Resin waste sand energy-saving regenerated coated sand and preparation method thereof

Abstract

The application discloses a kind of resin waste sand energy-saving regeneration coated sand and its preparation method.The method includes: phenolic resin waste sand is broken into single particle waste sand, and is carbonized at 750-850 DEG C under hot state for 5-10 min, makes residual phenolic resin film carbonization and is not completely oxidized and decomposed, and forms the carbonized film that remains on sand grain surface, obtains 150-200 DEG C hot state regenerated sand;0.05-0.1% carbon powder is added to hot state regenerated sand and is stirred, so that carbon powder is distributed on sand grain surface, to compensate and balance carbon layer;Then it is cooled to 135-150 DEG C, and phenolic resin, urotropine aqueous solution and calcium stearate are added to carry out residual heat coated sand mixing, and it is cooled to below 50 DEG C, to obtain regenerated coated sand.The application can utilize residual resin to form carbonized film and carbon powder to improve the strength and heat resistance of coated sand, and make full use of the waste heat of hot state regenerated sand, reduce the energy consumption of coating.

Description

Technical Field

[0001] This invention relates to the field of coated sand technology, and in particular to an energy-saving recycled coated sand from resin waste sand and its preparation method. Background Technology

[0002] Sand casting is a crucial process in foundry production, accounting for a significant proportion of the industry. The casting process typically requires large quantities of molding materials such as silica sand, resin, and hardeners, generating substantial amounts of foundry waste sand after pouring and casting. This waste sand usually contains residual resin film, hardener, lubricant, dust, and other impurities. Direct landfilling or stockpiling not only occupies land resources but also easily causes soil and water pollution. Furthermore, foundry companies need to continuously purchase and consume new sand to maintain continuous production, further increasing the consumption of natural silica sand resources and production costs. Therefore, recycling foundry waste sand and reusing it in coated sand production is an important direction for achieving energy conservation, emission reduction, and resource recycling in the foundry industry.

[0003] Existing foundry waste sand recycling technologies mainly include mechanical recycling, wet recycling, and thermal recycling. Among these, thermal recycling can effectively remove residual organic matter from the surface of waste sand, but it usually requires a long period of high-temperature roasting, resulting in high energy consumption and potentially generating significant amounts of flue gas and volatile organic compound emissions. When recycled sand is reused in the production of coated sand, it often needs to be reheated to the coating temperature before adding phenolic resin, curing agent, and lubricant for mixing, further increasing the overall energy consumption of the process. In addition, conventional recycling processes often focus on removing residual resin film from the sand grain surface, failing to fully utilize the surface structure that may form after heat treatment of the residual resin film. This means that there is still room for improvement in the heat resistance, strength stability, and surface quality of the recycled coated sand. Summary of the Invention

[0004] To address the above problems, this invention proposes an energy-saving regenerated coated sand from resin waste sand and its preparation method. The phenolic resin waste sand is crushed and then subjected to short-term hot carbonization regeneration to carbonize the residual resin film and retain it on the surface of the sand particles. Then, carbon powder, phenolic resin, hexamethylenetetramine aqueous solution and calcium stearate are added using the residual heat of the hot regenerated sand to form a coating. After cooling, the regenerated coated sand is obtained.

[0005] This invention can be achieved through the following technical solutions: A method for preparing energy-saving recycled coated sand from resin waste sand includes the following steps: S1. The phenolic resin waste sand is crushed and dispersed into single particles of waste sand. The single particles of waste sand are subjected to hot carbonization regeneration treatment at 750-850℃ for 5-10 minutes, so that the residual phenolic resin film on the surface of the single particles of waste sand is carbonized rather than completely oxidized and decomposed, and a retained carbonized film is formed on the surface of the sand particles. At the same time, low melting point substances in the single particles of waste sand are removed, and hot regenerated sand at a temperature of 150-200℃ is obtained. S2. Add carbon powder accounting for 0.05 to 0.1% of the mass of the hot-state regenerated sand to the hot-state regenerated sand and stir for 3 to 9 minutes to distribute the carbon powder on the surface of the sand particles in order to compensate for and balance the carbon layer on the surface of the sand particles, thereby obtaining carbon layer-adjusted regenerated sand. S3. Cool the carbon layer-conditioned regenerated sand to 135-150°C, add 1-3 parts by weight of phenolic resin to 100 parts by weight of carbon layer-conditioned regenerated sand and mix, then add hexamethylenetetramine aqueous solution and calcium stearate and mix, use the residual heat of carbon layer-conditioned regenerated sand to evaporate the moisture, and then cool to below 50°C to obtain resin waste sand energy-saving regenerated coated sand.

[0006] Preferably, the low-melting-point substance includes at least one of residual calcium stearate, residual hexamethylenetetramine, and water.

[0007] Preferably, the mass ratio of hexamethylenetetramine to water in the hexamethylenetetramine aqueous solution is 1:2, and the effective amount of hexamethylenetetramine added is 10-15% of the mass of the phenolic resin.

[0008] Preferably, the amount of calcium stearate added is 0.5 to 0.8% of the mass of the carbon layer-adjusted regenerated sand.

[0009] Preferably, the mixing time after adding phenolic resin is 30-50 s, the mixing time after adding hexamethylenetetramine aqueous solution is 30-40 s, and the mixing time after adding calcium stearate is 40-60 s.

[0010] Preferably, steps S2 to S3 utilize the residual heat of the hot recycled sand for coating and mixing, and no additional gas heating is applied to the recycled sand during the coating and mixing process.

[0011] The beneficial effects of this invention are: This invention involves crushing phenolic resin waste sand into single particles and then briefly regenerating it through hot carbonization at 750–850°C for 5–10 minutes. This process carbonizes the residual phenolic resin film on the sand particle surface, rather than completely oxidizing and decomposing it, thus retaining and forming a carbonized film. This carbonized film fills the grooves on the sand particle surface, improving the surface morphology and enhancing the bonding strength and heat resistance of the coated sand. Simultaneously, a small amount of carbon powder is added to the hot-regenerated sand, distributing it across the sand particle surface to compensate for and balance the carbon layer on different sand particle surfaces, further improving the heat resistance stability of the coated sand under high-temperature casting conditions. Compared to conventional hot regeneration followed by coating, this invention fully utilizes the residual heat of the hot-regenerated sand, directly performing phenolic resin coating and mixing of curing agents and lubricants at 135–150°C. This eliminates the need for additional gas heating of the recycled sand during the coating mixing process, thereby reducing energy consumption and production costs. The tensile strength and high-temperature resistance time of the coated sand obtained by this invention are superior to those of the original coated sand and the conventional recycled coated sand. It can improve the dimensional stability of the sand core, reduce the high-temperature damage of the molten metal to the sand particles and resin film, reduce the risk of sand adhesion, improve the surface finish of the casting, and realize the resource utilization and high-value utilization of foundry waste sand. Attached Figure Description

[0012] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 The tensile strength and high-temperature resistance time of the coated sand. Detailed Implementation

[0013] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0014] Example 1: A method for preparing energy-saving recycled coated sand from resin waste sand, comprising the following steps: S1. Take phenolic resin waste sand, crush it to disperse it into single-particle waste sand; place the obtained single-particle waste sand in a hot carbonization regeneration device and perform hot carbonization regeneration treatment at 750℃ for 5 min, so that the residual phenolic resin film on the surface of the single-particle waste sand is carbonized rather than completely oxidized and decomposed, and a retained carbonized film is formed on the surface of the sand particles. At the same time, the residual calcium stearate, residual hexamethylenetetramine and water and other low-melting-point substances in the single-particle waste sand are removed to obtain hot regenerated sand at a temperature of 150℃. S2. Based on 100 parts by weight of the hot regenerated sand obtained in step S1, add 0.05 parts by weight of carbon powder to the hot regenerated sand and stir slowly for 3 minutes to distribute the carbon powder on the surface of the sand particles in order to compensate for and balance the carbon layer on the surface of the sand particles, and obtain carbon layer regulated regenerated sand. S3. Cool the carbon-modified regenerated sand obtained in step S2 to 135°C; add 1 part by weight of phenolic resin to 100 parts by weight of carbon-modified regenerated sand, mix for 30 seconds to coat the sand particles with phenolic resin; then add a hexamethylenetetramine aqueous solution and mix for 30 seconds, wherein the mass ratio of hexamethylenetetramine to water in the hexamethylenetetramine aqueous solution is 1:2, and the effective amount of hexamethylenetetramine added is 10% of the mass of phenolic resin, i.e., 0.1 parts by weight of hexamethylenetetramine and 0.2 parts by weight of water are added; then add 0.5 parts by weight of calcium stearate and mix for 40 seconds; during the above coating and mixing process, the residual heat of the carbon-modified regenerated sand is used to evaporate the moisture, and no additional gas heating is applied to the regenerated sand; after the mixing is completed, cool the material to below 50°C to obtain resin waste sand energy-saving regenerated coated sand.

[0015] Example 2: A method for preparing energy-saving recycled coated sand from resin waste sand, comprising the following steps: S1. Take phenolic resin waste sand, crush it to disperse it into single-particle waste sand; place the obtained single-particle waste sand in a hot carbonization regeneration device and perform hot carbonization regeneration treatment at 800℃ for 7.5 min, so that the residual phenolic resin film on the surface of the single-particle waste sand is carbonized rather than completely oxidized and decomposed, and a retained carbonized film is formed on the surface of the sand particles. At the same time, the residual calcium stearate, residual hexamethylenetetramine and water and other low-melting-point substances in the single-particle waste sand are removed to obtain hot regenerated sand at a temperature of 175℃. S2. Based on 100 parts by weight of the hot regenerated sand obtained in step S1, add 0.075 parts by weight of carbon powder to the hot regenerated sand and stir slowly for 6 minutes to distribute the carbon powder on the surface of the sand particles in order to compensate for and balance the carbon layer on the surface of the sand particles, and obtain carbon layer regulated regenerated sand. S3. Cool the carbon-modified regenerated sand obtained in step S2 to 142.5℃; add 2 parts by weight of phenolic resin to 100 parts by weight of carbon-modified regenerated sand, mix for 40 s to coat the sand particles with phenolic resin; then add hexamethylenetetramine aqueous solution, mix for 35 s, wherein the mass ratio of hexamethylenetetramine to water in the hexamethylenetetramine aqueous solution is 1:2, and the effective amount of hexamethylenetetramine added is 12.5% ​​of the mass of phenolic resin, that is, 0.25 parts by weight of hexamethylenetetramine and 0.5 parts by weight of water are added; then add 0.65 parts by weight of calcium stearate, mix for 50 s; during the above coating mixing process, the residual heat of the carbon-modified regenerated sand is used to evaporate the moisture, and no additional gas heating is applied to the regenerated sand; after mixing, cool the material to below 50℃ to obtain resin waste sand energy-saving regenerated coated sand.

[0016] Example 3: A method for preparing energy-saving recycled coated sand from resin waste sand, comprising the following steps: S1. Take phenolic resin waste sand, crush it to disperse it into single-particle waste sand; place the obtained single-particle waste sand in a hot carbonization regeneration device and perform hot carbonization regeneration treatment at 850℃ for 10 min, so that the residual phenolic resin film on the surface of the single-particle waste sand is carbonized rather than completely oxidized and decomposed, and a retained carbonized film is formed on the surface of the sand particles. At the same time, the residual calcium stearate, residual hexamethylenetetramine and water and other low-melting-point substances in the single-particle waste sand are removed to obtain hot regenerated sand at a temperature of 200℃. S2. Based on 100 parts by weight of the hot regenerated sand obtained in step (1), add 0.1 parts by weight of carbon powder to the hot regenerated sand and stir slowly for 9 minutes to distribute the carbon powder on the surface of the sand particles in order to compensate and balance the carbon layer on the surface of the sand particles, and obtain carbon layer regulated regenerated sand. S3. Cool the carbon-modified regenerated sand obtained in step (2) to 150°C. Add 3 parts by weight of phenolic resin to 100 parts by weight of carbon-modified regenerated sand and mix for 50 seconds to coat the sand particles with phenolic resin. Then add hexamethylenetetramine aqueous solution and mix for 40 seconds. The mass ratio of hexamethylenetetramine to water in the hexamethylenetetramine aqueous solution is 1:2. The effective amount of hexamethylenetetramine added is 15% of the mass of phenolic resin, i.e., 0.45 parts by weight of hexamethylenetetramine and 0.9 parts by weight of water are added. Then add 0.8 parts by weight of calcium stearate and mix for 60 seconds. During the above coating and mixing process, the residual heat of the carbon-modified regenerated sand is used to evaporate the moisture, and no additional gas heating is applied to the regenerated sand. After the mixing is completed, cool the material to below 50°C to obtain resin waste sand energy-saving regenerated coated sand.

[0017] Comparative Example 1: The difference between this comparative example and Example 1 is that a higher temperature and a longer time are used to thermally regenerate the single-particle waste sand, so that the residual phenolic resin film on the surface of the single-particle waste sand is fully oxidized and decomposed.

[0018] The specific preparation method is as follows: S1. Take phenolic resin waste sand, crush it to disperse it into single-particle waste sand; place the obtained single-particle waste sand in a thermal regeneration device and perform thermal regeneration treatment at 900℃ for 15 min to fully oxidize and decompose the residual phenolic resin film on the surface of the single-particle waste sand, and remove low-melting-point substances such as residual calcium stearate, residual hexamethylenetetramine and water from the single-particle waste sand to obtain hot regenerated sand at 150℃. S2. Based on 100 parts by weight of the hot regenerated sand obtained in step S1, add 0.05 parts by weight of carbon powder to the hot regenerated sand and stir slowly for 3 minutes to distribute the carbon powder on the surface of the sand particles of the hot regenerated sand, thus obtaining carbon layer-adjusted regenerated sand. S3. Cool the carbon-modified regenerated sand obtained in step S2 to 135°C; add 1 part by weight of phenolic resin to 100 parts by weight of carbon-modified regenerated sand and mix for 30 seconds; then add a hexamethylenetetramine aqueous solution and mix for 30 seconds, wherein the mass ratio of hexamethylenetetramine to water in the hexamethylenetetramine aqueous solution is 1:2, and the effective amount of hexamethylenetetramine added is 10% of the mass of phenolic resin, that is, add 0.1 parts by weight of hexamethylenetetramine and 0.2 parts by weight of water; then add 0.5 parts by weight of calcium stearate and mix for 40 seconds; after mixing, cool the material to below 50°C to obtain regenerated coated sand.

[0019] Comparative Example 2: The difference between this comparative example and Example 1 is that no toner is added for carbon layer adjustment.

[0020] The specific preparation method is as follows: S1. Take phenolic resin waste sand, crush it to disperse it into single-particle waste sand; place the obtained single-particle waste sand in a hot carbonization regeneration device and perform hot carbonization regeneration treatment at 750℃ for 5 min, so that the residual phenolic resin film on the surface of the single-particle waste sand is carbonized rather than completely oxidized and decomposed, and a retained carbonized film is formed on the surface of the sand particles. At the same time, the residual calcium stearate, residual hexamethylenetetramine and water and other low-melting-point substances in the single-particle waste sand are removed to obtain hot regenerated sand at a temperature of 150℃. S2. Without adding carbon powder to the hot regenerated sand obtained in step S1, the hot regenerated sand is slowly stirred for 3 minutes to obtain regenerated sand without a compensated carbon layer. S3. Cool the uncompensated carbon layer of the regenerated sand obtained in step S2 to 135°C; add 1 part by weight of phenolic resin to 100 parts by weight of the uncompensated carbon layer regenerated sand and mix for 30 seconds; then add a hexamethylenetetramine aqueous solution and mix for 30 seconds, wherein the mass ratio of hexamethylenetetramine to water in the hexamethylenetetramine aqueous solution is 1:2, and the effective amount of hexamethylenetetramine added is 10% of the mass of phenolic resin, that is, add 0.1 parts by weight of hexamethylenetetramine and 0.2 parts by weight of water; then add 0.5 parts by weight of calcium stearate and mix for 40 seconds; during the above coating mixing process, the residual heat of the regenerated sand is used to evaporate the moisture, and no additional gas heating is applied to the regenerated sand; after the mixing is completed, cool the material to below 50°C to obtain regenerated coated sand.

[0021] Comparative Example 3: The difference between this comparative example and Example 1 is that it does not use the residual heat of the hot recycled sand for coating and mixing. Instead, the hot recycled sand is cooled to room temperature and then heated to the coating temperature for coating.

[0022] The specific preparation method is as follows: S1. Take phenolic resin waste sand, crush it to disperse it into single-particle waste sand; place the obtained single-particle waste sand in a hot carbonization regeneration device, and perform hot carbonization regeneration treatment at 750℃ for 5 min, so that the residual phenolic resin film on the surface of the single-particle waste sand is carbonized rather than completely oxidized and decomposed, and a retained carbonized film is formed on the surface of the sand particles. At the same time, the residual calcium stearate, residual hexamethylenetetramine and water and other low-melting-point substances in the single-particle waste sand are removed to obtain hot-regenerated sand; then cool the obtained hot-regenerated sand to room temperature. S2. Based on 100 parts by weight of the cooled regenerated sand obtained in step S1, add 0.05 parts by weight of carbon powder to the regenerated sand and stir slowly for 3 minutes to distribute the carbon powder on the surface of the sand particles to obtain carbon layer-conditioned regenerated sand; then, further heat the carbon layer-conditioned regenerated sand to raise its temperature to 135°C. S3. Taking 100 parts by weight of the heated carbon layer-conditioned regenerated sand obtained in step S2, add 1 part by weight of phenolic resin and mix for 30 seconds; then add a hexamethylenetetramine aqueous solution and mix for 30 seconds, wherein the mass ratio of hexamethylenetetramine to water in the hexamethylenetetramine aqueous solution is 1:2, and the effective amount of hexamethylenetetramine added is 10% of the mass of phenolic resin, that is, add 0.1 parts by weight of hexamethylenetetramine and 0.2 parts by weight of water; then add 0.5 parts by weight of calcium stearate and mix for 40 seconds; after mixing, cool the material to below 50°C to obtain regenerated coated sand.

[0023] Performance testing 1. Tensile strength The test was conducted according to JB / T 8583-2008 standard. The coated sand sample prepared according to this invention was placed in an environment with a temperature of 23±2℃ and a relative humidity of 50±10% for at least 2 hours to allow the temperature and humidity to become uniform. The sample was prepared using a standard figure-eight shaped tensile test mold. The coated sand was uniformly filled into the mold cavity and leveled. The mold was then heated and cured at a temperature of 230±5℃ for 120 seconds. After demolding, the sample was cooled in an environment of 23±2℃ for 30 minutes. At least five parallel samples were prepared for each group of samples. During testing, the sample was installed in the fixture of the coated sand tensile strength tester, and a tensile load was applied uniformly. The maximum load at which the sample fractured was recorded, and the tensile strength was calculated by the tester, with the unit being MPa.

[0024] 2. High temperature resistance time The test was conducted according to JB / T 13037-2017 standard. The coated sand sample prepared according to this invention was used to prepare a cured specimen of the same size as the tensile strength test under the same sample preparation conditions. After demolding, the specimen was cooled and placed for 30 min at a temperature of 23±2℃ and a relative humidity of 50±10%. Before testing, the high-temperature resistance testing device or high-temperature furnace was preheated to 1000±20℃ and the furnace temperature was kept stable for at least 10 min. During testing, the specimen was quickly placed in the high-temperature zone, so that the heated surface of the specimen was directly exposed to the stable high-temperature environment, and timing was started simultaneously. The softening, cracking, deformation, collapse, or loss of structural integrity of the specimen under high temperature was observed. Timing was stopped when the specimen showed through cracks, obvious collapse, or could not maintain its original shape contour. This time was recorded as the high-temperature resistance time, in seconds.

[0025] Table 1 Tensile strength and high temperature resistance time of coated sand

[0026] As shown in Table 1, compared with virgin sand coated with coating and conventionally recycled sand coated with coating, the resin waste sand energy-saving recycled coated sand prepared in Examples 1-3 of this invention has a tensile strength of 4.2 MPa and a high-temperature resistance time of 115 s, both significantly better than virgin sand coated with coating and conventionally recycled sand coated with coating. Compared with Example 1, Comparative Example 1 uses a stronger thermal regeneration condition of 900℃ for 15 min, which fully oxidizes and decomposes the residual phenolic resin film on the surface of the sand particles, making it difficult to form and retain an effective carbonized film. Its tensile strength and high-temperature resistance time both decrease, indicating that the short-time hot carbonization regeneration and carbonized film retention process of this invention is beneficial to improving the strength and heat resistance of the coated sand. Comparative Example 2 does not add carbon powder for carbon layer adjustment, and its high-temperature resistance time is significantly lower than that of Example 1, indicating that a small amount of carbon powder can compensate for and balance the carbon layer on the surface of the sand particles, improving the heat resistance stability of the coated sand.

[0027] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing energy-saving recycled coated sand from resin waste sand, characterized in that, Includes the following steps: S1. The phenolic resin waste sand is crushed and dispersed into single particles of waste sand. The single particles of waste sand are subjected to hot carbonization regeneration treatment at 750-850℃ for 5-10 minutes, so that the residual phenolic resin film on the surface of the single particles of waste sand is carbonized rather than completely oxidized and decomposed, and a retained carbonized film is formed on the surface of the sand particles. At the same time, low melting point substances in the single particles of waste sand are removed, and hot regenerated sand at a temperature of 150-200℃ is obtained. S2. Add carbon powder accounting for 0.05 to 0.1% of the mass of the hot-state regenerated sand to the hot-state regenerated sand and stir for 3 to 9 minutes to distribute the carbon powder on the surface of the sand particles in order to compensate for and balance the carbon layer on the surface of the sand particles, thereby obtaining carbon layer-adjusted regenerated sand. S3. Cool the carbon layer-conditioned regenerated sand to 135-150°C, add 1-3 parts by weight of phenolic resin to 100 parts by weight of carbon layer-conditioned regenerated sand and mix, then add hexamethylenetetramine aqueous solution and calcium stearate and mix, use the residual heat of carbon layer-conditioned regenerated sand to evaporate the moisture, and then cool to below 50°C to obtain resin waste sand energy-saving regenerated coated sand.

2. The method for preparing energy-saving recycled coated sand from resin waste sand according to claim 1, characterized in that, The low-melting-point substance includes at least one of residual calcium stearate, residual hexamethylenetetramine, and water.

3. The method for preparing energy-saving recycled coated sand from resin waste sand according to claim 1, characterized in that, The mass ratio of hexamethylenetetramine to water in the hexamethylenetetramine aqueous solution is 1:2, and the effective amount of hexamethylenetetramine added is 10-15% of the mass of the phenolic resin.

4. The method for preparing energy-saving recycled coated sand from resin waste sand according to claim 1, characterized in that, The amount of calcium stearate added is 0.5 to 0.8% of the mass of the carbon layer-adjusted regenerated sand.

5. The method for preparing energy-saving recycled coated sand from resin waste sand according to claim 1, characterized in that, The mixing time after adding phenolic resin is 30-50 s, the mixing time after adding hexamethylenetetramine aqueous solution is 30-40 s, and the mixing time after adding calcium stearate is 40-60 s.

6. The method for preparing energy-saving recycled coated sand from resin waste sand according to claim 1, characterized in that, Steps S2 to S3 utilize the residual heat of the hot recycled sand for coating and mixing, and no additional gas heating is applied to the recycled sand during the coating and mixing process.

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