Extra-thick-wall square and rectangular pipe production line and production process thereof

Abstract

The invention relates to an extra-thick-wall square and rectangular pipe production line and a production process thereof, and belongs to the field of hot-rolled steel pipe rolling equipment in the ferrous metallurgical industry. Comprising a steel pipe feeding rack used for feeding pierced billets; the heating device is used for heating the pierced billet, so that the pierced billet can deform; the diameter reducing unit is used for performing diameter reducing rolling on the heated pierced billet to change the diameter of the pierced billet and the thickness of the wall of the pierced billet; and the square and rectangular pipe forming rack is used for carrying out forming rolling on the pierced billets subjected to diameter reduction, so that the pierced billets form the square and rectangular pipes. An existing hot-rolling seamless steel pipe production line or an existing seamless steel pipe is utilized, a round-to-square forming rack is additionally arranged behind a sizing and reducing mill, and a round-section steel pipe is gradually changed into an arc-side-length-section steel pipe and finally changed into a square-rectangular-section steel pipe. The method solves the problems that an existing hot rolling process is difficult to mold the extra-thick-wall square and rectangular pipe, and the corner arc radius cannot reach the standard, and the seamless steel pipe can still be produced when the production line does not produce the square and rectangular pipe, so that the production cost of the extra-thick-wall square and rectangular pipe is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the field of hot-rolled steel pipe rolling equipment in the iron and steel metallurgy industry, and relates to a special thick-walled square and rectangular pipe production line and its production process. Background Art

[0002] At present, the forming methods of special thick-walled square and rectangular pipes generally include the following several types, namely welding, cold bending, casting, and hot rolling. Products in square and rectangular pipes that satisfy side length / wall thickness < 10 can be called special thick-walled square and rectangular pipes.

[0003] However, when producing thick-walled square pipes, the cold bending forming process has a large processing load, and the work hardening at the corners of the steel pipe is very serious, which is easy to produce defects and the product qualification rate is relatively low; although the casting forming ensures the product size accuracy, its toughness is relatively low and the production cost is relatively high; due to the existence of welds in the welded formed products, the tissue properties of the products are uneven, which affects both their quality and appearance.

[0004] Hot rolling is a more suitable forming method for producing thick-walled square and rectangular pipes. However, the special thick-walled square and rectangular pipes produced by hot rolling at present have the following several disadvantages. First, the arc radius of the four corners is either too large or each corner presents three arc surfaces. The main reason is that the wall thickness of the square and rectangular pipe is too thick. Directly rolling the tube blank into a square and rectangular pipe will cause difficulties in the forming of metal at the corners; second, the directly formed product size cannot meet the actual high-demand usage scenarios; third, the cost of building a separate square and rectangular pipe production line is too high.

[0005] Therefore, it is of great significance to invent a forming process for producing special thick-walled square and rectangular pipes with a specified arc radius. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a special thick-walled square and rectangular pipe production line and its production process, which solves the problems that it is difficult to form special thick-walled square and rectangular pipes by the existing hot rolling process and the arc radius of the corners cannot meet the standard. Moreover, when the production line does not produce square and rectangular pipes, it can still produce seamless steel pipes, which greatly reduces the production cost of special thick-walled square and rectangular pipes and promotes the development of special thick-walled square and rectangular pipe forming technology.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A special thick-walled square and rectangular pipe production line, comprising:

[0009] A heating device: heating the rough pipe so that the rough pipe can deform;

[0010] A reducing mill group: connected to the rear side of the heating device, and performing reducing rolling on the heated rough pipe to change the diameter and wall thickness of the rough pipe;

[0011] Square and rectangular pipe forming stand: Connected to the rear side of the said pipe reducing unit, it rolls the reduced semi-finished pipe into shape to form a square and rectangular pipe.

[0012] The said square and rectangular pipe forming stand includes multiple groups of arc-shaped pass stands arranged in sequence, an enclosed pass stand, and a forming pass stand.

[0013] The rolling pass of the arc-shaped pass stand has arcs on all four sides, and the arc radius of the rolling pass gradually increases, so that the semi-finished pipe gradually changes from round to square.

[0014] The rolling pass of the enclosed pass stand is square, and the upper and lower sides of the rolling pass are composed of a section of first straight line connected to two arcs and two sections of second straight lines. The first straight line corresponds to one side surface of the square and rectangular pipe, and the two arcs correspond to the pipe corner parts of the square and rectangular pipe; the left and right sides of the rolling pass are straight lines, which act together with the second straight lines on the two adjacent surfaces of this side surface of the square and rectangular pipe.

[0015] The rolling pass of the forming pass stand is square, so that the side length of the square and rectangular pipe is regularized to the set value.

[0016] Optionally, for the extra-thick wall square and rectangular pipe production line according to the present invention, it further includes a steel pipe loading bench, which is arranged in front of the heating device and is used to automatically load the semi-finished pipe onto the heating device.

[0017] Optionally, for the extra-thick wall square and rectangular pipe production line according to the present invention, it further includes a semi-finished pipe production line, and the semi-finished pipe production line includes:

[0018] Annular heating furnace: Used for heating the tube blank and heating the cut tube blank to 1200°C to 1300°C.

[0019] Piercing mill: Arranged at the rear side of the annular heating furnace, used to remove the oxide layer on the surface of the tube blank and then pierce and roll it into a semi-finished pipe.

[0020] Blowing and brushing station: Arranged at the rear side of the piercing mill, spraying nitrogen and borax into the semi-finished pipe to remove the oxide layer on the inner surface of the semi-finished pipe.

[0021] High-pressure water descaling device before rolling: Arranged at the rear side of the blowing and brushing station, performing high-pressure water descaling on the semi-finished pipe.

[0022] Tube rolling mill: Arranged at the rear side of the high-pressure water descaling device before rolling, and the semi-finished pipe and the mandrel enter the tube rolling mill together to be rolled into a semi-finished pipe.

[0023] Tube stripping machine: Arranged at the rear side of the tube rolling mill and connected to the heating device, used to strip the semi-finished pipe from the mandrel and directly transport it to the heating device for reheating treatment.

[0024] Optionally, in the extra-thick wall square and rectangular pipe production line according to the present invention, arc segments are used for transition at the roll gaps of the enclosed pass stands.

[0025] Optionally, in the extra-thick wall square and rectangular pipe production line according to the present invention, the included angle between the second straight line and the center line of the rolling pass of the enclosed pass stand is 8° to 12°.

[0026] Optionally, in the extra-thick wall square and rectangular pipe production line according to the present invention, the diameter reduction rate of the enclosed pass stand is 2.4% to 2.6%.

[0027] Optionally, in the extra-thick wall square and rectangular pipe production line according to the present invention, there are three or four groups of the arc pass stands.

[0028] Optionally, in the extra-thick wall square and rectangular pipe production line according to the present invention, the arc radius of the first group of the arc pass stands is between two and three times the radius of the rough pipe, and the maximum value of the arc radius of the arc pass stand is less than 2500 mm.

[0029] Optionally, in the extra-thick wall square and rectangular pipe production line according to the present invention, the diameter reduction rate of the forming pass stand is less than 1%.

[0030] In addition, the present invention also provides an extra-thick wall square and rectangular pipe production process, which uses the extra-thick wall square and rectangular pipe production line described in the above embodiments, and includes the following steps:

[0031] S1. Loading: The rough pipe is loaded through the steel pipe loading bench.

[0032] S2. Heating: The rough pipe is heated and descaled with high-pressure water.

[0033] S3. Sizing rolling: The heated rough pipe is sent into the sizing and reducing mill for rolling to change the diameter and wall thickness of the rough pipe.

[0034] S4. Forming rolling: The sized rough pipe is sent into the square and rectangular pipe forming mill for rolling to form the rough pipe into a square and rectangular pipe.

[0035] S5. Cooling: The formed square and rectangular pipe is subjected to controlled cooling.

[0036] The beneficial effects of the present invention are as follows:

[0037] Aiming at the problems of difficult production, unqualified dimensions and high production costs of hot-rolled extra-thick-walled square and rectangular pipes at present, the present invention proposes an extra-thick-walled square and rectangular pipe production line and its production process. The main technical solution is to use an existing hot-rolled seamless steel pipe production line or an existing seamless steel pipe, and add a square and rectangular pipe forming rack after the sizing mill, so that the round-section steel pipe gradually becomes an arc-side-length-section steel pipe, and finally becomes a square and rectangular-section steel pipe. It should be noted that a three-roll or four-roll type is used for the sizing mill, and a four-roll type is used for the square and rectangular pipe forming rack, and the pass of the penultimate rack needs to be an enclosed pass rack, so that the corner arc radius can be fully formed. This method solves the problems of difficult forming of extra-thick-walled square and rectangular pipes by the existing hot-rolled process and the inability to meet the standard of the corner arc radius. Moreover, the production line can still produce seamless steel pipes when not producing square and rectangular pipes, which greatly reduces the production cost of extra-thick-walled square and rectangular pipes and promotes the development of the forming technology of extra-thick-walled square and rectangular pipes.

[0038] Other advantages, objects and features of the present invention will be set forth in part in the following description, and in part will be obvious to those skilled in the art from a study of the following, or may be learned from the practice of the present invention. The objects and other advantages of the present invention may be realized and obtained by the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, wherein:

[0040] Figure 1 Schematic diagram of the extra-thick-walled square and rectangular pipe production line provided by the present invention;

[0041] Figure 2 Schematic diagram of the rolling pass of the square and rectangular pipe forming rack in the extra-thick-walled square and rectangular pipe production line provided by the present invention;

[0042] Figure 3 Schematic diagram of the pass of the enclosed pass rack provided by the present invention.

[0043] Reference numerals: 1 - billet; 2 - annular heating furnace; 3 - piercing mill; 4 - brushing station; 5 - high-pressure water descaling device before rolling; 6 - pipe rolling mill; 7 - pipe support machine; 8 - steel pipe loading table; 9 - heating device; 10 - high-pressure water descaling device before sizing; 11 - sizing unit; 12 - square and rectangular pipe forming rack; 13 - walking beam cooling bed; 14 - collection and sorting system;

[0044] 121 - first straight line; 122 - arc; 123 - second straight line. DETAILED DESCRIPTION OF THE INVENTION

[0045] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0046] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, rather than physical diagrams, and should not be construed as a limitation on the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which does not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0047] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, it is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and should not be construed as a limitation on the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0048] Embodiment 1:

[0049] Please refer to Figure 1 as shown, the present invention provides a production line for extra-thick-walled square and rectangular pipes, including:

[0050] Steel pipe loading bench 8: for loading the rough pipe.

[0051] Heating device 9: connected to the rear side of the steel pipe loading bench 8, heating the rough pipe so that the rough pipe can generate deformation.

[0052] Reducing mill unit 11: connected to the rear side of the heating device 9, performing reducing rolling on the heated rough pipe to change the diameter and wall thickness of the rough pipe.

[0053] Square and rectangular pipe forming rack 12: connected to the rear side of the reducing mill unit 11, performing forming rolling on the reduced rough pipe to form the rough pipe into a square and rectangular pipe.

[0054] The present invention performs rolling on the original seamless steel pipe, i.e., the raw pipe, from round to square. When selecting the size of the steel pipe at the entrance of the square and rectangular pipe forming stand 12, it should be determined according to the size of the product square and rectangular pipe. The circumferential compression coefficient of the steel pipe needs to be controlled between 1.06 and 1.14, so as to avoid the generation of green lines. Green lines refer to symmetrical or asymmetrical linear rolling marks on the outer surface of the steel pipe. The main reason for the generation of green lines lies in the rolling mills of the reducing mill 11 and the square and rectangular pipe forming stand 12. For example, factors such as the misalignment or severe wear of the sizing mill pass, the unreasonable design of the sizing mill roll pass, too small chamfer at the edge of the roll, and clearance, or too low temperature of the steel pipe itself will also cause the generation of green lines.

[0055] Therefore, in the production process of the present invention, first, the raw pipe needs to be heated so that the raw pipe can produce sufficient deformation under the action of the reducing mill 11 and the square and rectangular pipe forming stand 12, thereby changing the shape of the raw pipe into a square and rectangular pipe. Before reducing the diameter, it is also necessary to perform high-pressure water descaling on the raw pipe through the high-pressure water descaling device 10 before reducing the diameter. It should be noted that in the present invention, a three-roll or four-roll type is used for the sizing and reducing mill, and a four-roll type is used for the square and rectangular pipe forming stand 12, and the pass of the penultimate group of the square and rectangular pipe forming stand 12 needs to be an enclosed pass, so that the corner arc radius can be fully formed. This method solves the problem that it is difficult to form extra-thick-walled square and rectangular pipes in the existing hot rolling process and the corner arc radius cannot meet the standard. Moreover, when the production line does not produce square and rectangular pipes, it can still produce seamless steel pipes, which greatly reduces the production cost of extra-thick-walled square and rectangular pipes and promotes the development of the forming technology of extra-thick-walled square and rectangular pipes.

[0056] Please refer to Figure 2 As shown, it is a square and rectangular pipe forming stand, including a plurality of arc-shaped pass stands, an enclosed pass stand, and a forming pass stand arranged in sequence;

[0057] The four sides of the rolling pass of the arc-shaped pass stand are all arc-shaped, and the arc radius of the rolling pass gradually increases, so that the raw pipe gradually changes from round to square;

[0058] The rolling pass of the enclosed pass stand is square, and the upper and lower sides of the rolling pass are composed of a first straight line 121 connecting two arcs 122 and two second straight lines 123. The first straight line 121 corresponds to one side of the square and rectangular pipe, and the two arcs 122 correspond to the pipe corners of the square and rectangular pipe; the left and right sides of the rolling pass are straight lines, which act on the two adjacent faces of this side of the square and rectangular pipe together with the second straight line 123;

[0059] The rolling pass of the forming pass stand is square, so that the side length of the square and rectangular pipe is regularized to the set value.

[0060] In the implementation process of the present invention, a plurality of sets of arc-shaped pass stands are arranged to gradually roll the raw pipe from round to square, so as to ensure that the forming process of the square and rectangular pipe is smoother. Since the larger the arc radius of the rolling pass of the arc-shaped pass stand, the closer the corresponding arc length is to a straight line, by gradually increasing the arc radius, each rolling of the raw pipe by the roll will make the outer surface of the raw pipe gradually fit the pass of the arc-shaped pass stand, thereby gradually changing the outer surface of the raw pipe from round to square.

[0061] In addition, according to Figure 3 As shown, the upper and lower sides of the rolling pass of the surrounding pass stand are composed of a first straight line 121, two arcs 122 and two second straight lines 123 to form an inward concave U-shaped groove structure. After the last rolling of the above-mentioned arc-shaped pass stand, the raw pipe basically forms a square and rectangular pipe structure, but there are still certain arc surfaces on the four sides of the square and rectangular pipe, and the pipe corner formed by the adjacent two sides is also greater than 90°. The rolling pass of the surrounding pass stand of the present invention embeds the square and rectangular pipe into the inward concave U-shaped groove. The radii of the two arcs are the standard values of the corner radii of the formed square and rectangular pipe. During forming, through the rolling on the left and right sides of the surrounding pass stand, the metal of the square and rectangular pipe will fill the pass, and the corner radius of the pipe corner will reach the set value. The end of the two arcs 122 is connected to a second straight line 123, which can effectively avoid the generation of green lines.

[0062] The rolling pass of the forming pass stand is square. After the square and rectangular pipe is basically formed by the surrounding pass stand, the pass of the forming pass stand is set exactly according to the size of the product square and rectangular pipe, so as to roll the four sides of the square and rectangular pipe smoothly, and make the side length of the square and rectangular pipe regular to the set value.

[0063] Furthermore, after the last rolling of the arc-shaped pass stand, the raw pipe basically forms a square and rectangular pipe structure, but there are still certain arc surfaces on the four sides of the square and rectangular pipe, and the pipe corner formed by the adjacent two sides is also greater than 90°. Therefore, in order to prevent the preliminarily formed square and rectangular pipe from not being able to be embedded into the rolling pass of the surrounding pass stand, the included angle between the second straight line 123 and the center line of the rolling pass of the surrounding pass stand is 8° - 12°, which means that the two sides of the rolling pass of the surrounding pass stand need to expand outward by 8° - 12°, and the angles corresponding to the two arcs 122 are less than 90°.

[0064] Still further, as Figure 3As shown in the figure, arc segments are used for transition at the roll gaps of the enclosed pass stands. That is to say, there is a certain space at the roll gaps of the enclosed pass stands. During the process of filling the pass with the metal of the square and rectangular pipe, the excess metal can be squeezed towards the roll gaps of the enclosed pass stands, and the roll gaps are located on two sides of the square and rectangular pipe, which can effectively avoid affecting the dimensions of the four pipe corners of the square and rectangular pipe. At the same time, it can also avoid stress concentration on the rolls of the enclosed pass stands and prevent the appearance of green lines on the surface of the square and rectangular pipe at the roll gaps.

[0065] Further, there are three or four groups of the arc-shaped pass stands. During implementation, in the present invention, the initial rolling of the rough pipe from round to square is carried out by three or four groups of arc-shaped pass stands to ensure that the forming process of the square and rectangular pipe is smoother.

[0066] Still further, the arc radius of the first group of arc-shaped pass stands is between two and three times the radius of the rough pipe, and its arc radius is mainly determined according to the diameter of the steel pipe before the formation of the square and rectangular pipe, generally set to 3 times; and the maximum value of the arc radius of the arc-shaped pass stands is less than 2500 mm to avoid the square and rectangular pipe from having a collapsed waist and resulting in unqualified dimensions.

[0067] Still further, the reduction ratio of the square and rectangular pipe forming stands 12 including the arc-shaped pass stands should be gradually decreased. The reduction ratio of the enclosed pass stands is 2.5%. If it is too small, it is not conducive to corner forming. If it is too large, green lines are likely to appear. The reduction ratio of the forming pass stands should be less than 1%.

[0068] Further, when setting the speed of the reducing mill 11, no-tension or micro-tension is used for reducing rolling. The reducing mill 11 is used to carry out reducing rolling on the heated rough pipe so that the diameter and wall thickness of the rough pipe reach the preset values.

[0069] In addition, the present invention also provides a production process for extra-thick-walled square and rectangular pipes, using the production line for extra-thick-walled square and rectangular pipes in the above embodiment, and including the following steps:

[0070] S1. Loading: The rough pipe is loaded through the steel pipe loading bench 8.

[0071] S2. Heating: The rough pipe is heated and descaled with high-pressure water.

[0072] S3. Reducing rolling: The heated rough pipe is sent into the sizing and reducing mill 11 for rolling to change the diameter and wall thickness of the rough pipe.

[0073] S4. Forming rolling: The reduced rough pipe is sent into the square and rectangular pipe forming stands 12 for rolling to form the square and rectangular pipe; when setting the speed, no-tension or micro-tension should be used for rolling.

[0074] S5. Cooling: The formed square and rectangular pipes are controlled and cooled by the walking beam cooling bed 13, and the formed square and rectangular pipes are collected and sorted by the collecting and sorting system 14.

[0075] Embodiment 2:

[0076] The above is the process method directly using the existing seamless steel pipes in the present invention. In the prior art, the present invention can also directly use the existing hot-rolled seamless steel pipe production line to produce extra-thick-walled square and rectangular pipes.

[0077] Refer to again Figure 1 As shown, there is a production line for extra-thick-walled square and rectangular pipes, including a hot-rolled seamless steel pipe production line. The hot-rolled seamless steel pipe production line includes a pipe blank 1, a rotary hearth furnace 2, a piercing mill 3, a blowing and brushing station 4, a high-pressure water descaling device 5 before rolling, a pipe rolling mill 6, and a pipe stripping machine 7 connected in sequence. In the present invention, the production line for extra-thick-walled square and rectangular pipes is directly arranged in the subsequent process of the pipe stripping machine, and the rough pipe produced by the pipe stripping machine is directly loaded through the steel pipe loading table 8.

[0078] If directly using the steel pipes of the hot-rolled seamless steel pipe production line, the production process of the extra-thick-walled square and rectangular pipes includes the following steps:

[0079] S01. Heating: The cut pipe blank 1 is heated to 1200 °C;

[0080] S02. Piercing: Remove the oxide layer on the surface of the pipe blank 1, and then pierce and roll it into a rough pipe;

[0081] S03. Nitrogen and borax injection inside the rough pipe: Inject nitrogen and borax into the rough pipe to remove the oxide layer on the inner surface of the rough pipe, improve the lubrication effect of the inner surface of the rough pipe, and prevent secondary oxidation on the inner surface of the rough pipe;

[0082] S04. Rolling: Insert the mandrel into the rough pipe. After high-pressure water descaling, the rough pipe and the mandrel enter the pipe rolling mill 6 together and are rolled into a rough pipe;

[0083] S05. Pipe stripping: The rough pipe is stripped of the pipe, and the mandrel is separated;

[0084] S06. Loading: The rough pipe is loaded through the steel pipe loading table 8.

[0085] S07. Heating: Heat the rough pipe and perform high-pressure water descaling.

[0086] S08. Sizing rolling: Feed the heated rough pipe into the sizing and reducing mill 11 for rolling to change the diameter and wall thickness of the rough pipe.

[0087] S09. Forming rolling: Feed the sized rough pipe into the square and rectangular pipe forming stand 12 for rolling to form the rough pipe into a square and rectangular pipe; when setting the speed, the rolling should be carried out without tension or with micro-tension.

[0088] S10. Cooling: The formed square and rectangular tubes are controlled and cooled by the walking beam cooling bed 13, and the formed square and rectangular tubes are collected and sorted by the collection and sorting system 14.

[0089] Compared with the first embodiment, the second embodiment provided by the present invention utilizes an existing hot-rolled seamless steel pipe production line, and several round-to-square forming stands are added after the sizing mill, so that the circular-section steel pipe gradually becomes a steel pipe with an arc-shaped side length section, and finally becomes a square and rectangular section steel pipe. This method solves the problems that it is difficult to form extra-thick-walled square and rectangular tubes in the existing hot-rolling process and the corner arc radius cannot meet the standard. Moreover, the production line can still produce seamless steel pipes when it does not produce square and rectangular tubes, which greatly reduces the production cost of extra-thick-walled square and rectangular tubes and promotes the development of the forming technology of extra-thick-walled square and rectangular tubes.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. Super-thick-walled square and rectangular pipe production line, characterized in that: Comprising: Heating device: heating the raw pipe so that the raw pipe can be deformed; Sizing reduction unit: connected to the rear side of the heating device, sizing and rolling the heated raw pipe to change the diameter and wall thickness of the raw pipe; Square and rectangular pipe forming rack: connected to the rear side of the sizing reduction unit, forming and rolling the sized raw pipe to form a square and rectangular pipe; The square and rectangular pipe forming rack includes a plurality of groups of arc-shaped pass racks arranged in sequence, an enclosed pass rack, and a forming pass rack; The rolling pass of the arc-shaped pass rack has arcs on all four sides, and the arc radius of the rolling pass gradually increases so that the raw pipe gradually changes from round to square; The rolling pass of the enclosed pass rack is square, and the upper and lower sides of the rolling pass are composed of a first straight line, two arcs, and two second straight lines. The first straight line corresponds to one side surface of the square and rectangular pipe, and the two arcs correspond to the pipe corners of the square and rectangular pipe; the left and right sides of the rolling pass are straight lines, which act together with the second straight line on the two adjacent surfaces of this side surface of the square and rectangular pipe; The rolling pass of the forming pass rack is square, so that the side length of the square and rectangular pipe is regularized to a set value.

2. The extra-thick wall square and rectangular pipe production line according to claim 1, characterized in that: It further includes a steel pipe loading bench, which is arranged on the front side of the heating device and is used to automatically load the raw pipe into the heating device.

3. The extra-thick wall square and rectangular pipe production line according to claim 1, characterized in that: It further includes a raw pipe production line, and the raw pipe production line includes: Ring heating furnace: used for heating the tube blank and heating the cut tube blank to 1200°C to 1300°C; Piercing mill: arranged on the rear side of the ring heating furnace, used to remove the oxide layer on the surface of the tube blank and then pierce and roll it into a seamless tube; Blowing and brushing station: arranged on the rear side of the piercing mill, spraying nitrogen and borax into the seamless tube to remove the oxide layer on the inner surface of the seamless tube; High-pressure water descaling device before rolling: arranged on the rear side of the blowing and brushing station, performing high-pressure water descaling on the seamless tube; Tube rolling mill: arranged on the rear side of the high-pressure water descaling device before rolling, feeding the seamless tube and the mandrel into the tube rolling mill to roll into a raw pipe; Tube stripping machine: arranged on the rear side of the tube rolling mill and connected to the heating device, separating the raw pipe from the mandrel and directly transporting it to the heating device for reheating treatment.

4. The extra-thick wall square and rectangular pipe production line according to claim 1, wherein: The roll gap of the enclosed pass rack all adopts arc segment transition.

5. The thick-walled square and rectangular pipe production line according to claim 4, characterized in that: The included angle between the second straight line and the center line of the rolling pass of the enclosed pass rack is 8° to 12°.

6. The extra-thick wall square and rectangular pipe production line according to claim 1, characterized in that: The reduction rate of the enclosed pass rack is 2.4% to 2.6%.

7. The thick-walled square and rectangular pipe production line according to claim 1, characterized in that: There are three or four groups of the arc-shaped pass racks.

8. The extra-thick wall square and rectangular pipe production line according to claim 7, characterized in that: The arc radius of the rolling pass of the first group of the arc-shaped pass racks is between two and three times the radius of the raw pipe, and the maximum value of the arc radius of the rolling pass of the arc-shaped pass rack is less than 2500 mm.

9. The thick-wall square and rectangular pipe production line according to claim 1, wherein: The reduction rate of the forming pass rack is less than 1%.

10. The production process of extra-thick-walled square and rectangular tubes is characterized in that: Using the thick-walled square and rectangular pipe production line according to claim 8 or 9, and comprising the following steps: S1. Loading: The raw pipe is loaded through the steel pipe loading bench; S2. Heating: Heating the raw pipe and performing high-pressure water descaling; S3. Sizing and rolling: Feeding the heated raw pipe into the sizing and reduction unit for rolling to change the diameter and wall thickness of the raw pipe; S4. Forming and rolling: Feeding the sized raw pipe into the square and rectangular pipe forming unit for rolling to form a square and rectangular pipe; S5. Cooling: Controlling the cooling of the formed square and rectangular pipe.

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