Expansion system for two-way stretching of pipe

Abstract

The invention provides an expansion system for two-way stretching of a pipe, which relates to the technical field of pipe stretching and comprises a multi-stage temperature control flaring section, a constant pressure forming section and a cooling shaping section which are arranged in sequence. The multi-stage temperature control flaring section comprises an expansion mold with a conical step and an expansion hole, a temperature detection device and a circulating cooling channel. And an air outlet gap is formed between the constant-pressure forming section and the flaring section. The cooling shaping section is provided with air holes and air return holes. An air supply pull rod penetrates through the three sections, and multiple air supply pipelines are arranged in the air supply pull rod and connected with the expansion hole, the circulating cooling channel, the air outlet gap, the air hole and the air return hole correspondingly, so that air path integrated control is achieved. Through the synergistic effect of multi-stage temperature control flaring, constant-pressure air cushion forming and circulating cooling shaping, the temperature, pressure and friction force during pipe stretching can be accurately controlled, the size precision, roundness, mechanical property and surface quality of pipes are effectively improved, and the continuous production device is suitable for continuous production of high-performance plastic pipes.

Description

Technical Field

[0001] This invention relates to the field of pipe stretching technology, and specifically to an expansion system for bidirectional pipe stretching. Background Technology

[0002] Polypropylene pipes are increasingly widely used in chemical fluid transportation, hot water pipe networks, and other fields due to their excellent chemical corrosion resistance, high heat resistance, and relatively light weight. To meet the demand for pipe products with higher strength, better creep resistance, and lighter weight, the technology of biaxially stretching (axial tension and radial expansion) of polypropylene pipes to improve their mechanical properties and dimensional stability has become an important development direction for pipe deep processing.

[0003] Currently, biaxial stretching processes and equipment for pipes largely draw upon film stretching or are based on experience processing general-purpose plastic pipes. Traditional biaxial stretching equipment is typically designed to process conventional thermoplastic materials such as polyvinyl chloride (PVC). These materials have a wide thermoelastic processing window and relatively simple tensile deformation behavior, making the requirements for temperature control, stretching speed matching, and deformation coordination relatively relaxed for traditional equipment. Typical traditional equipment employs a single-stage or simple multi-stage flaring structure, coupled with a basic temperature zoning and cooling system, to achieve relatively stable stretching.

[0004] However, directly applying such traditional equipment and processes to polypropylene pipes faces a series of severe challenges, resulting in unstable stretching processes, low yields, and uneven product performance. This is mainly due to the unique inherent characteristics of polypropylene: First, polypropylene is a typical semi-crystalline polymer, and its crystal structure is extremely sensitive to temperature during stretching, exhibiting distinct glass transition temperature and melting temperature ranges. Precise and zoned temperature control is required to optimize molecular chain orientation and crystallization, rather than simple overall heating. Second, polypropylene has relatively low melt strength at high temperatures. During radial expansion, improper flaring gradient design or localized stress concentration can easily lead to uneven pipe wall thinning, localized necking, or even rupture. Third, the crystallization kinetics of polypropylene require rapid and uniform cooling after stretching to freeze the formed orientation structure and prevent shrinkage and changes in crystallinity. However, the cooling sections of traditional equipment are often insufficient in length or have low cooling efficiency, failing to meet the requirements for rapid polypropylene setting.

[0005] Therefore, traditional biaxial stretching systems designed for easily stretchable materials such as PVC are difficult to achieve stable and controllable high-quality biaxial stretching production of polypropylene pipes. Summary of the Invention

[0006] 1. The technical problem that the invention aims to solve: The present invention provides an expansion system for biaxial stretching of pipes to solve the technical problems existing in the background art.

[0007] 2. Technical Solution: To achieve the above objectives, the technical solution provided by the present invention is: an expansion system for biaxial stretching of pipes, comprising... It includes a multi-stage temperature-controlled flaring section, a constant-pressure forming section, and a cooling and shaping section; The multi-stage temperature-controlled flaring section includes an expansion mold, which gradually widens from the inlet end of the pipe to the outlet end, forming a conical stepped structure. Multiple spaced expansion holes are arranged in a ring around the stepped section of the expansion mold for inflating the space between the pipe and the mold. A temperature detection device is installed on the inner wall of the flaring section of the expansion mold, and a circulating cooling channel is located beside the temperature detection device. An air supply rod runs through the middle of the multi-stage temperature-controlled flaring section. The air supply rod has a hollow structure and contains multiple air supply pipes, which are respectively connected to the circulating cooling channel and each expansion hole. The constant pressure forming section and the multi-stage temperature-controlled flaring section are detachably connected, forming a sealed cavity inside. An air outlet gap is formed between the constant pressure forming section and the multi-stage temperature-controlled flaring section. The outer diameter of the constant pressure forming section is smaller than the outer diameter of the end of the multi-stage temperature-controlled flaring section. The air supply rod passes through the constant pressure forming section, and the air outlet gap allows air to flow outward, thus forming a stable upward airflow on the outside of the constant pressure forming section, reducing the frictional resistance when the pipe moves. The cooling and shaping section is connected to the constant pressure forming section, and the air supply rod passes through the cooling and shaping section and is locked in place. The diameter of the cooling and shaping section is smaller than that of the constant pressure forming section. It is provided with a vent hole and a return air hole. The vent hole and the return air hole are connected to two other air supply pipes in the air supply rod for circulating gas cooling of the inner wall of the pipe.

[0008] In this embodiment, the polypropylene pipe is heated and then fed into the multi-stage temperature-controlled flaring section by a pipe drawing machine. The conical stepped structure of the expansion mold expands the pipe step by step. Simultaneously, different air passages in the air supply rod sequentially supply adjustable-pressure gas to each expansion hole, ensuring uniform expansion of the pipe in both the axial and radial directions. The number and length of the steps in the expansion mold can be adjusted according to the pipe material and thickness to ensure that the pipe expands to the predetermined size. During the expansion process, a temperature detection device monitors the temperature of the contact area between the expansion mold and the pipe in real time. If the temperature is too high, another air passage in the air supply rod will supply cooling gas to the circulating cooling channel and allow it to flow back, achieving active control of the mold temperature. This ensures that the pipe is always formed within a suitable temperature range, avoiding material performance degradation or uneven deformation due to overheating. After being flared through multiple stages, the pipe enters the constant pressure forming section. The air supply rod delivers a stable airflow to the constant pressure forming section and the moving pipe cavity through the air outlet gap. Since the pipe will contract along the constant pressure forming section after expansion, the gas forms a uniform air cushion in the gap between the inner wall of the pipe and the constant pressure forming section. This air cushion provides radial constraint and significantly reduces the friction between the pipe and the mold surface, making the pipe more uniformly stressed and more stable in shape during the stretching process, which is beneficial to improving the wall thickness consistency and surface quality. Finally, the pipe enters the cooling and shaping section. Another airflow path from the air supply rod leads to the vent, where cooling gas enters the gap between the pipe and the cooling and shaping section. After absorbing heat from the inner wall of the pipe, the gas returns to the gas circuit through the return air hole, achieving active circulating cooling of the pipe. This structure accelerates pipe shaping, reduces residual stress, and prevents subsequent deformation. This system achieves precise control of temperature, pressure and friction during the stretching and expansion of pipes through the synergistic effect of multi-stage temperature-controlled flaring, constant-pressure air cushion forming and cyclic cooling shaping. It significantly improves the dimensional accuracy, mechanical properties and surface quality of the pipes and is suitable for continuous production of high-performance plastic pipes, especially polypropylene pipes.

[0009] Furthermore, the multi-stage temperature-controlled flaring section, the constant pressure forming section, and the cooling and shaping section are connected in sequence by locking bolts; the air supply rod passes through the multi-stage temperature-controlled flaring section, the constant pressure forming section, and the cooling and shaping section in sequence, and its two ends are fixed by fastening bolts; the air supply rod has a hollow internal structure and is provided with multiple independent air supply pipelines.

[0010] Furthermore, inside the air supply rod, at the connection positions corresponding to each expansion hole, circulating cooling channel, air outlet gap, vent hole, and return air hole, a flow divider is respectively provided; the flow divider is provided with a vent connector that is sealed to the end of the corresponding air supply pipeline; the outer periphery of the flow divider is provided with an annular air supply groove; the expansion hole, circulating cooling channel, air outlet gap, vent hole, and return air hole are respectively connected to the air supply groove of the corresponding flow divider through radial channels opened in the wall of the expansion mold, constant pressure forming section, or cooling and shaping section; The temperature detection device and the circulating cooling channel are arranged in a ring in the radial direction of the multi-stage temperature control flare section, and are respectively connected to different air supply pipelines.

[0011] Furthermore, the discharge end of the multi-stage temperature-controlled flaring section is connected to a connecting plate, which is detachably connected to the end of the expansion mold by fastening screws; an annular stepped gap is formed between the connecting plate and the mating end face of the expansion mold; the expansion mold has multiple L-shaped air-expanding holes circumferentially opened near the stepped gap; the air-supplying end of the L-shaped air-expanding hole is connected to the corresponding air-supplying pipe in the air-supplying pull rod, and the other end opens as the air-exiting end on the vertical end face of the step at the end of the expansion mold.

[0012] Furthermore, the expansion holes and L-shaped air expansion holes on the expansion mold are each set to sixteen, and are evenly spaced in a ring along the circumference of the expansion mold. The expansion mold is made of a metal material with high thermal conductivity and high surface hardness.

[0013] Furthermore, the constant pressure forming section includes a forming tube, one end of which is detachably coaxially connected to the connecting plate by a fastening bolt; the outer ring of the connecting plate is evenly distributed with multiple air outlet channels; an annular air outlet gap is formed between the connecting plate and the outer mating surface of the end of the expansion mold; the air outlet gap is connected to the air outlet channel.

[0014] Furthermore, a locking disc is coaxially engaged at the discharge end of the forming tube; the locking disc has multiple bolt holes distributed circumferentially; the locking bolts pass through the bolt holes on the locking disc in sequence and connect with the corresponding threaded holes on the connecting plate, thereby securely clamping the forming tube between the locking disc and the connecting plate.

[0015] On the end face of the locking disc facing the connecting plate, and on the end face of the connecting plate facing the forming tube, a matching annular sealing step structure is provided respectively.

[0016] Furthermore, the outer diameter of the rear end of the forming tube is smaller than its outer diameter of the front end; the outer diameter of the rear end of the locking disc is larger than its outer diameter of the front end, forming an axial stepped structure; on the annular surface of the stepped front end of the locking disc, a plurality of L-shaped ventilation grooves are uniformly opened circumferentially; the stepped structure of the locking disc is also provided with the flow divider, the flow divider has an annular airflow distribution cavity, and the outlet of the airflow distribution cavity is connected to the inlet of each of the L-shaped ventilation grooves.

[0017] Furthermore, the cooling and shaping section includes a cooling pipe, one end of which is connected to the locking disc via an intermediate pipe; one end of the intermediate pipe is coaxially engaged within the rear stepped structure of the locking disc; and multiple vent holes are circumferentially formed on the wall of the intermediate pipe, corresponding to the engagement area with the locking disc.

[0018] Furthermore, a sealing tube is coaxially snapped to the other end of the cooling pipe; a plurality of return air holes are evenly distributed in a ring around the circumference of the sealing tube wall; and at least two sealing rings are provided axially at intervals in the connection area between the sealing tube and the cooling pipe.

[0019] The sealing tube has a through hole at the center of its end, and the end of the air supply rod passes through the through hole coaxially; the end of the sealing tube is locked to the end of the air supply rod by fastening bolts. A step is provided at the connection between the sealing pipe and the cooling pipe.

[0020] 3. Beneficial effects: Compared with the prior art, the technical solution provided by this invention has the following advantages: This invention features a rational design, integrating multi-stage temperature-controlled flaring, constant-pressure air cushion forming, and cyclic cooling shaping functions to achieve precise control of process parameters throughout the entire pipe stretching and expansion process. Its modular design and centrally integrated air supply rod ensure the alignment and rigid connection of each functional section, with centralized and controllable air paths, greatly improving equipment stability and maintenance convenience. It is particularly effective for the bidirectional stretching of polypropylene pipes, exhibiting excellent forming results.

[0021] Specifically, the multi-stage temperature-controlled flaring and zoned cooling design ensures uniform expansion of the pipe at the optimal temperature, avoiding overheating damage and uneven deformation; the air cushion support in the constant pressure forming section significantly reduces pipe movement friction and improves wall thickness consistency; the end guide air ring and shrinkage guidance design ensure a smooth transition from hot forming to cold setting. Ultimately, this system can efficiently produce high-quality pipes with precise dimensions, high roundness, low residual stress, and excellent mechanical properties.

[0022] It should be noted that the structures not described in this invention are not related to the design points and improvement directions of this invention, and are the same as or can be implemented using existing technologies, so they will not be elaborated here. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the internal structure of the present invention; Figure 3 For the present invention Figure 2 Enlarged schematic diagram of the structure at point A; Figure 4 For the present invention Figure 2 Enlarged schematic diagram of the structure at point B; Figure 5 For the present invention Figure 2 A magnified schematic diagram of the structure at point C.

[0024] Figure label: 1. Multi-stage temperature-controlled flaring section; 11. Expansion mold; 12. Expansion hole; 13. Temperature detection device; 14. Circulating cooling channel; 2. Constant pressure forming section; 21. Air outlet gap; 22. Forming tube; 23. Air outlet channel; 3. Cooling and shaping section; 31. Vent hole; 32. Return air hole; 33. Cooling tube; 34. Intermediate tube; 35. Sealing tube; 4. Air supply pull rod; 5. Flow divider; 6. Connecting plate; 61. Stepped gap; 62. L-shaped vent hole; 7. Locking plate; 71. L-shaped vent groove; 72. Airflow distribution chamber. Detailed Implementation

[0025] To facilitate understanding of the present invention, a more complete description of the invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the invention will be more thorough and complete.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "page," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and 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 this invention.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0028] In this invention, unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," "fixed," "provided with," and "located in" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0029] It should be noted that structures not described in this invention do not involve the design points and improvement directions of this invention, and can all be achieved using existing technologies known to those skilled in the art.

[0030] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0031] See attached document Figure 1-5 The red arrow in the diagram indicates the airflow direction. It describes an expansion system for bidirectional stretching of pipes, including... It includes a multi-stage temperature-controlled flaring section 1, a constant-pressure forming section 2, and a cooling and shaping section 3; The multi-stage temperature-controlled flaring section 1 includes an expansion mold 11, which gradually widens from the inlet end of the pipe to the outlet end, forming a conical stepped structure. Multiple spaced expansion holes 12 are arranged in a ring around the stepped portion of the expansion mold 11 for inflating the space between the pipe and the mold. A temperature detection device 13 is installed on the inner wall of the flaring section of the expansion mold 11, and a circulating cooling channel 14 is located beside the temperature detection device 13. An air supply rod 4 passes through the middle of the multi-stage temperature-controlled flaring section 1. The air supply rod 4 has a hollow structure and contains multiple air supply pipes, which are respectively connected to the circulating cooling channel 14 and each expansion hole 12. The constant pressure forming section 2 is detachably connected to the multi-stage temperature-controlled flaring section 1, forming a sealed cavity inside. An air outlet gap 21 is formed between the constant pressure forming section 2 and the multi-stage temperature-controlled flaring section 1. The outer diameter of the constant pressure forming section 2 is smaller than the outer diameter of the end of the multi-stage temperature-controlled flaring section 1. The air supply rod 4 passes through the constant pressure forming section 2, and the air outlet gap 21 blows air outward, thereby forming a stable upward airflow on the outside of the constant pressure forming section 2, reducing the frictional resistance when the pipe moves. The cooling and shaping section 3 is connected to the constant pressure forming section 2, and the air supply rod 4 passes through the cooling and shaping section 3 and is locked in place. The diameter of the cooling and shaping section 3 is smaller than that of the constant pressure forming section 2. It is provided with a vent hole 31 and a return air hole 32. The vent hole 31 and the return air hole 32 are connected to two other air supply pipes in the air supply rod 4 for circulating gas cooling of the inner wall of the pipe.

[0032] In this embodiment, the polypropylene pipe is heated and then fed into the multi-stage temperature-controlled flaring section 1 by a pipe drawing machine. The conical stepped structure of the expansion mold 11 expands the pipe step by step. At the same time, different air passages in the air supply rod 4 sequentially supply adjustable pressure gas to each expansion hole 12, so that the pipe expands uniformly in the axial and radial directions. The number and length of the steps of the expansion mold 11 can be adjusted according to the material and thickness of the pipe to ensure that the pipe expands to the predetermined size. During the expansion process, the temperature detection device 13 monitors the temperature of the contact area between the expansion mold 11 and the pipe in real time. If the temperature is too high, another air passage of the air supply rod 4 will deliver cooling gas to the circulating cooling channel 14 and return it, realizing active control of the mold temperature, so that the pipe is always formed within a suitable temperature range, avoiding the degradation of material properties or uneven deformation due to overheating. After being flared through multiple stages, the pipe enters the constant pressure forming section 2. The air supply rod 4 delivers a stable airflow to the constant pressure forming section 2 and the moving pipe cavity through the air outlet gap 21. Since the pipe will contract along the constant pressure forming section 2 after expansion, the gas forms a uniform air cushion in the gap between the inner wall of the pipe and the constant pressure forming section 2. This air cushion provides radial constraint and significantly reduces the friction between the pipe and the mold surface, making the pipe more uniformly stressed and more stable in shape during the stretching process, which is beneficial to improving the wall thickness consistency and surface quality. Finally, the pipe enters the cooling and shaping section 3. Another airflow path from the air supply rod 4 leads to the vent 31. Cooling gas enters the gap between the pipe and the cooling and shaping section 3 through the vent 31, absorbs heat from the inner wall of the pipe, and then returns to the gas circuit through the return air hole 32, achieving active circulating cooling of the pipe. This structure accelerates pipe shaping, reduces residual stress, and prevents subsequent deformation. This system achieves precise control of temperature, pressure and friction during the stretching and expansion of pipes through the synergistic effect of multi-stage temperature-controlled flaring, constant-pressure air cushion forming and cyclic cooling shaping. It significantly improves the dimensional accuracy, mechanical properties and surface quality of the pipes and is suitable for continuous production of high-performance plastic pipes, especially polypropylene pipes.

[0033] The multi-stage temperature-controlled flaring section 1, constant pressure forming section 2, and cooling and shaping section 3 are sequentially connected by locking bolts. The air supply rod 4 sequentially passes through the multi-stage temperature-controlled flaring section 1, constant pressure forming section 2, and cooling and shaping section 3, and is fixed at both ends by fastening bolts. The air supply rod 4 has a hollow internal structure and is equipped with multiple independent air supply pipelines. In this embodiment, the functional sections of the system are connected by locking bolts, realizing a modular assembly method. This design allows the multi-stage temperature-controlled flaring section 1, constant pressure forming section 2, and cooling and shaping section 3 to be firmly combined into a rigid whole, ensuring the straightness and coaxiality of the path traversed by the pipe during the stretching and expansion process, providing a basic structural guarantee for the uniform forming of the pipe. At the same time, the modular connection facilitates the replacement or adjustment of specific functional sections according to the needs of producing different specifications of pipes, improving the applicability and maintenance convenience of the equipment.

[0034] As a core functional component, the air delivery lever 4 runs through and connects all functional sections, with both ends secured by fastening bolts. This design allows the air delivery lever 4 to not only deliver multiple airflows within the system but also to serve as a central frame for securing and positioning, further enhancing the structural stability and integrity of the entire expansion system and effectively preventing misalignment or loosening that may occur between sections during long-term operation.

[0035] The air supply rod 4 has a hollow internal structure and integrates multiple independent air supply pipelines. These pipelines converge into the air supply rod 4 from the feed end opening of the multi-stage temperature-controlled flaring section 1 and extend to the various holes that require air supply. Combined with the modular connection of locking bolts and the integrated multi-functional air supply rod 4 structure, this system ensures the overall structural rigidity and precision while achieving efficient, reliable, and centralized control of the air supply, which is beneficial to improving the stability, repeatability, and production efficiency of the pipe expansion process.

[0036] Inside the air supply rod 4, at the connection points corresponding to the expansion holes 12, circulating cooling channels 14, air outlet gaps 21, vent holes 31, and return air holes 32, a distributor 5 is provided. Each distributor 5 has a vent connector that is sealed to the end of the corresponding air supply pipeline. An annular air delivery groove is provided on the outer periphery of the distributor 5. The expansion holes 12, circulating cooling channels 14, air outlet gaps 21, vent holes 31, and return air holes 32 are respectively connected to the air delivery grooves of the corresponding distributor 5 through radial channels opened in the walls of the expansion mold 11, constant pressure forming section 2, or cooling and shaping section 3. In this embodiment, the distributor 5 is a columnar structure, fixedly installed on the inner wall of the air supply rod 4. Each distributor 5 corresponds to an independent gas function point, such as the inlet of an expansion hole 12 or a cooling channel. One end of the distributor 5 is provided with a vent connector, which is sealed to the outlet end of the gas supply line extending to that location by means of a thread or quick-connect method, thereby ensuring that gas from a specific gas supply line can be introduced into the distributor 5 without leakage.

[0037] The key feature of the distributor 5 is that an annular gas delivery groove is machined on its outer circumference. This gas delivery groove continuously surrounds the distributor 5 circumferentially, forming a pressure equalization chamber. When the distributor 5 is installed in place, its outer gas delivery groove is directly opposite a pre-machined radial hole in the functional section wall. Gas entering the distributor 5 from the gas supply line through the vent connector first flows into the annular gas delivery groove, and then is uniformly and stably delivered to the target hole through the radial connecting channel, such as the expansion hole 12 leading to the inner cavity of the pipe, or the circulating cooling channel 14 leading to the inside of the mold. The temperature detection device 13 and the circulating cooling channel 14 are arranged in a ring shape in the radial direction of the multi-stage temperature-controlled flaring section 1, and are respectively connected to different air supply pipelines. In this embodiment, there are multiple temperature detection devices 13 and their corresponding circulating cooling channels 14, which are arranged at intervals along the circumference of the expansion mold 11. As a preferred embodiment, there are four temperature detection devices 13 and circulating cooling channels 14, which are distributed in a roughly cross-shaped structure on the inner wall circumference of the expansion mold 11, with one set located at the top in the vertical direction.

[0038] This arrangement is designed based on a thorough understanding of the thermal characteristics of the pipe during actual tensile expansion. Due to the influence of factors such as heating devices, ambient heat dissipation, and the weight of the pipe itself, the actual temperature of the pipe at different points in contact with the mold is not completely uniform under the combined effects of axial tension and radial expansion. Specifically, the temperature of the pipe area at the top vertically tends to be higher. Four temperature detection devices 13 can independently and in real time monitor the temperature of at least four key points around the expansion mold 11, especially capturing the temperature difference that may exist between the top and bottom. These real-time temperature data form the basis for accurate evaluation and closed-loop control of the circumferential heating uniformity of the pipe. The distributor 5 at this location is divided into four arc-shaped ends, each connected to a different air supply pipeline through two circulation connectors. Each circulating cooling channel 14 is connected to the air source through an independent distributor 5 and air supply pipeline, and its cooling airflow and flow rate can be independently controlled. When the temperature detection device 13 located at the top detects that the mold temperature in this area exceeds the preset optimal process range, the control system can immediately instruct the top circulating cooling channel 14 associated with this detection point to introduce or increase the flow rate of cooling gas. The cooling gas flows through the channel inside the mold in this area, quickly carrying away the excess heat, thereby achieving rapid and precise cooling of the overheated area.

[0039] The discharge end of the multi-stage temperature-controlled flaring section 1 is connected to a connecting plate 6, which is detachably connected to the end of the expansion mold 11 by fastening screws. An annular stepped gap 61 is formed between the connecting plate 6 and the mating end face of the expansion mold 11. The expansion mold 11 has multiple L-shaped venting holes 62 circumferentially opened near the stepped gap 61. The air supply end of the L-shaped venting hole 62 is connected to the corresponding air supply pipe in the air supply pull rod 4, and the other end opens as the air outlet at the vertical end face of the step at the end of the expansion mold 11. In this embodiment, the connecting plate 6 is an independent connecting component, fixed to the end of the expansion mold 11 by fastening screws. This design not only realizes the modular connection between the multi-stage temperature-controlled flaring section 1 and the subsequent constant pressure forming section 2, facilitating assembly and maintenance, but more importantly, a precise annular gap with a stepped cross-section is formed between its mating surface and the expansion mold 11.

[0040] The stepped slit 61 works in conjunction with the L-shaped vent 62 located at the end of the expansion mold 11. The main body of the L-shaped vent 62 is located inside the expansion mold 11, and its path is L-shaped: one arm extends axially along the mold and connects to the final stage air supply line within the air supply rod 4 via a corresponding distributor 5 to introduce pressurized gas; the other arm turns radially or obliquely along the mold, and its outlet opening is precisely located on the vertical end face of the last step of the expansion mold 11, that is, the annular end face directly adjacent to the stepped slit 61. When the tube reaches the end of the expansion mold 11 after undergoing multiple stages of expansion, the pressurized gas from the air supply rod 4 is ejected from the vertical end face opening of the L-shaped vent 62. The gas then enters the annular stepped slit 61 area enclosed by the vertical end face, the inner wall of the tube, and the inner wall of the connecting plate 6. The local air cushion formed here provides uniform radial gas support force to the end area of ​​the tube. This force helps the pipe maintain its expanded size and shape in the final stage before it leaves the mold constraint, preventing end shrinkage or deformation due to material elastic recovery or stress release. This ensures the dimensional accuracy and shape integrity of the transition area between the flared section and the subsequent straight pipe section. The gas ejected from the stepped gap 61 and the L-shaped vent 62 together constitutes a dynamic sealing and buffering mechanism. The continuously flowing gas creates a positive pressure environment in the gap, effectively blocking external air interference or abnormal internal heat loss, providing a stable microenvironment for the end forming area. At the same time, this airflow buffer layer smooths the transition of the pipe from the surface of the expansion mold 11 to the inner surface of the connecting plate 6, reducing the risk of local friction and scratches during pipe movement.

[0041] The expansion mold 11 has sixteen expansion holes 12 and sixteen L-shaped expansion holes 62, which are evenly spaced in a ring along the circumference of the expansion mold 11. In this embodiment, the number of gas application points is increased to sixteen and strictly evenly distributed, so that compressed gas can act on the inner wall of the pipe from more positions at equal angular intervals. This greatly improves the continuity of gas pressure distribution in the circumferential direction of the pipe and can effectively offset the differences in local deformation resistance that may be caused by micro-inhomogeneity of pipe wall thickness, material anisotropy, or differences in initial heating. As a result, the circumferential stress field experienced by the pipe during radial expansion is extremely uniform, which fundamentally promotes the improvement of pipe roundness and ensures that the cross-section after expansion is a perfect circle, avoiding elliptical or irregular deformation. The expansion holes 12 and L-shaped expansion holes 62 can also be set to other numbers according to the pipe specifications, which will not be elaborated here. The expansion mold 11 is made of a metal material with high thermal conductivity and high surface hardness. In this embodiment, the expansion mold 11 is preferably made of heat-treated aluminum alloy or alloy steel. This material selection is an optimized design based on the specific requirements of the tube biaxial stretching process for mold performance. Using a metal with high thermal conductivity allows the mold itself to become an efficient heat transfer medium. When the temperature detection device 13 detects that the local temperature of the mold deviates from the set value, the mold can quickly transfer the cooling medium in the circulating cooling channel 14 to the entire contact surface through its good thermal conductivity, or quickly dissipate excess heat, thereby achieving rapid response and uniform distribution of the working surface temperature of the mold. At the same time, the high surface hardness ensures that the working surface of the mold can resist wear, crushing and plastic deformation when subjected to long-term thermal friction, expansion stress and potential scratches of the tube, maintaining dimensional accuracy and surface finish.

[0042] The constant pressure forming section 2 includes a forming tube 22, one end of which is detachably coaxially connected to the connecting plate 6 via a fastening bolt. Multiple air outlet channels 23 are evenly distributed around the outer ring of the connecting plate 6. An annular air outlet gap 21 is formed between the outer mating surface of the connecting plate 6 and the end of the expansion mold 11. The air outlet gap 21 is connected to the air outlet channels 23. In this embodiment, the constant pressure forming section 2, through its specific connection method with the connecting plate 6 and its gas passage design, achieves a smooth transition from the expansion section to the shaping section and provides constant pressure support. Constant pressure gas from the corresponding air supply pipe inside the air supply rod 4 is first delivered to each air outlet channel 23 on the connecting plate 6. Because the air outlet channels 23 are evenly distributed around the outer ring of the connecting plate 6, the gas is distributed equally and at equal pressure to all points on the circumference. Subsequently, the gas converges at the annular air outlet gap 21. This design integrates multiple discrete point air sources into a continuous, uniform annular surface air source before entering the forming area. The uniform gas flows out from the annular outlet slit 21 and immediately enters a wedge-shaped or parallel gap region formed by the inner wall of the forming tube 22, the flared outer wall of the tube, and the end face of the connecting plate 6. The continuously flowing gas establishes and maintains a stable positive pressure air cushion layer within this gap. This air cushion layer completely separates the moving outer wall of the tube from the stationary inner wall of the forming tube 22, transforming the sliding friction between solids into shear friction within the fluid, thereby significantly reducing the resistance to the tube's forward movement. This ensures smooth movement of the tube in the constant pressure section, avoiding surface scratches, tensile stress fluctuations, or tube stagnation caused by friction. The uniform annular air cushion not only provides lubrication, but its own uniform radial pressure also provides soft support and shaping for the outer wall of the tube. It can balance the slight springback tendency of the pipe due to the material memory effect, helping the pipe to achieve initial stability and maintain its size and shape before entering the cooling and shaping section 3 after leaving the expansion mold 11, preventing deformation or wrinkles, and laying the foundation for subsequent precise cooling and shaping. The bolted connection between the plate 6 and the forming pipe 22 ensures the structural strength and airtightness of this section, preventing gas leakage and pressure loss. The precise design of the air outlet gap 21 allows the gas to be smoothly and without turbulence introduced into the forming area, realizing a smooth and impact-free transition from the "active pressure expansion" mode of the multi-stage expansion mold 11 to the "constant pressure air cushion support" mode of the constant pressure forming section 2, which is beneficial to the stability of the entire stretching process.

[0043] The discharge end of the forming tube 22 is coaxially engaged with a locking disc 7. The locking disc 7 has multiple circumferentially distributed bolt holes. Locking bolts pass sequentially through the bolt holes on the locking disc 7 and connect to the corresponding threaded holes on the connecting plate 6, thereby securely clamping the forming tube 22 between the locking disc 7 and the connecting plate 6. In this embodiment, the locking disc 7 is an independent annular disc-shaped component, with its inner hole coaxially engaged with the outer diameter of the discharge end of the forming tube 22 using a tight fit or stepped bayonet joint for pre-positioning. The locking disc 7 has four through bolt holes evenly distributed circumferentially. During assembly, the feed end of the forming tube 22 is first fitted onto the corresponding boss on the connecting plate 6 for initial alignment, and then the locking disc 7 is engaged with the discharge end of the forming tube 22. Subsequently, a set of locking bolts is used, sequentially passing through the bolt holes on the locking disc 7 and screwed into the corresponding threaded holes on the outer circumference of the connecting plate 6. By uniformly tightening these locking bolts, the locking disc 7 and the connecting plate 6 generate opposing axial clamping forces, thereby firmly pressing and sealing the forming tube 22 between them. This snap-fit ​​and bolt-clamping structure breaks down the installation of the forming tube 22 into simple snap-fit ​​and bolt-tightening actions, making the assembly process convenient and efficient. The snap-fit ​​structure between the locking disc 7 and the discharge end of the forming tube 22, as well as the positioning boss at the feed end of the connecting plate 6, together ensure the precise positioning of the forming tube 22 in the radial and axial directions, guaranteeing the coaxiality between the inner wall of the forming tube 22 and the expansion mold 11 and the subsequent cooling and shaping section 3. This is crucial for the smooth and straight passage of the tube through each functional section, directly affecting the forming straightness and wall thickness uniformity of the tube. This design makes the forming tube 22 an independent and easily disassembled module. When it is necessary to clean the inner wall of the forming tube 22, check for wear, or replace the forming tube 22 with a different outer diameter for the production of tubes with different outer diameters, simply loosen the locking bolts to remove the entire forming tube 22 together with the locking disc 7 from the connecting plate 6. The operation is simple and does not require disassembling the entire system or complex positioning adjustments, which significantly reduces maintenance time and labor intensity, and improves equipment utilization and production flexibility.

[0044] On the end faces of the locking disc 7 and the connecting plate 6, and on the end faces of the connecting plate 6 and the forming tube 22, matching annular sealing step structures are respectively provided. In this embodiment, the sealing step structure is a key design to ensure the airtightness and coaxiality of the connection of the constant pressure forming section 2. When the locking bolt is tightened, the mating steps on the locking disc 7 and the connecting plate 6 first engage with each other. This engagement action achieves precise radial positioning, ensuring that the locking disc 7 and the connecting plate 6 are strictly coaxial, thereby ensuring that the forming tube 22 clamped therein is aligned with the system centerline. At the same time, the mating surfaces of the steps form the first metal-metal contact sealing band under axial clamping force, effectively preventing gas leakage along this path. Similarly, the mating steps between the connecting plate 6 and the feed end of the forming tube 22 also play the same positioning and initial sealing role. In practical applications, to further ensure absolute airtightness, flexible sealing rings, such as O-rings, may be placed at appropriate positions on the mating surfaces of the steps. The precise and robust stepped structure provides these seals with uniform mounting grooves or clamping surfaces that are less prone to misalignment, preventing shearing or wear of the seals caused by component misalignment, extending their service life, and enhancing the overall reliability of the seal.

[0045] The outer diameter of the rear end of the forming tube 22 is smaller than that of its front end; the outer diameter of the rear end of the locking disc 7 is larger than that of its front end, forming an axial stepped structure; multiple L-shaped ventilation grooves 71 are evenly distributed circumferentially on the annular surface of the stepped front end of the locking disc 7; the flow divider 5 is also provided at the stepped structure of the locking disc 7, the flow divider 5 has an annular airflow distribution chamber 72, and the outlet of the airflow distribution chamber 72 is connected to the inlet of each L-shaped ventilation groove 71. In this embodiment, although the tube is supported by an air cushion in the constant pressure forming section 2, it has already begun to cool naturally, and the material will undergo a slight thermal shrinkage. If it immediately enters the straight cylinder section with a constant outer diameter, the shrinking outer wall of the tube may come into contact with the inner wall of the mold, causing scratches or deformation. In this design, the slight reduction in the outer diameter of the rear end of the forming tube 22 is exactly matched with the expected cooling shrinkage of the tube at this stage. This provides a "guided" shrinkage space for the pipe, allowing it to remain in a non-contact state with the mold during shrinkage, ensuring a smooth transition and effectively avoiding wrinkles or dimensional fluctuations that may occur due to uneven free shrinkage. This creates stable initial conditions for subsequent precise cooling and shaping. The distributor 5 integrated into the stepped structure of the locking disc 7 and the L-shaped vent groove 71 constitute an independent and controllable end gas support unit. As the end of the pipe is about to leave the constant pressure forming section 2, the controlled gas from the gas delivery rod 4 is evenly distributed by the distributor 5 and ejected from each L-shaped vent groove 71. This gas forms a localized, flexible air ring between the inner wall of the pipe end and the inlet of the cooling and shaping section 3. Its functions are twofold: First, it provides radial pneumatic support for the pipe ends, which become stiffer due to cooling, preventing them from collapsing or deforming elliptically under their own weight or traction force due to the loss of support from the front mold. Second, this air ring acts as a "pneumatic guide sleeve," gently guiding the pipe end smoothly and centered into the cooling and shaping section 3, which has a smaller outer diameter and lower temperature, achieving a soft transition at the physical interface and avoiding mechanical impact or jamming. This synergistic design effectively solves the technical difficulties of the pipe at the transition point from hot forming to cold shaping. Through structural dimension compensation and active airflow intervention, it offsets the negative impacts of material phase change and temperature variation, ensuring that the pipe can continuously and stably transition from the expansion forming stage to the cooling and shaping stage under full traction. This significantly improves the continuity and stability of production and directly enhances the batch consistency of products, especially the dimensions and roundness of the pipe ends.

[0046] The cooling and shaping section 3 includes a cooling pipe 33, one end of which is connected to the locking disc 7 via an intermediate pipe 34. One end of the intermediate pipe 34 is coaxially engaged within the stepped structure at the rear end of the locking disc 7. Multiple vent holes 31 are circumferentially arranged on the wall of the intermediate pipe 34, corresponding to the engagement area with the locking disc 7. In this embodiment, the cooling gas from the distributor 5 within the locking disc 7 is guided by the L-shaped vent groove 71 and then collects in the annular chamber formed by the engagement of the locking disc 7 and the intermediate pipe 34. Subsequently, the gas is uniformly injected into the annular cooling channel formed by the inner wall of the cooling pipe 33, the inner wall of the intermediate pipe 34, and the outer wall of the pipe through the multiple vent holes 31 distributed annularly on the circumferential wall of the intermediate pipe 34. The uniform distribution of the vent holes 31 ensures that the cooling gas enters the cooling area synchronously and in equal amounts along the 360-degree circumference of the pipe, providing the pipe with uniform initial cooling conditions without eccentric loading or dead angles. This is crucial for ensuring the roundness and straightness of the pipe after cooling. An independent intermediate pipe 34 is used for connection, physically separating the locking disc 7, which undertakes the high-temperature forming transition function, from the cooling pipe 33, which undertakes the main cooling function. This modular design allows the cooling pipe 33 to be replaced or maintained independently according to the requirements of different products for cooling length, efficiency, or surface quality, without disturbing the constant pressure forming section 2 at the front end. By introducing the intermediate pipe 34 with annular vent holes 31 into the cooling and shaping section 3 and precisely engaging it with the locking disc 7, the system constructs an efficient, uniform, and reliably sealed cooling gas injection interface.

[0047] The other end of the cooling pipe 33 is coaxially connected to a sealing pipe 35. Multiple return air holes 32 are evenly distributed circumferentially on the wall of the sealing pipe 35. Furthermore, at least two sealing rings are axially spaced at intervals in the connection area between the sealing pipe 35 and the cooling pipe 33. In this embodiment, the sealing pipe 35 is a tubular component with a connecting structure at one end, and its end is coaxially connected and secured to the end of the cooling pipe 33 through a precise groove or flange structure, forming a rigid connection. A series of return air holes 32 are evenly distributed circumferentially in the area of ​​the sealing pipe 35 near the cooling pipe 33. Crucially, at least two annular sealing rings are axially spaced at intervals on the mating surface between the inner walls of the sealing pipe 35 and the cooling pipe 33. These sealing rings are typically installed in corresponding annular grooves on the outer wall of the sealing pipe 35. The heated gas that has completed heat exchange with the heat pipe material within the cooling pipe 33 flows to the end of the cooling section. The annularly distributed return air holes 32 on the sealing tube 35 constitute the total outlet for these hot air flows. The evenly distributed holes ensure that the hot air flows can be drawn and collected synchronously and smoothly from all directions of the tube circumference, avoiding uneven circumferential cooling rates or deformation of the tube caused by unilateral air extraction. The collected hot air flows are then guided through the internal cavity of the sealing tube 35 into the return pipe in the air supply rod 4, thus completing a complete cooling cycle.

[0048] The sealing tube 35 has a through hole at its center, through which the end of the air supply rod 4 coaxially passes. The end of the sealing tube 35 is locked to the end of the air supply rod 4 by fastening bolts. In this embodiment, the sealing tube 35 has a through hole machined at the center of its end face, the diameter of which matches the outer diameter of the end of the air supply rod 4, and it typically has a guide or positioning structure. The end of the air supply rod 4 passes sequentially through a multi-stage temperature-controlled flaring section 1, a constant-pressure forming section 2, and a cooling and shaping section 3, and finally coaxially passes through the through hole of the sealing tube 35. Corresponding threaded holes or flange structures are machined at the end of the air supply rod 4 or a specially designed connector, and at the end of the sealing tube 35, respectively. A set of circumferentially distributed fastening bolts tightens and fixes the two together. This connection typically also includes gaskets or seals to ensure the airtightness of the mating surfaces. The connection between the sealing pipe 35 and the cooling pipe 33 is provided with a step to achieve a sealing effect.

[0049] The above-described embodiments are merely illustrative of certain implementations of the present invention, and are described in a relatively specific and detailed manner. However, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. An expansion system for use in the biaxial stretching of pipe, characterized by: Comprising The multi-stage temperature control flared section (1) comprises an expansion die (11), and a plurality of expansion holes (12) are arranged at intervals around the step position of the expansion die (11) and used for inflating and expanding between the pipe and the die. The inner wall of the flared section of the expansion die (11) is provided with a temperature detection device (13), and a circulating cooling channel (14) is arranged beside the temperature detection device (13); a gas feeding pull rod (4) penetrates the middle of the multi-stage temperature control flared section (1), the gas feeding pull rod (4) is internally provided with a plurality of gas feeding pipelines, and the gas feeding pipelines are respectively connected with the circulating cooling channel (14) and each expansion hole (12); The constant pressure forming section (2) is detachably connected with the multi-stage temperature control flared section (1), and an air outlet gap (21) is formed between the constant pressure forming section (2) and the multi-stage temperature control flared section (1); the outer diameter of the constant pressure forming section (2) is smaller than that of the tail end of the multi-stage temperature control flared section (1); and the gas feeding pull rod (4) penetrates the constant pressure forming section (2); The cooling and shaping section (3) is connected with the constant pressure forming section (2), the gas feeding pull rod (4) penetrates the cooling and shaping section (3) and is locked and connected; the diameter of the cooling and shaping section (3) is smaller than that of the constant pressure forming section (2), and the cooling and shaping section (3) is provided with a gas permeation hole (31) and a gas return hole (32) and used for circulating gas cooling of the inner wall of the pipe. The multi-stage temperature control flared section (1), the constant pressure forming section (2) and the cooling and shaping section (3) are sequentially connected through locking bolts; the gas feeding pull rod (4) penetrates the multi-stage temperature control flared section (1), the constant pressure forming section (2) and the cooling and shaping section (3) in sequence, and both ends of the gas feeding pull rod (4) are fixed through fastening bolts; the gas feeding pull rod (4) is internally provided with a hollow structure and a plurality of mutually independent gas feeding pipelines.

2. An expansion system for use in the biaxial stretching of a tube according to claim 1, characterized in that: Corresponding to the connection positions of each expansion hole (12), the circulating cooling channel (14), the air outlet gap (21), the gas permeation hole (31) and the gas return hole (32), the gas feeding pull rod (4) is internally provided with a flow divider (5); the flow divider (5) is provided with an air inlet joint in sealed connection with the end of the corresponding gas feeding pipeline; the flow divider (5) is provided with an annular gas conveying groove; and the expansion hole (12), the circulating cooling channel (14), the air outlet gap (21), the gas permeation hole (31) and the gas return hole (32) are respectively connected with the gas conveying groove of the corresponding flow divider (5) through radial channels formed in the wall of the expansion die (11), the constant pressure forming section (2) or the cooling and shaping section (3).

3. An expansion system for use in the biaxial stretching of a tube as defined in claim 1, characterized in that: The temperature detection device (13) and the circulating cooling channel (14) are annularly distributed in the radial direction of the multi-stage temperature control flared section (1) and respectively connected with different gas feeding pipelines. ​ 4. An expansion system for use in the biaxial stretching of a tube according to claim 3, characterized in that: The multi-stage temperature control expansion section (1) is connected with a combination plate (6) at the discharge end, the combination plate (6) is detachably connected with the end of the expansion die (11) through fastening screws; an annular stepped gap (61) is formed between the combination plate (6) and the abutting end face of the expansion die (11); a plurality of L-shaped air expansion holes (62) are annularly and circumferentially formed in the expansion die (11) at the position adjacent to the stepped gap (61); the air supply end of the L-shaped air expansion hole (62) is communicated with the corresponding air supply pipeline in the air supply pull rod (4), and the other end is opened as an air outlet on the vertical end face of the end step of the expansion die (11).

5. An expansion system for use in the biaxial stretching of a tube according to claim 4, characterized in that: The expansion holes (12) and the L-shaped air expansion holes (62) on the expansion die (11) are respectively provided as sixteen, and are annularly and circumferentially uniformly distributed; The expansion die (11) is made of a metal material with high thermal conductivity and high surface hardness.

6. An expansion system for use in the biaxial stretching of a tube according to claim 5, characterized in that: The constant pressure forming section (2) comprises a forming pipe (22), one end of the forming pipe (22) is coaxially and detachably connected with the combination plate (6) through a fastening bolt; a plurality of air outlet channels (23) are uniformly distributed on the outer ring of the combination plate (6); an annular air outlet gap (21) is formed between the outer side abutting surface of the combination plate (6) and the end of the expansion die (11); the air outlet gap (21) is communicated with the air outlet channel (23).

7. An expansion system for use in the biaxial stretching of a tube according to claim 6, characterized in that: The discharge end of the forming pipe (22) is coaxially clamped with a locking disc (7); a plurality of bolt holes are formed on the locking disc (7) in the circumferential direction; locking bolts are connected with corresponding threaded holes on the combination plate (6) in sequence through the bolt holes on the locking disc (7), so that the forming pipe (22) is tightly clamped between the locking disc (7) and the combination plate (6); The end faces of the locking disc (7) and the combination plate (6) facing each other, and the end faces of the combination plate (6) and the forming pipe (22) facing each other are respectively provided with matching annular sealing step structures.

8. An expansion system for use in the biaxial stretching of a tube according to claim 7, characterized in that: The rear end outer diameter of the forming pipe (22) is smaller than the front end outer diameter; the rear end outer diameter of the locking disc (7) is larger than the front end outer diameter, forming an axial stepped structure; a plurality of L-shaped air permeable grooves (71) are uniformly formed on the circumferential surface of the front end step of the locking disc (7); the stepped structure of the locking disc (7) is also provided with the flow divider (5), the flow divider (5) has an annular air flow distribution cavity (72), and the outlet of the air flow distribution cavity (72) is communicated with the inlet of each L-shaped air permeable groove (71).

9. An expansion system for use in the biaxial stretching of a tube according to claim 8, characterized in that: The cooling and shaping section (3) comprises a cooling pipe (33), one end of the cooling pipe (33) is connected with the locking disc (7) through an intermediate pipe (34); one end of the intermediate pipe (34) is coaxially clamped in the rear end stepped structure of the locking disc (7); a plurality of air permeable holes (31) are annularly and circumferentially formed in the pipe wall of the intermediate pipe (34) corresponding to the clamping area of the intermediate pipe (34) and the locking disc (7).

10. A pipe expansion system for bi-directional stretching of the pipe according to claim 9, characterized in that: The other end of the cooling pipe (33) is coaxially clamped with a sealing pipe (35); a plurality of the gas return holes (32) are uniformly arranged on the pipe wall of the sealing pipe (35) along the circumferential direction; and at least two sealing rings are arranged along the axial direction at the connection area of the sealing pipe (35) and the cooling pipe (33); A through hole is arranged at the center of the end of the sealing pipe (35), and the end of the air feeding pull rod (4) passes through the through hole coaxially; the end of the sealing pipe (35) is locked and installed with the end of the air feeding pull rod (4) through fastening bolts; A step is arranged at the connection area of the sealing pipe (35) and the cooling pipe (33).

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