A low stress enhanced hollow wall tube and a manufacturing method thereof

Abstract

The present invention relates to the technical field of pipe processing, and in particular to a low-stress enhanced hollow wall pipe and a manufacturing method thereof, which specifically includes S1: extruding and molding a molten square pipe material through a square pipe molding device to form an inner square pipe; S2: winding mutually overlapping steel meshes on the surface of the inner square pipe; S3: pulling the inner square pipe into a coating device, coating and molding the molten square pipe material to form an outer square pipe, and together forming a composite square pipe with a sandwich structure; S4: pulling the composite square pipe to a winding molding device, and performing mutually abutting winding on the molding device to form a hollow wall pipe; S5: heating and annealing the pipe material through an electromagnetic heating device on the outside of the hollow wall pipe to achieve stress removal. The present invention can improve the stress removal scheme adopted by the existing hollow wall pipe, so that the wound square pipe obtains a higher axial strength, eliminates the stress caused by the bending of the square pipe from the inside to the outside, reduces the risk of cracking of the pipe, and improves the product quality.

Description

Technical Field

[0001] The invention relates to the technical field of pipe processing, and in particular to a low-stress enhanced hollow wall pipe and a manufacturing method thereof. Background Art

[0002] The forming method of hollow wall winding pipe is: using PE or PP resin as raw material, adopting extrusion process, first extrude square tube, send it to winding forming equipment, and then use another extruder to extrude welding material, through winding and welding, and axial compression at the same time. When extruding square tube, the square tube is pulled, the internal molecules will be oriented, resulting in lower strength of the tube in directions other than the pulling direction (especially the normal plane position perpendicular to the pulling direction), and finally the axial strength of the hollow wall tube is lowered. Moreover, it can be found in the seam tensile test that most of the locations where the specimens break are at the corners where the square tube and the molten glue are welded. On the other hand, when the hollow wall tube is formed, the square tube is bent and wound on the winding forming equipment, and there is a large residual stress, which is mainly the stress generated when the square tube is bent and the stress generated during the cooling process of the square tube and the molten glue welding, especially in the outer layer of the pipe, which makes the pipe easy to crack under the action of external force, posing a safety hazard.

[0003] Traditional stress relief methods include infrared method and bath method. Among them, the infrared method heats the surface of the pipe, which cannot fully release the stress inside the square pipe and has high energy consumption; the bath method is to bathe the pipe in a working medium of a specific temperature (such as oil, water, water vapor, etc.), which takes up a lot of space and has certain safety hazards. Moreover, if the square pipe is thicker, the effect becomes worse.

[0004] Chinese invention patent CN106079500B discloses a production process for a pipe, comprising the following steps: (1) making a joint by plasticizing; (2) putting the joint on a mold; (3) the mold rotates along the axis, and a physical heating device heats the joint to 120°C-150°C; the mold heating device moves along the axial direction of the mold to heat the mold to 120°C-150°C; (4) heating the raw material in the extrusion device to 180°C-190°C; (5) the extrusion device extrude the molten raw material, and the extrusion device moves along the axial direction of the mold, winding the raw material on the surface of the mold to form a pipe body, and the two ends of the pipe body are directly fused to the joint at high temperature; (6) cooling and demolding. The invention uses electromagnetic heating to fuse the pipe body at high temperature, but this method of directly heating the mold to assist injection molding cannot solve the problem of removing the stress of the pipe itself during the winding molding process of the existing hollow wall pipe. Summary of the invention

[0005] In order to solve the problems in the above-mentioned background technology, improve the axial strength of the hollow wall tube during the winding forming process and reduce its residual stress, the present invention provides a low-stress enhanced hollow wall tube and a manufacturing method thereof, which can improve the stress relief scheme adopted by the existing hollow wall tube, so that the wound square tube obtains higher axial strength, eliminates the stress generated by the bending of the square tube from the inside to the outside, reduces the risk of cracking of the tube, and improves product quality.

[0006] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0007] A method for manufacturing a low stress enhanced hollow wall tube comprises the following steps:

[0008] S1: Extruding the molten square tube material through a square tube forming device to form an inner layer square tube;

[0009] S2: Steel meshes are wound around the surface of the inner square tube and overlap each other as a reinforcement layer;

[0010] S3: The inner square tube is pulled into the coating equipment, and the molten square tube material is coated and shaped to form an outer square tube. The inner square tube, the steel mesh, and the outer square tube together form a composite square tube with a sandwich structure;

[0011] S4: pulling the composite square tube to a winding forming device, on which adjacent composite square tubes are wound in contact with each other, and the molten adhesive is used to fill and bond the adjacent composite square tubes to form a hollow wall tube;

[0012] S5: The tube is heated and annealed by an electromagnetic heating device outside the hollow wall tube to remove stress from the inner square tube and the outer square tube.

[0013] Compared with the prior art, the present invention achieves the technical effect that the square tube has high axial strength when being pulled and wound, will not break or deform, and the square tube at the bend will not crack due to stress removal, by overlapping the steel mesh as a reinforcement layer during the two forming processes of the square tube, winding it into a hollow wall tube, and then using an electromagnetic heating device for annealing and stress relief.

[0014] Preferably, the melting temperature of the square tube material in step S1 is 160°C-270°C, and the square tube material is preheated by electromagnetic heating in an oven before melting, the preheating temperature is 70°C-120°C, and the insulation duration after preheating is 20-60 minutes. Based on the above scheme, the square tube material can be preheated before melting, the particle size of the melted material is better, the material is uniform, and the preheated square tube material is easier to melt in the subsequent melting, saving melting energy and time.

[0015] Specifically, the overlapping methods in step S2 include two types: forward overlapping and staggered overlapping; in the forward overlapping method, the overlapping width B of adjacent steel meshes is 1-10mm, and the axial angle A when the steel mesh and the inner square tube are overlapped is in the range of 20-70 degrees. The steel mesh is a hollow structure, and the hollow shape is square. Through the overlapping steel meshes, a tight tensile reinforcement layer can be formed on the surface of the inner square tube. By setting a certain overlapping width B and inclined angle A, the overlapping steel mesh can be better compacted with the surface of the inner square tube. The hollow shape is set to be square, which can reduce the weight of the steel mesh and have a strong tensile strength.

[0016] Furthermore, the specific method of step S3 includes:

[0017] S31: Fix the coating equipment, vacuum sizing mold and cooling shaping mold in order and set the parameters;

[0018] S32: pulling the inner square tube onto the profile fixture in the coating equipment, clamping the inner square tube and the steel mesh overlapped thereon, and heating the square tube material to a molten state;

[0019] S33: pushing the clamped inner square tube and steel mesh into a vacuum sizing mold, pouring the molten square tube material into it for coating and shaping, sealing the vacuum sizing mold, delaying 10-20 seconds to complete the vacuum sizing, and pushing it into a cooling and shaping mold for liquid cooling and shaping to form an outer square tube;

[0020] S34: Liquid cooling for 20-30 seconds, liquid cooling using water, water temperature of 10-20°C, vacuum degree -0.04MPa±0.02MPa; obtaining a composite square tube with a middle layer of steel mesh and an outer square tube and an inner square tube of the same material.

[0021] Furthermore, the specific method of step S4 includes:

[0022] S41: After heating the composite square tube to a plastic state, the composite square tube is pulled to a hollow wall tube winding forming device, so that the forming device and the composite square tube are pushed synchronously, and the pressing wheel assembly of the forming device squeezes the composite square tube, so that the adjacent composite square tubes are successively abutted and combined and closely attached to the roller of the forming device, and the winding speed is 5-30 r / min;

[0023] S42: a melt adhesive extruder extrude a melt adhesive with a temperature of 180°C-270°C and a melt pressure of 10MPa-30MPa, and hot sprays the melt adhesive into a hollow wall tube winding molding device. When the composite square tube is stretched synchronously in the same direction, the melt adhesive fills the gaps between adjacent composite square tubes. After the gaps are filled, a pressing wheel is used to flatten the composite square tube.

[0024] S43: After cooling down by spraying cooling water through the liquid cooling device, a hollow wall tube is obtained, and the hollow wall tube is kept on the molding device without moving.

[0025] Furthermore, the specific method of step S5 includes:

[0026] S51: An electromagnetic heating device is arranged on one side of the molding device to heat the hollow wall tube on the molding device;

[0027] S52: synchronously rotate the rollers of the forming equipment at a speed of 10-40r / min, so that the hollow wall tube is evenly heated, the heating temperature is lower than the crystallization temperature of the square tube material, and the heating time is 3-20min;

[0028] S53: After the heating is completed, the electromagnetic heating device is turned off, and the tube is allowed to stand at room temperature for annealing for 30-60 minutes to remove stress from the hollow wall tube.

[0029] Furthermore, the inner square tube and the outer square tube are made of the same material, which is one of polyethylene, polypropylene, modified polypropylene and modified polyethylene.

[0030] A hollow wall tube made by the above method is formed by successively abutting composite square tubes of a sandwich structure through spiral winding, and the successively abutting composite square tubes are bonded by melt adhesive. The composite square tube includes an inner square tube, an outer square tube and a steel mesh in the middle layer made of the same material, wherein the longitudinal sections of the inner square tube and the outer square tube are both square, and the molding method is both thermoplastic.

[0031] Furthermore, the thickness T of the inner layer and the outer layer is the same, the thickness t of the steel mesh is 1 / 20-1 / 4 of the thickness T, the inner diameter D of the hollow wall tube is 5-20 times the height H of the composite square tube, and the width C of the composite square tube is 5-20 times the thickness L of the molten glue.

[0032] Furthermore, the molten adhesive is made of the same material as the composite square tube.

[0033] The present invention has the following beneficial effects:

[0034] 1. By overlapping the steel mesh as a reinforcement layer during the two forming processes of the composite square tube, winding it into a hollow wall tube and then using an electromagnetic heating device to anneal and relieve stress, the axial strength of the square tube can be improved when it is pulled and wound, and no fracture or deformation will occur. The square tube at the bend will not crack due to the removal of stress;

[0035] 2. During the electromagnetic heating process, the composite square tube with sandwich structure can release stress by heating from the inside to the outside, which can improve the efficiency of removing residual stress. Compared with the traditional method, it occupies less space, consumes less energy, and saves production costs;

[0036] 3. The steel mesh can generate eddy current heating under the action of the electromagnetic induction coil. The annealing heating temperature can be conveniently adjusted by controlling the output power. Moreover, the electromagnetic induction coil group can be set as one or more groups according to the production speed and length of the hollow wall tube, which is convenient and flexible to use.

[0037] 4. The steel mesh is arranged between the inner square tube and the outer square tube of the composite square tube. When heated by the electromagnetic heating device, the steel mesh can generate eddy current heat under the action of the electromagnetic induction coil. Compared with the outer square tube, the steel mesh heats up faster and gradually transfers the heat to the outer layer, so as to realize the heating of the composite square tube from the relative inner layer to the outer layer, thereby releasing the stress concentration caused by winding; compared with the traditional infrared method, the infrared method is equivalent to heating the outer surface of the composite square tube and then transferring the heat to the inner layer. Because of this heat transfer heating from the outside to the inside, the stress concentration generated in the inner layer cannot be released. Therefore, the scheme proposed in the present invention has obvious beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a longitudinal cross-sectional view of a composite square tube in an embodiment of the present invention;

[0039] Figure 2 is a longitudinal cross-sectional view of a hollow wall tube in an embodiment of the present invention;

[0040] Figure 3 Schematic diagram of the inner square tube and the steel mesh being overlapped in the forward direction in an embodiment of the present invention;

[0041] Figure 4 Schematic diagram of the staggered overlap of the inner square tube and the steel mesh in an embodiment of the present invention;

[0042] Figure 5 Schematic diagram of the equipment used in the winding and annealing process of the hollow wall tube in the embodiment of the present invention.

[0043] In the figure, marks 1-composite square tube, 11-inner square tube, 12-outer square tube, 13-steel mesh, 2-molding glue, 3-hollow wall tube, 4-molding equipment, 41-roller, 5-liquid cooling equipment, and 6-electromagnetic heating device. DETAILED DESCRIPTION

[0044] The technical solutions in the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. The components of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0045] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected to each other and the relative position relationship after the connection remains unchanged. It should be understood that when component A is fixedly connected to component C through component B, changes in the relative position relationship caused by the deformation of component A, component B and component C itself are allowed. "Rotational connection" means that they are connected to each other and can rotate relative to each other after the connection. "Sliding connection" means that they are connected to each other and can slide relative to each other after the connection. Among them, the two components are connected to obtain an integrated structure through an integrated molding process, which means that in the process of forming one of the two components, the component is connected to the other component, and there is no need to connect the two components together through reprocessing (such as bonding, welding, snap connection, screw connection).

[0046] The directional terms mentioned in the embodiments of the present invention, such as "upper", "lower", "side", "top", "bottom", etc., are only references to the directions of the drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0047] The term "plurality" means at least two. The term "above" includes the number itself. The term "and / or" is a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", etc. are used only for descriptive purposes and cannot be understood as suggesting or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" or "second" may explicitly or implicitly include one or more of the features.

[0048] In order to improve the axial strength of the hollow wall tube during the winding process and reduce its residual stress, the present invention provides a method for manufacturing a low-stress enhanced hollow wall tube, comprising the following steps:

[0049] See also Figure 1The longitudinal cross-sectional view of the square tube, S1: firstly extrude the molten square tube material through the first molding device to form the inner square tube 11; wherein the square tube material is polypropylene (PP), and the melting temperature is 160℃-270℃, and in this embodiment, it is 200℃. Before melting, the square tube material is preheated in an oven by electromagnetic heating, and the preheating temperature is 70℃-120℃, and in this embodiment, it is 100℃, and the insulation duration after preheating is 20-60min. The square tube material is preheated before melting, and the particle size of the melted material is better and the material is uniform. The preheated square tube material is easier to melt in the subsequent melting, saving melting energy and time.

[0050] See also Figure 3-4 Schematic diagram of the overlap of the inner square tube and the steel mesh, S2: The steel mesh 13 that overlaps each other is wrapped around the surface of the inner square tube 11 as a reinforcement layer; the overlap method includes two types: forward overlap and staggered overlap; please refer to Figure 3 , wherein in the forward overlap mode, the overlap width B of adjacent steel meshes 13 is 1-10mm, 5mm in this embodiment, the axial angle A of the steel mesh 13 and the inner square tube 11 when overlapped is in the range of 20-70 degrees, 45 degrees in this embodiment, and the steel mesh 13 is a hollow structure, and the hollow shape is square. Through the overlapping steel meshes 13, a tight tensile reinforcement layer can be formed on the surface of the inner square tube 11, and the overlapping width B of 5mm and the inclined angle A of 45 degrees are set, so that the overlapping steel mesh can be better compacted with the surface of the inner square tube, and the hollow shape is set to be square, which can reduce the weight of the steel mesh and have a strong tensile strength.

[0051] After the steel mesh 13 is overlapped, the outer square tube 12 is thermoplastically formed on this basis. The specific steps include S3: pulling the inner square tube 11 into the coating equipment, coating and shaping the molten square tube material to form the outer square tube 12; the specific method includes:

[0052] S31: Fix the coating equipment, vacuum sizing mold and cooling shaping mold in order and set the parameters;

[0053] S32: pulling the inner square tube 11 onto the profile fixture in the coating equipment, clamping the overlapping steel mesh 13 on the outer surface of the inner square tube 11, and heating the square tube material to a molten state;

[0054] S33: Push the clamped inner square tube 11 and steel mesh 13 into a vacuum sizing mold, pour in the molten square tube material for coating and shaping, seal the vacuum sizing mold, delay 10-20 seconds to complete the vacuum sizing, and push into a cooling and shaping mold for liquid cooling and shaping to form an outer square tube;

[0055] S34: Liquid cooling for 20-30 seconds, liquid cooling is carried out with water, the water temperature is 10-20℃, and the vacuum degree is -0.04MPa±0.02MPa.

[0056] The composite square tube 1 formed by thermoplasticization in the above process forms a sandwich structure in which the middle layer is a steel mesh 13, and the outer square tube 12 and the inner square tube 11 are made of the same material; then the composite square tube 1 is pulled by a pulling device to the roller 41 of the hollow wall tube winding forming device 4 for mutual abutment winding, and is filled and bonded by the extruded molten adhesive 2 to form a hollow wall tube 3; the specific process includes:

[0057] S41: After the composite square tube 1 is heated to a plastic state, it is pulled to the hollow wall tube winding forming device 4, so that the forming device 4 and the composite square tube 1 are pushed synchronously, and the pressing wheel assembly of the forming device 4 squeezes the composite square tube 1, so that the wound adjacent composite square tubes 1 are successively abutted and combined and closely attached to the roller 41 of the forming device 4, and the winding speed is 5-30 r / min, and is 20 r / min in this embodiment;

[0058] S42: The molten adhesive extruder extrude the molten adhesive 2 at a temperature of 180° C.-270° C., 200° C. in this embodiment, at a melt pressure of 10 MPa-30 MPa, and at a melt pressure of 15 MPa, and hot spray the molten adhesive 2 into the molding device 4 wound around the hollow wall tube 3. When the composite square tube 1 is stretched synchronously in the same direction, the molten adhesive 2 is filled in the gaps between the adjacent composite square tubes 1. After the filling, the composite square tube 1 is flattened by a pressing wheel.

[0059] S43: After cooling down by spraying cooling water through the liquid cooling device 5, a hollow wall tube 3 is obtained and kept on the molding device 4 without moving.

[0060] See also Figure 2 The longitudinal cross-section of the hollow wall tube and Figure 5 The schematic diagram of the equipment used in the winding and annealing process of the hollow wall tube is shown in FIG. It is necessary to heat and anneal the formed hollow wall tube 3 to remove the residual stress generated by the winding, especially at the bend of the composite square tube 1. The specific method is: the tube is heated and annealed by an electromagnetic heating device 6 outside the hollow wall tube 3, including:

[0061] S51: An electromagnetic heating device 6 is provided on one side of the molding device 4 to heat the hollow wall tube 3 on the molding device 4;

[0062] S52: synchronously rotating the roller 41 of the molding device 4 at a speed of 10-40 r / min, 30 r / min in this embodiment, so that the hollow wall tube 3 is evenly heated, the heating temperature is lower than the crystallization temperature of the square tube material, and the heating time is 3-20 min. In this embodiment, the material of the composite square tube is polypropylene, and the heating temperature is 150° C. lower than its crystallization temperature, and the heating time is 5 min; if the material of the composite square tube 1 is polyethylene, the heating temperature is 100° C. lower than its crystallization temperature, and the heating time is 3 min;

[0063] S53: After the heating is completed, the electromagnetic heating device 6 is turned off, and the tube is allowed to stand at room temperature for annealing. The standing time is 30-60 minutes, 30 minutes in this embodiment, and 60 minutes if the material is polyethylene, so that the hollow wall tube 3 can achieve a stress removal process from the inner square tube 11 to the outer square tube 12 from the inside to the outside layer by layer.

[0064] Please participate Figure 1-2 The hollow wall tube 3 obtained by the above method is formed by spirally winding the composite square tubes 1 of the sandwich structure, and the composite square tubes 1 that are successively abutted are bonded by the molten adhesive 2. The composite square tube 1 includes an inner square tube 11, an outer square tube 12 and a steel mesh 13 in the middle layer, wherein the longitudinal sections of the inner square tube 11 and the outer square tube 12 are both square, the thickness T of the inner square tube 11 and the outer square tube 12 are the same, the thickness t of the steel mesh 13 is 1 / 20-1 / 4 of the thickness T of the inner square tube 11 and the outer square tube 12, and t in this embodiment is 1 / 10 of T, the inner diameter D of the hollow wall tube 3 is 8-10 times the height H of the composite square tube 1, and D is 10 times H in this embodiment, the width C of the composite square tube 1 is 5-20 times the thickness L of the molten adhesive 2, and C is 15 times L in this embodiment, and the material of the molten adhesive 2 is the same as that of the composite square tube 1, both of which are polypropylene.

[0065] The following table compares the experimental data of the hollow wall tube prepared by the present invention with the existing hollow wall tubes on the market:

[0066] Compare Projects Hollow wall tube of the present invention Existing hollow wall tube Ring stiffness (kN / m²) 8~16 4~12.5 Impact performance Hammer weight: 12.5kg, impact height: 1m, sample conditioned at 0℃ for 1 hour Result: None of the 20 samples were broken Hammer weight: 12.5kg, impact height: 1m, sample conditioned at 0℃ for 1 hour Result: 20 samples cracked to varying degrees Residual hoop stress Method: Cut the pipe at random to a length of 150mm±5mm, cut it longitudinally to a width of 2ec, and measure the center distance between the two ends of the pipe cut after 7 days. Result: The outward expansion opening is ≤3ec (smaller residual stress) Method: Cut the pipe at random to a length of 150mm±5mm, cut it longitudinally to a width of 2ec, and measure the center distance between the two ends of the pipe cut after 7 days. Result: The outward expansion opening is ≥4ec (large residual stress) Pipe tensile strength ≥18MPa ≤15MPa

[0067] Note: In the above table, "ec" is the height of the structural wall of the pipe, which is the height H of the composite square pipe in combination with the present invention.

[0068] By overlapping the steel mesh 13 as a reinforcement layer during the two forming processes of the composite square tube 1, winding it into a hollow wall tube 3 and then using an electromagnetic heating device 6 to anneal and relieve stress, the axial strength of the composite square tube 1 when being pulled and wound can be improved, and no fracture or deformation will occur. The composite square tube at the bend will not crack due to the removal of stress; and the composite square tube 1 with a sandwich structure can be heated from the inside to the outside during the electromagnetic heating process to release stress, which can improve the efficiency of removing residual stress. Compared with traditional methods, it occupies less space, consumes less energy, and saves production costs; the steel mesh 13 can generate eddy current heat under the action of the electromagnetic induction coil, and the annealing heating temperature can be conveniently adjusted by controlling the output power, and the electromagnetic induction coil group can be set as one or more groups according to the production speed and length of the hollow wall tube 3, which is convenient and flexible to use.

[0069] It needs to be explained that the steel mesh 13 is arranged between the inner square tube 11 and the outer square tube 12 of the composite square tube 1. When heated by the electromagnetic heating device 6, the steel mesh 13 can generate eddy current heat under the action of the electromagnetic induction coil. Compared with the outer square tube 12, the steel mesh 13 heats up faster and gradually conducts heat to the outer layer, realizing the heating of the composite square tube 1 from the relative inner layer to the outer layer, thereby releasing the stress concentration caused by winding; compared with the traditional infrared method, the infrared method is equivalent to heating the outer surface of the composite square tube and then conducting the heat to the inner layer. Because of this heat conduction heating from the outside to the inside, the stress concentration generated in the inner layer cannot be released. Therefore, the scheme proposed in the present invention has obvious beneficial effects.

[0070] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved. In addition, it should be understood that although this specification is described in accordance with the implementation methods, not each implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for manufacturing a low stress enhanced hollow wall tube, characterized in that: The manufacturing method comprises the following steps: S1: Extruding the molten square tube material through a square tube forming device to form an inner layer square tube; S2: Steel meshes are wound around the surface of the inner square tube and overlap each other as a reinforcement layer; The overlapping method is a forward overlapping method. When the overlapping method is a forward overlapping method, the overlapping width B of adjacent steel meshes is 1-10 mm. When the steel mesh and the inner square tube are overlapped, the axial angle A ranges from 20 to 70 degrees. The steel mesh is a hollow structure, and the hollow shape is a square. S3: The inner square tube is pulled into the coating equipment, and the molten square tube material is coated and shaped to form an outer square tube. The inner square tube, the steel mesh, and the outer square tube together form a composite square tube with a sandwich structure; S4: pulling the composite square tube to a winding forming device, on which adjacent composite square tubes are wound in contact with each other, and the molten adhesive is used to fill and bond the adjacent composite square tubes to form a hollow wall tube; S5: heating and annealing the tube material by an electromagnetic heating device outside the hollow wall tube to remove stress from the inner square tube and the outer square tube; the specific process of step S5 includes: S51: An electromagnetic heating device is arranged on one side of the molding device to heat the hollow wall tube on the molding device; S52: synchronously rotate the rollers of the forming equipment at a speed of 10-40r / min, so that the hollow wall tube is evenly heated, the heating temperature is lower than the crystallization temperature of the square tube material, and the heating time is 3-20min; S53: After the heating is completed, the electromagnetic heating device is turned off, and the tube is allowed to stand at room temperature for annealing for 30-60 minutes to remove stress from the hollow wall tube.

2. The manufacturing method according to claim 1, characterized in that: The melting temperature of the square tube material in step S1 is 160° C.-270° C. Before melting, the square tube material is preheated in an oven by electromagnetic heating at a preheating temperature of 70° C.-120° C., and the insulation duration after preheating is 20-60 minutes.

3. The manufacturing method according to claim 1, characterized in that: The step S3 specifically includes: S31: Fix the coating equipment, vacuum sizing mold and cooling shaping mold in order and set the parameters; S32: pulling the inner square tube onto the profile fixture in the coating equipment, clamping the inner square tube and the steel mesh overlapped thereon, and heating the square tube material to a molten state; S33: pushing the clamped inner square tube and steel mesh into a vacuum sizing mold, pouring the molten square tube material into it for coating and shaping, sealing the vacuum sizing mold, delaying 10-20 seconds to complete the vacuum sizing, and pushing it into a cooling and shaping mold for liquid cooling and shaping to form an outer square tube; S34: Liquid cooling for 20-30 seconds, liquid cooling using water, water temperature of 10-20°C, vacuum degree -0.04MPa±0.02MPa; obtaining a composite square tube with a middle layer of steel mesh and an outer square tube and an inner square tube of the same material.

4. The manufacturing method according to claim 1, characterized in that: The step S4 specifically includes: S41: After heating the composite square tube to a plastic state, the composite square tube is pulled to a hollow wall tube winding forming device, so that the forming device and the composite square tube are pushed synchronously, and the pressing wheel assembly of the forming device squeezes the composite square tube, so that the adjacent composite square tubes are successively abutted and combined and closely attached to the roller of the forming device, and the winding speed is 5-30 r / min; S42: a melt adhesive extruder extrude a melt adhesive with a temperature of 180°C-270°C and a melt pressure of 10MPa-30MPa, and hot sprays the melt adhesive into a hollow wall tube winding molding device. When the composite square tube is stretched synchronously in the same direction, the melt adhesive fills the gaps between adjacent composite square tubes. After the gaps are filled, a pressing wheel is used to flatten the composite square tube. S43: After cooling down by spraying cooling water through the liquid cooling device, a hollow wall tube is obtained, and the hollow wall tube is kept on the molding device without moving.

5. The manufacturing method according to claim 1, characterized in that: The inner square tube and the outer square tube are made of the same material, which is one of polyethylene, polypropylene, modified polypropylene and modified polyethylene.

6. A hollow wall tube made by any one of the manufacturing methods of claims 1 to 5, characterized in that: The hollow wall tube is formed by successively abutting composite square tubes of a sandwich structure through spiral winding, and the successively abutting composite square tubes are bonded by melt adhesive. The composite square tube includes an inner square tube, an outer square tube and a steel mesh in the middle layer with the same material, wherein the longitudinal sections of the inner square tube and the outer square tube are both square, and the molding method is both thermoplastic.

7. The hollow wall tube according to claim 6, characterized in that: The thickness T of the inner square tube and the outer square tube is the same, the thickness t of the steel mesh is 1 / 20-1 / 4 of the thickness T, the inner diameter D of the hollow wall tube is 5-20 times the height H of the composite square tube, and the width C of the composite square tube is 5-20 times the thickness L of the molten glue.

8. The hollow wall tube according to claim 6, characterized in that: The molten adhesive is made of the same material as that of the composite square tube.

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