A regeneration method for used foundry sand and new coated sand obtained by the regeneration method

Abstract

The present invention belongs to the field of casting, and specifically relates to a method for regenerating old casting sand and new coated sand obtained by the regeneration method. The regeneration method includes wet scrubbing, roasting, grinding, hot melt air separation, strong magnetic separation, metal crushing and sand mixing processes in sequence. The regeneration method can relatively completely remove the metal and its oxide on the outer surface of the old casting sand, so that the silica content of the obtained regenerated sand is close to that of the new sand, and the metal substances separated from the old casting sand can be processed to prepare high-temperature resistant auxiliary agents for casting sand and be reused, thereby realizing the repeated circulation of metal substances and saving raw material costs. In addition, according to testing, the obtained new coated sand has excellent comprehensive performance and can fully meet the use requirements.

Description

Technical Field

[0001] The invention belongs to the field of casting, and in particular relates to a regeneration method for old casting sand and new coated sand obtained by the regeneration method. Background Art

[0002] Casting is the foundation of industry. With the rapid development of my country's manufacturing industry, the demand for casting raw materials is increasing. Sand casting is one of the most important casting processes, especially for complex, thin-walled, and large castings. As a result, my country produces tens of millions of tons of used foundry sand each year. Used foundry sand is a solid waste, and sand resources are non-renewable. From the perspective of environmental protection and resource conservation, the reuse of used sand is inevitable. In addition, the cost of using new sand has become a significant burden for foundries. From the perspective of economic benefits, recycling used foundry sand is also very meaningful.

[0003] The current regeneration processes for used foundry sand are mainly divided into thermal, wet and grinding methods, which mainly remove organic and inorganic resins on the surface of the used sand. However, most of them do not consider how to remove metals and metal oxides such as iron, aluminum, iron oxide, aluminum oxide, etc. on the surface of the used sand. These substances have sharp microscopic surface morphology, and excessive residue will seriously affect the reuse effect of the regenerated sand.

[0004] More specifically, the invention patent with publication number CN113134567A discloses a mixed waste sand regeneration method and regenerated sand of inorganic waste sand and wet mold waste sand, comprising the following steps: (1) mechanically grinding the mixed waste sand once to obtain primary regenerated sand; (2) calcining the primary regenerated sand at high temperature to obtain secondary regenerated sand, wherein the calcination temperature is 650°C to 670°C and the time is 6 to 8 hours; (3) after the secondary regenerated sand is cooled, mechanically grinding the secondary regenerated sand again to obtain tertiary regenerated sand; (4) removing impurities from the tertiary regenerated sand and screening it to obtain regenerated sand. However, the patent does not mention how the metals and metal oxides removed from the surface of the old sand are collected and reused: first, a process for removing the metals and metal oxides is not designed, and the quality of the regenerated sand cannot be guaranteed; second, the disposal method after the metal material on the surface of the regenerated sand is stripped is not considered. Currently, the environmental problem of indiscriminate landfill of solid waste is common, and there are great environmental risks.

[0005] Publication number CN114749599A discloses a slightly wet treatment process for waste foundry sand, including the following steps: S1. Crushing the waste foundry sand, followed by magnetic separation and screening; S2. Wet-treating the screened waste sand using a swing-arm mixer, followed by washing to obtain wet sand, which is then dried after heat exchange; S3. Calcination in a roasting furnace at a temperature of 800-900°C for 10-20 minutes; After calcination, steam grinding is performed in a heat exchange grinding device, while simultaneously exchanging heat with the wet sand in S2; S4. Cooling and screening the waste sand after heat exchange to obtain the initial regenerated sand. This patent, using the slightly wet method, roasting for 10-20 minutes, and grinding, fails to remove metals and oxides from the sand surface, and does not mention methods for reusing the collected metals and oxides during the regeneration process.

[0006] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0007] In order to solve the problems existing in the prior art, the present invention provides a method for regenerating old foundry sand and new coated sand obtained by the regeneration method. The regeneration method first uses wet scrubbing to remove the ash on the surface of the old foundry sand, and then uses roasting heat treatment to cause the sand particles and the metal on the surface of the sand particles to produce different degrees of thermal stress and cracks, and then the metal substances on the surface of the sand particles are peeled off by grinding. In addition, the back end is also provided with hot melt air separation to remove aluminum and aluminum oxide, and strong magnetism to remove the sand-iron mixture, thereby achieving complete separation of sand and metal substances, and the silica content of the obtained regenerated sand is close to that of new sand. The metal substances separated from the old foundry sand are processed and prepared as high-temperature resistant auxiliary agents for foundry sand, which also realizes the separation and reuse of metals in the old foundry sand.

[0008] The present invention provides a method for regenerating used foundry sand, which comprises the following steps:

[0009] (1) Mixing old foundry sand with water to obtain wet sand;

[0010] (2) roasting the wet sand, and then cooling it to obtain cooled sand;

[0011] (3) grinding the cooled sand to remove metal from the surface of the sand grains to obtain ground sand grains and surface metal;

[0012] (4) hot-melt air separation is performed on the ground sand to obtain hot-melt sand and a middle layer metal; the middle layer metal is an aluminum metal;

[0013] (5) subjecting the hot-melt sand particles to magnetic separation to obtain surface-cleaned regenerated sand and inner layer metal; the inner layer metal is an iron-based metal;

[0014] (6) mixing the surface metal, the middle metal, and the inner metal and crushing them to obtain a high-temperature resistant auxiliary agent;

[0015] (7) The surface cleaned regenerated sand, the high temperature resistant auxiliary agent, solid phenolic resin, urotropine and calcium stearate are mixed with coated sand to obtain new coated sand, thus completing the regeneration process of the old foundry sand.

[0016] For ease of understanding of the present invention, the regeneration method of the present invention is described:

[0017] After the old foundry sand is infiltrated by the casting of metal liquid, the surface is covered with a large amount of aluminum, iron and other oxides. The microstructure of these substances is sharp, which will seriously affect the strength of the regenerated sand. The regeneration method of the present invention is also targeted to remove the metal and oxide coatings on the surface of the regenerated sand, so that the regenerated sand has excellent performance. Specifically: due to the different expansion coefficients of the sand particles and the metal coating, the bonding force of the metal coating can be weakened after the roasting process, and the metal substances on the surface of the sand particles can be removed by grinding; and for the stubborn aluminum metal coating, the Hot melt air separation heats the sand to 670-750°C and blows air upwards through a fan. Since aluminum becomes molten at 650°C, the wind blows it away into fine particles, which are then drawn into a pipeline under negative pressure for collection. For stubborn iron-based metal coatings, strong magnetic separation is used, using magnetic separation rollers with a force of more than 10,000 gs to remove the iron-based metal coating before collection. Finally, the collected aluminum and iron-based metals are crushed to a fineness of less than 800 mesh and mixed in a mixer to create a high-temperature resistant additive. The treated foundry sand is then used as aggregate, and other ingredients, such as the high-temperature resistant additive, are added to create new coated sand.

[0018] Preferably, in step (1), the weight ratio of the used foundry sand to water is 1:0.3-5;

[0019] And / or, the stirring speed is 270-720 r / min, and the stirring time is 3-10 min.

[0020] Preferably, in step (2), the calcination temperature is 300-600° C., and the calcination time is 20-200 min.

[0021] Preferably, in step (3), the grinding speed is 120 to 360 r / min, and the grinding time is 2 to 8 min.

[0022] Preferably, in step (4), the temperature of the hot melt air separation is 670-750°C.

[0023] Preferably, in step (5), the magnetic strength of the magnetic separation is 10,000 to 20,000 gs.

[0024] Preferably, in step (6), the pulverization is performed to a size of 800 to 2000 mesh.

[0025] Preferably, in step (7), 100 parts of surface-cleaned regenerated sand, 0.1-2 parts of high-temperature resistant auxiliary agent, 1-3 parts of solid phenolic resin, 0.1-0.5 parts of urotropine and 0.1-0.2 parts of calcium stearate are mixed with coated sand by weight to obtain new coated sand, thereby completing the regeneration process of old foundry sand.

[0026] Based on the same technical concept, another solution of the present invention is to provide new coated sand obtained by the above-mentioned regeneration method of used foundry sand.

[0027] The beneficial effects of the present invention are:

[0028] The regeneration method described in this invention can relatively completely remove metal and its oxides from the outer surface of used foundry sand, resulting in a silica content close to that of new sand. Furthermore, the metal separated from the used foundry sand can be processed into a high-temperature-resistant additive for foundry sand and reused, achieving repeated recycling of the metal and saving raw material costs. Furthermore, testing has shown that the resulting new coated sand has excellent overall performance and fully meets application requirements. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] The present invention provides a method for regenerating used foundry sand, which comprises the following steps:

[0032] (1) In a wet mixer, old foundry sand and water were mixed in a weight ratio of 1:1, and stirred for 5 minutes at a stirring rotor speed of 360 r / min to scrub the mixture, and wet sand was obtained after completion;

[0033] (2) putting the wet sand into a roasting furnace and roasting it at 400° C. for 50 min. After roasting, the wet sand is rapidly cooled using cooling water to obtain cooled sand;

[0034] (3) putting the cooled sand into a grinder and grinding it for 3 minutes at a grinding rotor speed of 270 r / min to remove the metal on the surface of the sand particles, and obtaining ground sand particles; at the same time, the surface metal removed by grinding is collected by negative pressure;

[0035] (4) The ground sand is put into a hot melt air separation furnace with an internal temperature of 700°C. The furnace body is vertical, a blower is used at the bottom of the furnace to blow air upward, and a negative pressure exhaust is set at the top of the furnace. The entire air flow direction is from bottom to top. The aluminum metal material is in a molten state at high temperature, and the aluminum molten particles are collected by the air flow direction. After completion, hot melt sand and a middle layer of aluminum metal are obtained;

[0036] (5) The hot-melt sand particles are put into a strong magnetic separation drum, and the inner layer of iron-based metal is collected by strong magnetic adsorption under the condition of 15000gs, and the surface clean regenerated sand and the inner layer of iron-based metal are obtained after completion;

[0037] (6) mixing the surface metal, the middle metal, and the inner metal and crushing them into 1000 mesh to obtain a high temperature resistant auxiliary agent;

[0038] (7) 100 g of surface clean regenerated sand, 0.1 g of high temperature resistant auxiliary agent, 2 g of solid phenolic resin, 0.2 g of urotropine and 0.2 g of calcium stearate are mixed with coated sand to obtain new coated sand, thus completing the regeneration process of the old foundry sand.

[0039] Example 2

[0040] The present invention provides a method for regenerating used foundry sand, which comprises the following steps:

[0041] (1) In a wet mixer, old foundry sand and water were mixed in a weight ratio of 1:0.3, and stirred for 10 minutes at a stirring rotor speed of 270 r / min to scrub the mixture, and wet sand was obtained after completion;

[0042] (2) putting the wet sand into a roasting furnace and roasting it at 300° C. for 200 min. After roasting, the wet sand is rapidly cooled by cooling water to obtain cooled sand;

[0043] (3) putting the cooled sand into a grinder and grinding it for 8 minutes at a grinding rotor speed of 120 r / min to remove the metal on the surface of the sand particles, and obtaining ground sand particles; at the same time, the surface metal removed by grinding is collected by negative pressure;

[0044] (4) The ground sand is put into a hot melt air separation furnace with an internal temperature of 670°C. The furnace body is vertical, a blower is used at the bottom of the furnace to blow air upward, and a negative pressure exhaust is set at the top of the furnace. The entire air flow direction is from bottom to top. The aluminum metal material is in a molten state at high temperature, and the aluminum molten particles are collected by the air flow direction. After completion, hot melt sand and a middle layer of aluminum metal are obtained;

[0045] (5) The hot-melt sand particles are put into a strong magnetic separation drum, and the inner layer of iron-based metal is collected by strong magnetic adsorption under the condition of 10,000 gs, and the surface clean regenerated sand and the inner layer of iron-based metal are obtained after completion;

[0046] (6) mixing the surface metal, the middle metal, and the inner metal and crushing them into 800 meshes to obtain a high temperature resistant auxiliary agent;

[0047] (7) 100 g of surface clean regenerated sand, 0.1 g of high temperature resistant auxiliary agent, 1 g of solid phenolic resin, 0.1 g of urotropine and 0.1 g of calcium stearate are mixed with coated sand to obtain new coated sand, thus completing the regeneration process of the old foundry sand.

[0048] Example 3

[0049] The present invention provides a method for regenerating used foundry sand, which comprises the following steps:

[0050] (1) In a wet mixer, old foundry sand and water were mixed in a weight ratio of 1:5, and stirred for 3 minutes at a stirring rotor speed of 720 r / min to scrub the mixture, and wet sand was obtained after completion;

[0051] (2) putting the wet sand into a roasting furnace and roasting it at 600° C. for 20 min. After roasting, the wet sand is rapidly cooled using cooling water to obtain cooled sand;

[0052] (3) putting the cooled sand into a grinder and grinding it for 2 minutes at a grinding rotor speed of 360 r / min to remove the metal on the surface of the sand particles, and obtaining ground sand particles; at the same time, the surface metal removed by grinding is collected by negative pressure;

[0053] (4) The ground sand is put into a hot melt air separation furnace with an internal temperature of 750°C. The furnace body is vertical, a blower is used at the bottom of the furnace to blow air upward, and a negative pressure exhaust is set at the top of the furnace. The entire air flow direction is from bottom to top. The aluminum metal material is in a molten state at high temperature, and the aluminum molten particles are collected by the air flow direction. After completion, hot melt sand and a middle layer of aluminum metal are obtained;

[0054] (5) The hot-melt sand particles are put into a strong magnetic separation drum, and the inner layer of iron-based metal is collected by strong magnetic adsorption under the condition of 20,000 gs, and the surface clean regenerated sand and the inner layer of iron-based metal are obtained after completion;

[0055] (6) mixing the surface metal, the middle metal, and the inner metal and crushing them into 2000 mesh to obtain a high temperature resistant auxiliary agent;

[0056] (7) 100 g of surface clean regenerated sand, 2 g of high temperature resistant auxiliary agent, 3 g of solid phenolic resin, 0.5 g of urotropine and 0.2 g of calcium stearate are mixed with coated sand to obtain new coated sand, thus completing the regeneration process of the old foundry sand.

[0057] Comparative Example 1

[0058] Based on Example 1, this comparative example is set. The difference between Comparative Example 1 and Example 1 is that:

[0059] Comparative Example 1 removes step (1) and does not undergo wet scrubbing. Other implementation methods and conditions are the same as those of Example 1.

[0060] Comparative Example 2

[0061] This comparative example is set up on the basis of Example 1. The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 removes step (2) and does not undergo roasting. Other implementation methods and conditions are the same as Example 1.

[0062] Comparative Example 3

[0063] This comparative example is set up on the basis of Example 1. The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 removes step (3) and does not undergo grinding. Other implementation methods and conditions are the same as those of Example 1.

[0064] Comparative Example 4

[0065] This comparative example is set up based on Example 1. The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 removes step (4) and does not undergo hot melt air separation. Other implementation methods and conditions are the same as Example 1.

[0066] Comparative Example 5

[0067] This comparative example is set up on the basis of Example 1. The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 removes step (5) and does not undergo strong magnetic separation. Other implementation methods and conditions are the same as Example 1.

[0068] Comparative Example 6

[0069] This comparative example is set up on the basis of Example 1. The difference between Comparative Example 6 and Example 1 is that no high temperature resistant auxiliary agent is added in step (7) of Comparative Example 6, and other implementation methods and conditions are the same as those of Example 1.

[0070] Comparative Example 7

[0071] This comparative example is set up on the basis of Example 1. The difference between Comparative Example 7 and Example 1 is that new sand is used instead of regenerated sand in step (7) of Comparative Example 7, and other implementation methods and conditions are the same as those of Example 1.

[0072] Test Case

[0073] The physical and chemical properties of the coated sands obtained in Examples 1 to 3 and Comparative Examples 1 to 7 were tested, and the results are shown in Table 1.

[0074] Table 1 Physical and chemical properties

[0075]

[0076] From Table 1 we can see that:

[0077] Comparing the Example with Comparative Example 1, the conductivity of the reclaimed sand in Comparative Example 1 increased by 1314% and the mud content by 638%. The tensile strength of the coated sand decreased by 36%, the porosity of the casting increased by 67%, and the veining rate of the casting increased by 138%. This is primarily due to the high residual sodium silicate content on the surface of the reclaimed sand, which was not wet scrubbed. This high conductivity and mud content are the result of this surface mud. This surface mud reduces the tensile strength of the coated sand, resulting in poor air permeability and yieldability in the sand core, which directly leads to increased porosity and veining in the casting.

[0078] Comparing the Example with Comparative Example 2, the reclaimed sand in Comparative Example 2 showed a 1000% increase in electrical conductivity and a 175% increase in mud content. The tensile strength of the coated sand decreased by 32%, while the porosity and veining of the casting increased by 67% and 138%. This is primarily due to the high conductivity and mud content of the reclaimed sand, which is not calcined, due to the high activity of residual sodium silicate on the surface of the reclaimed sand. This surface mud reduces the tensile strength of the coated sand, resulting in poor air permeability and yield of the sand core, which directly leads to increased porosity and veining in the casting.

[0079] Comparing the Example with Comparative Example 3, the reclaimed sand in Comparative Example 3 showed a 261% increase in electrical conductivity and a 138% increase in mud content. The coated sand's tensile strength decreased by 28%, while the casting's porosity and veining increased by 142% and 125%. This is primarily due to the lack of grinding, which prevents the removal of brittle sodium silicate and ash from the reclaimed sand's surface, leading to high electrical conductivity and mud content. This surface mud reduces the tensile strength of the coated sand, resulting in poor air permeability and yield properties in the sand core, directly contributing to increased porosity and veining in the casting.

[0080] Comparing the Example with Comparative Example 4, the conductivity of the reclaimed sand in Comparative Example 4 increased by 81% and the mud content by 13%. The tensile strength of the coated sand decreased by 24%, the porosity of the casting increased by 58%, and the veining rate of the casting increased by 16%. The main reason is that without hot melt air separation, the reclaimed sand has a high level of aluminum oxide on its surface, which reduces the tensile strength of the coated sand. The aluminum oxide on the sand surface is remelted during molten metal casting, causing defects such as porosity and veining in the casting.

[0081] Comparing the Example with Comparative Example 5, the conductivity of the reclaimed sand in Comparative Example 5 increased by 133% and the mud content by 25%. The tensile strength of the coated sand decreased by 26%, the porosity of the casting increased by 67%, and the veining rate of the casting increased by 13%. The main reason for this is that without strong magnetic separation, the reclaimed sand has a high level of iron oxide on its surface, which reduces its tensile strength. During casting, the molten metal is chilled by the iron oxide, preventing the timely removal of gases and causing porosity defects in the casting.

[0082] Comparing Example 6 with Comparative Example 6, the porosity of the casting increased by 667% and the veining rate of the casting increased by 1538%. Without the addition of high-temperature resistant adjuvants, the high-temperature resistance of the sand core prepared by coated sand was greatly weakened, and the porosity and veining defects of the casting were greatly increased.

[0083] Comparing the Example with Comparative Example 7, the tensile strength of the coated sand in Comparative Example 7 decreased by 14%, the porosity of the casting increased by 25%, and the veining rate of the casting increased by 50%. Using new sand instead of reclaimed sand results in higher porosity and veining defects than using reclaimed sand due to its poorer angular coefficient and higher expansion rate.

[0084] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for regenerating used foundry sand, characterized in that: The regeneration method comprises the following steps: (1) Mix the old foundry sand with water to obtain wet sand; (2) roasting the wet sand and cooling it to obtain cooled sand; (3) grinding the cooled sand to remove metal from the surface of the sand grains to obtain ground sand grains and surface metal; (4) hot-melt air separation is performed on the ground sand to obtain hot-melt sand and a middle layer metal; the middle layer metal is an aluminum metal; the temperature of the hot-melt air separation is 670-750°C; (5) subjecting the hot-melt sand particles to magnetic separation to obtain surface-cleaned regenerated sand and inner layer metal; the inner layer metal is an iron-based metal; (6) mixing the surface metal, the middle metal and the inner metal and crushing them to obtain a high temperature resistant auxiliary agent; (7) The surface clean regenerated sand, the high temperature resistant auxiliary agent, solid phenolic resin, urotropine and calcium stearate are mixed with coated sand to obtain new coated sand, thus completing the regeneration process of the old foundry sand.

2. The method for regenerating used foundry sand according to claim 1, characterized in that: In step (1), the weight ratio of the used foundry sand to water is 1:0.3-5; And / or, the stirring speed is 270-720 r / min, and the stirring time is 3-10 min.

3. The method for regenerating used foundry sand according to claim 1, characterized in that: In step (2), the calcination temperature is 300-600° C., and the calcination time is 20-200 min.

4. The method for regenerating used foundry sand according to claim 1, characterized in that: In step (3), the grinding speed is 120-360 r / min, and the grinding time is 2-8 min.

5. The method for regenerating used foundry sand according to claim 1, characterized in that: In step (5), the magnetic strength of the magnetic separation is 10000~20000gs.

6. The method for regenerating used foundry sand according to claim 1, characterized in that: In step (6), the powder is crushed to 800-2000 mesh.

7. The method for regenerating used foundry sand according to claim 1, characterized in that: In step (7), 100 parts of surface clean regenerated sand, 0.1-2 parts of high temperature resistant auxiliary agent, 1-3 parts of solid phenolic resin, 0.1-0.5 parts of urotropine and 0.1-0.2 parts of calcium stearate are mixed with coated sand by weight to obtain new coated sand, thus completing the regeneration process of old foundry sand.

8. New coated sand obtained by the regeneration method of used foundry sand according to any one of claims 1 to 7.

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