JP4264336B2 - Roller, induction heating device, and roller manufacturing method - Google Patents

Description

  The present invention relates to an insulating sleeve, a roller, and an induction heating device used in a hot rolling line.

  In a hot rolling line that manufactures rolling materials such as steel, the slab or slab manufactured by continuous casting or slabbing is heated to a temperature at which it can be rolled in a heating furnace, or the metal is left as a hot piece. It is made into a rolled product of a predetermined thickness by carrying out a hot rolling process with a roller made of paper, a rough rolling mill and a finishing mill.

  The slab and slab are gradually thinned by the roll in the hot rolling process, but the temperature is lowered by self-heat radiation during the hot rolling process and high-pressure cooling water (Deske water). In particular, the temperature drop at both ends is large, which causes problems as a rolled product, such as material defects and cracks at the ends, and uneven rolling in the sheet width direction.

  To solve such a problem, as disclosed in Patent Literature 1 and Patent Literature 2 in many hot rolling lines, the temperature difference between the central portion and both end portions of the rolling material during the rolling process is reduced. For this purpose, an induction heating device for raising the temperature at both ends is installed. In this apparatus, a pair of induction heating apparatuses are installed at regular intervals at locations corresponding to both ends of the material to be heated conveyed by a roller.

  The induction heating apparatus is an excellent heating method in which a current is passed through a coil and both ends of the material to be heated are heated by the induced current.

  The induction heating device is roughly classified into a C-type iron core type and a U-type iron core type depending on the shape of the main iron core on which induction heating is applied. In the case of the U-type iron core type, the main iron core of one induction heating device has two poles, and has the effect of canceling the leakage magnetic flux by generating the magnetic flux φ in the opposite direction of each pole.

  On the other hand, in the case of the C-type iron core type, the main iron core of one induction heating device has one pole, and the magnetic flux φ is also generated in one direction. Therefore, a leakage magnetic flux is generated, and an induced electromotive force is generated in the rolling direction or the width direction of the heated rolled material by interlinking with the heated rolled material. A loop current is generated through the hot rolled material.

  The loop current generates a spark due to a change in contact resistance between the roller and the heated rolled material. By the electromotive force induced from the leakage magnetic flux, a loop current is formed in the length direction of the roller and in the rolling direction of the material to be heated.

  Since the C type iron core type is superior in heating efficiency compared to the U type iron core type, the hot rolling line introducing the C type iron core type induction heating device occupies the majority, and the problems caused by sparks are obvious. It is becoming. Of course, the direct wrinkle on the heated material due to sparks is a problem, but in addition to this, the spark marks on the roller are also transferred to the surface of the heated material, leading to a reduction in the quality of the heated material. , It becomes a problem.

  Therefore, when such a spark mark is generated on the roller, a grinding operation by a glider or the like is required to correct this, and the hot rolling process has to be stopped, so that productivity is lowered.

  Increasing the induction current to increase rolling efficiency, and further shortening the roller installation interval to improve the passability of heated material to be heated will increase the generation of spark marks. Countermeasures for scars are becoming more important.

  In order to solve this problem, Patent Document 3 proposes an end heating device that can prevent a spark generated between a transport roll and a rolled material. This device is a device using stepped transport rolls, paying attention to the fact that sparks are concentrated on the limited end of the material to be heated, and the end of the material to be heated and the transport roll do not contact each other. As described above, it is assumed that the conveyance roll is provided with a stepped conveyance roll, and the surface of the conveyance roll is sprayed with a thickness of 50 to 100 μm with ceramics such as alumina and zirconia to improve insulation.

  Since the passing portion of the material to be heated is a groove due to the use of the stepped transfer roll, the loop current in the rolling direction of the material to be heated is interrupted. However, when external cooling water is used to prevent seizure flaws on the surface of the stepped conveyance roll, the material to be heated and the stepped conveyance are conveyed through high-pressure cooling water whose electric resistance has decreased over a long period of use. A loop current was formed in the roll length direction of the roll, and spark was generated due to energization.

  In addition, when cooling water is not used, seizure defects occur on the surface of the stepped transport roll, and the sprayed coating is peeled off during use, resulting in poor insulation, and sparks are generated at the front and rear ends of the heated rolling material. In addition, minute sparks are generated in the passing portion of the material to be heated, that is, the contact portion between the stepped transport roll and the product, and in any case, it is difficult to solve the quality problem.

  Alumina ceramics have a low room temperature bending strength of about 350 MPa and a high temperature bending strength of 1000 ° C. of 200 MPa or less. Therefore, alumina ceramics cannot withstand the impact of 20 tonnes of rolling material, and the temperature difference of occurrence of thermal shock cracks in the submerged dropping method. Is as low as about ΔT = 200 ° C., it is considered that a heavy material heated to 1000 ° C. or higher passes through and is damaged by thermal shock.

  Moreover, according to patent document 4 and patent document 5, the table roller provided with the electrically insulating layer which has heat resistance is proposed. As a method of forming an electrically insulating layer having heat resistance, fitting of an alumina-based ceramic sleeve or a silicon nitride-based ceramic sleeve to the outside of a table roller core metal is disclosed, and direct thermal spraying of ceramics on the table roller core metal is disclosed. Is disclosed.

  In these methods, since the surface of the table roller is electrically insulated, no current circulation path is formed between the table roller and the heated rolling material, and therefore no spark is generated when the table roller and the rolling material are separated. It is said.

  However, as in Patent Document 4, even if a roller insulated using alumina and zirconia is used, the weight of the rolled material (20 ton) with increased mass, the induced current value further increased, and the higher It has become clear that the roller itself is broken or the ceramic sprayed film is peeled off due to the heating temperature at the end of the rolled material, and stable use for a long time is impossible.

  Further, even when a silicon nitride sleeve as in Patent Document 5 is used, when silicon nitride ceramics having insufficient oxidation resistance is used, oxidation proceeds by the heated material being heated to 1000 ° C., The sleeve is damaged, causing troubles such as line stoppage.

  According to the proposals in Patent Document 4 and Patent Document 5, since the electrical insulating layer is formed on the table roller, the loop current in the rolling direction of the material to be heated is interrupted.

  However, since the surface temperature of the material to be heated is about 1000 ° C., it is indispensable to cool the electrical insulating layer as a thermal shock protection of the electrical insulating layer by contact, and the external cooling water for cooling this is Since it is usually reused, a scale is formed with the metal peeled off from the surface of the rolled material during use, and the electric resistance of the high-pressure cooling water decreases.

  In addition, a loop current is formed in the body length direction of the material to be heated and the table roller through the high pressure cooling water with reduced electrical resistance due to the mixture of scales, which causes sparks and eliminates product quality degradation. could not.

  In addition, when cooled, a phenomenon occurs in which a loop current is formed from the cooling water with reduced electrical resistance as described above. For example, although it is unrealistic in terms of cost, pure water with a large specific resistance is used. Although the melting point of alumina and zirconia is 1000 ° C. or higher and the heat resistance is high, the difference in temperature of occurrence of thermal shock cracking in the water dropping method is 200 ° C. for alumina and 350 ° C. for zirconia in Patent Document 3. Silicon nitride that does not focus on the oxidation resistance of Document 5 is 800 ° C., and since it has not reached the thermal shock corresponding to the needs of this application, it is fully expected that problems will occur.

  Regarding the manufacturing method, in Patent Document 5, the granulated granule is filled into a molding die composed of a rubber mold for sleeve molding and a core metal for molding, and the green compact is molded by a hydrostatic pressure device. In addition, it is specified that after a cylindrical molded body is manufactured, degreased by heating to 500 ° C. at low speed, and then processed into a predetermined shape by an NC lathe equipped with a carbide tool.

  This is unsuitable because it significantly reduces the handleability of the molded body before processing the substrate and greatly reduces the production yield. Furthermore, no description about the heat treatment for crystallizing the sintering aid of the hardly sinterable silicon nitride powder is recognized in the firing process, and in the examples, the description is that firing is performed at 1700 ° C. for 1 hour. Is only seen.

JP-A 63-126609 JP-A-61-273888 Utility Model Registration No. 2555161 Japanese Utility Model Publication No. 6-38563 JP 2002-178020 A

  Therefore, the present invention is excellent in oxidation resistance at a high temperature of 1000 ° C. or higher, and has a thermal shock resistance against rapid heating and rapid cooling of ΔT = 1000 ° C. for the purpose of solving the problems of the prior art described above. In order to improve rolling efficiency, the spark does not break even when the induction current value or the heating temperature of the rolling material is increased, and the spark that has been generated between the roller and the heated rolling material over the entire length of the rolling material. It is an object of the present invention to provide an insulating sleeve for a hot rolling line roller that can be prevented.

  In addition, by providing a roller using this insulating sleeve and an induction heating device, it is possible to realize a more stable hot rolling line operation with less maintenance pauses, and to produce rolled products such as steel products produced therefrom. It is to further improve quality.

As a result of various studies to achieve the above-mentioned object, the present inventors have excellent oxidation resistance as an electrical insulating layer of a roller, and the difference in temperature of occurrence of thermal shock cracking in water dropping method is ΔT = 1000. Ceramics having a melting point of not less than 1 ° C., for example, a grain boundary phase is highly crystallized with a crystalline phase having a high melting point (for example, an auxiliary component that promotes the sintering of difficult-to-sinter silicon nitride powder is not less than 1300 ° C. A silicon phase having a high melting point and a very stable crystal phase at a high temperature up to 1250 ° C., such as RE ₂ Si ₂ O ₇ (RE is a rare earth element), heat treatment for crystallization into Si ₂ N ₂ O, or the like It has been found that by using a sleeve made of a sialon sintered body, it is possible to prevent the occurrence of sparks in the rolled material.

  Furthermore, the present inventor has found that the above object can be achieved by providing a roller for a hot rolling line and an induction heating device having a structure in which the sleeve is externally fitted to the roller.

  That is, the gist of the present invention is as follows.

(1) induced to heating have your coil hot rolling line arranged to feed transportable rolling material, an insulating sleeve of ceramic ing with transport rollers fitted to the outside of the metal core of the roller The insulating sleeve is made of silicon nitride or a sialon sintered body having a grain boundary phase crystallized at a high melting point, and the grain boundary phase includes RE ₂ Si ₂ O ₇ (RE is a rare earth element) and Si ₂ N. ₂ O, having an oxidation resistance within a range of ± 0.1 mg / cm ² within a range of 1000 to 1250 ° C. in the atmosphere and holding for 64 hours , and having a difference in temperature of occurrence of thermal shock cracks in the submerged dropping method of 1000 ° C. It has the above thermal shock resistance, has a bending strength of 600 MPa or more in the temperature range of 20 to 1250 ° C., and the sleeve outer diameter is larger than the diameter in the trunk length direction of the metal cored bar. 50 between the insulating sleeve and the metal cored bar. A buffer layer made of ceramic fibers having heat resistance up to 0 ° C., the thickness h (mm) of the buffer layer being αm (K−1) as the thermal expansion coefficient of the metal core, and the thermal expansion coefficient of the insulating sleeve A roller, wherein αc (K-1), where the core metal radius is r (mm), 50r (αm−αc) ≦ h ≦ 300r (αm−αc) .

(2) The insulating sleeve total length of the roller barrel length direction a 50 to 1000 mm, characterized that you have fitted into the site at least the rolling material ends in contact of the metal core (1 ) Roller .

(3) An induction heating device that arranges induction heating coils opposed to each other from above and below the rolling material of the hot rolling line, and heats both ends in the width direction of the rolling material, either directly below the induction heating coil or Before and after that, the induction heating apparatus characterized by arrange | positioning the roller as described in (1) or (2).

(4) A method for producing the roller according to (1) or (2), wherein a predetermined amount of rare earth oxide, silicon oxide powder sintering aid is added to the silicon nitride raw material, or nitriding is performed. A predetermined amount of rare earth oxide, a predetermined amount of silicon oxide and aluminum oxynitride powder sintering aid are added to the silicon raw material, a predetermined amount of granulating binder and water are added and wet mixed, and a spray dryer is added. The granule is dried and granulated to produce granules, and the granule produced by dry granulation is filled into a molding die composed of a rubber mold for sleeve molding and a core metal for molding, and hydrostatic pressure is applied. A cylindrical shaped green body having a predetermined size based on the size of the metal core is manufactured by a process of manufacturing a cylindrical molded body using an apparatus and an NC lathe equipped with a carbide tool. Process and 5 A step of debinding by heating at a low speed of 5 to 10 ° C./hour up to 00 ° C., and baking the debindered green body in a pressurized atmosphere of nitrogen gas, followed by crystallization treatment, Forming a silicon nitride or sialon sintered body, and finishing and insulating the silicon nitride or sialon sintered body to fit the metal cored bar using a resin bond diamond grindstone A method for producing a roller, comprising: a step of producing a sleeve; and a step of inserting and fixing a ceramic core sheet between the insulating sleeve and a separately produced metal core as a buffer layer.

  According to the insulating sleeve of the present invention, it has excellent thermal shock resistance and does not break even when the induction current value or the heating temperature of the rolling material is increased to improve rolling efficiency, and is conventionally generated between the roller and the rolling material. It has become possible to prevent sparks that have occurred over the entire length of the rolled material.

  Further, the present invention provides a more stable operation of a hot rolling line with less maintenance pauses by using a roller fitted with the insulating sleeve and an induction heating device using the roller immediately below or before and after the induction heating coil. As a result, the quality of rolled products such as steel produced therefrom can be further improved.

  Hereinafter, an example of the hot rolling line which manufactures rolling materials, such as a steel strip, provided with the insulating sleeve of this invention and the roller which fitted this is demonstrated.

  In the hot rolling line, one or more sets of induction heating devices are installed in order to reduce the temperature drop at both ends in the width direction of the material to be heated that is conveyed at a constant period. In this induction heating device, an electric current is passed through the coil, and the induction current rapidly heats both ends of the material to be heated while passing through the induction current.

  At this time, in the conventional conductive roller, a loop current is generated in the roller body length direction and the rolling direction of the heated rolling material, respectively, and this loop current is sparked at the time of contact between the heated rolling material and the conventional roller. This is very dangerous and causes brazing of the rolled material, leading to the generation of defective materials.

  The spark prevention of the roller for hot rolling lines of the present invention will be described. The center part in the barrel length direction of the roller for the hot rolling line is covered with an insulating sleeve and does not come into direct contact with the material to be heated. There is no risk of affecting the rolling material.

  Since the surface layer of the hot rolling line roller through which the rolled material to be heated passes is in contact with the ceramic sleeve that is an insulator, the surface of the heated rolling material and the surface of the hot rolled line roller is between The loop current is insulated, and the insulating effect of the roller base material itself can be obtained.

  From the above, since the roller loop current that contributes to the occurrence of sparks is interrupted by the insulating sleeve, danger due to sparks and a decrease in yield are prevented.

The insulating sleeve of the present invention has a high resistivity of 10 × 10 ⁻¹⁰ Ω · cm or more in volume resistivity. For this reason, the loop current generated in the roller body length direction and the rolling direction of the heated material to be heated is inserted into the insulating sleeve, so the heated material and the roller base material are not in contact with each other. Therefore, it is possible to eliminate the occurrence of sparks.

  In developing the roller for the hot rolling line of the present invention, the ceramic insulating sleeve fitting roller is fixed to the V block, the cold piece or the heated piece sample bar is dropped freely from the top, the ceramic sleeve is cracked, surface defects An impact resistance test apparatus for performing flaw detection inspections and the like was manufactured and tested.

  At the same time, the mechanical strength and safety factor were derived from the comparison between the actual plant and the collision energy between the test equipment, the material and the shape were selected, and sufficient conditions that could withstand the actual plant for a long time were set off-line.

  Based on these results, it is essential that the ceramic sleeve material must have oxidation resistance and high-temperature strength, including temperature rise during sliding, in addition to thermal shock resistance corresponding to the temperature difference between the water-cooled and rolled material. found.

More specifically, in order to be able to withstand contact with a high-temperature heated rolled material, the underwater dropping method thermal shock crack generation temperature difference ΔT is preferably 1000 ° C. or more, and at various humidity settings in the atmosphere, In order to ensure the mechanical strength at the time of collision, it is preferable that the mass change in the oxidation test by holding at 1000 to 1250 ° C. for 64 hours according to JIS R 1601 is within ± 0.1 mg / cm ² . The bending strength of the ceramic sleeve is preferably 600 MPa or more in the temperature range of 20 to 1250 ° C.

  As a material satisfying these properties, the present inventor has intensively studied. As a result, oxides and oxynitrides to be added to sinter difficult-to-sinter silicon nitride powder are added to the high-melting crystal at the grain boundaries of the silicon nitride matrix. It has been found that a special material highly crystallized in the phase is effective.

It is suitable for this application that at least one phase of RE ₂ Si ₂ O ₇ (RE is a rare earth element) or Si ₂ N ₂ O is formed at the grain boundary of the silicon nitride sintered body crystallized at a high melting point. It is.

In addition, as a sialon whose grain boundary is crystallized at a high melting point, the matrix phase is predominantly β′-Si ₆ -Z Al _Z O _Z N _8-Z phase (Z = 0.2 to 4), and sintered. In the grain boundary of the body, Al ₉ O ₃ N ₇ , Al ₇ O ₃ N ₅ , Al ₆ O ₃ N ₄ , Si ₃ N ₄ .Y ₂ O ₃ , RE ₂ Si ₂ O ₇ (RE is a rare earth element), A material in which at least one phase of Si ₂ N ₂ O or Y ₃ Al ₅ O ₁₂ is formed is suitable for this application.

  The rolled material to be heated meanders to the left and right with respect to the rolling direction as the rolling progresses. The sleeve portion made of ceramics, that is, the roller large-diameter portion in contact with the heated material, By securing 50 mm or more, the roller base material portion (metal cored bar) is prevented from coming into contact with the material to be heated and no spark is generated.

  In order to reduce the manufacturing cost of the insulation sleeve, the total length of the sleeve is about half of the maximum width of the rolled material per unit, that is, the maximum length of the general steel material is 2100 to 2400 mm. It is preferable to set it as 1000 mm.

  In addition, the length of the insulating sleeve alone fitted into the middle part in the trunk length direction where the load is applied most is about 50 to 200 mm, more preferably 100 to 200 mm.

  Next, the roller of the present invention is a roller for conveying a rolling material in a hot rolling line in which an induction heating coil is arranged, and the above-described insulating sleeve is fitted to a portion where at least the end of the rolling material contacts the roller. It is characterized by becoming.

  The number of insulating sleeves to be fitted to the roller is not particularly limited, and is optimal so that the rolled material does not come into contact with the metal core bar of the roller from the width of the rolled material and the length of the insulating sleeve in the body length direction. A proper number may be selected. That is, when the length of the insulating sleeve is longer than the width of the rolling material, one insulating sleeve may be fitted.

  Further, when the length of the insulating sleeve is shorter than the width of the rolling material, two sets of the insulating sleeves may be fitted so that the insulating sleeves are disposed at both ends in the width direction of the rolling material. Furthermore, when the central part in the width direction of the rolling material is bent by its own weight and may come into contact with the metal core, it is desirable to arrange an arbitrary number of insulating sleeves in the central part as well as both ends.

When the ceramic sleeve is fitted to the metal core of the roller, the average gap h (mm) between the core and the sleeve indicates the coefficient of thermal expansion of the core and sleeve, respectively, α _m (K ⁻¹ ) and When α _c (K ⁻¹ ), the core metal radius is r (mm), the maximum temperature of the core metal surface in the rolling material passing material is 500 ° C., and the safety factor is 1.5, approximately h = 1.5 X ([alpha] _{m- [} alpha] _c ) * r * (500-20) = 720r ([alpha] _{m- [} alpha] _c ).

Ceramic fibers that have heat resistance up to 500 ° C and excellent long-term wear resistance to prevent foreign matter from being mixed when gaps widen when the temperature drops due to cooling water, and to prevent fragmentation and wear due to misalignment It is preferable to insert a buffer layer made of The thickness of the insert to the buffer layer is preferably from _{50r (α m -α c) ~300r} (α m -α c), more preferably at _{100r (α m -α c) ~200r} (α m -α c) is there.

  In a hot rolling line, an induction heating coil facing each other from the top and bottom of a rolled material such as a steel plate is arranged, and the metal is arranged directly below or before and after the induction heating device that heats both ends in the width direction of the rolled material. About the metal material of the metal core metal of the roller for hot rolling lines which fitted the ceramic sleeve to the metal core, it is preferable that it is Cr-Mo steel or stainless steel. These rollers for hot rolling lines can be suitably used as transport rollers or pinch rollers.

  The induction heating device of the present invention is an induction heating device that arranges induction heating coils opposed to each other from above and below the rolling material of the hot rolling line, and heats both ends in the width direction of the rolling material, It is characterized in that the above-mentioned roller is arranged immediately below or before and after the induction heating coil.

  In this apparatus, as described above, since the rolling material and the roller are insulated by the insulating sleeve, even if the induction current for induction heating is increased, spark wrinkles that have conventionally occurred between the rolling material and the roller are not generated. Since it does not occur and the frequency of roller maintenance can be greatly reduced, a high-quality rolled material can be produced with high efficiency for a long period of time.

  That is, for the purpose of solving the long-term stability which has been a problem in the prior art, the present invention is excellent in high-temperature strength from room temperature (20 ° C.) to 1250 ° C., and is various in the atmosphere from 1000 ° C. to about 1250 ° C. Rolling efficiency is improved because ceramic materials are provided as insulating sleeves that have excellent resistance to oxidation under humidity and high temperature, and have repeated thermal shock resistance (spall resistance) against rapid heating and rapid cooling at ΔT = 1000 ° C. Even if the induction current value is increased, the heating temperature of rolling materials such as steel strips is increased, or high-pressure cooling water is injected, the strength at high temperatures is excellent, and damage and wear are unlikely to occur. Can be used.

  In addition to the steel material, various metal materials such as titanium, magnesium, copper, and aluminum can be used as the rolling material, and the present invention is a rolling condition with a conventional metal roller, more specifically, The production cost of the rolling material is reduced by further relaxing restrictions on the rolling temperature, the plate thickness, the rolling reduction, the threading speed, and the like.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

(Example 1)
A predetermined amount of yttrium oxide (average particle size 0.7 μm, purity 99%) and ytterbium oxide (average particle size 0.8 μm, purity 97%) are added to a silicon nitride raw material (average particle size 0.4 μm, purity 98%). Wet mixing of rare earth oxide and silicon oxide (average particle size 0.2μm, purity 99.5%) powder sintering aid and a predetermined amount of granulating binder (water-soluble polyvinyl alcohol, solid content concentration 40% by mass) Then, it was dried and granulated with a spray dryer.

  Here, 3.5% by mass of yttrium oxide powder, 1.7% by mass of ytterbium oxide powder, and 2.8% by mass of silicon oxide powder are added as sintering aids to 92% by mass of the silicon nitride raw material. To 100 parts by mass of powder, 10 parts by mass of a granulating binder and 80 parts by mass of water were added, and the mixture was wet-mixed with a rotary ball mill at 40 rpm for 48 hours, and the granules subjected to spray-dry granulation were used for sleeve molding. A cylindrical mold was manufactured by filling a molding die composed of a rubber die and a molding metal core and molding a green compact of φ500 mm × L270 mm with a hydrostatic pressure press.

  This silicon nitride ceramic molded body was processed into a cylindrical shape of φ480 mm (inner diameter 368 mm) × L250 mm using an NC lathe equipped with a carbide tool.

  The obtained green body was debindered by low-speed heating at 5 to 10 ° C./hour up to 500 ° C. during air circulation, then held at 1780 ° C. in a pressurized atmosphere of nitrogen gas 392 kPa for 10 hours, and then 1550 ° C. The crystallization treatment was carried out for 24 hours to obtain a silicon nitride sintered body of φ384 mm (inner diameter 290 mm) × L208 mm of the present invention.

As for the structure of the sintered body, the matrix was only a β-Si ₃ N ₄ phase, and the grain boundary layer was a mixture of Si ₂ N ₂ O, Y ₂ Si ₂ O ₇ and Er ₂ Si ₂ O ₇ phases. .

Further, the three-point bending strength at 20 ° C. was 950 MPa, and the same strength at 1250 ° C. in the atmosphere was 680 MPa. Furthermore, the mass change in the oxidation test by holding at 1000 to 1250 ° C. for 64 hours in the air was 0.05 mg / cm ² , and the temperature difference ΔT at which the thermal shock cracking occurred in the submerged dropping method was 1000 ° C.

(Example 2)
To 91% by mass of the silicon nitride raw material, a powder sintering aid of 4.5% by mass of yttrium oxide, 1.2% by mass of silicon oxide, and 3.3% by mass of aluminum oxynitride was added. After adding 10 parts by mass of a granulating binder and 85 parts by mass of water, the mixture was wet-mixed with a rotary ball mill at 45 rpm for 24 hours, and then subjected to spray-dry granulation to obtain granules. In the same manner as in Example 1, the molding die was filled, the green compact was molded, a cylindrical molded body was manufactured, and the base was processed into φ485 mm (inside diameter 370 mm) × L253 mm with a carbide tool.

  The resulting green body was debindered by low-speed heating at 5 to 10 ° C./hour up to 500 ° C. in the atmosphere, then held at 1750 ° C. for 8 hours in an atmospheric pressure of nitrogen gas, and then at 1400 ° C. Crystallization treatment for 12 hours was performed to obtain a sialon sintered body of φ384 mm (inner diameter 295 mm) × L210 mm of the present invention.

In the sintered body, the β′-Si ₄ Al ₂ O ₂ N ₆ phase is dominant as a matrix, and the grain boundary layer includes Al ₉ O ₃ N ₇ , Al ₇ O ₃ N ₅ , Al ₆ O _3. N ₄ , Si ₃ N ₄ .Y ₂ O ₃ , Y ₂ Si ₂ O ₇ , Si ₂ N ₂ O, and Y ₃ Al ₅ O ₁₂ phases were mixed.

Further, the three-point bending strength at 20 ° C. was 900 MPa, and the same strength at 1250 ° C. in the atmosphere was 620 MPa. Furthermore, the mass change in the oxidation test after holding at 1000 to 1250 ° C. for 64 hours in the atmosphere is 0.08 mg / cm ² , and the temperature difference ΔT at which the strength of thermal shock is reduced by the water dropping method is 1000 ° C. It was.

  The sintered bodies obtained in Examples 1 and 2 were finished using a resin bond diamond grindstone, and an insulating sleeve made of silicon nitride and sialon having an outer diameter of 380 mm, an inner diameter of 300 mm, and a length of 200 mm was manufactured.

  The material of the core metal of the roller for hot rolling lines was made of Cr-Mo steel, and a metal core metal having a diameter of 300 mm incorporating a predetermined shape such as a bearing built-in shaft shape and an internal cooling water channel was manufactured.

The thermal expansion coefficient α _m of the core metal is 12 × 10 ⁻⁶ K ⁻¹ , and the thermal expansion coefficients α _c of silicon nitride and sialon are 3.8 × 10 ⁻⁶ k ⁻¹ and 2.1 × 10 ^{−6, respectively.} a K ^-1, the core metal of the radius (150 mm), the maximum temperature 500 ° C. of the core surface during rolling material longerons, when the safety factor is 1.5, the core metal and the inner diameter of the insulating sleeve The gap h (mm) in the radial direction is an insulating sleeve made of silicon nitride, h = 720 × 150 × (12 × 10 ⁻⁶ −3.8 × 10 ⁻⁶ ) = 0.89 (mm), manufactured by Sialon With an insulating sleeve, h = 720 × 150 × (12 × 10 ⁻⁶ −2.1 × 10 ⁻⁶ ) = 1.07 (mm).

  Therefore, as the buffer layer inserted between the core metal and the insulating sleeve, ceramic fiber sheets having a thickness of 0.15 mm and 0.20 mm in which silicon carbide fibers are woven are used, respectively.

  As shown in FIG. 1, insulating sleeves 3 having an outer diameter of 380 mm, an inner diameter of 300 mm and a length of 200 mm are provided on both sides of the cored bar 2 of the conveying roller 1 having an overall length of 1700 mm and an outer diameter of 300 mm in total. The metal sleeve (outer diameter 340 mm × inner diameter 300 mm × length 100 mm, not shown) is inserted on both sides of the insulating sleeve 3, and the metal sleeve and the core metal 2 arranged at both ends are inserted. Was fixed with screws to complete the transfer roller 1.

  This conveying roller was installed directly under the C-type iron core induction heating device, and the edge was heated while water-cooling the roller surface together with the insulating sleeve to convey a steel strip (coarse bar) having a width of 600 to 1500 mm. . And the presence or absence of the spark at the time of steel strip passage, the surface state of the steel strip passed, and the roller surface state were confirmed and evaluated. The results are shown in Table 1.

  In addition, a buffer layer made of silica fiber having a thickness of 1/3 with respect to the gap caused by the difference between the thermal expansion coefficient of the ceramic material of the present invention and the thermal expansion coefficient of the cored bar material (see FIGS. 1 and 4). When the insert was inserted, it was possible to suppress the intrusion of the scale and the like, and to reduce uneven wear due to misalignment.

(Comparative Example 1)
High-purity alumina (purity 99.5%) ceramics was sprayed onto the Cr-Mo steel core roller used in Examples 1 and 2 to produce a transport roller. The sprayed thickness was 0.5 mm, the length of the roller was 1700 mm, and the outer diameter was 380 mm over the entire body length direction.

  Evaluation was performed in the same manner as in Examples 1 and 2 using this transport roller. The results are shown in Table 1. In this system, due to the lack of thermal shock resistance of the alumina material, innumerable cracks occur and peeling occurs.

(Comparative Example 2)
A silicon nitride ceramic (crystal structure) in which the grain boundary phase fired only at 1700 ° C. for 1 hour in nitrogen gas is not crystallized on the roller of the Cr—Mo steel core used in Examples 1 and 2 Was externally fitted with an insulating sleeve (φ380 mm (inner diameter 340 mm) × L100 mm) made of β-Si ₃ N ₄ phase and glass phase) to produce a conveying roller.

  Using this transport roller, a gap of 0.6 mm with the base steel material was calculated in the same manner as in Examples 1 and 2, and evaluation was performed without a cushioning material. The results are shown in Table 1.

  Silicon nitride ceramics with a low melting point glass phase in the grain boundary layer is not only low in high-temperature strength but also inferior in oxidation resistance and thermal shock resistance, so it cannot be used for a long period of time. It is.

(Comparative Example 3)
The transport roller (outer diameter 380 mm) of the Cr—Mo steel core used in Examples 1 and 2 was used without a ceramic sleeve. Evaluation was performed in the same manner as in Examples 1 and 2 using this transport roller. The results are shown in Table 1.

  Rollers sprayed with alumina ceramics, silicon nitride ceramics without crystallizing the grain boundary phase, and steel rollers generate sparks in a short period of time, causing defects directly or indirectly to the product, or In the worst case, line breaks were caused by damage to the sleeve.

  However, the conveying roller in which the insulating sleeve using the silicon nitride or sialon sintered body, which is highly crystallized with the crystal phase having a high melting point, is externally fitted on both sides in the body length direction is a spark. In any case, it was confirmed that the product quality of rolled materials such as steel strips could be prevented from being deteriorated and the oxidation resistance was excellent, so that it could be used stably over a long period of time.

  According to the insulating sleeve of the present invention, it has excellent thermal shock resistance and does not break even when the induction current value or the heating temperature of the rolling material is increased to improve rolling efficiency, and is conventionally generated between the roller and the rolling material. It has become possible to prevent sparks that have occurred over the entire length of the rolled material. In addition, the present invention realizes a more stable operation of a hot rolling line with less maintenance pauses by using a roller fitted with the insulating sleeve and an induction heating device using the roller directly under or before the induction heating coil. In addition, it has an excellent effect that the quality of rolled products such as steel produced therefrom can be further improved.

  Therefore, the present invention improves the steel rolling technology and contributes to the development of the steel industry.

It is sectional drawing which shows one Example of the roller for hot rolling lines.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Conveying roller 2 ... Core metal 3 ... Insulating sleeve 4 ... Buffer layer 5 ... Heated rolled steel strip

Claims (4)

Induced to heating have your coil hot rolling line arranged to feed transportable rolling material, an Ru insulation sleeve name of ceramics a transport roller which is fitted to the outside of the metal core of the roller,
The insulating sleeve is
It is composed of silicon nitride or sialon sintered body having a grain boundary phase crystallized at a high melting point, and the grain boundary phase is RE ₂ Si ₂ O ₇ (RE is a rare earth element) and Si ₂ N ₂ O, Having a resistance to oxidation within a range of ± 0.1 mg / cm ² by mass retention at 1000 to 1250 ° C. for 64 hours ,
Underwater dropping method thermal shock cracking temperature difference of 1000 ° C or more, thermal shock resistance of 600MPa or more in the temperature range of 20 to 1250 ° C, sleeve outer diameter is the metal cored bar large diameter der than body length direction central portion diameter is,
A buffer layer made of ceramic fibers having heat resistance up to 500 ° C. is provided between the insulating sleeve and the metal core, and the thickness h (mm) of the buffer layer determines the thermal expansion coefficient of the metal core as αm. (K-1), where the thermal expansion coefficient αc (K-1) of the insulating sleeve and the core metal radius is r (mm), 50r (αm−αc) ≦ h ≦ 300r (αm−αc),
The roller characterized by being. The insulating sleeve is a 50~1000mm total length of the roller barrel length direction, to claim 1, characterized that you have fitted into the site at least the rolling material end of the metal core is in contact The roller described . An induction heating device that arranges induction heating coils opposed to each other from above and below a rolling material of a hot rolling line and heats both ends in the width direction of the rolling material, immediately below or before and after the induction heating coil An induction heating apparatus comprising the roller according to claim 1 or 2 . A method for producing the roller according to claim 1 or 2,
Add a predetermined amount of rare earth oxide and silicon oxide powder sintering aid to the silicon nitride raw material, or add a predetermined amount of rare earth oxide, predetermined amount of silicon oxide and aluminum oxynitride powder to the silicon nitride raw material A step of adding a sintering aid, adding a predetermined amount of a granulating binder and water, wet-mixing, and dry granulating with a spray dryer to produce granules;
Filling the granules produced by dry granulation into a molding die composed of a rubber mold for sleeve molding and a core metal for molding, and producing a cylindrical molded body by a hydrostatic pressure device;
A step of producing a cylindrical green body having a predetermined size based on the size of the metal core bar by using an NC lathe equipped with a cemented carbide tool.
A step of removing the binder by heating at a low speed of 5 to 10 ° C./hour up to 500 ° C. in the air flow, and
Firing the debindered green body in a pressurized atmosphere of nitrogen gas, followed by crystallization treatment to produce a crystallized silicon nitride or sialon sintered body;
The silicon nitride or sialon sintered body is processed using a resin bond diamond grindstone to finish the metal cored bar to produce an insulating sleeve, and
A step of inserting and fixing the insulating sleeve and a separately manufactured metal core between the ceramic fiber sheet as a buffer layer therebetween;
The manufacturing method of the roller characterized by comprising.

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