A method for repairing stand rollers of hot rolling mill

Abstract

The present invention provides a method for repairing stand rollers in a hot rolling mill. The method involves first forming a mold of the stand roller body using a thermoplastic polymer material. A sand mold is then made based on the molded shape, and a roller sleeve is cast to fit the defects of the stand roller body. The sleeve undergoes continuous annealing to obtain a uniform bainite structure, rapidly increasing its hardness. The sleeve is then embedded in the exterior of the stand roller body and secured by welding, completing the repair of the stand roller body. This method not only rapidly repairs the stand roller surface, imparting excellent hardness and wear resistance, thereby extending its service life, but also allows for the reuse of discarded roller cores, achieving environmental protection.

Description

Technical Field

[0001] The present invention relates to the technical field of rolling mill equipment, in particular to a method for repairing a stand roller of a hot rolling mill. Background Art

[0002] The stand rollers of a hot rolling mill are among the most closely connected pieces of equipment during the rolling process. They are installed in both the roughing and finishing mills. The stand rollers of the roughing mill are installed between the roughing vertical rolls and the roughing work rolls, and between the roughing work rolls and the exit roller table. The stand rollers of the finishing mill are installed before and after the descaling nozzles of the descaling box. They smoothly feed the slab into the mill roll gap and receive the finished product. The most important components of the stand rollers are the stand roller body and the bearing housing. The bearing housing is a monolithic structure, while the stand rollers are through-holes in the frame and secured to the mill frame by fastening bolts on the bearing seats. High-pressure water descaling nozzles are also installed at the bottom of the stand rollers to descale the slab.

[0003] Due to the harsh operating conditions of the stand rollers, which are subject to high temperatures, impact, high pressure erosion, heavy loads, and friction, the rollers are prone to wear. This can cause the roller surface to become grooved, uneven, and even eroded into a wavy shape, resulting in a change in roller diameter. In severe cases, the diameter difference decreases by approximately 50 mm, making it unable to resist the erosion of the slab by the high-pressure descaling water. The rollers cannot perform their intended function and need to be replaced. However, the removal and installation of the stand rollers requires 24 to 36 hours of downtime, which is not only time-consuming and labor-intensive, but also seriously affects the continuous rolling process. Therefore, it is necessary to find a method to quickly repair the stand roller surface to reduce the replacement time.

[0004] At present, one idea to solve the above problem is to disassemble the stand rollers and send them to a machining plant for surfacing repair. For example, Chinese Patent 201711033594.6 discloses a laser cladding repair method for stand rollers, which includes removing the fatigue layer, surfacing to restore the size, annealing, outer diameter turning, low-carbon surfacing, preheating, laser cladding, slow cooling, and argon arc welding repair, thereby increasing the service life of the stand rollers. However, this method not only has a long production cycle, but also requires a professional roll repair team. At the same time, the number of times the rolls can be repaired is limited. If the number of times is too high, the yield strength of the roll core will exceed the design range, causing the stand roller to break. The large number of scrap rollers that have been replaced becomes a difficult problem to deal with. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the purpose of the present invention is to provide a hot rolling mill stand roller repair method to reduce the replacement and repair time of the stand roller, extend the utilization rate of the roller core, thereby increasing its service life and saving costs.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for repairing a stand roller of a hot rolling mill comprises the following steps:

[0008] S1. Take shape

[0009] The thermoplastic polymer material is stuck on the surface of the worn frame roller, and the worn frame roller body is demolded online so that the inside of the polymer model fully fits the defective part and the outer diameter of the polymer model is consistent with the outer diameter of the new roller of the frame roller; after the polymer model is completed, it is locked to obtain the macroscopic shape of the worn part;

[0010] S2. Sand mold making

[0011] Based on the polymer model obtained in S1, the macroscopic morphology of the roller sleeve is drawn, and then a sand mold of the roller sleeve with matching shape is made. The size of the sand mold is the same as that of the roller body of the frame roller.

[0012] S3. Roller sleeve production

[0013] The molten steel is poured into a sand mold and naturally cooled to room temperature to obtain a roller sleeve;

[0014] S4. Heat treatment

[0015] The roller sleeve is taken out and sent to a resistance furnace for annealing to obtain a uniform graphite + bainite + carbide structure, and the roller sleeve hardness is controlled at 70HSD ~ 80HSD;

[0016] S5. Grinding

[0017] The outer surface of each roller sleeve is ground by 0.5mm to 1.0mm to make the surface roughness Ra≤0.8; each roller sleeve is then cut into two semicircular shapes, with the cut surface designed to be a V-shaped surface from the outside to the inside, and the beveled surface is chamfered at 45°;

[0018] S6. Installation and welding

[0019] Through the matching relationship between the internal shape of the roller sleeve and the worn position of the frame roller, the corresponding sleeve of the complete set of semicircular roller sleeves is placed on the worn part of the frame roller and positioned through the positioning hole; the gap is repaired from the inside to the outside by argon arc welding until it is equal to the outer diameter and no defects are found in the color flaw detection, and the repair of the frame roller is completed.

[0020] In step S1, the thermoplastic polymer material used is acrylonitrile-butadiene-styrene copolymer. After the polymer model is cooled and solidified, two positioning holes are drilled in the polymer model at radially symmetrical positions along the roller body. The positioning holes penetrate the polymer model and the roller body of the frame roller, and the two positioning holes have different apertures.

[0021] In step S2, to facilitate replacement, production, and installation, the polymer model is evenly cut into N segments along the length of the roller body. N sets of sand molds are prepared based on the N segments of the polymer model, where N is an integer between 2 and 6. To ensure subsequent installation and positioning, dovetail grooves and dovetails that engage with each other are provided in the corresponding sand molds according to the connection sequence of the N segments of the polymer model.

[0022] In step S3, the cast molten steel is high nickel chromium molybdenum molten steel, and its components specifically include: W C =3.35%~3.45%, W Mn =0.70%~0.90%, W Si =0.85%~1.05%, W Cr =1.75%~1.95%, W Mo =0.2%~0.40%, W Ni =3.95%~4.15%, the rest is Fe and unavoidable impurities.

[0023] The specific steps of annealing in step S4 are: the first annealing temperature is controlled at 390°C ± 10°C, kept at this temperature for 18 hours, cooled to 230°C with the furnace, and then air-cooled; the second annealing temperature is controlled at 510°C ± 10°C, kept at this temperature for 18 hours, cooled to 150°C with the furnace, and then air-cooled.

[0024] In step S6, when N sections of roller sleeves are used for connection, the connection between the roller sleeves is completed while the positioning holes are positioned. After the two adjacent roller sleeves are fixed by the matching connection of the dovetail groove and the dovetail, they are circumferentially welded to connect the four sections of roller sleeves into one. The welding between adjacent roller sleeves is done by spot welding.

[0025] Due to the adoption of the above technical solution, the technical advancements achieved by the present invention are:

[0026] The present invention provides a method for repairing stand rollers in a hot rolling mill. This method not only rapidly repairs the stand roller surface, improving its hardness and wear resistance and extending its service life, but also allows for the reuse of discarded roller cores, achieving environmental protection. The repair process does not require disassembly or installation of the stand rollers or bearing housing, making it simple and convenient, significantly reducing maintenance time.

[0027] Field production practice has proved that the hot rolling mill frame roller repair method of the present invention has good use effect, the rolling cycle is extended by more than 50%, the steel passing capacity is significantly increased, the roller surface has higher wear resistance, and the erosion of the slab by high-pressure water is reduced. At the same time, the replacement time due to the wear of the frame roller body is greatly reduced. It only takes three hours to realize online disassembly-free installation and repair, which saves time and effort and improves the continuity of rolling line production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1Schematic diagram of the method of the present invention;

[0029] Figure 2 It is a schematic diagram of the roller sleeve structure located in the middle;

[0030] Figure 3 Schematic diagram of the roller sleeve structure at the end;

[0031] Figure 4 It is a schematic diagram of the transverse cross-sectional structure of the roller sleeve.

[0032] The list of numbers in the figure is: 1. Bearing box, 2. Fastening bolts, 3. Bearing seat, 4. Frame roller, 5. Wear surface, 6. Repair surface, 7. Roller sleeve, 8. Dovetail groove, 9. Dovetail, 10. First positioning hole, 11. Second positioning hole. Implementation Method

[0033] The present invention will be described in further detail below with reference to the accompanying drawings.

[0034] A method for repairing a stand roller of a hot rolling mill comprises the following steps: firstly, a thermoplastic polymer material is used to form a stand roller body; then, a sand mold is made based on the mold shape; and a roller sleeve is cast to match the defects of the stand roller body; the roller sleeve is continuously annealed to obtain a uniform bainite structure, and the hardness is rapidly increased; and the roller sleeve is embedded in the outside of the stand roller body and fixed by welding, thereby completing the repair of the stand roller body.

[0035] The hot rolling mill stand roller repair method specifically comprises the following steps:

[0036] S1. Take shape

[0037] A thermoplastic polymer material is clamped onto the surface of the worn roll body, and the worn roll body is then profiled online, ensuring that the interior of the polymer model fully conforms to the defective area and that the outer diameter of the polymer model matches the outer diameter of the new roll. Generally, the polymer model is formed by two semicircular rings, which are clamped together with a clamp. After forming, the clamp is released and the two semicircular polymer models are removed, revealing the macroscopic shape of the worn area.

[0038] The thermoplastic polymer material is preferably acrylonitrile-butadiene-styrene copolymer, whose chemical formula is (C8H8) x (C4H6) y (C3H3N) z A common thermoplastic polymer.

[0039] Taking into account the uneven axial wear of the frame roller, in order to ensure that the roller sleeve made by molding can be completely combined with the frame roller body during installation, when molding, after the polymer model is cooled and solidified, two positioning holes are drilled on the polymer model at radially symmetrical positions along the roller body. The positioning holes pass through the polymer model and the frame roller body. In this way, when the roller sleeve is installed later, the positioning holes on the roller sleeve can be aligned with the positioning holes on the frame roller body to achieve precise positioning of the roller sleeve.

[0040] Furthermore, since the frame roller is cylindrical, in order to avoid circumferential positioning errors, the apertures of the two positioning holes are different, such as Figure 4 As shown, the diameter φ1 of the first positioning hole is 20 mm, and the diameter φ2 of the second positioning hole opposite thereto is 10 mm.

[0041] S2. Sand mold making

[0042] Based on the polymer model obtained in S1, the macroscopic morphology of the roller sleeve is drawn, and then a sand mold of the roller sleeve with matching shape is made. The size of the sand mold is the same as that of the roller body of the frame roller.

[0043] To facilitate replacement, production, and installation, the polymer model is evenly cut along the length of the roller body into N segments. N sets of matching roller sleeve sand molds are then produced from each of these N segments, where N is an integer between 2 and 6. This reduces the mold footprint and allows for partial replacement and maintenance of the roller sleeve after installation based on actual wear, making it more convenient. The value of N can be adjusted based on the actual length of the roll stand in production. In our company's actual production, the polymer model is evenly cut along the length of the roller body into four segments. Four sets of sand molds are prepared for each segment, each with a length of L = 300 mm and a diameter of φ = 380 mm. The four sets of sand molds are individually numbered to identify the roller sleeve's position and avoid confusion. It is important to emphasize that if the polymer model is to be cut, the locating holes in S1 must be drilled in each segment to ensure that each cast roller sleeve segment precisely matches the roll stand.

[0044] Furthermore, in order to ensure the subsequent installation positioning, according to the connection sequence of the N-segment polymer model, dovetail grooves and dovetails that fit together are set in the corresponding sand mold. The roller sleeve is locked by the dovetail grooves and dovetails and connected into one piece; the end of the dovetail is 10 mm long and the R angle is 45°.

[0045] The corners of the sand mold are rounded, so that after the manufactured roller sleeve is spliced ​​and locked, adjacent rounded edges form a weld.

[0046] S3. Roller sleeve production

[0047] The molten steel is poured into the sand mold to form the roll, cooled naturally to room temperature, and then the roll sleeve is obtained by disassembling the mold;

[0048] The casting molten steel is high nickel chromium molybdenum molten steel, and its composition specifically includes: W C =3.35%~3.45%, W Mn =0.70%~0.90%, W Si =0.85%~1.05%, W Cr =1.75%~1.95%, W Mo =0.2%~0.40%, W Ni =3.95%~4.15%, the rest is Fe and inevitable impurities. High nickel chromium molybdenum molten steel has good wear resistance and impact resistance, which can effectively improve the service life of the stand roller.

[0049] S4. Heat treatment

[0050] The roller sleeve is taken out and placed in a resistance furnace for annealing. The first annealing temperature is controlled at 390℃±10℃, kept at this temperature for 18 hours, cooled to 230℃ with the furnace and then air-cooled. The second annealing temperature is controlled at 510℃±10℃, kept at this temperature for 18 hours, cooled to 150℃ with the furnace and then air-cooled to eliminate the internal stress during the cooling process, ensure that the roller sleeve has no crack defects, obtain a uniform graphite + bainite + carbide structure, control its hardness at 70HSD~80HSD, and obtain good thermal crack resistance and wear resistance.

[0051] S5. Grinding

[0052] The outer surface of each roller sleeve is ground by 0.5mm to 1.0mm to a surface roughness of Ra ≤ 0.8 to ensure the surface quality of the roller sleeve. Each roller sleeve is then cut into two semicircular shapes, with the cut surface designed to be a V-shaped surface from the outside to the inside, and the beveled surface is chamfered at 45°; the curvature of the roller sleeve is maintained as much as possible during cutting.

[0053] When cutting the roller sleeve, the cutting line is preferably perpendicular to the line connecting the centers of the two positioning holes, such as Figure 4 shown.

[0054] S6. Installation and welding

[0055] Based on the matching relationship between the internal shape of the roller sleeve and the worn position of the frame roller, the corresponding sleeve of the semicircular roller sleeve is placed on the worn position of the frame roller and positioned through the positioning hole; the gap is repaired from the inside to the outside by argon arc welding until it is equal to the outer diameter and no defects are found in the color flaw detection;

[0056] N sections of roller sleeves are installed in sequence, and two adjacent roller sleeves are fixed by the dovetail groove and the dovetail, and then circumferentially welded to obtain a complete frame roller.

[0057] The roller sleeves are welded by spot welding, which is convenient for later cutting and removal. After spot welding, there is a certain gap between the welds of the roller sleeves, which does not affect the function of the frame rollers.

[0058] In actual production, multiple roller sleeves can be cast simultaneously, heat treated, and ground before being stored for future use. If, after a period of use, the repaired roller sleeve no longer meets the required dimensions for the stand roller, the sleeve on the stand roller surface can simply be cut, and the spare sleeve installed and welded for continued use, making the replacement process simpler and more convenient. There is no need to cut and install the fastening bolts 2 at each end of the stand roller 4, and no need to remove and install the bearing box 1, bearing seat 3, and stand roller 4. This effectively reduces maintenance time and allows for faster and more efficient repairs of the stand roller 4, creating favorable conditions for efficient rolling on the rolling line.

[0059] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for repairing a hot rolling mill stand roller, characterized in that The steps include: S1. Take shape The thermoplastic polymer material is stuck on the surface of the worn frame roller, and the worn frame roller body is demolded online so that the inside of the polymer model fully fits the defective part and the outer diameter of the polymer model is consistent with the outer diameter of the new roller of the frame roller; after the polymer model is completed, it is locked to obtain the macroscopic shape of the worn part; After the polymer model is cooled and solidified, two positioning holes are drilled on the polymer model at radially symmetrical positions along the roller body. The positioning holes pass through the polymer model and the roller body of the frame roller, and the apertures of the two positioning holes are different. S2. Sand mold making Based on the polymer model obtained in S1, the macroscopic morphology of the roller sleeve is drawn, and then a sand mold of the roller sleeve with matching shape is made. The size of the sand mold is the same as that of the roller body of the frame roller. In order to facilitate replacement, production and installation, the polymer model is evenly cut into N sections along the length of the roller body, and N groups of sand molds are prepared according to the N sections of the polymer model, where N is any integer from 2 to 6; S3. Roller sleeve production The molten steel is poured into a sand mold and naturally cooled to room temperature to obtain a roller sleeve; S4. Heat treatment The roller sleeve is taken out and sent to a resistance furnace for annealing to obtain a uniform graphite + bainite + carbide structure, and the roller sleeve hardness is controlled at 70HSD ~ 80HSD; S5. Grinding Grind the outer surface of each roller sleeve by 0.5mm to 1.0mm to make the surface roughness Ra≤0.8; then cut each roller sleeve into two semicircular shapes, with the cut surface designed to be a V-shaped surface from the outside to the inside, and the beveled surface having a 45° chamfer; S6. Installation and welding Through the matching relationship between the internal shape of the roller sleeve and the worn position of the frame roller, the corresponding sleeve of the complete set of semicircular roller sleeves is placed on the worn part of the frame roller and positioned through the positioning hole; the gap is repaired from the inside to the outside by argon arc welding until it is equal to the outer diameter and no defects are found in the color flaw detection, and the repair of the frame roller is completed.

2. A method for repairing a stand roller of a hot rolling mill according to claim 1, characterized in that: In the step S1, the thermoplastic polymer material used is acrylonitrile-butadiene-styrene copolymer.

3. The method for repairing a stand roller of a hot rolling mill according to claim 1, wherein: In order to ensure the subsequent installation positioning, dovetail grooves and dovetails that fit each other are set in the corresponding sand mold according to the connection sequence of the N-segment polymer model.

4. The method for repairing a stand roller of a hot rolling mill according to claim 1, wherein: In step S3, the cast molten steel is high nickel chromium molybdenum molten steel, and its components specifically include: W C =3.35%~3.45%, W Mn =0.70%~0.90%, W Si =0.85%~1.05%, W Cr =1.75%~1.95%, W Mo =0.2%~0.40%, W Ni =3.95%~4.15%, the rest is Fe and unavoidable impurities.

5. The method for repairing a stand roller of a hot rolling mill according to claim 1, wherein: The specific steps of annealing in step S4 are: the first annealing temperature is controlled at 390°C ± 10°C, kept at this temperature for 18 hours, cooled to 230°C with the furnace, and then air-cooled; the second annealing temperature is controlled at 510°C ± 10°C, kept at this temperature for 18 hours, cooled to 150°C with the furnace, and then air-cooled.

6. The method for repairing a stand roller of a hot rolling mill according to claim 3, wherein: In step S6, when N sections of roller sleeves are used for connection, the connection between the roller sleeves is completed while the positioning holes are positioned. After the two adjacent roller sleeves are fixed by the matching connection of the dovetail groove and the dovetail, they are circumferentially welded to connect the four sections of roller sleeves into one. The welding between adjacent roller sleeves is done by spot welding.

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