HDPE winding pipe and preparation method thereof

Abstract

The invention relates to the technical field of pipe manufacturing, in particular to an HDPE winding pipe and a preparation method thereof.The HDPE winding pipe comprises a winding strip, the winding strip is spirally wound into a pipe shape along the axis, the winding strip comprises an outer pipe and a reinforcing rib connected to the inner wall of the outer pipe, and the reinforcing rib comprises an inner foaming core layer and a solid layer located outside the foaming core layer. The reinforcing ribs are arranged in the outer pipe and provide support for the whole structure, the foaming core layer is arranged on the inner layer of the reinforcing ribs, the weight of the pipe is reduced, light weight is achieved, the outer layer of the reinforcing ribs is the solid layer, the density is high, the compression resistance foundation is guaranteed, the pipe fitting has high surface layer compression resistance while light weight is guaranteed, raw materials are saved, and the environment-friendly manufacturing trend is met.

Description

Technical Field

[0001] This invention relates to the field of pipe manufacturing technology, and more specifically, to an HDPE spiral wound pipe and its preparation method. Background Technology

[0002] HDPE hollow-wall spiral wound pipes, with their excellent corrosion resistance, high ring stiffness, and long service life, have become an important pipe material choice in municipal drainage, sewage systems, and agricultural irrigation. In current production technology, the reinforcing ribs of these spiral wound pipes are mainly designed as solid, hollow, or with physical openings. These designs directly affect the pipe's mechanical properties, material usage, and engineering applicability.

[0003] However, existing hollow-wall spiral pipes face a significant performance-cost trade-off in terms of reinforcing rib structure: if solid reinforcing ribs are used, although high ring stiffness and compressive strength can be guaranteed, it will significantly increase the consumption of raw materials, leading to an increase in the self-weight of the pipe, and thus greatly increasing the overall cost of transportation, handling and construction installation; if hollow or perforated reinforcing ribs are used to reduce weight, the ring stiffness of the pipe will often be weakened to some extent, reducing its resistance to external pressure and making it difficult to meet the high requirements of engineering scenarios such as deep burial.

[0004] For example, SN8 grade pipes, which are commonly found on the market, are often limited in deep burial applications due to insufficient strength. Many projects, which require greater burial depth or higher external pressure resistance, have to choose pipes with higher ring stiffness or use other materials. This not only increases project costs but also limits the application of HDPE hollow wall spiral pipes in a wider range of scenarios. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that the existing technology lacks a reinforcing rib structure that combines lightweight and high strength, and to provide a wound pipe and its preparation method, so that the pipe has strong surface compressive strength while ensuring lightweight.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: An HDPE spiral wound pipe is provided, comprising a spiral wound strip, the spiral wound strip being spirally wound into a tubular shape along an axis, the spiral wound strip comprising an outer tube and a reinforcing rib connected to the inner wall of the outer tube, the reinforcing rib comprising an inner foamed core layer and a solid layer located outside the foamed core layer.

[0007] The present invention provides an HDPE spiral wound pipe with reinforcing ribs set inside the outer pipe to provide support for the overall structure. The inner layer of the reinforcing ribs is set with a foamed core layer to reduce the weight of the pipe and achieve lightweighting. The outer layer is a solid layer with high density to ensure compressive strength. The pipe has strong surface compressive strength while ensuring lightweighting, saving raw materials and conforming to the trend of green manufacturing.

[0008] Furthermore, the thickness of the foamed core layer accounts for 60%-80% of the total thickness of the reinforcing ribs. The proportion of the foamed core layer needs to be kept within a suitable range. If the proportion is too high, it will lead to insufficient strength of the reinforcing ribs and reduce the overall compressive strength of the pipe. If the proportion is too low, it will lead to excessive weight of the pipe, waste of manufacturing materials and difficulty in handling.

[0009] Furthermore, the reinforcing rib has a cross-shaped cross-section, while the outer tube has a quadrilateral cross-section. The four arms of the reinforcing rib are respectively connected to the four inner sides of the outer tube. By using the cross-shaped reinforcing rib to support the four relatively weak sides of the outer tube, the ring stiffness of the HDPE hollow wall spiral pipe can be effectively improved.

[0010] Furthermore, a molten adhesive layer is provided between the winding gaps of the winding strip. Here, the winding gap refers to the gap that exists between two adjacent turns of the winding strip during winding. By providing a molten adhesive layer in the winding gap, the long strip of winding strip can be better wound into a spiral winding tube, further enhancing the strength of the winding tube.

[0011] Furthermore, the outer tube and the reinforcing rib are integrally formed.

[0012] The above-described method for preparing an HDPE spiral wound pipe includes the following steps: Step 1: Raw material preparation; Pure HDPE resin is added to the first extruder for melting to obtain a solid layer melt; HDPE resin, AC foaming agent, zinc oxide and zinc stearate are mixed and added to the second extruder for melting to obtain a core layer melt; Pure HDPE resin is added to the third extruder for melting to obtain an outer tube melt; Step 2: Co-extrusion molding; The solid layer melt and the core layer melt are extruded into the co-extrusion die through the first extruder and the second extruder, respectively, and the reinforcing rib is formed by the co-extrusion die; Step 3; Shaping; Cooling and shaping the formed reinforcing ribs; Step 4: Composite; The outer tube melt is extruded through the third extruder into the forming die, and the outer tube is obtained through the forming die. The shaped reinforcing ribs are pulled into the interior of the outer tube, so that the reinforcing ribs and the outer tube are composited to form a winding strip. The formed winding strip is cooled and shaped. Step 5: Winding; The shaped winding strip is fed to the winding machine and heated to soften it. The winding strip is wound around the outside of the mold at a spiral angle. The wound pipe is cooled and solidified into the final pipe.

[0013] Furthermore, in step one, the first extruder and the second extruder are controlled to ensure that the pressure of the core layer melt is lower than the pressure of the solid layer melt. This slight reduction in the core layer melt pressure prevents the core layer melt from penetrating into the solid layer melt within the molding cavity of the die.

[0014] Furthermore, in step one, the first extruder and the second extruder are controlled to ensure that the temperature of the solid layer melt is higher than that of the core layer melt. This higher temperature of the solid layer melt ensures better fluidity of the solid layer melt, allowing it to quickly coat the core layer within the co-extrusion die.

[0015] Furthermore, the raw material formulation of the core layer melt is as follows by weight: 100 parts HDPE resin; 0.5-1.0 parts AC foaming agent; 0.1-0.3 parts zinc oxide; and 0.2-0.5 parts zinc stearate. Among them, the AC foaming agent is used for foaming, the zinc oxide is a foaming accelerator, and the zinc stearate is a lubricant.

[0016] Furthermore, the AC foaming agent exhibits a bimodal particle size distribution, composed of a 1:1 mixture of 6-10μm and 20-30μm particles. Essentially, the bimodal AC foaming agent is an azodicarbonamide (AC) foaming agent with two concentrated particle size distribution ranges. Unlike traditional AC foaming agents with a single particle size distribution, it optimizes the foaming effect through the synergistic effect of particles of different sizes.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. The present invention provides an HDPE spiral pipe with reinforcing ribs set inside the outer pipe to provide support for the overall structure. The inner layer of the reinforcing ribs is set with a foamed core layer to reduce the weight of the pipe and achieve lightweighting. The outer layer is a solid layer with high density to ensure compressive strength. The pipe has strong surface compressive strength while ensuring lightweighting, saving raw materials and conforming to the trend of green manufacturing. 2. By using cross-shaped reinforcing ribs to support the four relatively weak sides of the outer pipe, the ring stiffness of HDPE hollow wall spiral pipe can be effectively improved. 3. By providing a molten adhesive layer in the winding gap, the long winding strip is better wound into a spiral winding tube, further enhancing the strength of the winding tube. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of an HDPE spiral wound pipe; Figure 2 for Figure 1 A magnified view of a portion of position A; Figure 3 This is a cross-sectional schematic diagram of an embodiment of an HDPE spiral wound pipe; Figure 4This is a cross-sectional schematic diagram of a second embodiment of an HDPE spiral wound pipe; Figure 5 This is a schematic diagram of the structure of a co-extrusion die for reinforcing ribs, as shown in Example 5. Figure 6 This is a schematic diagram of the internal structure of a co-extrusion die for reinforcing ribs, as shown in Example 5.

[0019] In the attached diagram: 100, outer tube; 200, reinforcing rib; 210, foamed core layer; 220, solid layer; 300, fused bonding layer; 400, die; 410, second injection runner; 420, solid layer runner; 430, molding cavity; 431, shrinkage section; 500, mold core; 510, first injection runner; 511, spiral guide vane; 520, core layer runner. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only, representing schematic diagrams rather than actual physical objects, and should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0021] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0022] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," and "fitting," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] In the description of this specification, references to terms such as "embodiment" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0024] Example 1 A first embodiment of an HDPE spiral wound pipe, such as Figure 1 and Figure 2 As shown, it includes a winding strip, which is spirally wound into a tubular shape along the axis. A molten adhesive layer 300 is also provided between the winding gaps of the winding strip. Here, the winding gap refers to the gap that exists between two adjacent turns of the winding strip during winding. The winding strip includes an outer tube 100 and reinforcing ribs 200 connected to the inner wall of the outer tube 100. Figure 2 and Figure 3 As shown, the reinforcing rib 200 includes an inner foamed core layer 210 and a solid layer 220 located outside the foamed core layer 210. The thickness of the foamed core layer 210 accounts for 60%-80% of the total thickness of the reinforcing rib 200, preferably 80%. The cross-section of the reinforcing rib 200 is cross-shaped, and the cross-section of the outer tube 100 is quadrilateral (preferably rectangular). The four arms of the reinforcing rib 200 are respectively connected to the four inner sides of the outer tube 100. The outer tube 100 and the reinforcing rib 200 are integrally formed by welding.

[0025] The working principle of this embodiment is as follows: This invention provides an HDPE spiral wound pipe with reinforcing ribs 200 disposed inside the outer pipe 100, providing support for the overall structure. A foamed core layer 210 is disposed inside the reinforcing ribs 200 to reduce the weight of the pipe, achieving lightweighting. The outer layer is a solid layer 220 with high density, ensuring compressive strength. The pipe fitting achieves lightweighting while possessing strong surface compressive strength, saving raw materials and conforming to the trend of green manufacturing. The cross-shaped reinforcing ribs 200 support the four relatively weak sides of the outer pipe 100, effectively improving the ring stiffness of the HDPE hollow wall spiral wound pipe. By providing a molten adhesive layer 300 in the winding gap, the long, strip-shaped winding strips are better wound into a spiral shape, further enhancing the strength of the spiral wound pipe.

[0026] Example 2 A second embodiment of an HDPE spiral wound pipe, such as Figure 1 and Figure 2As shown, it includes a spiral wound strip, which is spirally wound into a tubular shape along the axis. A molten adhesive layer 300 is also provided between the winding gaps of the spiral wound strip. The spiral wound strip includes an outer tube 100 and reinforcing ribs 200 connected to the inner wall of the outer tube 100. Figure 2 and Figure 4 As shown, the reinforcing rib 200 includes an inner foamed core layer 210 and a solid layer 220 located outside the foamed core layer 210. The thickness of the foamed core layer 210 accounts for 80% of the total thickness of the reinforcing rib 200. The cross-section of the reinforcing rib 200 is circular, and the cross-section of the outer tube 100 is quadrilateral (preferably rectangular). The reinforcing rib 200 is tangent to the four inner sides of the outer tube 100. The outer tube 100 and the reinforcing rib 200 are integrally formed by fusion welding.

[0027] In addition, the cross-section of the reinforcing rib 200 can also be triangular, straight, or other shapes.

[0028] Example 3 This embodiment is a first embodiment of a method for preparing HDPE spiral wound pipe, the method including the following steps: Step 1: Raw material preparation; Pure HDPE resin is added to the first extruder for melting to obtain a solid layer melt; the raw material formula for the foamed core layer is as follows by weight: 100 parts HDPE resin; 1.0 part AC foaming agent; 0.3 parts zinc oxide; 0.5 parts zinc stearate, wherein the AC foaming agent has a bimodal particle size distribution and is composed of 10μm and 30μm particles mixed in a 1:1 ratio. The raw material formula for the foamed core layer 210 is added to the second extruder for melting to obtain a core layer melt; Pure HDPE resin is added to the third extruder for melting to obtain an outer tube melt. Step 2: Co-extrusion molding; In this embodiment, the outer layer of the co-extrusion die is a solid layer flow channel, and the inner layer is a core layer flow channel. A molding cavity is provided at the end of the solid layer flow channel and the core layer flow channel. The first extruder extrudes the solid layer melt into the solid layer flow channel for conveying, and the second extruder extrudes the core layer melt into the core layer flow channel for conveying. The solid layer melt and the core layer melt fuse and form in the molding cavity of the co-extrusion die to obtain a reinforcing rib; Step 3; Shaping; The formed reinforcing ribs are cooled and shaped using an "external wall water cooling" method: circulating water is circulated to the water jacket on the outer wall of the reinforcing ribs to cool the solid layer quickly, while the core layer of the reinforcing ribs cools naturally at a slower rate. This allows the foaming agent in the core layer to decompose fully and the bubbles to stabilize and solidify.

[0029] Step 4: Composite; The outer tube melt is extruded through the third extruder into the forming die, and the outer tube is obtained through the forming die. The shaped reinforcing ribs are pulled into the interior of the outer tube, so that the reinforcing ribs and the outer tube are composited to form a winding strip. The formed winding strip is then cooled and shaped. Step 5: Winding; The shaped winding strip is fed to the winding machine, and the winding strip is heated and softened using a hot air gun. The winding strip is wound around the outside of the mold at a spiral angle, and the adhesive material is extruded into the winding gap using an extruder to form a molten adhesive layer. Then the wound pipe is sprayed to cool and solidify into the final pipe.

[0030] Example 4 This embodiment is a first embodiment of a co-extrusion mold for preparing the reinforcing ribs with a foamed core layer of Embodiment 1. This embodiment is similar to Embodiment 3, except that in step 1, the parameters of the first extruder and the second extruder are adjusted so that the pressure of the core layer melt is lower than the pressure of the solid layer melt and the temperature of the solid layer melt is higher than the temperature of the core layer melt. For example, by adjusting the parameters of the first extruder, the temperature of the core layer flow channel is controlled at 195℃-200℃ and the pressure of the core layer melt is controlled at 10MPa-15MPa.

[0031] By adjusting the parameters of the second extruder, the temperature of the solid layer flow channel is controlled at 205℃-210℃, and the solid layer melt pressure is controlled at 8MPa-12MPa.

[0032] The melt pressure of the core layer is slightly lower than that of the solid layer, which can prevent the core layer melt from penetrating into the solid layer melt in the molding cavity of the molding die. The temperature of the solid layer melt is higher than that of the core layer melt, ensuring better fluidity of the solid layer melt. It can quickly coat the core layer in the co-extrusion die, and the appropriate temperature can prevent the foaming agent from decomposing prematurely.

[0033] The remaining working principles of this embodiment are the same as those of Embodiment 3.

[0034] Example 5 This embodiment is a first embodiment of a co-extrusion mold for reinforcing ribs, used to prepare the reinforcing rib 200 described in Embodiment 1, as follows. Figure 5 As shown, it includes a die 400 and a mold core 500 installed in the inner cavity of the die 400, as... Figure 6 As shown, the mold core 500 has a first injection runner 510 and a core layer runner 520 connected to the first injection runner 510. A solid layer runner 420 is formed between the die 400 and the mold core 500. A molding cavity 430 is formed inside the die 400, and the molding cavity 430 is connected to the outlet end of the solid layer runner 420 and the outlet end of the core layer runner 520. A second injection runner 410 connected to the solid layer runner 420 is formed on the outer side of the die 400. Figure 3 and Figure 4As shown, the molding cavity 430 is provided with a shrinkage section 431 that shrinks towards the axis of the mold core 500 at one end near the core layer flow channel 520. The shrinkage angle of the shrinkage section 431 is 5°, and the length of the molding cavity 430 is 30mm. Three spiral guide vanes 511 are provided in the first injection flow channel 510, which are evenly distributed along the circumference of the mold core 500. The spiral guide vanes 511 are fixed to the inner wall of the mold core 500. The spiral helix angle of the spiral guide vanes 511 is 25°, and the length of the spiral guide vanes 511 is 50mm.

[0035] The working principle of this embodiment is as follows: During injection molding, the first extruder extrudes the core layer melt containing foamed adhesive through the first injection runner 510 into the core layer runner 520, forming a reinforcing core layer in the core layer runner 520. The second extruder extrudes the solid layer melt through the second injection runner 410 into the solid layer runner 420, forming a reinforcing outer layer in the solid layer runner 420. The solid layer melt and the core layer melt meet and fuse together in the molding cavity 430. Due to the shrinkage angle of the inner diameter of the shrinkage section 431, the solid layer melt and the core layer melt are compressed and bonded more tightly. Finally, after being extruded from the mold and cooled and shaped, the reinforcing rib 300 is formed.

[0036] In the specific implementation of the above embodiments, the technical features can be combined in any non-contradictory way. For the sake of brevity, not all possible combinations of the above technical features are described. However, as long as the combination of these technical features is not contradictory, it should be considered to be within the scope of this specification.

[0037] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make various variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An HDPE spiral wound pipe, comprising a spiral wound strip, wherein the spiral wound strip is spirally wound along an axis to form a tubular shape, characterized in that, The winding strip includes an outer tube (100) and a reinforcing rib (200) connected to the inner wall of the outer tube (100). The reinforcing rib (200) includes an inner foamed core layer (210) and a solid layer (220) located outside the foamed core layer (210).

2. The HDPE spiral wound pipe according to claim 1, characterized in that, The thickness of the foamed core layer (210) accounts for 60%-80% of the total thickness of the reinforcing ribs (200).

3. The HDPE spiral wound pipe according to claim 1, characterized in that, The cross-section of the reinforcing rib (200) is cross-shaped, the cross-section of the outer tube (100) is quadrilateral, and the four arms of the reinforcing rib (200) are respectively connected to the four inner sides of the outer tube (100).

4. The HDPE spiral wound pipe according to claim 1, characterized in that, A molten adhesive layer (300) is also provided between the winding gaps of the winding strip.

5. The HDPE spiral wound pipe according to claim 1, characterized in that, The outer tube (100) and the reinforcing rib (200) are integrally formed.

6. A method for preparing an HDPE spiral wound pipe as described in any one of claims 1-5, characterized in that, The method includes the following steps: Step 1: Raw material preparation; Pure HDPE resin is added to the first extruder for melting to obtain a solid layer melt; HDPE resin, AC foaming agent, zinc oxide and zinc stearate are mixed and added to the second extruder for melting to obtain a core layer melt; Pure HDPE resin is added to the third extruder for melting to obtain an outer tube melt; Step 2: Co-extrusion molding; The solid layer melt and the core layer melt are extruded into the co-extrusion die through the first extruder and the second extruder, respectively, and the reinforcing rib is formed by the co-extrusion die; Step 3; Shaping; Cooling and shaping the formed reinforcing ribs; Step 4: Composite; The outer tube melt is extruded through the third extruder into the forming die, and the outer tube is obtained through the forming die. The shaped reinforcing ribs are pulled into the interior of the outer tube, so that the reinforcing ribs and the outer tube are composited to form a winding strip. The formed winding strip is cooled and shaped. Step 5: Winding; The shaped winding strip is fed to the winding machine and heated to soften it. The winding strip is wound around the outside of the mold at a spiral angle. The wound pipe is cooled and solidified into the final pipe.

7. The method for preparing an HDPE spiral wound pipe according to claim 6, characterized in that, In step one, the first extruder and the second extruder are controlled to make the pressure of the core layer melt lower than the pressure of the solid layer melt.

8. The method for preparing an HDPE spiral wound pipe according to claim 6, characterized in that, In step one, the first extruder and the second extruder are controlled to make the temperature of the solid layer melt higher than the temperature of the core layer melt.

9. A method for preparing an HDPE spiral wound pipe according to claim 6, characterized in that, The raw material formula of the core layer melt is as follows by weight: 100 parts HDPE resin; 0.5-1.0 parts AC foaming agent; 0.1-0.3 parts zinc oxide; 0.2-0.5 parts zinc stearate.

10. A method for preparing an HDPE spiral wound pipe according to claim 9, characterized in that, AC foaming agent has a bimodal particle size distribution and is composed of 6-10μm and 20-30μm particles mixed in a 1:1 ratio.

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