High-temperature-resistant high-silicon precoated sand for casting and preparation method thereof

Abstract

The present application relates to a kind of high-temperature-resistant high-silicon precoated sand for casting and its preparation method, wherein the precoated sand includes the following components by mass: high-silicon sand 100-200 parts, natural iron ore sand 5-10 parts, slightly ceramicized phenolic resin 1-5 parts, high-temperature-resistant spherical graphite powder 0.1-1 part, silane coupling agent 3-7 parts, urotropine 0.02-2 parts, and calcium stearate 0.05-0.5 part. In the present application, special proportioned natural mineral powder is added to modify the phenolic resin binder, and the heat resistance of the resin is improved through slight ceramicization during the casting process. Spherical graphite powder is selected as the heat conductor, which has high thermal conductivity, can strengthen the heat transfer in the mold, expand the heat affected zone, improve the thermal strength of the precoated sand, avoid the shell defect during the molding process, and at the same time, the improved heat dissipation capacity can also make the resin carbonize completely and improve the collapsibility of the precoated sand. The precoated sand has the advantages of high-temperature resistance, erosion resistance, small product surface roughness, simple manufacturing process, and excellent process performance, etc., which can effectively improve the product quality and production efficiency of the manufacturer.

Description

Technical Field

[0001] This invention relates to the field of casting materials technology, and in particular to a high-temperature resistant, high-silica coated sand for casting and its preparation method. Background Technology

[0002] With the rapid development of society and economy, the application fields of steel materials are becoming increasingly widespread. As one of the most important materials in the foundry industry, coated sand, in terms of its quality such as collapsibility and gas generation, has a significant impact on castings.

[0003] Currently, the aggregates used in the preparation of high-temperature resistant coated sand are generally silica sand, zirconia sand, and zircon sand. However, silica sand has a large angular coefficient and poor fluidity, which consumes a large amount of binder during the production of coated sand; zirconia sand has a small angular coefficient and an overall shape similar to a sphere, but its production cost is high and it causes significant environmental pollution; zircon sand has excellent comprehensive performance, but it is expensive and also has a large angular coefficient.

[0004] Adhesives are polymeric materials that can bond two different materials together. In recent years, the application of synthetic adhesives in aerospace, electronics, automotive, and machinery manufacturing fields has hindered their development. Therefore, higher performance requirements have been placed on synthetic adhesives, especially in terms of high-temperature resistance. Phenolic resins hold a very important position in the field of high-temperature adhesives due to their advantages such as low price, excellent mechanical properties, good heat resistance, good flame retardancy, and low smoke emission. However, the high number of rigid groups in their molecular chains and high crosslinking density result in relatively poor toughness. With the development of science and technology, many fields have placed higher demands on the comprehensive performance of phenolic resins, especially their high-temperature resistance. Therefore, how to develop phenolic resins with strong thermal stability and good mechanical properties without affecting their bonding strength has always been a focus of attention.

[0005] Chinese patent CN107262662A describes a high-temperature resistant coated sand for cast steel, formulated with Hainan silica sand, iron oxide sand, phenolic resin, curing agent, chromite powder, and lubricant. The process involves uniformly mixing iron oxide sand and Hainan silica sand, with chromite powder coating the surfaces of both. During steel pouring, the chromite powder first contacts the chromite powder, rapidly forming a steel film to effectively prevent steel penetration. After the resin film burns out, the iron oxide quickly dissipates excess heat. Utilizing the dual cooling effect of the chromite powder and iron oxide sand, an ultra-high-temperature resistant coated sand for cast steel is obtained. While the heat resistance of the coated sand prepared by this formula is improved, the slow cooling rate of large castings means the mold remains at a high temperature for extended periods. Therefore, to meet the casting requirements for large castings, the amount of iron oxide added needs to be increased. However, excessive iron oxide addition can affect the room temperature strength of the coated sand core and reduce its collapsibility.

[0006] Chinese patent CN114367629A uses 90-96% high-silica recycled sand and 4-10% natural iron ore sand as aggregates, and phenolic resin modified with isopropyltriphenyl phosphate, combined with high-temperature resistant additives and graphite to formulate a high-temperature resistant coated sand. The high-silica recycled sand and natural iron ore sand are mixed evenly, and then graphite, high-temperature resistant additives, modified phenolic resin, curing agent, and lubricant are added sequentially. After mixing evenly, the mixture is crushed and sieved. The phenolic resin is modified with isopropyltriphenyl phosphate, which catalyzes the thermo-oxidative crosslinking reaction of the polymer, forming a carbonized film on the polymer surface. This weakens the heat and mass transfer effects during material combustion, providing a flame-retardant effect during high-temperature resin combustion, giving the resin characteristics of flame resistance and high strength. Although the heat resistance of the coated sand prepared by the above formula is improved, the graphite used is earthy graphite or ordinary flake graphite. While this can improve the heat resistance of the coated sand to a certain extent, it greatly reduces the bonding effect of the resin binder, thereby weakening the room temperature strength of the mold. Summary of the Invention

[0007] The purpose of this invention is to provide a high-temperature resistant, high-silica coated sand for casting and its preparation method. This high-temperature resistant coated sand is modified by adding natural mineral powder to a resin binder, forming a slightly ceramicized structure during casting and creating an easily peelable buffer glass layer with the surface quartz sand. This significantly improves the surface quality of the casting while meeting high-temperature resistance requirements. By selecting spherical graphite micropowder as a thermal conductive agent, its narrow particle size distribution, small angular coefficient, easy dispersion without tearing the matrix, and high thermal conductivity allow for a significant increase in thermal conductivity with a small amount of addition. This enhances heat transfer in the mold, expands the heat-affected zone, improves the hot strength of the coated sand, and avoids shelling defects during the mold (core) process. Simultaneously, improved heat dissipation also ensures complete resin carbonization and improves the collapsibility of the coated sand.

[0008] This invention provides a high-temperature resistant, high-silica coated sand for casting, comprising the following components in parts by weight: 100-200 parts high-silica sand, 5-10 parts natural iron ore sand, 1-5 parts slightly ceramizable phenolic resin, 0.1-1 parts high-temperature resistant spherical graphite powder, 3-7 parts silane coupling agent, 0.02-2 parts hexamethylenetetramine, and 0.05-0.5 parts calcium stearate.

[0009] Furthermore, the particle size of the high-temperature resistant spherical graphite powder is 0.1-50 micrometers.

[0010] Furthermore, the silane coupling agent contains epoxy groups.

[0011] Furthermore, the method for preparing the high-silica sand is as follows:

[0012] (1) Acid washing is performed on silica sand with a silica content of 98% or more to remove mud and impurities;

[0013] (2) Wash the pickled silica sand with water to remove the acid detergent;

[0014] (3) The washed silica sand is calcined at a temperature of 500-800℃ for 25-35 minutes to obtain the high silica sand.

[0015] Furthermore, the silica sand mentioned in step (1) is Hainan high silica sand with a mesh size of 70 to 270 mesh.

[0016] Furthermore, the method for preparing the slightly ceramic-modified resin is as follows:

[0017] 1) Dissolve phenolic resin in anhydrous ethanol to obtain a phenolic resin solution;

[0018] 2) Place the obtained phenolic resin solution into an ultrasonic disperser, and simultaneously add composite ceramic powder, high-temperature resistant spherical graphite powder, flux and silane coupling agent in proportion. While mechanically stirring, perform ultrasonic dispersion to make the materials mix evenly and obtain a homogeneous slurry.

[0019] 3) Place the homogeneous slurry into a constant temperature forced-air drying oven to remove the solvent and obtain gel resin;

[0020] 4) The gel resin is placed in a melt granulator for granulation to obtain granular phenolic resin that can be slightly ceramicized.

[0021] Further, the composite ceramic powder mentioned in step 2) is a natural mineral powder such as kaolin, microcrystalline muscovite, and talc, as well as one or more of MgO, Al2O3, and SiO2 powders, with a particle size of 0.1-50 micrometers; the flux is one or more of B2O3, Fe2O3, Bi2O3, K2O, and Na2O, with a particle size of 0.1-50 micrometers; and the high-temperature resistant spherical graphite powder has a particle size of 0.1-50 micrometers.

[0022] Furthermore, in step 2), the ultrasonic disperser has a frequency of 35 kHz, an ultrasonic dispersion time of 15–60 min, and a temperature of 50 °C; the constant temperature drying oven has a temperature of 80 °C.

[0023] The present invention also provides a method for preparing the aforementioned high-temperature resistant, high-silica coated sand for casting, comprising the following steps:

[0024] Step 1: After preheating the high silica sand and natural iron ore sand to 120-130°C, put them into a sand mixer together with the silane coupling agent and stir.

[0025] Step 2: After the materials are mixed evenly, add the slightly ceramicizable phenolic resin and hexamethylenetetramine to the sand mixer and stir.

[0026] Step 3: After the materials are mixed evenly, add calcium stearate and stir to obtain coated sand particles;

[0027] Step 4: Crush and sieve the obtained coated sand particles, and cool them to room temperature to obtain high-temperature resistant coated sand.

[0028] Furthermore, the stirring time in step 1 is 10-20 seconds, the stirring time in step 2 is 60-70 seconds, and the stirring time in step 3 is 30-40 seconds.

[0029] By employing the above-mentioned scheme, and through the preparation method of high-temperature resistant, high-silica coated sand for casting, a specially formulated ratio of natural mineral powder is added to the phenolic resin binder for modification. This modification enhances the resin's heat resistance through slight ceramization during the casting process. Spherical graphite micropowder is selected as the thermal conductivity agent. Its narrow particle size distribution, small angular coefficient, easy dispersion without damaging the matrix, and high thermal conductivity allow for significant improvement in thermal conductivity with a small addition amount. This strengthens heat transfer in the mold, expands the heat-affected zone, improves the hot strength of the coated sand, and avoids shelling defects during the mold (core) process. Simultaneously, improved heat dissipation also ensures complete resin carbonization and improves the collapsibility of the coated sand. This coated sand possesses advantages such as high temperature resistance, erosion resistance, low surface roughness, simple manufacturing process, and excellent process performance, effectively improving product quality and production efficiency for manufacturers.

[0030] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in further detail below with reference to the examples. These examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] This embodiment provides a high-temperature resistant, high-silica coated sand for casting, comprising the following components in parts by weight: 100-200 parts high-silica sand, 5-10 parts natural iron ore sand, 1-5 parts slightly ceramizable phenolic resin, 0.1-1 parts high-temperature resistant spherical graphite powder, 3-7 parts silane coupling agent, 0.02-2 parts hexamethylenetetramine, and 0.05-0.5 parts calcium stearate.

[0033] In this embodiment, the particle size of the high-temperature resistant spherical graphite powder is 0.1-50 micrometers.

[0034] In this embodiment, the silane coupling agent contains epoxy groups.

[0035] In this embodiment, the method for preparing high-silica sand is as follows:

[0036] (1) Acid washing is performed on silica sand with a silica content of 98% or more to remove mud and impurities;

[0037] (2) Wash the pickled silica sand with water to remove the acid detergent;

[0038] (3) The washed silica sand is calcined at a temperature of 500-800℃ for 25-35 minutes to obtain the high silica sand.

[0039] In this embodiment, the silica sand mentioned in step (1) is Hainan high silica sand with a mesh size of 70 to 270.

[0040] In this embodiment, the method for preparing the slightly ceramic-modified resin is as follows:

[0041] 1) Dissolve phenolic resin in anhydrous ethanol to obtain a phenolic resin solution;

[0042] 2) Place the obtained phenolic resin solution into an ultrasonic disperser, and simultaneously add composite ceramic powder, high-temperature resistant spherical graphite powder, flux and silane coupling agent in proportion. While mechanically stirring, perform ultrasonic dispersion to make the materials mix evenly and obtain a homogeneous slurry.

[0043] 3) Place the homogeneous slurry into a constant temperature forced-air drying oven to remove the solvent and obtain gel resin;

[0044] 4) The gel resin is placed in a melt granulator for granulation to obtain granular phenolic resin that can be slightly ceramicized.

[0045] In this embodiment, the composite ceramic powder in step 2) is a natural mineral powder such as kaolin, microcrystalline muscovite, and talc, as well as one or more of MgO, Al2O3, and SiO2 powders, with a particle size of 0.1-50 micrometers; the flux is one or more of B2O3, Fe2O3, Bi2O3, K2O, and Na2O, with a particle size of 0.1-50 micrometers; and the high-temperature resistant spherical graphite powder has a particle size of 0.1-50 micrometers.

[0046] In this embodiment, the ultrasonic disperser in step 2) has a frequency of 35 kHz, an ultrasonic dispersion time of 15–60 min, and a temperature of 50 °C; the constant temperature drying oven has a temperature of 80 °C.

[0047] This embodiment also provides a method for preparing the aforementioned high-temperature resistant, high-silica coated sand for casting, comprising the following steps:

[0048] Step 1: After preheating the high silica sand and natural iron ore sand to 120-130°C, put them together with the silane coupling agent into a sand mixer for stirring; the stirring time is 10-20 seconds.

[0049] Step 2: After the materials are mixed evenly, add the slightly ceramicizable phenolic resin and hexamethylenetetramine to the sand mixer and stir for 60-70 seconds.

[0050] Step 3: After the materials are mixed evenly, add calcium stearate and stir to obtain coated sand particles; the stirring time is 30-40 seconds.

[0051] Step 4: Crush and sieve the obtained coated sand particles, and cool them to room temperature to obtain high-temperature resistant coated sand.

[0052] Slightly ceramization phenolic resin can undergo a slight ceramization reaction in the high-temperature environment of casting, forming an easily peelable buffer glass layer on the surface of the mold. This not only improves the heat resistance of the mold, but also prevents the molten steel from washing away and cracking the mold, thus avoiding surface quality problems such as sand adhesion and veins in the casting.

[0053] Spherical graphite powder possesses advantages such as good sphericity, good dispersibility, and good thermal conductivity. Using spherical graphite powder to modify phenolic resin can significantly improve the thermal conductivity of the resin, thereby enhancing heat transfer in the mold, expanding the heat-affected zone, improving the hot strength of the coated sand, and avoiding shell-shedding defects during the mold (core) making process. While meeting the high-temperature resistance requirements of the mold and sand core, it also improves the internal heat transfer efficiency of the material.

[0054] The ceramic powder used in the following examples and comparative examples is prepared by mixing kaolin, microcrystalline muscovite, talc powder, and Al2O3 powder in a mass ratio of 3:3:4:2.

[0055] The preparation methods of the slightly ceramizable modified resins used in the following examples and comparative examples are as follows:

[0056] (1) Add 100 kg of phenolic resin to 100 kg of ethanol to obtain 200 kg of phenolic resin solution;

[0057] (2) Place the material obtained in step (1) into an ultrasonic mixer, and add 10 kg of ceramic composite powder, 5 kg of high temperature resistant spherical graphite powder and 1.5 kg of flux at the same time. Perform ultrasonic dispersion and mechanical stirring to make the material mix evenly and obtain a homogeneous slurry.

[0058] (3) The homogeneous slurry was placed in an 80℃ constant temperature forced-air drying oven to remove the solvent and obtain gel resin;

[0059] (4) The gel resin is placed in a melt granulator for granulation to obtain granular phenolic resin that can be slightly ceramicized.

[0060] In the following examples, aggregates were prepared using 100-mesh high-silica sand and 100-mesh natural iron ore sand; phenolic resin was purchased from Shandong Shengquan Group; the curing agent was hexamethylenetetramine; the ultra-high temperature ceramic powder was obtained by mixing one or more of kaolin, microcrystalline mica, talc, MgO, Al2O3, and SiO2 powders in a certain proportion; the flux was one or more of B2O3, Fe2O3, Bi2O3, K2O, and Na2O; the lubricant was 400-mesh calcium stearate; the graphite powder was 200-mesh spherical graphite powder; and the silane coupling agent was purchased from Anhui Sibao Organosilicon New Materials Co., Ltd., model KH-560. Hot tensile strength, room temperature tensile strength, hot flexural strength, room temperature flexural strength, gas evolution, and curing rate were tested according to JB / T 8583; particle size AFS was tested according to GB / T2684; and high temperature resistance time and high temperature expansion were tested according to T / CFA 010604.1.

[0061] Example 1

[0062] The manufacturing process of the high-temperature resistant coated sand in this embodiment is as follows:

[0063] (1) Weigh 475 kg of high silica sand and 25 kg of natural iron ore sand, and heat them to 150°C;

[0064] (2) Add the aggregate at 150℃ into the sand mixer, and at the same time add 5kg of silane coupling agent and 5kg of high temperature resistant spherical graphite powder and stir for 14s.

[0065] (3) Add 15kg of slightly ceramizable phenolic resin, 1.6kg of flux and 0.5kg of hexamethylenetetramine into the mixing equipment and stir for 64s to make the ceramizable phenolic resin completely mixed with the flux and curing agent.

[0066] (4) After the materials are completely mixed evenly, add 0.1 kg of calcium stearate and stir for 34 seconds to disperse the lumps and form coated particles;

[0067] (5) After the sand is mixed, it is crushed and sieved three times and cooled to room temperature to obtain high temperature resistant coated sand.

[0068] Example 2

[0069] The manufacturing process of the high-temperature resistant coated sand in this embodiment is as follows:

[0070] (1) Weigh 475 kg of high silica sand and 25 kg of natural iron ore sand, and heat them to 150°C;

[0071] (2) Add the aggregate at 150℃ into the sand mixer, and at the same time add 5kg of silane coupling agent and 10kg of high temperature resistant spherical graphite powder and stir for 14s.

[0072] (3) Add 15kg of slightly ceramizable phenolic resin, 1.6kg of flux and 0.5kg of hexamethylenetetramine into the mixing equipment and stir for 64s to make the ceramizable phenolic resin completely mixed with the flux and curing agent.

[0073] (4) After the materials are completely mixed evenly, add 0.1 kg of calcium stearate and stir for 34 seconds to disperse the lumps and form coated particles;

[0074] (5) After the sand is mixed, it is crushed and sieved three times and cooled to room temperature to obtain high temperature resistant coated sand.

[0075] Example 3

[0076] The manufacturing process of the high-temperature resistant coated sand in this embodiment is as follows:

[0077] (1) Weigh 475 kg of high silica sand and 25 kg of natural iron ore sand, and heat them to 150°C;

[0078] (2) Add the aggregate at 150℃ into the sand mixer, and at the same time add 5kg of silane coupling agent and 15kg of high temperature resistant spherical graphite powder and stir for 14s.

[0079] (3) Add 15kg of slightly ceramizable phenolic resin, 1.6kg of flux and 0.5kg of hexamethylenetetramine into the mixing equipment and stir for 64s to make the ceramizable phenolic resin completely mixed with the flux and curing agent.

[0080] (4) After the materials are completely mixed evenly, add 0.1 kg of calcium stearate and stir for 34 seconds to disperse the lumps and form coated particles;

[0081] (5) After the sand is mixed, it is crushed and sieved three times and cooled to room temperature to obtain high temperature resistant coated sand.

[0082] Example 4

[0083] The manufacturing process of the high-temperature resistant coated sand in this embodiment is as follows:

[0084] (1) Weigh 475 kg of high silica sand and 25 kg of natural iron ore sand, and heat them to 150°C;

[0085] (2) Add the aggregate at 150℃ into the sand mixer, and at the same time add 5kg of silane coupling agent and 20kg of high temperature resistant spherical graphite powder and stir for 14s.

[0086] (3) Add 15kg of slightly ceramizable phenolic resin, 1.6kg of flux and 0.5kg of hexamethylenetetramine into the mixing equipment and stir for 64s to make the ceramizable phenolic resin completely mixed with the flux and curing agent.

[0087] (4) After the materials are completely mixed evenly, add 0.1 kg of calcium stearate and stir for 34 seconds to disperse the lumps and form coated particles;

[0088] (5) After the sand is mixed, it is crushed and sieved three times and cooled to room temperature to obtain high temperature resistant coated sand.

[0089] Comparative Example 1

[0090] The only difference between Comparative Example 1 and Example 1 is that earthy graphite powder is used in step (2).

[0091] Comparative Example 2

[0092] The only difference between Comparative Example 2 and Example 2 is that unmodified phenolic resin was used in step (3). Table 1 shows the performance parameters of the examples and comparative examples.

[0093] Table 1 Performance parameters of the examples and comparative examples

[0094]

[0095]

[0096] As shown in Table 1, compared to the comparative example, the embodiments of the present invention exhibit higher hot tensile strength, room temperature tensile strength, hot flexural strength, room temperature flexural strength, curing rate, and high-temperature resistance. This is because after the natural high-silica sand undergoes calcination, impurities such as crystal water and oxides mixed in the natural high-silica sand are removed, and the high-temperature calcination causes a phase change in the sand particles, improving the quality of the original sand and reducing its linear expansion rate. The phenolic resin is modified with composite ceramic powder, which can undergo a slight ceramization reaction under the high-temperature environment of casting, forming an easily peelable buffer glass layer on the mold surface. This not only improves the heat resistance of the mold but also prevents the molten steel from eroding and cracking the mold, avoiding surface quality problems such as sand adhesion and veining in the casting. Spherical graphite micro powder is selected as a thermal conductive agent. It has a narrow particle size distribution range and a small angular coefficient, making it easy to disperse without cutting the matrix. It has high thermal conductivity, and a small amount of addition can significantly improve thermal conductivity. It can enhance heat transfer in the mold, expand the heat-affected zone, improve the hot strength of the coated sand, and avoid shelling defects in the mold (core) process. At the same time, it can improve heat dissipation capacity, make the resin carbonize completely, and improve the collapsibility of the coated sand.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-temperature resistant, high-silica coated sand for casting, characterized in that, Includes the following steps: Step 1: Weigh out high-silica sand and natural iron ore sand, and heat them to 150°C; Step 2: Add aggregates at 150°C into the sand mixer, and simultaneously add silane coupling agent and high-temperature resistant spherical graphite powder and stir. Step 3: Add the slightly ceramizable phenolic resin, flux, and hexamethylenetetramine into the mixing equipment and stir to completely mix the ceramizable phenolic resin with the flux and curing agent. Step 4: After the materials are completely and evenly mixed, add calcium stearate and stir to disperse the lumps and form coated particles. Step 5: After the sand is mixed, it is crushed and sieved three times, and then cooled to room temperature to obtain high-temperature resistant coated sand. The high-temperature resistant coated sand includes the following components in parts by weight: 100-200 parts of high silica sand, 5-10 parts of natural iron ore sand, 1-5 parts of slightly ceramizable phenolic resin, 0.1-1 parts of high-temperature resistant spherical graphite powder, 3-7 parts of silane coupling agent, 0.02-2 parts of hexamethylenetetramine, and 0.05-0.5 parts of calcium stearate. The stirring time in step 2 is 10-20 seconds, the stirring time in step 3 is 60-70 seconds, and the stirring time in step 4 is 30-40 seconds. The method for preparing high-silica sand is as follows: (1) Acid washing is performed on silica sand with a silica content of more than 98% to remove mud and impurities; the silica sand is Hainan high silica sand with a mesh size of 70~270 mesh; (2) Wash the pickled silica sand with water to remove the acid detergent; (3) The washed silica sand is roasted at a temperature of 500~800℃ for 25~35min to obtain the high silica sand. The method for preparing the slightly ceramic-modified resin is as follows: 1) Dissolve phenolic resin in anhydrous ethanol to obtain a phenolic resin solution; 2) The obtained phenolic resin solution is placed in an ultrasonic disperser, and composite ceramic powder, high-temperature resistant spherical graphite powder, flux, and silane coupling agent are added in proportion. Ultrasonic dispersion is performed while mechanical stirring to ensure uniform mixing and obtain a homogeneous slurry. The composite ceramic powder is one or more of the following: kaolin, microcrystalline mica, talc, MgO, Al2O3, and SiO2 powders, with a particle size of 0.1-50 micrometers. The flux is B2O3 or Fe2O3. 3、 One or more of Bi2O3, K2O, and Na2O, with a particle size of 0.1-50 micrometers; the high-temperature resistant spherical graphite powder has a particle size of 0.1-50 micrometers; the ultrasonic disperser has a frequency of 35 kHz, an ultrasonic dispersion time of 15-60 min, and a temperature of 50°C. 3) The homogeneous slurry is placed in a constant temperature forced-air drying oven to remove the solvent, thereby obtaining gel resin; the temperature of the constant temperature forced-air drying oven is 80℃; 4) The gel resin is placed in a melt granulator for granulation to obtain granular phenolic resin that can be slightly ceramicized.

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