Roller compacted concrete pouring temperature control method

Abstract

The invention discloses a roller compacted concrete pouring temperature control method which comprises the following steps: determining the material and shape of a metal pipeline according to the terrain of the position where roller compacted concrete needs to be poured and the external temperature; manufacturing the metal pipeline according to the material and the shape of the metal pipeline; the metal pipeline is installed at the position where roller compacted concrete needs to be poured, and the two ends of the metal pipeline are located on the outer sides of the position where roller compacted concrete needs to be poured; cooling devices are connected to the two ends of the metal pipeline respectively, so that cooling liquid circulates in the metal pipeline, and metal cooling devices are connected to the pipe walls of the two ends of the metal pipeline respectively, so that the pipe walls of the metal pipeline are in a low-temperature state all the time; and pouring roller compacted concrete, and finishing the shaping of the concrete in a rolling manner. According to the method, the specific metal pipeline is pre-buried before concrete pouring, circulating cooling is conducted on the metal pipeline, the pouring temperature of the roller compacted concrete is controlled, one-time pouring is achieved, and therefore the construction efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of concrete construction, in particular to a temperature control method for pouring roller compacted concrete. Background Art

[0002] Roller-compacted concrete (RCC) is like the "compressed biscuits" of the construction industry, a particularly strong concrete. Its key differences from ordinary concrete include: simpler materials, using less cement, a large amount of fly ash, and carefully selected sand and gravel. Its construction is more robust, using heavy rollers to repeatedly compact the concrete, rather than vibrating it with a tamper, much like compacting a road surface. Its unique properties also make it hard as stone, yet dense and impermeable, making it particularly suitable for building thick and heavy projects like dams and highways.

[0003] When pouring large volumes of roller-compacted concrete (RCC), internal temperatures can soar to over 70°C. Engineers primarily use these methods to reduce this temperature: First, cool the raw materials. Aggregate yards are shaded and sprayed with water mist. Cement is stored in cool, dark warehouses, and ice is added when mixing is necessary. Second, the concrete is poured in layers, 30-50 cm thick, like a crepe pancake. Covering with a thermal blanket is done immediately after compaction. Third, cooling pipes are embedded in the concrete, with plastic pipes pre-embedded to circulate cold water. Fourth, after compaction, geotextiles are covered and sprayed regularly with water. Mist cannons are used to humidify the concrete at night to prevent cracking.

[0004] Although the above method can play a certain cooling role when pouring RCC, the cooling effect is not obvious, and the cooling process will be interspersed throughout the entire construction period, which obviously has a certain impact on the construction efficiency. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide a temperature control method for pouring roller-compacted concrete. By pre-embedding specific metal pipes before pouring concrete and circulating the metal pipes to cool them, the temperature of the roller-compacted concrete pouring can be controlled and one-time pouring can be achieved, thereby improving construction efficiency.

[0006] To solve the above technical problems, the present invention adopts a technical solution: a temperature control method for pouring roller compacted concrete, comprising: Determine the material and shape of the metal pipe based on the terrain of the location where the RCC needs to be poured and the external temperature; manufacturing a metal pipe according to the material and shape of the metal pipe; Install the metal pipe at the location where the roller compacted concrete needs to be poured, and make the two ends of the metal pipe be located outside the location where the roller compacted concrete needs to be poured; Connect cooling devices to both ends of the metal pipe so that coolant flows through the metal pipe. At the same time, connect metal cooling devices to the pipe walls at both ends of the metal pipe so that the pipe walls of the metal pipe are always in a low temperature state. Pour roller compacted concrete and complete the shaping of the concrete by rolling.

[0007] Furthermore, the metal pipe has a plurality of metal thorns on its wall, the metal thorns are perpendicular to the wall of the metal pipe, and the metal thorns are made of the same material as the metal pipe and are integrally formed.

[0008] Furthermore, the metal spikes located below the metal pipe are in contact with the ground.

[0009] Furthermore, an inner ring pipe is provided inside the metal pipe, and the inner ring pipe is connected to the inner wall of the metal pipe through a plurality of evenly distributed connecting rods.

[0010] Furthermore, the gap between the metal pipe and the inner ring pipe is used to circulate cold air, and the cold air is supplied by an air conditioner.

[0011] Furthermore, the cooling devices are connected to both ends of the metal pipe so that the cooling liquid flows in the metal pipe, including: Connect the two ends of the inner ring pipe to the coolant inlet and outlet of the cooling equipment respectively, so that the coolant circulates in the inner ring pipe; The inlet and outlet of the air conditioner are connected to both ends of the gap between the metal pipe and the inner ring pipe through connecting channels of specific shapes, so that cold air can flow through the gap between the metal pipe and the inner ring pipe.

[0012] Furthermore, the material and shape of the metal pipe are determined according to the topography of the location where the RCC needs to be poured and the external temperature, including: The shape and material of the metal pipe are determined according to the topography of the location where the RCC needs to be poured; The coating material of the metal pipe is determined according to the external temperature of the location where the RCC needs to be poured.

[0013] Furthermore, the method for manufacturing the metal pipe according to the material and shape of the metal pipe is 3D printing technology.

[0014] Furthermore, the outer wall of the metal pipe is provided with a thread structure, and the thread structure is made of the same material as the outer covering of the metal pipe and is integrally formed.

[0015] Compared with the prior art, the present invention has the following advantages: 1. Precise temperature control adapted to terrain and temperature By dynamically selecting metal pipe materials (e.g., titanium alloy for steep slopes and aluminum alloy for flat areas) and shapes (corrugation depth / rib configuration) based on the terrain's slope, undulation, and ambient temperature, and applying targeted functional coatings (phase change coating for high-temperature areas and radiation coating for low-temperature areas), the pipeline system's adaptability to complex construction environments is significantly improved. This design dynamically matches the pipe's thermal conductivity to the concrete's temperature rise curve. Field measurements show that in areas with high temperatures and steep slopes above 35°C, the internal temperature difference in the concrete can be controlled to within ±1.5°C (a 60% improvement in accuracy compared to conventional methods), effectively suppressing interlaminar cracks caused by temperature gradients.

[0016] 2. Efficient heat dissipation with dual-medium collaborative cooling A dual cooling mechanism, combining circulating coolant (a liquid medium) within the inner ring pipe and cooling air (a gaseous medium) within the interlayer, creates a "liquid-gas composite heat dissipation channel." The coolant transfers the underlying heat load (due to its specific heat capacity advantage), while the cooling air rapidly reduces the pipe wall temperature through forced convection (increasing thermal conductivity response by three times). The unique connection structure of this invention ensures independent operation of the two channels without interfering with each other's cooling capacity. The measured maximum heat dissipation output reaches 4.8kW / m², delaying the onset of peak temperatures in the concrete core by 6-8 hours and providing a wider window for compaction.

[0017] 3. Dual strengthening effect of metal thorns and thread structure The vertical metal spike design in this invention has both heat conduction and structural anchoring functions: Thermally: The spikes expand the heat dissipation interface deep into the concrete (increasing the effective contact area by 35%) and achieve a "heat short-circuit effect" through direct contact with the foundation, accelerating heat diffusion into the ground. Mechanical level: Metal spikes are embedded in the foundation to form shear keys. Combined with the outer wall thread structure of the present invention, the shear strength of the pipe-concrete interface is increased to 2.3MPa (only 1.1MPa for the thornless structure), eliminating the risk of interlayer dislocation during the rolling process.

[0018] 4. Breakthrough in reliability of integrated molding technology The metal spikes and threaded structure in this invention are integrally formed with the pipe body (e.g., by 3D printing), completely eliminating the interfacial thermal resistance issues associated with traditional welding or bonding processes. Experimental data shows that the integrated pipe has a 42% higher thermal conductivity than a welded structure. Furthermore, under the vibration load of a roller (amplitude ±2mm), no spikes fall off or threads peel off, and the equipment durability meets the requirement of ≥1 million fatigue cycles.

[0019] 5. Systematic optimization of construction efficiency The pre-buried piping system achieves "integrated temperature control structure in a single pour," eliminating the subsequent grouting and sealing steps required for traditional water cooling. The 3D printing technology employed in this invention enables rapid on-site customization of custom-shaped piping (such as universal joints across fault zones), reducing construction preparation time in complex terrain to one-third of conventional methods. Engineering validation has shown that this method reduces the labor required for temperature control operations by 52% and shortens the overall construction period by 19% in similar-sized dam construction.

[0020] In summary, the present invention pre-buries specific metal pipes before pouring concrete and circulates the temperature of the metal pipes to cool them, thereby controlling the pouring temperature of the roller-compacted concrete and achieving one-time pouring, thereby improving construction efficiency.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention provides a schematic diagram of the overall process of a temperature control method for pouring roller compacted concrete. DETAILED DESCRIPTION

[0023] like Figure 1 As shown, the present invention provides a temperature control method for pouring roller compacted concrete, which includes the following steps: Step 1: Determine the material and shape of the metal pipe based on the terrain of the location where the RCC needs to be poured and the external temperature; Step 2: Making a metal pipe according to the material and shape of the metal pipe; Step 3: Install the metal pipe at the location where the roller compacted concrete needs to be poured, and ensure that both ends of the metal pipe are located outside the location where the roller compacted concrete needs to be poured; Step 4: Connect cooling devices to both ends of the metal pipe so that coolant flows through the metal pipe. At the same time, connect metal cooling devices to the pipe walls at both ends of the metal pipe so that the pipe walls of the metal pipe are always at a low temperature. Step 5: Pour the roller-compacted concrete and complete the shaping of the concrete by rolling.

[0024] The present invention pre-buries specific metal pipes before pouring concrete and circulates the temperature of the metal pipes to control the pouring temperature of the roller compacted concrete and achieves one-time pouring, thereby improving construction efficiency.

[0025] In step 1, the material and shape of the metal pipe are determined according to the terrain of the location where the RCC is to be poured and the external temperature, in the following way: First, determine the shape and material of the metal pipe according to the terrain of the location where the RCC needs to be poured; Second, the coating material of the metal pipe is determined according to the external temperature of the location where the RCC needs to be poured.

[0026] Among them, the first one is the influence of terrain on pipeline selection. The present invention provides the following examples for selection.

[0027] (1) Steep / complex terrain (slope > 15° or bedrock undulation > 2m) Material selection: Titanium alloy (Ti-6Al-4V) Tensile strength ≥895MPa (2.3 times that of aluminum alloy) Elastic modulus 110GPa, adaptable to foundation deformation Shape design: deep bellows + radial reinforcement ribs Corrugation depth ≥15mm (1.5 times that of standard pipe) to improve bending resistance Annular reinforcement is provided every 2m (section stiffness is increased by 40%) (2) Flat / gentle slope terrain (slope ≤ 15°) Material selection: 6061-T6 aluminum alloy Thermal conductivity 167W / (m·K) (7 times that of titanium alloy) Density 2.7g / cm³, reducing transportation costs Shape design: standard sinusoidal corrugated tube Corrugation depth 10mm, wave distance 50mm (optimizes airflow turbulence) No need for reinforcement ribs, simplifying installation In the second, it is the correction of pipeline treatment by ambient temperature, and the following is a specific example.

[0028]

[0029] This invention significantly improves the pipeline system's adaptability to complex construction environments by dynamically selecting the metal pipe material (e.g., titanium alloy for steep slopes and aluminum alloy for flat areas) and shape (corrugation depth / rib configuration) based on the terrain's slope, undulation, and ambient temperature. Furthermore, it applies targeted functional coatings (phase change coating for high-temperature areas and radiation coating for low-temperature areas). This design dynamically matches the pipe's thermal conductivity to the concrete's temperature rise curve. Field measurements show that in areas with high temperatures and steep slopes above 35°C, the internal temperature difference in the concrete can be controlled to within ±1.5°C (a 60% improvement in accuracy compared to conventional methods), effectively suppressing interlaminar cracking caused by temperature gradients.

[0030] In step 2, a metal pipe is manufactured according to the material and shape of the metal pipe. Currently, a commonly used method is to use 3D printing technology to manufacture the metal pipe.

[0031] Regarding the styles of metal pipes, the present invention provides the following styles of metal pipes in order to better cool the concrete during concrete pouring.

[0032] Model 1: The metal pipe has a plurality of metal spikes on its wall, the spikes being perpendicular to the pipe wall, the spikes being made of the same material as the pipe and being integrally formed, and the spikes located below the pipe being in contact with the ground.

[0033] The vertical metal spike design in this invention has both heat conduction and structural anchoring functions: Thermally: The spikes expand the heat dissipation interface deep into the concrete (increasing the effective contact area by 35%) and achieve a "heat short-circuit effect" through direct contact with the foundation, accelerating heat diffusion into the ground. Mechanical level: Metal spikes are embedded in the foundation to form shear keys. Combined with the outer wall thread structure of the present invention, the shear strength of the pipe-concrete interface is increased to 2.3MPa (only 1.1MPa for the thornless structure), eliminating the risk of interlayer dislocation during the rolling process.

[0034] Style 2: The metal pipe is provided with an inner ring pipe, which is connected to the inner wall of the metal pipe via a plurality of evenly distributed connecting rods. The gap between the metal pipe and the inner ring pipe is used to circulate cold air, which is supplied by the air conditioner.

[0035] This invention utilizes a dual cooling mechanism: a coolant (liquid medium) circulating through an inner ring pipe and cold air (gaseous medium) circulating through an interlayer, forming a "liquid-gas composite heat dissipation channel." The coolant is responsible for transferring the basic heat load (due to its specific heat capacity advantage), while the cold air rapidly reduces the pipe wall temperature through forced convection (increasing the thermal conductivity response speed by three times). The unique connection structure of this invention ensures that the two channels operate independently without interfering with each other's cooling capacity. The measured maximum heat dissipation power reaches 4.8kW / m², delaying the onset of peak temperatures in the core concrete zone by 6-8 hours, thus providing a wider window for compaction.

[0036] Style three: The outer wall of the metal pipe is provided with a threaded structure, and the threaded structure is made of the same material as the outer covering of the metal pipe and is integrally formed.

[0037] The metal spikes and threaded structure in this invention are integrally formed with the pipe body (e.g., by 3D printing), completely eliminating the interfacial thermal resistance issues associated with traditional welding or bonding processes. Experimental data shows that the integrated pipe has a 42% higher thermal conductivity than a welded structure. Furthermore, under the vibration load of a roller (amplitude ±2mm), no spikes fall off or threads peel off, and the equipment durability meets the requirement of ≥1 million fatigue cycles.

[0038] The above-mentioned styles 1, 2 and 3 can be used in combination, that is, the metal pipe not only has metal spikes on the outer wall, but also has an inner ring pipe on the inner wall. This can combine the above-mentioned two technical advantages at the same time.

[0039] In step 3, install the metal pipe at the location where the RCC will be poured, with both ends of the pipe located outside the concrete area. The outer metal pipe will connect the cooling equipment and the metal cooling equipment. Generally, 30 cm of exposed metal pipe at both ends is sufficient for construction.

[0040] In step 4, there are two processes. The first process is to connect cooling equipment at both ends of the metal pipe so that coolant flows in the metal pipe. The second process is to connect metal cooling equipment to the pipe walls at both ends of the metal pipe so that the pipe walls of the metal pipe are always in a low temperature state.

[0041] The two processes are carried out simultaneously.

[0042] In the first process, based on the above, it is necessary to inject cold air into the metal pipe, that is, to connect cooling devices at both ends of the metal pipe so that coolant flows in the metal pipe, including the following methods: Connect the two ends of the inner ring pipe to the coolant inlet and outlet of the cooling equipment respectively, so that the coolant circulates in the inner ring pipe; The inlet and outlet of the air conditioner are connected to both ends of the gap between the metal pipe and the inner ring pipe through connecting channels of specific shapes, so that cold air can flow through the gap between the metal pipe and the inner ring pipe.

[0043] In the second process, metal cooling equipment is connected to the pipe walls at both ends of the metal pipe, so that the pipe walls of the metal pipe are always in a low temperature state.

[0044] This invention utilizes a dual cooling mechanism: a coolant (liquid medium) circulating through an inner ring pipe and cold air (gaseous medium) circulating through an interlayer, forming a "liquid-gas composite heat dissipation channel." The coolant is responsible for transferring the basic heat load (due to its specific heat capacity advantage), while the cold air rapidly reduces the pipe wall temperature through forced convection (increasing the thermal conductivity response speed by three times). The unique connection structure of this invention ensures that the two channels operate independently without interfering with each other's cooling capacity. The measured maximum heat dissipation power reaches 4.8kW / m², delaying the onset of peak temperatures in the core concrete zone by 6-8 hours, thus providing a wider window for compaction.

[0045] In step 5, the roller compacted concrete is poured and the concrete is shaped by rolling, thereby completing the pouring of the roller compacted concrete.

[0046] In this invention, the pre-buried piping system achieves "integrated temperature control structure in a single pour," eliminating the subsequent grouting and sealing steps required for traditional water cooling. The 3D printing technology employed in this invention enables rapid on-site customization of custom-shaped piping (such as universal joints across fault zones), reducing construction preparation time in complex terrain to one-third of conventional methods. Engineering validation has shown that this method reduces the labor required for temperature control operations by 52% and shortens the overall construction period by 19% in similar-sized dam construction.

[0047] The technical solution of the present invention is described below through several specific embodiments.

[0048] Example 1: Conventional environment construction (taking roadbed engineering in plain areas as an example) Step 1: Pipeline parameter decisions Topographic data: Slope ≤ 8°, foundation undulation < 0.5m → Select 6061-T6 aluminum alloy standard corrugated pipe (corrugation depth 10mm, wave distance 50mm) Temperature data: Ambient temperature 25°C → External wall sprayed with black chrome radiation coating (emissivity 0.92) Step 2: Pipeline fabrication and installation Laser selective melting 3D printing (parameters: laser power 2000W, layer thickness 30μm) is used to form a one-piece threaded outer wall (pitch 8mm) and vertical metal spikes (height 50mm, spacing 200mm×200mm). The lower metal spikes are embedded in the foundation ≥15cm Lay the grid with a spacing of 1.8m×1.8m, leaving 30cm exposed at both ends for connecting equipment Step 3: Dual-medium cooling The inner ring pipe (diameter 40mm) is passed through 5℃ ethylene glycol solution (flow rate 1.2m3 / h) -5℃ cold air is passed through the interlayer (flow rate 12m / s, pressure 0.3MPa) Step 4: Concrete pouring Layered pouring of roller-compacted concrete (layer thickness 35cm), roller load 18t, vibration frequency 28Hz The following is a comparison of the measured data:

[0049] Example 2: High-temperature steep slope construction (taking the dam abutment of a hydropower station as an example) Terrain response: Slope 22° → Use Ti-6Al-4V titanium alloy deep corrugated pipe (corrugation depth 15mm, circumferential reinforcement spacing 1m) Temperature response: Daytime temperature 38°C → External wall composite lauric acid-graphene phase change coating (phase change temperature 32°C, thickness 200μm) Cooling system optimization: Air conditioning temperature drops to -15°C (compensates for heat loss in high temperature environments) The density of metal spikes increased to 150mm×150mm (for enhanced anchoring) The following is a comparison of the measured data:

[0050] Example 3: Special terrain processing (1) Construction across fault zones Pipe material: Nickel-titanium shape memory alloy (phase transition temperature -10°C) Structural design: Universal joint segment connection (single segment length 1.5m, allowable deflection 15°) Cold air duct: Add PTFE hydrophobic membrane (to prevent water seepage and freezing at faults) (2) Alpine permafrost areas (<0℃) Inner ring pipeline: Antifreeze (-30℃ freezing point) Interlayer cooling: switch to 10℃ dry air (anti-freeze mode) Metal thorn end: wrapped with carbon fiber heating sleeve (power 50W / m, maintain the foundation contact temperature) In addition, when designing the method of the present invention, reliability verification of the one-piece molding process (ASTM E466 fatigue test) was also performed. The following is the experimental data.

[0051]

[0052] For the economic analysis of the construction efficiency of the present invention, we obtained the following data:

[0053] The present invention solves the above-mentioned technical deficiencies through “three core innovations”: 1-Environmental Adaptive Design By dynamically selecting titanium alloy / aluminum alloy based on the terrain slope and combining it with temperature-responsive coatings (such as phase change materials for heat absorption and black chrome coatings for radiation), the concrete temperature difference can be controlled to ±2.1°C in a certain project (4,500m above sea level) with a 30°C difference between day and night.

[0054] 2-Dual-medium synergy mechanism The independent cooling liquid and cooling air channel design breaks through the limitations of traditional single medium: The cold air layer stabilizes the pipe wall temperature below 5°C (traditional water pipe wall temperature>15°C); When the interlayer air flow velocity is greater than 10m / s, the convection heat transfer coefficient reaches 140W / (m²·K) (pure water cooling is only 90W / (m²·K)).

[0055] 3-Structural and functional integration The metal spikes reduce the thermal resistance between concrete and foundation to 0.015K·m / W (0.027K·m / W for the non-spiked structure); The tensile strength of the threaded interface reaches 18kN / m (smooth pipe is only 7kN / m), completely eliminating the risk of structural debonding during compaction construction.

[0056] The above implementation method has been verified in a roller-compacted concrete dam project on the Qinghai-Tibet Plateau (dam height 120m). After applying this technology, the maximum temperature rise was controlled at 24.3℃ (design limit 28℃), and the permeability coefficient of the interlayer interface was reduced to 1×10⁻ 9 cm / s (one order of magnitude better than the design standard).

[0057] In summary, the present invention pre-buries specific metal pipes before pouring concrete and circulates the temperature of the metal pipes to cool them, thereby controlling the pouring temperature of the roller-compacted concrete and achieving one-time pouring, thereby improving construction efficiency.

[0058] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A temperature control method for pouring roller compacted concrete, characterized in that: include: Determine the material and shape of the metal pipe based on the terrain of the location where the RCC needs to be poured and the external temperature; manufacturing a metal pipe according to the material and shape of the metal pipe; Install the metal pipe at the location where the roller compacted concrete needs to be poured, and make the two ends of the metal pipe be located outside the location where the roller compacted concrete needs to be poured; Connect cooling devices to both ends of the metal pipe so that coolant flows through the metal pipe. At the same time, connect metal cooling devices to the pipe walls at both ends of the metal pipe so that the pipe walls of the metal pipe are always in a low temperature state. Pour roller compacted concrete and complete the shaping of the concrete by rolling.

2. A temperature control method for pouring roller compacted concrete according to claim 1, characterized in that: The metal pipe has a plurality of metal thorns on its wall, the metal thorns are perpendicular to the wall of the metal pipe, and the metal thorns are made of the same material as the metal pipe and are integrally formed.

3. A temperature control method for pouring roller compacted concrete according to claim 2, characterized in that: The metal spikes located below the metal pipe are in contact with the ground.

4. A temperature control method for pouring roller compacted concrete according to claim 1, characterized in that: An inner ring pipe is arranged inside the metal pipe, and the inner ring pipe is connected to the inner wall of the metal pipe through a plurality of evenly distributed connecting rods.

5. A temperature control method for pouring roller compacted concrete according to claim 4, characterized in that: The gap between the metal pipe and the inner ring pipe is used for circulating cold air, and the cold air is supplied by an air conditioner.

6. A temperature control method for pouring roller compacted concrete according to claim 5, characterized in that: Connecting cooling devices to both ends of the metal pipe so that the coolant flows through the metal pipe includes: Connect the two ends of the inner ring pipe to the coolant inlet and outlet of the cooling equipment respectively, so that the coolant circulates in the inner ring pipe; The inlet and outlet of the air conditioner are connected to both ends of the gap between the metal pipe and the inner ring pipe through connecting channels of specific shapes, so that cold air can flow through the gap between the metal pipe and the inner ring pipe.

7. A temperature control method for pouring roller compacted concrete according to claim 1, characterized in that: The material and shape of the metal pipe are determined according to the terrain of the location where the RCC is to be poured and the external temperature, including: The shape and material of the metal pipe are determined according to the topography of the location where the RCC needs to be poured; The coating material of the metal pipe is determined according to the external temperature of the location where the RCC needs to be poured.

8. A temperature control method for pouring roller compacted concrete according to claim 7, characterized in that: The method for manufacturing the metal pipe according to the material and shape of the metal pipe is 3D printing technology.

9. A temperature control method for pouring roller compacted concrete according to claim 1, characterized in that: The outer wall of the metal pipe is provided with a thread structure, and the thread structure is made of the same material as the outer covering of the metal pipe and is integrally formed.

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