CN118977384A

CN118977384A - A low stress enhanced hollow wall tube and a manufacturing method thereof

Info

Publication number: CN118977384A
Application number: CN202411468546.XA
Authority: CN
Inventors: 张健生; 林细勇; 周俊迎; 田从陆; 王永达
Original assignee: Rifeng New Material Co ltd; Rifeng Enterprise Foshan Co Ltd; Rifeng Enterprise Group Co Ltd
Current assignee: Rifeng New Material Co ltd; Rifeng Enterprise Foshan Co Ltd; Rifeng Enterprise Group Co Ltd
Priority date: 2024-10-21
Filing date: 2024-10-21
Publication date: 2024-11-19
Anticipated expiration: 2044-10-21
Also published as: CN118977384B

Abstract

The invention relates to the technical field of pipe processing, in particular to a low-stress reinforced hollow wall pipe and a manufacturing method thereof, and specifically comprises the following steps of S1, extruding and forming a molten square pipe material through square pipe forming equipment to form an inner square pipe; s2: winding steel nets which are overlapped with each other on the surface of the inner square pipe; s3: drawing the inner square tube into cladding equipment, and cladding and shaping the molten square tube material to form an outer square tube, so as to jointly form a composite square tube with a sandwich structure; s4: drawing the composite square pipe to winding forming equipment, and winding the composite square pipe on the forming equipment in a mutually abutting mode to form a hollow wall pipe; s5: and (3) heating and annealing the pipe outside the hollow wall pipe through an electromagnetic heating device to remove stress. The invention can improve the stress relieving scheme adopted by the existing hollow wall pipe, so that the wound square pipe can obtain higher axial strength, the stress generated by bending the square pipe is eliminated from inside to outside, the cracking risk of the pipe is reduced, and the product quality is improved.

Description

Low-stress reinforced hollow wall pipe and manufacturing method thereof

Technical Field

The invention relates to the technical field of pipe processing, in particular to a low-stress reinforced hollow wall pipe and a manufacturing method thereof.

Background

The forming method of the hollow wall winding pipe comprises the following steps: the method is characterized in that PE or PP resin is used as a raw material, an extrusion process is adopted, square tubes are extruded first, the square tubes are sent to winding forming equipment, and then the welding materials are extruded by another extruder, are welded while being wound, and are axially compressed. When the square tube is extruded, the square tube is pulled, and internal molecules are oriented, so that the strength of the square tube in other directions than the pulling direction is lowered (particularly, the normal plane position perpendicular to the pulling direction), and finally, the axial strength of the hollow wall tube is lowered. And in the seam tensile test, the position where the sample breaks is mostly found at the corner where the square tube is welded with the melt adhesive. On the other hand, when the hollow wall pipe is formed, the square pipe is bent and wound on winding forming equipment, larger residual stress exists, mainly the stress generated when the square pipe is bent and the stress generated in the welding and cooling process of the square pipe and the melt adhesive are generated, particularly in the outer layer of the pipe, so that the pipe is easy to crack under the action of external force, and potential safety hazards exist.

The traditional stress relief method includes an infrared method and a bath method. The infrared method is to heat the surface of the pipe, so that the stress in the square pipe cannot be fully released, and the energy consumption is high; the bath method is to bath the pipe in a working medium (such as oil, water vapor, etc.) with a certain temperature, which has large occupied space and certain potential safety hazard, and the effect is poor if the square pipe is thicker.

The Chinese patent CN106079500B discloses a production process of a pipe, which comprises the following steps: (1) manufacturing a joint by a plasticizing molding mode; (2) fitting the adapter sleeve over the mold; (3) The die rotates along the axis, and the physical heating device heats the joint by 120-150 ℃; the die heating device moves along the axial direction of the die to heat the die to 120-150 ℃; (4) Heating the raw materials in the extrusion equipment to 180-190 ℃; (5) Extruding raw materials in a molten state by using extrusion equipment, moving the extrusion equipment along the axial direction of a die, winding the raw materials on the surface of the die to form a pipe body, and directly fusing two ends of the pipe body on a joint at high temperature; and (6) cooling and demolding. The invention adopts electromagnetic heating to carry out high-temperature fusion on the pipe, but the mode of directly heating the die to assist injection molding can not solve the problem that the stress of the pipe is removed in the winding molding process of the existing hollow wall pipe.

Disclosure of Invention

In order to solve the problems in the background art, the invention provides a low-stress reinforced hollow wall pipe and a manufacturing method thereof, which can improve the stress relieving scheme adopted by the existing hollow wall pipe, enable the wound square pipe to obtain higher axial strength, eliminate the stress generated by bending the square pipe from inside to outside, reduce the cracking risk of the pipe and improve the product quality.

In order to achieve the above purpose, the technical scheme provided by the invention is as follows:

a method of manufacturing a low stress reinforced hollow wall tube comprising the steps of:

S1, extruding and forming a molten square tube material through square tube forming equipment to form an inner layer square tube;

s2: winding steel nets which are mutually overlapped on the surface of the inner square pipe to serve as a reinforcing layer;

S3: drawing the inner-layer square tube into cladding equipment, and cladding and shaping the molten square tube material to form an outer-layer square tube, wherein the inner-layer square tube, the steel mesh and the outer-layer square tube jointly form a composite square tube with a sandwich structure;

S4: drawing the composite square tubes to winding forming equipment, winding adjacent composite square tubes in an abutting mode on the winding forming equipment, and filling and adhering the adjacent composite square tubes by using a melt adhesive to form hollow wall tubes;

S5: and (3) heating and annealing the pipe outside the hollow wall pipe through an electromagnetic heating device, so that the inner square pipe and the outer square pipe are subjected to stress removal.

Compared with the prior art, the technical scheme that the steel mesh is lapped as the reinforcing layer in the twice forming process of the square tube, and the square tube is wound and formed into the hollow wall tube and then is assisted with the electromagnetic heating device for annealing and stress relief is achieved, so that the technical effects that the axial strength of the square tube is high when the square tube is pulled and wound, the square tube cannot break and deform, and the bending square tube cannot crack due to stress removal are achieved.

Preferably, in the step S1, the melting temperature of the square tube material is 160-270 ℃, the square tube material is preheated in an oven by electromagnetic heating before melting, the preheating temperature is 70-120 ℃, and the heat preservation duration is 20-60min after preheating. Based on the scheme, the square tube material can be preheated before melting, the granularity of the melted material is better, the material is uniform, the preheated square tube material is easier in the subsequent melting, and the melting energy consumption and time are saved.

Specifically, the lapping mode in the step S2 includes two modes of forward lapping and staggered lapping; and in the forward lapping mode, the lapping and overlapping width B of the adjacent steel nets is 1-10mm, the axial included angle A between the steel nets and the inner square pipe is 20-70 degrees in the lapping process, the steel nets are hollow structures, and the hollow shapes are square. Through the steel mesh of mutual overlap joint, can form the closely tensile enhancement layer of one deck in the surface of inlayer side pipe, set up certain overlap width B and slope contained angle A, can make the better with the compaction of inlayer side pipe surface of lapped steel mesh, the shape of fretwork sets up to square, can alleviate the weight of steel mesh and have stronger tensile strength.

Further, the specific method of step S3 includes:

S31, fixing the coating equipment, the vacuum sizing die and the cooling sizing die in sequence and setting parameters;

s32, pulling the inner square tube to a section bar clamp in the cladding equipment, clamping the inner square tube and a steel mesh overlapped on the inner square tube, and heating the square tube material to a molten state;

S33, pushing the clamped inner-layer square tube and steel net into a vacuum sizing die, pouring molten square tube material for cladding and shaping, sealing the vacuum sizing die, completing vacuum sizing after 10-20 seconds of time delay, and pushing the vacuum sizing die into a cooling shaping die for liquid cooling shaping to form an outer-layer square tube;

s34, liquid cooling and shaping for 20-30 seconds, wherein liquid cooling is carried out by adopting water, the water temperature is 10-20 ℃, and the vacuum degree is-0.04 MPa +/-0.02 MPa; and obtaining the composite square tube with the middle layer of steel mesh and the outer square tube and the inner square tube of the same material.

Further, the specific method of step S4 includes:

s41, after the composite square tube is heated to a plastic state, the composite square tube is pulled to a forming device wound by the hollow wall tube, so that the forming device and the composite square tube are synchronously pushed, and a pinch roller assembly of the forming device extrudes the composite square tube, so that the wound adjacent composite square tubes are sequentially abutted and combined and are tightly attached to a roller of the forming device, and the winding rotating speed is 5-30 r/min;

s42, extruding the melt adhesive by using melt adhesive extruding equipment, wherein the temperature of the melt adhesive is 180-270 ℃, the melt pressure is 10-30 MPa, and the melt adhesive is thermally sprayed into forming equipment wound by a hollow wall pipe, when the composite square pipes are synchronously stretched in the same direction, the melt adhesive is filled in gaps between every two adjacent composite square pipes, and after filling, pressing wheels are adopted to flatten the composite square pipes;

s43, spraying cooling water through the liquid cooling equipment to cool to obtain the hollow wall pipe, and keeping the hollow wall pipe on the forming equipment.

Further, the specific method of step S5 includes:

s51, arranging an electromagnetic heating device on one side of the forming equipment to heat the hollow wall pipe on the forming equipment;

s52: synchronously rotating a roller of the forming equipment at the rotating speed of 10-40r/min to uniformly heat the hollow wall pipe, wherein the heating temperature is lower than the crystallization temperature of the square pipe material, and the heating time is 3-20min;

s53: and after the heating is finished, the electromagnetic heating device is closed, and the annealing is performed by standing at normal temperature for 30-60min, so that the stress of the hollow wall tube is removed.

Further, the inner square tube and the outer square tube are made of the same material and are made of one of polyethylene, polypropylene, modified polypropylene and modified polyethylene.

The hollow wall pipe manufactured by the method is formed by sequentially propping up composite square pipes of a sandwich structure through spiral winding, the sequentially propped up composite square pipes are adhered through melt adhesive, the composite square pipes comprise inner-layer square pipes, outer-layer square pipes and steel nets positioned in the middle layer, wherein the inner-layer square pipes and the outer-layer square pipes are all square in longitudinal section, and the forming mode is thermoplastic.

Further, the thickness T of the inner layer and the thickness T of the outer layer are 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 pipe is 5-20 times of the height H of the composite square pipe, and the width C of the composite square pipe is 5-20 times of the thickness L of the melt adhesive.

Further, the material of the melt adhesive is the same as that of the composite square tube.

The invention has the beneficial effects that:

1. By overlapping the steel mesh as a reinforcing layer in the process of twice forming the composite square tube, winding and forming the composite square tube into a hollow wall tube, and then annealing and stress removing by assisting an electromagnetic heating device, the axial strength of the square tube can be improved when the composite square tube is pulled and wound, the square tube cannot be broken and deformed, and the bent square tube cannot crack due to stress removal;

2. In the electromagnetic heating process, the composite square tube with the sandwich structure can release stress from inside to outside, so that the efficiency of removing residual stress can be improved, and compared with the traditional method, the composite square tube with the sandwich structure occupies small space, has low energy consumption and saves production cost;

3. the steel mesh can produce the vortex under electromagnetic induction's coil effect and generate heat, can conveniently adjust the temperature of annealing heating through control output, and electromagnetic induction coil group can set up one or multiunit according to hollow wall pipe's production speed and length moreover, convenient to use is nimble.

4. The steel mesh is arranged between the inner square tube and the outer square tube of the composite square tube, when the composite square tube is heated by the electromagnetic heating device, the steel mesh can generate eddy current heating under the action of the electromagnetic induction coil, compared with the outer square tube, the steel mesh is faster in temperature rise and gradually conducts heat to the outer layer, so that the composite square tube is heated from the opposite inner layer to the outer layer, and stress concentration caused by winding is released; compared with the traditional infrared method, the infrared method is equivalent to heating the surface of the outer layer of the composite square tube, and then conducting heat to the inner layer, and stress concentration generated by the inner layer cannot be released due to the fact that the heat is conducted and heated from outside to inside, so that the scheme provided by the invention has obvious beneficial effects.

Drawings

FIG. 1 is a longitudinal cross-sectional view of a composite square tube in an embodiment of the invention;

FIG. 2 is a longitudinal cross-sectional view of a hollow wall tube in an embodiment of the invention;

FIG. 3 is a schematic illustration of the forward overlap of an inner square tube and a steel mesh in an embodiment of the invention;

FIG. 4 is a schematic illustration of an inner layer square tube and steel mesh overlap joint in an embodiment of the invention;

fig. 5 is a schematic view of equipment used in the winding and annealing process of the hollow wall tube in the embodiment of the present invention.

The drawing is marked with 1-composite square tube, 11-inner square tube, 12-outer square tube, 13-steel mesh, 2-melt adhesive, 3-hollow wall tube, 4-forming equipment, 41-roller, 5-liquid cooling equipment and 6-electromagnetic heating device.

Detailed Description

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. The components of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Accordingly, the following detailed description of the invention, as provided in the accompanying drawings, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without making any inventive effort, are intended to be within the scope of the present invention.

In describing embodiments of the present invention, it should be noted that, unless explicitly stated and limited otherwise, the terms "mounted," "connected," and "connected" should be construed broadly, and for example, the terms "connected" may be removably connected or non-removably connected; may be directly connected or indirectly connected through an intermediate medium. Wherein, "fixedly connected" means that the relative positional relationship is unchanged after being connected with each other. It will be appreciated that when part a is fixedly connected to part C by part B, a change in the relative positional relationship due to deformation of parts a, B and C themselves is permitted. "rotationally coupled" means coupled to each other and capable of relative rotation after coupling. "slidingly coupled" means coupled to each other and capable of sliding relative to each other after being coupled. Wherein, the two parts are integrally formed to form an integrated structure, which means that in the process of forming one of the two parts, the one part is connected with the other part, and the two parts are not required to be connected together by a reworking (such as bonding, welding, buckling connection and screw connection) mode.

References to orientation terms, such as "upper", "lower", "side", "top", "bottom", etc., in the embodiments of the present application are merely to refer to the orientation of the drawings, and thus the use of orientation terms is intended to better and more clearly illustrate and understand the embodiments of the present application, rather than to indicate or imply that the devices or elements being referred to must have a particular orientation, be constructed and operate in a particular orientation, and therefore should not be construed as limiting the embodiments of the present application.

The term "plurality" means at least two. The term "above" includes this number. The term "and/or" is an association relationship describing an associated object, meaning that there may be three relationships, e.g., a and/or B, which may represent: a exists alone, A and B exist together, and B exists alone. The terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as implying or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.

In order to improve the axial strength of the hollow wall pipe in the winding forming process and reduce the residual stress of the hollow wall pipe, the invention provides a manufacturing method of a low-stress reinforced hollow wall pipe, which comprises the following steps:

Referring to the square tube longitudinal section of fig. 1, S1, extruding molten square tube material through a first molding device to form an inner square tube 11; wherein the square tube material is polypropylene (PP), the melting temperature is 160-270 ℃, in this embodiment 200 ℃, the square tube material is preheated in an oven by electromagnetic heating before melting, the preheating temperature is 70-120 ℃, in this embodiment 100 ℃, and the heat preservation duration after preheating is 20-60min. The square tube material is preheated before melting, the granularity of the melted material is better, the material is uniform, and the preheated square tube material is easier in the subsequent melting, so that the melting energy consumption and the melting time are saved.

Please refer to the lap joint schematic diagrams of the inner square tube and the steel net in fig. 3-4, S2: steel mesh 13 which is lapped with each other is wound on the surface of the inner square pipe 11 to be used as a reinforcing layer; the lapping mode comprises forward lapping and staggered lapping; referring to fig. 3, in the forward lapping mode, the overlapping width B of the adjacent steel mesh 13 is 1-10mm, in this embodiment, 5mm, and the axial included angle a between the steel mesh 13 and the inner square tube 11 is 20-70 degrees, in this embodiment, 45 degrees, where the steel mesh 13 is in a hollow structure, and the hollow shape is square. Through the steel mesh 13 of mutual overlap joint, can form the closely tensile enhancement layer of one deck in the surface of inlayer side pipe 11, set up overlap width B of 5mm and 45 degrees inclination contained angle A, can make the better and inner layer side pipe surface compact of lapped steel mesh, the shape of fretwork sets up to square, can alleviate the weight of steel mesh and have stronger tensile strength.

After being lapped with the steel mesh 13, the outer square tube 12 is formed by thermoplastic molding on the basis, and the specific steps comprise S3: drawing the inner square tube 11 into cladding equipment, and cladding and shaping the molten square tube material to form an outer square tube 12; the specific method comprises the following steps:

s32, pulling the inner square tube 11 to a section bar clamp in cladding equipment, clamping a steel net 13 overlapped on the outer surface of the inner square tube 11, and heating the square tube material to a molten state;

S33, pushing the clamped inner square tube 11 and steel mesh 13 into a vacuum sizing die, pouring molten square tube material for cladding and sizing, sealing the vacuum sizing die, completing vacuum sizing after 10-20 seconds of time delay, and pushing into a cooling sizing die for liquid cooling sizing to form an outer square tube;

S34, liquid cooling and shaping for 20-30 seconds, wherein the liquid cooling adopts water for liquid cooling, the water temperature is 10-20 ℃, and the vacuum degree is-0.04 MPa +/-0.02 MPa.

The composite square tube 1 manufactured by thermoplastic in the process forms a sandwich structure with the middle layer of steel mesh 13 and the outer layer square tube 12 and the inner layer square tube 11 made of the same material; then the manufactured composite square tube 1 is pulled to a roller 41 of a forming device 4 for winding the hollow wall tube by a pulling device to be mutually abutted and wound, and the extruded melt adhesive 2 is used for filling and adhering to form the hollow wall tube 3; the specific process comprises the following steps:

S41, after the composite square tube 1 is heated to a plastic state, the composite square tube 1 is pulled to a forming device 4 wound by a hollow wall tube, so that the forming device 4 and the composite square tube 1 are synchronously pushed, and a pinch roller assembly of the forming device 4 extrudes the composite square tube 1, so that the wound adjacent composite square tube 1 is sequentially abutted against, combined and tightly attached to a roller 41 of the forming device 4, and the winding rotating speed is 5-30 r/min, and in the embodiment, 20r/min;

S42, extruding the molten adhesive 2 by using a molten adhesive extruding device, wherein the temperature of the molten adhesive 2 is 180-270 ℃, the temperature is 200 ℃ in the embodiment, the molten pressure is 10-30 MPa, the molten pressure is 15MPa, the molten adhesive is thermally sprayed into a forming device 4 wound by a hollow wall pipe 3, when the composite square pipes 1 are synchronously stretched in the same direction, the molten adhesive 2 is filled in gaps between every two adjacent composite square pipes 1, and after the gaps are filled, the composite square pipes 1 are flattened by using a pinch roller;

S43, spraying cooling water through the liquid cooling device 5 to cool to obtain the hollow wall pipe 3, and keeping the hollow wall pipe on the forming device 4.

Referring to the longitudinal sectional view of the hollow wall tube in fig. 2 and the schematic equipment used in the winding and annealing process of the hollow wall tube in fig. 5, the formed hollow wall tube 3 needs to be heated and annealed to remove residual stress generated by winding, and the specific method is as follows: the pipe is heated and annealed outside the hollow wall pipe 3 by an electromagnetic heating device 6, comprising:

S51, arranging an electromagnetic heating device 6 on one side of the forming equipment 4 to heat the hollow wall pipe 3 on the forming equipment 4;

S52: the roller 41 of the forming equipment 4 is synchronously rotated at the rotating speed of 10-40r/min, 30r/min in the embodiment, so that the hollow wall pipe 3 is uniformly heated, the heating temperature is lower than the crystallization temperature of the square pipe material, the heating time is 3-20min, the material of the composite square pipe in the embodiment is polypropylene, and the heating temperature is lower than the crystallization temperature of 150 ℃ and the heating time is 5min; if the material of the composite square tube 1 is polyethylene, the heating temperature is lower than the crystallization temperature of the composite square tube by 100 ℃ and the heating time is 3min;

S53: after the heating is finished, the electromagnetic heating device 6 is closed, standing is performed at normal temperature for annealing, the standing time is 30-60min, in the embodiment, 30min, and if the material is polyethylene, the standing time is 60min, so that the hollow wall pipe 3 realizes the process of removing stress from the inner layer square pipe 11 to the outer layer square pipe 12 layer by layer from inside to outside.

Referring to fig. 1-2, the hollow wall pipe 3 manufactured by the above method is formed by sequentially abutting and spirally winding composite square pipes 1 with a sandwich structure, the composite square pipes 1 abutted successively are adhered by a melt adhesive 2, the composite square pipes 1 comprise an inner square pipe 11, an outer square pipe 12 and a steel net 13 positioned in an intermediate layer, wherein the longitudinal sections of the inner square pipe 11 and the outer square pipe 12 are square, the thicknesses T of the inner square pipe 11 and the outer square pipe 12 are the same, the thickness T of the steel net 13 is 1/20-1/4 of the thicknesses T of the inner square pipe 11 and the outer square pipe 12, T is 1/10 of the thickness T in the embodiment, the inner diameter D of the hollow wall pipe 3 is 8-10 times the height H of the composite square pipe 1, D is 10 times the height H in the embodiment, the width C of the composite square pipe 1 is 5-20 times the thickness L of the melt adhesive 2, C is 15 times the thickness L in the embodiment, and the material of the melt adhesive 2 is the same as the composite square pipe 1.

The following table shows the experimental data comparison between the hollow wall pipe prepared by the invention and the existing hollow wall pipe in the market:

Comparison item	Hollow wall tube of the present invention	Existing hollow wall pipe
			Ring stiffness (kN/m)	8~16	4~12.5
Impact Property	Hammer weight 12.5kg, impact height: 1m, sample 0 ℃ for 1 hour: experiment 20 were all unbroken	Hammer weight 12.5kg, impact height: 1m, sample 0 ℃ for 1 hour: experiment 20 occurrences of cracking to different extents
			Residual hoop stress	The method comprises the following steps: randomly intercepting the length 150mm plus or minus 5mm of the pipe, longitudinally cutting the pipe to a width of 2ec, and measuring the center distance results of two ends of the cut of the pipe after the pipe is placed for 7 days: the outward expansion opening is less than or equal to 3ec (residual stress is smaller)	The method comprises the following steps: randomly intercepting the length 150mm plus or minus 5mm of the pipe, longitudinally cutting the pipe to a width of 2ec, and measuring the center distance results of two ends of the cut of the pipe after placing the pipe for 7 days: the outward expansion opening is more than or equal to 4ec (high residual stress)
Tensile Strength of pipe	≥18MPa	≤15MPa

Note that: in the table, "ec" is the structural wall height of the pipe, and the height H of the composite square pipe is obtained by combining the invention.

By overlapping the steel mesh 13 as a reinforcing layer in the process of twice forming the composite square tube 1, winding and forming the hollow wall tube 3 and then annealing and stress removing by the electromagnetic heating device 6, the axial strength of the composite square tube 1 can be improved when the composite square tube 1 is pulled and wound, the composite square tube at the bending position is not broken and deformed, and the composite square tube at the bending position is not cracked due to stress removal; in addition, the composite square tube 1 with the sandwich structure can release stress from inside to outside in the electromagnetic heating process, so that the residual stress removing efficiency can be improved, and compared with the traditional method, the composite square tube 1 has the advantages of small occupied space, low energy consumption and production cost saving; the steel mesh 13 can generate eddy current to generate heat under the action of the electromagnetic induction coil, the annealing heating temperature can be conveniently adjusted by controlling the output power, and the electromagnetic induction coil group can be arranged into one group or a plurality of groups according to the production speed and the length of the hollow wall pipe 3, so that the electromagnetic induction coil is convenient and flexible to use.

It should be explained that, the steel mesh 13 is disposed between the inner layer square tube 11 and the outer layer square tube 12 of the composite square tube 1, when the composite square tube 1 is heated by the electromagnetic heating device 6, the steel mesh 13 can generate eddy current heating under the action of the electromagnetic induction coil, compared with the outer layer square tube 12, the steel mesh 13 heats up faster and gradually conducts heat to the outer layer, thereby realizing the heating of the composite square tube 1 from the opposite inner layer to the outer layer, and further releasing stress concentration generated by winding; compared with the traditional infrared method, the infrared method is equivalent to heating the surface of the outer layer of the composite square tube, and then conducting heat to the inner layer, and stress concentration generated by the inner layer cannot be released due to the fact that the heat is conducted and heated from outside to inside, so that the scheme provided by the invention has obvious beneficial effects.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned. Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to 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;

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: 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.

2. The manufacturing method according to claim 1 is characterized in that 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.

3. The manufacturing method according to claim 1 is characterized in that the overlapping method in step S2 is forward overlapping. During the forward overlapping, the overlapping width B of adjacent steel meshes is 1-10 mm, 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.

4. The manufacturing method according to claim 1, characterized in that the step S3 specifically comprises:

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.

5. The manufacturing method according to claim 1, characterized in that the step S4 specifically comprises:

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.

6. The manufacturing method according to claim 1, characterized in that the step S5 specifically comprises:

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.

7. The manufacturing method according to claim 1 is 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.

8. A hollow wall tube made according to any one of the manufacturing methods of claims 1-7, characterized in that the hollow wall tube is formed by spirally winding composite square tubes of a sandwich structure that are successively abutted against each other, and the composite square tubes that are successively abutted against each other are bonded by melt adhesive, and the composite square tube comprises 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.

9. The hollow wall tube according to claim 8 is 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 melt.

10 . The hollow wall tube according to claim 8 , wherein the molten adhesive is made of the same material as the composite square tube.