Inorganic thermal insulation pipe shell based on gradient distribution of hollow glass beads and preparation method of inorganic thermal insulation pipe shell

Abstract

The invention provides an inorganic thermal insulation pipe shell based on gradient distribution of hollow glass beads and a preparation method thereof.The preparation method comprises the steps that a base material is averagely divided into three parts, one part of the base material is mixed with the first type of modified hollow glass beads, and an inner layer material is prepared; mixing the first type of modified hollow glass beads and the second type of modified hollow glass beads with a second part of base material to prepare a middle layer material; mixing a third part of the base material with a second type of modified hollow glass beads to prepare an outer layer material; 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. The method can improve the integrity of the internal structure of the inorganic thermal insulation pipe shell, improve the compressive strength, reduce the heat conductivity coefficient and reduce the heat dissipation temperature difference fluctuation.

Description

TECHNICAL FIELD

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

[0002] Common insulation pipe shells, such as composite silicate insulation pipe shells, rock wool pipe shells, aluminum silicate insulation pipe shells, calcium silicate pipe shells, etc., also have many problems. On the one hand, their thermal conductivity is generally high, and the insulation effect needs to be improved. Moreover, their compressive strength is low, and they are easily compressed and deformed or worn out under the influence of gravity, thermal expansion and cold contraction during installation or operation, resulting in uneven insulation layer thickness, increased thermal bridges, and poor insulation effect. On the other hand, these insulation pipe shells are prone to produce dust during production and construction, which is very harmful to the health of construction workers. At the same time, their insulation performance will decay over time, greatly reducing the insulation effect and seriously affecting the service life, increasing the cost of later maintenance and replacement.

[0003] In order to reduce the thermal conductivity, hollow glass microspheres and vitrified microspheres are currently used to prepare insulation pipe shells. For example, the patent for invention 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 includes 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 mass ratio of 100 parts, including fly ash 30 to 35 parts, coal gangue 15 to 20 parts, hollow glass microspheres 15 parts, vitrified microspheres 15 parts, glass fiber 10 to 15 parts, aerogel powder 15 parts, and wood ash 7 parts. The liquid phase composition is calculated by weight ratio of 100 parts, including water glass 35 parts, hydrogen peroxide 15 parts and water 50 parts. The preparation method includes first mixing wood ash and water glass with water, adding fly ash and calcined and crushed coal gangue, and putting pre-dispersed glass fiber into the stirring mill together 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 hollow glass microspheres with unmodified surface, and the interface between the hollow glass microspheres and the geopolymer matrix, i.e. the fly ash-coal gangue-water glass system, relies on physical embedding, lacks chemical bonding design, and weak interface bonding will form stress concentration points, resulting in reduced interface strength and formation of organizational defects, which reduces the overall strength of the pipe material and affects the stability of the thermal conductivity under long-term thermal cycling. Summary of the Invention

[0005] To improve the bonding force between hollow glass microspheres and other materials, increase the compressive strength of the inorganic thermal insulation pipe shell prepared from them, reduce the thermal conductivity, and reduce heat dissipation temperature fluctuations, the technical solution adopted in this invention is: a method for preparing an inorganic thermal insulation pipe shell based on the gradient distribution of hollow glass microspheres, comprising the following steps: In the raw material preparation process, the matrix material is divided into three equal parts. One part of the matrix material is mixed separately with the first type of modified hollow glass microspheres to prepare the inner layer material. The first type of modified hollow glass microspheres and the second type of modified hollow glass microspheres are mixed together with the second part of the matrix material to prepare the middle layer material. The third part of the matrix material is mixed separately with the second type of modified hollow glass microspheres to prepare the outer layer material. The matrix materials include cement, nano-silica gel, basalt fiber, hard silica calcium stone powder, water-reducing agent, water-retaining agent, reinforcing agent, retarder, 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 8s to 15s; after the middle layer material is injected, a pressure of 0.5MPa to 0.75MPa is applied and held for 8s to 15s; after the outer layer material is injected, a pressure of 0.5MPa to 1.0MPa is applied and held for 8s to 15s to obtain an inorganic thermal insulation pipe shell blank. The inorganic insulation pipe shell blank is first cured at 20℃~29℃ and 90% humidity for 10h~14h, and then cured at 65℃~75℃ and 95% humidity for 45h~55h. The first type of modified 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.

[0006] The second type of modified hollow glass microspheres have 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.

[0007] Beneficial effects: It can comprehensively improve compressive strength, reduce bulk density and reduce thermal conductivity.

[0008] Based on the above, both the first type of modified hollow glass microspheres and the second type of modified hollow glass microspheres are obtained by treating the hollow glass microsphere raw materials with silane coupling agents and nano-calcium carbonate.

[0009] Beneficial effect: can increase the hollow glass beads and the matrix interface bonding force.

[0010] Based on the above, in the middle layer material, the mass ratio of the first type of modified hollow glass beads to the second type of modified hollow glass beads is (1.5-3):1.

[0011] Beneficial effect: can continue the heat preservation effect of the inner layer, and can also improve the strength of the intermediate layer through the skeleton support of the modified HL60 type hollow glass beads, and provide transitional support for the overall strength of the inorganic thermal pipe shell.

[0012] Based on the above, by weight, including cement 150-300 parts, nano-silica gel 50-100 parts, basalt fiber 100-150 parts, xonotlite powder 100-200 parts, water reducing agent 1.5-3 parts, water retaining agent 0.5-1.0 parts, reinforcing agent 5-6 parts, retarder 0.5-1.0 parts, water 1000-1300 parts, modified hollow glass beads total amount 500-600 parts; Among them, the total amount of modified hollow glass beads refers to the sum of the total amount of all first type of modified hollow glass beads and all second type of modified hollow glass beads.

[0013] Specifically, in the inner layer material, the first type of modified hollow glass beads accounts for 40%-50% of the total amount of modified hollow glass beads, and in the outer layer material, the second type of hollow glass beads accounts for 20%-30% of the total amount of modified hollow glass beads.

[0014] Beneficial effect: by optimizing the weight of each raw material, further ensure the compressive strength of the product, reduce the bulk density and reduce the thermal conductivity.

[0015] Based on the above, in the compaction step, the inner layer thickness of the inorganic thermal pipe shell body is 1cm-2cm, the middle layer thickness is 1cm-2cm, and the outer layer thickness is 1cm-2cm.

[0016] Based on the above, when preparing the inner layer material, the middle layer material and the outer layer material, first dry mix the cement, the xonotlite powder and the corresponding specification of hollow glass beads for 1-2 minutes; Then add the basalt fiber, the water retaining agent, the retarder, the reinforcing agent and dry mix for 1-2 minutes; finally add water, the water reducing agent, the nano-silica gel and stir for 1-2 minutes.

[0017] Beneficial effect: by optimizing the steps, to ensure the performance of each layer material.

[0018] Based on the above, the basalt fiber includes basalt fiber with a length of 3mm and basalt fiber with a length of 6mm.

[0019] Based on the above, the water reducing agent is a polycarboxylic acid water reducing agent; the retarder is compounded by tartaric acid, citric acid and sodium citrate, and the mass ratio of tartaric acid, citric acid and sodium citrate is 4:3:3; the water retaining agent is HPK400; and the reinforcing agent is an aluminate reinforcing agent.

[0020] Beneficial effects: by optimizing the type and mass ratio of each reagent, the performance of the product in the preparation process is ensured.

[0021] The application also provides an inorganic thermal insulation pipe shell based on hollow glass microsphere gradient distribution, which is prepared by the above preparation method.

[0022] In the application, the first type of modified hollow glass microsphere is referred to as modified HL15 type hollow glass microsphere, and the second type of modified hollow glass microsphere is referred to as modified HL60 type hollow glass microsphere.

[0023] Specifically, in the preparation method of the inorganic thermal insulation pipe shell based on hollow glass microsphere gradient distribution provided by the application, the functions and reaction processes of each component are as follows: The modified HL15 type hollow glass microsphere located in the inner layer has a true density of ≤0.15 g / cm³ and a thermal conductivity of ≤0.028 W / (m·K), and can directly block heat transfer, which is a core factor for realizing that the thermal conductivity of the inorganic thermal insulation pipe shell is 0.038 W / (m·K) at 35℃. The closed pore structure of the modified HL15 type hollow glass microsphere can reduce air convection heat transfer, and cooperate with the low-pressure compaction to retain porosity, so as to form an efficient thermal insulation barrier. The composite microsphere located in the middle layer is mixed by the modified HL15 type hollow glass microsphere and the modified HL60 type hollow glass microsphere, and has a density between the inner layer and the outer layer, which can not only continue the thermal insulation effect of the inner layer, but also improve the strength of the middle layer through the skeleton support of the modified HL60 type hollow glass microsphere, and provide transition support for the overall strength of the inorganic thermal insulation pipe shell. The modified HL60 type hollow glass microsphere located in the outer layer has a true density of ≥0.6 g / cm³, has high true density and high strength characteristics, cooperates with the high-pressure compaction process of the outer layer to form a dense outer layer structure, and can further improve the overall strength of the inorganic thermal insulation pipe shell.

[0024] Specifically, the cement is 725 high-alumina cement. The 725 high-alumina cement as the main cementitious material can generate crystals such as aluminate tri-calcium hexahydrate through hydration to form a rigid skeleton structure, provide basic strength for the inorganic thermal insulation pipe shell, and the compatibility of the hydration product with other components ensures the overall structural stability.

[0025] Nano-silica gel: its size effect can fill the gap between cement hydration products, react with Ca(OH)2 to generate more hydrated calcium silicate (C-S-H) gel, and improve the density of the matrix. At the same time, it forms a SiO2-rich transition layer at the interlayer interface, enhances the interlayer adhesion, and reduces the heat and stress transmission loss.

[0026] Xonotlite powder: the hydrolysis released Ca²⁺ and SiO3²⁻ ions promote the hydration reaction, and its acicular crystal structure is inserted into the matrix, which improves the toughness of the material and reduces the micro-cracks caused by temperature changes, which plays an important role in stabilizing the heat difference.

[0027] The reinforcing agent stimulates the activity of the hydration product and promotes the growth of tricalcium aluminate hexahydrate crystals. The retarder controls the hydration rate of each layer to be consistent, avoiding internal stress caused by different reaction rates and ensuring the uniformity of the density. The water reducing agent improves the fluidity of the slurry to ensure uniform pouring of each layer of material; the water retaining agent maintains the moisture required for hydration, reduces structural defects caused by moisture loss, and ensures stable development of strength.

[0028] Therefore, the present application has outstanding substantial characteristics and significant progress compared with the prior art. Specifically, the preparation method of the inorganic thermal insulation pipe shell based on the gradient distribution of hollow glass microbeads provided by the present application has the following advantages: (1) Breaks through the limitations of traditional inorganic thermal insulation pipe shell "high strength must be high conductivity, low conductivity must be low strength", "high strength must be super heavy", and realizes the comprehensive advantages of compressive strength ≥13.5MPa, thermal conductivity ≤0.038W / (m·K) at 35℃ environment, and bulk density ≤180kg / m³.

[0029] (2) Through the gradient design of particle size in the middle layer and the lamination fusion process, the heat dissipation temperature difference fluctuation of the outer surface of the pipe shell is ≤5℃ under the working condition of 150℃, thereby improving the thermal uniformity of the pipe shell and avoiding the risk of local overheating.

[0030] (3) Using gradient compaction process, i.e. designing different pressures when forming the inner layer, middle layer and outer layer, can greatly reduce the breakage rate of microbeads. At the same time, combining with the segmented curing process to strengthen the interlayer bonding, the compressive strength can be significantly improved compared with the traditional process.

[0031] (4) The layered and thickness of the inorganic thermal insulation pipe shell can be flexibly designed according to the pipe diameter, actual working condition and temperature requirement of the inorganic thermal insulation pipe shell, which greatly improves the applicability of the inorganic thermal insulation pipe shell. DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be further described in detail through specific embodiments.

[0033] Example 1 The embodiment provides a preparation method of an inorganic thermal insulation pipe shell based on hollow glass microsphere gradient distribution, and specific steps include the following. Raw material preparation: the base material is evenly divided into three parts, one part of the base material is mixed with the first type of modified hollow glass microsphere to prepare an inner layer material; the first type of modified hollow glass microsphere and the second type of modified hollow glass microsphere are mixed with the second part of the base material to prepare a middle layer material; the third part of the base material is mixed with the second type of modified hollow glass microsphere to prepare an outer layer material.

[0034] The base material includes cement, nanosilica gel, basalt fiber, xonotlite powder, water reducing agent, water retaining agent, reinforcing agent, retarder and water.

[0035] Compaction: the inner layer material is injected into the mold, 0.25 MPa pressure is applied for 10 s, the middle layer material is injected, 0.5 MPa pressure is applied for 20 s, and the outer layer material is injected, 0.5 MPa pressure is applied for 10 s, to obtain an inorganic thermal insulation pipe shell body.

[0036] Curing: the inorganic thermal insulation pipe shell body is cured in turn under the conditions of 25 DEG C and 90% humidity for 12 h and under the conditions of 70 DEG C and 95% humidity for 48 h.

[0037] Specifically, in the preparation of the inner layer material, the middle layer material and the outer layer material, the cement, the xonotlite powder and the corresponding hollow glass microspheres are dry mixed for 2 min; then the basalt fiber, the water retaining agent, the retarder and the reinforcing agent are dry mixed for 1 min; finally, water, the water reducing agent and the nanosilica gel are stirred for 2 min.

[0038] In the embodiment, the first type of modified hollow glass microsphere is denoted as modified HL15 type hollow glass microsphere, and the second type of modified hollow glass microsphere is denoted as modified HL60 type hollow glass microsphere.

[0039] The modified HL15 type hollow glass microsphere is obtained by treating HL15 type hollow glass microspheres with silane coupling agent and nanometer calcium carbonate, and the mass ratio of the silane coupling agent KH-550 to the nanometer calcium carbonate is 1:1. The modified HL60 type hollow glass microsphere is obtained by treating HL60 type hollow glass microspheres with silane coupling agent and nanometer calcium carbonate, and the mass ratio of the silane coupling agent KH-550 to the nanometer calcium carbonate is 1:1.

[0040] Specifically, the cement is selected as high-grade 725 high-alumina cement. The silane coupling agent is selected as KH-550. The nano-silica gel is selected as VK-SP50. The retarder is compounded by tartaric acid, citric acid and sodium citrate, and the mass ratio of the three is 4:3:3. The polycarboxylic acid superplasticizer is selected as PCE-101, the water retaining agent is selected as HPK400, and the reinforcing agent is selected as aluminate reinforcing agent.

[0041] More specifically, in the embodiment, the total amount of modified hollow glass beads is 500 parts by weight, and the total matrix material is composed of high-grade 725 high-alumina cement 150 parts, nano-silica gel 50 parts, basalt fiber 100 parts, xonotlite powder 100 parts, polycarboxylic acid superplasticizer 1.5 parts, water retaining agent 0.5 parts, reinforcing agent 0.5 parts, retarder 0.5 parts and water 1000 parts.

[0042] In the embodiment, the basalt fiber is composed of fibers with a length of 3 mm and fibers with a length of 6 mm mixed in a mass ratio of 5:5. The total amount of modified hollow glass beads is the sum of the mass of modified HL60 type hollow glass beads and all modified HL15 type hollow glass beads.

[0043] And in the inner layer material, the modified HL15 type hollow glass beads account for 40% of the total amount of modified hollow glass beads. In the outer layer material, the modified HL60 type hollow glass beads account for 20% of the total amount of modified hollow glass beads. In the middle layer material, the mass ratio of the modified HL15 type hollow glass beads to the modified HL60 type hollow glass beads is 2:1.

[0044] Specifically, in the compaction step, the specific operation is as follows: (1) Physical isolation: The mold is composed of an inner layer mold, a middle layer mold and an outer layer mold, and the molds are isolated by a pre-laid nano-silica isolation film, which can be fused with the pipe shell after curing. A 5mm to 8mm thick elastic isolation component, such as a silicone seal ring, is arranged between the layers to separate them. The elastic deformation can buffer the pressure transmission, and a release agent is sprayed on the inner wall of the mold to ensure that the layers are easily separated and the surface is complete after compaction.

[0045] (2) Layered pressure application: Inner layer low-pressure compaction: After the inner layer material is uniformly mixed, it is spread into the inner layer mold cavity, and then the inner layer compaction is started. The pressure is slowly increased to the target pressure at a rate of 0.1 MPa / min, and the pressure is maintained for 10s. During this process, the pressure change is monitored in real time by the pressure sensor of the equipment to ensure that the pressure is stable within the set range, and the porosity of the inner layer matrix is maintained to ensure the heat preservation performance. After the pressure maintaining is completed, the pressure is slowly released to 0, and the inner layer compaction is completed, providing a foundation for the subsequent middle layer pressure application.

[0046] Middle layer middle pressure compaction: when the middle layer material is uniformly mixed, the middle layer is compacted after being spread into the middle layer cavity of the mold; slowly pressurize at a rate of 0.15 MPa / min to the target pressure, and keep pressure for 20 s. At this time, the elastic isolation component will be slightly deformed due to the pressure, and the deformation amount is ≤2 mm, which can absorb part of the pressure energy and reduce the pressure transmission to the inner layer. After the pressure keeping is completed, the pressure is released at a rate of 0.08 MPa / min, so that the intermediate layer forms a certain toughness buffer transition layer, further blocking the influence of the subsequent outer layer high pressure.

[0047] Outer layer high pressure compaction: when the outer layer material is uniformly mixed, the outer layer is compacted after being spread into the outer layer cavity of the mold. Slowly pressurize at a rate of 0.2 MPa / min to the target pressure, and keep pressure for 10 s. After the pressure keeping is completed, slowly release the pressure at a rate of 0.1 MPa / min, and complete the outer layer compaction.

[0048] In the embodiment, the inner layer thickness of the inorganic thermal insulation pipe shell blank is 2 cm, the middle layer thickness is 2 cm, and the outer layer thickness is 2 cm.

[0049] The embodiment also provides an inorganic thermal insulation pipe shell prepared by the preparation method.

[0050] According to GB / T 5486-2008 “Test methods for inorganic rigid thermal insulation products”, the compressive strength, bending strength and bulk density of the inorganic thermal insulation pipe shell are detected.

[0051] According to GB / T 10294-2008 “Determination of steady-state thermal resistance and related properties of thermal insulation materials by guarded hot plate method”, the thermal conductivity of the inorganic thermal insulation pipe shell is detected.

[0052] According to GB / T 8174-2008 “Test and evaluation of thermal insulation effect of equipment and pipelines”, the heat dissipation temperature difference of the inorganic thermal insulation pipe shell is detected.

[0053] After detection, the compressive strength of the inorganic rigid thermal insulation pipe shell prepared in the embodiment is 12.8 MPa, the thermal conductivity (35℃) is 0.040 W / (m·K), the bulk density is 215 kg / m³, and the heat dissipation temperature difference under the condition of 150℃ is 10℃.

[0054] Embodiment 2 The embodiment provides a preparation method of an inorganic thermal insulation pipe shell based on hollow glass microsphere gradient distribution, and the main difference from the embodiment 1 is that in the embodiment: The raw materials include 225 parts of high-grade 725 high-alumina cement, 80 parts of nano-silicon dioxide gel, 130 parts of basalt fiber, 140 parts of xonotlite powder, 2 parts of polycarboxylic acid superplasticizer, 0.8 parts of water retaining agent, 6 parts of reinforcing agent, 0.5 parts of retarder, 1150 parts of water, and 560 parts of total amount of modified hollow glass microbeads.

[0055] In the inner layer material, the modified HL15 type hollow glass microbeads account for 44% of the total amount of modified hollow glass microbeads. In the outer layer material, the modified HL60 type hollow glass microbeads account for 26% of the total amount of modified hollow glass microbeads. In the middle layer material, the mass ratio of the modified HL15 type hollow glass microbeads to the modified HL60 type hollow glass microbeads is 3:2.

[0056] The basalt fiber is mixed by 6:4 of 3mm long fiber and 6mm long fiber by mass ratio.

[0057] In the compaction step, the inner layer material is injected into the mold, then 0.35MPa pressure is applied for 10s, the middle layer material is injected, then 0.65MPa pressure is applied for 20s, and the outer layer material is injected, then 0.85MPa pressure is applied for 10s, to obtain the inorganic thermal insulation pipe shell blank.

[0058] The embodiment also provides an inorganic thermal insulation pipe shell prepared by the preparation method.

[0059] In the embodiment, the compressive strength, the bending strength and the bulk density of the inorganic thermal insulation pipe shell are detected according to GB / T 5486-2008 "Test Methods for Inorganic Hard Insulation Products".

[0060] The thermal conductivity of the inorganic thermal insulation pipe shell is detected according to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials by Guarded Hot Plate Method".

[0061] The heat dissipation temperature difference of the inorganic thermal insulation pipe shell is detected according to GB / T 8174-2008 "Test and Evaluation of Insulation Effect of Equipment and Pipes".

[0062] After detection, the compressive strength of the inorganic hard thermal insulation pipe shell prepared in the embodiment is 13.5MPa, the thermal conductivity (35℃) is 0.038W / (m·K), the bulk density is 180kg / m³, and the heat dissipation temperature difference under 150℃ working condition is 5℃.

[0063] Embodiment 3 The embodiment provides a preparation method of inorganic thermal insulation pipe shell based on gradient distribution of hollow glass microbeads, and the main difference from the embodiment 1 is that in the embodiment: The raw materials include 300 parts of high-grade 725 high-alumina cement, 100 parts of nano-silicon dioxide gel, 600 parts of total amount of modified hollow glass microbeads, 150 parts of basalt fiber (length 3 mm and length 6 mm, mass ratio 7:3), 200 parts of xonotlite powder, 3 parts of polycarboxylic acid high-efficiency water reducing agent, 1 part of water retaining agent, 6 parts of reinforcing agent, 1 part of retarder, and 1300 parts of water.

[0064] The basalt fiber is mixed by 3 mm long fiber and 6 mm long fiber at a mass ratio of 7:3.

[0065] In the inner layer material, the modified HL15 type hollow glass microbead accounts for 50% of the total amount of the modified hollow glass microbead, and in the outer layer material, the modified HL60 type hollow glass microbead accounts for 30% of the total amount of the modified hollow glass microbead. In the middle layer material, the mass ratio of the modified HL15 type hollow glass microbead to the modified HL60 type hollow glass microbead is 3:1.

[0066] In the compaction step, 0.5 MPa pressure is applied for 10 s after the inner layer material is injected into the mold, 0.75 MPa pressure is applied for 20 s after the middle layer material is injected, and 1.0 MPa pressure is applied for 10 s after the outer layer material is injected, to obtain the inorganic thermal insulation pipe shell blank.

[0067] The embodiment also provides an inorganic thermal insulation pipe shell prepared by the preparation method.

[0068] In the embodiment, the compressive strength, the bending strength and the bulk density of the inorganic thermal insulation pipe shell are detected according to GB / T 5486-2008 “Test Methods for Inorganic Hard Thermal Insulation Products”.

[0069] The thermal conductivity of the inorganic thermal insulation pipe shell is detected according to GB / T 10294-2008 “Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials by Guarded Hot Plate Method”.

[0070] The heat dissipation temperature difference of the inorganic thermal insulation pipe shell is detected according to GB / T 8174-2008 “Test and Evaluation of Thermal Insulation Effect of Equipment and Pipes”.

[0071] After detection, the compressive strength of the inorganic hard thermal insulation pipe shell prepared in the embodiment is 14.2 MPa, the thermal conductivity (35℃) is 0.042 W / (m·K), the bulk density is 252 kg / m³, and the heat dissipation temperature difference under the condition of 150℃ is 15℃.

[0072] Comparative Example 1 The main difference between the comparative example 1 and the embodiment 2 is that the single particle size of the modified HL60 type hollow glass microbead is used, and in the compaction process, the single layer compaction with 0.65 MPa pressure for 20 s is used.

[0073] The compressive strength and the bending strength and the bulk density of the inorganic thermal insulation pipe shell prepared from the Comparative Example 1 were detected according to GB / T 5486-2008 "Test methods for inorganic rigid thermal insulating products".

[0074] The thermal conductivity of the inorganic thermal insulation pipe shell was detected according to GB / T 10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulations - Guarded hot plate method".

[0075] The heat dissipation temperature difference of the inorganic thermal insulation pipe shell was detected according to GB / T 8174-2008 "Test and evaluation of thermal insulation effect of equipment and piping".

[0076] After detection, the compressive strength of the inorganic rigid thermal insulation pipe shell prepared from the Comparative Example 1 was 14.2 MPa, the thermal conductivity (35℃) was 0.058 W / (m·K), the bulk density was 325 kg / m³, and the heat dissipation temperature difference under 150℃ working condition was 16℃.

[0077] Comparative Example 2 The main difference between the Comparative Example 2 and the Example 2 was that the modified HL60 type hollow glass microbeads and the modified HL15 type hollow glass microbeads were used, and in the compaction process, the single layer compaction was used with 0.65 MPa pressure for 20 s.

[0078] The compressive strength and the bending strength and the bulk density of the inorganic thermal insulation pipe shell prepared from the Comparative Example 2 were detected according to GB / T 5486-2008 "Test methods for inorganic rigid thermal insulating products".

[0079] The thermal conductivity of the inorganic thermal insulation pipe shell was detected according to GB / T 10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulations - Guarded hot plate method".

[0080] The heat dissipation temperature difference of the inorganic thermal insulation pipe shell was detected according to GB / T 8174-2008 "Test and evaluation of thermal insulation effect of equipment and piping".

[0081] After detection, the compressive strength of the inorganic rigid thermal insulation pipe shell prepared from the Comparative Example 2 was 10.4 MPa, the thermal conductivity (35℃) was 0.046 W / (m·K), the bulk density was 285 kg / m³, and the heat dissipation temperature difference under 150℃ working condition was 13℃.

[0082] Comparative Example 3 The main difference between the Comparative Example 3 and the Example 2 was that the modified HL15 type hollow glass microbeads were added in the inner layer, accounting for 44% of the total amount of microbeads; the modified HL60 type hollow glass microbeads were added in the outer layer, accounting for 56% of the total amount of microbeads. And in the compaction process, 0.35 MPa pressure was applied to the inner layer for 10 s, and 0.85 MPa pressure was applied to the outer layer for 10 s.

[0083] The compressive strength and the bending strength and the bulk density of the inorganic thermal insulation pipe shell prepared from the Comparative Example 3 were detected according to GB / T 5486-2008 “Test methods for inorganic rigid thermal insulating products”.

[0084] The thermal conductivity of the inorganic thermal insulation pipe shell was detected according to GB / T 10294-2008 “Determination of steady-state thermal resistance and related properties of thermal insulations by guarded hot plate method”.

[0085] The heat dissipation temperature difference of the inorganic thermal insulation pipe shell was detected according to GB / T 8174-2008 “Test and evaluation of thermal insulation effect of equipment and piping”.

[0086] Through detection, the compressive strength of the inorganic rigid thermal insulation pipe shell prepared from the Comparative Example 3 was 13.0 MPa, the thermal conductivity (35℃) was 0.042 W / (m·K), the bulk density was 210 kg / m³, and the heat dissipation temperature difference under the working condition of 150℃ was 10.5℃.

[0087] It can be seen that only when the three-layer gradient microbead distribution (inner thermal resistance / middle transition / outer bearing force) and the three-layer differential compaction process are met at the same time, can the ultra-low thermal conductivity, high strength, light weight and thermal uniformity be achieved.

[0088] Through analysis, it can be known that the above materials realize performance synergy through the gradient design of “inner layer insulation priority, outer layer strength priority, and intermediate layer transition buffer”.

[0089] Specifically, the low thermal conductivity of the inner layer modified HL15 type microbead and the high strength of the outer layer modified HL60 type microbead are smoothly connected through the intermediate layer composite microbead, avoiding performance mutation. While ensuring the strength, the proportion of the cementitious system and the microbead reduces the overall density through a large number of microbeads, realizing the unity of light weight and high performance.

[0090] And the calcium aluminate hydrate (CAH 10 ), the C3AH6 crystal generated by the hydration of high-alumina cement, and the hydrated calcium silicate (C-S-H) gel generated by the nano-silicon dioxide gel form a complementary structure. The crystal provides rigid support, and the gel fills the pores. The ions released by the xonotlite powder accelerate the generation of the gel, and the fibers enhance the adhesion of the gel-crystal interface, forming a “crystal-gel-fiber” three-dimensional reinforced network, which significantly improves the strength.

[0091] More importantly, in the preparation process of the inorganic thermal insulation pipe shell, the gradient compaction process is adopted, the inner layer pressure is 0.25-0.5 MPa, the intermediate layer pressure is 0.5-0.75 MPa, and the outer layer pressure is 0.5-1.0 MPa. The material components are matched, the high porosity required for the low pressure adaptation of the inner layer insulation is realized, the medium pressure meets the transition requirement of the intermediate layer, and the high pressure guarantees the density of the outer layer. At the same time, combined with the staged curing, the interlayer fusion and strength construction are promoted in turn, so that the hydration products are uniformly distributed in the gradient structure, and the performance loss is reduced.

[0092] And in the preliminary curing stage, the following processes will occur: first, the interlayer transition zone is initially formed. The pores reserved by the inner layer under the low pressure of 0.25-0.5 MPa become the channels for water and ion migration, and under the capillary action, the water carries the hydration product particles to penetrate into the intermediate layer. In the early curing stage, the free water in the material gradually changes into bound water, and the water in the inner layer pores continuously migrates outward, driving the calcium silicate hydrate (C-S-H) gel to deposit on the pore wall. At the same time, the relatively dense structure formed by the intermediate layer under the medium pressure of 0.5-0.75 MPa forms a gradient connection with the inner layer pores, avoiding stress concentration caused by sudden change of pores.

[0093] Subsequently, early bonding of the fiber-matrix interface will occur. That is, the basalt fiber surface is wrapped by cement hydration products to form an interfacial transition layer, and the hydroxyl groups (-OH) on the fiber surface form hydrogen bonds with the oxygen atoms in the calcium silicate hydrate (C-S-H) gel, so that the bonding strength of the fiber and the matrix is improved.

[0094] And in the second stage curing, i.e. 50-75℃, curing for 48-72h, the following processes will occur: First, the transformation and stabilization of hydration products: under the high temperature environment of 50-75℃, the crystals generated in the first stage are unstable and gradually change into more stable aluminum hydroxide (C3AH6) and AH3 gel, which has excellent chemical stability and becomes the core framework supporting the strength of the pipe shell.

[0095] Then the deepening of nano-silica gel reaction: high temperature accelerates the pozzolanic reaction of nano-silica gel, and fully reacts with the remaining Ca(OH)2 to generate more and more dense type B calcium silicate hydrate (C-S-H) gel. This gel fills the small pores in the interlayer transition zone, improving the interlayer bonding strength.

[0096] Activation of the contained reinforcing agent: the solubility of the reinforcing agent increases at high temperature, and the released aluminum ions (Al 3+ ) combine with silicate ions in the calcium silicate hydrate (C-S-H) gel to form calcium alumino-silicate gel, which forms a reinforcing layer on the fiber surface and the microsphere interface, further improving the overall strength of the material.

[0097] Meanwhile, in the second stage curing stage, 50-75°C will promote the continuous growth of tricalcium aluminate hexahydrate (C3AH6) crystals and calcium silicate hydrate (C-S-H) gel, the number of "crystal bridges" across the layers increases and the size increases. At the same time, the hollow glass microsphere surface reacts with the calcium silicate hydrate (C-S-H) gel at 50-75°C to form Si-O-Si covalent bonds, which improves the interfacial bonding strength between the microspheres and the matrix, and the modified HL60 type microspheres in the outer layer are more closely arranged under 0.5-1.0 MPa high pressure compaction, and the contact points between the microspheres are filled with tricalcium aluminate hexahydrate (C3AH6) crystals.

[0098] After the second stage curing, the inner layer retains uniform distribution of heat preservation pores, and the intermediate layer and the outer layer are mainly microporous. This gradient pore structure not only ensures the heat preservation performance of the inner layer, but also realizes the overall high strength through the low porosity of the outer layer. Through the chemical reaction regulation and organization optimization of two-stage curing, the inorganic heat preservation pipe shell realizes the firm fusion between layers and the effective construction of overall strength, meeting the dual demands of heat preservation and mechanical properties. The interlayer is combined and strengthened from macro to micro, overcoming the problem of weak combination caused by composition difference in gradient materials.

[0099] In terms of microstructure, the transition zone between layers forms a continuous SiO2 network through the diffusion of nano-silica gel, and calcium aluminate decahydrate (CAH 10 ) acicular crystals and tricalcium aluminate hexahydrate (C3AH6) cubic crystals interpenetrate in the transition zone. This microstructure improves the interlayer shear strength and avoids performance degradation caused by interlayer peeling. Moreover, the second stage high temperature curing promotes the uniform growth of tricalcium aluminate hexahydrate (C3AH6) and the close combination with calcium silicate hydrate (C-S-H) gel, forming a "crystal framework-gel filling" structure. The needle-like crystals of tobermorite powder interpenetrate between the hydration products, and the fiber surface is wrapped by the gel to form a reinforced interface, and the overall microstructure has no obvious defects, so that the material can still maintain high mechanical strength under the condition of lightweight density.

[0100] In summary, the components realize functional division through gradient distribution, the hydration reaction of cementitious materials and active components generates high-strength framework, the synergy of fibers and microspheres balances heat preservation and strength, and the gradient process ensures the optimization of microstructure. Microscopically, the uniform distribution of closed pores reduces the thermal conductivity, and the dense outer layer and the reinforced transition zone improve the strength. Finally, through the synergistic mechanism of "component gradient design-precise process control-microstructure optimization", the excellent performance of strength 13.5 MPa, thermal conductivity (35°C) 0.038 W / (m·K), density 180 kg / m³, and heat dissipation temperature difference less than 5°C is realized.

[0101] It should be pointed out finally that the above examples are only used to illustrate the technical solutions of the present application but not to limit it; although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the specific embodiments of the present application can be modified or some technical features can be replaced by equivalent ones without departing from the spirit of the technical solutions of the present application, and all of them should be covered in the technical solution range claimed by the present application.

Claims

1. A method for preparing an inorganic thermal insulation tube shell based on a hollow glass bead gradient distribution, comprising the following steps: Preparation of raw materials: divide the base material into three equal parts, mix one part of the base material with the first type of modified hollow glass beads to prepare an inner layer material; Mix the first type of modified hollow glass beads and the second type of modified hollow glass beads with the second part of the base material to prepare a middle layer material; mix the third part of the base material with the second type of modified hollow glass beads to prepare an outer layer material; wherein the base material comprises cement, nano-silica gel, basalt fiber, xonotlite powder, water reducing agent, water retaining agent, reinforcing agent, retarder, and water; Compaction: inject the inner layer material into the mold, apply a pressure of 0.25 MPa to 0.5 MPa for 8 s to 15 s, inject the middle layer material, apply a pressure of 0.5 MPa to 0.75 MPa for 8 s to 15 s, and inject the outer layer material, apply a pressure of 0.5 MPa to 1.0 MPa for 8 s to 15 s, to obtain an inorganic thermal insulation tube shell body; Curing: first, cure the inorganic thermal insulation tube shell body at 20 ℃ to 29 ℃ and 90% humidity for 10 h to 14 h, and then cure it at 65 ℃ to 75 ℃ and 95% humidity for 45 h to 55 h; wherein the first type of modified hollow glass beads have 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, a D50 of 80 μm, and a D90 of 120 μm in the particle size distribution; the second type of modified hollow glass beads have 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, a D50 of 40 μm, and a D90 of 65 μm in the particle size distribution.

2. The method for preparing the inorganic thermal insulation tube shell based on the hollow glass microsphere gradient distribution according to claim 1, characterized in that: Both the first type of modified hollow glass beads and the second type of modified hollow glass beads are obtained by treating hollow glass bead raw materials with a silane coupling agent and nano calcium carbonate.

3. The method for preparing the inorganic thermal insulation tube shell based on the hollow glass microsphere gradient distribution according to claim 1, characterized in that: In the middle layer material, the mass ratio of the first type of modified hollow glass beads to the second type of modified hollow glass beads is (1.5-3):

1. 4.The method according to claim 1 or 2 or 3, characterized in that: by weight, the base material comprises cement 150-300 parts, nano-silica gel 50-100 parts, basalt fiber 100-150 parts, xonotlite powder 100-200 parts, water reducing agent 1.5-3 parts, water retaining agent 0.5-1.0 parts, reinforcing agent 5-6 parts, retarder 0.5-1.0 parts, water 1000-1300 parts, and modified hollow glass beads 500-600 parts in total; wherein in the inner layer material, the first type of modified hollow glass beads account for 40%-50% of the total amount of modified hollow glass beads, and in the outer layer material, the second type of modified hollow glass beads account for 20%-30% of the total amount of modified hollow glass beads. ​ 5. The method for preparing the inorganic thermal insulation tube shell based on the hollow glass microsphere gradient distribution according to claim 1 or 2 or 3, characterized in that: In the compacting step, the inner layer thickness of the inorganic thermal insulation pipe shell body is 1-2 cm, the middle layer thickness is 1-2 cm, and the outer layer thickness is 1-2 cm.

6. The method for preparing the inorganic thermal insulation tube shell based on the hollow glass microsphere gradient distribution according to claim 1, characterized in that: In the preparation of the inner layer material, the middle layer material and the outer layer material, the cement, the xonotlite powder and the modified hollow glass microsphere of the corresponding specification are dry mixed for 1-2 min; Then the basalt fiber, the water retaining agent, the retarder, the reinforcing agent are added and dry mixed for 1-2 min; finally, water, the water reducing agent and the nano silicon dioxide gel are added and stirred for 1-2 min.

7. The method for preparing the inorganic thermal insulation tube shell based on the hollow glass microsphere gradient distribution according to claim 1 or 2 or 3, characterized in that: The basalt fiber includes basalt fiber with a length of 3 mm and basalt fiber with a length of 6 mm.

8. The method for preparing the inorganic thermal insulation tube shell based on the hollow glass microsphere gradient distribution according to claim 1 or 2 or 3, characterized in that: The water reducing agent is a polycarboxylic acid water reducing agent; the retarder is compounded by tartaric acid, citric acid and sodium citrate, and the mass ratio of tartaric acid, citric acid and sodium citrate is 4:3:3; the water retaining agent is HPK400; and the reinforcing agent is an aluminate reinforcing agent.

9. An inorganic thermal insulation pipe shell based on a gradient distribution of hollow glass microspheres, characterized by: The inorganic thermal insulation pipe shell is prepared by the preparation method of any one of claims 1-8.