level generated during processing, and adjusting a machining cost or a grinding cost according to the sound pressure level.

[0012] Note that the method for maintaining a metal surface according to the present invention is (a) the sound pressure level is an A characteristic sound pressure level, (b) the operation is machining of metal, (c) using a machine scarf for machining the metal; (d) reducing the machining cost when the A-weighted sound pressure level rises by a predetermined value or more from the average value of the A-weighted sound pressure level during preheating; (e) reducing the machining cost when the A-weighted sound pressure level rises by a predetermined value or more from the maximum value of the A-weighted sound pressure level excluding abnormal values in the range of 2 to 5 s from the start of machining; etc. can be more preferable solutions.

[0013] The method for manufacturing a steel slab according to the present invention that advantageously solves the above problems includes a loading step of transporting the steel slab to a machine scarf, a loading step of loading the steel slab to a processing position in the machine scarf, and a first machining step of machining the surface of the steel slab loaded in the loading step. Further, optionally, a photographing step of photographing the machined surface of the steel slab, and, if necessary, a grinding step of automatically grinding the portions of the steel slab surface that need cleaning obtained from the surface photograph taken in the photographing step using a grinding carriage and a reversing traverser. When repeatedly performing the machining operation from the loading step on the next steel slab to be processed after the processing of the steel slab is completed, the machining cost is adjusted according to the method for cleaning the metal surface according to any of the above during machining of the steel slab surface in the first machining step.

[0014] In addition, the method for manufacturing a steel slab according to the present invention is such that the machining operation further includes, if necessary, a reloading step of automatically reversing or turning over the steel slab using a reversing machine and automatically pulling the steel slab back to the processing position again, and a second machining step of machining the un-machined surface of the steel slab. Further, optionally, applying the photographing step and, if necessary, the grinding step to the un-photographed machined surface of the steel slab, and if necessary, automatically reversing or turning over the steel slab, and repeating the reloading step to the grinding step until there is no surface that needs to be machined. When machining the steel slab surface in the second machining step, adjusting the machining cost according to the method for cleaning the metal surface according to any of the above can be more preferable solutions.

Advantages of the Invention

[0015] According to the method for maintaining a metal surface according to the present invention, it has become possible to quantitatively evaluate an abnormal reaction during work based on the A characteristic sound pressure level. Therefore, the level and occurrence frequency of the abnormal reaction can be associated with, for example, the processing conditions of the slab. And under the processing conditions of the slab where the abnormal reaction hardly occurs or the level of the abnormal reaction is low, it is possible to improve work efficiency such as increasing the melting cost. When high-level abnormal reactions occur frequently, it has become possible to prevent disaster troubles such as investigating the cause by equipment inspection. By applying such a method for maintaining a metal surface to a method for manufacturing steel slabs, work efficiency is improved, work safety is also improved, and productivity is increased by a synergistic effect.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be specifically described. Further, the following embodiments illustrate equipment and methods for embodying the technical idea of the present invention, and do not specify the configuration to the following. That is, the technical idea of the present invention can be variously modified within the technical scope described in the claims.

[0018] First, regarding the method for maintaining a metal surface according to an embodiment of the present invention, as an operation of shaving the thickness of the metal surface, the gouging operation of a steel slab will be described as an example. FIG. 1(a) is a graph showing an example of the transition of the noise level during the gouging operation of a steel slab as a steel piece. FIG. 1(b) is a schematic cross-sectional view showing the normal gouging state of a steel piece. FIG. 1(c) is a schematic cross-sectional view showing the state where the gouging of the steel piece is in an abnormal reaction state.

[0019] The noise level was measured by a noise meter installed indoors at a position 8 m away from the machine scarf. The noise meter converts the measured sound pressure into the A-weighted sound pressure level (dB) specified in JIS Z 8731:2019 and outputs it as the noise level (dB). The A-weighted sound pressure (Pa) refers to the sound pressure (Pa) measured by multiplying the frequency weighting characteristic A (see Appendix JA) specified in JIS C 1509-1. The sound pressure level (dB) is calculated as 10 times the common logarithm of the value obtained by dividing the square of the effective value of the sound pressure by the square of the reference sound pressure. Although the Z-weighted sound pressure level can also be used, it is preferable to use the A-weighted sound pressure level, which is closer to the hearing of the operator, as an evaluation index.

[0020] In the example of FIG. 1(a), the average value N0 of the noise level during the non-treatment period t0 is about 64 dB. Here, the average value of the noise level is the energy average value of the fluctuating noise level, and the equivalent noise level is used as a physical index obtained by time-averaging the total exposure amount of the acoustic energy. The average value NP of the noise level during the preheating period tP is about 68 dB. During the gouging of a normal steel piece, the maximum value NSmax of the noise level that appears in the range of 2 to 5 s from the start of the gouging treatment period tS is about 80 dB. As shown in FIG. 1(b), during the gouging of a normal steel piece 1, the gouging slag 3 melted by the oxidation heat of oxygen and iron supplied from the scarfing unit 2 is washed away and removed by the high-pressure jet water 4.

[0021] In the example of Fig. 1(a), a peak of 90 dB or more is observed as the noise level NA related to the abnormal reaction of the machining of the steel slab. This abnormal reaction is considered to be caused by, for example, the occurrence of an overflow 5 of the machining slag 3 when the machining slag 3 cannot be removed by the high-pressure jet water 4 as shown in Fig. 1(c). When the high-temperature machining slag 3 covers the water droplets, the machining slag 3 is blown away to the surroundings due to the explosive expansion of water vapor. Since the machining slag 3 remains at a high temperature, it may cause a disaster-related trouble if it adheres to the hydraulic hoses of the surrounding equipment, etc. For example, it is classified according to the peak value of the noise level NA related to the abnormal reaction, and a small reaction is defined as 80 dB or more and less than 90 dB, a medium reaction is defined as 90 dB or more and less than 95 dB, and a large reaction is defined as 95 dB or more. Note that this determination criterion is determined by a noise meter installed indoors at a position 8 m away from the machine scarf as described above. The noise level NA related to the abnormal reaction varies depending on individual circumstances such as the installation position of the noise meter, and it is necessary to determine it by tests, etc. before implementation.

[0022] From the mechanism of the abnormal reaction of the machining of the steel slab, the conditions under which the abnormal reaction frequently occurs are considered as follows. (A) Insufficient pressure of the high-pressure jet water (B) Increase in the amount of machining slag generated

[0023] When the abnormal reaction is judged to be due to insufficient pressure of the high-pressure jet water, it is conceivable to adjust the frequency of equipment inspections such as replacing the compressor, inspecting the high-pressure piping system, and inspecting and replacing the nozzles.

[0024] The abnormal reaction of machining that occurs despite the appropriate pressure of the high-pressure jet water is considered to be due to an increase in the amount of machining slag generated. For example, the machining allowance of the steel slab varies depending on the steel type, destination, and continuous casting conditions of the steel slab. When strict surface quality is required, machining may be performed by 4 mm or more. Also, the amount of machining slag 3 generated depends on the machining allowance, slab width, slab temperature, and machining speed.

[0025] Figure 2 shows the influence of the relationship between the slab width and the slab temperature in the steel slab cutting operation on the occurrence frequency of abnormal reactions. The abnormal reactions were evaluated based on the above criteria using the noise level. Also, in the example of Figure 2, the cutting allowance was set at 3 mm. In Figure 2, when a minor reaction or no abnormal reaction with a noise level NA for the abnormal reaction less than 90 dB was observed, it is indicated by the symbol 〇. Also, when a medium reaction and a major reaction with a noise level NA for the abnormal reaction of 90 dB or more were observed, it is indicated by the symbol ▲. Under the conditions of Figure 2, abnormal reactions of medium reaction or more frequently occurred when the slab width was 1100 mm or more or the slab temperature was 200 °C or more.

[0026] Therefore, below the boundary line (dashed-dotted line) shown in Figure 2, that is, under the conditions of a narrow slab width or a low slab temperature, the cutting allowance was increased to 4 mm. As a result, no significant increase in the noise level or deterioration of the abnormal reaction evaluation was observed. Therefore, productivity was improved without causing abnormal reactions. On the other hand, above the boundary line (dashed-dotted line), that is, under the conditions of a wide slab width and a high slab temperature, the cutting allowance was decreased to 2 mm. As a result, the steel slab cutting operation could be carried out without the occurrence of medium reactions or major reactions in the abnormal reaction evaluation. Therefore, disaster prevention troubles were reduced.

[0027] Furthermore, even though the generation amount of cutting slag 3 did not increase, when abnormal reactions frequently occurred, equipment inspection was carried out, and it was found that the nozzle direction of the high-pressure jet water was misaligned and could be corrected. In this way, the measurement of the noise level is also useful for the early detection and countermeasures of equipment abnormalities, leading to the maintenance of high productivity in operation.

[0028] As described above, as a method for maintaining a metal surface, the use of noise level measurement during the machining of steel pieces, for example, steel slabs, has been explained. The steel pieces can be applied not only to steel slabs but also to steel blooms, steel billets, round billets, etc. Further, it can be applied not only to steel pieces but also to operations for cutting the thickness of metal surfaces such as copper ingots and aluminum alloys. Furthermore, the operation is not limited to machining, but can also be applied to grinding operations using a grindstone or the like. In the grinding operation using a grindstone, the noise level depends on the grinding cost and the grinding speed. As abnormal reactions, chipping of the grindstone, increase in machining resistance, and running out of the grinding fluid can be considered. As described above, the sound pressure level defined in JIS Z 8731:2019, which measures sound as a physical quantity, is used. By using the A-weighted sound pressure level as the sound pressure level, a judgment closer to the operator's perception can be made, which is preferable. It is preferable to use it for the machining of metals, particularly for the machining of metals using a machine scarf, as it leads to a reduction in high-temperature flying objects and also leads to an improvement in productivity through automation.

[0029] In the above, the abnormal reaction was evaluated using the absolute noise level as an index. As another evaluation method, it is also possible to evaluate an abnormal reaction when the noise level rises by a predetermined value or more from the average value NP of the noise level during the preheating period tP. Further, during the machining of normal steel chips during the machining step, the maximum noise level NSmax appears in the range of 2 to 5 s after the start of machining. Therefore, it is also possible to evaluate an abnormal reaction when the noise level rises by a predetermined value or more from the maximum value of the noise level excluding abnormal values in the range of 2 to 5 s from the start of machining. Preferably, the maximum value of the noise level excluding abnormal values in the range of 3 to 4 s from the start of machining is used. Here, the abnormal value refers to a noise level value that is higher than the noise level values before and after and that fluctuates suddenly due to an abnormal reaction. Further, the degree of the abnormal reaction may be classified, and depending on the degree, the adjustment of the machining cost and the equipment inspection as described above may be carried out. For example, in the example of FIG. 1, the average value NP of the noise level during the preheating period tP is about 68 dB, and the maximum value NSmax of the noise level appearing in the range of 2 to 5 s from the start of the machining process period tS is about 80 dB. Therefore, it is possible to evaluate an abnormal reaction when the noise level rises by 13 dB or more from NP or when the noise level rises beyond NSmax. It is more preferable to use the noise level value obtained by adding 5 dB to those values as a judgment criterion.

[0030] Next, a method for manufacturing a steel chip according to another embodiment of the present invention will be described. The method for manufacturing a steel chip according to the present embodiment includes a machining operation using a machine scarf, and includes a loading step, a charging step, and a first machining step, and further optionally includes a photographing step and a grinding step performed as necessary. After the completion of the machining operation of the previous steel chip, the machining operation is repeatedly performed on the next steel chip to be processed from the loading step. Further, the machining operation includes a reloading step and a second machining step as necessary.

[0031] In the loading step, a steel chip cast by continuous casting or the like is transported to the machine scarf. For example, the steel chip is transported onto the turntable of the machine scarf.

[0032] In the charging step, for example, the steel chip on the turntable is charged to the processing position inside the machine scarf.

[0033] The gouging process includes an ignition step, a preheating step, and a gouging step. In the ignition step, for example, combustible gas is supplied from the scarfing unit 2 and the combustible gas is ignited by an ignition device. This corresponds to the peak of the noise level that appears at the initial stage of the preheating period tP shown in Fig. 1(a). Next, in the preheating step, a part of the surface of the steel slab 1 is melted by the heat of the burning combustible gas to form a molten pool, which serves as a heat source. Next, in the gouging step, oxygen gas is supplied toward this molten pool, and the surface of the steel slab 1 is melted to a depth of about 1 to 4 mm by the heat of the oxidation reaction between the oxygen gas and iron, removing the surface defects of the steel slab 1.

[0034] In this gouging process, the noise level is measured and the gouging allowance is adjusted according to the method of cleaning the metal surface. It is preferable to gouge the necessary amount of gouging for ensuring the surface quality in one gouging as much as possible. When an abnormal reaction of gouging is predicted or measured, it is preferable to reduce the gouging allowance or perform equipment inspection.

[0035] The photographing process photographs the gouged surface of the steel slab. Then, the presence or absence of surface defects is determined, and further gouging or processing for the next grinding process is determined. This photographing process is preferably applied to steel grades that require strict surface quality.

[0036] Based on the determination in the photographing process, the grinding process automatically grinds the portions of the steel slab surface that need to be cleaned obtained from the surface photograph taken in the photographing process using a grinding carriage and a reversing traverser, thereby removing surface defects.

[0037] In the gouging step, gouging can be performed once across the entire circumference of the steel slab. Also, the surfaces of the steel slab can be gouged one by one or a plurality of surfaces can be gouged simultaneously. The reload process automatically reverses or rolls over the steel slab using a reversing machine in order to gouge the surfaces of the steel slab that were not processed in the first gouging process, and then automatically pulls the steel slab back to the processing position again.

[0038] The second scarfing process machines the un-machined surface of the steel slab. Each processing step is the same as that of the first scarfing process. Then, further, optionally, a photographing process and, if necessary, the grinding process are applied.

[0039] Furthermore, the reloading process to the grinding process is repeatedly carried out until there is no surface of the steel slab that needs to be machined.

[0040] By applying this embodiment to the manufacturing method of steel slabs, the evaluation based on the measurement of the noise level was changed from the conventional change of scarfing conditions relying on the sense of operators, and a productivity improvement of about 3000 t / month was achieved. "t" representing the unit of mass corresponds to 1000 kg.

Industrial Applicability

[0041] According to the method for maintaining the metal surface and the manufacturing method of steel slabs of the present invention, the working efficiency is improved, the working safety is also improved, the productivity is increased by a synergistic effect, and it is industrially useful.

Explanation of Signs

[0042] 1 Steel slab (steel slab) 2 Scarfer unit 3 Scarfing slag 4 High-pressure jet water 5 Overflow t0 Non-processing period tP Preheating period tS Scarfing processing period N0 Average value of noise level (during non-processing period) NP Average value of noise level (during preheating period) NSmax Maximum noise level (during scarfing processing) NA Noise level for abnormal reaction

Claims

1. An operation of shaving the thickness of a metal surface, wherein the operation is metal gouging, measuring the A-weighted sound pressure level generated during the process, adjusting the gouging cost during the process according to the A-weighted sound pressure level, or adjusting the gouging cost to be a gouging cost with reduced abnormal reaction based on the A-weighted sound pressure level and processing conditions associated in advance, or implementing a countermeasure of performing equipment inspection. A method for maintaining a metal surface.

2. The method for maintaining a metal surface according to Claim 1, wherein machine scarfing is used for the gouging of the metal.

3. The method for maintaining a metal surface according to Claim 2, wherein the gouging cost is reduced when the A-weighted sound pressure level rises by a predetermined value or more from the average value of the A-weighted sound pressure level during preheating.

4. The method for maintaining a metal surface according to Claim 2, wherein the gouging cost is reduced when the A-weighted sound pressure level rises by a predetermined value or more from the maximum value of the A-weighted sound pressure level excluding abnormal values in the range of 2 to 5 s from the start of gouging.

5. A loading process of transporting steel pieces to a machine scarfing; A loading process of loading the steel pieces to a processing position in the machine scarfing; A first gouging process of gouging the surface of the steel pieces loaded in the loading process; including; furthermore, optionally, a photographing process of photographing the gouged surface of the steel pieces; optionally, a grinding process of automatically grinding the necessary parts for maintaining the surface of the steel pieces obtained from the surface photograph taken in the photographing process using a grinding carriage and a reversing traverser as needed; when performing a gouging operation including the above and repeating the gouging operation from the loading process for the next steel piece to be processed after the processing of the steel piece is completed, during the gouging of the surface of the steel piece in the first gouging process, adjusting the gouging cost according to the method for maintaining a metal surface according to any one of Claims 2 to 4. A method for manufacturing a steel piece.

6. The gouging operation further includes; optionally, a reloading process of automatically reversing or rolling over the steel piece using a reversing machine and automatically pulling the steel piece back to the processing position again; A second gouging process of gouging the un-gouged surface of the steel piece; including; furthermore, optionally, applying the photographing process and, if necessary, the grinding process to the un-photographed gouged surface of the steel piece, when repeating the reloading process to the grinding process as needed until there is no surface that needs to be gouged by automatically reversing or rolling over the steel piece as needed. The method for manufacturing a steel sheet according to claim 5, wherein during the machining of the surface of the steel sheet in the second machining step, the machining cost is adjusted in accordance with the method for maintaining the metal surface according to any one of claims 2 to 4.

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