Inorganic thermal insulation pipe shell with gradient distribution of composite hollow glass beads and preparation method of inorganic thermal insulation pipe shell

Abstract

The invention provides an inorganic thermal insulation pipe shell with gradient distribution of composite hollow glass beads and a preparation method. The preparation method comprises the following steps: preparing the composite hollow glass beads, averagely dividing a base material into three parts, mixing 35-50% of the composite hollow glass beads with one part of the base material, and preparing an inner layer material; 20%-45% of composite hollow glass beads are mixed with one part of the base material, and a middle layer material is prepared; 20%-30% of composite hollow glass beads are taken to be mixed with one part of the base material, and an outer layer material is prepared; sequentially injecting the inner-layer material into the mold and then applying pressure, injecting the middle-layer material and injecting the outer-layer material and then applying pressure to obtain an inorganic thermal insulation pipe shell blank; and finally, the inorganic thermal insulation pipe shell blank is subjected to staged curing and curing. According to the method, the continuity of the hierarchical pore structure in the inorganic thermal insulation pipe shell can be improved, the compressive strength is remarkably improved, the heat conductivity coefficient is reduced, and the purposes of high hydrophobicity and low linear shrinkage are synchronously achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of pipeline insulation materials, in particular, relates to a composite hollow glass microsphere gradient distribution inorganic insulation pipe shell and preparation method. BACKGROUND

[0002] The current mainstream insulation technology mainly uses polyurethane, rock wool and aluminum silicate insulation material technology for high temperature pipeline insulation, but there are problems such as high thermal conductivity, high energy loss rate, short service life of the insulation layer, and difficulty in installing the protective outer plate. The common pipeline insulation materials on the market are mainly organic polymer foams, such as polyurethane foam, phenolic foam, polystyrene foam, etc. However, these materials are flammable and have high fire risk. In order to reduce the thermal conductivity, hollow glass microspheres and vitrified microspheres are used to prepare insulation pipe shells.

[0003] An application patent with the application publication number CN112408938A discloses a preparation method of a micro-nano size multi-level pore insulation pipe shell material: the raw material composition is composed of solid phase and liquid phase, and the solid phase and liquid phase are composed of 7:3 in mass ratio. The solid phase composition is calculated by 100 parts of mass ratio, including 30 to 35 parts of fly ash, 15 to 20 parts of coal gangue, 15 parts of hollow glass microspheres, 15 parts of vitrified microspheres, 10 to 15 parts of glass fiber, 15 parts of aerogel powder, and 7 parts of wood ash. The liquid phase composition is calculated by 100 parts of weight ratio, including 35 parts of water glass, 15 parts of hydrogen peroxide and 50 parts of water. The preparation method includes first mixing wood ash, water glass and water, adding fly ash and calcined and crushed coal gangue, and putting pre-dispersed glass fiber into the stirring mill for stirring. Hollow glass microspheres, vitrified microspheres and aerogel powder are added to the obtained slurry, and put into a drum mixer for mixing. Finally, hydrogen peroxide is added for foaming. The porosity of the micro-nano size multi-level pore insulation pipe shell material is between 50% and 70%, the thermal conductivity is 0.04 W / (m·K), the compressive strength can reach 12 MPa, and it can withstand 800℃ high temperature, with the characteristics of low thermal conductivity, high strength, non-combustible and good high temperature resistance.

[0004] However, the micro-nano size multi-level pore insulation pipe shell material uses only a single type of hollow glass microspheres, which has not been specially designed, and there is a problem that the insulation performance and mechanical properties cannot be considered simultaneously. SUMMARY

[0005] In order to improve the hydrophobicity and compressive strength of the inorganic insulation pipe shell, reduce the linear shrinkage and thermal conductivity, and realize the simultaneous improvement of the insulation performance and mechanical properties of the inorganic insulation pipe shell without modifying the hollow glass microspheres, the technical scheme adopted by the present application is: a preparation method of a composite hollow glass microsphere gradient distribution inorganic insulation pipe shell, comprising the following steps: Composite hollow glass microspheres were prepared by mixing first-type hollow glass microspheres, second-type hollow glass microspheres and third-type hollow glass microspheres in a weight ratio of 4:(2~6):(2~6) to obtain composite hollow glass microspheres. In the raw material preparation, the matrix material is divided into three equal parts. 35% to 50% of the composite hollow glass microspheres are mixed with one part of the matrix material to prepare the inner layer material; 20% to 45% of the composite hollow glass microspheres are mixed with one part of the matrix material to prepare the middle layer material; and 20% to 30% of the composite hollow glass microspheres are mixed with one part of the matrix material to prepare the outer layer material. The matrix materials include cement, water glass, aluminum silicate fiber, aerogel, water-reducing agent, water-retaining agent, adhesive powder, water-repellent agent, dispersant, and water. After the inner layer material is injected into the mold in sequence, a pressure of 0.25MPa to 0.5MPa is applied and held for 10s to 20s; after the middle layer material is injected, a pressure of 0.5MPa to 0.75MPa is applied and held for 10s to 20s; after the outer layer material is injected, a pressure of 0.5MPa to 1.0MPa is applied and held for 10s to 20s to obtain an inorganic thermal insulation pipe shell blank. The inorganic insulation pipe shell blank is first cured at 20℃~35℃ and 80% humidity for 20h~24h, and then cured at 50℃~75℃ and 95% humidity for 45h~50h. The first type of hollow glass microspheres has a true density of 0.13 g / cm³ to 0.17 g / cm³, a bulk density of 0.08 g / cm³ to 0.09 g / cm³, a compressive strength of 500 Psi, and a particle size distribution with a D50 of 80 μm and a D90 of 120 μm. The true density of the second type of hollow glass microspheres is 0.36 g / cm³ to 0.40 g / cm³, the bulk density is 0.19 g / cm³ to 0.22 g / cm³, the compressive strength is 5500 Psi, and the particle size distribution has a D50 of 40 μm and a D90 of 65 μm. The true density of the third type of hollow glass microspheres is 0.58 g / cm³ to 0.62 g / cm³, the bulk density is 0.29 g / cm³ to 0.34 g / cm³, the compressive strength is 12000 Psi, and the particle size distribution has a D50 of 40 μm and a D90 of 65 μm.

[0006] Beneficial effects: Performance optimization can be achieved from three aspects: component function, synergistic mechanism and microstructure.

[0007] Based on the above, by weight, the composition includes 200-300 parts cement, 30-80 parts water glass, 400-500 parts composite hollow glass microspheres, 80-180 parts aluminum silicate fiber, 100-150 parts aerogel, 1-3 parts polycarboxylate superplasticizer, 1.0-1.5 parts water-retaining agent, 5-8 parts adhesive powder, 2-3.5 parts water-repellent agent, 1-1.5 parts dispersant, and 900-1250 parts water. The total amount of composite hollow glass refers to the sum of the weight parts of all first-class hollow glass microspheres, the weight parts of all second-class hollow glass microspheres, and the weight parts of third-class hollow glass microspheres.

[0008] Beneficial effects: By optimizing parameters, the ratio between raw materials can be further clarified, achieving optimal results.

[0009] Based on the above, in the compaction step, the inner layer thickness of the inorganic insulation pipe shell blank is 1cm to 2cm, the middle layer thickness is 1cm to 2cm, and the outer layer thickness is 2cm to 3cm.

[0010] Beneficial effects: It can optimize the thickness ratio of the inner middle layer and the outer layer, ensuring that the inorganic insulation shell has comprehensive mechanical and thermal insulation properties.

[0011] Based on the above, when preparing the inner layer material, the middle layer material and the outer layer material, the cement, the aerogel and the composite hollow glass of the corresponding specifications are first dry-mixed for 1 min to 2 min. Then add the aluminum silicate fiber, the water-retaining agent, the adhesive powder, and the water-repellent agent and dry mix for 1 to 2 minutes; finally add water, the water-reducing agent, the dispersant, and the water glass and stir for 1 to 2 minutes.

[0012] Beneficial effects: By limiting the order in which raw materials are added to the inner, middle, and outer layers, it ensures that the raw materials can be mixed evenly.

[0013] Based on the above, the aluminum silicate fiber includes aluminum silicate fiber with a length of 6 mm and aluminum silicate fiber with a length of 9 mm.

[0014] Based on the above, the water-reducing agent is a polycarboxylate water-reducing agent; the aerogel is a silicone aerogel; the water-repellent agent is an organosilicon; the dispersant is an aminosulfonate dispersant; the water-retaining agent is HPK400; and the adhesive powder is a VAE-type polymer adhesive powder.

[0015] The present invention also provides an inorganic heat-insulating pipe shell with a gradient distribution of composite hollow glass microspheres, which is prepared by the above-mentioned preparation method.

[0016] In this invention, the first type of hollow glass microspheres is designated as HL15 type hollow glass microspheres, the second type of hollow glass microspheres is designated as HL38 type hollow glass microspheres, and the third type of hollow glass microspheres is designated as HL60 type hollow glass microspheres.

[0017] Specifically, in the method for preparing inorganic thermal insulation pipe shells with gradient distribution of composite hollow glass microspheres provided by the present invention, the roles and reaction processes of each component are as follows: Composite hollow glass microspheres: These are composites of three types of hollow glass microspheres—HL15, HL38, and HL60—in a specific ratio. This design retains the low thermal conductivity of HL15 to ensure insulation performance, while the transition with HL38 and the reinforcement with HL60 solves the problem of balancing insulation and mechanical properties inherent in single-microsphere materials. The composite microspheres achieve an optimal balance between density and thermal conductivity, with a lightweight microsphere framework that significantly reduces overall material density, thus decreasing weight while enhancing insulation performance.

[0018] Aerogels: Their nanoporous structure further reduces the overall density of the material, and works in synergy with microbeads to achieve the dual effects of "lightweight + low thermal conductivity".

[0019] Sulfoaluminate cement: 725 sulfuroaluminate cement has low water demand and high density of hydration products, which reduces the amount of cementitious materials while ensuring strength and avoids the increase in density caused by excessive cement.

[0020] Sulphoaluminate cement + water glass: Sulphoaluminate cement hydrates to produce ettringite and aluminum hydroxide gel. Water glass acts as an activator, reacting with the hydration products of sulphoaluminate cement to generate more aluminosilicate gels, thereby improving the bonding strength of the matrix.

[0021] Aluminosilicate fibers: distributed across each layer, they can inhibit crack propagation, while enhancing the interfacial bonding between microspheres and the cementitious matrix, thus improving the flexural strength and toughness of the material.

[0022] Adhesive powder: During the hydration process, it disperses at the interface of cementitious materials to form a flexible transition layer, which enhances the bonding strength between microspheres, fibers and cement matrix, and reduces the strength loss caused by interface defects.

[0023] Meanwhile, to ensure low thermal conductivity, on the one hand, a dual thermal barrier of "microsphere-air" is formed by combining a high-dosage composite microsphere inner layer with low-pressure compaction, directly blocking heat transfer. On the other hand, the nanoporous structure of the aerogel can suppress air convection and thermal radiation, filling the gaps between microspheres and further reducing the overall thermal conductivity. In the intermediate transition structure, the composite microspheres and cementing material intertwine to form a gradient transition zone of "microsphere-cement," avoiding abrupt changes in thermal conductivity between the high porosity of the inner layer and the dense structure of the outer layer, thus reducing thermal bridging effects.

[0024] Therefore, this invention has outstanding substantive features and significant progress compared to the prior art. Specifically, the method for preparing inorganic thermal insulation pipe shells with gradient distribution of composite hollow glass microspheres provided by this invention has the following advantages: (1) It can achieve a balance mechanism of "lightweight-high strength". Through a gradient design prioritizing inner insulation, outer strength, and a middle transition buffer, synergistic performance is achieved. Composite microspheres and aerogel constitute a "lightweight matrix." Through gradient dosing design, while meeting the high insulation requirements of the inner layer, the outer layer with low microsphere dosing and high-pressure compaction achieves "dense load-bearing capacity." The cementitious system of sulfur-aluminum cement and water glass provides basic strength, while aluminum silicate fiber and adhesive powder strengthen interfacial bonding, forming a synergistic structure of "lightweight skeleton + high-strength matrix," ultimately achieving a compressive strength of ≥13.2MPa when the density is ≤180kg / m³.

[0025] (2) It can achieve synergistic optimization of "thermal insulation and hydrophobicity". The inner layer, with a high concentration of HL15 microspheres, forms a highly efficient thermal insulation layer with aerogel. The aerogel and hydrophobic agent synergistically construct a nano-hydrophobic network. Its closed-cell structure reduces heat transfer paths; the hydrophobic agent forms a hydrophobic film on the material surface and pore walls, which neither affects the internal porous insulation structure nor prevents moisture penetration, achieving dual stability of "low thermal conductivity + high hydrophobicity".

[0026] (3) By adapting gradient compaction and segmented curing, performance loss can be reduced. The gradient compaction process is matched with the material composition. Low pressure is suitable for the high porosity required for the inner insulation layer, medium pressure meets the transition requirements of the intermediate layer, and high pressure ensures the density of the outer layer. Staged curing promotes interlayer fusion and strength building in sequence, so that hydration products are evenly distributed in the gradient structure, reducing performance loss.

[0027] (4) It can achieve synergistic enhancement of microscopic hydration reactions. From a microscopic perspective, the high-dosage composite microspheres in the inner layer form a large dispersed phase dominated by HL15, with the microspheres connected by a cementitious material. The pores are evenly distributed and numerous, exhibiting a loose yet highly insulating microstructure. In the middle layer of composite microspheres, HL15, HL38, and HL60 are evenly distributed. The microspheres intertwine with cementitious materials and fibers to form a transitional microstructure, with the number and size of pores falling between the inner and outer layers, achieving a smooth transition in performance. In the outer layer of composite microspheres, HL60 has a relatively high proportion. The microspheres are densely encapsulated by a cementitious material, with fewer and smaller pores, resulting in a dense microstructure and exhibiting high strength, matching the functional requirements of "inner layer insulation, middle layer transition, and outer layer load-bearing."

[0028] In summary, this solution achieves performance optimization from component function, synergistic mechanism to microstructure through scientific and reasonable mixing ratios of composite microspheres, gradient dosing design, targeted raw material selection, and process synergy: high-dosage lightweight components ensure lightweight properties, the cementation system and fiber reinforcement achieve high strength, porous structure and low thermal conductivity components synergistically reduce thermal conductivity, hydrophobic agents and dispersants enhance hydrophobicity, low-shrinkage components and fibers inhibit shrinkage, and chemically stable components and crack-resistant structures enhance weather resistance. Ultimately, this solution achieves the comprehensive advantages of inorganic thermal insulation pipe shells with compressive strength ≥13.2MPa, thermal conductivity (35℃) ≤0.039W / (m·K), bulk density ≤180kg / m³, hydrophobicity ≥99%, and linear shrinkage ≤0.8%. Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0030] Example 1 This embodiment provides a method for preparing an inorganic heat-insulating pipe shell with a gradient distribution of composite hollow glass microspheres, the specific steps of which include: Composite hollow glass microspheres were prepared by mixing first-type hollow glass microspheres, second-type hollow glass microspheres and third-type hollow glass microspheres in a weight ratio of 4:3:3 to obtain composite hollow glass microspheres. In the raw material preparation, the matrix material is divided into three equal parts. 45% of the composite hollow glass microspheres are mixed with one part of the matrix material to prepare the inner layer material; 30% of the composite hollow glass microspheres are mixed with one part of the matrix material to prepare the middle layer material; and 25% of the composite hollow glass microspheres are mixed with one part of the matrix material to prepare the outer layer material. The matrix materials include cement, water glass, aluminum silicate fiber, aerogel, water-reducing agent, water-retaining agent, adhesive powder, water-repellent agent, dispersant, and water. After the inner layer material is injected into the mold in sequence, a pressure of 0.3 MPa is applied and held for 10 seconds; after the middle layer material is injected, a pressure of 0.6 MPa is applied and held for 15 seconds; after the outer layer material is injected, a pressure of 0.8 MPa is applied and held for 20 seconds to obtain an inorganic thermal insulation pipe shell blank. The inorganic insulation pipe shell blank is first cured at 30°C and 80% humidity for 24 hours, and then cured at 65°C and 95% humidity for 48 hours. In the preparation of the inner layer material, the middle layer material and the outer layer material, the cement, the aerogel and the composite hollow glass of the corresponding specifications are first dry-mixed for 2 minutes; then the aluminum silicate fiber, the water-retaining agent, the adhesive powder and the water-repellent agent are added and dry-mixed for 2 minutes; finally, water, the water-reducing agent, the dispersant and the water glass are added and stirred for 2 minutes.

[0031] Specifically, the cement used is high-grade 725 sulfur-aluminum cement. The water-reducing agent is a polycarboxylate water-reducing agent; the aerogel is a silica-based aerogel; the water-repellent agent is an organosilicon; the dispersant is an aminosulfonate dispersant; the water-retaining agent is HPK400; and the adhesive powder is a VAE-type polymer adhesive powder.

[0032] More specifically, in this embodiment, by weight, there are 250 parts of cement, 50 parts of water glass, 450 parts of composite hollow glass microspheres, 150 parts of aluminum silicate fiber, 130 parts of aerogel, 2 parts of polycarboxylate superplasticizer, 1.5 parts of water-retaining agent, 7 parts of adhesive powder, 3 parts of water-repellent agent, 1.5 parts of dispersant, and 1150 parts of water. In this embodiment, the aluminum silicate fiber is made by mixing fibers with a length of 6 mm and fibers with a length of 9 mm in a mass ratio of 4:6.

[0033] The first type of hollow glass microspheres has a true density of 0.13 g / cm³ to 0.17 g / cm³, a bulk density of 0.08 g / cm³ to 0.09 g / cm³, a compressive strength of 500 Psi, and a particle size distribution with a D50 of 80 μm and a D90 of 120 μm.

[0034] The true density of the second type of hollow glass microspheres is 0.36 g / cm³ to 0.40 g / cm³, the bulk density is 0.19 g / cm³ to 0.22 g / cm³, the compressive strength is 5500 Psi, and the particle size distribution has a D50 of 40 μm and a D90 of 65 μm.

[0035] The third type of hollow glass microspheres has a true density of 0.58 g / cm³ to 0.62 g / cm³, a bulk density of 0.29 g / cm³ to 0.34 g / cm³, a compressive strength of 12000 Psi, and a particle size distribution with a D50 of 40 μm and a D90 of 65 μm. The first type of hollow glass microspheres is HL15, the second type is HL38, and the third type is HL60.

[0036] Specifically, the compaction step includes the following operations: (1) Physical isolation: The mold consists of an inner mold, a middle mold, and an outer mold. The interfaces of each layer are coated with a nano-silica-aerogel composite isolation slurry. The slurry is prepared by weight ratio of nano-silica gel:aerogel powder:water = 5:3:2 and is uniformly coated onto the surface of the already formed inner / middle layer using a spraying device, forming a composite isolation layer with a thickness of 1-2 mm. After the composite isolation layer cures, the nano-silica component undergoes a hydration reaction with the cementitious material in the tube shell matrix to achieve chemical fusion, while the aerogel component retains its microporous structure to enhance the interfacial thermal insulation transition. A 5-6 mm thick silicone-PTFE composite buffer strip is installed between each layer to absorb pressure during compression. A fluorocarbon-modified silane release agent is sprayed onto the inner wall of the mold to ensure easy separation of each layer and a complete surface after compaction.

[0037] (2) Layered pressure application: Inner layer low-pressure compaction: After the inner layer material is evenly mixed, it is spread into the inner cavity of the mold, and inner layer compaction is initiated. Pressure is slowly increased to the target pressure at a rate of 0.08 MPa / min and held for 10 seconds. During this process, pressure changes are monitored in real time by the equipment's pressure sensor to ensure the pressure remains stable within the set range, maintaining a certain porosity in the inner layer matrix to ensure thermal insulation performance. After the pressure holding period, the depressurization rate is reduced to 0.04 MPa / min to slowly release the pressure to 0, completing the inner layer compaction and providing a foundation for subsequent middle layer pressure application.

[0038] Intermediate Layer Compaction: After the intermediate layer material is evenly mixed, it is spread into the intermediate layer cavity of the mold, and intermediate layer compaction is initiated; pressure is slowly increased to the target pressure at a rate of 0.12 MPa / min and held for 15 seconds. At this time, the composite buffer strip undergoes slight deformation due to pressure, with the deformation controlled within 1.5-2.2 mm, which can absorb some pressure energy and reduce pressure transmission to the inner layer. After the pressure holding period, the pressure is released at a rate of 0.06 MPa / min, forming a "flexible-rigid transition" structure in the intermediate layer, further blocking the influence of subsequent high pressure from the outer layer.

[0039] Outer layer high-pressure compaction: After the outer layer material is evenly mixed, it is spread into the outer cavity of the mold, and the outer layer compaction is started. The pressure is slowly increased to the target pressure at a rate of 0.18 MPa / min and held for 20 seconds. After the pressure holding is completed, the pressure is slowly released at a rate of 0.08 MPa / min to complete the outer layer compaction.

[0040] In this embodiment, the inner layer thickness of the inorganic heat-insulating pipe shell blank is 2cm, the middle layer thickness is 2cm, and the outer layer thickness is 3cm.

[0041] This embodiment also provides an inorganic heat-insulating pipe shell prepared by the same method.

[0042] The compressive strength, flexural strength, density, and linear shrinkage rate of the inorganic thermal insulation pipe shell were tested according to GB / T 5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products".

[0043] The thermal conductivity of inorganic thermal insulation pipe shells was tested according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method".

[0044] According to GBT10299-2011 "Test Method for Hydrophobicity of Thermal Insulation Materials", the hydrophobicity of inorganic thermal insulation pipe shells was tested.

[0045] After testing, the inorganic rigid thermal insulation shell prepared in this embodiment has a compressive strength of 13.2 MPa, a thermal conductivity (35℃) of 0.039 W / (m·K), a bulk density of 180 kg / m³, a water repellency of ≥99%, and a linear shrinkage of ≤0.8%.

[0046] Example 2 This embodiment provides a method for preparing an inorganic heat-insulating pipe shell with a gradient distribution of composite hollow glass microspheres. The main difference from Embodiment 1 is that in this embodiment: The raw materials, by weight, are: 200 parts cement, 30 parts water glass, 400 parts composite hollow glass microspheres, 80 parts aluminum silicate fiber, 100 parts aerogel, 1.0 part polycarboxylate superplasticizer, 1.0 part water-retaining agent, 5 parts adhesive powder, 2 parts water-repellent agent, 1 part dispersant, and 900 parts water. The inner layer material contains 50% composite hollow glass microspheres; the middle layer material contains 20% composite hollow glass microspheres; and the outer layer material contains 30% composite hollow glass microspheres. Aluminosilicate fibers are made by mixing 6mm long fibers and 9mm long fibers in a mass ratio of 6:4.

[0047] In the compaction step, the inner layer material is injected into the mold sequentially, and a pressure of 0.25 MPa is applied and held for 10 seconds. The middle layer material is injected and a pressure of 0.5 MPa is applied and held for 15 seconds. The outer layer material is injected and a pressure of 0.5 MPa is applied and held for 20 seconds to obtain an inorganic thermal insulation pipe shell blank.

[0048] This embodiment also provides an inorganic heat-insulating pipe shell prepared by the same method.

[0049] The compressive strength, flexural strength, density, and linear shrinkage rate of the inorganic thermal insulation pipe shell were tested according to GB / T 5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products".

[0050] The thermal conductivity of inorganic thermal insulation pipe shells was tested according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method".

[0051] According to GBT10299-2011 "Test Method for Hydrophobicity of Thermal Insulation Materials", the hydrophobicity of inorganic thermal insulation pipe shells was tested.

[0052] After testing, the inorganic rigid thermal insulation shell prepared in this embodiment has a compressive strength of 11.5 MPa, a thermal conductivity (35℃) of 0.038 W / (m·K), a bulk density of 195 kg / m³, a water repellency of ≥98%, and a linear shrinkage of ≤1.5%.

[0053] Example 3 This embodiment provides a method for preparing an inorganic heat-insulating pipe shell with a gradient distribution of composite hollow glass microspheres. The main difference from Embodiment 1 is that in this embodiment: The raw materials, by weight, are: 300 parts cement, 80 parts water glass, 500 parts composite hollow glass microspheres, 180 parts aluminum silicate fiber, 150 parts aerogel, 3 parts polycarboxylate superplasticizer, 1.5 parts water-retaining agent, 8 parts adhesive powder, 3.5 parts water-repellent agent, 1.5 parts dispersant, and 1250 parts water. The composite hollow glass microspheres in the inner layer material account for 35% of the total composite hollow glass microspheres; the composite hollow glass microspheres in the middle layer material account for 45% of the total composite hollow glass microspheres; and the composite hollow glass microspheres in the outer layer material account for 20% of the total composite hollow glass microspheres.

[0054] Aluminosilicate fibers are made by mixing 6mm long fibers and 9mm long fibers in a mass ratio of 3:7.

[0055] In the compaction step, the inner layer material is injected into the mold sequentially, and a pressure of 0.45 MPa is applied and held for 10 seconds. The middle layer material is injected and a pressure of 0.70 MPa is applied and held for 15 seconds. The outer layer material is injected and a pressure of 0.95 MPa is applied and held for 20 seconds to obtain an inorganic thermal insulation pipe shell blank.

[0056] This embodiment also provides an inorganic heat-insulating pipe shell prepared by the same method.

[0057] The compressive strength, flexural strength, density, and linear shrinkage rate of the inorganic thermal insulation pipe shell were tested according to GB / T 5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products".

[0058] The thermal conductivity of inorganic thermal insulation pipe shells was tested according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method".

[0059] According to GBT10299-2011 "Test Method for Hydrophobicity of Thermal Insulation Materials", the hydrophobicity of inorganic thermal insulation pipe shells was tested.

[0060] After testing, the inorganic rigid thermal insulation shell prepared in this embodiment has a compressive strength of 14.1 MPa, a thermal conductivity (35℃) of 0.043 W / (m·K), a bulk density of 205 kg / m³, a water repellency of ≥98%, and a linear shrinkage of ≤1.2%.

[0061] Comparative Example 1 The main difference between Comparative Example 1 and Example 1 is that HL60 type hollow glass microspheres with a single particle size are used, and in the compaction process, a single layer is compacted with a pressure of 0.6MPa for 20s.

[0062] The compressive strength, flexural strength, density, and linear shrinkage rate of the inorganic thermal insulation pipe shell prepared in Comparative Example 1 were tested according to GB / T 5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products".

[0063] The thermal conductivity of inorganic thermal insulation pipe shells was tested according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method".

[0064] According to GBT10299-2011 "Test Method for Hydrophobicity of Thermal Insulation Materials", the hydrophobicity of inorganic thermal insulation pipe shells was tested.

[0065] After testing, the inorganic rigid thermal insulation pipe shell prepared in Comparative Example 1 has a compressive strength of 14.4 MPa, a thermal conductivity (35℃) of 0.051 W / (m·K), a bulk density of 290 kg / m³, a water repellency of ≥98%, and a linear shrinkage of ≤2%.

[0066] Comparative Example 2 The main difference between this comparative example and Example 1 is that the composite hollow glass microspheres used are prepared by mixing HL15 type hollow glass microspheres and HL60 type hollow glass microspheres in a weight ratio of 4:6, and in the compaction process, a single-layer compaction is performed with a pressure of 0.6MPa for 20s.

[0067] The compressive strength, flexural strength, density, and linear shrinkage rate of the inorganic thermal insulation pipe shell prepared in Comparative Example 2 were tested according to GB / T 5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products".

[0068] The thermal conductivity of inorganic thermal insulation pipe shells was tested according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method".

[0069] According to GBT10299-2011 "Test Method for Hydrophobicity of Thermal Insulation Materials", the hydrophobicity of inorganic thermal insulation pipe shells was tested.

[0070] After testing, the inorganic rigid thermal insulation pipe shell prepared in Comparative Example 2 has a compressive strength of 11.2 MPa, a thermal conductivity (35℃) of 0.046 W / (m·K), a bulk density of 265 kg / m³, a water repellency of ≥98.5%, and a linear shrinkage of ≤1.8%.

[0071] Comparative Example 3 The main difference between this comparative example and Example 1 is that the composite hollow glass microspheres used are prepared by mixing HL15 type hollow glass microspheres and HL60 type hollow glass microspheres in a weight ratio of 4:6.

[0072] The inner layer material contains 45% of the total composite hollow glass microspheres; the outer layer material contains 55% of the total composite hollow glass microspheres. In the compaction process, the inner layer is subjected to a pressure of 0.3 MPa for 10 seconds, and the outer layer is subjected to a pressure of 0.8 MPa for 20 seconds.

[0073] The compressive strength, flexural strength, density, and linear shrinkage rate of the inorganic thermal insulation shell prepared in Comparative Example 3 were tested according to GB / T 5486-2008 "Test Methods for Inorganic Rigid Thermal Insulation Products".

[0074] The thermal conductivity of inorganic thermal insulation pipe shells was tested according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method".

[0075] According to GBT10299-2011 "Test Method for Hydrophobicity of Thermal Insulation Materials", the hydrophobicity of inorganic thermal insulation pipe shells was tested.

[0076] After testing, the inorganic rigid thermal insulation pipe shell prepared in Comparative Example 3 has a compressive strength of 12.4 MPa, a thermal conductivity (35℃) of 0.043 W / (m·K), a bulk density of 215 kg / m³, a water repellency of ≥98.8%, and a linear shrinkage of ≤1.4%.

[0077] In summary, this invention optimizes performance from component function and synergistic mechanism to microstructure through a scientifically sound and rationally proportioned composite microspheres, a gradient dosing design, and synergistic process (layered compaction + segmented curing). By employing a gradient design prioritizing inner layer insulation, outer layer strength, and intermediate layer transition buffer, it satisfies the high insulation requirements of the inner layer while achieving "dense load-bearing capacity" through low microsphere dosing in the outer layer and high-pressure compaction. This achieves synergistic performance of the overall structure, solving the problem of simultaneously achieving insulation and mechanical properties with a single microsphere. Ultimately, this invention achieves comprehensive advantages for inorganic insulation pipe shells, including compressive strength ≥13.2MPa, thermal conductivity (35℃) ≤0.039W / (m·K), bulk density ≤180kg / m³, hydrophobicity ≥99%, and linear shrinkage ≤0.8%. This achieves the goal of improving the hydrophobicity and compressive strength of inorganic thermal insulation pipe shells, and reducing linear shrinkage and thermal conductivity without modifying the hollow glass microspheres, thereby simultaneously improving the thermal insulation and mechanical properties of inorganic thermal insulation pipe shells.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for preparing an inorganic thermal insulation pipe shell with a gradient distribution of composite hollow glass microspheres, comprising the following steps: preparing composite hollow glass microspheres: mixing first, second and third hollow glass microspheres according to a weight ratio of 4: (2-6) : (2-6) to obtain the composite hollow glass microspheres; preparing raw materials: dividing the base material into three equal parts, mixing 35%-50% of the composite hollow glass microspheres with one part of the base material to prepare an inner layer material, mixing 20%-45% of the composite hollow glass microspheres with one part of the base material to prepare a middle layer material, and mixing 20%-30% of the composite hollow glass microspheres with one part of the base material to prepare an outer layer material; wherein the base material comprises cement, water glass, aluminum silicate fiber, aerogel, water reducing agent, water retaining agent, glue powder, water repellent agent, dispersant and water; compacting: sequentially injecting the inner layer material into a mold, applying a pressure of 0.25-0.5 MPa for 10-20 s, injecting the middle layer material, applying a pressure of 0.5-0.75 MPa for 10-20 s, and injecting the outer layer material, applying a pressure of 0.5-1.0 MPa for 10-20 s to obtain an inorganic thermal insulation pipe shell body; curing: curing the inorganic thermal insulation pipe shell body at 20-35 ℃ and 80% humidity for 20-24 h, and then at 50-75 ℃ and 95% humidity for 45-50 h; wherein the first hollow glass microspheres have a true density of 0.13-0.17 g / cm3, a bulk density of 0.08-0.09 g / cm3, a compressive strength of 500 Psi, a D50 of 80 μm and a D90 of 120 μm in the particle size distribution; the second hollow glass microspheres have a true density of 0.36-0.40 g / cm3, a bulk density of 0.19-0.22 g / cm3, a compressive strength of 5500 Psi, a D50 of 40 μm and a D90 of 65 μm in the particle size distribution; the third hollow glass microspheres have a true density of 0.58-0.62 g / cm3, a bulk density of 0.29-0.34 g / cm3, a compressive strength of 12000 Psi, a D50 of 40 μm and a D90 of 65 μm in the particle size distribution.

2. The method of claim 1, wherein the method further comprises: mixing the hollow glass microspheres with the inorganic binder to form a mixture; and extruding the mixture to form the inorganic thermal insulation pipe shell. by weight, the base material comprises cement 200-300 parts, water glass 30-80 parts, composite hollow glass microspheres 400-500 parts, aluminum silicate fiber 80-180 parts, aerogel 100-150 parts, polycarboxylic acid superplasticizer 1-3 parts, water retaining agent 1.0-1.5 parts, glue powder 5-8 parts, water repellent agent 2-3.5 parts, dispersant 1-1.5 parts, and water 900-1250 parts.

3. The method of claim 1 or 2, wherein the method is characterized by: in the compacting step, the inorganic thermal insulation pipe shell body has an inner layer thickness of 1-2 cm, a middle layer thickness of 1-2 cm, and an outer layer thickness of 2-3 cm.

4. The method of claim 1, wherein the method further comprises: adding a binder to the mixture of hollow glass microspheres and inorganic material. In the preparation of the inner layer material, the middle layer material and the outer layer material, the cement, the aerogel and the composite hollow glass microspheres of corresponding specifications are first dry mixed for 1-2 minutes; Then the aluminum silicate fiber, the water retaining agent, the glue powder and the water repellent agent are added and dry mixed for 1-2 minutes; finally, water, the water reducing agent, the dispersing agent and the water glass are added and stirred for 1-2 minutes.

5. The method of claim 1 or 2 or 3 or 4, wherein the method is characterized by: The aluminum silicate fiber includes aluminum silicate fiber with a length of 6mm and aluminum silicate fiber with a length of 9mm; the water reducing agent is polycarboxylic acid water reducing agent; the aerogel is silicon aerogel; the water repellent agent is organosilicon; the dispersing agent is amino sulfonate dispersing agent; the water retaining agent is HPK400; and the glue powder is VAE high molecular polymer glue powder.

6. A composite inorganic thermal insulating pipe shell with a gradient distribution of hollow glass microspheres, characterized in that: The inorganic thermal insulation pipe shell is prepared by the preparation method of any one of claims 1-5.