JP2008290175A - Hot slab surface layer care method and hot rolled steel manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a smooth maintenance surface and to efficiently remove defects on the surface of the hot slab and the subcutaneous surface without deteriorating the quality of the surface and surface layer of the hot slab. A method for cleaning the surface layer of a hot slab is provided.
SOLUTION: A part or all of a surface layer part of one or two or more of a front surface, a back surface, and a side surface of a hot slab 12 manufactured by a continuous casting machine and cut to a predetermined length. Using a milling surface cutting device composed of a rotary cutting tool 2 having a large number of cutting blades 3 that are rotated by the driving force of an electric motor, a thickness range of 1 mm or more is cut from the as-cast slab skin.
[Selection] Figure 6

Description

  The present invention relates to a method for cleaning a surface layer portion of a hot slab cast by a continuous casting machine, and also relates to a method for producing a hot-rolled steel material using a slab maintained by this surface layer portion cleaning method.

  In a continuous casting facility, a slab having a length of about 10 m is produced from molten steel and sent to a hot rolling line in the next process as a rolling material. Usually, in a hot rolling line, this slab is heated in a heating furnace and then hot rolled into a thin steel plate. In this case, if the slab produced in the continuous casting line is charged into the heating furnace of the hot rolling line at a high temperature of about 700 ° C. or higher, the amount of heating in the heating furnace is reduced, and the fuel intensity is reduced. It becomes possible to reduce. Such an operation method is called hot charge rolling (HCR) and has been widely attempted.

  However, slabs have inclusion defects that occur in the casting stage. In particular, inclusion defects that are present up to several millimeters below the surface of the slab are lined on the surface of the thin steel sheet in the rolling process or the plating process after the next process. Generate a state defect. This inclusion defect originates from deoxidation products such as mold powder and alumina used during continuous casting, and inclusions having a size of several hundred microns are said to cause defects.

  Therefore, conventionally, a slab produced by a casting facility is either hot or cold after being cooled, and the entire surface of the slab surface is melted (scarfed) with a hot scurfer or a cold scurfer. Or grinding with a grinder has been generally performed.

  However, the care method using a hot scurfer is a method in which the slab surface layer portion is melted with high heat and scraped off while the melt is blown off, so that the slab surface layer portion is locally heated. As a result, concentration of specific elements such as phosphorus (P) and nickel (Ni) in the slab surface layer part or decarburization of the surface layer part may be caused, and there is a concern that the surface layer quality of the slab deteriorates.

  In the care method using cold scurfers for slabs that have become flaky, the slab temperature does not change, so the depth of cutting does not fluctuate. There are many advantages such as difficulty, but the energy loss due to slab cooling is significant.

  In both hot and cold scurfers, when slab furring is used, the surface of the slab surface will be roughened with a slab. Often occurs. This occurs because the flammable gas outlet from the nozzle of the sker fur is divided, and the pitch of the swell generated on the surface to be cut after scouring by the scurfer coincides with the nozzle division pitch. This waviness may cause new surface defects in the hot rolled steel material in the hot rolling process.

  Since the grinder's surface layer removal ability (care ability) is low, the efficiency of the grinder is significantly lower than that of a scarf. In addition, there is a lack or adhesion of a grindstone that causes surface flaws in steel products, and the use with a slab in a hot state is only used to remove gas cutting blades at the end of the slab.

  As described above, any conventional general cleaning method has a risk of causing defects that cause new surface flaws on the skin or surface layer of the slab after being cleaned, and thus solves this problem. Therefore, several slab care methods have been proposed for obtaining a slab having no defects in the skin and the surface layer portion with high productivity when the hot slab surface portion is maintained.

For example, Patent Document 1 uses a rotatable cutting blade having a circular cutting edge before cutting a continuously cast slab into a predetermined length by a gas cutting machine at the end of the continuous casting machine. There has been proposed a care method in which the surface layer portion of the slab in the hot state is cut and removed to the steel portion beyond the oxide film while rotating with a cutting reaction force from the slab which is a non-cutting body.
JP 2004-181561 A

  The care method proposed in Patent Document 1 is a method of cutting a plane with a single-blade cutting device called a shaper. In order to extend the life of the cutting blade, it has a free rotating circular cutting blade that rotates by the cutting reaction force.When the cutting blade is sent, the cutting blade rotates by the cutting reaction force, the cutting blade surface is constantly updated, and it is in one place. The heat load is not applied and the blade tip is devised to avoid wear.

  Here, the rotary circular cutting blade satisfies the function only by having a rotatable structure, but a mechanism for feeding the rotary circular cutting blade along the cutting surface of the slab is separately required. In patent document 1, it is supposed that the slab drive force by the pinch roll of a continuous casting machine or the slab transfer force of the roller table for slab transfer is applied to the drive force of the cutting feed of a rotary circular cutting blade.

  The removal amount of the defective portion in the slab surface immediately after casting is empirically about 2 to 4 mm from the skin. Assuming the cutting reaction force when cutting the entire width of one side of the slab under a temperature condition of 4 mm thickness and 800 ° C., a cutting reaction force of 120 to 250 tons is received when the slab width is 1500 mm. As proposed in Patent Document 1, it is difficult to obtain a driving force corresponding to such a cutting reaction force from a slab driving force by a pinch roll or a slab conveying force of a slab conveying roller table.

  For example, a cutting method of reciprocating a plurality of times with a cutting amount per blade as 100 mm instead of the full width of the slab is also conceivable. However, even when reciprocal cutting is performed with a cutting reaction force of about 18 tons and a cutting speed of 1 m / sec. Considering the overlap of the cutting pitch, a large number of reciprocating motions of the circular cutting blade are necessary, and the cutting time is prolonged and not realistic.

  The present invention has been made in view of such circumstances, the purpose of which is to obtain a smooth care surface, without causing deterioration of the quality of the skin and surface layer of the hot slab, It provides a hot slab surface layer cleaning method that can efficiently remove defects in the skin and surface layer of a hot slab cast by a continuous casting machine, and at the same time uses a slab that has been cleaned by this surface layer cleaning method. Another object of the present invention is to provide a method for producing a hot-rolled steel material having excellent surface properties.

  A method for cleaning a surface portion of a hot slab according to the first aspect of the present invention for solving the above-mentioned problem is the production of the surface, back surface, and side surface of a hot slab manufactured by a continuous casting machine and cut to a predetermined length. Either or all of the surface layer part of one or more of the surfaces is cast as it is using a milling surface cutting device configured with a rotary cutting tool having a large number of cutting blades that are rotated by the driving force of the electric motor. A thickness range of 1 mm or more is cut from the slab skin.

  According to a second aspect of the present invention, in the first aspect of the invention, the milling surface cutting device includes a rotary cutting tool for cutting the front surface or the back surface of the slab, and a side surface of the slab. And a rotary cutting tool.

  According to a third aspect of the present invention, in the first or second aspect, the hot slab surface layer portion cleaning method is characterized in that the cutting edge of the cutting blade of the rotary cutting tool is composed of a thermal spray layer of a nickel-based alloy. It is what.

  A hot slab surface layer cleaning method according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the rotary cutting tool has an internal water cooling structure.

  According to a fifth aspect of the present invention, there is provided a hot slab surface layer cleaning method according to any one of the first to fourth aspects, wherein the rotary cutting tool has a lower part made of a heat insulating material or a heat resistant alloy. To do.

  A hot slab surface layer cleaning method according to a sixth aspect of the present invention is the milling surface layer cutting apparatus according to any one of the first to fifth aspects, wherein the milling surface layer cutting device further removes chips cut by the rotary cutting tool with high-pressure water. It comprises a chip cooling device that cools by spraying, a cutting blade cooling device that air-cools or mist-cools the cutting blade of the rotary cutting tool, and a chip collection device that collects the chip.

  A method for producing a hot-rolled steel material according to a seventh aspect of the present invention is a heating furnace in which a slab that has been maintained by the method for cleaning a hot slab according to any one of the first to sixth aspects is in a hot state. It is characterized by charging and then hot rolling.

  According to the present invention, the surface layer part of the hot slab is cleaned using the surface layer cutting device constituted by the rotary cutting tool, so that the surface and the surface layer and the surface layer part of all the surfaces of the hot slab, the back surface and the side surface. It is possible to reliably remove defects in the hot state, and even if inclusion defects occur in the skin or surface layer of the slab during continuous casting, the slab does not cool down to a cold piece. In addition, it becomes possible to insert a slab having no defects in the skin and the surface layer portion into a heating furnace of a hot rolling line in a hot state, and the heat of the slab can be effectively utilized. In addition, since the smoothness of the slab skin after the cleaning is significantly improved in the cleaning method according to the present invention compared to the conventional cleaning method, the steel sheet caused by the slab skin and surface layer defects in the rolling process and the plating process. Surface wrinkles can be reliably reduced, and energy saving and quality improvement of the steel sheet can be achieved.

  In addition, with conventional slab surface cleaning, which is used to clean the entire surface of the slab surface, the layer scraped off by the slab becomes complete iron oxide and can be reused as an iron source. Requires a reducing agent and thermal energy associated with the reduction, which increases the manufacturing cost accordingly. On the other hand, in the care method of the present invention, chips generated by cutting the surface layer are recovered as a bare metal with a low iron oxide content. Is unnecessary, and the manufacturing cost can be reduced as compared with the prior art.

  In addition, when a slab that has been subjected to surface layer care by the care method according to the present invention is hot-charge rolled, a hot-rolled steel material with extremely few surface defects can be obtained.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a flowchart showing the flow of a slab from a continuous casting line to a heating furnace of a hot rolling line in the present invention.

  As shown in FIG. 1, the slab manufactured by the continuous casting line is conveyed to the heating furnace of the hot rolling line of the next process with a hot state. During this transfer process, drive the motor at least on defective parts of the front, back and side surfaces of the slab in the hot state at an appropriate place such as on the transfer roller table or in a dedicated surface layer maintenance area. Using a surface layer cutting device composed of a rotary cutting tool having a large number of cutting blades rotated by force, a thickness range of 1 mm or more is cut from an as-cast slab skin. Prior to the cutting process by this surface layer cutting device, whether or not the slab surface layer needs to be maintained is determined by information by a defect detection device such as an optical surface flaw detection device, a magnetic particle flaw detection device, an ultrasonic flaw detection device, or an eddy current sensor, Judgment is made based on casting performance information such as the amount of surface fluctuation, and based on the judgment result, a defective portion of the skin or the surface layer portion is partially cut, or the entire surface where the defect exists is cut. In addition, when excellent surface properties are required in the product, it is necessary to cut the entire surface of the slab surface, the back surface, and both side surfaces without determining whether the slab surface layer needs to be maintained. Also good. A slab heated at a predetermined temperature and a predetermined time in a heating furnace of a hot rolling line is hot rolled to produce a hot rolled steel material.

  Usually, the hot slab unloaded from the casting line is about 1200 ° C. when it is high, and the temperature of the slab charged into the heating furnace as hot-charge rolling through the care process is 700 slab internal temperature. It is about ℃. The slab is air-cooled in the atmosphere from the time when it is unloaded from the casting line to the next process, and the temperature of the slab skin surface decreases. FIG. 2 shows the slab temperature change simulation results obtained by analyzing the surface and center temperatures of the slab using a general-purpose heat transfer analysis code with each initial temperature being 1200 ° C. FIG. 3 shows a simulation result of the temperature distribution in the cross section of the slab when about 30 minutes have passed since the slab was discharged from the continuous casting machine.

  When the surface layer of the slab in the hot state is treated, it is usually maintained within 30 minutes after being discharged from the continuous casting machine, and the slab skin temperature at the time of slab surface layer maintenance is shown in FIG. As can be inferred from FIG. 3, the temperature is about 800 ° C. (the internal temperature of the slab is about 1000 ° C.). However, it seems that the slab corner and the like are further lowered to 600 to 700 ° C.

  FIG. 4 shows the shear stress at each temperature of the steel material (JIS SS400). It can be seen that the shear stress is proportional to the cutting resistance of the steel material, and that the cutting resistance of the steel material decreases as the temperature rises. With respect to the cutting resistance of the cold slab, the cutting resistance in the care of the slab having a temperature of 600 to 800 ° C. is reduced to 1/2 to 2/3.

  FIG. 5 is a diagram showing respective cutting resistances with respect to cutting conditions when machining carbon steel, cast iron, and aluminum alloy by milling at room temperature. As is clear from FIG. 5, if the cutting resistance of carbon steel becomes 1/2 or less by raising the temperature at the time of cutting, the cutting resistance of carbon steel becomes almost equal to the cutting resistance of aluminum alloy. High-speed and high-efficiency cutting is possible.

  That is, in the present invention, a steel slab at a high temperature of about 800 ° C. is cut using a milling surface layer cutting device constituted by a rotary cutting tool having a large number of cutting blades that are rotated by the driving force of an electric motor. It is possible to cut the slab surface layer at a cutting speed more than twice as high as that at room temperature, and even a milling surface layer cutting device can sufficiently maintain the steel slab. .

  FIG. 6 shows an example in which a milling surface cutting device is applied as a care device for a slab surface layer portion. FIG. 6 is an example of a milling surface layer cutting device provided with one rotary cutting tool 2, and the rotary cutting tool 2 includes a disk-shaped holder 4 and a number of cutting blades attached around the holder 4. 3. In this case, the rotary cutting tool 2 has a size greater than or equal to the width of the slab 12, and the entire width of the slab 12 is cut and cared for with one rotary cutting tool 2. In FIG. 6, the entire configuration of a milling surface cutting device such as an electric motor for rotating the rotary cutting tool 2 is omitted.

  The number of rotary cutting tools 2 constituting the milling surface layer cutting device is not limited to one, and a plurality of rotary cutting tools 2 can be installed in the width direction of the slab 12. FIG. 7 is a diagram showing an example in which a milling surface layer cutting device provided with a plurality of rotary cutting tools 2 is applied as a slab surface layer cleaning device. FIG. 7A shows two rotary cutting tools 2. FIG. 7B is an example of a milling surface layer cutting device including three rotary cutting tools 2. In the case where two rotary cutting tools 2 are provided, the size of each rotary cutting tool 2 can be about ½ of the slab width. The size can be about 1 / n of the slab width.

  The slab 12 carried out from the continuous casting machine has relatively little deformation, and is often compatible with a milling surface layer cutting apparatus having a single rotary cutting tool 2 as shown in FIG. The secondary cooling water distribution in the slab becomes non-uniform in the width direction, and the deformation in the width direction of the slab increases, and if the slab width is large, the difference in cutting allowance increases even if the deformation in the width direction is small. Since this happens, it is preferable to install a milling surface cutting device provided with a plurality of rotary cutting tools 2 as shown in FIGS. 7 (A) and 7 (B). By providing the rotary cutting tool 2 by dividing the slab 12 in the width direction, uneven cutting can be prevented.

  FIG. 8 is a diagram illustrating an example of a milling surface layer cutting device for cutting and cleaning the entire surface of the slab 12. As shown in FIG. 8, the milling surface cutting device 1 is installed above a roller table 11 for conveying a slab, and has two surface cutting rotary cutting tools 2 a for cutting the surface of the slab 12. And two side cutting rotary cutting tools 2c for cutting the side surface of the slab 12. The milling surface layer cutting device 1 includes an electric motor for driving the surface cutting rotary cutting tool 2a and the side surface cutting rotary cutting tool 2c and a gantry for holding them, but is omitted in FIG.

  In order to care for the slab 12 using this milling type surface layer cutting device 1, for example, as shown in FIG. 9, the above configuration is shown as an example of the configuration of the milling type surface layer cutting device for online cutting and care of the front and back surfaces of the slab 12. The two milling type surface layer cutting devices can be quickly arranged by arranging them in series above the slab conveying roller table 11 with the slab reversing machine 10 in between. First, after cutting the surface and side surface of the slab 12 with the milling surface layer cutting device 1, the slab 12 is reversed with the slab reversing machine 10, and then the back surface of the slab 12 is cut with the milling surface layer cutting device 1A. The milling surface layer cutting apparatus 1A has the same configuration as the milling surface layer cutting apparatus 1, but includes two rotary cutting tools 2b for back surface cutting because the back surface of the slab 12 is cut. The slab 12 in the hot state is clamped by the roller table 11 at the lower side of the slab 12 or the lower part of the front and rear surfaces, and the milling surface layer cutting device 1, 1A is cut while traveling in the direction of the roller table 11, or The milling surface layer cutting device 1, 1 </ b> A is fixed, and the slab 12 is cut while being moved on the roller table 11. Since the milling surface cutting device 1 and the milling surface cutting device 1A have the same configuration, they are hereinafter collectively referred to as “milling surface cutting device 1”.

  Since the casting speed of the continuous casting machine is about 2 m / min, the slab 12 stays in the milling surface cutting apparatus 1 when the slab 12 is maintained, that is, when the cutting feed speed of the slab 12 is slower than the casting speed. It will be. Although the feed rate for milling steel is 2 m / min, the slab 12 is in a hot state, so that a cutting feed comparable to that of aluminum can be obtained and realized as described above.

  Specifically, the cutting speed is 500 to 1000 m / min, the feed per blade is 0.5 to 1.0 mm, and the number of cutting blades 3 attached to the rotary cutting tool 2 is 20 to 36 (18 degrees). By attaching the cutting blade 3 to a pitch of 10 degrees, a cutting feed speed of 2 to 3 m / min can be realized even if the slab surface layer portion is cut at full width and full length. The total power required for the cutting spindle at that time is less than 500 kW if the cutting resistance is 1000 MPa (100 kgf / mm) or less, which is a practical facility. Further, in the actual line, by providing several rows of slab care lines shown in FIG. 9, it is possible to perform cutting care of the full width and full length of all the slabs without retaining the slabs transported from the continuous casting machine.

  A major problem when cutting a hot slab with the milling surface layer cutting device 1 is that the slab, which is a material to be cut, is at a high temperature of 800 ° C. and is affected by the heat of the slab. Since the cutting time of one surface of the slab is about 5 to 7 minutes, the cutting blade 3 of the rotary cutting tool 2, the holder 4, and the entire apparatus of the milling surface cutting device 1 are in contact with the hot slab during that time. Exposed to heat transfer, radiant heat, etc. In particular, the cutting edge of the cutting blade 3 is the most severe condition. However, since the cutting resistance is less than half that of cold steel, the temperature rise of the cutting blade 3 due to cutting is extremely small.

  Since the cutting speed is as high as 500 m / min to 1000 m / min, the time during which one cutting blade 3 is in contact with the hot slab for cutting is less than 2 seconds, and the time of contact with the hot slab Since there are several times the idling part, there is inherently sufficient air cooling time. However, in the milling surface cutting device 1, as shown in FIG. 10, the entire rotary cutting tool 2 is at a distance that is extremely close to the skin surface of the hot slab, and in particular, the lower surface of the rotary cutting tool 2 is 800 ° C. Therefore, the cutting edge 3 and the lower surface of the holder 4 have a very large heat load. Further, in the present invention, a reduction in cutting resistance due to the high temperature of the hot slab is utilized, and the coolant that cools the cutting edge of the cutting portion causes a decrease in the temperature of the skin and surface layer of the slab. It cannot be used actively for cooling.

  For these reasons, it is preferable to implement the following four heat insulation measures for the cutting blade 3 and the holder 4 of the rotary cutting tool 2. That is, (1) the cutting edge 3 is formed of a heat-resistant Ni-base alloy sprayed layer, (2) a heat-resistant Ni-base alloy is sprayed on the lower part of the holder 4, or the lower part of the holder 4 is thermally insulated. (3) A cooling water channel is provided inside the holder 4 of the rotary cutting tool 2 and the holder 4 has an internal water cooling structure. (4) The cutting blade when idling cooling of the cutting blade 3 The 3 cutting edges are cooled with a coolant. Below, each heat-proof measure is demonstrated.

(1) Cutting Edge Material of Cutting Blade When cutting a high-temperature material, the thermal load on the cutting edge is large, wear may be accelerated, and chipping (chip) may occur due to thermal shock. Further, when chips are cut along the rake face of the cutting blade 3, the chip is welded due to the high temperature and the surface pressure due to the cutting (similar to the formation of a component edge). However, a phenomenon in which the chips themselves adhere to the rake face of the cutting edge) may occur.

  In order to prevent this welding phenomenon, a surface cutting test with a cutting width of 100 mm and a cutting depth of several mm is used for ceramics, cermets (TiC, TiN), superalloys (WC), and gas turbine blades for hot steel materials at 1000 ° C. It was performed using a cutting tool made of each material of super heat resistant alloys (Fe-based alloy, Co-based alloy, Ni-based alloy).

  As a result of the experiment, chip adhesion did not occur in the ceramic cutting tool and the Ni-base alloy cutting tool. However, ceramic cutting tools could not withstand the surface pressure, and cracks immediately occurred and broke. On the other hand, the Ni-base alloy cutting tool withstood the heat load and the cutting load, and there was no chip adhesion. In particular, in the Ni-based alloy, the in-use state gave better results for chip welding than the newly formed state. It has been found that the Ni-based alloy concentrates a specific element such as Al on the surface layer and forms an oxide such as Al on the surface, thereby further preventing chip adhesion during cutting.

  That is, it has been found that Ni-based alloys are particularly excellent as the cutting edge material of the cutting blade 3. Since the Ni-based alloy is basically an alloy that can withstand a high temperature of 1000 ° C. or higher, there is no problem even if the cutting edge 3 is not cooled if the hot slab is cut in a short time.

  The components of the Ni-based alloy suitable as the cutting edge material of the cutting blade 3 used in the present invention are C: 0.01 to 0.1% by mass, Cr: 17 to 20% by mass, Mo: 4 to 7% by mass, Co : 10-14% by mass, Al: 1-3% by mass, with the balance being Ni and a small amount of inevitable impurities. The cutting edge 3 has a cutting edge structure as shown in FIG. 11, and a Ni-based alloy sprayed layer 5 having a finishing thickness of about 5 mm may be formed on the base material.

(2) Lower structure of holder As shown in FIG. 10 described above, the lower part of the holder 4 of the rotary cutting tool 2 continues to receive high-temperature radiant heat from the surface of the hot slab during cutting. Due to the structure of the rotary cutting tool 2, the lower part cannot be directly cooled by spraying cooling water. Therefore, as shown in FIG. 11 described above, the ceramic plate 6 that is a heat insulating material is attached to the entire lower surface of the holder 4, or the lower portion of the holder 4 is configured with the sprayed layer 5 of the aforementioned Ni-base heat resistant alloy, The heat resistance of the holder 4 is improved.

(3) Internal Water Cooling of Holder FIG. 12 shows a cooling water passage 7 for cooling inside the holder 4 as a further heat-proof measure for the holder 4 so that the lower part of the holder 4 is cooled. This cooling water channel 7 is exclusively for preventing the temperature of the entire holder 4 or the lower part thereof from rising. As shown in FIG. 12, cooling water is sent from the upper part of the holder 4 to the inside of the holder 4, and the cooling water flows toward the lower part of the holder 4. The cooling water is allowed to leak out from a gap between the holder 4 and the ceramic plate 6 that is a heat insulating material or from a water channel outlet provided in a circumferential portion of the holder 4. If the cooling water is made into a circulation system, it becomes complicated and basically an open system, but the cooling water channel 7 may be a closed circuit to form a circulation system. Moreover, it is preferable that the cooling water channel 7 in the holder 4 is devised so that the entire lower part of the holder 4 can be cooled and the part of the cutting blade 3 can also be cooled.

(4) Cooling of the cutting edge When repeated rapid heating due to contact with the hot slab and rapid cooling by direct injection of cooling water onto the cutting edge, the Ni-based alloy sprayed layer 5 and the mother There is a risk that the Ni-based alloy sprayed layer 5 may be peeled off due to a difference in thermal expansion from the material. Therefore, although the cutting edge of the cutting blade 3 is not actively cooled with cooling water, since it is necessary to suppress the temperature rise at the time of cutting blade idling due to radiant heat from the hot slab, as shown in FIG. The coolant injection nozzle 8 is installed in the idling range of the cutting blade 3, and cooling is performed so as not to cause a thermal shock by the coolant injection nozzle 8 when the cutting blade 3 is idling. Specifically, the cutting blade 3 is cooled by spraying air or mist of air and water from the coolant spray nozzle 8.

  Another problem in the case of cutting a hot slab with the milling surface layer cutting device 1 is that it is difficult to treat the chips because the chips produced by cutting are hot.

  As shown in FIG. 14, the chips 13 are discharged along the rake face 3 a of the cutting blade 3 basically in the same manner as in ordinary cold cutting in the hot slab cutting. However, the high-temperature chip 13 is weak in strength and easily bends during discharging, and the cutting speed of the chip 13 is slow due to the weldability between the chip 13 and the rake face 3a when cutting high-temperature material, and the chip compression ratio is large. Tend to be. For this reason, the chip thickness becomes larger than the cut thickness. In particular, in the hot slab surface portion care, the cutting width becomes the slab width, the length of the chip 13 is also equal to the cutting width, and the chip 13 having a length equivalent to the slab width is discharged while curling.

  Because of the above, chips 13 are not discharged smoothly during hot cutting, and there is a risk of clogging between the cutting blades 3 of the rotary cutting tool 2 or being caught in the rotary cutting tool 2. In order to solve this problem, as shown in FIG. 14, a cooling water injection nozzle 9 is provided as a chip cooling device, and high-pressure water is applied to the chip 13 from the cooling water injection nozzle 9 to improve discharge of the chip 13. Is preferred. In this case, since a temperature drop is caused, high pressure water is not directly applied to the cutting edge of the cutting blade 3, and cooling water is sprayed to a predetermined position of the chips 13 discharged along the rake face 3a. As shown in FIG. 13 described above, one cooling water injection nozzle 9 is provided for each cutting blade 3, and the cooling water injection nozzle 9 also rotates in synchronization with the cutting blade 3.

  The injection pressure of the cooling water is preferably injected at a water pressure higher than that which breaks the boiling film because the target is the high-temperature chips 13, and therefore, the injection is performed at a pressure of about 0.2 MPa or more. Moreover, the height position which injects cooling water injects cooling water in the position where the chip 13 is discharged | emitted on the upper surface of the holder 4 along the rake face 3a of the cutting blade 3, and the chip 13 begins to curl.

  By cooling the chips in this way, the chips are not folded, and the chips are curled in accordance with the shape of the rake face, and the discharge of the chips is improved. When chip discharge at the top of the cutting edge rake face is improved by cooling the chip, the entire chip is also cooled and indirectly cooled to the chip near the cutting edge. This cooling effect improves the discharge speed, improves the chip compression ratio on the rake face of the cutting edge, and reduces the chip thickness, making chip processing methods such as chip breakers effective, and the shape of the chip. Since it becomes easy to become a favorable spiral shape or spiral shape, chip recovery is also facilitated. Furthermore, since the chip surface is prevented from being oxidized by cooling the chips, the scrap quality of the chips is greatly improved.

  As a chip collection device for collecting chips, a method in which a suction duct is provided on the upper periphery of the rotary cutting tool 2 of the milling surface cutting device 1 and suctioned by a suction blower through this suction duct can be used. Further, a chip recovery pit is provided on the side of the roller table 11 for conveying the slab, and the chips are dropped in the chip recovery pit by flying the chips laterally by the centrifugal force of the rotary cutting tool 2, or the chips remaining on the slab skin surface. The chips may be recovered by dropping them into a chip recovery pit beside the transport line with a mechanical scraper, high-pressure air, high-pressure water, or the like.

  In addition, it is necessary to take measures for heat resistance of the entire milling surface cutting device 1. Basically, in order to prevent radiant heat from the hot slab, a shielding plate or the like is installed on the main movable shaft, and the local cooling of the apparatus is performed by air cooling or mist cooling.

  As described above, according to the present invention, since the surface layer of the hot slab is cleaned using the surface cutting device 1 configured by the rotary cutting tool 2, the surface, back surface, and side surfaces of the hot slab are It is possible to reliably remove all surface skin and surface layer defects in a hot state. Even if inclusion defects occur in the slab skin or surface layer during continuous casting, Without cooling, it is possible to insert a slab having no defects in the skin and surface layer into a hot rolling furnace in a hot state, and as a result, even in hot charge rolling, the surface properties It is possible to manufacture a steel plate excellent in the above.

  In addition, this invention is not limited to the range of the said description, A various change is possible. Although the said description demonstrated in the example of the milling type surface cutting device 1 which has the disk shaped rotary cutting tool 2, the milling type surface layer comprised from the cylindrical cutting tool (screw blade for cylindrical milling) which has a screw blade on the surface. The present invention can also be implemented using a cutting device.

It is a flowchart which shows the flow of the slab from the continuous casting line in this invention to the heating furnace of a hot rolling line. It is a figure which shows the simulation result of the slab temperature change analyzed using the general purpose heat transfer analysis code. It is a figure which shows the simulation result of the temperature distribution in the slab cross section at the time of paying out from the continuous casting machine for about 30 minutes. It is a figure which shows the shear stress in each temperature of steel materials. It is a figure which compares and shows the cutting resistance of carbon steel, cast iron, and an aluminum alloy. It is a figure which shows the example which applied the milling-type surface layer cutting device provided with one rotary cutting tool as a care apparatus of a slab surface layer part. It is a figure which shows the example which applied the milling-type surface layer cutting device provided with the some rotary cutting tool as a care apparatus of a slab surface layer part. It is a figure which shows the example of the milling type surface layer cutting device for carrying out cutting care of the whole surface of a slab. It is a figure which shows the structural example of the milling type surface layer cutting apparatus for carrying out cutting care of the front and back of a slab online. It is a figure which shows the positional relationship of the rotary cutting tool and hot slab at the time of cutting. It is a figure which shows the blade edge | tip structure of a cutting blade. It is a schematic sectional drawing of an internal cooling type holder. It is a figure which shows the installation position of the coolant injection nozzle for cooling a cutting blade, and the cooling water injection nozzle for cooling chips. It is a figure which shows a mode that the chip is discharged | emitted along a cutting-blade rake face, and the installation position of the cooling water injection nozzle for cooling a chip.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Milling type surface cutting machine 2 Rotating cutting tool 2a Rotating cutting tool for surface cutting 2b Rotating cutting tool for back surface cutting 2c Rotating cutting tool for side cutting 3 Cutting blade 3a Rake face 4 Holder 5 Sprayed layer 6 Ceramic plate 7 Cooling channel 8 Coolant Injection nozzle 9 Cooling water injection nozzle 10 Slab reversing machine 11 Roller table 12 Slab 13 Chip

Claims (7)

  The driving force of the motor is applied to a part or all of the surface layer part of one or more of the front surface, back surface, and side surface of a hot slab manufactured by a continuous casting machine and cut to a predetermined length. Of a hot slab characterized by cutting a thickness range of 1 mm or more from an as-cast slab skin using a milling surface cutting device composed of a rotary cutting tool having a number of cutting blades rotating at How to care for the surface layer.   The milling surface cutting device includes a rotary cutting tool for cutting a front surface or a back surface of a slab, and a rotary cutting tool for cutting a side surface of the slab. The surface layer part care method of the hot slab as described.   The method for cleaning a surface layer portion of a hot slab according to claim 1 or 2, wherein a cutting edge of the cutting blade of the rotary cutting tool is composed of a thermal spray layer of a nickel base alloy.   The hot slab surface layer cleaning method according to any one of claims 1 to 3, wherein the rotary cutting tool has an internal water cooling structure.   The method for cleaning the surface layer of a hot slab according to any one of claims 1 to 4, wherein a lower portion of the rotary cutting tool is made of a heat insulating material or a heat resistant alloy.   The milling surface cutting device further includes a chip cooling device that cools the chips cut by the rotary cutting tool by spraying high-pressure water, a cutting blade cooling device that cools the cutting blade of the rotary cutting tool by air or mist, and A method for cleaning a surface layer portion of a hot slab according to any one of claims 1 to 5, further comprising a chip collection device for collecting chips.   The slab, which is maintained by the method for cleaning a hot slab according to any one of claims 1 to 6, is charged in a heating furnace in a hot state and then hot-rolled. The manufacturing method of hot-rolled steel materials.

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