A high-temperature resistant regenerated coated sand and its preparation method

Abstract

The present invention provides a high-temperature resistant recycled coated sand and a preparation method thereof. The preparation method of the high-temperature resistant recycled coated sand comprises the following steps: grinding and pre-treating the used sodium silicate sand; performing wet recycling on the pre-treated used sodium silicate sand to obtain recycled sand; adding salicylic acid, liquid phenolic resin, metal oxide powder, and microsilica powder to the recycled sand for surface modification to obtain modified recycled sand; adding solid phenolic resin, hexamine, and calcium stearate to the modified recycled sand for coated sand mixing to obtain the finished product of the high-temperature resistant recycled coated sand. The high-temperature resistant recycled coated sand prepared by this method has a simple process and excellent performance, and can be widely used in casting complex thin-walled castings; at the same time, it also solves the environmental protection pressure of solid waste in foundry enterprises, enabling the non-renewable silica sand resources to be reused.

Description

Technical Field

[0001] The present invention belongs to the technical field of coated sand for casting, and particularly relates to a high-temperature resistant regenerated coated sand and a preparation method thereof. Background Art

[0002] Casting complex thin-walled castings is a key technology in high-end equipment manufacturing industries such as aerospace and the automotive industry. Such castings have complex internal cavities and high dimensional accuracy requirements. Generally, coated sand is used to prepare internal cavity sand cores, and then finished castings are obtained through casting. These sand cores are also complex in structure and relatively thin in size, so the coated sand is required to have a high melting point, high strength, and good heat resistance.

[0003] For the casting part, the sodium silicate sand casting process is adopted. It is estimated that the generated sodium silicate used sand exceeds 1 million tons per year. A large amount of sodium silicate used sand solid waste has become an environmental protection problem for casting enterprises. At the same time, the main raw material of sodium silicate sand, silica sand, is a non-renewable resource. In the past, rough landfill treatment and other methods wasted a large amount of silica sand resources.

[0004] Patent document CN111331071A discloses a method for modifying and regenerating sodium silicate used sand, including the following steps: (1) preparing a modified solution: using an NH4Cl aqueous solution as the basic modified solution, adding an appropriate amount of metal salt mixture to the NH4Cl aqueous solution to generate a repair modified solution; (2) soaking and modifying: putting the sodium silicate used sand into the modified solution for soaking; soaking and modifying the sodium silicate used sand in the hot repair modified solution for 10 - 120 min, or soaking and modifying the sodium silicate used sand with the normal temperature repair modified solution for 30 - 200 min, and stirring the sodium silicate used sand regularly during the modification process. This invention uses a modified liquid to regenerate the sodium silicate used sand, which belongs to a chemical method. The residual film on the surface of the used sand still exists, and even the covering layer is thicker. The regenerated sand obtained is quite different from the new sand.

[0005] Patent document CN115229122A discloses a high-temperature resistant coated sand for casting and a preparation method thereof. By adding organosilicon polymer, ethylene glycol, boric acid, resorcinol, and polyphenylene ether to phenolic resin, the phenolic resin is modified. Utilizing the mutual synergistic effect between substances, a coated sand with high fluidity, high strength, low curing temperature, and high heat resistance is prepared. However, practice has proved that randomly adding modifiers to phenolic resin will cause the connection bridges between resins to be extremely unstable, and the application prospect is poor. Summary of the Invention

[0006] In view of this, the present invention provides a high-temperature resistant regenerated coated sand and a preparation method thereof, which can achieve the above purposes. The present invention adopts the following technical solutions:

[0007] The present invention provides a preparation method for a high-temperature resistant regenerated coated sand, including the following steps:

[0008] S1. Grind and pre-treat the sodium silicate used sand;

[0009] S2. Wet regenerate the pre-treated sodium silicate used sand to obtain regenerated sand;

[0010] S3. Add salicylic acid, liquid phenolic resin, metal oxide powder, and microsilica powder to the regenerated sand for surface modification to obtain modified regenerated sand;

[0011] S4. Add solid phenolic resin, hexamethylenetetramine, and calcium stearate to the modified regenerated sand for coated sand mixing to obtain a finished product of high-temperature resistant regenerated coated sand.

[0012] Further, in the step S1, the rotation speed for grinding pre-treatment is 120 - 360 r / min, and the grinding time is 2 - 8 min.

[0013] Further, in the step S2, the process parameters for wet regeneration are: the mass ratio of sand to water is 1:(0.5 - 3), the stirring rotation speed is 270 - 720 r / min, the stirring time is 3 - 10 min, the pH value of the acid solution is adjusted to 6 - 7, and the water content of the regenerated sand is 2 - 5%.

[0014] Further, in the step S3, the addition amounts of salicylic acid, liquid phenolic resin, metal oxide powder, and microsilica powder are respectively 0.1 - 0.5%, 0.3 - 0.8%, 0.2 - 1%, and 0.1 - 0.5% of the mass of the regenerated sand.

[0015] Further, the particle sizes of the metal oxide powder and microsilica powder are 1000 mesh - 5000 mesh; and / or the viscosity of the liquid phenolic resin at 25°C is 2 - 3 Pa·s, the solid content is ≥70%, the free phenol is 15 - 25%, and the water content is ≤3%.

[0016] Further, the metal oxide is one or two of aluminum oxide and iron oxide.

[0017] Further, in the step S3, there is also a curing step after surface modification: the curing temperature is 80 - 105°C, and the time is 1 - 5 h.

[0018] Further, in the step S4, the addition amounts of solid phenolic resin, hexamethylenetetramine, and calcium stearate are respectively 1 - 3%, 10 - 20%, and 5 - 10% of the mass of the modified regenerated sand.

[0019] Further, the softening point of the solid phenolic resin is 98 - 115°C, the polymerization speed is 20 - 40 s, and the free phenol is ≤5%.

[0020] A coated sand obtained by preparing according to the preparation method of a kind of high-temperature resistant regenerated coated sand as described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The process flow of the present invention is simple, and the prepared high-temperature resistant regenerated coated sand can be widely used in casting complex thin-walled castings and improving the qualified rate of castings.

[0023] (2) The present invention uses sodium silicate used sand as raw material, and after regeneration and modification, a regenerated sand with performance superior to that of new sand is obtained, which solves the environmental protection pressure of solid waste in foundry enterprises and at the same time enables the non-renewable silica sand resources to be reused.

[0024] (3) In the preparation process of the present invention, grinding is carried out first to remove the residual brittle film on the surface of sand grains. In the wet process, acid solution is also added to react with the firmly bonded sodium silicate to achieve the effect of strengthening the removal of the covering.

[0025] (4) In the preparation process of the present invention, through surface modification, metal oxides and liquid phenolic resin can increase the melting point of the coated sand, and microsilica powder and salicylic acid strengthen the phenolic resin connecting bridge, improving the tensile strength of the coated sand.

[0026] (5) A small amount of sodium silicate remaining on the surface of the regenerated sand prepared by the present invention can undergo sintering vitrification during high-temperature casting of molten metal, enabling the coated sand to have excellent heat resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the process flow chart of Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can understand the present invention more clearly.

[0029] Sources and physicochemical parameters of key test materials:

[0030] The sodium silicate used sand comes from the used sand exhausted by the foundry, and the physicochemical parameters are: particle size 20 - 200 mesh, acid consumption value 20 - 40 ml, pH value 10 - 13, conductivity 2000 - 6000 us / cm;

[0031] The liquid phenolic resin is purchased from Nantong Kanglin New Materials Co., Ltd., and the physicochemical parameters are: viscosity 2000 - 3000, solid content ≥ 70%, free phenol 15 - 25%, moisture content ≤ 3%;

[0032] The solid phenolic resin is purchased from Jinan Shengquan Foundry Materials Co., Ltd., and the physicochemical parameters are: softening point 98 - 115 °C, polymerization rate 20 - 40 s, free phenol ≤ 5%;

[0033] The microsilica powder is purchased from Henan Borun New Materials Co., Ltd., and the physicochemical parameters are: silicon dioxide content ≥ 98%, particle size 1000 mesh - 5000 mesh;

[0034] The aluminum oxide powder was purchased from Aluminum Corporation of China Limited, with physical and chemical parameters: aluminum oxide content ≥ 98%, particle size 1000 mesh - 5000 mesh;

[0035] The ferric oxide powder was purchased from Chilean Metallurgy, with physical and chemical parameters: ferric oxide content ≥ 98%, particle size 1000 mesh - 5000 mesh.

[0036] In the present invention, if no specific raw materials are described, they are all existing substances and can be directly purchased on the market.

[0037] Example 1

[0038] This example provides a preparation method of high-temperature resistant regenerated coated sand, and the specific steps are as follows:

[0039] Take water glass used sand and grind it under the conditions of a grinding rotor speed of 270 r / min and a grinding time of 5 min to obtain pretreated water glass used sand.

[0040] Mix the pretreated water glass used sand and water at a mass ratio of 1:1, and carry out wet regeneration under the conditions of a stirring rotor speed of 360 r / min and a stirring time of 6 min. Add oxalic acid during the wet regeneration process to make the pH = 6. After the wet regeneration is completed, filter to obtain regenerated sand with a water content of 3%.

[0041] Put the regenerated sand into a disk rotating machine with an inclination angle of the rotating machine of 45° with the horizontal direction and a rotation speed of 30 r / min. First, add 0.2% of salicylic acid and 0.3% of liquid phenolic resin (viscosity 3 Pa·s at 25°C, solid content 75%, free phenol 20%, water content 2%) based on the weight of the regenerated sand, rotate and coat for 30 s, then add 0.1% of aluminum oxide powder (particle size 2000 mesh), 0.2% of ferric oxide powder (particle size 2000 mesh), and 0.1% of microsilica powder (particle size 2000 mesh) based on the weight of the regenerated sand, rotate and coat for 30 s to complete surface modification. Finally, put it into a curing kiln at a temperature of 90°C and a curing time of 2 h to obtain modified regenerated sand.

[0042] Screen the modified regenerated sand, take the 50 / 100 mesh modified regenerated sand, add 1.9% of solid phenolic resin (softening point 110°C, polymerization speed 30 s, free phenol 3%), 15% of hexamine, and 7% of calcium stearate for coated sand sand mixing to obtain the finished product of high-temperature resistant regenerated coated sand.

[0043] Example 2

[0044] This example provides a preparation method of high-temperature resistant regenerated coated sand, and the specific steps are as follows:

[0045] Take the sodium silicate used sand and grind it under the conditions of a grinding rotor speed of 120 r / min and a grinding time of 2 min to obtain the pretreated sodium silicate used sand.

[0046] Perform wet regeneration on the pretreated sodium silicate used sand and water at a mass ratio of 1:0.5 under the conditions of a stirring rotor speed of 270 r / min and a stirring time of 3 min. Add acetic acid during the wet regeneration process to make the pH = 6.5. After the wet regeneration is completed, filter to obtain the regenerated sand with a water content of 2%.

[0047] Put the regenerated sand into a disk rotating machine with an inclination angle of 45° with the horizontal direction and a rotation speed of 20 r / min. First, add 0.1% salicylic acid and 0.5% liquid phenolic resin (viscosity 3 Pa·s at 25°C, solid content 75%, free phenol 20%, water content 2%) by weight of the regenerated sand, rotate and coat the film for 20 s. Then, add 0.3% aluminum oxide powder (particle size 1000 mesh), 0.1% iron oxide powder (particle size 1000 mesh), and 0.3% microsilica powder (particle size 1000 mesh) by weight of the regenerated sand, rotate and coat the film for 50 s to complete surface modification. Finally, put it into a curing kiln at a temperature of 80°C for a curing time of 1 h to obtain the modified regenerated sand.

[0048] Screen the modified regenerated sand, take the 50 / 100 mesh modified regenerated sand, add 1% solid phenolic resin (softening point 110°C, polymerization speed 30 s, free phenol 3%), 10% hexamethylenetetramine, and 5% calcium stearate by weight of the modified regenerated sand for coated sand mixing to obtain the finished product of high-temperature resistant regenerated coated sand.

[0049] Example 3

[0050] This example provides a preparation method of high-temperature resistant regenerated coated sand, and the specific steps are as follows:

[0051] Take the sodium silicate used sand and grind it under the conditions of a grinding rotor speed of 360 r / min and a grinding time of 8 min to obtain the pretreated sodium silicate used sand.

[0052] Perform wet regeneration on the pretreated sodium silicate used sand and water at a mass ratio of 1:3 under the conditions of a stirring rotor speed of 720 r / min and a stirring time of 10 min. Add oxalic acid during the wet regeneration process to make the pH = 7. After the wet regeneration is completed, filter to obtain the regenerated sand with a water content of 5%.

[0053] Put the recycled sand into a disk rotary machine with an inclination angle of 45° to the horizontal direction and a rotation speed of 60 r / min. First, add 0.5% salicylic acid and 0.8% liquid phenolic resin (viscosity 3 Pa·s at 25°C, solid content 75%, free phenol 20%, moisture 2%) based on the weight of the recycled sand, and rotate for film coating for 50 s. Then, add 0.5% aluminum oxide powder (particle size 5000 mesh), 0.5% iron oxide powder (particle size 5000 mesh), and 0.5% microsilica powder (particle size 5000 mesh) based on the weight of the recycled sand, and rotate for film coating for 60 s to complete surface modification. Finally, put it into a curing kiln at a temperature of 105°C for a curing time of 5 h to obtain modified recycled sand.

[0054] Screen the modified recycled sand, take the 50 / 100 mesh modified recycled sand, add 3% solid phenolic resin (softening point 110°C, polymerization speed 30 s, free phenol 3%), 15% hexamethylenetetramine, and 10% calcium stearate for sand mixing of coated sand to obtain the finished product of high-temperature resistant recycled coated sand.

[0055] Comparative Example 1

[0056] This comparative example provides a preparation method of high-temperature resistant recycled coated sand, and the raw materials and process steps used are basically the same as those in Example 1, with the specific differences as follows: This comparative example omits the grinding pretreatment process.

[0057] Comparative Example 2

[0058] This comparative example provides a preparation method of high-temperature resistant recycled coated sand, and the raw materials and process steps used are basically the same as those in Example 1, with the specific differences as follows: This comparative example omits the wet recycling process.

[0059] Comparative Example 3

[0060] This comparative example provides a preparation method of high-temperature resistant recycled coated sand, and the raw materials and process steps used are basically the same as those in Example 1, with the specific differences as follows: This comparative example omits the surface modification process.

[0061] Comparative Example 4

[0062] This comparative example provides a preparation method of high-temperature resistant recycled coated sand, and the raw materials and process steps used are basically the same as those in Example 1, with the specific differences as follows: This comparative example omits the curing process.

[0063] Comparative Example 5

[0064] This comparative example provides a preparation method of high-temperature resistant recycled coated sand, and the specific steps are as follows:

[0065] The sodium silicate new sand was screened, and 50 / 100 mesh sodium silicate new sand was taken. Solid phenolic resin (softening point 110°C, polymerization rate 30 s, free phenol 3%) accounting for 1.9% of the mass of the sodium silicate new sand, 15% of hexamethylenetetramine, and 7% of calcium stearate were added for coating sand mixing to obtain the finished high-temperature resistant recycled coating sand.

[0066] The indicators of each product in Examples 1-3 and Comparative Examples 1-5 were detected, and the results are shown in Table 1.

[0067] The specific test methods are as follows:

[0068] The reference standard JB / T8583-2008 was referred to for testing the conductivity of recycled sand, the melting point of coating sand, the tensile strength of coating sand, and the high-temperature strength of coating sand.

[0069] Core making yield: 100 identical sand cores were prepared, and the yield was counted.

[0070] Casting yield: 100 identical castings were prepared, and the yield was counted.

[0071] Table 1 Performance indicators of the products in Examples 1-3 and Comparative Examples 1-5

[0072]

[0073] The following conclusions can be drawn from the data in Table 1:

[0074] Compared with Examples 1-3, the most significant change in the data of Comparative Examples 1 and 2 is the conductivity of recycled sand. The main residue on the surface of used sodium silicate sand is sodium silicate. Testing the conductivity can evaluate the regeneration effect. The lower the conductivity, the better the regeneration effect, indicating that grinding pretreatment, wet regeneration, and adding acid during wet regeneration can effectively remove a large amount of residual film on the surface of used sand, achieving a good regeneration effect.

[0075] Compared with Examples 1-3, the obvious changes in the data of Comparative Example 3 are the melting point of coating sand, the tensile strength of coating sand, and the high-temperature strength of coating sand. It shows that the metal oxides and liquid phenolic resin components covering the surface of recycled sand after surface modification can increase the melting point of coating sand. Micro-silica powder and salicylic acid strengthen the phenolic resin connection bridge, improving the tensile strength of coating sand. A small amount of sodium silicate remaining on the surface of recycled sand can undergo sintering vitrification during high-temperature casting with molten metal, making the coating sand have excellent heat resistance.

[0076] Compared with Examples 1-3, multiple data in Comparative Example 4 decreased, indicating that the curing process can effectively promote the stability of product quality.

[0077] Compared with Examples 1-3, although the sand conductivity in Comparative Example 5 is slightly higher, the other indicators are all decreasing, indicating that the overall performance of the high-temperature resistant coated sand prepared by this method is superior to that of new sand, turning waste into treasure and being worthy of popularization and application.

[0078] In summary, all the data of the high-temperature resistant coated sand prepared by the present invention are relatively balanced. Except that the conductivity of the regenerated sand is lower than that of the new sand, its coated sand melting point, coated sand tensile strength, coated sand high-temperature strength, core-making yield, and casting yield are all relatively high. The prepared high-temperature resistant coated sand has excellent performance and can be widely used in the casting of complex thin-walled castings.

[0079] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of high-temperature resistant regenerated coated sand, characterized in that, It includes the following steps: S1. Grind and pre-treat the water glass used sand; S2. Carry out wet regeneration on the pre-treated water glass used sand, add acid during the wet regeneration process, and adjust the pH to 6 - 7 with the acid solution to obtain regenerated sand; S3. Add salicylic acid, liquid phenolic resin, metal oxide powder, and microsilica powder to the regenerated sand and mix them for surface modification to obtain modified regenerated sand; Among them, there is a curing step after surface modification: the curing temperature is 80 - 105 °C, and the curing time is 1 - 5 h; S4. Add solid phenolic resin, hexamine, and calcium stearate to the modified regenerated sand for coated sand mixing to obtain a finished product of high-temperature resistant regenerated coated sand.

2. The preparation method according to claim 1, characterized in that, In the step S1, the rotation speed of the grinding pre-treatment is 120 - 360 r / min, and the grinding time is 2 - 8 min.

3. The preparation method according to claim 1, wherein The process parameters of the wet regeneration in the step S2 are: the mass ratio of sand to water is 1:(0.5 - 3), the stirring rotation speed is 270 - 720 r / min, the stirring time is 3 - 10 min, and the water content of the regenerated sand is 2 - 5%.

4. The preparation method according to claim 1, wherein, In the step S3, the addition amounts of salicylic acid, liquid phenolic resin, metal oxide powder, and microsilica powder respectively account for 0.1 - 0.5%, 0.3 - 0.8%, 0.2 - 1%, and 0.1 - 0.5% of the mass of the regenerated sand.

5. The preparation method according to claim 4, characterized in that, The particle sizes of the metal oxide powder and microsilica powder are 1000 mesh - 5000 mesh; and / or The liquid phenolic resin has a viscosity of 2 - 3 Pa·s at 25 °C, a solid content of ≥70%, a free phenol content of 15 - 25%, and a water content of ≤3%.

6. The preparation method according to claim 4, characterized in that, The metal oxide is one or more of aluminum oxide, iron oxide, and chromium oxide.

7. The preparation method according to claim 1, characterized in that, In the step S4, the addition amounts of the solid phenolic resin, hexamine, and calcium stearate are respectively 1 - 3%, 10 - 20%, and 5 - 10% of the mass of the modified regenerated sand.

8. The preparation method according to claim 7, characterized in that, The softening point of the solid phenolic resin is 98 - 115 °C, the polymerization speed is 20 - 40 s, and the free phenol content is ≤5%.

9. The high-temperature resistant regenerated coated sand prepared by the preparation method according to any one of claims 1 - 8.

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