Halogen-free low-smoke low-toxicity heat insulation composite pipe for conveying gas as well as preparation method and application thereof

Abstract

The invention discloses a halogen-free low-smoke low-toxicity heat insulation composite pipe for conveying gas as well as a preparation method and application thereof, and belongs to the technical field of mining pipes. A middle layer of the halogen-free low-smoke low-toxicity heat insulation composite pipe for conveying gas is a steel pipe layer, hot melt adhesive layers are arranged inside and outside the steel pipe layer, a flame-retardant anti-static layer is arranged outside the hot melt adhesive layer on the inner side, and a flame-retardant heat insulation anti-static layer is arranged outside the hot melt adhesive layer on the outer side. The flame-retardant heat-insulating antistatic layer contains unexpanded vermiculite powder; the unexpanded vermiculite powder is formed by crushing and grinding vermiculite concentrate, the grinding temperature is 100-150 DEG C, the grinding time is 5-10 min, and water glass accounting for 3-5% of the mass of the vermiculite concentrate is added in the grinding process to serve as a pretreating agent. The halogen-free low-smoke low-toxicity heat insulation composite pipe prepared by the invention has the use performance, fireproof performance and antistatic performance meeting the standard requirements, and also has the performance of foaming and expanding on-fire parts to obstruct heat conduction, the heat insulation performance slows down the temperature rise in the pipe body, and the safety of a gas conveying pipeline is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of mining pipes, and in particular relates to a halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas, and a preparation method and application thereof. Background Art

[0002] Coal mines, non-coal mines, and tunneling operations all require a large number of pipelines for gas transportation. Due to geological constraints, pipelines must not only meet normal operating requirements but also possess antistatic and fire-resistant properties. There are two potential sources of fire in mines: static sparks and external ignition sources. Non-metallic and composite pipes, made of non-metallic materials with antistatic properties, can effectively dissipate static electricity generated by gas flow and other sources during pipeline transportation, thereby preventing the generation of static sparks. To address external ignition sources, pipelines must also possess fire-resistant properties. Flame retardancy is one aspect of fire resistance, referring to the ability of a pipeline to delay ignition or inhibit, slow, or terminate flame propagation. Currently, all domestic laws, regulations, systems, standards, and implementation rules related to mine safety only require that pipes possess flame-retardant properties. However, fire-resistant properties should also include ensuring that the pipe does not generate large amounts of toxic and harmful gases during a fire. This requires pipes to be halogen-free, low-smoke, and low-toxic. This facilitates miner escape, rescue, and equipment protection. Therefore, simply possessing flame-retardant properties in mining pipes is insufficient to meet fire-resistant requirements.

[0003] Chinese patent CN114017548A discloses a halogen-free, low-smoke, low-toxic composite pipe for conveying gas, and its processing method and application. The composite pipe produced with inorganic flame retardants such as aluminum hydroxide as raw materials can meet the requirements of flame retardancy and halogen-free, low-smoke, and low-toxicity in the combustion process. However, the halogen-free, low-smoke, and low-toxic composite pipe has the following problems, that is, once the pipe body encounters an external fire source and catches fire, the heat will quickly conduct to the inside of the pipe body, causing the temperature inside the pipe body to rise rapidly. The pipeline system will not be able to be used normally in a short period of time, thereby affecting mine production and timely rescue. In order to prevent the temperature inside the pipe body from rising rapidly, the best solution is to wrap the outside of the pipe body with flame-retardant and heat-insulating materials to block the heat conduction process. Wrapping with foam materials such as flame-retardant polyurethane is a common method, but the disadvantage of this method is that it occupies limited space in the mine, and combustion will also produce a large amount of toxic and harmful gases.

[0004] Raw vermiculite is a halogen-free aluminosilicate mineral rich in interlayer water. Its total water content (interlayer water + structural water) exceeds 40%. During calcination, it loses water and expands, rapidly increasing its volume by 8-15 times, and in some cases by up to 30 times. This high content of interlayer and structural water makes it an environmentally friendly inorganic flame retardant material, while the resulting porosity contributes to its excellent thermal insulation properties. Currently, vermiculite is widely used as a filling material for fire doors and in the preparation of fireproof panels. Before use, the vermiculite is calcined to expand and form a powder, which is then pressed into panels.

[0005] Raw vermiculite contains a high amount of water, generating a large amount of water vapor during combustion. Simultaneously, it foams and expands, forming a thermal insulation layer. However, adding small amounts of raw vermiculite is ineffective; larger amounts are required to achieve optimal results. Due to its high surface polarity, raw vermiculite (unexpanded vermiculite) has poor compatibility and dispersibility with non-polar polymers such as polyolefins. Adding large amounts can significantly reduce the mechanical strength of these polymers. Furthermore, raw vermiculite (unexpanded vermiculite) has a high water content, which easily generates small amounts of water vapor during processing, reducing the mechanical strength of the polymer. Therefore, there are currently no reports of adding raw vermiculite (unexpanded vermiculite) to organic polyolefins for mine fire protection and thermal insulation.

[0006] For example, Chinese patent CN113184866A discloses a method for preparing vermiculite micro-nano flakes separated by high-temperature oxide nanoparticles. The method uses a chemical modifier to replace ions between vermiculite layers, weakening the interlayer bonding through hydration to produce a weakly bonded vermiculite-water slurry. High-temperature oxide nanoparticles are dispersed in the vermiculite-water slurry, and the slurry consistency is adjusted. High-speed shear stirring then separates the vermiculite flakes and makes them highly dispersed in the nano-oxide slurry. The mixed slurry has a high viscosity, and the vermiculite flakes are exfoliated into micro-nano flakes separated by the nanoparticles and stably suspended in the slurry.

[0007] For example, Chinese patent CN116854402A discloses a fire-resistant expanded vermiculite with water-absorbing properties and a preparation method thereof, comprising the following steps: (1) incompletely expanding and calcining the vermiculite; (2) taking acrylic acid monomer, sodium hydroxide, acrylamide monomer, initiator potassium persulfate, crosslinking aid pentaerythritol polyglycidyl ether, incompletely expanded vermiculite, and water, stirring them uniformly and performing ultrasonic dispersion to obtain a first reaction solution, and placing the solution in a reactor for reaction to obtain a gel material; (3) preliminarily crushing and drying the gel material, and then further pulverizing it in a ball mill to obtain a fire-resistant expanded vermiculite with water-absorbing properties. Summary of the Invention

[0008] To address the problem of rapid internal temperature rise in existing halogen-free, low-smoke, and low-toxic composite pipes after fire, the present invention provides a halogen-free, low-smoke, and low-toxicity insulated composite pipe for gas transportation, as well as its preparation method and application. With this composite pipe, when any part of the pipe is exposed to an external fire source, the unexpanded vermiculite powder blended into the flame-retardant, heat-insulating, and antistatic material layer in that area rapidly expands upon exposure to fire, forming a foamed insulation layer that blocks heat conduction into the pipe, thereby slowing the temperature rise and improving the safety of gas pipelines. Pretreatment overcomes the poor compatibility and dispersibility of unexpanded vermiculite in non-polar polymers such as polyolefins.

[0009] The present invention is achieved through the following technical solutions: The present invention discloses a halogen-free, low-smoke, low-toxicity heat-insulating composite pipe for conveying gas. The intermediate layer of the halogen-free, low-smoke, low-toxicity heat-insulating composite pipe for conveying gas is a steel pipe layer. Hot-melt adhesive layers are arranged inside and outside the steel pipe layer. A flame-retardant antistatic layer is arranged outside the inner hot-melt adhesive layer. A flame-retardant, heat-insulating, antistatic layer is arranged outside the outer hot-melt adhesive layer. The flame-retardant, heat-insulating, antistatic layer contains unexpanded vermiculite powder. The unexpanded vermiculite powder is prepared by the following method: unexpanded vermiculite concentrate is crushed and ground at a grinding temperature of 100-150° C. for 5-10 minutes, and water glass (3-5% by weight of the unexpanded vermiculite concentrate) is added as a pretreatment agent during the grinding process.

[0010] Furthermore, flange connection pipe fittings are injection-molded at both ends of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas, and metal flanges are installed between the flange connection pipe fittings.

[0011] Furthermore, the raw material composition of the flame retardant, heat-insulating and antistatic layer is: 20-40 parts of base resin I, 20-40 parts of flame retardant, 15-30 parts of unexpanded vermiculite powder, and 3-15 parts of conductive material; the raw material composition of the flame retardant and antistatic layer is 20-40 parts of base resin I, 40-60 parts of flame retardant, and 3-15 parts of conductive material; the material of the flange connection pipe fittings is 30~40 parts of base resin II, 40~60 parts of flame retardant, and 3-15 parts of conductive material; the parts mentioned are parts by weight.

[0012] Furthermore, the base resin I is one or more of linear low-density polyethylene, low-density polyethylene and EVA; the flame retardant is one or more of aluminum hydroxide, magnesium hydroxide and zinc borate; the conductive material is one or more of conductive carbon black, graphite and carbon fiber; the base resin II is a mixture of POE elastomer and olefin thermoplastic elastomer, and the mass ratio of POE elastomer to olefin thermoplastic elastomer is 0.5-3:1; the hot melt adhesive is maleic anhydride grafted modified polyethylene resin.

[0013] Furthermore, the flame retardant, unexpanded vermiculite powder and conductive material are all treated with a surfactant before use, and the surfactant is one or more of a silane coupling agent, polyethylene wax, stearic acid and paraffin.

[0014] Furthermore, the thickness of the steel pipe layer is 0.5-4.0 mm, the thickness of the hot melt adhesive layer is 0.1-0.4 mm, the thickness of the flame retardant and antistatic layer and the flame retardant, heat-insulating and antistatic layer is 0.5-4.5 mm, and the nominal diameter of the steel pipe is 150-1600 mm; the steel pipe layer is welded from steel strips, and the pipe wall has outward-protruding spiral reinforcement grooves, the top of the reinforcement rib is arc-shaped, and the height of the spiral reinforcement rib is 10-30 mm.

[0015] The present invention discloses a method for preparing the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas, comprising the following steps: (1) The raw materials of the hot melt adhesive layer, the flame retardant antistatic layer and the flame retardant heat insulation antistatic layer are extruded by a screw extruder respectively; (2) heating the steel pipe layer, laminating the layers of material extruded in step (1) together through a co-extrusion die, laminating and rolling them onto the inner and outer walls of the steel pipe, and obtaining a halogen-free, low-smoke, low-toxicity, thermal insulation composite pipe semi-finished product after cooling; (3) Put the metal flange on the semi-finished product of the halogen-free, low-smoke, low-toxic thermal insulation composite pipe, and use the direct injection molding method to inject the flange connection pipe fittings and fix them on both ends of the semi-finished product of the halogen-free, low-smoke, low-toxic thermal insulation composite pipe to obtain the finished product of the halogen-free, low-smoke, low-toxic thermal insulation composite pipe.

[0016] Furthermore, the processing method of the steel pipe layer is: pressing the reinforcing rib groove along the longitudinal direction of the steel strip, spirally curling the steel strip with the pressed reinforcing rib groove, welding along the spiral lap seam of the steel strip, and processing it into a steel pipe layer with spiral reinforcing ribs on the pipe wall; the flange connection type pipe fittings are covered with at least one spiral reinforcing rib.

[0017] Furthermore, the processing temperature of the flame retardant antistatic layer and the flame retardant heat insulating antistatic layer is controlled at 130-170°C.

[0018] The present invention also discloses the application of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas in non-coal mines, coal mines and tunnels.

[0019] The halogen-free, low-smoke, low-toxic, heat-insulated composite pipe for conveying gas in the present invention does not use halogen, phosphorus-based flame retardants or other flame retardants in its coating materials (hot-melt adhesive, flame-retardant antistatic layer materials and flame-retardant heat-insulating antistatic layer materials) and pipe fitting special materials. The flame retardant components are aluminum hydroxide, magnesium hydroxide, zinc borate and unexpanded vermiculite powder. When a gas explosion, dust explosion, fire or other external fire source occurs in a mine, the composite pipe itself burns mainly to produce carbon dioxide and water. The toxic effect and concentration of the toxic smoke generated during combustion will not cause death of living organisms within 30 minutes. Even if the pipe is The surrounding flames do not go out. Due to the instantaneous foaming and expansion of the fire site and the structure of the pipe, the temperature inside the pipe rises slowly, and the gas can continue to be transported for at least 15 minutes. During normal use, the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for transporting gas does not need to occupy the limited space of the mine tunnel like polyurethane insulated steel pipes. The pipes are light in weight, quick to install, easy to disassemble, reusable, and low in cost. In the event of roof or impact ground pressure, even if the pipe is buried or hit by boulders, the pipe body will be deformed, but the pipe body will not be cracked or damaged and can continue to be used.

[0020] Raw vermiculite (unexpanded vermiculite) has high surface polarity, resulting in poor compatibility and dispersibility with non-polar polymers such as polyolefins. Excessive addition can reduce the mechanical strength of these polymers. Surface modification reduces polarity, thereby improving compatibility and dispersibility while minimizing the impact on mechanical strength. Sodium silicate (water glass) is added as a pretreatment agent during the grinding process to effectively reduce the polarity of raw vermiculite and prevent the generation of moisture during processing (premature partial expansion). When combined with inorganic flame retardants such as aluminum hydroxide, unexpanded vermiculite powder not only achieves flame retardancy, halogen-free, low-smoke, and low-toxicity properties, but also significantly reduces its toxicity index. Furthermore, when an external fire source is encountered in an underground pipeline, the burning area rapidly foams and expands, blocking heat transfer to the interior of the pipe, slowing the internal temperature rise and allowing the pipeline to continue transporting gas, potentially saving over 15 minutes for production and rescue efforts.

[0021] The beneficial effects achieved by the present invention are: The halogen-free, low-smoke, low-toxicity thermal insulation composite pipe prepared by the present invention has the performance of use, flame retardancy and antistatic properties that meet the standard requirements, and is environmentally friendly (halogen-free, low-smoke, low-toxicity) and thermal insulation. It has the characteristics of impact resistance, light weight, high ring stiffness, corrosion resistance, quick installation, easy disassembly, reusability, and low cost. It is particularly suitable for large-diameter gas extraction, positive pressure ventilation, and negative pressure ventilation pipes in non-coal mines, coal mines, and tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the structure of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe of this application; Figure 2This is a partial enlarged schematic diagram of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for this application 1. Spiral reinforcement, 2. Weld, 3. Flange, 4. Flange-connected pipe fittings, 5. Steel pipe layer, 6. Hot-melt adhesive layer, 7. Flame-retardant and antistatic layer, 8. Flame-retardant, heat-insulating and antistatic layer. DETAILED DESCRIPTION

[0023] The following is a detailed description of a specific embodiment of the present invention in conjunction with the accompanying drawings. This case is only a detailed implementation plan and specific operating process based on the technical invention solution, and is not intended to limit the scope of protection of the present invention. Any modifications, improvements, etc. made within the principles of the present invention shall be included in the scope of protection.

[0024] The steel strip, linear low-density polyethylene, low-density polyethylene, EVA, aluminum hydroxide, magnesium hydroxide, zinc borate, conductive carbon black, graphite, carbon fiber, unexpanded vermiculite powder, POE elastomer, olefin thermoplastic elastomer, water glass, hot-melt adhesive and surfactant in the following examples and comparative examples are all commercially purchased raw materials and remain consistent during use. The parts described in the following examples and comparative examples are parts by weight.

[0025] The structural diagram of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for transporting gas of the present invention is as follows: Figure 1 As shown, the local schematic diagram is as follows Figure 2 The middle structural layer of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for transporting gas is a steel pipe layer 5, which is welded from steel strips. The pipe wall has spiral reinforcement ribs 2 protruding outwards, with arc-shaped tops. The height of the spiral reinforcement ribs 2 is 10-30mm, and every two spiral reinforcement ribs 2 are welded as a unit. The inside and outside of the steel pipe layer 5 are hot-melt adhesive layers 6, and a flame-retardant antistatic layer 7 is provided outside the inner hot-melt adhesive layer 6, and a flame-retardant, heat-insulating, antistatic layer 8 is provided outside the outer hot-melt adhesive layer 6. Flange connection pipe fittings 4 are injection molded at both ends of the pipe, and metal flanges 3 are installed between the flange connection pipe fittings; the thickness of the steel pipe layer 5 is 0.5-4.0 mm, the thickness of the hot melt adhesive layer is 0.1-0.4 mm, the thickness of the flame retardant and antistatic layer 7 and the flame retardant, heat-insulating and antistatic layer 8 are 0.5-4.5 mm respectively, and the nominal diameter of the steel pipe in the steel pipe layer is 150-1600 mm; the flange connection pipe fittings 4 are injection molded by the method disclosed in patent CN117028716A.

[0026] The raw material composition of the flame retardant, heat-insulating and antistatic layer is: 20-40 parts of base resin I, 20-40 parts of flame retardant, 15-30 parts of unexpanded vermiculite powder, and 3-15 parts of conductive material; the raw material composition of the flame retardant and antistatic layer is 20-40 parts of base resin I, 40-60 parts of flame retardant, and 3-15 parts of conductive material; the material of the flange connection pipe fittings is 30~40 parts of base resin II, 40~60 parts of flame retardant, and 3~15 parts of conductive material; the base resin I is one or more of linear low-density polyethylene, low-density polyethylene and EVA; the flame retardant is one or more of aluminum hydroxide, magnesium hydroxide, and zinc borate; the conductive material is one or more of conductive carbon black, graphite, and carbon fiber; the base resin II is a mixture of POE elastomer and olefin thermoplastic elastomer, and the mass ratio of POE elastomer to olefin thermoplastic elastomer is 0.5-3:1; the hot melt adhesive is maleic anhydride grafted modified polyethylene resin. The flame retardant and the conductive material are both treated with a surfactant before use. The surfactant is a silane coupling agent (KH560 silane coupling agent). The amount of silane coupling agent added is 5% of the mass of the flame retardant or conductive material.

[0027] The unexpanded vermiculite powder is obtained by crushing and grinding vermiculite concentrate at a grinding temperature of 100-150°C and a grinding time of 5-10 minutes. During the grinding process, 3-5% of water glass by mass of the vermiculite concentrate is added as a pretreatment agent to change the polarity of the unexpanded vermiculite powder.

[0028] The following examples and comparative examples are prepared by grinding vermiculite concentrate to obtain particles with a particle size of 50-100 mesh, grinding the sieved particles, adding 4% of the raw material weight of water glass (Baume 39-44° Be, density 1.36-1.50 g / cm³), controlling the grinding temperature to 120°C, and grinding time to 10 min.

[0029] Example 1 The raw materials of halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for gas transportation are as follows: Hot melt adhesive layer 6: maleic anhydride grafted modified polyethylene resin; The flame retardant antistatic layer 7 is composed of the following raw materials in parts by weight: linear low-density polyethylene: 30 parts, aluminum hydroxide: 20 parts, magnesium hydroxide: 20 parts, zinc borate: 18 parts, conductive carbon black: 12 parts; The flame retardant, heat-insulating and antistatic layer 8 is composed of the following raw materials in parts by weight: linear low-density polyethylene: 30 parts, unexpanded vermiculite powder 25 parts, aluminum hydroxide 15 parts, magnesium hydroxide 12 parts, zinc borate 8 parts, and conductive carbon black 12 parts; The injection molding material of the flange connection pipe fitting 4 is composed of the following raw materials in parts by weight: 20 parts of POE elastomer, 20 parts of olefin thermoplastic elastomer, 20 parts of aluminum hydroxide, 20 parts of magnesium hydroxide, 10 parts of zinc borate, and 4 parts of carbon fiber; Preparation method of halogen-free, low-smoke, low-toxic thermal insulation composite pipe for gas transportation: (1) The components of the hot melt adhesive layer 6, the flame retardant antistatic layer 7 and the flame retardant heat-insulating antistatic layer 8 for preparing the halogen-free, low-smoke, low-toxicity heat-insulating composite pipe for conveying gas are dried and extruded separately by a screw extruder at a processing temperature of 150±5°C; (2) Derust the surface of the steel strip, and then pull the derusted steel strip to the groove pressing machine to press two reinforcing rib grooves along the longitudinal direction of the steel strip. The height of the reinforcing rib is 16 mm; (3) The steel strip with the reinforced rib groove is spirally curled and welded along the spiral lap seam of the steel strip (every two reinforced ribs constitute a welding unit) to form a steel pipe layer 5 with spiral reinforced ribs 1 on the pipe wall. The steel pipe layer 5 is welded along the circumferential direction of the thin-walled steel pipe to form a weld 2 protruding upward along the circumferential direction of the steel pipe; at the same time, the steel pipe layer 5 is heated (180±5°C), and the extruded hot melt adhesive layer 6 is laminated with the flame retardant antistatic layer 7 and the flame retardant heat-insulating antistatic layer 8 through a co-extrusion die head, and then rolled onto the inner and outer walls of the steel pipe layer 5. After cooling, the length is cut according to the requirements to obtain a semi-finished halogen-free, low-smoke, low-toxicity heat-insulating composite pipe for conveying gas; (4) Put the metal flange 3 on the semi-finished product of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas, place one end of the semi-finished composite pipe in the injection mold, use the injection molding machine to directly inject the injection molding material into the flange connection pipe fitting 4, the injection molding temperature is 155±5℃, remove the mold after cooling, and use the same operation to inject the flange connection pipe fitting on the other end of the semi-finished composite pipe to obtain the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas; During the preparation of the halogen-free, low-smoke, low-toxic thermal insulation composite pipe for conveying gas, the thickness of the steel strip is 2.5 mm, the diameter of the steel pipe layer 5 is 1000 mm, the thickness of the hot-melt adhesive layer 6 is 0.2 mm, and the thickness of the flame-retardant antistatic layer 7 and the flame-retardant heat-insulating antistatic layer 8 after lamination are both 1.8 mm.

[0030] Example 2 The preparation of unexpanded vermiculite powder is the same as in Example 1; The raw materials of halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for gas transportation are as follows: Hot melt adhesive layer 6: maleic anhydride grafted modified polyethylene resin; The flame retardant antistatic layer 7 is composed of the following raw materials in parts by weight: 30 parts of linear low-density polyethylene, 10 parts of EVA, 18 parts of aluminum hydroxide, 20 parts of magnesium hydroxide, 12 parts of zinc borate, and 12 parts of conductive carbon black; The flame retardant, heat-insulating and antistatic layer 8 is composed of the following raw materials in parts by weight: linear low-density polyethylene: 40 parts, unexpanded vermiculite powder: 20 parts, aluminum hydroxide: 15 parts, magnesium hydroxide: 15 parts, zinc borate: 5 parts, carbon fiber: 4 parts; The injection molding material of the flange connection pipe fitting 4 is composed of the following raw materials in parts by weight: 30 parts of POE elastomer, 10 parts of olefin thermoplastic elastomer, 25 parts of aluminum hydroxide, 18 parts of magnesium hydroxide, 7 parts of zinc borate, and 4 parts of carbon fiber; The processing method and thickness of each layer of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas are the same as those in Example 1.

[0031] Example 3 The preparation of unexpanded vermiculite powder is the same as in Example 1; The raw materials of halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for gas transportation are as follows: Hot melt adhesive layer 6: maleic anhydride grafted modified polyethylene resin; The flame retardant antistatic layer 7 is composed of the following raw materials in parts by weight: 25 parts of low-density polyethylene, 10 parts of EVA, 25 parts of aluminum hydroxide, 20 parts of magnesium hydroxide, 15 parts of zinc borate, and 10 parts of conductive graphite; The flame retardant, heat-insulating and antistatic layer 8 is composed of the following raw materials in parts by weight: low-density polyethylene: 15 parts, EVA 15 parts, unexpanded vermiculite powder 30 parts, aluminum hydroxide 12 parts, magnesium hydroxide 10 parts, zinc borate 8 parts, and conductive carbon black 12 parts; The injection molding material of the flange connection pipe fitting 4 is composed of the following raw materials in parts by weight: 15 parts of POE elastomer, 15 parts of olefin thermoplastic elastomer, 20 parts of aluminum hydroxide, 25 parts of magnesium hydroxide, 5 parts of zinc borate, and 4 parts of carbon fiber; The processing method and thickness of each layer of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas are the same as those in Example 1.

[0032] Comparative Example 1 Compared with Example 1, the constituent materials of the flame retardant antistatic layer 7 and the flame retardant heat-insulating antistatic layer 8 in Comparative Example 1 are the same, namely, 30 parts of linear low-density polyethylene, 20 parts of aluminum hydroxide, 20 parts of magnesium hydroxide, 18 parts of zinc borate, and 12 parts of conductive carbon black. The remaining operations are the same as in Example 1.

[0033] Comparative Example 2 Compared with Example 1, in Comparative Example 2, water glass was not added during the grinding of the unexpanded vermiculite powder, and the remaining operations were the same as in Example 1.

[0034] Performance Testing The halogen-free, low-smoke, low-toxicity thermal insulation composite pipes for conveying gas prepared in the above-mentioned Examples 1 to 3 and the comparative example not only meet all the performance requirements specified in the standards, but also far exceed the standard requirements in terms of tensile properties, ring stiffness, drop weight impact performance, antistatic properties, and flame retardant properties, and have halogen-free, low-smoke, low-toxicity, and thermal insulation properties.

[0035] Thermal insulation performance test: The flame retardant, heat-insulating and antistatic layer 8 processed according to the ratio of Example 1 expands to 5.48 mm after the temperature reaches 900°C, and the expansion height at each position is uniform, and the surface expansion height difference does not exceed 0.5 mm; the flame retardant, heat-insulating and antistatic layer 8 processed according to the ratio of Example 2 expands to 4.83 mm after the temperature reaches 900°C, and the expansion height at each position is uniform, and the surface expansion height difference does not exceed 0.5 mm; the flame retardant, heat-insulating and antistatic layer 8 processed according to the ratio of Example 3 expands to 6.20 mm after the temperature reaches 900°C. mm, the expansion height at each position is uniform, and the surface expansion height difference does not exceed 0.5mm; Comparative Example 1 has no obvious expansion; Comparative Example 2 flame retardant, heat-insulating and antistatic layer 8 is found to expand significantly after the temperature reaches 900°C, but the expansion height at each position is different, the highest expansion height is 8.32mm, and the lowest expansion height is only 2.25mm. The difference is quite obvious. This is due to the uneven bonding and dispersion of the unexpanded vermiculite powder. If a fire occurs, heat is conducted inward through the low expansion area, affecting its flame retardant and heat-insulating effects. When a fire occurs in an underground pipeline of the halogen-free, low-smoke, and low-toxicity thermal insulation composite pipe for conveying gas prepared by the method of the embodiment of the present invention, the fire part quickly foams and expands, thereby blocking the conduction of heat to the inside of the pipe body, making the temperature inside the pipe body rise more slowly, and the pipeline can continue to convey gas, which can win more than 15 minutes for production and rescue.

Claims

1. A halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for transporting gas, characterized in that: The middle layer of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas is a steel pipe layer, hot-melt adhesive layers are arranged inside and outside the steel pipe layer, a flame-retardant antistatic layer is arranged outside the inner hot-melt adhesive layer, and a flame-retardant, heat-insulating, antistatic layer is arranged outside the outer hot-melt adhesive layer; the flame-retardant, heat-insulating, antistatic layer contains unexpanded vermiculite powder; The unexpanded vermiculite powder is prepared by the following method: unexpanded vermiculite concentrate is crushed and ground at a grinding temperature of 100-150° C. for 5-10 minutes, and water glass (3-5% by weight of the unexpanded vermiculite concentrate) is added as a pretreatment agent during the grinding process.

2. The halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas according to claim 1 is characterized in that: Both ends of the halogen-free, low-smoke, low-toxicity heat-insulated composite pipe for conveying gas are injection-molded with flange connection pipe fittings, and metal flanges are sleeved between the flange connection pipe fittings.

3. The halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas according to claim 2, characterized in that: The raw material composition of the flame retardant, heat-insulating and antistatic layer is: 20-40 parts of base resin I, 20-40 parts of flame retardant, 15-30 parts of unexpanded vermiculite powder, and 3-15 parts of conductive material; the raw material composition of the flame retardant and antistatic layer is: 20-40 parts of base resin I, 40-60 parts of flame retardant, and 3-15 parts of conductive material; the material of the flange connection pipe fittings is 30-40 parts of base resin II, 40-60 parts of flame retardant, and 3-15 parts of conductive material; the parts mentioned are by weight.

4. The halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas according to claim 3 is characterized in that: The base resin I is one or more of linear low-density polyethylene, low-density polyethylene, and EVA; the flame retardant is one or more of aluminum hydroxide, magnesium hydroxide, and zinc borate; the conductive material is one or more of conductive carbon black, graphite, and carbon fiber; the base resin II is a mixture of POE elastomer and olefin thermoplastic elastomer, and the mass ratio of POE elastomer to olefin thermoplastic elastomer is 0.5-3:1; The hot melt adhesive is maleic anhydride grafted modified polyethylene resin.

5. The halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for transporting gas according to claim 3 is characterized in that: The flame retardant, unexpanded vermiculite powder and conductive material are all treated with a surfactant before use. The surfactant is one or more of a silane coupling agent, polyethylene wax, stearic acid and paraffin.

6. The halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas according to claim 1, characterized in that: The thickness of the steel pipe layer is 0.5-4.0mm, the thickness of the hot melt adhesive layer is 0.1-0.4㎜, the thickness of the flame retardant and antistatic layer and the flame retardant, heat-insulating and antistatic layer are 0.5-4.5mm respectively, and the nominal diameter of the steel pipe is 150-1600mm; the steel pipe layer is welded from steel strips, and the pipe wall has outward-protruding spiral reinforcement grooves, the top of the reinforcement rib is arc-shaped, and the height of the spiral reinforcement rib is 10-30mm.

7. A method for preparing the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for transporting gas according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) The raw materials of the hot melt adhesive layer, the flame retardant antistatic layer and the flame retardant heat insulation antistatic layer are extruded by a screw extruder respectively; (2) heating the steel pipe layer, laminating the layers of material extruded in step (1) together through a co-extrusion die head, laminating and rolling them onto the inner and outer walls of the steel pipe layer, and obtaining a halogen-free, low-smoke, low-toxicity, heat-insulating composite pipe semi-finished product after cooling; (3) Put the metal flange on the semi-finished product of the halogen-free, low-smoke, low-toxic thermal insulation composite pipe, and use the direct injection molding method to inject the flange connection pipe fittings and fix them on both ends of the semi-finished product of the halogen-free, low-smoke, low-toxic thermal insulation composite pipe to obtain the finished product of the halogen-free, low-smoke, low-toxic thermal insulation composite pipe.

8. The method for preparing the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for transporting gas according to claim 7, characterized in that: The processing method of the steel pipe layer is: pressing reinforcing rib grooves along the longitudinal direction of the steel strip, spirally curling the steel strip with the pressed reinforcing rib grooves, welding along the spiral lap seam of the steel strip, and processing it into a steel pipe layer with spiral reinforcing ribs on the pipe wall; the flange connection type pipe fittings are covered with at least one spiral reinforcing rib.

9. The method for preparing the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for transporting gas according to claim 7, characterized in that: The processing temperature of the flame retardant antistatic layer and the flame retardant heat-insulating antistatic layer is controlled at 130-170°C.

10. Use of the halogen-free, low-smoke, low-toxicity thermal insulation composite pipe for conveying gas according to any one of claims 1 to 6 in non-coal mines, coal mines, and tunnels.

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