High-temperature resistant thermal insulation coating for kiln, its preparation method and application

Abstract

The present invention provides a high-temperature resistant thermal insulation coating for a kiln, and its preparation method and application. The thermal insulation coating includes a primer and a topcoat. By mass, the A component of the primer mainly consists of sodium silicate with a modulus of 2.0, and the B component mainly consists of metakaolin, mineral powder, 200-mesh quartz sand, 80-120-mesh quartz sand, and 40-80-mesh quartz sand; the A component of the topcoat mainly consists of sodium silicate with a modulus of 2.0, and the B component mainly consists of metakaolin, mineral powder, expanded vermiculite, expanded perlite, diatomite zeolite mixed modifier, air-entraining agent, and basalt fiber. Among them, sodium silicate, metakaolin, and mineral powder are used as film-forming substances, which have a strong binding force with metals. At the same time, the raw materials in each formula of the primer and the topcoat cooperate with each other, and the primer and the topcoat cooperate with each other and act synergistically, so that when the above thermal insulation coating is applied to the metal shell of a kiln, etc., it has the characteristics of high bonding strength, good thermal insulation performance, and good freeze-thaw resistance.

Description

Technical Field

[0001] The present invention relates to the field of high-temperature resistant coatings, and particularly to a high-temperature resistant and heat-insulating coating for kilns, a preparation method thereof, and an application thereof. Background Art

[0002] At present, in the total energy consumption of our country, the energy consumption of industrial kilns accounts for about 25-40%, and the thermal efficiency of the kilns is only about 30%, especially for industrial kilns with an internal temperature above 1000°C. In order to effectively improve the thermal efficiency of the kilns, people have carried out transformations on the inner walls of the kilns, such as designing and researching new refractory bricks inside the kilns, redesigning the internal structure of the kilns, and designing and manufacturing infrared radiation heating devices by cooperating infrared radiation coatings with heating elements. As confirmed by production practice, the thermal efficiency and productivity of the kilns have been greatly improved, the heat loss has been reduced, the service life of the kiln walls has been extended, and the purpose of energy conservation and emission reduction has been achieved to a certain extent.

[0003] However, research shows that the heat energy loss on the surfaces of the rotary kiln and the preheater at the kiln tail of cement plants is quite huge. Huang Yangyang obtained in the thermal calibration analysis of a 2500t / d new dry-process cement production line that the heat carried away by the waste gas at the first-stage outlet of the preheater is 18.99% of the total heat energy, the surface heat dissipation of the system is 10.45%, and the heat carried away by the clinker is 5.14%. Only the surface heat dissipation of the system accounts for 10.45%, which is a quite large heat loss. Therefore, how to reduce the surface heat loss of the system and achieve the purpose of energy conservation and consumption reduction is also one of the research hotspots.

[0004] For example, the Chinese utility model patent CN204329612U authorized to Wuhan Iron and Steel (Group) Corporation on May 13, 2015 discloses a composite heat-insulating board for preparing a kiln shell, which mainly consists of a silicate heat-insulating board layer, a ceramic fiber board layer, a heat-resistant metal wire mesh layer bonded between the silicate heat-insulating board layer and the ceramic fiber board layer, a metal-based reflective layer bonded on the silicate heat-insulating board layer, a blackbody radiation coating bonded on the metal-based emission layer, and a high-temperature resistant adhesive layer bonded on the lower end surface of the ceramic fiber board layer. This composite heat-insulating board can be bent and directly attached to the furnace shell. Through its low thermal conductivity and the surface coating reducing the outward conduction of heat by anti-radiation, the heat preservation effect of the kiln is effectively improved. However, the structure of this composite heat-insulating board is complex, the preparation process is complex, and problems such as small adhesion and easy blistering and peeling are likely to occur during the temperature alternation caused by the start and stop of the kiln.

[0005] For another example, a high-temperature resistant and corrosion-resistant topcoat for furnaces and kilns is disclosed in Chinese Patent Application CN109943225A published by Nanjing Dongding New Materials Technology Co., Ltd. on June 28, 2019. It is composed of the following components in parts by weight: 40-60 parts of epoxy-modified silicone resin, 10-25 parts of aluminum powder, 5-10 parts of titanium dioxide, 3-8 parts of coupling agent, 1-3 parts of stabilizer, 0.1-2 parts of wetting and dispersing agent, 0.1-2 parts of leveling agent, and 15-30 parts of solvent. Although the above high-temperature resistant and corrosion-resistant topcoat has excellent properties such as high temperature resistance and aging resistance, and good high-temperature stability, the high-temperature resistant and corrosion-resistant topcoat mainly consists of silicone resin. Due to the characteristics of silicone resin itself, its service life at high temperatures usually shows phenomena such as bulging, blistering, peeling, etc. within less than half a year. Moreover, when the temperature alternates due to the start and stop of the furnace and kiln, problems such as blistering and peeling are also likely to occur. Summary of the Invention

[0006] In view of this, it is indeed necessary for the present invention to provide a high-temperature resistant and heat-insulating coating for furnaces and kilns, its preparation method and application. When the heat-insulating coating is applied to the metal shell of furnaces and kilns, it has characteristics such as high bonding strength, good heat-insulating performance, and good freeze-thaw resistance.

[0007] Specifically, the technical solution provided by the present invention is: a high-temperature resistant and heat-insulating coating for furnaces and kilns, including a primer and a topcoat.

[0008] Among them, the primer is a two-component coating, including component A and component B. By mass, component A mainly consists of 20-25 of sodium silicate with a modulus of 2.0, and component B mainly consists of 15-20 of metakaolin, 10-15 of mineral powder, 5-10 of 200-mesh quartz sand, 15-30 of 80-120-mesh quartz sand, and 10-30 of 40-80-mesh quartz sand.

[0009] The topcoat is a two-component coating, including component A and component B. By mass, component A mainly consists of 20-25 of sodium silicate with a modulus of 2.0, and component B mainly consists of 10-20 of metakaolin, 10-15 of mineral powder, 5-10 of expanded vermiculite, 15-30 of expanded perlite, 10-20 of diatomite zeolite mixed modifier, 0.5-1 of air-entraining agent, and 0.5-1 of basalt fiber.

[0010] Preferably, the particle sizes of the raw materials in the coating are as follows: the particle size of metakaolin is above 1000 mesh, the particle size of mineral powder is above 600 mesh, the particle size of expanded vermiculite is above 3-5 mm, the particle size of expanded perlite is above 1-7 mm, the particle size of diatomite zeolite mixed modifier is above 400 mesh, the air-entraining agent is preferably a water-soluble air-entraining agent, and the length of basalt fiber is preferably basalt fiber above 3 mm.

[0011] The surface coating agent uses geopolymers as the adhesive material and is composed of inorganic materials, having good high-temperature resistance. By adding expanded vermiculite and closed-cell perlite with low thermal conductivity as lightweight heat-insulating fillers, and diatomite zeolite mixed modifier as heat-insulating fillers for porous vacuum and semi-vacuum, and combining with an air-entraining agent to introduce tiny closed air bubbles during stirring and construction, through multiple composite technologies, the surface coating film formed after the surface coating agent forms a film can effectively prevent heat conduction, significantly improve the heat insulation ability, achieve excellent heat insulation and heat preservation performance, and achieve the purpose of energy conservation and carbon reduction. To make the surface temperature of the metal shell on the surface of the kiln furnace reach above 1000 °C, the surface coating film is still not easy to fall off and has a relatively good heat insulation effect. The surface coating agent is a thickness-type coating, and the coating thickness is 15-20 mm.

[0012] During the construction and application process, the primer uses geopolymers as the main adhesive material, has a relatively high bonding strength with the metal shell of the kiln furnace, especially with the steel plate shell, and this bonding strength is greater than the cracking strength of the primer film formed after the primer forms a film. When the high-temperature heat-insulating coating is at high temperature, a large number of tiny cracks formed due to the expansion of the steel plate do not affect the heat insulation effect of the high-temperature heat-insulating coating. At the same time, by using countless micro-cracks generated by the primer film itself, the goal of increasing the expansion coefficient is achieved, ensuring that the expansion coefficients of the high-temperature heat-insulating coating and the steel plate are relatively close, so that the primer film is difficult to detach from the steel plate, and it can effectively solve the problem that the high-temperature energy-saving coating forms air pockets during the construction process, resulting in a reduction in its adhesion to the surface of the kiln furnace. The primer is a thin coating type, and its coating thickness is preferably 0.1-0.2 mm.

[0013] In addition, the quartz sand in the primer is designed with different particle sizes, increasing the surface roughness of the primer film, effectively enhancing the bonding strength between the primer film and the surface coating film, and reducing or avoiding the situation where the surface coating film falls off from the primer film during use; thus, when the surface temperature of the kiln furnace shell reaches above 1000 °C, each coating is still not easy to fall off. At the same time, the matching of different particles of quartz sand is also to ensure that the primer slurry formed after adding water and stirring the primer has a certain viscosity and suspension, and to ensure that larger aggregates do not settle to the bottom to form precipitation; if the quartz sand of the primer is only designed as 40-80 mesh quartz sand, the aggregates will settle and segregate about 5 minutes after adding water and stirring to form the primer slurry, and it will not play its due role when brushing the primer slurry; selecting too fine adapted sand, products of 200 mesh or finer, although there is no problem of sedimentation and segregation, the roughness of the primer film formed by it is smaller and cannot be effectively combined with the surface coating film, resulting in the coating being easy to fall off.

[0014] Based on the above coatings, the diatomite zeolite mixed modifier is mainly prepared by the following method:

[0015] Mixed roasting: First, diatomite powder and zeolite powder are stirred at high speed in a high-speed mixing and modification machine until fully mixed to obtain a mixed raw material. Then, the mixed raw material is roasted at a temperature of 400°C to 450°C to form a porous material powder. After cooling and drying, impurity removal treatment is carried out;

[0016] Secondary modification: The porous material powder after impurity removal treatment is added again to the high-speed mixing and modification machine, and stearic acid is added and stirred at high speed until the temperature in the high-speed mixing and modification machine rises to 70 - 80°C. After cooling and drying, the diatomite-zeolite mixed modified material is obtained.

[0017] Among them, in the above-mentioned mixed roasting step, diatomite powder with a particle size of more than 600 meshes and zeolite powder with a particle size of more than 400 meshes can minimize the crystal water inside the material, remove the organic matter in the pores and pore diameters, and increase the void volume through the above-mentioned mixed roasting treatment; at the same time, the zeolite powder and diatomite powder are fully mixed during high-speed stirring, and the powder with different particle sizes is mutually coated, which can form a closed pore in the powder void during high-temperature roasting; reduce the thermal conductivity of the material and improve the heat insulation performance of the material; dry and cool the roasted material and sieve it to remove larger impurities. Therefore, preferably, the mass ratio of the diatomite powder to the zeolite powder is 1:0.9 - 1.3, and the roasting time is 1 - 3h; more preferably, the mass ratio of the diatomite powder to the zeolite powder is 1:1, the roasting temperature is 450°C, and the roasting time is 2h.

[0018] In the above-mentioned secondary modification step, the diatomite-zeolite mixed modified material prepared by modifying the porous material powder after impurity removal treatment with stearic acid in a high-speed mixing and modification machine has certain surface hydrophobicity, which can reduce the water absorption of the diatomite-zeolite mixed modified material during construction with water stirring and ensure the vacuum degree of the voids therein. Preferably, the addition amount of stearic acid is 1 - 2% of the total mass of the diatomite powder and zeolite powder. Since the dissolution temperature of stearic acid is 70 - 80°C, stearic acid will vaporize at too high a temperature and cannot melt at too low a temperature, so the temperature of the secondary modification step is limited to 70 - 80°C.

[0019] Therefore, the above-mentioned diatomite-zeolite mixed modified material is an excellent porous vacuum and semi-vacuum heat insulation filler, which can ensure that the excellent heat insulation performance of diatomite and zeolite powder is not reduced during the construction process, and can also effectively reduce the influence caused by the low strength of diatomite.

[0020] The present invention also provides a preparation method of the above-mentioned high-temperature resistant heat insulation coating for a kiln, including the following steps:

[0021] Preparation of the primer: First, mix metakaolin and mineral powder evenly to obtain the first mixture; then mix the first mixture, 200-mesh quartz sand, 80-200-mesh quartz sand, and 40-80-mesh quartz sand evenly to prepare the B component of the primer; the A component of the primer mainly consists of sodium silicate with a modulus of 2.0.

[0022] Preparation of the topcoat: First, evenly mix metakaolin, mineral powder, diatomite zeolite mixed modifier, air-entraining agent, and basalt fiber to form a second mixture; then mix the second mixture, expanded vermiculite, and expanded perlite to obtain the B component of the evenly mixed topcoat; the A component of the topcoat mainly consists of sodium silicate with a modulus of 2.0.

[0023] Preferably, in the step of preparing the primer, first mix and stir metakaolin and mineral powder at a speed of 1000-1500 rpm to form the first mixture; mix and stir the first mixture, 200-mesh quartz sand, 80-200-mesh quartz sand, and 40-80-mesh quartz sand at a speed of 20-40 rpm to prepare the B component of the primer.

[0024] In the step of preparing the topcoat, first mix and stir metakaolin, mineral powder, diatomite zeolite mixed modifier, air-entraining agent, and basalt fiber at a speed of 1000-1800 rpm, then add expanded vermiculite and expanded perlite and stir at a speed of 20-40 rpm to obtain the B component of the topcoat.

[0025] The present invention also provides an application of the above-mentioned high-temperature resistant and heat-insulating coating for kilns, including the steps:

[0026] Application of the primer: First, completely dissolve its A component in water according to the mass ratio of primer to water of 1:0.3 and let it stand; then add its B component and stir evenly to form a primer slurry; then apply the primer slurry on the surface of the metal shell of the kiln to form a primer film.

[0027] Application of the topcoat: First, completely dissolve its A component in water according to the mass ratio of topcoat to water of 1:0.7 and let it stand; then add its B component and stir evenly to form a topcoat slurry; then apply the topcoat slurry on the surface of the primer film to form a topcoat film.

[0028] Among them, in the application step of the primer, methods such as roller coating or brush coating can be used to roller coat or brush coat the construction part on the surface of the kiln furnace. The construction thickness should not exceed the particle size of 40 - 80 mesh quartz sand. After the primer construction is completed to form a primer film, the topcoat construction can be carried out. Among them, the construction thickness not exceeding the particle size of 40 - 80 mesh quartz sand disperses the 40 - 80 mesh quartz sand on the coating surface in a discontinuous manner, increasing the roughness of the primer film, thereby increasing the interfacial bonding strength between the primer film and the topcoat film.

[0029] In the application step of the topcoat, methods such as batch coating or spraying can be used to batch coat or spray on the construction part of the primer film, and the construction thickness should not be less than 1.5 cm.

[0030] Therefore, in the high-temperature heat-insulating coating for kiln furnaces provided by the present invention, sodium silicate with a modulus of 2.0, metakaolin, and mineral powder are used as raw materials for the adhesive material. Among them, sodium silicate with a modulus of 2.0 is used as the activator, and substances such as metakaolin and mineral powder are used as aluminosilicate materials. Under a certain alkalinity, a chemical reaction occurs between the activator and the aluminosilicate materials to produce a new substance with a silicon-aluminum long-chain structure as the film-forming substance. This film-forming substance has good high-temperature resistance and is firmly bonded to the metal shell substrate of the kiln furnace, which can improve or overcome the problem of easy aging in high-temperature environments caused by traditional coatings. Expanded vermiculite and closed-cell perlite are used as lightweight heat-insulating fillers, and diatomite zeolite mixed modifier is used as a heat-insulating filler for porous vacuum and semi-vacuum. The air-entraining agent can introduce a large number of closed micro-bubbles into the above high-temperature heat-insulating coating during the construction stirring process. The mutual cooperation and synergistic effect of these components are beneficial to reducing the thermal conductivity of the coating after film formation, improving the heat insulation ability, making the above high-temperature heat-insulating coating have excellent heat insulation and heat preservation performance after film formation, and achieving the purpose of reducing heat loss, saving energy consumption, and reducing carbon emissions.

[0031] Therefore, sodium silicate, metakaolin, and mineral powder in the above high-temperature heat-insulating coating for kiln furnaces are used as film-forming substances and have a strong binding force with metals, especially with steel materials. At the same time, the raw materials in each formula of the primer and the topcoat cooperate with each other, and the primer and the topcoat cooperate with each other and act synergistically. When the above heat-insulating coating is brushed on the metal outer surface of high-temperature kiln furnaces, high-temperature equipment, and high-temperature pipelines, it has the characteristics of convenient construction, high bonding strength, good heat insulation and heat preservation performance, is firmly bonded to the metal matrix, and can withstand high temperatures above 1000 °C for a long time. In addition, the above coating has good freeze-thaw resistance and is not prone to phenomena such as bubbles and peeling during heat and cold alternation. Specific Embodiments

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

[0033] Among them, the diatomite-zeolite mixed modifier provided in the following examples is prepared by the following method: Mix and modify diatomite and zeolite powder. After mixing in a ratio of 1:1, stir at a high speed of 1400 revolutions per minute in a high-speed mixing and modifying machine for 3 minutes to make the materials fully mixed and uniform; Bake the uniformly mixed materials at a temperature of 450 °C for 2 hours to obtain a baked mixture; Add the baked mixture to the high-speed heating and mixing modifier again, add 1% of stearic acid, and stir at high speed until the equipment temperature rises to 80 °C. The surface modification of the diatomite and zeolite mixture is completed, and the diatomite-zeolite mixed modifier is obtained. Among them, the diatomite is composed of diatomite with particle sizes of 600 mesh, 800 mesh, and 1250 mesh in a mass ratio of 10:4:1; The zeolite is composed of zeolite with particle sizes of 400 mesh, 600 mesh, and 800 mesh in a mass ratio of 10:4:1.

[0034] The coatings provided in each example are verified for performance by the following method:

[0035] 1) Place the corresponding coating slurry in a stirring bucket and observe the change in its fluidity to judge its workability. Among them, the initial setting time refers to: at room temperature of 25 °C, the time from adding water to the coating to when the fluidity of the slurry basically remains unchanged; Both too long and too short initial setting times are not good. Generally, it is greater than 60 minutes, preferably 60 - 90 minutes, and about 60 minutes is the best.

[0036] 2) Test method for seismic resistance test: Drop the sample from a height of 1.5 meters, and check the adhesion of the coating on the steel plate to the steel plate or the dropped area after landing; Among them, the judgment standard for the seismic resistance performance level is as follows:

[0037] Excellent: The dropped area does not exceed 1 / 5 of the total area, or the dropped part is located 1 - 2 cm from the edge of the sample;

[0038] Good: The dropped area does not exceed 1 / 4 of the total area, or the dropped part is located 2 - 3 cm from the edge of the sample;

[0039] General: The dropped area does not exceed 1 / 3 of the total area, or the dropped part is located 3 - 4 cm from the edge of the sample;

[0040] Poor: Other situations are judged as poor.

[0041] 3) Bond strength test method: Use the method for determining bond strength in the standard GB14907 - 2018 "Fireproof Coatings for Steel Structures".

[0042] 4) Heat insulation performance test method: Use the method of baking on the back fire. Use a constant temperature heater to heat the steel plate on the back of the coating, heat it to 300 °C, keep it warm for 2 hours, and then use a thermometer to measure the temperature on the surface of the coating.

[0043] 5) Freeze-thaw resistance test: Place each sample at room temperature for 48 hours, bake it above an electric furnace at 300 °C for 2 hours, cool it to room temperature, put it in a freezer and freeze for 24 hours, then take it out. After thawing, bake it again for 2 hours. This is one cycle. If there are no phenomena such as cracking, warping, peeling, or flaking of the top coat after one cycle, it is considered normal. If there are no abnormalities after 3 cycles, it is a qualified product.

[0044] I. Influence of the primer

[0045] Example 1 of the present invention provides a high-temperature resistant and heat-insulating coating for a kiln, which includes a primer and a top coat. Among them, the primer is a two-component coating. By mass, component A: composed of 20 - 25 of sodium silicate with a modulus of 2.0; the raw materials of component B include: 15 - 20 of metakaolin with a particle size of 1250 mesh, 10 - 15 of ore powder with a particle size of 1000 mesh, 5 - 10 of quartz sand with a particle size of 200 mesh, 15 - 30 of quartz sand with a particle size of 80 - 120 mesh, and 10 - 30 of quartz sand with a particle size of 40 - 80 mesh. The preparation method of this component B: According to the ratio, first add metakaolin and ore powder into a high-speed stirrer, and mix and stir at a speed of 1500 revolutions per minute for 2 minutes to form a first mixture. Then add the first mixture, quartz sand with a particle size of 200 mesh, quartz sand with a particle size of 80 - 200 mesh, and quartz sand with a particle size of 40 - 80 mesh into a low-speed stirring pot, and stir at a speed of 30 revolutions per minute for 30 minutes to obtain component B of the primer.

[0046] The top coat is a two-component coating. By mass, component A: 20 - 25 of sodium silicate with a modulus of 2.0; component B: 10 - 20 of metakaolin with a particle size of 1250 mesh, 10 - 15 of ore powder with a particle size of 1000 mesh, 5 - 10 of expanded vermiculite with a particle size of 3 - 5 mm, 15 - 30 of expanded closed-cell perlite with a particle size of 1 - 7 mm, 10 - 20 of diatomite zeolite mixed modified material with a particle size of more than 400 mesh, 0.5 - 1 of AE-3 type water-soluble air-entraining agent, and 0.5 - 1 of basalt fiber with a length of 6 mm. The preparation method of this component B: According to the ratio, add metakaolin, ore powder, diatomite zeolite mixed modified material, air-entraining agent, and basalt fiber into a high-speed stirrer, and mix and stir at a speed of 1500 revolutions per minute for 2 minutes to obtain a second mixture. The high-speed stirrer can fully mix the basalt fiber and various materials. Place the second mixture, expanded vermiculite, and expanded closed-cell perlite in a low-speed stirring pot, and stir at a speed of 30 revolutions per minute for 30 minutes to obtain component B of the top coat.

[0047] The raw material ratios of the high-temperature resistant and heat-insulating coatings provided by Example 1 and Comparative Examples 1 - 4 are shown in Table 1. Among them, the main difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not use a primer.

[0048] Table 1 Raw material mass ratio table of high-temperature resistant and heat-insulating coatings:

[0049]

[0050] Application

[0051] The high-temperature resistant and heat-insulating coatings provided by Example 1 and Comparative Examples 1 to 4 are used as follows:

[0052] Application of the primer: According to the primers provided by Example 1 and Comparative Examples 2 to 4, first dissolve 2.0 modulus sodium silicate in water at a mass ratio of 1:0.3 with water, and let it stand; then add other components and stir evenly to form a primer slurry; then apply the primer slurry on a 3.5 mm thick steel plate to form a primer film.

[0053] Application of the topcoat: According to the topcoats provided by Example 1 and Comparative Examples 1 to 4, first dissolve 2.0 modulus sodium silicate in water at a mass ratio of 1:0.7 with water, and let it stand; then add other components and stir evenly to form a topcoat slurry; then apply the topcoat slurry on the surface of the corresponding primer film or on a 3.5 mm thick steel plate to form a topcoat film, thereby obtaining Example Sample 1 and Comparative Sample 1 to 2, and the total thickness of the coating on each sample is about 1 - 1.5 cm.

[0054] The test results of the workability of the primer slurry, and the seismic performance, bond strength, heat-insulating performance and freeze-thaw resistance of the energy-saving coatings in the high-temperature resistant and heat-insulating coatings for kilns provided by Example 1 and Comparative Examples 1 to 4 are shown in Table 2.

[0055] Table 2 Performance test results of high-temperature resistant and heat-insulating coatings for kilns:

[0056]

[0057] It can be seen from Table 2 that: for the coating provided by Example 1 of the present invention, its seismic performance reaches good or above, even excellent; its bond strength of 0.08 MPa is greater than or equal to 0.04 MPa (as stipulated in GB14907-2018 "Fireproof Coatings for Steel Structures", the bond strength should be greater than 0.04 MPa); when the internal temperature is 300 °C, the surface temperature of the coating drops to 125 °C, and the heat-insulating effect is good; the coating provided by Example 1 can withstand 5 cold and hot alternating cycles, and has good freeze-thaw resistance.

[0058] In Comparative Example 1, the primer was not used, and the topcoat slurry was directly applied to the steel plate. The bonding strength between the topcoat film and the steel plate was limited. Therefore, when the topcoat film was heated at high temperature, the coating peeling phenomenon occurred. However, in Example 1, the primer slurry was first coated on the steel plate, and an uneven primer film with a relatively large surface roughness could be formed on the surface of the steel plate, which could not only increase the bonding strength between the primer film and the steel plate, but also increase the bonding strength between the topcoat film and the primer film, thereby improving the bonding strength between the coating and the steel plate.

[0059] In the primer of Comparative Example 2, the quartz sand with a mesh size of 40 - 80 was missing, and the proportion of quartz sand with a mesh size of 80 - 120 was relatively large. Although the primer slurry formed in this way did not show precipitation after standing for 60 minutes, its surface roughness was small, and the bonding force between the topcoat and the primer was not strong. In Comparative Example 3, the 200 - mesh quartz sand was missing in the primer formulation, and the proportion of sand with a mesh size of 40 - 80 was relatively large. The primer slurry formed by it quickly showed precipitation, which was not conducive to construction. Moreover, when combined with its primer, the formed coating had a cracking phenomenon during the calcination process. In Comparative Example 4, the quartz sand used in the primer was fine sand. After the primer was applied, there was no roughness, resulting in easy peeling of the topcoat and poor seismic performance. Therefore, the quartz sand in the primer is preferably composed of 5 - 10 parts of 200 - mesh, 15 - 30 parts of 80 - 120 - mesh, and 10 - 30 parts of 40 - 80 - mesh; in this way, the particle size and mass fraction of the quartz sand in the primer are coordinated. When combined with sodium silicate with a modulus of 2.0, metakaolin, and mineral powder, the primer has a good bonding strength with the metal shell of the kiln furnace and also has a good bonding strength with the topcoat.

[0060] II. Influence of Adhesive Materials

[0061] In each of the following examples or comparative examples, the adhesive materials in the primer and topcoat of the thermal insulation coating provided are the same, and the influence of the ratio of each raw material on the performance of the high - temperature resistant thermal insulation coating is analyzed.

[0062] Sodium silicate, mineral powder, and metakaolin are common raw materials for geopolymers and are usually used as adhesive materials and film - forming substances in coatings.

[0063] 1) Influence of the raw material selection of the binder on its performance:

[0064] In order to better investigate the influence of raw materials on the adhesive material, the ratios between sodium silicate with a modulus of 2.0, mineral powder, and metakaolin are shown in Table 3. After the sample was stirred well, it was poured into a circular mold with a diameter of 10 cm and a height of 2 cm, sealed with plastic wrap and left to stand, and the setting time and the stability after solidification were tested. The stability test method was to observe the change in the surface state of the round cake after standing for a period of time to see if there were cracks or the size of the cracks on the round cake.

[0065] Table 3 Raw material ratio of the adhesive material:

[0066]

[0067] As can be seen from Table 3, the reaction rate of sodium silicate with a modulus of 2.0 and mineral powder is very fast, and it can solidify in 2 hours. However, after solidification, cracks appear after being placed indoors for a period of time, indicating that there is a risk of cracking when using mineral powder alone; the reaction rate of sodium silicate with a modulus of 2.0 and metakaolin is too slow. When testing sodium silicate with a modulus of 2.0 and metakaolin separately, the hardening time reached more than 24 hours. If other filler components are added, the setting time will be even longer.

[0068] 2) Influence of the mass ratio of mineral powder and metakaolin on the performance of high-temperature resistant and heat-insulating coatings for kilns:

[0069] The main components of metakaolin are silicon and aluminum components, which provide the silicon and aluminum components required for the adhesive material, and form silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons in the polymerization reaction. Such a composition structure endows the adhesive material with a certain tensile strength. The main components of mineral powder are calcium and silicon components, and the main product in the geopolymerization reaction is calcium polymer, which enables the strength of the coating to be exerted faster.

[0070] Therefore, Example 2 of the present invention provides a high-temperature resistant and heat-insulating coating for kilns, which has basically the same raw material composition as the heat-insulating coating provided in Example 1. The main difference is that: in this example, the total mass fraction of metakaolin and mineral powder is 30 parts, and the mass ratio of mineral powder to metakaolin in each group is shown in Table 6, and other components, preparation methods and application methods are the same; thus, the test results of the initial setting time and bonding strength of the heat-insulating coatings provided in each group of Example 2 of the present invention are shown in Table 4.

[0071] Table 4 Influence of the mass ratio of mineral powder and metakaolin on the performance of the adhesive material:

[0072] Serial number Mineral powder: Metakaolin Initial setting time Bonding strength (MPa) 1 3:1 35 - 40 min 0.2 2 2:1 55 - 60 min 0.3 3 1:1 70 - 80 min 0.5 4 1:2 90 - 100 min 0.5 5 1:3 Above 120 min 0.4

[0073] As can be seen from Table 4, when the addition amount of mineral powder is large, the reaction is fast, but the bonding strength is low. When the addition amount of metakaolin reaches 1:3, the initial setting time increases, the reaction rate decreases significantly, and the bonding strength also decreases; considering comprehensively, the mass ratio of mineral powder to metakaolin is 1:1 to 2. 3) Influence of the addition amount of sodium silicate with a modulus of 2.0 on the performance of high-temperature resistant and heat-insulating coatings for kilns.

[0074] Example 3 of the present invention provides a high-temperature resistant and heat-insulating coating for kilns, which is basically the same as the high-temperature resistant and heat-insulating coating for kilns provided in Example 1. The main difference is that: the formulations of the primer and topcoat in this example and Example 1 are different, but the preparation methods are the same.

[0075] Specifically, by mass parts, component A of the primer in Example 3 consists of 15 - 30 parts of sodium silicate with a modulus of 2.0. The raw materials of component B include 18 parts of metakaolin with a particle size of 1250 mesh, 12 parts of ore powder with a particle size of 1000 mesh, 10 parts of quartz sand with a particle size of 200 mesh, 20 parts of quartz sand with a particle size of 80 - 120 mesh, and 20 parts of quartz sand with a particle size of 40 - 80 mesh;

[0076] Component A of the topcoat in Example 3: 15 - 30 parts of sodium silicate with a modulus of 2.0; Component B: 18 parts of metakaolin with a particle size of 1250 mesh, 12 parts of ore powder with a particle size of 1000 mesh, 8 parts of expanded vermiculite with a particle size of 3 - 5 mm, 25 parts of expanded closed - cell perlite with a particle size of 2 - 6 mm, 15 parts of diatomite zeolite mixed modified material with a particle size of over 400 mesh, 0.7 parts of air - entraining agent, and 0.7 parts of basalt fiber with a length of 3 mm.

[0077] The application methods of the above - mentioned primer and topcoat in this example are the same.

[0078] In this example, four - level tests were set for the addition amount of sodium silicate with a modulus of 2.0. The first group: 15 parts, the second group: 20 parts, the third group: 25 parts, and the fourth group: 30 parts. The test results of the bonding strength and heat - insulation performance of the energy - saving coatings provided in each group of tests in this example are shown in Table 5.

[0079] Table 5 Influence of the addition amount of sodium silicate with a modulus of 2.0 on the performance of high - temperature resistant and heat - insulating coatings for kilns:

[0080] Classification Bonding strength (MPa) Surface temperature (°C) The first group 0.2 Phenomenon of powdering occurred during calcination The second group 0.4 125 The third group 0.5 140 The fourth group 0.6 A piece exploded in the middle part during calcination

[0081] It can be seen from Table 5 that: the addition amount of sodium silicate has obvious effects on both the bonding strength and heat - insulation effect of the high - temperature resistant and heat - insulating coatings for kilns; sodium silicate is an important component of the coating, and the dosage of sodium silicate has a direct impact on the products generated by the geopolymerization reaction. Sodium silicate not only provides part of the alkalinity for the reaction, but mainly provides the silicate ions required for the reaction. The amount of silicate ions determines the form of the main products of the product. If the content of sodium silicate is low, it will cause insufficient generation of products and low strength; if the addition amount is too large, it will cause the silicate ions not to fully participate in the reaction, and the excess sodium silicate is likely to form a solidified layer on the surface after reaction curing. When the kiln is heated, the crystal water inside the product is not easy to volatilize, resulting in coating cracking. Therefore, the addition amount of sodium silicate in the present invention is preferably 20 - 25 mass parts.

[0082] 4) Influence of the ratio of sodium silicate and aluminosilicate components on the performance of high - temperature resistant and heat - insulating coatings for kilns:

[0083] Metakaolin and mineral powder, as siliceous-aluminous components, are the main raw material components of the adhesive material in the coating. The ratio of the siliceous-aluminous component composed of metakaolin and mineral powder to sodium silicate with a modulus of 2.0 determines the performance of the high-temperature resistant thermal insulation coating for kilns provided by the embodiments of the present invention; the influence of the ratio of sodium silicate with a modulus of 2.0 to the siliceous-aluminous component on the high-temperature resistant thermal insulation coating for kilns is investigated through flexural strength and compressive strength tests below.

[0084] Specifically, Embodiment 4 of the present invention provides a high-temperature resistant thermal insulation coating for kilns, which has basically the same raw material composition as the thermal insulation coating provided in Embodiment 1. The main difference is that: the mass ratio of sodium silicate with a modulus of 2.0 to the siliceous-aluminous component in this embodiment is the same, both as shown in Table 6, and the mass ratio of metakaolin to mineral powder is 3:2, and other components, preparation methods and application methods are the same. According to the provisions of GB / T17671, the mortar strength is tested to detect the flexural strength and compressive strength at different mass ratios of sodium silicate to the siliceous-aluminous component, and the results are shown in Table 6.

[0085] Table 6 Influence of the ratio of sodium silicate to the siliceous-aluminous component on the performance of the thermal insulation coating:

[0086]

[0087] It can be seen from Table 6 that when the mass ratio of sodium silicate to the siliceous-aluminous component (mineral powder and metakaolin) is 1:1.5, the flexural strength and compressive strength are relatively high.

[0088] Therefore, considering Tables 3-6 comprehensively, when the mass ratio of sodium silicate with a modulus of 2.0, metakaolin and mineral powder is 1:1-2:1-2, the performance of the cementitious material is the best.

[0089] III. Influence of diatomite zeolite mixed modifier and air-entraining agent on the performance of the thermal insulation coating:

[0090] Embodiment 5 of the present invention provides a high-temperature resistant thermal insulation coating for kilns, which has the same raw materials, preparation method and application method as the thermal insulation coating provided in Embodiment 1. The main difference is that: the raw material ratio of the primer and topcoat in this embodiment is different from that in the embodiment. Specifically, in this embodiment, the formula of the primer consists of the following raw materials in parts by mass: 25 parts of sodium silicate with a modulus of 2.0, 20 parts of metakaolin with a particle size of 1250 mesh, 15 parts of mineral powder with a particle size of 1000 mesh, 8 parts of quartz sand with a particle size of 200 mesh, 27 parts of quartz sand with a particle size of 80-120 mesh, and 20 parts of quartz sand with a particle size of 40-80 mesh; the topcoat consists of the following raw materials in parts by mass: 25 parts of sodium silicate with a modulus of 2.0, 20 parts of metakaolin with a particle size of 1250 mesh, 15 parts of mineral powder with a particle size of 1000 mesh, 8 parts of expanded vermiculite with a particle size of 3-5 mm, 25 parts of expanded closed-cell perlite with a particle size of 3-6 mm, 15 parts of diatomite zeolite mixed modifier with a particle size of more than 400 mesh, 0.3 part of air-entraining agent, and 0.3 part of basalt fiber with a length of 3 mm.

[0091] Compared with Example 5, Comparative Example 5 uses a simple mixture of diatomite and zeolite provided for the high-temperature resistant and heat-insulating coating to replace the diatomite-zeolite mixed modifier in Example 5, and the particle size and its ratio of diatomite in both are the same, and the particle size and its ratio of zeolite in both are the same; others are the same.

[0092] Compared with Example 5, Comparative Example 6 does not add an air-entraining agent to the high-temperature resistant and heat-insulating coating, and others are the same.

[0093] The heat-insulating performance results of the heat-insulating coatings provided by Example 5 and Comparative Examples 5-6 and the state of the topcoat slurry are shown in Table 7.

[0094] Table 7 Influence of diatomite-zeolite mixed modifier and air-entraining agent on coating performance:

[0095] Project Surface temperature State of surface coating slurry Example 5 118℃ Volume increases and appears fluffy Comparative example 5 170℃ Volume increases and appears fluffy Comparative example 6 150℃ Did not show the state of adding air-entraining agent

[0096] It can be seen from Table 7 that under the same conditions, compared with Comparative Example 5, Example 2 uses a diatomite-zeolite mixed modifier, making the surface temperature of the topcoat after film formation relatively low, thus indicating that the diatomite-zeolite mixed modifier adopted in the examples of the present invention has excellent heat-insulating performance.

[0097] Compared with Comparative Example 6, adding an air-entraining agent to the topcoat provided by Example 5 can significantly reduce the surface temperature of the steel plate.

[0098] IV. Practical Application

[0099] From July 24th to July 28th, 2022, the high-temperature resistant and heat-insulating coating for kilns provided by Example 1 was constructed and tested on the kiln head hood (steel material) of the rotary kiln in Ruyang Zhonglian Cement Factory and has been in use ever since. Among them, the total thickness of the coating is about 15 mm. From August 28th to September 3rd, 2022, when the internal temperature of the kiln and the surface temperature of the coating are as shown in Table 8 below. The internal temperature of the kiln and the surface temperature of the coating were measured using a precision temperature measuring gun.

[0100] Among them, the specific construction process of the high-temperature resistant and heat-insulating coating for kilns provided by Example 1 includes the following steps:

[0101] Application of the primer: First, completely dissolve 2.0 modulus sodium silicate in water according to the mass ratio of primer to water of 1:0.3 and let it stand; then add other components and stir evenly to form a primer slurry; then construct the primer slurry on the surface of the steel shell of the kiln to form a primer film;

[0102] Application of the topcoat: First, completely dissolve 2.0 modulus sodium silicate in water according to the mass ratio of the topcoat to water of 1:0.7, and let it stand; then add other components and stir evenly to form a topcoat slurry; then apply the topcoat slurry on the surface of the bottom coating film to form a topcoat film.

[0103] Table 8 Actual application effect table of high-temperature heat-insulating coating for kiln

[0104] Kiln temperature (°C) Surface temperature (°C) 200～300 130～145 400～500 220～245 Above 800 440～460

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or perform equivalent replacements on some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered by the scope of the technical solutions claimed by the present invention.

Claims

1. A high-temperature resistant thermal insulation coating for kilns, characterized in that: It includes a primer and a topcoat. Among them, the primer is a two-component coating, including component A and component B. By mass, component A mainly consists of 20 - 25 of sodium silicate with a modulus of 2.0, and component B mainly consists of 15 - 20 of metakaolin, 10 - 15 of mineral powder, 5 - 10 of quartz sand with a mesh size of 200, 15 - 30 of quartz sand with a mesh size of 80 - 120, and 10 - 30 of quartz sand with a mesh size of 40 - 80. The topcoat is a two-component coating, including component A and component B. By mass, component A mainly consists of 20 - 25 of sodium silicate with a modulus of 2.0, and component B mainly consists of 10 - 20 of metakaolin, 10 - 15 of mineral powder, 5 - 10 of expanded vermiculite, 15 - 30 of expanded perlite, 10 - 20 of diatomite zeolite mixed modifier, 0.5 - 1 of air-entraining agent, and 0.5 - 1 of basalt fiber. Among them, the diatomite zeolite mixed modifier is mainly prepared by the following method: Mixed calcination: First, diatomite powder with a mesh size above 600 and zeolite powder with a mesh size above 400 are rapidly stirred in a high-speed mixing modifier until fully mixed to obtain a mixed raw material. Then, the mixed raw material is calcined at a temperature of 400°C - 450°C to form a porous material powder body, and after cooling and drying, impurity removal treatment is carried out. Secondary modification: The porous material powder body after impurity removal treatment is added into the high-speed mixing modifier again, and stearic acid is added and rapidly stirred until the temperature of the high-speed mixing modifier rises to 70 - 80°C. After cooling and drying, the diatomite zeolite mixed modifier is obtained.

2. The heat-insulating coating according to claim 1, characterized in that: The mass ratio of the mineral powder to metakaolin in both the topcoat and the primer is 1:1 - 2.

3. The heat-insulating paint according to claim 2, wherein: The ratio of the mass of sodium silicate with a modulus of 2.0 to the total mass of metakaolin and mineral powder in both the topcoat and the primer is 1:1.

5.

4. The heat-insulating coating according to any one of claims 1 to 3, characterized in that: In the step of the mixed calcination, the mass ratio of the diatomite powder to the zeolite powder is 1:0.9 - 1.3, and the calcination time is 1 - 3 h.

5. The heat-insulating paint according to any one of claims 1 to 3, characterized in that: In the step of the secondary modification, the addition amount of stearic acid is 1 - 2% of the total mass of the diatomite powder and the zeolite powder.

6. A preparation method of the heat-insulating coating according to any one of claims 1 - 5, including the following steps: Preparation of the primer: First, metakaolin and mineral powder are mixed evenly to obtain a first mixed material. Then, the first mixed material, quartz sand with a mesh size of 200, quartz sand with a mesh size of 80 - 200, and quartz sand with a mesh size of 40 - 80 are mixed evenly to prepare component B of the primer. Component A of the primer mainly consists of sodium silicate with a modulus of 2.

0. Preparation of the topcoat: First, metakaolin, mineral powder, diatomite zeolite mixed modifier, air-entraining agent, and basalt fiber are evenly mixed to form a second mixed material. Then, the second mixed material, expanded vermiculite, and expanded perlite are mixed to obtain component B of the evenly mixed topcoat. Component A of the topcoat mainly consists of sodium silicate with a modulus of 2.

0.

7. The preparation method according to claim 6, characterized in that: In the step of preparing the primer, first mix and stir metakaolin and ore powder at a speed of 1000 - 1500 revolutions per minute to form the first mixture; mix and stir the first mixture, 200 - mesh quartz sand, 80 - 200 - mesh quartz sand, and 40 - 80 - mesh quartz sand at a speed of 20 - 40 revolutions per minute to obtain the B component of the primer. In the step of preparing the topcoat, first mix and stir metakaolin, ore powder, diatomite zeolite mixed modifier, air-entraining agent, and basalt fiber at a speed of 1000 - 1800 revolutions per minute, then add expanded vermiculite and expanded perlite and stir at a speed of 20 - 40 revolutions per minute to obtain the B component of the topcoat.

8. Application of the heat-insulating coating according to any one of claims 1 - 4, comprising the steps: Application of the primer: First, completely dissolve its A component in water according to the mass ratio of primer to water of 1:0.3, and let it stand; then add its B component and stir evenly to form a primer slurry; then apply the primer slurry on the surface of the metal shell of the kiln furnace to form a primer film. Application of the topcoat: First, completely dissolve its A component in water according to the mass ratio of topcoat to water of 1:0.7, and let it stand; then add its B component and stir evenly to form a topcoat slurry; then apply the topcoat slurry on the surface of the primer film to form a topcoat film.

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