Nodular cast iron micro-jacking pipe containing polyurethane composite layer and preparation process of nodular cast iron micro-jacking pipe

Abstract

The invention discloses a nodular cast iron micro-jacking pipe containing a polyurethane composite layer and a preparation process of the nodular cast iron micro-jacking pipe, and relates to the technical field of micro-jacking pipes, the micro-jacking pipe comprises an outer glass steel pipe and an inner nodular cast iron pipe, and further comprises a polyurethane thermal insulation material filled in an annular space defined by the nodular cast iron pipe and the glass steel pipe, the outer side of the nodular cast iron pipe is sleeved with multiple layers of cylindrical reinforcing meshes at intervals in the radial direction, meshes of the reinforcing meshes and gaps between the layers in the annular space are filled with the polyurethane heat preservation materials, and the polyurethane heat preservation materials and the reinforcing meshes form an integrated composite layer. According to the preparation technology, an outer-layer mold is adopted to replace a glass reinforced plastic pipe to serve as a forming constraint structure of a polyurethane composite layer, damage to the glass reinforced plastic pipe in the foaming process of a polyurethane thermal insulation material can be avoided, the polyurethane composite layer can be tightly wrapped by utilizing relatively mild contractility generated when the glass reinforced plastic material is cured, the attaching degree between the layers is improved, and the thermal insulation performance of the polyurethane thermal insulation material is improved. The overall design meets the requirements of structural stability and light weight.

Description

Technical Field

[0001] This invention relates to the field of micro jacking technology, specifically to a ductile iron micro jacking pipe with a polyurethane composite layer and its preparation process. Background Technology

[0002] Traditional ductile iron micro-jacking pipes consist of an inner ductile iron pipe, an outer fiberglass pipe, and reinforced concrete filling the space between them. In low-temperature environments, this structure lacks thermal insulation performance, has a large self-weight, and high jacking resistance. Especially in cold regions, the fluid inside the pipe is prone to freezing, and the jacking construction efficiency is greatly affected by friction. To address this, we have developed a micro-jacking pipe with polyurethane insulation material to replace reinforced concrete.

[0003] Using polyurethane insulation material as the intermediate layer combines the characteristics of heat preservation, heat insulation and lightweight. However, simply replacing reinforced concrete will result in insufficient structural strength and will not be able to meet the axial jacking force requirements of pipe jacking construction.

[0004] In addition, the original micro-jacking pipe manufacturing process involved first manufacturing fiberglass pipes, and then using the fiberglass pipes as an outer mold to directly and integrally manufacture the polyurethane insulation intermediate layer. However, the fiberglass pipes are easily damaged during demolding and other processes, and the polyurethane material exerts significant compressive force on the outermost fiberglass pipe during the foaming and curing process. If the fiberglass pipe is too thin, it may even damage the outermost fiberglass pipe. On the other hand, manufacturing thicker fiberglass pipes is not only costly but also fails to meet the requirements for lightweighting. Summary of the Invention

[0005] To address the technical problems mentioned above, this invention provides a ductile iron micro-jacking pipe with a polyurethane composite layer and its preparation process.

[0006] The technical solution of the present invention is as follows: A ductile iron micro-jacking pipe with a polyurethane composite layer includes an outer fiberglass pipe and an inner ductile iron pipe, and also includes polyurethane insulation material filling the annular space formed between the ductile iron pipe and the fiberglass pipe.

[0007] Furthermore, the outer side of the ductile iron pipe is fitted with multiple layers of cylindrical steel mesh at radial intervals, and polyurethane insulation material is filled in the mesh openings of each layer of steel mesh and the gaps between each layer in the annular space, forming an integrated composite layer with each layer of steel mesh.

[0008] A process for preparing a ductile iron micro jacking pipe with a polyurethane composite layer, used to produce the aforementioned ductile iron micro jacking pipe with a polyurethane composite layer, includes the following steps: Step 1: Place the ductile iron pipe vertically on the work platform, and arrange the steel mesh and outer mold at intervals on the outside of the ductile iron pipe; Step 2: Using a pressing device, press vertically downwards onto the upper end of the ductile iron pipe and the upper end of each layer of steel mesh and the outer mold to achieve concentric positioning; Step 3: Fill the space between the ductile iron pipe and the outer mold with polyurethane insulation material, and remove the outer mold after the polyurethane insulation material has completely cured. Step 4: Apply fiberglass material to the outside of the polyurethane insulation material using a winding process, and then perform infrared curing treatment to obtain a ductile iron micro-jacking pipe with a polyurethane composite layer.

[0009] As described above, a ductile iron micro-jacking pipe with a polyurethane composite layer has multiple support structures spaced circumferentially around one end of the ductile iron pipe. Each support structure includes a first support part and a second support part on one side. The outer side of the first support part is in contact with the inner wall of the fiberglass pipe. The second support part is inclined towards the other end of the ductile iron pipe and points towards the center. The second support part also has slots for insertion and mating with the ends of each steel mesh. Before step 1, each support structure is first set on the outer ring of the ductile iron pipe. When performing step 1, the lower ends of each layer of steel mesh are inserted into the corresponding slots of each support structure.

[0010] As a further implementation, a groove is provided on the working platform corresponding to the lower end of the outer mold. The side wall of the groove is adapted to the outer wall of the outer mold, and a boss is provided in the middle of the groove to adapt to the inner wall of the ductile iron pipe. The pressing device includes two pressing parts and a telescopic component that drives them to rise and fall vertically. The telescopic component drives the two pressing parts to press down on the upper end of the ductile iron pipe and the upper end of each layer of steel mesh and the outer mold.

[0011] Preferably, at least six support structures are evenly distributed along the outer circumference of the ductile iron pipe.

[0012] Furthermore, before proceeding to step 4, the outer surface of the cured polyurethane insulation material is first roughened by sandblasting.

[0013] In the preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described above, in step 3, when filling the space between the ductile iron pipe and the outer mold with polyurethane insulation material, the filling is carried out in a predetermined number of segments from bottom to top along the length of the outer mold. After each segment is filled, the filling is paused for a predetermined time until the filled polyurethane material has initially foamed and cured before the next segment is filled.

[0014] Furthermore, a vibrator is installed below the work platform. The vibrator is activated during the preset pause time after each section of polyurethane insulation material is filled to help expel the gas generated during the filling and foaming process.

[0015] Preferably, the polyurethane insulation material is a rigid polyurethane insulation material with a long-term low-temperature resistance of -40℃ and a Shore hardness ≥ D50 after curing.

[0016] In the preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described above, in step 4, the fiberglass pipe is made by winding and curing fiberglass cloth and unsaturated polyester resin.

[0017] The beneficial effects of this invention are as follows: by replacing the traditional reinforced concrete layer with an integrated composite layer formed by multiple layers of steel mesh and rigid polyurethane insulation material, the invention fully retains the lightweight and low thermal conductivity characteristics of polyurethane, effectively reducing the self-weight and jacking resistance of the micro-jacking pipe. Furthermore, the rigid support of the steel mesh compensates for the insufficient strength of a single polyurethane material. Simultaneously, the process sequence of first injecting and curing polyurethane, followed by winding the outer fiberglass pipe, utilizes a temporary outer mold to withstand the extrusion pressure generated during polyurethane foaming and curing, fundamentally avoiding damage to the thin-walled fiberglass pipe from the foaming pressure. This eliminates the need to thicken the fiberglass pipe to ensure structural integrity, significantly reducing production costs while meeting lightweight requirements. In addition, the gentle shrinkage force generated during the curing of the fiberglass material tightly wraps the fiberglass pipe, polyurethane composite layer, and ductile iron pipe, ensuring interlayer adhesion, without deforming or damaging the polyurethane composite layer or the inner ductile iron pipe. This further enhances the structural stability of the micro-jacking pipe, ultimately achieving a dual improvement in structural stability and insulation functionality under low-temperature conditions. Attached Figure Description

[0018] In the attached diagram: Figure 1 This is a cross-sectional schematic diagram of a ductile iron micro-jacking pipe containing a polyurethane composite layer according to the present invention. Figure 2 for Figure 1 A schematic diagram of the fabrication and installation structure of a ductile iron micro-jacking pipe containing a polyurethane composite layer (with hidden pressing device). Figure 3 for Figure 1 A schematic diagram of the lateral structure of the central support structure; Figure 4 for Figure 1 A schematic diagram of the axial section of a ductile iron micro-jacking pipe containing a polyurethane composite layer; Figure 5 This is another implementation structure of the ductile iron micro-jacking pipe with polyurethane composite layer of the present invention (schematic axial section). The components represented by the various reference numerals in the diagram are: 1. Fiberglass pipe; 2. Ductile iron pipe; 3. Polyurethane insulation material; 4. Steel mesh; 5. Support structure; 51. First support part; 52. Second support part; 53. Slot; 6. Spacer; 7. Working platform; 71. Boss; 8. Outer mold. Detailed Implementation

[0019] Example 1 This embodiment provides a ductile iron micro-jacking pipe with a polyurethane composite layer and its manufacturing process, aiming to solve the problems of insufficient thermal insulation performance of the reinforced concrete layer, heavy self-weight of the pipe body, and high jacking resistance in traditional ductile iron micro-jacking pipes. It also overcomes the insufficient structural strength caused by simply replacing the reinforced concrete layer with polyurethane material, as well as the technical defects of traditional manufacturing processes, such as the easy breakage of fiberglass pipes used as outer molds, high cost of thickened fiberglass pipes, and the inability to achieve lightweighting. The specific solution is as follows: Combination Figures 1-3 The ductile iron micro-jacking pipe with a polyurethane composite layer in this embodiment includes an outer fiberglass pipe 1 and an inner ductile iron pipe 2. The ductile iron pipe 2 and the fiberglass pipe 1 form an annular space, which is filled with a polyurethane composite layer. The polyurethane composite layer includes rigid polyurethane insulation material 3 (preferably with a density of not less than 60 kg / m³). 3 The rigid polyurethane insulation material is adapted to meet the load-bearing requirements of medium-diameter micro-jacking pipes with diameters of Φ300~500mm, while high-density closed-cell rigid polyurethane insulation material is preferred to meet the heavy-load conditions of large-diameter micro-jacking pipes with diameters of Φ500~800mm. Multiple layers of reinforcing mesh 4 (such as two or three layers) are used. The multiple layers of cylindrical reinforcing mesh 4 are evenly distributed radially along the outer side of the ductile iron pipe 2. Rigid polyurethane insulation material 3 fills the mesh openings of each layer of reinforcing mesh 4 and the gaps between layers within the annular space, forming a tight, integrated composite layer with each layer of reinforcing mesh 4. The rigid support of the reinforcing mesh 4 enhances the axial load-bearing capacity of the polyurethane composite layer. Simultaneously, the thermal insulation properties of the polyurethane insulation material 3 provide thermal insulation. This polyurethane composite layer replaces the traditional reinforced concrete layer, achieving lightweighting, reducing jacking resistance, and providing low-temperature protection while ensuring load-bearing strength.

[0020] At least six support structures 5 are evenly distributed around the outer circumference of one end of the ductile iron pipe 2. Each support structure 5 includes an integrally formed first support part 51 and a second support part 52. The outer side of the first support part 51 is tightly fitted with the inner wall of the fiberglass pipe 1, which plays a radial limiting role. The second support part 52 is inclined towards the other end of the ductile iron pipe 2 and points towards the center. The second support part 52 has a slot 53 that is opened at the end of each layer of steel mesh 4 to fit into it. Through the matching connection between the slot 53 and the end of the steel mesh 4, the steel mesh 4 is positioned on the outside of the ductile iron pipe 2, preventing the steel mesh 4 from shifting during the subsequent polyurethane material filling process.

[0021] Unlike previous products, in this embodiment of the ductile iron micro-jacking pipe, the fiberglass pipe 1 is formed by curing fiberglass raw materials onto the outer layer of polyurethane insulation material 3, applying curing shrinkage force to the polyurethane insulation material 3. Therefore, the manufacturing process of this embodiment of the ductile iron micro-jacking pipe with a polyurethane composite layer, used to produce the aforementioned ductile iron micro-jacking pipe with a polyurethane composite layer, uses an outer mold 8 instead of the fiberglass pipe 1 as the molding constraint structure for the polyurethane composite layer. This avoids damage to the fiberglass pipe 1 during the foaming process of the polyurethane insulation material 3. Simultaneously, the relatively mild shrinkage force generated during the curing of the fiberglass material can be used to tightly wrap the polyurethane composite layer and the ductile iron pipe 2, ensuring interlayer adhesion without causing significant deformation or damage to the polyurethane composite layer and the inner ductile iron pipe 2. This eliminates the need to manufacture a thick-walled fiberglass pipe 1, thus balancing product structural stability and lightweight requirements. The specific solution is as follows: Combination Figure 4 The tooling used in this preparation process includes a temporary outer mold 8, a working platform 7, a pressing device, and a vibrator. The outer mold 8 is a split design to facilitate removal after the polyurethane composite layer is prepared. A groove is provided on the working platform 7 at the lower end of the outer mold 8. The sidewall of the groove is adapted to the outer wall of the outer mold 8 to provide radial positioning of the outer mold 8. A boss 71 protrudes upward in the middle of the groove and is adapted to the inner wall of the ductile iron pipe 2 for initial centering when the ductile iron pipe 2 is placed vertically. The pressing device includes two pressing parts and a telescopic component that drives them to move vertically. The two pressing parts press down on the upper end of the ductile iron pipe 2 and the upper end of each layer of steel mesh 4 and the outer mold 8 to achieve concentric positioning of multiple components. The vibrator is located below the working platform 7 to assist in the discharge of gas during the polyurethane material filling process and avoid void defects in the composite layer.

[0022] In the specific preparation process, before proceeding with the formal procedures, at least six support structures 5 are evenly arranged and welded around the outer circumference of one end of the ductile iron pipe 2. The support structure 5 is integrally welded to the socket end of the ductile iron pipe 2. During jacking construction, the axial jacking force can be directly transmitted to the support structure 5 through the socket, and then transmitted to the multi-layer steel mesh 4 that is inserted and matched with the support structure 5 via the second support part 52. This force is then distributed to the entire polyurethane composite layer, so that the jacking force is borne by the composite layer as a whole. This can significantly improve the anti-jacking deformation ability of the micro jacking pipe, avoid defects such as cracking and denting at the socket due to local stress concentration, and ensure the structural stability and continuity of the jacking construction.

[0023] Then, step 1 is performed, the ductile iron pipe 2 is placed vertically on the work platform 7, so that the boss 71 in the middle of the groove of the work platform 7 extends into the inner wall of the ductile iron pipe 2. Next, each layer of cylindrical steel mesh 4 is placed radially at intervals on the outside of the ductile iron pipe 2, and the lower end of each layer of steel mesh 4 is inserted into the slot 53 of the second support part 52 of the support structure 5 to complete the positioning of the steel mesh 4. Finally, the outer mold 8 is placed on the outside of the outermost layer of steel mesh 4 to complete the component arrangement before assembly.

[0024] Next, step 2 is executed, and the telescopic component of the pressing device is activated, driving the two pressing parts to press vertically downwards onto the upper end of the ductile iron pipe 2 and the upper end of each layer of steel mesh 4 and the outer mold 8, respectively, so as to achieve concentric positioning of the ductile iron pipe 2, the steel mesh 4 and the outer mold 8, and avoid displacement of each component during the subsequent polyurethane material filling process.

[0025] Next, proceed to step 3. Fill the annular space between the ductile iron pipe 2 and the outer mold 8 from the upper end of the ductile iron pipe 2 and the outer mold 8 with polyurethane insulation material 3. The polyurethane insulation material 3 is a rigid polyurethane insulation material with a long-term low temperature resistance of -40℃ and a Shore hardness ≥ D50 after curing. During filling, fill from bottom to top along the length of the outer mold 8 at predetermined intervals. After each segment is filled, pause for a predetermined time. (For example, when making Φ300-500mm medium-diameter micro-jacking pipes, the predetermined number of segments can be set to 3, and the conventional curing pause time can be set to 10-12 minutes; when making Φ500-800mm large-diameter micro-jacking pipes, the predetermined number of segments can be set to 4-5, and the conventional curing pause time can be set to 10-12 minutes.) The pause time is set to 12-15 minutes. Alternatively, a curing accelerator can be added to reduce the pause time. During this pause time, a vibrator can be started (the vibrator operating parameters can be a low frequency of 20-30Hz, an amplitude of ≤1mm, and a vibration time of 30-60s) to help expel the gas generated during the filling and foaming process. After the polyurethane material in this section has initially foamed and cured, the next section of filling operation can be carried out. After all the polyurethane insulation material 3 has been filled and completely foamed and cured, the telescopic component moves upward away from the upper end of the ductile iron pipe 2 and the upper end of each layer of steel mesh 4 and the outer mold 8. The outer mold 8 is then removed. At this time, the polyurethane insulation material 3 and each layer of steel mesh 4 form a stable integrated composite layer.

[0026] Before performing step 4, the outer surface of the cured polyurethane insulation material 3 is roughened by sandblasting to increase its roughness and improve its adhesion to the subsequently laid fiberglass material. Then, step 4 is performed, where fiberglass material is laid on the outside of the polyurethane insulation material 3 using a winding process. The material is then sent to a curing device for infrared curing to form a fiberglass layer to be cured. The infrared curing temperature is controlled between 50℃ and 55℃, and the curing time is 45-60 minutes. Verification has shown that this temperature range ensures sufficient cross-linking and curing of the unsaturated polyester resin, forming a high-strength outer protective layer for the fiberglass pipe 1, while also preventing the polymerization of unsaturated polyester resin. Due to high temperatures, the polyurethane insulation material 3 experiences softening, thermal deformation, and structural strength reduction. However, it maintains the original low thermal conductivity and low-temperature resistance of polyurethane, ensuring that the insulation effect is not affected. After curing, a ductile iron micro-jacking pipe with a polyurethane composite layer is obtained. The fiberglass material is glass fiber cloth impregnated with unsaturated polyester resin. Curing can be carried out by pressing the two ends of the ductile iron pipe 2 in the same direction and rotating the entire pipe body to be cured. During this process, the temperature curve and the rotation of the pipe body need to be controlled to ensure uniform curing. During the molding process of the fiberglass pipe 1, the fiberglass material and the outer surface of the polyurethane insulation material 3 are tightly bonded, and finally a micro-jacking pipe with a stable overall structure is obtained.

[0027] This embodiment replaces the traditional reinforced concrete layer with an integrated composite layer formed by multiple layers of steel mesh 4 and polyurethane insulation material 3. This retains the lightweight and thermal insulation properties of polyurethane, reducing the self-weight and jacking resistance of the micro-jacking pipe, while the supporting effect of the steel mesh 4 compensates for the insufficient strength of polyurethane alone, meeting the axial jacking force requirements of pipe jacking construction. At the same time, the process sequence of first injecting and curing polyurethane and then making the outer fiberglass pipe 1, with the outer mold 8 bearing the extrusion pressure during polyurethane foaming, fundamentally avoids damage to the thin-walled fiberglass pipe 1 caused by foaming pressure. The coordinated positioning of the support structure 5 and the pressing device, as well as the process design of segmented filling and vibration venting, further ensure the forming quality of the micro-jacking pipe, achieving a unity of structural stability and thermal insulation function of the micro-jacking pipe under low-temperature conditions.

[0028] It should be noted that although the present invention mainly describes the scheme of arranging a polyurethane composite layer on the outside of the ductile iron pipe 2 and the inside of the fiberglass pipe 1 through detailed embodiment 1, embodiment 1 should not constitute a limitation on the present invention. In particular, since the present invention does not limit the ductile iron pipe 2 to a single-structure cast iron pipe, those skilled in the art should not interpret the interlayer structure of embodiment 1 as a limitation on the interlayer structure of the present invention. The ductile iron pipe 2 of the present invention does not exclude composite structure schemes, which will be illustrated by example in the following embodiment 2.

[0029] Example 2 As mentioned above, to support the scope of protection claimed in this invention, this embodiment is an example in the case where the ductile iron pipe 2 is a composite structure, combined with... Figure 5 This embodiment is based on the ductile iron micro-jacking pipe with polyurethane composite layer and its preparation process in Embodiment 1. The difference is that the ductile iron pipe 2 is not a single-structure cast iron pipe, but a composite structure with a phase change heat storage layer on the outer wall. That is, there is a phase change heat storage layer on the inner side of the polyurethane composite layer and the outer side of the ductile iron pipe 2. The phase change heat storage layer is used to absorb and store the heat of the liquid flowing in the ductile iron pipe 2. When the temperature of the liquid in the ductile iron pipe 2 decreases, it releases heat to replenish the temperature. The outer polyurethane composite layer plays a passive heat insulation and temperature locking role. The two together can form a double heat preservation structure, which further enhances the heat preservation and antifreeze effect of the micro-jacking pipe under low temperature conditions.

[0030] like Figure 5 One specific implementation shown is that the phase change heat storage layer includes a spacer 6 sleeved on the outside of the ductile iron pipe 2 and a phase change heat storage material. The spacer 6 is made of plastic or similar plastic material and includes a spacer body and 6-8 spacer plates evenly distributed circumferentially on its inner side. Each spacer plate is arranged axially along the spacer body, dividing the annular space between the spacer 6 and the ductile iron pipe 2 into multiple independent fan-shaped filling spaces. The filling spaces are filled with a phase change heat storage material adapted to the required low-temperature operating conditions, such as a paraffin-based phase change heat storage material. The phase change heat storage material can be open-filled or pre-encapsulated using a sealed structure.

[0031] The difference between the preparation process in this embodiment and that in embodiment 1 is that, in step 1, a spacer 6 and a corresponding sealing element are pre-fitted on the outside of the ductile iron pipe 2. The length of the spacer 6 does not need to cover the entire length of the ductile iron pipe 2, and space is still left at the end for arranging the support structure 5. The inner side of the support structure 5 extends by a corresponding dimension to match the thickening brought by the spacer 6. The rest of the process remains unchanged. After the fiberglass material is prepared in step 4, phase change heat storage material is filled into each filling cavity between the spacer 6 and the ductile iron pipe 2 through the reserved filling port and then sealed. When filling, care should be taken to reserve 10% volume space for expansion and contraction during the phase change process.

[0032] Specifically, during the molding process of the polyurethane composite layer and the outer fiberglass pipe 1, the spacer 6 is further tightened, so that its inner partition is tightly attached to the outer wall of the ductile iron pipe 2, thereby forming multiple relatively independent and well-sealed filling chambers between it and the outer wall of the ductile iron pipe 2, providing a stable and sealed spatial basis for the filling of the phase change heat storage material.

[0033] During the sealing process described above, polyurethane insulation material can be filled into each gap at the end to fill any gaps that may exist between the two ends of the phase change heat storage layer and the surrounding structure. After the polyurethane insulation material has cured, the two ends of the phase change heat storage layer are sealed.

[0034] Ductile iron pipes with a composite phase change heat storage layer can directly absorb and store heat from the fluid inside the pipe, achieving active temperature regulation and heat replenishment. The polyurethane composite layer is wrapped around the outside of the phase change heat storage layer, achieving passive heat insulation and temperature lock-in to prevent heat loss. The two work together to improve the heat preservation and temperature control effect by more than 35% under low temperature conditions compared with micro jacking pipes with single polyurethane insulation, making them suitable for jacking construction in extremely cold regions.

Claims

1. A ductile iron micro-jacking pipe with a polyurethane composite layer, characterized in that, It includes an outer fiberglass pipe (1) and an inner ductile iron pipe (2), and also includes polyurethane insulation material (3) filling the annular space formed between the ductile iron pipe (2) and the fiberglass pipe (1).

2. The ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 1, characterized in that, The ductile iron pipe (2) is radially spaced with multiple layers of cylindrical steel mesh (4), and the polyurethane insulation material (3) fills the mesh holes of each layer of steel mesh (4) and the gaps between each layer in the annular space, forming an integrated composite layer with each layer of steel mesh (4).

3. A manufacturing process for a ductile iron micro-jacking pipe containing a polyurethane composite layer, characterized in that, The method for producing the ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 2 includes the following steps: Step 1: Place the ductile iron pipe (2) vertically on the work platform (7), and arrange the steel mesh (4) and outer mold (8) at intervals on the outside of the ductile iron pipe (2); Step 2: Using a pressing device, press vertically downwards onto the upper end of the ductile iron pipe (2) and the upper end of each layer of steel mesh (4) and the outer mold (8) for concentric positioning; Step 3: Fill the space between the ductile iron pipe (2) and the outer mold (8) with polyurethane insulation material (3), and remove the outer mold (8) after the polyurethane insulation material (3) has completely cured. Step 4: Apply fiberglass material to the outside of polyurethane insulation material (3) using a winding process and perform curing treatment to obtain ductile iron micro-jacking pipe with polyurethane composite layer.

4. The preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 3, characterized in that, The ductile iron pipe (2) has multiple support structures (5) spaced circumferentially around one end of its outer ring. The support structure (5) includes a first support part (51) and a second support part (52) on one side. The outer side of the first support part (51) is attached to the inner wall of the fiberglass pipe (1). The second support part (52) is inclined toward the other end of the ductile iron pipe (2) and points to the center. The second support part (52) is also provided with a slot (53) for insertion and mating with the end of each steel mesh (4). Before performing step 1, each support structure (5) is placed on the outer ring of the ductile iron pipe (2), and when performing step 1, the lower end of each layer of steel mesh (4) is inserted into the corresponding slot (53) of each support structure (5).

5. The preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 4, characterized in that, The working platform (7) is provided with a groove at the lower end of the outer mold (8). The side wall of the groove is adapted to the outer wall of the outer mold (8), and a boss (71) adapted to the inner wall of the ductile iron pipe (2) is provided in the middle of the groove. The pressing device includes two pressing parts and a telescopic component that drives them to move vertically up and down. The telescopic component drives the two pressing parts to press down on the upper end of the ductile iron pipe (2) and the upper end of each layer of steel mesh (4) and the outer mold (8).

6. The preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 5, characterized in that, The support structure (5) has at least six of them evenly distributed around the outer circumference of the ductile iron pipe (2).

7. The preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 3 or 4, characterized in that, Before proceeding to step 4, the outer surface of the cured polyurethane insulation material (3) is roughened by sandblasting.

8. The preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 7, characterized in that, In step 3, when filling polyurethane insulation material (3) between the ductile iron pipe (2) and the outer mold (8), the filling is carried out from bottom to top in a predetermined number of segments along the length of the outer mold (8). After each segment is filled, the filling is paused for a predetermined time until the filled polyurethane material has initially foamed and cured before the next segment is filled.

9. The preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 8, characterized in that, A vibrator is provided below the work platform (7). The vibrator is activated during the preset pause time after each polyurethane insulation material (3) is filled to help discharge the gas generated during the filling and foaming process.

10. The preparation process of a ductile iron micro-jacking pipe with a polyurethane composite layer as described in claim 7, characterized in that, In step 4, the fiberglass pipe (1) is made by winding and curing fiberglass cloth and unsaturated polyester resin.

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