Improved large-diameter aluminum-plastic composite pipe and manufacturing method

Abstract

The invention discloses an improved large-diameter aluminum-plastic composite pipe and a manufacturing method, and belongs to the technical field of pipeline materials, the improved large-diameter aluminum-plastic composite pipe comprises five layers of symmetrical composite structures: an inner plastic layer, a first bonding layer, an aluminum base layer, a second bonding layer and an outer plastic layer; wherein the surface of the aluminum base layer is subjected to pre-oxidation treatment to form a nanoscale Al2O3 transition layer of 50-200 nm, the interface bonding force is remarkably improved, the ring stiffness and oxygen resistance are improved through a five-layer symmetrical composite structure (an inner plastic layer / a bonding layer / a pre-aluminum oxide base layer / a bonding layer / an outer plastic layer), and mounting is conducted by combining a connector, a reinforcing ring and a reinforcing rib; according to the manufacturing method, co-extrusion molding and pre-oxidation treatment are adopted, the structural stability is high, the oxygen barrier performance is excellent, the connection reliability is high, the production efficiency solves the problems that a large-diameter aluminum-plastic pipe is prone to layering and low in production efficiency, and the aluminum-plastic pipe is suitable for high-pressure and long-life conveying scenes.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of pipeline materials, and particularly relates to a large-diameter aluminum-plastic composite pipe suitable for high-pressure and long-life conveying scenarios, and a manufacturing method thereof, and is particularly suitable for municipal water supply, gas conveying, industrial fluid transmission and the like. BACKGROUND

[0002] Aluminum-plastic composite pipes (PAP pipes) are widely used in building water supply, gas and the like due to the composite advantages of metal and plastic (such as corrosion resistance, oxygen resistance and good flexibility). However, the traditional large-diameter (DN110mm or more) aluminum-plastic composite pipe still has the following defects in actual application:

[0003] 1. Insufficient ring stiffness: due to the increase in the radial size of the large-diameter pipe material, the difference in the thermal expansion coefficients of the aluminum layer and the plastic layer (the thermal expansion coefficient of aluminum is about 23x10 -6 / ℃, and the thermal expansion coefficient of polyethylene is about 10x10 -6 / ℃) easily leads to stress concentration between the layers, which easily causes delamination during long-term use, affecting the structural stability;

[0004] 2. Low connection reliability: the traditional aluminum-plastic pipe is mostly connected by crimping or flaring. Due to the increase in the wall thickness and the increase in the material rigidity of the large-diameter pipe material, problems such as poor sealing and virtual welding easily occur at the connection, leading to the risk of leakage;

[0005] 3. Unstable oxygen resistance: if the aluminum layer has microcracks or is not tightly combined with the plastic layer, oxygen easily penetrates through the interface, accelerating the oxidation and corrosion of the fluid (such as hot water and gas) in the pipe;

[0006] 4. Low production efficiency: when the large-diameter pipe material is co-extruded, the difference in the melting states of the aluminum layer and the plastic layer is large, which easily leads to problems such as poor interface combination and rough surface, and multiple edge trimming or post-processing is required, increasing the cost.

[0007] Therefore, it is urgent to develop a large-diameter aluminum-plastic composite pipe with optimized structure, reliable connection, strong oxygen resistance and suitable for industrial production, and a manufacturing method thereof. SUMMARY

[0008] (I) Technical problems solved

[0009] In view of the deficiencies of the prior art, the present application provides an improved large-diameter aluminum-plastic composite pipe and a manufacturing method thereof, which solves the problems of easy delamination, unreliable connection, poor oxygen resistance and low production efficiency of the large-diameter aluminum-plastic pipe through structural design and process optimization.

[0010] (II) Technical solutions

[0011] In order to achieve the above object, the present application is implemented by the following technical scheme: An improved large-diameter aluminum-plastic composite pipe comprises a five-layer symmetrical composite structure: an inner plastic layer, a first adhesive layer, an aluminum base layer, a second adhesive layer, and an outer plastic layer; wherein the surface of the aluminum base layer is pre-oxidized to form a 50-200nm nanoscale Al2O3 transition layer.

[0012] Preferably, the thickness of the inner plastic layer and the outer plastic layer is 1.5-3.0mm, and the material is HDPE / PP-R and LLDPE / CPVC, respectively.

[0013] Preferably, the outer plastic layer is further provided with an anti-corrosion coating made of a mixture of nanometer titanium dioxide and organic silicone resin, further improving the corrosion resistance of the pipe.

[0014] Preferably, a socket joint is arranged at each end of the composite pipe, the inner wall of the socket joint is provided with an annular groove, and a sealing rubber ring is installed in the annular groove, which can effectively improve the sealing performance of the connection; the outer wall of the socket joint is provided with an external thread, which is used in cooperation with a connecting pipe fitting with an internal thread to enhance the connection strength.

[0015] Preferably, a reinforcing ring is arranged at both ends of the aluminum base layer, the reinforcing ring is made of aluminum alloy with the same material as the aluminum layer, and is fixed on the aluminum base layer by welding, the outer diameter of the reinforcing ring matches the inner diameter of the socket joint, and when connected, the reinforcing ring is inserted into the socket joint, further improving the strength and stability of the connection part.

[0016] Preferably, reinforcing ribs are installed between the aluminum base layer and the inner plastic layer and between the aluminum base layer and the outer plastic layer, the reinforcing ribs are spirally wound, which improves the flexibility of the pipe while enhancing the compressive strength of the pipe.

[0017] Preferably, the thickness of the first adhesive layer and the second adhesive layer is 0.1-0.3mm, and the first adhesive layer and the second adhesive layer are made of maleic anhydride grafted polyethylene (PE-g-MAH) or ethylene-vinyl acetate copolymer (EVA), which is used to enhance the bonding force between the inner plastic layer and the aluminum layer.

[0018] A manufacturing method of an improved large-diameter aluminum-plastic composite pipe comprises the following steps:

[0019] Step 1: Pretreatment of the aluminum base layer

[0020] After the aluminum coil (thickness 1.0-2.5mm) is unwound, it is sequentially subjected to cleaning (oil removal), alkaline cleaning (60g / L NaOH solution, 60°C, 30s), acid cleaning (150g / L H2SO4 solution, room temperature, 15s), deionized water cleaning to remove surface impurities; it is then subjected to pre-oxidation treatment: air is passed at 400-450°C for 5-10 minutes to form a 50-200nm Al2O3 transition layer.

[0021] Step 2: co-extrusion of inner and outer plastic layers and adhesive layer

[0022] Three extruders (one each for the inner and outer layers, and one for the adhesive layer) are used in conjunction with an aluminum strip compounding device:

[0023] - inner plastic layer: the extruder temperature is set to 180-220°C (HDPE) or 200-240°C (PP-R), and the melt is extruded through the die to coat one side of the pretreated aluminum strip;

[0024] - first adhesive layer: the extruder temperature is set to 160-190°C (PE-g-MAH) or 150-180°C (EVA), and the melt is coated onto the surface of the inner plastic layer and contacts the aluminum strip;

[0025] - aluminum strip conveying: the aluminum strip is uniformly conveyed at a speed of 0.5-2m / min by a traction roller to ensure that the aluminum strip is synchronously attached to the adhesive layer;

[0026] - second adhesive layer and outer plastic layer: the extrusion process of the adhesive layer and the plastic layer described above is repeated to complete the preliminary formation of the five-layer composite structure.

[0027] Step 3: cooling and sizing and online detection

[0028] The composite pipe is rapidly cooled by passing through a vacuum cooling sizing sleeve (water temperature 20-30°C), and the wall thickness of the pipe is monitored in real time by a laser thickness gauge (accuracy ±0.1mm), and unqualified products are automatically rejected; after cooling, an X-ray flaw detector is used to detect whether there are bubbles or delamination at the interface between the aluminum layer and the plastic layer (allowable defect area ≤0.5%).

[0029] Step 4: installation of socket-type connector: a socket-type connector is installed at each end of the composite pipe, a sealing rubber ring is first installed in the annular groove of the connector, then the socket-type connector is fitted over the end of the composite pipe, and a dedicated welding device is used to weld and fix the socket-type connector to the outer plastic layer of the composite pipe, with the welding temperature controlled at 200-220°C and the welding time controlled at 10-15s to ensure the connection strength of the socket-type connector to the composite pipe.

[0030] Step 5. Reinforcing ring and reinforcing rib installation: the pre-prepared reinforcing ring is fixed on both ends of the aluminum base layer by welding; then the reinforcing rib is installed between the aluminum base layer and the inner plastic layer, and between the aluminum base layer and the outer plastic layer, one end of the reinforcing rib is fixedly connected with the inner plastic layer or the outer plastic layer by using hot melt adhesive, and the other end is tightly attached with the aluminum base layer, the heating temperature of the hot melt adhesive is controlled at 180-200℃ to ensure the fixing effect of the reinforcing rib;

[0031] Step 6. Coating an anti-corrosion coating; mix nano titanium dioxide and silicone resin in a certain proportion (for example, nano titanium dioxide accounts for 20%-40%, silicone resin accounts for 60%-80%, and the specific proportion can be adjusted according to actual needs) to form an anti-corrosion coating; the anti-corrosion coating is evenly coated on the surface of the outer plastic layer by spraying or dipping; when spraying, the pressure of the spray gun is controlled at 0.3-0.5MPa, and the distance between the spray gun and the surface of the pipe is kept at 20-30cm to obtain a uniform coating thickness; when dipping, the pipe is slowly dipped into the coating and slowly taken out after 5-10 seconds to allow the coating to flow naturally; after coating is completed, the pipe is placed in a drying oven and dried at a temperature of 80-100℃ for 30-60 minutes to completely cure the anti-corrosion coating, thereby further improving the corrosion resistance of the pipe.

[0032] (Three) beneficial effects

[0033] The present application provides an improved large-diameter aluminum-plastic composite pipe and a manufacturing method. It has the following beneficial effects:

[0034] 1. High structural stability: the Al2O3 transition layer formed by pre-oxidizing the surface of the aluminum layer significantly improves the interfacial bonding strength, and after 10000 cold and hot cycles (-40℃ to 80℃), the interlayer peeling strength is still ≥5N / cm (≤3N / cm for traditional aluminum-plastic pipes);

[0035] 2. Excellent oxygen barrier performance: the outer plastic layer is added with an antioxidant, combined with the oxygen barrier of the aluminum layer (oxygen transmission rate ≤0.1g / (m 2 ·day)), suitable for the transportation of oxygen-sensitive fluids (such as hot water, fuel oil);

[0036] 3. High connection reliability: the double-sealing groove + hot melt welding process improves the connection strength of large-diameter pipes by 40%, and there is no leakage after 1.6MPa pressure test (pressure holding for 1 hour);

[0037] 4. High production efficiency: the co-extrusion molding process controls the temperature accurately and detects online, with a waste rate ≤1% (≥5% for traditional processes), suitable for large-scale industrial production.

[0038] 5. The improved large-diameter aluminum-plastic composite pipe of the present application adopts a socket joint, cooperates with a sealing rubber ring and a reinforcing ring, effectively improves the strength and sealing performance of the connection, can adapt to high-pressure conveying environment, reduces the risk of leakage and improves the safety in use.

[0039] 6. By arranging the reinforcing ribs between the aluminum layer and the plastic layer, the deformation resistance of the pipe material is enhanced, which can effectively cope with external pressure and temperature changes and prolong the service life of the pipe material. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a structural schematic view of the improved large-diameter aluminum-plastic composite pipe of the present application;

[0041] Figure 2 is an SEM micrograph of the surface of the aluminum base layer after pre-oxidation (showing the Al2O3 transition layer);

[0042] Figure 3 is a connection structure schematic view of the socket joint of the present application;

[0043] Figure 4 is a process flow chart of the manufacturing method of the present application.

[0044] In the figure: 1, inner plastic layer; 2, first adhesive layer; 3, aluminum base layer; 4, second adhesive layer; 5, outer plastic layer; 6, corrosion-resistant coating; 7, socket joint; 8, annular groove; 9, sealing rubber ring; 10, reinforcing ring; 11, reinforcing rib; 12, connecting pipe fitting. DETAILED DESCRIPTION

[0045] The present application provides an improved large-diameter aluminum-plastic composite pipe and a manufacturing method, as shown in the figure, the aluminum-plastic composite pipe is a five-layer symmetrical composite structure (in the radial direction from inside to outside in turn): inner plastic layer 1, first adhesive layer 2, aluminum base layer 3, second adhesive layer 4, outer plastic layer 5. Figures 1-4

[0046] Among them, the surface of the aluminum base layer 3 is pre-oxidized to form a 50-200nm nanoscale Al2O3 transition layer.

[0047] Preferably, the thickness of the inner plastic layer 1 and the outer plastic layer 5 is 1.5-3.0mm, and the material is HDPE / PP-R and LLDPE / CPVC respectively.

[0048] Preferably, the outer plastic layer 5 is also provided with a corrosion-resistant coating 6, which is made of a mixture of nanometer titanium dioxide and organic silicone resin, further improving the corrosion resistance of the pipe material.

[0049] ​Preferably, a socket joint 7 is arranged at each end of the composite pipe, the inner wall of the socket joint 7 is provided with an annular groove 8, and a sealing rubber ring 9 is arranged in the annular groove 8, so that the sealing performance of the joint can be effectively improved; the outer wall of the socket joint 7 is provided with external threads, and is used in cooperation with a joint pipe fitting 12 with internal threads, so that the joint strength is enhanced.

[0050] Preferably, a reinforcing ring 10 is arranged at each end of the aluminum base layer 3, the reinforcing ring 10 is made of aluminum alloy with the same material as the aluminum layer, and is fixed on the aluminum base layer 3 by welding, the outer diameter of the reinforcing ring 10 matches the inner diameter of the socket joint 7, and when the joint is connected, the reinforcing ring 10 is inserted into the socket joint 7, so that the strength and stability of the joint part are further improved.

[0051] Preferably, a reinforcing rib 11 is arranged between the aluminum base layer 3 and the inner plastic layer 1 and between the aluminum base layer 3 and the outer plastic layer 5, the reinforcing rib 11 is spirally wound, so that the flexibility of the pipe is improved and the compressive strength of the pipe is enhanced.

[0052] Preferably, the first adhesive layer 2 has a thickness of 0.1-0.3mm, and is made of maleic anhydride grafted polyethylene (PE-g-MAH) or ethylene-vinyl acetate copolymer (EVA), which is used to enhance the bonding force between the inner plastic layer 1 and the aluminum layer.

[0053] A manufacturing method of an improved large-diameter aluminum-plastic composite pipe, comprising the following steps:

[0054] 1. Pretreatment of the aluminum base layer 3: after cleaning, alkali washing and acid washing, air is introduced to oxidize at 400-450℃ for 5-10 minutes to form an Al2O3 transition layer;

[0055] 2. Co-extrusion molding: the inner plastic layer 1, the adhesive layer and the outer plastic layer 5 are respectively extruded through three extruders, and are synchronously compounded with the pretreated aluminum strip;

[0056] 3. Cooling and shaping: cooling and shaping are performed through a vacuum cooling and shaping sleeve, and wall thickness and interface defects are detected online at the same time;

[0057] Key improvement points:

[0058] The surface of the aluminum base layer 3 is pre-oxidized to form a nanoscale Al2O3 transition layer, the dense oxide film on the surface of the aluminum is destroyed (the thickness of the natural oxide film on the surface of the traditional aluminum layer is about 5-10nm), the surface roughness (Ra=0.8-1.2μm) is increased, and the mechanical interlocking force and the chemical bonding effect with the adhesive layer are improved;

[0059] The outer plastic layer 5 is made of LLDPE or CPVC, and the environmental stress cracking resistance (ESCR) is 3-5 times higher than that of ordinary PE, so that the service life of the pipe is prolonged;

[0060] - The thickness of the inner and outer plastic layers 5 is symmetrically designed (1.5-3.0 mm) to balance the radial stiffness and axial flexibility of the pipe, avoiding deformation caused by gravity or external pressure in large-diameter pipes.

[0061] Manufacturing method

[0062] The manufacturing method of the present application comprises the following steps:

[0063] Step 1: Pretreatment of aluminum base layer 3

[0064] After unwinding the aluminum coil (thickness 1.0-2.5 mm), sequentially perform cleaning (remove oil stains), alkali washing (60 g / L NaOH solution, 60°C, 30s), acid washing (150 g / L H2SO4 solution, room temperature, 15s), deionized water cleaning to remove surface impurities; then perform pre-oxidation treatment: pass air at 400-450°C, oxidation time 5-10 minutes, forming a 50-200 nm Al2O3 transition layer.

[0065] Step 2: Co-extrusion of inner and outer plastic layers 5 and adhesive layer

[0066] Use three extruders (one for each inner and outer layers, and the middle layer as the adhesive layer) in conjunction with an aluminum strip compounding device:

[0067] - Inner plastic layer 1: extruder temperature set to 180-220°C (HDPE) or 200-240°C (PP-R), the melt is extruded through the die to coat one side of the pretreated aluminum strip;

[0068] - First adhesive layer 2: extruder temperature set to 160-190°C (PE-g-MAH) or 150-180°C (EVA), the melt covers the surface of the inner plastic layer 1 and contacts the aluminum strip;

[0069] - Aluminum strip conveying: uniform speed conveying at 0.5-2 m / min through the traction roller to ensure synchronous lamination of the aluminum strip and the adhesive layer;

[0070] - Second adhesive layer 4 and outer plastic layer 5: repeat the above extrusion process of the adhesive layer and the plastic layer to complete the preliminary formation of the five-layer composite structure.

[0071] Step 3: Cooling and sizing

[0072] The composite pipe is rapidly cooled through a vacuum cooling sizing sleeve (water temperature 20-30°C), while the wall thickness is monitored in real time by a laser thickness gauge (accuracy ±0.1 mm), and unqualified products are automatically rejected; after cooling, an X-ray flaw detector is used to detect whether there are bubbles or delamination at the interface between the aluminum layer and the plastic layer (allowable defect area ≤0.5%).

[0073] Step 4: Installation of the socket joint 7: Install the sealing rubber ring 9 in the annular groove 8 of the socket joint 7, then put the socket joint 7 on the end of the composite pipe, and use special welding equipment to weld and fix the socket joint 7 with the outer plastic layer 5 of the composite pipe, with the welding temperature controlled at 200-220℃ and the welding time at 10-15s to ensure the connection strength of the socket joint 7 with the composite pipe.

[0074] Step 5: Installation of the reinforcing ring 10 and the reinforcing rib 11: Fix the pre-prepared reinforcing ring 10 on both ends of the aluminum base layer 3 by welding; then install the reinforcing rib 11 between the aluminum base layer 3 and the inner plastic layer 1 and between the aluminum base layer 3 and the outer plastic layer 5, with one end of the reinforcing rib 11 fixed and connected with the inner plastic layer 1 or the outer plastic layer 5 and the other end closely attached to the aluminum base layer 3 by using hot melt adhesive, with the heating temperature of the hot melt adhesive controlled at 180-200℃ to ensure the fixing effect of the reinforcing rib 11;

[0075] Step 6: Application of the anti-corrosion coating 6: Mix nano titanium dioxide and silicone resin in a certain proportion (for example, nano titanium dioxide accounts for 20%-40% and silicone resin accounts for 60%-80%, and the specific proportion can be adjusted according to actual needs) to form an anti-corrosion coating; uniformly apply the anti-corrosion coating to the surface of the outer plastic layer 5 by spraying or dipping; when spraying, control the pressure of the spray gun at 0.3-0.5MPa and keep the distance between the spray gun and the surface of the pipe at 20-30cm to obtain a uniform coating thickness; when dipping, slowly immerse the pipe in the coating, stay for 5-10s, and then slowly take it out to allow the coating to flow naturally; after the coating is completed, put the pipe into a drying oven and dry it at a temperature of 80-100℃ for 30-60min to completely cure the anti-corrosion coating 6, thereby further improving the corrosion resistance of the pipe.

[0076] Example 1: DN160mm aluminum-plastic composite pipe for municipal water supply

[0077] Structural parameters: inner plastic layer 1 (HDPE, thickness 2.0mm), first adhesive layer 2 (PE-g-MAH, thickness 0.2mm), aluminum base layer 3 (3003 aluminum, thickness 2.0mm, Al2O3 layer thickness 100nm after pre-oxidation), second adhesive layer 4 (PE-g-MAH, thickness 0.2mm), outer plastic layer 5 (LLDPE, thickness 2.0mm, containing 0.5% antioxidant 1010 and 0.3% ultraviolet absorber UV-531).

[0078] Manufacturing process:

[0079] Aluminum base pretreatment: 420℃ oxidation for 8min to form a uniform Al2O3 layer;

[0080] Co-extrusion temperature: inner layer 200°C (HDPE), adhesive layer 170°C (PE-g-MAH), outer layer 220°C (LLDPE);

[0081] Cooling water temperature 25°C, pulling speed 1.2 m / min;

[0082] Welding parameters: preheating temperature 230°C, pressure 0.2 MPa, cooling time 15 minutes.

[0083] Performance test: ring stiffness (8 kN / m 2 ) ≥ 10 kN / m 2 (standard requirement ≥ 8 kN / m 2 ), oxygen permeation rate ≤ 0.08 g / (m 2 ·day), no leakage under 1.6 MPa pressure for 1 hour.

[0084] Example 2: DN200 mm industrial gas pipeline

[0085] Structural parameters: inner plastic layer 1 (PP-R, thickness 2.5 mm), first adhesive layer 2 (EVA, thickness 0.3 mm), aluminum base layer 3 (pure aluminum, thickness 2.5 mm, Al2O3 layer thickness 150 nm after pre-oxidation), second adhesive layer 4 (EVA, thickness 0.3 mm), outer plastic layer 5 (CPVC, thickness 2.5 mm, containing 1.0% antioxidant 1076).

[0086] Manufacturing process:

[0087] Aluminum base pretreatment: 450°C oxidation for 10 minutes, forming a thicker Al2O3 layer;

[0088] Co-extrusion temperature: inner layer 230°C (PP-R), adhesive layer 180°C (EVA), outer layer 250°C (CPVC);

[0089] Cooling water temperature 30°C, pulling speed 0.8 m / min;

[0090] Welding parameters: preheating temperature 260°C, pressure 0.25 MPa, cooling time 20 minutes.

[0091] Performance test: gas permeation resistance (methane) ≤ 0.01 g / (m 2 ·day) (standard requirement ≤ 0.05 g / (m 2 ·day), no delamination after cold and hot cycle (-40°C ~ 80°C, 1000 times).

[0092] In summary, the improved large-diameter aluminum-plastic composite pipe improves ring stiffness and oxygen resistance through a five-layer symmetrical composite structure (inner plastic layer 1 / adhesive layer / pre-oxidized aluminum base layer 3 / adhesive layer / outer plastic layer 5), and is combined with connector installation, reinforcement ring 10 and reinforcing rib 11 installation; the manufacturing method adopts co-extrusion molding and pre-oxidation treatment, has high structural stability, excellent oxygen resistance performance, high connection reliability, solves the problems of easy delamination and low production efficiency of large-diameter aluminum-plastic pipes, and is suitable for high-pressure and long-life conveying scenes.

[0093] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely divergences of the principles and spirit of the application and that numerous modifications, changes, replacements, and variations can be made thereto by those of ordinary skill in the art without departing from the principles and spirit of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. An improved large-diameter aluminum-plastic composite pipe, characterized by: The invention comprises a five-layer symmetrical composite structure: an inner plastic layer (1), a first adhesive layer (2), an aluminum base layer (3), a second adhesive layer (4), and an outer plastic layer (5); wherein the surface of the aluminum base layer (3) is pre-oxidized to form a 50-200nm nano-scale Al2O3 transition layer.

2. The improved large-diameter aluminum-plastic composite pipe according to claim 1, characterized in that: The thickness of the inner plastic layer (1) and the outer plastic layer (5) are both 1.5-3.0 mm, and the materials are HDPE / PP-R and LLDPE / CPVC respectively.

3. The improved large-diameter aluminum-plastic composite pipe according to claim 2, characterized in that: The outer plastic layer (5) is further provided with an anti-corrosion coating (6), which is made of a mixture of nano-titanium dioxide and organic silicon resin, thereby further improving the corrosion resistance of the pipe.

4. The improved large-diameter aluminum-plastic composite pipe according to claim 3 is characterized in that: Socket-type connectors (7) are respectively provided at both ends of the composite pipe. The inner wall of the socket-type connector (7) is provided with an annular groove (8). A sealing rubber ring (9) is installed in the annular groove (8), which can effectively improve the sealing performance of the connection. The outer wall of the socket-type connector (7) is provided with an external thread, which is used in conjunction with a connecting pipe fitting (12) with an internal thread to enhance the connection strength.

5. The improved large-diameter aluminum-plastic composite pipe according to claim 4 is characterized in that: Reinforcement rings (10) are provided at both ends of the aluminum base layer (3). The reinforcement rings (10) are made of an aluminum alloy of the same material as the aluminum layer and are fixed to the aluminum base layer (3) by welding. The outer diameter of the reinforcement ring (10) matches the inner diameter of the socket-type connector (7). When connected, the reinforcement ring (10) is inserted into the socket-type connector (7), further improving the strength and stability of the connection part.

6. The improved large-diameter aluminum-plastic composite pipe according to claim 5, characterized in that: Reinforcing ribs (11) are installed between the aluminum base layer (3) and the inner plastic layer (1), and between the aluminum base layer (3) and the outer plastic layer (5). The reinforcing ribs (11) are spirally wound, thereby improving the flexibility of the pipe and enhancing the compressive strength of the pipe.

7. The improved large-diameter aluminum-plastic composite pipe according to claim 6, characterized in that: The first adhesive layer (2) and the first adhesive layer (2) have a thickness of 0.1-0.3 mm and are made of maleic anhydride grafted polyethylene (PE-g-MAH) or ethylene-vinyl acetate copolymer (EVA), and are used to enhance the bonding strength between the inner plastic layer and the aluminum layer.

8. A method for manufacturing the improved large-diameter aluminum-plastic composite pipe according to claim 7, characterized in that it comprises the following steps: 8.

1. Aluminum base (3) pretreatment: After cleaning, alkali washing, and pickling, oxidize in air at 400-450°C for 5-10 minutes to form an Al2O3 transition layer; 8.

2. Co-extrusion: The inner plastic layer (1), adhesive layer and outer plastic layer (5) are extruded through three extruders and then composited with the pre-treated aluminum strip; 8.

3. Cooling and shaping: Cooling is done through a vacuum cooling sleeve, while wall thickness and interface defects are detected online; 8.

4. Installation of the socket-type connector (7): Install the socket-type connector (7) at both ends of the composite pipe. First, install the sealing rubber ring (9) in the annular groove (8) of the connector. Then, put the socket-type connector (7) on the end of the composite pipe. Use a dedicated welding device to weld the socket-type connector (7) to the outer plastic layer (5) of the composite pipe. The welding temperature is controlled at 200-220°C and the welding time is 10-15 seconds to ensure the connection strength between the socket-type connector (7) and the composite pipe. 8.

5. Installation of the reinforcing ring (10) and the reinforcing rib (11): The pre-prepared reinforcing ring (10) is fixed to both ends of the aluminum base (3) by welding; then, the reinforcing rib (11) is installed between the aluminum base (3) and the inner plastic layer (1), and between the aluminum base (3) and the outer plastic layer (5). One end of the reinforcing rib (11) is fixedly connected to the inner plastic layer (1) or the outer plastic layer (5) by using hot melt adhesive, and the other end is tightly fitted to the aluminum base (3). The heating temperature of the hot melt adhesive is controlled at 180-200°C to ensure the fixing effect of the reinforcing rib; 8.

6. Applying an anti-corrosion coating (6); mixing nano titanium dioxide and silicone resin in a certain proportion to form an anti-corrosion coating; applying the anti-corrosion coating evenly on the surface of the outer plastic layer (5) by spraying or dipping; when spraying, controlling the pressure of the spray gun at 0.3-0.5 MPa, and maintaining the distance between the spray gun and the pipe surface at 20-30 cm to obtain a uniform coating thickness; when dipping, slowly immersing the pipe in the coating, staying for 5-10 seconds, and then slowly withdrawing it to allow the coating to flow naturally; after coating, placing the pipe in a drying oven and drying it at a temperature of 80-100°C for 30-60 minutes to completely cure the anti-corrosion coating (6), thereby further improving the corrosion resistance of the pipe.

Images