An inorganic potassium silicate-based heat-insulating coating for high-temperature resistant stainless steel and its preparation method

Abstract

This invention discloses an inorganic potassium silicate-based heat-insulating coating for high-temperature resistant stainless steel and its preparation method. The key technical points are: 40%–50% potassium silicate solution, 1%–3% fumed silica, 15%–25% calcined kaolin, 10%–15% hollow ceramic microspheres, 5%–10% silica sol, and 10%–20% deionized water. The preparation method includes: liquid premixing; distribution thickening; filler dispersion; microsphere mixing; and adjustment filtration. This invention, by using a completely inorganic potassium silicate and silica composite, without any organic components, completely solves the problem of high-temperature carbonization failure of organic coatings.

Description

Technical Field

[0001] This invention relates to the field of high-temperature protective coating technology, and in particular to an inorganic potassium silicate-based heat-insulating coating for high-temperature resistant stainless steel and its preparation method. Background Technology

[0002] Stainless steel, with its excellent mechanical properties, corrosion resistance, and processing performance, is widely used in core components such as high-temperature containers, pipes, and heat exchange equipment in industries such as power generation, petrochemicals, high-temperature food processing, and industrial heat treatment. These stainless steel equipment operate in environments with long-term high-temperature and alternating hot and cold cycles. Excessive surface temperature not only causes significant heat loss and reduces thermal efficiency but also accelerates high-temperature oxidation and thermal fatigue damage to the stainless steel substrate, drastically shortening the equipment's lifespan. Furthermore, it poses safety hazards such as burns from high temperatures and equipment overload failure.

[0003] Currently, the mainstream high-temperature insulation coatings on the market are mainly divided into two categories: silicone resin-based high-temperature coatings and ordinary inorganic silicate high-temperature coatings. However, both types of products have obvious shortcomings under high-temperature conditions of 600℃ and cannot meet the requirements for long-term stable protection.

[0004] Among them, the upper limit of temperature resistance of silicone resin-based coatings is generally lower than 400℃. When the operating temperature reaches 600℃, the organic resin components inside the coating will undergo rapid thermal decomposition, carbonization, and powdering reactions, resulting in overall cracking and peeling of the coating, completely losing its heat insulation and protection functions. It is only suitable for medium and low temperature protection scenarios and cannot be adapted to high temperature operating conditions.

[0005] Ordinary inorganic silicate coatings are entirely inorganic systems, and their high-temperature resistance is better than that of organic coatings. They can withstand temperatures above 500°C. However, the thermal expansion coefficients of these coatings are poorly matched with those of stainless steel substrates. Under the thermal cycling conditions of high-temperature heating and low-temperature cooling, huge thermal stress will be generated between the coating and the substrate, eventually leading to cracking, peeling, and blistering of the coating, resulting in extremely poor protective stability.

[0006] A new solution is proposed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an inorganic potassium silicate-based thermal insulation coating and its preparation method, which is entirely inorganic, has a coefficient of thermal expansion that is highly compatible with that of stainless steel, exhibits excellent adhesion, can withstand long-term high-temperature conditions up to 600℃, and has stable thermal insulation performance. This solves the problems of high-temperature failure, easy peeling, and large batch-to-batch performance differences of traditional coatings, and meets the industrial needs for long-term thermal insulation protection of stainless steel high-temperature equipment.

[0008] The above-mentioned technical objective of the present invention is achieved through the following technical solution: comprising 40%~50% potassium silicate solution, 1%~3% fumed silica, 15%~25% calcined kaolin, 10%~15% hollow ceramic microspheres, 5%~10% silica sol; 10%~20% deionized water, wherein the conductivity of the deionized water is less than 5μS / cm, the modulus of the potassium silicate solution is 2.8-3.2, and the particle size of the hollow ceramic microspheres is 30-60μm.

[0009] Includes the following steps:

[0010] S1. Liquid premixing: Mix a quantitative amount of potassium silicate solution with alkaline silica sol, add 50% of the total water volume of deionized water, stir at low speed until uniform, and form a stable inorganic colloidal base liquid to avoid subsequent filler agglomeration;

[0011] S2. Stepwise thickening: Add the hydrophilic fumed silica slowly to the base liquid in 3-4 batches, and do not add it all at once to prevent clumping; after each batch, shear and stir at 800-1200 rpm for 3 minutes until there are no dry powder lumps in the system and the whole is uniform. Stepwise high-speed dispersion achieves coating thickening and anti-sagging effects, and improves the suspension stability of the system.

[0012] S3. Filler dispersion: Add a certain amount of high-temperature calcined kaolin to the thickened system, stir continuously until completely uniform, stop stirring and let stand for 5 minutes to release the stirring stress of the system, ensure uniform dispersion of filler, and optimize the dense structure of coating;

[0013] S4. Microsphere Mixing: Add hollow ceramic microspheres, adjust the stirring speed to ≤500 rpm, and use a low-speed, gentle stirring mode to mix evenly. Throughout the process, avoid high shear force to prevent damage to the hollow structure of the microspheres and preserve the heat insulation core structure to the greatest extent.

[0014] S5. Adjusting the filtration: Use the remaining 50% deionized water to adjust the overall viscosity of the coating and control the viscosity at the Coating Cup 4.

[0015] The temperature is adjusted for 30-40 seconds; after adjustment, impurities and trace agglomerates are filtered through an 80-100 mesh sieve. After filtration, the mixture is left to stand for 15 minutes to complete the curing process, resulting in the finished heat-insulating coating.

[0016] Substrate surface treatment: The stainless steel substrate surface is sandblasted to achieve a cleanliness level of Sa2.0 or higher, with a surface roughness controlled between Ra6 and 12μm. This removes oxide scale, oil, and impurities from the substrate surface. To avoid secondary oxidation of the substrate, the coating operation is completed within 4 hours after the sandblasting treatment.

[0017] Pre-treatment: Before applying the main coating, a 5% concentration of silica sol dilution is sprayed onto the surface of the stainless steel substrate as a primer to further enhance the interfacial bonding between the main coating and the stainless steel substrate and eliminate interfacial stress.

[0018] Stepped vacuum oven high-temperature curing program: Employs a gradient temperature curing mode, strictly controlling the heating rate.

[0019] ≤5℃ / min, specific process: stand at room temperature → keep warm at 60℃ for 30min → keep warm at 150℃ for 30min → keep warm at 300℃ for 30min → keep warm at 600℃ for 30min. Gradually evaporate the moisture in the system and solidify the film by stepping up the temperature to avoid rapid heating that may cause the coating to blister, crack, or peel off.

[0020] In summary, the present invention has the following beneficial effects:

[0021] 1. It adopts a composite of inorganic potassium silicate and silicon dioxide, without any organic components, which completely solves the problem of high-temperature carbonization failure of organic coatings. After testing, the coating can be continuously aged at 600℃ for 100 hours without powdering, cracking or peeling. It has extremely strong high-temperature structural stability and can be adapted to 600℃ high-temperature working conditions for a long time.

[0022] 2. Excellent substrate adhesion and strong thermal shock resistance. Through silica sol primer pretreatment and formula optimization, the difference in thermal expansion coefficient between the coating and the stainless steel substrate is greatly reduced, and the interfacial bonding force is significantly improved. Using the cross-cut test, the coating adhesion reaches the 0-level standard. After 10 cycles of 600℃-room temperature cold and hot cycle tests, the coating did not peel off or crack, and the thermal shock resistance is excellent.

[0023] 3. The low-speed, gentle stirring process protects the intact hollow structure of the hollow ceramic microspheres, and a large number of closed heat-insulating pores can be formed inside the coating to effectively block heat transfer. The thermal conductivity of the finished coating is ≤0.08 W / (m·K), with excellent heat insulation effect and stable performance.

[0024] 4. The preparation process parameters are clear, quantifiable, and easy to replicate industrially. The coating and curing process is simple, suitable for on-site coating operations of various stainless steel high-temperature containers or pipes, and has high industrial application value. Attached Figure Description

[0025] Figure 1 This is a flow chart of the heat-insulating coating preparation process of the present invention;

[0026] Figure 2 This is a flow chart of the coating and curing process of the present invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0028] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "set up / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] The present invention will now be described in detail with reference to the accompanying drawings.

[0031] An inorganic potassium silicate-based heat-insulating coating for high-temperature resistant stainless steel and its preparation method, such as Figure 1 As shown, the composition includes 40%~50% potassium silicate solution, 1%~3% fumed silica (hydrophilic type, with excellent anti-sagging and thickening effects, improving coating suspension stability), 15%~25% calcined kaolin (≥1200℃ calcination grade, high purity, high temperature resistance, good filling properties, optimizing coating density), 10%~15% hollow ceramic microspheres, 5%~10% silica sol (SiO2 content 30%, alkaline, improving coating adhesion to stainless steel substrate), and 10%~20% deionized water (conductivity less than 5μS / cm, free of calcium and magnesium ions, ensuring coating system stability). The potassium silicate solution has a modulus of 2.8-3.2, serving as the main film-forming component, ensuring coating high temperature resistance and film-forming properties. The hollow ceramic microspheres have a particle size of 30-60μm and a hollow structure, providing core thermal insulation performance for the coating.

[0032] Specific implementation method: Accurately weigh each raw material according to the standard formula for 1000g of finished coating: 450g of potassium silicate solution with modulus 3.0, 80g of alkaline silica sol with SiO2 content of 30%, 150g of deionized water with conductivity <5μS / cm, 20g of hydrophilic fumed silica A200, 180g of calcined kaolin at 1250℃, and 120g of hollow ceramic microspheres with a particle size of 40-50μm.

[0033] Preparation process: First, mix potassium silicate solution with silica sol, add 75g of deionized water and stir at low speed for 2 minutes to complete liquid premixing; add 20g of fumed silica in 3 batches, dispersing each batch at high speed of 1000r / min for 3 minutes to completely eliminate dry powder lumps; add 180g of calcined kaolin and stir evenly, then let stand for 5 minutes; finally, add hollow ceramic microspheres, adjust the speed to 400r / min and stir gently at low speed for 3 minutes to protect the integrity of the microsphere structure; use the remaining 75g of deionized water to adjust the viscosity of the coating to 35s of Forecast cup 4, filter through a 90-mesh sieve and let stand for 15 minutes to mature, obtaining the finished coating.

[0034] Coating test: 304 stainless steel plate was selected as the test substrate, sandblasted to Sa2.0 grade with a roughness of Ra8μm, and a 5% silica sol solution was sprayed as a primer within 4 hours. After drying, the main coating prepared according to this invention was sprayed on. Curing was strictly carried out according to a stepped curing procedure, with the heating rate controlled at 4℃ / min.

[0035] Test results: The cured coating surface is smooth, without bubbles or cracks; after continuous heating at 600℃ for 1 hour, the back temperature of the stainless steel plate is reduced by 85℃ compared to the bare plate, showing significant heat insulation effect; after aging at 600℃ for 100 hours, the coating shows no powdering or cracking, has a cross-cut adhesion rating of 0, and does not peel off after 10 cycles of hot and cold, demonstrating excellent overall performance.

[0036] To verify the optimal addition ratio of fumed silica, a small-scale comparative experiment was conducted with the total mass of the coating reduced to 100g. The proportions of other raw materials and the preparation process were kept completely consistent. Three experimental groups were set up with fumed silica addition ratios of 1.5%, 2%, and 3%.

[0037] Experimental results: The 1.5% additive group coating had insufficient anti-sagging performance, and was prone to flow marks and wall adhesion after coating; the 3% additive group coating had excessively high viscosity, poor leveling properties, and a rough and uneven coating surface; the 2% additive group coating had both excellent leveling and anti-sagging properties, stable suspension, no layering or clumping, and the best coating effect, verifying the rationality and optimality of the 2% fumed silica ratio parameter of this invention.

[0038] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A high-temperature resistant stainless steel inorganic potassium silicate-based heat-insulating coating and its preparation method, characterized in that: The mixture comprises 40%–50% potassium silicate solution, 1%–3% fumed silica, 15%–25% calcined kaolin, 10%–15% hollow ceramic microspheres, and 5%–10% silica sol; 10%–20% deionized water, wherein the conductivity of the deionized water is less than 5 μS / cm, the modulus of the potassium silicate solution is 2.8–3.2, and the particle size of the hollow ceramic microspheres is 30–60 μm.

2. The inorganic potassium silicate-based heat-insulating coating for high-temperature resistant stainless steel and its preparation method according to claim 1, characterized in that: Includes the following steps: S1. Liquid premixing: Mix potassium silicate solution with silica sol, add 50% of the total water volume of deionized water, and stir until homogeneous to obtain the substrate mixture; S2. Stepwise thickening: Add fumed silica to the base mixture in 3-4 batches, stirring at high speed of 800-1200 rpm for 3 minutes for each batch until there are no dry powder lumps; S3. Filler dispersion: Add calcined kaolin to the thickened system, stir evenly, and let stand for 5 minutes; S4. Microbead mixing: Add hollow ceramic microbeads and gently stir at a low speed of ≤500 rpm until homogeneous; S5. Adjusting and filtering: Adjust the viscosity of the coating to 30-40 seconds using the remaining 50% deionized water. After filtering through an 80-100 mesh sieve, let it stand for 15 minutes to mature, and obtain the finished coating.

3. The inorganic potassium silicate-based heat-insulating coating for high-temperature resistant stainless steel and its preparation method according to claim 1, characterized in that: The coating is cured using a stepped curing process after application, with a total heating rate of ≤5℃ / min. The stepped curing process is as follows: after standing at room temperature, it is successively heated to 60℃ for 30min, 150℃ for 30min, 300℃ for 30min, and 600℃ for 30min.

4. The inorganic potassium silicate-based heat-insulating coating for high-temperature resistant stainless steel and its preparation method according to claim 1, characterized in that: The stainless steel substrate needs to be pretreated by sandblasting before coating.

5. The inorganic potassium silicate-based heat-insulating coating for high-temperature resistant stainless steel and its preparation method according to claim 4, characterized in that: The pretreatment method involves spraying a 5% concentration of silica sol solution onto the surface of a stainless steel substrate.

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