Limiting mandrel continuous pipe mill unit and process method using similar pass design

Abstract

This invention provides a continuous rolling mill and process method using a mandrel with similar pass design. The original fixed pass is redesigned into three similar passes with dimensions differing by 2-3 mm, allowing the production of steel pipes with three wall thicknesses using a single mandrel. Furthermore, the similar pass design also enables the production of steel pipes with the same wall thickness using mandrels of different outer diameters within different similar passes, making production organization and tool change more flexible and convenient. This invention is applicable to various continuous rolling mills with limited mandrels, including two-roll and three-roll limited mandrel continuous rolling mills. Using this similar pass design improves product dimensional accuracy, optimizes the elongation deformation of the continuous rolling mill, significantly reduces mandrel specifications and quantity, greatly reduces mandrel spares, reduces capital occupation, lowers tool consumption, and reduces costs.

Description

Technical Field

[0001] This invention belongs to the field of continuous rolling tube technology, and particularly relates to a continuous rolling tube unit and process method using a mandrel with similar pass design. Background Technology

[0002] Seamless steel pipe production is a fundamental and important method of steel production. Since the invention of the mandrel continuous rolling mill in Italy in the 1980s, the mandrel continuous rolling process has gradually become the mainstream of seamless steel pipe production units worldwide. In China, the seamless steel pipe production units put into operation in the past two decades have also primarily adopted the mandrel continuous rolling process. The mandrel continuous rolling process boasts advantages such as high output, good product quality, low consumption, and a wide range of product specifications that can be produced, making it the absolute mainstream model for seamless steel pipe production in China today.

[0003] In the limited-movement mandrel continuous rolling process, a billet with a certain outer diameter is typically used to produce steel pipes with a specific range of outer diameters. For example, a billet with a diameter of φ200mm corresponds to steel pipes with an outer diameter range of φ108~φ168mm. The piercing mill produces tubes with a single outer diameter but different wall thicknesses from a billet by changing the mandrel specifications. The continuous rolling mill, by changing the mandrel specifications within a rolling pass system, produces rough tubes with different outer diameters but different wall thicknesses from the same pass. These are then processed by a reducing mill to produce steel pipes with different outer diameters and wall thicknesses. Therefore, in principle, the number of mandrels should correspond to the number of wall thickness specifications of steel pipes. Generally, a group of 6-7 mandrels of the same specification is used for the production of steel pipes with one wall thickness specification. In practical applications, when the wall thickness of steel pipes is close, to reduce the number of mandrel specifications and lower costs, the roll gap is lowered and raised to produce steel pipes with similar wall thicknesses, thus reducing the number of mandrel specifications required. The disadvantage is that raising and lowering the roll gap during rolling creates an additional tolerance for the wall thickness of the steel pipe. Therefore, this method can only produce steel pipes with a certain range of additional tolerance and similar wall thickness. For wall thicknesses within 10mm, the wall thickness difference is limited to within 0.5mm, and the additional wall thickness tolerance is controlled within 2%.

[0004] In the limited-motion mandrel continuous rolling process, the mandrel speed is limited and constant, resulting in stable rolling conditions, good product quality, and large deformation and elongation. However, due to the low speed of the mandrel, the speed difference between the mandrel and the inner wall of the steel pipe increases with each stand, with a maximum speed difference of about 4 m / s. Coupled with the high temperature, high pressure, and lack of cooling during rolling, the mandrel is the tool with the harshest working conditions and the highest requirements in the entire unit, and it is also the tool with the highest cost. About 1 kg of mandrel is consumed per ton of steel pipe, which currently accounts for more than 50-60 yuan / ton in cost (reaching as high as 150 yuan / ton at times). Based on the number of pipes rolled, each mandrel can only roll 1500-2000 steel pipes. Moreover, due to severe wear or chipping of the mandrel, if it is not replaced in time, defects on the inner surface of the steel pipe are likely to occur, such as internal straight scratches, internal scars, and uneven inner surface. When rolling difficult-to-deform steel grades and thin-walled pipes, the use of severely worn mandrels may also cause dents and holes. Summary of the Invention

[0005] The technical problem solved by this invention is achieved through the following technical solution:

[0006] The limited mandrel continuous rolling mill unit adopts a similar pass design. Each stand of the continuous rolling mill unit is equipped with three passes of similar size under the basic pass system. The size specifications of the three passes of similar size differ by 2-3mm, and the three passes of similar size correspond to the same specification of round billet.

[0007] The maximum elongation coefficient of the continuous rolling mill is set. Generally, the maximum elongation coefficient of the continuous rolling mill with a limited mandrel with a similar pass type is set to below 4.5, and the maximum elongation coefficient of the continuous rolling mill with a limited mandrel and a special continuous rolling pass type is set to below 3.6.

[0008] Furthermore, when setting up the three hole types with similar dimensions under the basic hole type system, the following steps are included:

[0009] Determine the deformation elongation coefficient of each stand in the continuous rolling mill; among them, stands 1 to 3 are roughing stands, with a single stand elongation coefficient between 1.3 and 1.6, and stands 4 to 7 are finishing stands, with a single stand deformation elongation coefficient between 1.01 and 1.35.

[0010] Determine the dimensions of the hole structure for each frame, including the radius and angle of each hole arc;

[0011] Based on production practice, the parameters of the hole design are optimized and modified until they meet normal production requirements.

[0012] Furthermore, the aforementioned limited-motion mandrel continuous rolling mill units with similar pass profiles include a 6-8 stand two-roll mode, a 5-stand Mini-MPM mode, and a 5-6 stand three-roll mode; wherein, the maximum elongation coefficient of the 6-8 stand two-roll limited-motion mandrel continuous rolling mill unit is set to 4.5, the maximum elongation coefficient of the 5-stand Mini-MPM two-roll limited-motion mandrel continuous rolling mill unit is set to no more than 3.6, and the maximum elongation coefficient of the 5-6 stand three-roll limited-motion mandrel continuous rolling mill unit is set to 4.2.

[0013] Furthermore, the aforementioned special continuous rolling pass refers to a pass designed specifically for the production of difficult-to-deform steel grades and thin-walled tubes.

[0014] Furthermore, when each stand of the continuous rolling mill of the limited mandrel rolling mill is equipped with three similar-sized pass patterns under the basic pass pattern system, two new pass patterns with similar sizes can be added on the basis of the original pass pattern system; or, according to the principle of being conducive to the production of medium and thin-walled tubes, three pass patterns with similar sizes can be redesigned.

[0015] A tube rolling process using a mandrel with a similar bore design, the process including a hollow billet diameter reduction step;

[0016] The hollow billet reduction process provides three tubes with similar outer diameters and different wall thicknesses for the similar pass pattern process of the continuous rolling process.

[0017] Furthermore, the hollow billet diameter reduction process can be carried out in the following manner:

[0018] A hollow billet reducing mill should be arranged between the piercing mill and the continuous rolling mill. The hollow billet reducing mill should adopt a three-roll, three-stand configuration, with an outer diameter reduction rate not exceeding 5%; or...

[0019] A hollow billet reducing mill is arranged at the entrance of the continuous rolling mill. The frame type is the same as the roll type of the continuous rolling mill, that is, a two-roll hollow billet reducing mill is used for two-roll continuous rolling, and a three-roll hollow billet reducing mill is used for three-roll continuous rolling.

[0020] Furthermore, the hollow blank diameter reduction process, which provides three outer diameter caps for processes with similar die profiles, can also be implemented in the following manner:

[0021] Adjustments were made to the piercing process parameters, including the distance between the piercing mill guide disc / plate and the position of the mandrel. Three tubes with similar outer diameters but different wall thicknesses were produced directly in the piercing process, providing three tubes with three outer diameter specifications for the continuous rolling mill. At the same time, the die design of the first stand at the entrance of the continuous rolling mill was adapted to the fluctuation of the outer diameter of the tubes.

[0022] The advantages and positive effects of this invention are:

[0023] The present invention relates to a mandrel-based continuous rolling mill and process with similar bore design, which can produce steel pipe products with three wall thicknesses using a single mandrel without incurring additional tolerances. While achieving the above-mentioned process objectives, it optimizes the deformation distribution between piercing and continuous rolling, thereby improving the quality of steel pipe products, significantly reducing the number of mandrel specifications and the amount of mandrel spares, reducing costs, and making production organization more flexible and convenient. Detailed Implementation

[0024] First, it should be noted that the specific structure, features, and advantages of the present invention will be described in detail below by way of examples. However, all descriptions are for illustrative purposes only and should not be construed as limiting the present invention in any way. Furthermore, any single technical feature described or implied in the various embodiments mentioned herein can still be arbitrarily combined or deleted among these technical features (or their equivalents) to obtain more other embodiments of the present invention that may not be directly mentioned herein.

[0025] The limiting mandrel continuous rolling mill unit provided in this embodiment adopts a similar pass design. Each stand of the continuous rolling mill unit of the limiting mandrel continuous rolling mill unit is equipped with three passes of similar size under the basic pass system. The size specifications of the three passes of similar size differ by 2-3mm, and the three passes of similar size correspond to the same specification of round billet.

[0026] The maximum elongation coefficient of the continuous rolling mill is set. Generally, the maximum elongation coefficient of the continuous rolling mill with a limited mandrel with a similar pass type is set to below 4.5, and the maximum elongation coefficient of the continuous rolling mill with a limited mandrel and a special continuous rolling pass type is set to below 3.6.

[0027] Specifically, the design method for three hole types with similar sizes is as follows:

[0028] Two new pass types with similar dimensions can be added to the original pass type system. Alternatively, three pass types with similar dimensions can be redesigned in combination with the deformation and elongation of the continuous rolling process. According to the principle of being conducive to the production of medium and thin-walled tubes, the difference in pass type size should be 2 to 3 mm, provided that the three similar pass types correspond to the same specification of round billet.

[0029] Hole design is carried out in the following three steps:

[0030] 1) Selecting the basic parameters of the roll pass mainly involves allocating and determining the deformation elongation coefficient of each stand of the continuous rolling mill, and determining the basic dimensions of the roll pass structure, the width expansion coefficient, the roll gap, etc. Among these, determining the deformation elongation coefficient is the most important, as it is a key parameter for product deformation quality, tool consumption, and unit consumption. Stands 1 to 3 are roughing mill stands, and the elongation coefficient of a single stand is taken as the upper limit, between 1.3 and 1.6. Stands 4 to 7 are finishing mill stands, and the deformation elongation coefficient of a single stand is taken as the lower limit, between 1.01 and 1.35.

[0031] 2) Analyze and calculate the structural dimensions of each frame's die, including the arc radius and arc angle of each die's arc; generally, it is divided into the arc radius of the top arc of the die, the arc radius of the side wall separation arc, the arc radius of the roll gap arc, the separation arc angle between the outer wall of the steel pipe and the roll die, and the separation arc angle between the inner wall of the steel pipe and the mandrel at the roll gap;

[0032] 3) Optimize and modify the main parameters of the hole design based on production practice until they meet normal production needs; mainly optimize and modify the extension coefficient and width coefficient of each frame.

[0033] When setting the maximum elongation coefficient of a continuous rolling mill, the determination of the maximum elongation coefficient of the mandrel-controlled continuous rolling should not only consider achieving greater elongation deformation, but also comprehensively analyze key factors such as the maximum load of the mill, the deformability of difficult-to-deform steel grades, the minimum rollable wall thickness of the steel pipe, and mandrel consumption. Therefore, this patent proposes the concept and implementation method of optimizing the deformation elongation of the continuous rolling process by combining a new process with similar pass shapes. The main purpose is to reduce rolling defects in the continuous rolling process, expand the rolling range of steel grades, and improve the service life of the mandrel. Currently, limited-motion mandrel continuous rolling mills include 6-8 stand two-high mills, 5 stand Mini-MPM mills, and 5-6 stand three-high mills, with corresponding maximum elongation coefficients of approximately 6, 4, and 5, respectively. Considering factors such as rolling difficult-to-deform steel grades, reducing quality defects caused by unreasonable deformation, and improving mandrel lifespan, the maximum elongation coefficient for the 6-8 stand two-high limited-motion mandrel rolling mill can be set at 4.5, the maximum elongation coefficient for the 5 stand two-high Mini-MPM mill is set to no more than 3.6, and the maximum elongation coefficient for the 3 stand limited-motion mandrel continuous rolling mill can be set at 4.2. Furthermore, a pass can be designed specifically for producing difficult-to-deform steel grades and thin-walled tubes, allowing for a further reduction in the mill elongation coefficient. For example, the original total elongation coefficients for the 180-pass two-high continuous rolling mill (7 stand and 5 stand) were 4.833 and 3.628, respectively; the optimized total elongation coefficients are 4.10 and 3.21. The elongation coefficients for each stand and the total elongation coefficient are shown in Table 1 below.

[0034] Table 1

[0035]

[0036] This embodiment also provides a tube rolling process using a limited mandrel with a similar die design, the process including a hollow billet diameter reduction process;

[0037] The hollow billet reduction process provides three tubes with similar outer diameters and different wall thicknesses for the similar pass pattern process of the continuous rolling process.

[0038] The hollow billet diameter reduction process can be carried out in the following manner:

[0039] A hollow billet reducing mill should be arranged between the piercing mill and the continuous rolling mill. The hollow billet reducing mill should adopt a three-roll, three-stand configuration, with an outer diameter reduction rate not exceeding 5%; or...

[0040] A hollow billet reducing mill is arranged at the entrance of the continuous rolling mill. The frame type is the same as the roll type of the continuous rolling mill, that is, a two-roll hollow billet reducing mill is used for two-roll continuous rolling, and a three-roll hollow billet reducing mill is used for three-roll continuous rolling.

[0041] To provide three outer diameter specifications for similar bore diameter processes, the hollow billet diameter reduction process can also be considered as follows:

[0042] Adjustments were made to the piercing process parameters, including the distance between the piercing mill guide disc / plate and the position of the mandrel. Three tubes with similar outer diameters but different wall thicknesses were produced directly in the piercing process, providing three tubes with three outer diameter specifications for the continuous rolling mill. At the same time, the die design of the first stand at the entrance of the continuous rolling mill was adapted to the fluctuation of the outer diameter of the tubes.

[0043] It should be noted that, to provide tubes with different outer diameter series for similar pass processes, the optimal process is to arrange a hollow billet reducing mill between the piercing mill and the continuous rolling mill, which is especially recommended for newly built units. This arrangement not only meets the tube size requirements of similar pass processes but also facilitates process adjustments to the piercing mill. Specifically, the piercing mill can be adjusted primarily based on tube wall thickness. The hollow billet reducing mill should adopt a three-roll, three-stand configuration, with an outer diameter reduction rate not exceeding 5%. A second hollow billet reducing process option involves arranging a hollow billet reducing mill stand at the entrance of the continuous rolling mill. The billet reducing mill has the same stand configuration as the roll pattern of the continuous rolling mill, i.e., a two-roll hollow billet reducing mill is used for two-roll continuous rolling, and a three-roll hollow billet reducing mill is used for three-roll continuous rolling. Under the condition that it is difficult to arrange a hollow billet reducing mill in the existing unit space layout, the tube required by similar pass pattern processes should be achieved by increasing the number of piercing mandrel specifications and adjusting the piercing mill. This places higher demands on the setting and adjustment accuracy of the piercing process specifications, but it can meet the requirements through careful setting and adjustment. In addition, the pass pattern design of the first stand of the continuous rolling mill should be adapted to the fluctuation of the outer diameter of the tube as much as possible.

[0044] As an example, in this embodiment, to address the issues of excessive mandrel usage and consumption, extend their service life, and improve quality defects such as dents, holes, and internal scratches in steel pipes during the production of difficult-to-deform steel grades and thin-walled specifications, a mandrel of one specification is used to produce steel pipe products of three wall thicknesses without incurring additional tolerances. This achieves the aforementioned process objectives while optimizing the deformation distribution between piercing and continuous rolling, thereby improving the quality of steel pipe products, significantly reducing the number of mandrel specifications and spare mandrels, lowering costs, and making production organization more flexible and convenient. To achieve the above process goals, two more similar-sized pass types are added to the original single pass design of the unit, making it a basic pass type system with three similar-sized pass types. A mandrel of one specification is used to produce steel pipe products of three wall thicknesses. The straightness of the three pass types... A diameter difference of 2-3mm is ideal, primarily focusing on the specifications of medium and thin-walled steel pipes, particularly those with wall thicknesses below 10mm, which constitute the majority of market demand. For example, if the original design used a φ180 die to produce a 180*5.45mm rough pipe with a mandrel size of 168.9mm, adding two similar die sizes, φ178 and φ183, would allow for the production of steel pipes with wall thicknesses of 178*4.45mm and 183*6.95mm, while maintaining the same 168.9mm mandrel size. Through diameter reduction deformation, three wall thickness specifications can be produced, such as φ168*4.5mm, φ168*5.5mm, and φ168*7mm. Combined with optimized continuous rolling process extension deformation, this approach can significantly reduce the number of spare mandrels and extend their service life while improving product quality and wall thickness accuracy.

[0045] If only one hole type is used, such as the φ180 hole type, the conventional design wall thickness range is 4.75~26mm, requiring 14 sizes of mandrels. However, with a new process design using a similar hole type, the same 4.75~26mm wall thickness range can be produced using only six sizes of mandrels. See Table 2, which shows the range of steel pipe products that can be covered by mandrels with diameters of 168.9, 163.3, 157.8, 150.7, 142.8, and 130.8.

[0046] Table 2 Specifications for rolling mandrels with similar bore profiles

[0047]

[0048] Optimizing the deformation distribution in piercing and continuous rolling processes: The limited-movement mandrel continuous rolling process, due to its constant mandrel speed and stable rolling condition, can achieve greater deformation elongation than the floating mandrel process, typically reaching a maximum elongation coefficient of 7, far exceeding the maximum elongation coefficient of 5 achievable by the floating mandrel process. However, on the other hand, the large speed difference between the mandrel and the steel pipe leads to severe mandrel wear under high temperature and high pressure conditions, worsening working conditions. Furthermore, the maximum elongation coefficient in continuous rolling is limited by the mill's maximum allowable load, the plasticity of the rolled steel grade, and the minimum rollable steel pipe wall thickness. Generally, a single steel pipe production unit must adapt to the rolling production of multiple steel grades, and the maximum elongation coefficient of a single pass system can only be achieved by comprehensively considering the steel grade and continuous rolling load. After considering factors such as load, wall thickness rolling range, and cost, a new process with similar pass profiles is adopted, which provides the possibility of optimizing the deformation distribution in the piercing continuous rolling process. For example, a similar pass profile can be specifically set for the production of thin-walled tubes and difficult-to-roll steel grades, that is, reducing the maximum elongation coefficient of the continuous rolling mill to below 4. At the same time, the maximum elongation coefficient of the continuous rolling mill can be appropriately reduced for similar pass profiles, creating better conditions for improving product deformation quality and mandrel life. The maximum elongation coefficient of the special pass profile can be set at around 3.6, and that of the general similar pass profiles can be set below 4.5. Finally, the maximum elongation coefficient of the continuous rolling mill should be comprehensively determined after considering the rolling grade, number of stands, and unit type (two-roll or three-roll).

[0049] To achieve the above continuous rolling process requirements, three sets of pierced tubes with similar outer diameters but different wall thicknesses need to be provided at the continuous rolling mill inlet. For ease of production, solid round billets of the same specification should be used. The change in billet diameter should correspond to different basic pass profile settings without changing the overall profile. Two new processes are adopted to achieve the similar pass profile requirements: 1) Add a hollow billet reduction process between the piercing mill and the continuous rolling mill. For a pierced tube with one outer diameter but different wall thicknesses, it is transformed into three tubes with different outer diameters and wall thicknesses by a hollow billet reduction mill. For example, corresponding to the aforementioned φ178, φ180, and φ183 pass profiles, tubes with an outer diameter of φ223mm and different wall thicknesses are reduced to φ222 and φ219 by the hollow billet reduction mill. The three outer diameter specifications of φ217 meet the requirement of providing three similar outer diameter tubes with different wall thicknesses for similar pass profile processes; 2) By adjusting the distance of the guide plate / guide plate of the piercing mill, the position of the mandrel, or other process parameters, the requirement of producing three outer diameter tubes with different wall thicknesses directly in the piercing process can be met. Since the outer diameter difference does not change much due to similar pass profile processes, it is easy to form a phenomenon where the outer diameter tolerance fluctuation of the tube after piercing overlaps with the outer diameter difference of the tube required by the similar pass profile process. Therefore, the process parameter adjustment accuracy of the piercing mill must be high. At the same time, the pass profile design of the first stand at the entrance of the continuous rolling mill should be adapted to the fluctuation of the outer diameter of the tube as much as possible. When space conditions permit, the first process scheme should be selected first in the design.

[0050] The improved product quality, extended mandrel life, reduced mandrel specifications and spare parts, and lower cost resulting from the adoption of the aforementioned new process with similar piercing profiles, combined with optimization of deformation in the continuous rolling process, are mainly reflected in the following aspects: 1) Due to the optimized deformation distribution in the piercing and continuous rolling processes, the maximum deformation elongation coefficient in the continuous rolling process has been reduced from a maximum of 6 to below a maximum of 4.5, greatly reducing the risk of denting and hole formation during continuous rolling. The probability of defects is significantly reduced, especially when rolling thin-walled and difficult-to-deform steel products. This also provides conditions for reducing mandrel wear, extending service life, and reducing rolling load and mill consumption. 2) As mentioned above, the new process of using similar pass profiles can achieve the effect of expanding and optimizing the continuous rolling deformation elongation, and producing three steel pipes with different wall thicknesses using a mandrel of one specification. In addition, when the outer diameter of the pierced tube is three similar specifications and the wall thickness is the same, the new process of using similar pass profiles can also achieve the production of steel pipe products with the same wall thickness using three different specifications of mandrels. See Table 2. When using a φ167.3mm mandrel to produce a φ183mm pass profile, a φ165.6mm mandrel to produce a φ180mm pass profile, and a φ163.3mm mandrel to produce a φ178mm pass profile, all can produce a raw tube with a wall thickness of 7.1mm. The corresponding raw tube specifications are φ222×22, φ219×22, and φ217×22. This is particularly important for the production of large quantities of products of the same specifications in the market, especially thin-walled tube products. It provides flexible and convenient production to meet market demands, and creates conditions for the rational use, uniform wear, and extended service life of mandrels due to changes in mandrel specifications and usage conditions; 3) The new process with similar pass profiles uses a mandrel of one specification to produce products of three wall thicknesses, which can reduce the number of spare mandrel specifications by more than half, or even more, as shown in Table 2; reducing the number of spare mandrels greatly reduces capital occupation and production costs. A continuous rolling mill with three basic pass profiles can reduce capital occupation by more than 20 million. Combined with the application of producing products of the same wall thickness with mandrels of different specifications, the number of spare mandrel specifications can be further reduced; 4) The service life of mandrels is improved. The new process with similar pass profiles provides good conditions for extending the service life of mandrels. First, optimizing the deformation and elongation in the continuous rolling process reduces the elongation coefficient, lowers the rolling load, and lessens mandrel wear. Second, using one mandrel specification to roll three wall thickness specifications, and then combining different mandrel specifications to roll a single wall thickness specification, creates conditions for the rational use and uniform consumption of mandrels. Because the maximum rolling force differs when rolling steel pipes of different wall thicknesses, coupled with variations in the mandrel's limiting speed, the maximum wear segment of the mandrel changes from one segment when rolling a single specification to two or three segments. Thus, when two or three wear segments all reach their maximum... Repairing and re-machinering at the appropriate time will greatly extend the service life of the mandrel; 5) Since the three similar pass sizes used in the new process of similar pass size are similar, the amount of re-machinering of the new pass size of the continuous rolling mill rolls is greatly reduced, which is very beneficial to the rational use of the continuous rolling mill rolls and the reduction of consumption; 6) In addition to the above advantages, the adoption of the new process of similar pass size will also lead to an increase in the number of spare roll sets of continuous rolling mill rolls, the addition of the hollow billet diameter reduction process, or an increase in the number of spare mandrel specifications, but these results are negligible compared with the aforementioned improvements in product quality, reduction in mandrel consumption, and cost reduction.

[0051] In summary, the new process with similar pass profiles provides feasibility for rolling steel pipes of different wall thicknesses using a single mandrel, and also creates conditions for flexible production organization of the mandrel continuous rolling mill, i.e., flexible production of products. The setting of the number of mandrel specifications should first meet the requirements of the product outline for the dimensions of steel pipes of various wall thicknesses; secondly, for steel pipe products of various wall thicknesses, especially large-volume specifications, should be rolled at the nominal wall thickness as much as possible to improve the wall thickness accuracy of the products; and thirdly, it should provide convenience for production organization based on the different market demands for products of various wall thicknesses. That is, the same mandrel can produce steel pipe products of different wall thicknesses in different similar pass profiles, and different mandrels can produce products of the same wall thickness in different similar pass profiles, all with a certain degree of wall thickness overlap, providing flexibility and convenience for production organization. As shown in Table 2, a 168.9mm mandrel can produce steel pipes with a wall thickness of 5.0mm in both the φ178 and φ180 pass profiles. A 168.9mm mandrel can produce steel pipes with a wall thickness of 7.0mm in both the φ183 and φ178 pass profiles. Under similar pass profile process conditions, the number of mandrel specifications selected should be about half that of the conventionally designed pass profiles. In addition, the new process with similar pass profiles significantly reduces the number of spare mandrels, lowers capital occupation costs, and optimizes and reduces the deformation elongation coefficient of the continuous rolling mill. One mandrel specification can be used to roll steel pipes with different wall thicknesses, and different mandrel specifications can be used to roll steel pipes with the same wall thickness in similar pass profiles. This creates conditions for reducing mandrel wear and extending mandrel service life. In actual production, by adjusting the pre-insertion length of the mandrel rolling and adjusting the mandrel limiting speed, the mandrel can form two to three maximum wear sections during operation, thus maximizing the extension of mandrel service life.

[0052] It should be noted that, due to the change in the outer diameter of the steel pipe exiting the continuous rolling mill using a new process with similar pass patterns, theoretically, both the tube stripping mill and the sizing and reducing mill should have corresponding pass pattern changes. However, since the outer diameter of the pass pattern set for similar pass patterns is not much different, within 2-3 mm, and the reduction rate of the tube stripping mill is less than 1.5%, only the pass pattern of the first stand tube stripping mill should be adapted and changed, while the pass patterns of the second and third stands should remain unchanged. When the outer diameter difference of similar pass patterns is large, the pass pattern of the three-stand tube stripping mill should be redesigned. Since the outer diameter difference is small, the pass pattern setting of the sizing and reducing mill can remain unchanged.

[0053] The above embodiments have provided a detailed description of the present invention, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A continuous rolling mill for tubes using a mandrel with a similar pass design, characterized in that: Each stand of the continuous rolling mill of the limited mandrel rolling mill is equipped with three similar-sized passes under the basic pass system. The size specifications of the three similar-sized passes differ by 2-3mm, and the three similar-sized passes correspond to the same specification of round billet. The maximum elongation coefficient of the continuous rolling mill is set. Generally, the maximum elongation coefficient of the continuous rolling mill with a limited mandrel with a similar pass type is set to below 4.5, and the maximum elongation coefficient of the continuous rolling mill with a limited mandrel and a special continuous rolling pass type is set to below 3.

6.

2. The mill set of claim 1, wherein the mill set is a mill set of a mandrel mill with a close pass design, characterized in that: When setting up three similarly sized hole types under the basic hole type system, the following steps are included: Determine the deformation elongation coefficient of each stand in the continuous rolling mill; among them, stands 1 to 3 are roughing stands, with a single stand elongation coefficient between 1.3 and 1.6, and stands 4 to 7 are finishing stands, with a single stand deformation elongation coefficient between 1.01 and 1.

35. Determine the dimensions of the hole structure for each frame, including the radius and angle of each hole arc; Based on production practice, the parameters of the hole design are optimized and modified until they meet normal production requirements.

3. The mill set of claim 1, wherein the mill set is a mill set of a mandrel mill with a close pass design, characterized in that: The aforementioned limited-motion mandrel continuous rolling mill units with similar pass profiles include a 6-8 stand two-roll mode, a 5 stand Mini-MPM mode, and a 5-6 stand three-roll mode; wherein, the maximum elongation coefficient of the 6-8 stand two-roll limited-motion mandrel continuous rolling mill unit is set to 4.5, the maximum elongation coefficient of the 5 stand Mini-MPM two-roll limited-motion mandrel continuous rolling mill unit is set to no more than 3.6, and the maximum elongation coefficient of the 5-6 stand three-roll limited-motion mandrel continuous rolling mill unit is set to 4.

2.

4. The continuous rolling mill for mandrels with similar pass profiles as described in claim 1, characterized in that: The aforementioned special continuous rolling pass refers to a pass designed specifically for the production of difficult-to-deform steel grades and thin-walled tubes.

5. The continuous rolling mill for mandrels with similar pass profiles as described in claim 1, characterized in that: When each stand of the continuous rolling mill of the limited mandrel rolling mill is equipped with three similar-sized pass patterns under the basic pass pattern system, two new pass patterns with similar sizes are added on the basis of the original pass pattern system; or, according to the principle of being conducive to the production of medium and thin-walled tubes, three pass patterns with similar sizes are redesigned.

6. A continuous rolling mill process using a mandrel with a similar pass design, wherein the process employs the mill unit described in any one of claims 1-5, characterized in that... The process includes a hollow billet diameter reduction step; The hollow billet reduction process provides three tubes with similar outer diameters and different wall thicknesses for the similar pass pattern process of the continuous rolling process.

7. The continuous rolling tube process using a mandrel with a similar pass design as described in claim 6, characterized in that: The hollow billet diameter reduction process is carried out in the following manner: A hollow billet reducing mill is arranged between the piercing mill and the continuous rolling mill. The hollow billet reducing mill adopts a three-roll, three-stand configuration, and the outer diameter reduction rate does not exceed 5%; or... A hollow billet reducing mill is set up at the entrance of the continuous rolling mill. The two-roll continuous rolling uses a two-roll hollow billet reducing mill, and the three-roll continuous rolling uses a three-roll hollow billet reducing mill.

8. The continuous rolling tube process using a mandrel with a similar pass design as described in claim 6, characterized in that: The hollow blank diameter reduction process is carried out in the following manner to provide three outer diameter caps for processes with similar die profiles: Adjustments were made to the piercing process parameters, including the distance between the piercing mill guide disc / plate and the position of the mandrel. Three tubes with similar outer diameters but different wall thicknesses were produced directly in the piercing process, providing three tubes with three outer diameter specifications for the continuous rolling mill. At the same time, the die design of the first stand at the entrance of the continuous rolling mill was adapted to the fluctuation of the outer diameter of the tubes.

Images