Plastic pipe heating and bending process based on expansion inner hole

Abstract

The invention relates to a plastic pipe heating and bending process based on an expanded inner hole, which is suitable for processing large-diameter plastic pipes (with the pipe diameter of 20-200mm) such as PVC (polyvinyl chloride), PE (polyethylene), PPR (polypropylene random) and the like, and solves the problems that the large-diameter plastic pipes are easy to deform when being bent and depend on elbow connection in the traditional process. The process comprises the following steps: automatically conveying a plastic pipe to a heating area according to a step pitch by feeding rollers driven by an upper servo motor and a lower servo motor, and heating a to-be-bent part (80-150 DEG C) by a heating pipe; then the inflatable pipe / hydraulic pipe in the pipe is inflated through an air pipe, so that the inflatable pipe / hydraulic pipe is expanded to be attached to the inner wall of the pipe (the expansion difference value is 0.5-2 mm) to form stable support; the plastic pipe is pushed to a hot bending die (the gap between the plastic pipe and the outer wall ranges from 0.1 mm to 0.3 mm), and the plastic pipe is guided to be bent by 30 degrees to 180 degrees; and finally, the inflatable tube is deflated and contracted, and multi-section bending (spiral shape, L shape and the like) is realized by repeating the operation. The process effectively prevents bending deformation, ensures smoothness of the inner wall and accurate angle (the error is less than or equal to + / -2 degrees), reduces interface leakage, and is suitable for complex pipeline layout of water supply and drainage, electric energy storage and the like.

Description

Technical Field

[0001] The invention relates to the technical field of plastic processing, in particular to a plastic pipe heating bending process based on expanding inner holes. Background Art

[0002] In the field of traditional plastic pipe processing, for large-diameter plastic pipes made of materials such as PVC, PE, and PPR (pipe diameter ≥ 20mm), especially in scenarios where arbitrary angle bending is required (such as bend connections in water supply and drainage systems and fluid pipeline layouts for electrical energy storage devices), existing technologies face significant technical bottlenecks: On the one hand, due to the strong material rigidity and limited thermoplastic deformation capacity of large-diameter plastic pipes, the traditional cold bending process can easily lead to pipe wall wrinkles, outer wall depressions, or fractures, which cannot meet the requirements of use; on the other hand, even if a heated bending process is used, the inner hole of the plastic pipe lacks effective support, and the inner hole is prone to collapse due to stress concentration during the bending process, causing deformation at the bend, ultimately affecting the sealing and reliability of the pipeline fluid connection. Therefore, in traditional technology, the bending processing of large-diameter plastic pipes usually relies on prefabricated elbow connections, but elbow connections have problems such as multiple interfaces, complex construction, and high leakage risks. The leakage risks are particularly prominent in scenarios with high pressure or frequent bending.

[0003] Furthermore, existing plastic pipe bending processes typically rely on single, fixed-angle bends, making it difficult to achieve multiple, continuous bends (such as spiral and L-shaped combinations). Furthermore, the consistency of different bend angles cannot be guaranteed (the angle error often exceeds ±5°), making it unsuitable for complex pipeline layouts. Consequently, a process technology is urgently needed that can achieve the free bending of large-diameter plastic pipes at any angle, maintain deformation after bending, and be suitable for complex pipeline connections. Summary of the Invention

[0004] The purpose of the present invention is to provide a plastic pipe heating bending process based on an expanded inner hole, which solves the problem that large-diameter plastic pipes are difficult to bend freely and are easy to deform. It realizes bending at any angle (30°-180°) with a smooth inner wall and a flat outer wall without deformation, reduces the risk of leakage at the pipeline interface, and is suitable for complex pipeline layouts.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a plastic pipe heating bending process based on expansion inner hole, comprising the following steps: a. The plastic pipe to be bent is transported to the heating area in the horizontal direction by feeding rollers driven by servo motors arranged in parallel above and below, and the feeding step is automatically matched by the servo motor according to the bending pitch of the plastic pipe; b. The part of the pipe body to be bent is heated by a heating pipe extending along the outside of the plastic pipe in the form of a dotted line, and the heating area covers at least 80% of the part to be bent. The heating temperature is set to 80-150°C according to the material of the plastic pipe (PVC, PE, PPR, etc.) to soften the pipe body; c. The air expansion tube / hydraulic tube horizontally embedded in the inner hole of the plastic pipe is inflated with air or hydraulic oil, and the expansion pressure is controlled by the air pipe (or hydraulic pipe) and the air pipe joint laterally connected to the left side of the plastic pipe. Apply force to expand the inflatable tube / hydraulic tube and make it fit tightly against the inner wall of the plastic tube (the difference between the expanded diameter and the inner diameter of the plastic tube during expansion is 0.5-2mm), forming a stable expanded inner hole; d. Push the expanded plastic tube to the bending area of ​​the hot bending die embedded in the right square area (the gap between the inner side of the hot bending die and the outer wall of the plastic tube is 0.1-0.3mm), and complete the bending of a predetermined angle of 30°-180° through the right-angle bending guiding effect of the hot bending die; e. After the bending is completed, seal the right end of the inflatable tube / hydraulic tube with a plug, and release the gas or hydraulic oil in the inflatable tube / hydraulic tube to shrink and separate from the inner wall of the plastic tube; f. Repeat steps a and e until multiple sections of the plastic tube are bent (each section has a bending angle of 30°-180°), ultimately forming a spiral, L-shaped, or any combination of bent structures.

[0006] Claim 1, the core process step of this invention, fully defines the entire process from feeding, heating, expansion, and bending to a multi-stage cycle, providing the fundamental technical solution for achieving the unrestricted bending of large-diameter plastic tubes without deformation. The coordinated action of these components (feed rollers, heating tubes, expansion tubes, and hot bending dies, among others) addresses the traditional issues of large-diameter plastic tubes being prone to deformation and unable to be processed continuously in multiple stages.

[0007] Furthermore, the feeding rollers are two rollers arranged in parallel up and down, which are driven to rotate by a servo motor. The surface of the rollers is provided with anti-slip grooves for clamping and conveying plastic tubes. The step distance of the automatic feeding of the servo motor matches the bending pitch of the plastic tube (error ≤±1mm).

[0008] Define the specific structure and drive method of the feed rollers, and clarify their matching mechanism with the bending pitch. The servo motor-driven upper and lower rollers can stably clamp the plastic tube to prevent it from slipping during transportation. Pitch matching ensures precise bending position, which is a key prerequisite for ensuring the consistency of the final bend angle and shape.

[0009] Furthermore, the heating tube is an annular heating tube, which extends along the outside of the plastic tube in the form of a dotted line. The heating area covers at least 80% of the part to be bent of the plastic tube (for example, the length of the part to be bent is L, and the length of the heating area is ≥0.8L). The heating temperature is set according to the material of the plastic tube (PVC: 80-100°C, PE: 90-120°C, PPR: 110-150°C), and the distance between the heating tube and the outer wall of the plastic tube is 5-10 mm.

[0010] The core technical features of the heating bending process are to clearly define the type (ring-shaped), coverage (≥80%) and temperature parameters (set by material) of the heating tube, and to soften the plastic tube to a bendable state through precise heating (avoiding collapse due to being too soft or cracking due to being too hard).

[0011] Furthermore, the inflation tube / hydraulic tube is a cylindrical hollow tube, horizontally embedded in the middle part of the plastic tube (1 / 4-1 / 3 of the tube length from the left end), the left end is connected to an external air source (such as an air compressor) or a hydraulic source (such as a hydraulic pump) through an air tube (or hydraulic tube) and an air tube joint, and the right end is connected to the plug through a threaded seal. When expanded, the difference between the expanded diameter and the inner diameter of the plastic tube is 0.5-2mm (for example, when the tube diameter is 50mm, the diameter after expansion is 50.5-52mm).

[0012] The installation position, connection method, and expansion amount of pneumatic / hydraulic tubes are defined to ensure that they evenly support the inner wall of the plastic tube after expansion, preventing the inner hole from collapsing or the outer wall from denting during bending. The expansion range (0.5-2mm) is a key parameter for balancing support force and tube integrity.

[0013] Furthermore, the hot bending mold is a metal mold (such as a steel mold) with a right-angle bend, which is embedded in the square area on the right side (perpendicular to the feeding direction), and the gap between its inner side and the outer wall of the plastic tube is 0.1-0.3 mm (for example, when the tube diameter is 100 mm, the gap is 0.15-0.3 mm), and the bending angle of the hot bending mold is 90° (or other angles such as 45°, 135°, etc. can be achieved by replacing the mold).

[0014] The material (metal), shape (right-angle bend) and installation position (square area on the right) of the hot bending mold are clearly defined. The tiny gap (0.1-0.3mm) between the mold and the outer wall of the plastic tube can guide the tube to bend precisely, avoiding displacement or excessive deformation of the tube during the bending process. It is the core mold to ensure the accuracy of the bending angle.

[0015] Furthermore, the air pipe (or hydraulic pipe) is a flexible pipe (such as a rubber pipe), which is laterally connected to the left part of the plastic pipe (located between the feeding roller and the heating pipe), and is connected to the air expansion pipe / hydraulic pipe through an air pipe joint. The air pipe joint is a quick plug-in joint, which is used to control the on and off and size adjustment of the expansion pressure (the pressure range is 0.2-0.8MPa).

[0016] The type of air pipe (or hydraulic pipe) (flexible pipe), connection position (left side) and connector form (quick plug-in type) are limited to achieve flexible control of the expansion pressure (on and off, size adjustment) and ensure that the inner hole support force can be dynamically adjusted in different bending stages (such as initial bending and maintaining bending).

[0017] Furthermore, the plastic pipe is a square spiral multi-layer bending structure, with the leftmost part being a vertical long pipe part (length L1), which is bent to the right in sequence to form four layers of spirals (the bending radius of each layer of spiral is R, R = 2-5 times the pipe diameter), which is suitable for multi-layer pipe bend connections in water supply and drainage systems or compact pipeline layout of electrical energy storage equipment without the need for additional elbows.

[0018] The typical product form of plastic pipes (square spiral multi-layer bending) is clarified, and the application scenarios in which they can replace traditional elbow connections (water supply and drainage, electric energy storage) are explained, solving the problems of traditional elbow connections with multiple interfaces and high leakage risks.

[0019] Furthermore, the process of expanding the inner hole ensures that the inner wall of the plastic tube is wrinkle-free (roughness Ra ≤ 3.2 μm) and the outer wall is free of depressions (depression depth ≤ 0.1 mm) after bending, the material stress distribution at the bending part is uniform (residual stress detected by X-ray diffraction is ≤ 20% of the material yield strength), and the bending angle error is ≤ ± 2° (for example, when the target angle is 90°, the actual angle is 88°-92°).

[0020] The quality indicators after bending (inner wall smoothness, outer wall flatness, stress distribution, and angular error) were quantified to verify the effectiveness of the inner hole expansion process, proving that the present invention can significantly improve the structural reliability and sealing of the bent part.

[0021] Furthermore, the plastic pipe is made of PVC, PE or PPR, and the pipe diameter range is 20-200mm (for example, 20mm, 40mm, 100mm, 150mm, 200mm). After bending, fluid connection in any direction can be achieved (such as vertical to horizontal, horizontal to 45° oblique), reducing the number of pipeline interfaces (reducing 30%-50% of interfaces compared to traditional elbow connections).

[0022] The applicable materials (PVC, PE, PPR) and pipe diameter range (20-200mm) of the process are limited, and the achievable connection direction (any direction) and interface reduction effect are clarified to highlight the universality and economy of the process in water supply and drainage, electric energy storage and other industries.

[0023] Furthermore, the process achieves multi-segment bending of the plastic pipe by repeating steps ae, with the angle of each bending segment being 30°-180° (for example, 30°, 60°, 90°, 180°), ultimately forming a spiral (pitch is D, D = 5-15 times the pipe diameter), L-shaped (two vertical bends) or any combination (such as L-shaped + spiral) bending structure, which is suitable for complex pipeline layout requirements (such as multi-layer coils of electrical energy storage equipment).

[0024] The application scope of the process is expanded (multi-section bending), and the achievable bending angles (30°-180°) and final structures (spiral, L-shaped, etc.) are explained to solve the problem that traditional processes cannot process complex pipelines and meet the demand for flexible pipeline layout in industrial scenarios.

[0025] The present invention provides a plastic pipe heating bending process based on expanding the inner hole, which has the following beneficial effects:

[0026] The plastic pipe heating bending process based on the expansion inner hole described in the present invention effectively solves the problems of large-diameter plastic pipes in the prior art, such as difficulty in bending, easy deformation, and inability to bend multiple sections continuously, through the innovative expansion inner hole design and coordinated control of the heating bending. The specific advantages are as follows:

[0027] Breaking through the bending limitations of large-diameter plastic pipes: Through the coordination of the feeding roller and the hot bending die, combined with the precise heating of the pipe by the heating tube (temperature 80-150°C, covering at least 80% of the part to be bent), large-diameter plastic pipes such as PVC, PE, and PPR (diameter 20-200mm) can be freely bent at any angle (30°-180°), breaking through the limitation that traditional processes cannot process large-diameter plastic pipes.

[0028] Expansion inner hole anti-deformation technology ensures bending quality: the inner hole of the plastic tube is inflated with air or hydraulic oil through the expansion tube / hydraulic tube, so that the expansion tube fits tightly with the inner wall of the tube after expansion (the inner diameter difference during expansion is 0.5-2mm), forming a stable internal support structure. During the heating and bending process, it effectively suppresses tube wall wrinkles, outer wall depressions and inner hole collapse, ensuring a smooth inner wall and flat outer wall after bending, uniform material stress distribution, and a bending angle error of ≤±2°, significantly improving the quality and reliability of the bending part.

[0029] Automated feeding and precise guiding improve processing efficiency: The servo motors arranged in parallel above and below drive the feeding rollers to automatically adjust the feeding pitch according to the bending pitch. Combined with the 0.1-0.3mm small gap between the inner side of the hot bending die and the outer wall of the plastic tube, precise feeding and directional bending of the plastic tube are achieved, reducing manual intervention and improving processing efficiency and consistency.

[0030] Multi-section continuous bending to meet complex piping requirements: By repeating steps ae to e, multiple sections of continuous bending of plastic pipes can be achieved (each section has an angle of 30°-180°), ultimately forming a spiral, L-shaped, or any combination of bending structures. This is suitable for complex scenarios such as multi-layer spiral bends in water supply and drainage systems and compact piping layouts for electrical energy storage equipment, without the need for additional elbow connections.

[0031] Reduce interface leakage risks and improve system reliability: The bent plastic pipe can be used directly as a continuous pipeline, avoiding the multiple interfaces connected by traditional elbows and reducing the risk of leakage. At the same time, the expansion and tightening of the inner hole process ensures the structural strength of the bent part, making it suitable for high-pressure fluid transportation scenarios (such as high-pressure pipelines of electrical energy storage equipment) and extending the service life of the pipeline system.

[0032] Wide range of material and size adaptability: The process of the present invention is applicable to a variety of large-diameter plastic pipes (diameter 20-200mm) such as PVC, PE, PPR, etc. The heating temperature, expansion pressure and bending angle can be adjusted according to actual needs. It has strong versatility and flexibility and can be widely used in water supply and drainage, electrical energy storage, chemical pipelines and other industries.

[0033] Special optimization of the square spiral multi-layer bending structure: In response to the typical needs of the water supply and drainage and electric energy storage industries, the present invention specially designed a square spiral multi-layer bending structure (the vertical part on the far left is longer, and four layers of spirals are formed in sequence to the right). Through the synergistic effect of the expansion inner hole and the hot bending mold, the consistency and sealing of the multi-layer spiral bending are ensured, which further simplifies the pipeline connection structure and improves the system integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can, without inventive effort, derive other implementation drawings based on the provided drawings.

[0035] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0036] Figure 2 This is a schematic diagram of the servo motor feeding of the present invention;

[0037] Figure 3 This is a schematic diagram of bending on a machine according to the present invention;

[0038] Figure 4 This is a diagram of the plastic product after bending according to the present invention. DETAILED DESCRIPTION

[0039] Exemplary embodiments will be described in detail herein, examples of which are illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present disclosure. Rather, they are merely examples of devices consistent with certain aspects of the present disclosure, as detailed in the appended claims.

[0040] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] Example 1: Manufacturing of square spiral multi-layer elbows for water supply and drainage systems

[0042] Application scenario: Multi-layer spiral elbow connection in urban underground drainage network, replacing the traditional combination of multiple 90° elbows.

[0043] Process parameters:

[0044] Material: PE pipe (diameter 150mm)

[0045] Heating temperature: 90-110℃ (PE softening point)

[0046] Expansion pressure: 0.5MPa (compressed air is filled into the expansion tube)

[0047] Bending angle: 90° per section, four sections of spiral bending, pitch D = 10 times the pipe diameter (1500mm)

[0048] Implementation steps:

[0049] Feeding and heating: The servo roller conveys the PE pipe to the heating zone with a step distance of 50mm (matching the spiral pitch). The annular heating pipe covers 85% of the part to be bent and is heated to 95℃ to soften the pipe.

[0050] Expand the inner hole: Inflate the air tube (difference 1.5mm) to 0.5MPa to support the inner hole and prevent it from collapsing.

[0051] Bending: The hot bending die (gap 0.2mm) guides the pipe to complete four 90° bends to form a square spiral structure ( Figure 4 ).

[0052] Quality verification: After bending, the inner wall roughness Ra≤3.2μm, the angle error is ±1.5°, and there are no wrinkles or depressions.

[0053] Advantages: Reduce the number of interfaces by 80%, compressive strength reaches 1.6MPa, suitable for deep buried drainage systems.

[0054] Example 2: Bending Processing of High-Voltage Pipelines for Electric Energy Storage Equipment

[0055] Application scenario: The internal cooling pipes of lithium battery packs need to withstand a high pressure of 2.5MPa and are space-constrained.

[0056] Process parameters:

[0057] Material: PPR pipe (diameter 80mm)

[0058] Heating temperature: 120-140℃ (PPR softening point)

[0059] Tightening pressure: 0.8MPa (hydraulic oil, hydraulic pump control)

[0060] Bending angle: 180° bend + partial spiral section (R = 3 times the pipe diameter)

[0061] Implementation steps:

[0062] Multi-stage bending: The first bend is 180° to form a U-shaped structure, followed by a spiral bend (pitch 5 times the pipe diameter) on the inside of the U-shaped elbow to adapt to compact spaces.

[0063] Dynamic expansion: The hydraulic system adjusts the expansion pressure (0.6-0.8MPa) in real time to prevent deformation of the inner hole under high pressure.

[0064] Cooling and shaping: Cool with water immediately after bending, residual stress ≤15MPa (X-ray detection).

[0065] Advantages: Replaces 12 traditional elbows, reduces leakage rate to below 0.05mL / min, and meets IP67 waterproof requirements.

[0066] Example 3: Complex ventilation piping system for industrial plants

[0067] Application scenario: Factory ventilation ducts need to achieve L-shaped and spiral combined bending in a limited space.

[0068] Process parameters:

[0069] Material: PVC pipe (diameter 100mm)

[0070] Heating temperature: 80-95℃ (PVC softening point)

[0071] Expansion pressure: 0.3MPa (dynamic adjustment of air spring)

[0072] Bending angle: L-type (2×90°) + spiral section (pitch 8 times the pipe diameter)

[0073] Implementation steps:

[0074] L-shaped bending: The first bend is 90° to form a right angle, and the second bend is 90° to complete the L-shaped structure. The gap between the hot bending mold is 0.15mm.

[0075] Spiral transition: The third section adopts spiral bending (R=4 times the tube diameter), and the difference of the expansion tube is 0.8mm to adapt to the airflow turning.

[0076] Automatic connection: The servo roller automatically adjusts the feeding according to the preset path of the BIM model, reducing manual intervention.

[0077] Advantages: Pipeline length is shortened by 40%, the number of elbows is reduced by 50%, and wind resistance is reduced by 25%, making it suitable for clean workshop ventilation systems.

[0078] Comparison of Examples and Advantages of Patented Technologies

[0079]

[0080] Summary of technical effects: By expanding the inner hole and coordinating heating and bending, the three embodiments respectively verified the reliability of the process in high pressure, multi-layer spiral, and complex spatial layout, solving the three major pain points of deformation, leakage, and low efficiency of the traditional process, and complying with the technical features defined in claims 1-10.

[0081] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A plastic pipe heating bending process based on expanding inner hole, characterized in that: The following steps are involved: a. The plastic tube to be bent (1) is transported to the heating area by the feed roller (2); b. Using a heating tube (3) to heat the portion of the plastic tube (1) to be bent to reach a set temperature; c. Inflate the air / hydraulic tube (7) in the inner hole of the plastic tube (1) with air or hydraulic oil, and control the expansion pressure through the air pipe joint (5) and the air pipe (or hydraulic pipe) (4), so that the air / hydraulic tube (7) expands and fits tightly against the inner wall of the plastic tube (1), forming an expanded inner hole; d. Push the expanded plastic tube (1) to the bending area of ​​the hot bending die (6), and complete the bending at a predetermined angle through the guiding effect of the hot bending die (6); e. After the bending is completed, the right end of the inflation tube / hydraulic tube (7) is closed by the plug (8), and the gas or hydraulic oil in the inflation tube / hydraulic tube (7) is released to shrink the inflation tube / hydraulic tube (7); f. Repeat steps ae and cycle until the multiple bending of the plastic tube (1) is completed.

2. The plastic pipe heating bending process based on the expansion inner hole according to claim 1 is characterized in that: The feeding rollers (2) are two rollers arranged in parallel up and down, driven to rotate by a servo motor, and used to clamp and convey the plastic pipe (1). The automatic feeding step of the servo motor matches the bending pitch of the plastic pipe (1).

3. The plastic pipe heating bending process based on the expansion inner hole according to claim 1 is characterized in that: The heating pipe (3) extends in a dotted line along the outside of the plastic pipe (1), and the heating area covers at least 80% of the portion of the plastic pipe (1) to be bent. The heating temperature is set to 80-150° C. according to the material of the plastic pipe (1) (PVC, PE, PPR, etc.).

4. The plastic pipe heating bending process based on expanding inner hole according to claim 1 is characterized in that: The inflatable tube / hydraulic tube (7) is horizontally embedded in the middle part of the plastic tube (1), the left end of which is connected to an external air source or hydraulic source via an air tube (or hydraulic tube) (4) and an air tube joint (5), and the right end is sealed with a plug (8). When tightened, the difference between the expanded diameter and the inner diameter of the plastic tube (1) is 0.5-2 mm.

5. The plastic pipe heating bending process based on expanding inner hole according to claim 1 is characterized in that: The hot bending die (6) is bent at a right angle and embedded in the right square area. The gap between its inner side and the outer wall of the plastic tube (1) is 0.1-0.3 mm, and is used to guide the plastic tube (1) to complete a 90° or arbitrary angle bend.

6. The plastic pipe heating bending process based on expanding inner hole according to claim 1 is characterized in that: The air pipe (or hydraulic pipe) (4) is laterally connected to the left side of the plastic pipe (1) and is connected to the air expansion pipe / hydraulic pipe (7) through the air pipe joint (5) to control the on / off and size adjustment of the expansion pressure.

7. The plastic pipe heating bending process based on expanding inner hole according to claim 1 is characterized in that: The plastic pipe (1) is a square spiral multi-layer bending structure, with a longer vertical portion on the left, which is bent to the right in sequence to form four or more layers of spirals, and is suitable for pipe bend connections in the water supply and drainage and electric energy storage industries without the need for additional elbows.

8. The plastic pipe heating bending process based on expanding inner hole according to claim 1 is characterized in that: The process of expanding the inner hole ensures that the inner wall of the plastic pipe (1) has no wrinkles and the outer wall has no depressions after bending, the material stress distribution at the bending part is uniform, and the bending angle error is ≤±2°.

9. The plastic pipe heating bending process based on expanding the inner hole according to any one of claims 1 to 8, characterized in that: The plastic pipe (1) is made of PVC, PE or PPR, has a pipe diameter range of 20-200 mm, and can achieve fluid connection in any direction after bending, thereby reducing the risk of leakage at the pipeline interface.

10. The plastic pipe heating bending process based on expanding inner hole according to claim 1, characterized in that: The process achieves multi-section bending of the plastic pipe (1) by repeating steps ae, with each bending angle being 30°-180°, ultimately forming a spiral, L-shaped or any combination of bending structures, which is suitable for complex pipeline layout requirements.

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