Cold-rolled seamless tube with unequal wall thickness and manufacturing method thereof

Abstract

The invention relates to the technical field of pipe manufacturing, and particularly discloses an unequal-wall-thickness cold-rolled seamless pipe and a manufacturing method thereof.The manufacturing method of the unequal-wall-thickness cold-rolled seamless pipe comprises the steps that S100, a seamless round pipe is selected as a pipe blank; s200, wall thickness partition design is conducted in the circumferential direction and the axial direction of the pipe blank, and the specific positions and wall thickness values of a thick-wall area and a thin-wall area are determined; and S300, the pipe blank is loaded into a cold rolling mill, asymmetric cold rolling forming is adopted to enable the pipe blank to form an unequal-wall-thickness structure with two thin-wall areas and two thick-wall areas, the two thin-wall areas and the two thick-wall areas are sequentially connected in the circumferential direction, and the thin-wall areas and the thick-wall areas are alternately arranged. According to the process, through the preset wall thickness distribution design, a single seamless round pipe is directly formed, optimal configuration of materials is achieved, the thick-wall area is planned and formed in the area needing high strength through thickening, the thin-wall area is planned and formed in the non-key area through thinning, unification of light weight and high performance is achieved, and the flexibility of pipe body manufacturing and machining is improved.

Description

Technical Field

[0001] This invention relates to the field of pipe manufacturing technology, and in particular to a cold-rolled seamless pipe with unequal wall thickness and its manufacturing method. Background Technology

[0002] While the precision stainless steel pipe industry has achieved the capability to produce high-precision, uniform-wall-thickness cold-rolled pipes, there are still limitations in the proactive and controllable manufacturing of irregularly shaped pipes with varying wall thicknesses. The main production process remains at the "homogeneous deformation" stage, which struggles to meet the precise control requirements for complex cross-sections and non-uniform wall thicknesses. Especially for critical components requiring "structural-functional integration," the traditional manufacturing method of "homogeneous materials + subsequent connections (such as welding)" is largely relied upon. This approach not only increases the complexity of the production process but also introduces inherent reliability risks into the product. Specifically, in practical applications, if the pipe body needs to achieve a diversion function, ordinary uniform-wall-thickness round or square steel pipes are typically used, with holes drilled in the pipe wall and multiple outlets connected by welding. However, this structure has significant drawbacks: weak overall pressure-bearing capacity, and the weld seams are prone to fatigue cracking due to stress concentration, leading to leakage and other problems that seriously affect the product's service life and safety performance.

[0003] Therefore, there is an urgent need for a cold-rolled seamless tube with unequal wall thickness and its manufacturing method to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a cold-rolled seamless tube with unequal wall thickness and its manufacturing method, especially an integrated seamless square cold-rolled tube with unequal wall thickness for a server liquid cooling water distributor and its manufacturing method, which can realize flexible design of tube wall thickness and improve its structural stability and reliability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] On one hand, the present invention provides a cold-rolled seamless tube with unequal wall thickness. The cold-rolled seamless tube with unequal wall thickness has an unequal wall thickness structure, which includes two thin-walled regions and two thick-walled regions. The two thin-walled regions and the two thick-walled regions are connected sequentially along the circumference, and the thin-walled regions and the thick-walled regions are alternately arranged.

[0007] As a preferred technical solution for the above-mentioned cold-rolled seamless tube with unequal wall thickness, the wall thickness of the thick-walled region is T1, the wall thickness of the thin-walled region is T2, and T1 and T2 satisfy: 2≤T1 / T2≤9.

[0008] As a preferred technical solution for the above-mentioned cold-rolled seamless tube with unequal wall thickness, the wall thickness value T2 of the thin-walled region (102) is in the range of 6mm≥T2≥2mm.

[0009] On the other hand, the present invention also provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness, used to form a cold-rolled seamless tube with unequal wall thickness in any of the above-mentioned embodiments, the method for manufacturing the cold-rolled seamless tube with unequal wall thickness includes the following steps:

[0010] S100: Seamless round tubes are selected as tube blanks;

[0011] S200: The tube blank is divided into sections according to its circumference to determine the specific locations of the thick-walled and thin-walled sections, the range of wall thickness values ​​for the thick-walled sections, and the range of wall thickness values ​​for the thin-walled sections.

[0012] S300: The tube blank is loaded into a cold rolling mill and formed by asymmetric cold rolling to form a tube blank with unequal wall thickness, so that the wall thickness of the thick wall region is greater than the wall thickness of the thin wall region, and both the wall thickness of the thick wall region and the wall thickness of the thin wall region are within the designed wall thickness range.

[0013] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, in step S100, the wall thickness of the tube blank is 4mm~22mm.

[0014] Preferably, in step S100, the tube blank is a tube blank with equal wall thickness. As a preferred technical solution of the above-mentioned method for manufacturing cold-rolled seamless tubes with unequal wall thickness, in step S300, the tube blank is subjected to multiple passes of non-uniform rolling so that the tube blank has a preset unequal wall thickness distribution along its circumference.

[0015] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, in step S300, the number of rolling passes is 3 to 8.

[0016] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, in step S300, the rolling reduction rate of each pass is 2~30%.

[0017] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, in each rolling process, non-uniform plastic deformation is generated in different regions of the tube blank, so that the material of the tube blank flows directionally from the preset thin-walled region to the thick-walled region to gradually accumulate the wall thickness difference.

[0018] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, in step S300, the rolling includes a roughing stage, a transition stage and a finishing stage performed sequentially.

[0019] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, in step S300, during the rough rolling stage and the transition stage, the reduction ratio in the thin-walled region is greater than that in the thick-walled region.

[0020] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the total reduction rate of the thin-walled region in the rough rolling stage is 40~82%.

[0021] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the total reduction rate of the thin-walled region in the transition stage is 10~30%.

[0022] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tubes with unequal wall thickness, the total reduction rate of the thin-walled region in the finishing rolling stage is 2~15%.

[0023] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the reduction rate of each subsequent pass in the thin-walled region is smaller than that of the previous pass during the roughing stage, transition stage and finishing stage.

[0024] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the reduction rate of the thick-walled region in the rolling stage is 10~30%.

[0025] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the rolling speed of the roughing stage is 45 times / min to 50 times / min, and the single feed amount is 2mm to 3.5mm.

[0026] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the rolling speed in the transition stage is controlled at 45 times / min to 50 times / min, and the single feed amount is 2mm to 3.5mm.

[0027] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the rolling speed in the finishing rolling stage is controlled at 40 times / min to 45 times / min, and the single feed amount is 3.5mm to 5mm.

[0028] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the rolling pressure in the roughing stage is 1200KN~1800KN.

[0029] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the rolling pressure in the transition stage is 800KN~1200KN.

[0030] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tubes with unequal wall thickness, the rolling pressure in the finishing rolling stage is 400KN~800KN.

[0031] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tubes with unequal wall thickness, lubricating oil is used for cooling during the rolling process.

[0032] In a preferred embodiment of the manufacturing method for the aforementioned cold-rolled seamless tubes with unequal wall thicknesses, the temperature of the lubricating oil is 35~40℃.

[0033] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the tube blank is driven to rotate 90 degrees around its axis during the gap between adjacent rolling passes.

[0034] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the cold rolling mill is provided with a roll system, the roll system includes a pair of main forming rolls and an auxiliary mandrel, the auxiliary mandrel is used to insert and fit against the inner wall of the tube blank, the working surface of the main forming rolls is provided with an asymmetric cavity corresponding to the unequal wall thickness structure, the asymmetric cavity is located at the position corresponding to the thick wall area of ​​the tube blank, the gap distance between the asymmetric cavity and the tube blank is D1, the asymmetric cavity is located at the position corresponding to the thin wall area of ​​the tube blank, the gap between the asymmetric cavity and the tube blank is D2, wherein D1 and D2 satisfy: D1 is greater than D2.

[0035] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the range of D1 is 1.2~17mm.

[0036] In a preferred embodiment of the above-mentioned method for manufacturing cold-rolled seamless tubes with unequal wall thicknesses, the range of D2 is 1~3mm.

[0037] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the contour of the asymmetric cavity can gradually roll the tube blank into a square structure with transition rounded corners.

[0038] As a preferred technical solution for the manufacturing method of the above-mentioned cold-rolled seamless tube with unequal wall thickness, the outer contour of the cross-section of the square structure is a quadrilateral, and the two adjacent sides of the quadrilateral are connected by the transition fillet.

[0039] As a preferred embodiment of the above-mentioned method for manufacturing cold-rolled seamless tubes with unequal wall thicknesses, after step S300, the method for manufacturing cold-rolled seamless tubes with unequal wall thicknesses further includes:

[0040] S400: The unequal wall thickness structure obtained in step S300 is subjected to sizing rolling to control the outer dimensions and straightness of the unequal wall thickness structure, thereby forming an integral unequal wall thickness molded tube.

[0041] The beneficial effects of this invention are as follows:

[0042] This invention provides a cold-rolled seamless tube with unequal wall thickness and its manufacturing method. The manufacturing method includes the following steps: S100, selecting a seamless round tube as the tube blank; S200, designing wall thickness partitions in the circumferential and axial directions of the tube blank, determining the specific locations and wall thickness values ​​of the thick-walled and thin-walled regions; S300, loading the tube blank into a cold rolling mill, and using asymmetric cold rolling to form an unequal wall thickness structure with two thin-walled regions and two thick-walled regions. The two thin-walled regions and the two thick-walled regions are sequentially connected along the circumference, and the thin-walled and thick-walled regions are alternately arranged. With this configuration, the above process, through a preset wall thickness distribution design, directly forms from a single seamless round tube, achieving optimized material configuration. Thickening is planned to form thick-walled regions in areas requiring high strength (such as interfaces and pressure-bearing surfaces), while thinning is planned to form thin-walled regions in non-critical areas. This achieves a balance between lightweight and high performance, completing the customized wall thickness design. It can effectively improve the flexibility of tube manufacturing and processing, and enhance its structural stability and reliability.

[0043] Specifically, the mechanical properties of the cold-rolled seamless tubes with unequal wall thickness provided by the present invention can meet the requirements of the national standard GB / T14976-2025, and the yield reaches 100% under preferred conditions. Attached Figure Description

[0044] Figure 1 A schematic flowchart of the manufacturing method of cold-rolled seamless tubes with unequal wall thickness provided by the present invention;

[0045] Figure 2 Schematic diagram of the roll system and tube blank provided by the present invention Figure 1 ;

[0046] Figure 3 Schematic diagram of the roll system and tube blank provided by the present invention Figure 2 ;

[0047] Figure 4 Schematic diagram of the roll system and tube blank provided by the present invention Figure 3 ;

[0048] Figure 5 Schematic diagram of the roll system and tube blank provided by the present invention Figure 4 .

[0049] in:

[0050] 1. Tubular embryo; 101. Thick-walled region; 102. Thin-walled region;

[0051] 2. Main forming roll; 3. Auxiliary mandrel. Detailed Implementation

[0052] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0053] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions.

[0054] Unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and connections within two components or interactions between two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0055] Unless otherwise expressly specified and limited, "above" or "below" a second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of a second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" of a second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0056] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0057] like Figures 1 to 5As shown, this embodiment provides a cold-rolled seamless tube with unequal wall thickness. This unequal wall thickness cold-rolled seamless tube has an unequal wall thickness structure, comprising two thin-walled regions 102 and two thick-walled regions 101. The two thin-walled regions 102 and the two thick-walled regions 101 are sequentially connected circumferentially, and the thin-walled regions 102 and thick-walled regions 101 are alternately arranged. This arrangement differs from the design of existing uniform wall thickness tubes. It adopts a "two thin, two thick" structure, and through asymmetrical material distribution, extremely high strength and stiffness can be obtained in the thick-walled region 101 (the main stress area), while weight can be reduced to the maximum extent in the thin-walled region 102 (the non-main stress area), achieving an integrated structural and functional design.

[0058] Furthermore, the wall thickness of the thick-walled region 101 is T1, and the wall thickness of the thin-walled region 102 is T2, and T1 and T2 satisfy: 2 ≤ T1 / T2 ≤ 9, for example, it can be 2, 3, 4, 5, 6, 7, 8, or 9, etc. Further, in this embodiment, T1 / T2 = 5.1. Of course, in other embodiments, the specific value of T1 / T2 can be set according to actual needs, and no further restrictions are imposed here.

[0059] Furthermore, the wall thickness value T2 of the thin-walled region 102 is within the range of 6mm ≥ T2 ≥ 2mm, for example, it can be 6mm, 5.5mm, 5mm, 4.5mm, 4mm, 3.5mm, 3mm, 2.5mm, or 2mm, etc. By controlling the wall thickness value T2 of the thin-walled region 102 within the above range and controlling the ratio of T1 / T2, the range of wall thickness difference between the thin-walled region and the thick-walled region can be controlled, thereby ensuring the mechanical properties of the cold-rolled seamless tube while obtaining the desired unequal wall thickness.

[0060] This embodiment also provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness, used to form the cold-rolled seamless tube with unequal wall thickness in the above-mentioned scheme. The method for manufacturing the cold-rolled seamless tube with unequal wall thickness includes the following steps:

[0061] S100, a seamless round tube is selected as tube blank 1;

[0062] S200. The wall thickness of the tube blank 1 is divided into zones along the circumference of the tube blank 1 to determine the specific locations of the thick wall zone 101 and the thin wall zone 102, the range of wall thickness values ​​of the thick wall zone 101 and the range of wall thickness values ​​of the thin wall zone 102.

[0063] S300. The tube blank 1 is loaded into a cold rolling mill and asymmetric cold rolling is used to form a tube blank 1 with an unequal wall thickness structure, so that the wall thickness value of the thick wall region 101 is greater than the wall thickness value of the thin wall region 102, and the wall thickness values ​​of the thick wall region 101 and the thin wall region 102 are both within the designed wall thickness value range.

[0064] S400: The unequal wall thickness structure obtained in step S300 is subjected to sizing rolling to control the outer dimensions and straightness of the unequal wall thickness structure, thereby forming an integral unequal wall thickness shaped tube.

[0065] With this setup, the above process achieves optimized material configuration by directly forming a single seamless round tube through a preset wall thickness distribution design. Thick-walled areas 101 are planned to be thickened in areas requiring high strength (such as interfaces and pressure-bearing surfaces), while thin-walled areas 102 are planned to be thinned in non-critical areas. This achieves a balance between lightweight and high performance, enabling customized wall thickness design. It can effectively improve the flexibility of tube manufacturing and processing, and enhance its structural stability and reliability.

[0066] Further, in step S100, the wall thickness of the tube blank (1) is 4mm to 22mm, for example, it can be 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm or 22mm, etc.

[0067] Preferably, in step S100, the tube blank (1) is a tube blank with equal wall thickness.

[0068] Furthermore, in step S300, the tube blank 1 is subjected to multi-pass, non-uniform rolling so that the tube blank 1 has a preset unequal wall thickness distribution along its circumference. Multi-pass rolling can ensure that the uniform thickness tube blank is processed into a preset unequal thickness shape in a stable and controllable manner, while avoiding material defects (such as wrinkling, tearing, and excessive residual stress).

[0069] In this embodiment, the rolling passes range from 3 to 4, which is an efficient choice that ensures rapid forming, reduces equipment costs, energy consumption, and production time, thereby increasing profits and improving production yield. Of course, in other embodiments, the range of rolling passes can be adaptively extended to 3-8 passes, for example, 3, 4, 5, 6, 7, or 8 passes.

[0070] As a preferred technical solution for the manufacturing method of the aforementioned cold-rolled seamless tube with unequal wall thickness, in step S300, the rolling reduction rate for each pass is 2-30%, for example, it can be 2%, 3%, 4%, 5%, 6%, 10%, 15%, 20%, 25%, or 30%. Controlling the rolling reduction rate within the above range can further improve the production yield.

[0071] Furthermore, in step S300, the rolling process includes a roughing stage, a transition stage, and a finishing stage performed sequentially.

[0072] The overall asymmetric cold rolling process is based on a pass-by-pass optimization strategy, specifically divided into three stages: roughing, transition, and finishing. In the roughing stage, the metal material is in a softened state after annealing, exhibiting good plasticity and capable of withstanding significant deformation. A larger rolling pressure can be used to quickly establish the basic profile of the wall thickness difference. In the transition stage, it is necessary to begin eliminating the uneven internal stress generated by roughing and precisely control the dimensions, gradually reducing the rolling pressure to accurately adjust the wall thickness distribution, resulting in a smooth and natural thickness transition zone. The finishing stage requires fine-tuning of the thick-walled region 101 and finishing of the thin-walled region 102 to achieve a good surface finish. In each stage, the rolling pressure in the thin-walled region 102 is less than that in the thick-walled region 101, and the rolling pressure can be adaptively set according to the difference between the actual target wall thickness and the wall thickness of the tube blank 1. For example, the corresponding rolling pressure can be 3.5mm-6.5mm to balance forming quality and efficiency.

[0073] In step S300, the rolling speeds of the three stages—roughing, transition, and finishing—can be precisely controlled during the rolling process. Specifically, the rolling speeds of the roughing and transition stages are greater than those of the finishing stage, so as to achieve rapid large deformation and balance efficiency and uniformity in the roughing and transition stages. In the finishing stage, the rolling speed is reduced to improve the quality of the rolled product at a lower speed, thereby ensuring stable rolling and rolling accuracy.

[0074] Furthermore, in step S300, during the roughing and transition stages, the reduction rate in the thin-walled region 102 is greater than that in the thick-walled region 101. By ensuring that the reduction rate in the thin-walled region 102 is greater than that in the thick-walled region 101, the thickness difference between the thin-walled and thick-walled regions can be gradually accumulated during the rolling process, thereby achieving the manufacturing of seamless tubes with unequal thicknesses.

[0075] Furthermore, the total reduction rate of the thin-walled region 102 in the roughing stage is 40-82%, for example, it can be 40%, 45%, 50%, 54%, 59%, 64%, 68%, 73%, 78%, or 82%. The present invention preferably achieves a larger thickness difference in the roughing stage; therefore, controlling the total reduction rate of the thin-walled region within the above range can improve the yield.

[0076] Furthermore, the total downward pressure rate of the thin-walled region 102 in the transition stage is 10-30%, for example, it can be 10%, 13%, 15%, 17%, 19%, 22%, 24%, 26%, 28% or 30%, etc.

[0077] Furthermore, the total reduction rate of the thin-walled region 102 in the finishing rolling stage is 2 to 15%, for example, it can be 2%, 4%, 5%, 7%, 8%, 10%, 11%, 13%, 14% or 15%, etc.

[0078] Furthermore, during the roughing, transition, and finishing rolling stages, the reduction rate of the thin-walled region 102 in each subsequent pass is smaller than that in the previous pass.

[0079] Furthermore, the rolling process has a reduction rate of 10-30% in the thick-walled region 101, for example, it can be 10%, 13%, 15%, 17%, 19%, 22%, 24%, 26%, 28%, or 30%.

[0080] Furthermore, the rolling speed in the roughing stage is 45 to 50 times per minute, for example, 45, 46, 47, 47, 48, 48, 49, 49, 50 times per minute, or 50 times per minute, and the single feed amount is 2 mm to 3.5 mm, for example, 2 mm, 2.2 mm, 2.4 mm, 2.5 mm, 2.7 mm, 2.9 mm, 3 mm, 3.2 mm, 3.4 mm, or 3.5 mm, etc.

[0081] Furthermore, the rolling speed in the transition stage is controlled at 45 to 50 times per minute, for example, it can be 45, 46, 47, 47, 48, 48, 49, 49, 50 times per minute or 50 times per minute, etc., and the single feed amount is 2 mm to 3.5 mm, for example, it can be 2 mm, 2.2 mm, 2.4 mm, 2.5 mm, 2.7 mm, 2.9 mm, 3 mm, 3.2 mm, 3.4 mm or 3.5 mm, etc.

[0082] Furthermore, the rolling speed in the finishing rolling stage is controlled at 40 to 45 times per minute, for example, it can be 40, 41, 42, 42, 43, 43, 44, 44, 45 or 45 times per minute, etc., and the single feed amount is 3.5 mm to 5 mm, for example, it can be 3.5 mm, 3.7 mm, 3.9 mm, 4 mm, 4.2 mm, 4.4 mm, 4.5 mm, 4.7 mm, 4.9 mm or 5 mm, etc.

[0083] Furthermore, the rolling pressure in the roughing stage is 1200KN~1800KN, for example, it can be 1200KN, 1267KN, 1334KN, 1400KN, 1467KN, 1534KN, 1600KN, 1667KN, 1734KN, or 1800KN, etc. This is a stage with large deformation, a large contact area, and the initial formation of a coordinated wall thickness difference.

[0084] Furthermore, the rolling pressure during the transition stage is 800KN~1200KN, for example, it can be 800KN, 845KN, 889KN, 934KN, 978KN, 1023KN, 1067KN, 1112KN, 1156KN, or 1200KN, etc. During the wall thickness difference widening stage, the thickness difference between the thin-walled and thick-walled regions further increases.

[0085] Furthermore, the rolling pressure in the finishing rolling stage is 400KN~800KN, for example, it can be 400KN, 445KN, 489KN, 534KN, 578KN, 623KN, 667KN, 712KN, 756KN, or 800KN. Minor adjustments are made to ultimately ensure that the wall thickness T1 of the thick-walled region 101 and the wall thickness T2 of the thin-walled region 102 can be precisely controlled.

[0086] Optionally, lubricating oil is used for lubrication and cooling during the rolling process. The lubricating oil temperature is 35°C to 40°C, for example, 35°C, 36°C, 37°C, 38°C, 39°C, or 40°C, to ensure the smooth operation of the main forming roll 2 and to remove the heat during the rolling process, thus ensuring rolling accuracy and reliability.

[0087] Optionally, during each rolling stroke, by adjusting the relative position, reduction, and rolling speed of the main forming roll 2 and the auxiliary mandrel 3, non-uniform plastic deformation is generated in different regions of the tube blank 1. This causes the material (metallic material) of the tube blank 1 to flow directionally from the preset thin-walled region 102 to the thick-walled region 101, gradually accumulating the wall thickness difference. With this setup, "incremental forming" can be achieved in each rolling pass of the main forming roll 2. Based on a multi-pass, non-uniform rolling strategy, it actively guides the plastic flow direction of the metal, realizing the redistribution of material in the circumferential direction, thereby efficiently forming a significant target wall thickness difference.

[0088] Optionally, during the interval between adjacent rolling passes, the tube blank 1 is driven to rotate 90 degrees around its axis. This configuration, through its own 90-degree rotation, effectively compensates for and corrects the tendency of the cross-section to become "rhomboid" or "asymmetrical" due to roll gaps, wear, or uneven metal flow. This ensures that the four sides of the final formed tube are straight, with distinct edges and consistent rounded corners. Furthermore, the rotation alters the flow path of the metal material, preventing excessive accumulation in one direction and further promoting uniform metal flow. This makes plastic deformation more uniform and controllable across the entire circumference, contributing to a more precise wall thickness distribution. Simultaneously, the rotation changes the rolling direction, helping to release and homogenize residual stress generated in the previous process, preventing the tube from twisting or warping, and improving the dimensional stability and straightness of the tube.

[0089] Specifically, such as Figures 2-5As shown, this embodiment provides the following technical solution by way of example: A roll system is provided inside the cold rolling mill. The roll system includes a pair of main forming rolls 2 and an auxiliary mandrel 3. The auxiliary mandrel 3 is used to insert and fit against the inner wall of the tube blank 1. The working surface of the main forming roll 2 is provided with an asymmetric cavity corresponding to the unequal wall thickness structure. The asymmetric cavity is located at the position of the thick wall region 101 of the tube blank 1, and the gap distance between the asymmetric cavity and the tube blank 1 is D1. The asymmetric cavity is located at the position of the thin wall region 102 of the tube blank 1, and the gap between the asymmetric cavity and the tube blank 1 is D2. Wherein, D1 and D2 satisfy: D1 is greater than D2. With this configuration, the asymmetric cavity has a larger gap D1 with the tube blank 1 at the thick-walled region 101 position to reduce the thinning amount, and a smaller gap D2 with the tube blank 1 at the thin-walled region 102 position to increase the thinning amount. That is, the asymmetric cavity is precisely calculated and processed to ensure that during the rolling process, a smaller radial reduction is applied to the planned thick-walled region 101 and a larger radial reduction is applied to the planned thin-walled region 102, so that the tube blank can be rolled into a tube with a predetermined unequal wall thickness distribution in one step.

[0090] Furthermore, the range of D1 is 1.2~17mm, for example, it can be 1.2mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 14mm, 15mm or 17mm, etc.

[0091] Furthermore, the range of D2 is 1~3mm, for example, it can be 1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2mm, 2.2mm, 2.5mm, 2.8mm or 3mm, etc.

[0092] It should be noted that the main function of the auxiliary mandrel 3 is to support the tube blank and prevent it from becoming unstable, twisting, or crushed under asymmetric rolling force. The position and pressure of the auxiliary mandrel 3 are adjustable and are coordinated with the movement of the main forming roll 2 to form a stable "deformation zone". Figure 5 The arrow in the figure indicates the rolling direction of the main forming roll 2 during rolling.

[0093] Optionally, the contour of the asymmetric cavity can gradually roll the tube blank 1 into a square structure with transition rounded corners. This configuration, through the composite asymmetric cavity, allows for simultaneous control of unequal wall thickness and the formation of the square cross-section in a single rolling process, ensuring the inherent coordination and high precision of the wall thickness distribution and geometric structure. This achieves synchronous and precise forming. Simultaneously, the formed transition rounded corner structure effectively avoids stress concentration at sharp corners, optimizes stress distribution, and improves the fatigue strength and pressure-bearing capacity of the tube.

[0094] Optionally, the outer contour of the square structure cross-section is quadrilateral, and adjacent sides of the quadrilateral are connected by transition fillets. This design, while ensuring structural strength, also provides a flat mounting and sealing surface for the quadrilateral structure, facilitating the installation and sealing of pipes and other components, and simplifying subsequent assembly work.

[0095] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0096] Example 1

[0097] This embodiment provides a method for manufacturing cold-rolled seamless tubes with unequal wall thicknesses, the method comprising the following steps:

[0098] S100: S30408 ​​stainless steel seamless round tube with a wall thickness of 20mm is selected as tube blank 1;

[0099] S200: The tube blank 1 is divided into sections according to its circumference to determine the specific locations of the thick-walled section 101 and the thin-walled section 102, the range of wall thickness values ​​of the thick-walled section 101 and the range of wall thickness values ​​of the thin-walled section 102.

[0100] S300: The tube blank 1 is loaded into a cold rolling mill and formed by asymmetric cold rolling to form a structure with unequal wall thickness, so that the wall thickness value of the thick wall region 101 is greater than the wall thickness value of the thin wall region 102, and the wall thickness values ​​of the thick wall region 101 and the thin wall region 102 are both within the designed wall thickness value range.

[0101] The cold rolling mill is equipped with a roll system, which includes a pair of main forming rolls 2 and an auxiliary mandrel 3. The auxiliary mandrel 3 is used to insert into and fit against the inner wall of the tube blank 1. The working surface of the main forming rolls 2 has an asymmetric cavity corresponding to the unequal wall thickness structure. The asymmetric cavity is located at the position corresponding to the thick wall region 101 of the tube blank 1, and its gap distance with the tube blank 1 is D1. The asymmetric cavity is located at the position corresponding to the thin wall region 102 of the tube blank 1, and its gap distance with the tube blank 1 is D2. D1 and D2 satisfy the following conditions: D1 is greater than D2; before rolling, D1 is 12.6 mm; and D2 is 1 mm. The contour of the asymmetric cavity can gradually roll the tube blank 1 into a square structure with transition rounded corners. The outer contour of the cross-section of the square structure is quadrilateral, and the two adjacent sides of the quadrilateral are connected by the transition rounded corners.

[0102] Specifically, the method of forming the tube blank 1 into a structure with unequal wall thickness by asymmetric cold rolling includes: performing multi-pass, non-uniform rolling on the tube blank 1 so that the tube blank 1 has a preset unequal wall thickness distribution along its circumference, and during each rolling pass, causing non-uniform plastic deformation in different areas of the tube blank 1 so that the material of the tube blank 1 flows directionally from the preset thin-walled region 102 to the thick-walled region 101 to gradually accumulate the wall thickness difference; and driving the tube blank 1 to rotate 90 degrees around its axis during the interval between adjacent rolling passes.

[0103] The rolling process uses lubricating oil for cooling, with the oil temperature set at 38°C. The rolling process includes a roughing stage, a transition stage, and a finishing stage performed sequentially. The roughing stage has a rolling speed of 48 passes / min, a single feed rate of 2.5 mm, and a rolling pressure of 1500 kN. The total reduction rate of the thin-walled region 102 in the roughing stage is 60%, and it is performed in three passes with equal reduction rates. The transition stage has a rolling speed controlled at 49 passes / min, a single feed rate of 2.5 mm, and a rolling pressure of 100 kN. The rolling pressure is 0 kN. During the transition stage, the total reduction rate of the thin-walled region 102 is 25%. In the finishing stage, the rolling speed is controlled at 42 passes / min, with a single feed of 4 mm. The rolling pressure in the finishing stage is 700 kN. During the finishing stage, the total reduction rate of the thin-walled region 102 is 10%, and the total reduction rate of the thick-walled region 101 is 15%. The reduction rate is the same for each pass, ultimately forming a tube with a "thin on both sides, thick on both sides" structure. The wall thickness of the thick-walled region 101 is 17 mm, and the wall thickness of the thin-walled region 102 is 5.4 mm. The reduction rate is calculated as: (wall thickness before rolling - wall thickness after rolling) / wall thickness before rolling.

[0104] S400: The unequal wall thickness structure obtained in step S300 is subjected to sizing rolling to control the outer dimensions and straightness of the unequal wall thickness structure, thereby forming an integral unequal wall thickness molded tube.

[0105] Example 2

[0106] This embodiment provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness. The difference between this method and Embodiment 1 is that: in S100, a stainless steel seamless round tube S30403 with a wall thickness of 22mm is selected as the tube blank 1; before rolling, D1 is 14mm; and D2 is 1mm.

[0107] The rolling process uses lubricating oil for cooling, with the oil temperature set at 40°C. The rolling process includes a roughing stage, a transition stage, and a finishing stage performed sequentially. In the roughing stage, the rolling speed is 50 times / min, the single feed rate is 3.5 mm, and the rolling pressure is 1800 kN. The total reduction rate of the thin-walled region 102 in the roughing stage is 82%, and it is performed in three passes with equal reduction rates. In the transition stage, the rolling speed is controlled at 45 times / min, the single feed rate is 2 mm, and the rolling pressure is 1200 kN. In the transition stage, the total reduction rate of the thin-walled region 102 is 30%; in the finishing stage, the rolling speed is controlled at 40 times / min, the single feed amount is 3.5mm, the rolling pressure in the finishing stage is 800KN, the total reduction rate of the thin-walled region 102 in the finishing stage is 15%, and the reduction rate of the thick-walled region 101 in the rolling stage is 30%. The reduction rate is the same for each pass, and finally a tube with a "thin on both sides and thick on both sides" structure is formed. The wall thickness of the thick-walled region 101 is 15.4mm, and the wall thickness of the thin-walled region 102 is 2.36mm.

[0108] Example 3

[0109] This embodiment provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness. The difference between this method and Embodiment 1 is that: in S100, a stainless steel seamless round tube S31603 with a wall thickness of 4.5mm is selected as the tube blank 1; before rolling, D1 is 3mm and D2 is 1mm.

[0110] The rolling process uses lubricating oil for cooling, with the oil temperature set at 35°C. The rolling process includes a roughing stage, a transition stage, and a finishing stage, performed sequentially. The roughing stage has a rolling speed of 45 strokes / min, a single feed rate of 2 mm, and a rolling pressure of 1200 kN. The total reduction rate of the thin-walled region 102 in the roughing stage is 49%, and it is performed in two passes with equal reduction rates. The transition stage has a rolling speed controlled at 50 strokes / min, a single feed rate of 3.5 mm, and a rolling pressure of 800 kN. N, the total reduction rate of the thin-walled region 102 in the transition stage is 10%; the rolling speed in the finishing stage is controlled at 45 times / min, the single feed amount is 5mm, the rolling pressure in the finishing stage is 400KN, the total reduction rate of the thin-walled region 102 in the finishing stage is 2%, the reduction rate of the thick-walled region 101 in the rolling stage is 10%, the reduction rate of each pass is the same, and finally a pipe with a "thin on both sides and thick on both sides" structure is formed, wherein the wall thickness of the thick-walled region 101 is 4.05mm, and the wall thickness of the thin-walled region 102 is 2.02mm.

[0111] Example 4

[0112] This embodiment provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness. The only difference between this method and Embodiment 1 is that the wall thickness of the tube blank 1 is 3mm, while all other process parameters are the same as in Embodiment 1. The final seamless tube has a wall thickness of 2.55mm in the thick-walled region 101 and a wall thickness of 0.81mm in the thin-walled region 102.

[0113] Example 5

[0114] This embodiment provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness. The only difference between this method and Embodiment 1 is that the wall thickness of the tube blank 1 is 28 mm, while all other process parameters are the same as in Embodiment 1. The final seamless tube has a wall thickness of 23.8 mm in the thick-walled region 101 and a wall thickness of 7.56 mm in the thin-walled region 102.

[0115] Example 6

[0116] This embodiment provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness. The only difference between this method and Embodiment 1 is that the total reduction rate of the thin-walled region 102 in the rough rolling stage is 50%, and the total reduction rate of the thin-walled region 102 in the transition stage is 40%. The wall thickness value of the thin-walled region 102 in the final seamless tube is the same as that in Embodiment 1, which is 5.4 mm. All other process parameters are the same as those in Embodiment 1.

[0117] Example 7

[0118] This embodiment provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness. The only difference between this method and Embodiment 1 is that the finishing rolling stage is not performed. Instead, the total reduction rate of the thin-walled region 102 in the transition stage is directly adjusted to 32.5%. The wall thickness of the thin-walled region 102 in the final seamless tube is the same as that in Embodiment 1, which is 5.4 mm. The total reduction rate of the thick-walled region (101) is maintained at 15%. All other process parameters are the same as those in Embodiment 1.

[0119] Example 8

[0120] This embodiment provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness. The only difference between this method and Embodiment 1 is that: there is no transition stage, and the reduction rate of the thin-walled region 102 is adjusted to 32.5% in the direct finishing stage. The wall thickness value of the thin-walled region 102 in the final seamless tube is the same as that in Embodiment 1, which is 5.4 mm. The total reduction rate of the thick-walled region 101 is maintained at 15%. All other process parameters are the same as those in Embodiment 1.

[0121] Example 9

[0122] This embodiment provides a method for manufacturing a cold-rolled seamless tube with unequal wall thickness. The only difference between this method and Embodiment 1 is that the roughing stage is no longer divided into three passes, but is carried out in one pass with a reduction rate of 60%. All other process parameters are the same as in Embodiment 1.

[0123] Comparative Example 1

[0124] This comparative example provides a method for manufacturing a cold-rolled seamless tube. The only difference between this method and Example 1 is that the tube is rolled into a uniform wall thickness circular tube with a wall thickness of approximately 17 mm, and then rolled in four passes (the same total number of passes as in Example 1). The rolling speed, feed rate, and rolling pressure are the same as in the roughing stage of Example 1. Comparative Example 2

[0125] This comparative example provides a method for manufacturing seamless tubes with unequal wall thicknesses, wherein the manufacturing method involves milling the flow channels from a solid blank as a whole. This comparative example suffers from extremely high material waste (over 70%), high costs, and the machining process interrupts metal flow lines, reducing the overall fatigue strength of the part.

[0126] Comparative Example 3

[0127] This comparative example provides a method for manufacturing pipes with unequal wall thicknesses. The method uses a 17mm uniform wall thickness circular pipe, and drills holes in the pipe wall and welds multiple water outlets to achieve a diversion function. In Example 1, water outlets are simply opened in the thick-walled area. Comparing Example 1 and Comparative Example 3, it can be seen that in Comparative Example 3, due to the presence of a welded area, fatigue cracking is very likely to occur at the weld under long-term liquid phase pressure, leading to liquid phase leakage. In Example 1, since there is no weld, the above problem does not exist.

[0128] The good cold-rolled seamless tubes obtained in Examples 1-3 and Comparative Example 1 were annealed at 1100℃ for 18 minutes and then water-cooled at 25℃ to obtain cold-rolled seamless tubes with unequal wall thicknesses. The tensile strength and elongation strength of the steel tubes were tested according to GB / T 14976-2025. The results are shown in Table 1.

[0129] Table 1

[0130]

[0131] As can be seen from Table 1, the unequal thickness cold-rolled seamless tubes provided by the present invention can achieve mechanical properties similar to or even higher than those of equal thickness seamless tubes, and the tensile strength and elongation strength can meet the requirements of the national standard GB / T 14976-2025.

[0132] Manufacture according to the manufacturing method of cold-rolled seamless pipes in the above-mentioned Embodiments 1 to 9, and count the product yield in 20 production runs. Those with a thickness within ±0.1 mm of the target design thickness and without cracking of the pipe during cold rolling are recorded as qualified. The test results of the above-mentioned embodiments and comparative examples are shown in Table 2.

[0133] Table 2

[0134]

[0135] As can be seen from Table 2, the product yield of stainless steel in Embodiments 1 to 3 reaches 100%, and the manufacture of cold-rolled seamless pipes with unequal wall thicknesses can be achieved.

[0136] Comparing Embodiment 1 and Embodiment 4, it can be seen that the wall thickness in the thin-wall area is too thin, which will reduce the yield rate under the same number of rolling passes. In Embodiment 5, the wall thickness in the thin-wall area is too thick. Although a 100% yield rate can be achieved, the unit mass of the overall pipe increases significantly, making it difficult to achieve the lightweight effect of the unequal-wall-thickness cold-rolled seamless pipes in the present invention. In Embodiment 6, the total reduction rate in the rough rolling stage is insufficient, resulting in a single-pass reduction rate of 40% in the transition stage, thus reducing the yield rate and the control of thickness accuracy. In Embodiment 7, no finish rolling is performed, resulting in an easy occurrence of unqualified wall thickness accuracy control and a decrease in the yield rate. In Embodiment 8, no transition stage is carried out, and the finish rolling stage is directly carried out. Not only is the yield rate likely to decrease, but the control of wall thickness accuracy is insufficient, and unqualified situations are likely to occur. In Embodiment 9, only one pass is used in the rough rolling stage, and the manufacturing yield rate drops to 70%. This shows that the present invention divides the rolling stage into three stages, and controlling the reduction rate of each pass can improve the yield rate and the control level of wall thickness accuracy.

[0137] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly explaining the present invention, and are not intended to limit the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A cold-rolled seamless pipe of unequal wall thickness, characterized in that, The unequal wall thickness cold-rolled seamless pipe is of unequal wall thickness structure, which comprises two thin wall zones (102) and two thick wall zones (101), the two thin wall zones (102) and the two thick wall zones (101) are sequentially connected in the circumferential direction, and the thin wall zones (102) and the thick wall zones (101) are alternately arranged.

2. The cold rolled seamless pipe of unequal wall thickness as claimed in claim 1 wherein, The wall thickness value of the thick wall zone (101) is T1, the wall thickness value of the thin wall zone (102) is T2, and T1 and T2 satisfy: 2≤T1 / T2≤9; Preferably, the wall thickness value T2 of the thin wall zone (102) ranges from 6mm to 2mm.

3. A method of manufacturing a cold-rolled seamless pipe with unequal wall thicknesses, characterized by, The manufacturing method of the unequal wall thickness cold-rolled seamless pipe of claim 1 or 2 comprises the following steps: S100: selecting a seamless round pipe as a pipe blank (1); S200: designing the wall thickness of the pipe blank (1) in the circumferential direction, determining the specific positions of the thick wall zone (101) and the thin wall zone (102), the wall thickness value range of the thick wall zone (101), and the wall thickness value range of the thin wall zone (102); S300: loading the pipe blank (1) into a cold rolling mill, and forming the pipe blank (1) into an unequal wall thickness structure by asymmetric cold rolling, so that the wall thickness value of the thick wall zone (101) is greater than the wall thickness value of the thin wall zone (102), and the wall thickness value of the thick wall zone (101) and the wall thickness value of the thin wall zone (102) are both within the designed wall thickness value range.

4. The method of manufacturing unequal wall thickness cold rolled seamless pipe as claimed in claim 3 wherein, In step S100, the wall thickness of the pipe blank (1) is 4mm-22mm; Preferably, in step S100, the pipe blank (1) is an equal wall thickness pipe blank.

5. The method of manufacturing unequal wall thickness cold rolled seamless pipe as claimed in claim 4 wherein, In step S300, the pipe blank (1) is subjected to multi-pass and non-uniform rolling to make the pipe blank (1) have a preset unequal wall thickness distribution in the circumferential direction; Preferably, in step S300, the number of passes of the rolling is 3-8 passes; Preferably, in step S300, the reduction rate of each pass of the rolling is 2-30%; Preferably, during each pass of rolling, non-uniform plastic deformation is generated in different regions of the pipe blank (1) to make the material of the pipe blank (1) flow from the preset thin wall zone (102) to the thick wall zone (101) to gradually accumulate the wall thickness difference; Preferably, in step S300, the rolling comprises a rough rolling stage, a transition stage and a finish rolling stage which are sequentially performed; Preferably, in the rough rolling stage and the transition stage, the reduction rate of the thin wall zone (102) is greater than that of the thick wall zone (101); Preferably, the total reduction rate of the thin wall zone (102) in the rough rolling stage is 40-82%; Preferably, the total reduction rate of the thin wall zone (102) in the transition stage is 10-30%; Preferably, the total reduction rate of the thin wall zone (102) in the finish rolling stage is 2-15%; Preferably, in the rough rolling stage, the transition stage and the finish rolling stage, the reduction rate of the thin wall zone (102) in each subsequent pass is smaller than that in the previous pass. Preferably, the reduction rate of the thick wall area (101) in the rolling stage is 10-30%; Preferably, the rolling speed of the rough rolling stage is 45-50 times / min, and the single feeding amount is 2-3.5 mm; Preferably, the rolling speed of the transition stage is controlled at 45-50 times / min, and the single feeding amount is 2-3.5 mm; Preferably, the rolling speed of the finish rolling stage is controlled at 40-45 times / min, and the single feeding amount is 3.5-5 mm; Preferably, the rolling pressure of the rough rolling stage is 1200-1800 KN; Preferably, the rolling pressure of the transition stage is 800-1200 KN; Preferably, the rolling pressure of the finish rolling stage is 400-800 KN; Preferably, lubricating oil is used for cooling in the rolling process; Preferably, the oil temperature of the lubricating oil is 35-40℃.

6. The method of manufacturing unequal wall thickness cold rolled seamless pipe, as claimed in claim 4 wherein, In the gap between adjacent passes, the pipe blank (1) is driven to rotate 90 degrees around its axis.

7. The method of manufacturing unequal wall thickness cold rolled seamless pipe, as claimed in claim 4 wherein, The cold rolling mill is provided with a roller system, which includes a pair of main forming rollers (2) and an auxiliary mandrel (3), the auxiliary mandrel (3) is used for inserting and fitting on the inner wall of the pipe blank (1), and the working surface of the main forming roller (2) is provided with an asymmetric cavity corresponding to the unequal wall thickness structure, the asymmetric cavity corresponds to the position of the thick wall area (101) of the pipe blank (1), and the gap distance between the asymmetric cavity and the pipe blank (1) is D1, the asymmetric cavity corresponds to the position of the thin wall area (102) of the pipe blank (1), and the gap distance between the asymmetric cavity and the pipe blank (1) is D2, wherein D1 and D2 satisfy: D1 is greater than D2; Preferably, the range of D1 is 1.2-17 mm; Preferably, the range of D2 is 1-3 mm.

8. The method of manufacturing unequal wall thickness cold rolled seamless pipe, as claimed in claim 7, wherein, The profile of the asymmetric cavity can gradually roll the pipe blank (1) into a square structure with a transition round corner.

9. The method of manufacturing unequal wall thickness cold rolled seamless tube as claimed in claim 8 wherein, The square structure cross section outer contour is a quadrilateral, and adjacent two sides of the quadrilateral are connected through the transition round corner.

10. The method of manufacturing unequal wall thickness cold rolled seamless pipe, as claimed in claim 3 wherein, After step S300, the method for manufacturing the unequal wall thickness cold-rolled seamless pipe further comprises: S400: performing sizing rolling on the unequal wall thickness structure obtained in step S300 to control the outer contour size and straightness of the unequal wall thickness structure, and forming an integrated unequal wall thickness forming pipe body.

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