Low-odor anti-shelling precoated sand and preparation method thereof

Abstract

The invention relates to low-odor anti-shelling precoated sand and a preparation method thereof applied to the related technical field of precoated sand, and the low-odor anti-shelling precoated sand and the preparation method thereof are characterized in that the low-odor and anti-shelling effects of the precoated sand are realized by reducing the dosage of urotropin, selecting proper resin and optimizing the granularity composition; besides, through the arrangement of the bidirectional aeration unit, when the resin is cured, air can be actively diffused into sand from top to bottom and from outside to inside in a bidirectional manner, so that the air is in full contact with the sand and then overflows and takes away redundant heat, and compared with an aeration mode that the air is in contact with the sand only from the upper part, the aeration efficiency is greatly improved. And the problem that sand close to the inner wall of the equipment shell is difficult to make full contact with air can be effectively solved, the uniformity of heat exchange with the sand is greatly improved, then the problem of local temperature difference inside and outside the sand in the equipment shell is effectively solved, the resin curing effect is effectively improved, and then the quality of precoated sand is guaranteed.

Description

Technical Field

[0001] The present invention relates to a low-odor anti-shelling coated sand and a preparation method thereof, and in particular to a low-odor anti-shelling coated sand and a preparation method thereof applied to the technical field related to coated sand. Background Art

[0002] Coated sand occupies an important position in castings and has a great influence on the cost, surface roughness, and machining of castings. In particular, coated sand for shell cores requires low odor, resistance to shelling, prevention of allergies among core makers, and uniform crust thickness. For example, the specification of Chinese patent CN108971418A discloses a coated sand additive for preventing sand core shelling, anti-shelling coated sand and a preparation method thereof, and the specification of Chinese patent N104014718A discloses an anti-shelling coated sand and a preparation method thereof.

[0003] However, in the above-mentioned prior art, due to the high content of methenamine and the selection of resin types, it is difficult to well meet the functions of low odor and anti-shelling; in addition, during the production process of coated sand, a large amount of heat will be generated when the resin is cured, and air is generally required to be introduced to take away a large amount of excess heat, maintain the stable and uniform curing of the resin, and then ensure the quality of the finished coated sand. However, in the prior art, when air is introduced, the air is generally directly poured into the sand mixer, and then discharged with the heat. In this process, the air will take away most of the heat on the surface of the sand, but the heat removal effect inside the sand is poor, resulting in the problem of uneven local heat distribution in the sand, resulting in cross-curing uniformity of the coated sand, affecting the quality of the finished product.

[0004] To solve the above problems, during the cooling process, the stirring structure will generally stir the sand to keep it in a dynamic state. However, due to the certain gap between the stirring component and the inner wall of the equipment, some sand will accumulate locally, making it difficult to fully contact with the incoming air. There is a local temperature difference, which affects the resin curing quality of this part and affects the overall quality of the coated sand. Summary of the invention

[0005] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is that the existing coated sand has a strong odor due to the use of a large amount of hexamethylenetetramine, and during the aeration process of the coated sand in the production process, part of the sand is difficult to fully contact with the air, there is a local temperature difference, which affects the overall quality.

[0006] In order to solve the above problems, the present invention provides a low-odor anti-shelling coated sand, comprising the following ingredients by weight: 100% raw sand, 1.2-1.8% resin, 5% calcium stearate, 4-8% hexamethylenetetramine, the resin includes thermoplastic resin and environmentally friendly liquid resin, and the environmentally friendly liquid resin accounts for 20%-30% of the total resin; The preparation process of low-odor anti-shelling coated sand includes the following steps: S1. First, heat the raw sand. When heated to 120-135℃, send the raw sand heated by the automatic temperature control system into the sand mixer; S2, after stirring for a while, add the thermoplastic resin and mix for 50-70 seconds; S3, after mixing evenly, add liquid resin and mix for 20-50 seconds, and finally add hexamethylenetetramine and mix for 10-30 seconds; S4. Then, the blower is turned on to continuously introduce air into the sand mixer for 30-50 seconds. Under the action of the two-way aeration unit, the air enters the sand mixer from the bottom of the equipment, passes through the sand and then is discharged, thereby fully and evenly blowing out the heat in the resin curing process, so that the resin is uniformly and stably cured; S5. Finally, turn off the blower, then add calcium stearate and mix for 10-20 seconds, then discharge the material to complete the preparation of low-odor and anti-shelling coated sand; The sand mixer includes an equipment casing, the upper end of which is fixedly connected with a feed pipe, an auxiliary material pipe and an exhaust pipe, the lower end of which is fixedly connected with a discharge pipe, a stirring assembly is also arranged inside the equipment casing, a motor is installed at the top center of the equipment casing, the motor is used to drive the stirring assembly, a two-way aeration unit is fixedly connected with the lower outer end of the equipment casing, the two-way aeration unit includes a conical shell fixedly connected to the outer end of the equipment casing, an aeration main pipe fixedly connected to the outer end of the conical shell and a compartment assembly located in the conical shell, the end of the aeration main pipe is fixedly passed through the conical shell and is fixedly connected to the equipment casing, two exhaust holes are drilled at the upper end of the conical shell, the upper end of the aeration main pipe outside the conical shell is also fixedly connected with an aeration branch pipe, and the aeration branch pipe is fixed and communicated with the equipment casing.

[0007] In the above-mentioned low-odor and anti-shelling coated sand and its preparation method, the low-odor and anti-shelling effects of the coated sand are achieved by reducing the dosage of hexamine, selecting a suitable resin, and optimizing the particle size composition; in addition, under the setting of the two-way aeration unit, when the resin is solidified, the air can actively diffuse from the outside to the sand, and then overflow and discharge. Compared with the aeration method that only contacts the sand from above, the uniformity of heat exchange with the sand is greatly improved, thereby effectively alleviating the problem of local temperature difference between the inside and outside of the sand in the equipment casing, so that the resin curing effect is effectively improved, and the quality of the coated sand is guaranteed.

[0008] As a further improvement of the present application, a double-round-headed long hole is bored at the lower end of the aeration main pipe located inside the conical shell, and a changing sleeve is provided on the outer movable sleeve of the aeration main pipe. The changing sleeve includes a pipe wrapping sleeve sleeved outside the aeration main pipe, an air guide pipe fixedly connected to the lower end of the pipe wrapping sleeve, and an electromagnetic sheet fixedly embedded in the outer end of the equipment housing, the electromagnetic sheet is opposite to the pipe wrapping sleeve, and an air hole coaxial with the air guide pipe is bored at the lower end of the pipe wrapping sleeve.

[0009] As a further improvement of the present application, the width of the tube wrapping sleeve is smaller than the distance between the inner wall of the conical shell and the outer wall of the equipment shell, and the tube wrapping sleeve completely covers the double round-headed long holes. When the tube wrapping sleeve collides with the inner wall of the conical shell and the outer wall of the equipment shell, the double round-headed long holes and the air holes partially overlap.

[0010] As a further improvement of the present application, the compartment assembly includes a conical interlayer fixedly connected between the inner wall of the conical shell and the outer wall of the equipment shell and fixedly connected to the middle part of the lower end, the lower end edge of the conical interlayer is fixedly connected to the outer wall of the equipment shell, the conical interlayer divides the interior of the conical shell into a sealed compartment and an open compartment, and has an inner compartment opening and an outer compartment opening, the inner compartment opening is communicated with the open compartment, and the outer compartment opening is communicated with the sealed compartment.

[0011] As a further improvement of the present application, the air duct is a conical structure, and the lower end of the air duct is larger than the inner diameter of the inner porthole. When the tube sleeve collides with the inner wall of the conical shell and the outer wall of the equipment shell, the air duct is coaxial with the outer porthole and the inner porthole respectively.

[0012] As a further improvement of the present application, the conical interlayer includes a cylindrical section fixedly connected, a conical section fixedly connected between the cylindrical section and the outer wall of the equipment housing, and a changing layer fixedly connected to the outer surface of the conical section, the cylindrical section is a hard structure, the conical section is an elastic structure, the changing layer is a flexible sealing structure, and the changing layer is filled with a non-Newtonian fluid, and a plurality of aeration holes are drilled on the inner wall of the lower conical surface of the conical shell, each aeration hole is provided with a one-way sealing unit, and the plurality of aeration holes are connected to the opening bin.

[0013] As a further improvement of the present application, the one-way sealing unit includes a hard ball for the hole fixedly connected to the cylindrical segment, and a breathable protective layer fixedly connected to the middle of one end of the hard ball for the hole facing the axis of the equipment housing, the outer edge of the breathable protective layer is fixedly connected to the inner wall of the equipment housing, and the hard ball for the hole is fixedly connected through the conical segment and extends into the redirection layer.

[0014] As a further improvement of the present application, the inner wall of the aeration hole is an arc-shaped structure that fits the surface of the hard ball in the hole, and the maximum span of the aeration hole is smaller than the diameter of the hard ball in the hole, and the breathable protective layer is made of a flexible porous material.

[0015] In summary, by reducing the dosage of hexamine, selecting suitable resins, and optimizing the particle size composition, the effects of low odor and anti-shelling of coated sand are achieved; in addition, under the setting of the two-way aeration unit, when the resin is solidified, the air can diffuse into the sand in both directions from top to bottom and from outside to inside. Compared with the existing technology, it can effectively make up for the problem that the sand near the inner wall of the equipment casing is difficult to fully contact with the air. Compared with the aeration method that only contacts the sand from above, the uniformity of heat exchange with the sand is greatly improved, thereby effectively alleviating the problem of local temperature difference between the inside and outside of the sand in the equipment casing, so that the resin curing effect is effectively improved, thereby ensuring the quality of the coated sand. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the main process of preparing coated sand according to the first embodiment of the present application; Figure 2 A three-dimensional diagram of a sand mixer according to a first embodiment of the present application; Figure 3 A partial stereoscopic diagram of a bidirectional aeration unit according to a first embodiment of the present application; Figure 4 A three-dimensional diagram of the internal part of the bidirectional aeration unit according to the first embodiment of the present application; Figure 5 This is a cross-sectional schematic diagram of a bidirectional aeration unit according to a first embodiment of the present application; Figure 6 This is a comparative schematic diagram of the direction-changing sleeve in different positions according to the first embodiment of the present application; Figure 7 for Figure 6 Schematic diagram at A in the middle; Figure 8 This is a partial cross-sectional view of the one-way sealing unit in the first embodiment of the present application when aeration is not performed and the one-way sealing unit is in a sealed state; Fig. 9 This is a partial cross-sectional view of the first embodiment of the present application when the one-way sealing unit is in an open state during aeration.

[0017] Description of the numbers in the figure: 1 Equipment shell, 101 feed pipe, 102 auxiliary material pipe, 103 exhaust pipe, 104 discharge pipe, 2 conical shell, 201 exhaust hole, 202 inner warehouse opening, 203 outer warehouse opening, 21 conical interlayer, 211 cylindrical section, 212 conical section, 213 change direction layer, 3 aeration main pipe, 31 aeration branch pipe, 4 change direction sleeve, 41 pipe sleeve, 42 air guide pipe, 401 double round head long hole, 402 ferry hole, 501 open warehouse, 502 sealed warehouse, 5 pairs of hard balls, 6 breathable protective layer. DETAILED DESCRIPTION

[0018] Two implementation modes of the present application are described in detail below with reference to the accompanying drawings.

[0019] The first implementation method: Figure 1 A low-odor, anti-shelling coated sand is shown, comprising the following ingredients by weight: 100% raw sand, 1.5% resin, 5% calcium stearate, 6% hexamethylenetetramine, the resin includes thermoplastic resin and environmentally friendly liquid resin, and the environmentally friendly liquid resin accounts for 25% of the total resin; The preparation process of low-odor anti-shelling coated sand includes the following steps: S1. First, heat the raw sand. When heated to 120-135℃, send the raw sand heated by the automatic temperature control system into the sand mixer; S2, after stirring for a while, add the thermoplastic resin and mix for 50-70 seconds; S3, after mixing evenly, add liquid resin and mix for 20-50 seconds, and finally add hexamethylenetetramine and mix for 10-30 seconds; S4. Then, the blower is turned on to continuously introduce air into the sand mixer for 30-50 seconds. Under the action of the two-way aeration unit, the air enters the sand mixer from the bottom of the equipment, passes through the sand and then is discharged, thereby fully and evenly blowing out the heat in the resin curing process, so that the resin is uniformly and stably cured; S5. Finally, turn off the blower, then add calcium stearate and mix for 10-20 seconds, then discharge the material to complete the preparation of low-odor and anti-shelling coated sand; Specifically, the ingredients used in the above-mentioned are only one implementation method. During the specific implementation, they can be appropriately increased or decreased within the range according to actual needs.

[0020] In addition, according to the above ingredients and steps, the odor and shelling resistance of different dosages of methenamine were tested. The specific data are as follows: Low odor anti-shelling coated sand experimental data table The following conclusions can be drawn from the above data: 1. With the decrease of the amount of methenamine added, the gas emission of the coated sand gradually decreased. At the same time, the reduction of methenamine added affected the curing degree of phenolic resin. The two aspects made the gas emission gradually decrease. The reduction of gas emission reduced the odor of the coated sand. 2. The reduction in the amount of hexamethylenetetramine added changes the curing rate of phenolic resin, so the anti-shelling rate of coated sand gradually increases.

[0021] In the above-mentioned low-odor and anti-shelling coated sand and its preparation method, the low-odor and anti-shelling effects of the coated sand are achieved by reducing the dosage of hexamine, selecting a suitable resin, and optimizing the particle size composition. A modified resin with a relatively high softening point and a fast polymerization speed, such as a thermoplastic resin and a liquid resin, is selected to accelerate the crusting speed of the coated sand in the core making process. On the one hand, the crust thickness becomes thinner, and on the other hand, the curing speed is accelerated, thereby avoiding the shelling phenomenon.

[0022] like Figure 2 The sand mixer includes an equipment shell 1, the upper end of the equipment shell 1 is fixedly connected with a feed pipe 101, an auxiliary material pipe 102 and an exhaust pipe 103, the lower end of the equipment shell 1 is fixedly connected with a discharge pipe 104, and a discharge valve is installed at the discharge pipe 104 to facilitate the stable and uniform discharge of the coated sand after solidification. A stirring component is also arranged in the equipment shell 1, and a motor is installed at the top center of the equipment shell 1. The motor is used to drive the stirring component. The lower outer end of the equipment shell 1 is fixedly connected with a two-way aeration unit, such as Figure 3 The bidirectional aeration unit includes a conical shell 2 fixedly connected to the outer end of the equipment housing 1, an aeration main pipe 3 fixedly connected to the outer end of the conical shell 2, and a compartment assembly located in the conical shell 2. The end of the aeration main pipe 3 is fixedly passed through the conical shell 2 and is fixedly connected to the equipment housing 1. Two exhaust holes 201 are drilled at the upper end of the conical shell 2. The upper end of the aeration main pipe 3 located outside the conical shell 2 is also fixedly connected to an aeration branch pipe 31. Solenoid valves are installed on the aeration branch pipe 31 and the aeration main pipe 3. The aeration branch pipe 31 is fixed and communicated with the equipment housing 1. When aeration is required, on the one hand, part of the gas The air flows along the aeration branch pipe 31 into the equipment casing 1, which is consistent with the aeration method in the prior art, so that the air is directly injected into the equipment casing 1. During aeration, the stirring component continuously stirs the raw sand, so that the sand can fully contact with the air. On the other hand, part of the air diffuses into the sand from the inner wall of the equipment casing 1, thereby greatly improving the uniformity of heat exchange with the sand, thereby effectively alleviating the problem of local temperature difference between the inside and outside of the sand in the equipment casing, and thereby effectively assisting the resin adhered to the surface of the sand to solidify more evenly and with better effect, thereby effectively ensuring the quality of the finished coated sand product.

[0023] Under the setting of the two-way aeration unit, when the resin is solidifying, the air can actively diffuse from the outside into the sand, and then overflow and discharge. Compared with the aeration method that only contacts the sand from above, the uniformity of heat exchange with the sand is greatly improved, thereby effectively alleviating the problem of local temperature difference between the inside and outside of the sand in the equipment casing, effectively improving the resin solidification effect, and ensuring the quality of the coated sand.

[0024] like Figure 6-7The lower end of the aeration main pipe 3 located in the conical shell 2 is drilled with a double round head long hole 401, and the outer sleeve of the aeration main pipe 3 is provided with a change-direction sleeve 4, which includes a pipe sleeve 41 sleeved outside the aeration main pipe 3, an air guide pipe 42 fixedly connected to the lower end of the pipe sleeve 41, and an electromagnetic sheet fixedly embedded in the outer end of the equipment shell 1, the electromagnetic sheet is directly opposite to the pipe sleeve 41, and a magnetic ring is embedded in the pipe sleeve 41. The lower end of the pipe sleeve 41 is drilled with an air hole 402 coaxial with the air guide pipe 42, and the width of the pipe sleeve 41 is The distance between the inner wall of the conical shell 2 and the outer wall of the equipment housing 1 is smaller than that between the inner wall of the conical shell 2 and the outer wall of the equipment housing 1, and the tube sleeve 41 completely covers the double round head long hole 401. When the tube sleeve 41 conflicts with the inner wall of the conical shell 2 and the outer wall of the equipment housing 1, the double round head long hole 401 and the air ferry hole 402 are partially overlapped. By changing the current of the electromagnetic sheet, the direction of the magnetic force on the tube sleeve 41 can be changed, thereby achieving the effect of changing the position of the tube sleeve 41, so that when blowing, air can enter different spaces according to actual needs.

[0025] The compartment assembly includes 22 fixedly connected between the inner wall of the conical shell 2 and the outer wall of the equipment shell 1, and a conical interlayer 21 fixedly connected to the middle of the lower end of 22. The lower end edge of the conical interlayer 21 is fixedly connected to the outer wall of the equipment shell 1. The conical interlayer 21 divides the interior of the conical shell 2 into a sealed compartment 502 and an open compartment 501. An inner compartment opening 202 and an outer compartment opening 203 are cut on 22. The inner compartment opening 202 communicates with the open compartment 501, and the outer compartment opening 203 communicates with the sealed compartment 502. The air guide tube 42 is a conical structure, and the lower end of the air guide tube 42 is larger than the inner diameter of the inner compartment opening 202. When the tube cover 41 contacts the inner wall of the conical shell 2 and the outer wall of the device housing 1, the air guide tube 42 is coaxial with the outer compartment opening 203 and the inner compartment opening 202 respectively. When blowing, the electromagnetic sheet can be energized by controlling the electromagnetic sheet to adsorb the tube cover 41, so that it moves toward the device housing 1 and adheres to it. At this time, the air guide tube 42 cover is set outside the inner compartment opening 202, so that the blower blows in The air enters the open bin 501, and this part of the air can push the conical interlayer 21 outward to deform it outward, thereby separating the hard ball 5 from the aeration hole. At this time, this part of the air can enter the equipment housing 1 along the inner wall of the equipment housing 1 along the aeration hole, diffuse into the sand, carry heat, and then overflow into the equipment housing 1 and be discharged from the exhaust pipe 103. When ventilation and heat dissipation are not required, the electromagnetic sheet can be controlled to pass a reverse current to generate a reverse magnetic force and The tube sleeve 41 generates a repulsive force, causing it to move toward the conical shell 2 and adhere to its inner wall. At this time, the air guide tube 42 is opposite to the outer chamber opening 203, and the blown air enters the sealing chamber 502, which can generate a thrust on the conical interlayer 21 toward the equipment casing 1, thereby causing the hard ball 5 to collide with the aeration hole, thereby sealing the place, making it difficult for the original sand in the equipment casing 1 to cause the breathable protective layer 6 to deform, and causing part of the sand to sink into the aeration hole, making it difficult for the hard ball 5 to match the aeration hole again.

[0026] The conical interlayer 21 includes a cylindrical section 211 fixedly connected to 22, a conical section 212 fixedly connected between the cylindrical section 211 and the outer wall of the equipment housing 1, and a redirecting layer 213 fixedly connected to the outer surface of the conical section 212. The cylindrical section 211 is a hard structure, and the conical section 212 is an elastic structure, so that when air enters the open bin 501 or the sealed bin 502, it can deform in different directions, which is convenient for controlling the opening and closing of the aeration holes. The redirecting layer 213 is a flexible sealing structure, and the redirecting layer 213 is filled with a non-Newtonian fluid. The inner wall of the lower conical surface of the conical shell 2 is cut with A plurality of aeration holes are provided, and the plurality of aeration holes are all connected to the opening bin 501, and a one-way sealing unit is provided at each aeration hole, and the one-way sealing unit comprises a hard ball 5 fixedly connected to the cylindrical section 211, and a breathable protective layer 6 fixedly connected to the middle of one end of the hard ball 5 facing the axis of the equipment housing 1, and the outer edge of the breathable protective layer 6 is fixedly connected to the inner wall of the equipment housing 1, and the hard ball 5 is fixedly passed through the conical section 212 and extends into the redirecting layer 213, and the inner wall of the aeration hole is an arc structure that fits the surface of the hard ball 5, and the maximum span of the aeration hole is smaller than the diameter of the hard ball 5, and the breathable The protective layer 6 is made of a flexible porous material. When there is no need for blast heat dissipation, the solenoid valve on the aeration branch pipe 31 can be closed, the solenoid valve on the aeration main pipe 3 can be opened, and then the direction-changing sleeve 4 can be controlled to communicate with the sealing chamber 502. When air enters the sealing chamber 502, compressed gas is introduced into the sealing chamber 502 to generate pressure on the conical surface section 212, thereby hardening it, thereby generating better support for the hard ball 5 for the hole, so that the hard ball 5 for the hole can stably contact the aeration hole, and then the solenoid valves on the aeration branch pipe 31 and the aeration main pipe 3 are closed, thereby stabilizing the aeration hole. It can not only seal but also effectively protect the breathable protective layer 6, so that when inflation is not needed, it will not be easily pulled and deformed toward the aeration holes due to the squeezing of the sand; and after the air enters the open bin 501, under the action of air pressure, it will push the redirecting layer 213 away from the aeration holes, so that the pair of hard balls 5 in the holes will be away from the aeration holes, so that the gas can pass through the breathable protective layer 6 and enter the equipment housing 1 along the wall, and then diffuse from the outside to the inside and from the bottom to the top into the sand, thereby effectively improving the uniformity of heat dissipation during resin curing, thereby making the resin curing effect more uniform and the quality of the coated sand better.

[0027] It is worth noting that the breathable protective layer 6 is made of breathable material, and the pores therein are smaller than the particle size of sand.

[0028] In summary, by reducing the dosage of hexamethylenetetramine, selecting a suitable resin, and optimizing the particle size composition, the effects of low odor and anti-shelling of the coated sand are achieved; in addition, under the setting of the two-way aeration unit, when the resin is cured, the air can diffuse into the sand in both directions from top to bottom and from outside to inside. Compared with the prior art, it can effectively make up for the problem that the sand near the inner wall of the equipment casing 1 is difficult to fully contact with the air. Compared with the aeration method that only contacts the sand from above, the uniformity of heat exchange with the sand is greatly improved, thereby effectively alleviating the problem of local temperature difference between the inside and outside of the sand in the equipment casing, so that the resin curing effect is effectively improved, thereby ensuring the quality of the coated sand.

[0029] The second implementation method: Based on the first embodiment, this embodiment adds a plurality of electromagnetic strips corresponding to the plurality of aeration holes on the conical shell 2, and the rest of the parts are consistent with the first embodiment.

[0030] A rectangular magnetic core is fixedly embedded inside the hard ball 5 for holes. When energized, the electromagnetic strip generates a magnetic repulsion force on the rectangular magnetic core, thereby squeezing the multiple hard balls 5 for holes so as to fit tightly with the aeration holes. Then, compressed gas is introduced into the sealing bin 502 to squeeze the conical interlayer 21, thereby stably limiting the multiple hard balls 5 for holes. After that, the electromagnetic strip is controlled to cut off the power. Compared with directly inflating the hard ball 5 for holes to match the aeration holes, it is less likely that the hard ball 5 for holes will be difficult to return to the aeration holes due to the pressure of sand, thereby effectively ensuring the protection effect of the hard ball 5 for holes and the breathable protective layer 6 when aeration and heat dissipation are not required.

[0031] In view of current practical needs, the above-mentioned implementation mode adopted in this application is not limited to the scope of protection. Various changes made within the knowledge scope of technical personnel in this field without departing from the concept of this application still fall within the scope of protection of the present invention.

Claims

1. A low-odor, anti-shelling coated sand, characterized in that: Contains the following ingredients by weight: 100% raw sand, 1.2-1.8% resin, 5% calcium stearate, 4-8% hexamethylenetetramine, the resin includes thermoplastic resin and environmentally friendly liquid resin, the environmentally friendly liquid resin accounts for 20%-30% of the total resin; The preparation process of the low-odor anti-shelling coated sand comprises the following steps: S1. First, heat the raw sand. When heated to 120-135℃, send the raw sand heated by the automatic temperature control system into the sand mixer; S2, after stirring for a while, add the thermoplastic resin and mix for 50-70 seconds; S3, after mixing evenly, add liquid resin and mix for 20-50 seconds, and finally add hexamethylenetetramine and mix for 10-30 seconds; S4. Then, the blower is turned on to continuously introduce air into the sand mixer for 30-50 seconds. Under the action of the two-way aeration unit, the air enters the sand mixer from the bottom of the equipment, passes through the sand and then is discharged, thereby fully and evenly blowing out the heat in the resin curing process, so that the resin is uniformly and stably cured; S5. Finally, turn off the blower, then add calcium stearate and mix for 10-20 seconds, then discharge the material to complete the preparation of low-odor and anti-shelling coated sand; The sand mixer comprises an equipment housing (1), the upper end of the equipment housing (1) being fixedly connected to a feed pipe (101), an auxiliary material pipe (102) and an exhaust pipe (103), the lower end of the equipment housing (1) being fixedly connected to a discharge pipe (104), a stirring assembly being further arranged in the equipment housing (1), a motor being installed at the top center of the equipment housing (1), the motor being used to drive the stirring assembly, a bidirectional aeration unit being fixedly connected to the lower outer end of the equipment housing (1), the bidirectional aeration unit comprising a A conical shell (2) at the outer end of an equipment housing (1), an aeration main pipe (3) fixedly connected to the outer end of the conical shell (2), and a compartment assembly located inside the conical shell (2); the end of the aeration main pipe (3) is fixedly passed through the conical shell (2) and is fixedly connected to the equipment housing (1); two exhaust holes (201) are drilled at the upper end of the conical shell (2); an aeration branch pipe (31) is also fixedly connected to the upper end of the aeration main pipe (3) located outside the conical shell (2); and the aeration branch pipe (31) is fixed to and communicates with the equipment housing (1).

2. The method for preparing a low-odor anti-shelling coated sand according to claim 1, characterized in that: The lower end of the aeration main pipe (3) located inside the conical shell (2) is bored with a double-round-headed long hole (401); the outer sleeve of the aeration main pipe (3) is provided with a direction-changing sleeve (4); the direction-changing sleeve (4) comprises a pipe-wrapping sleeve (41) sleeved outside the aeration main pipe (3), an air guide pipe (42) fixedly connected to the lower end of the pipe-wrapping sleeve (41), and an electromagnetic sheet fixedly embedded in the outer end of the equipment housing (1); the electromagnetic sheet is directly opposite to the pipe-wrapping sleeve (41); and the lower end of the pipe-wrapping sleeve (41) is bored with an air hole (402) coaxial with the air guide pipe (42).

3. The method for preparing a low-odor anti-shelling coated sand according to claim 2, characterized in that: The width of the tube-wrapping sleeve (41) is smaller than the distance between the inner wall of the conical shell (2) and the outer wall of the device housing (1), and the tube-wrapping sleeve (41) completely covers the double-round-headed long hole (401). When the tube-wrapping sleeve (41) contacts the inner wall of the conical shell (2) and the outer wall of the device housing (1), the double-round-headed long hole (401) and the air-transmitting hole (402) partially overlap.

4. The method for preparing a low-odor anti-shelling coated sand according to claim 3, characterized in that: The compartment assembly comprises a (22) fixedly connected between the inner wall of the conical shell (2) and the outer wall of the equipment shell (1), and a conical interlayer (21) fixedly connected to the middle part of the lower end of (22), the lower end edge of the conical interlayer (21) being fixedly connected to the outer wall of the equipment shell (1), the conical interlayer (21) dividing the interior of the conical shell (2) into a sealed compartment (502) and an open compartment (501), the (22) being provided with an inner compartment opening (202) and an outer compartment opening (203), the inner compartment opening (202) being in communication with the open compartment (501), and the outer compartment opening (203) being in communication with the sealed compartment (502).

5. The method for preparing a low-odor anti-shelling coated sand according to claim 4, characterized in that: The air guide tube (42) is a conical structure, and the lower end of the air guide tube (42) is larger than the inner diameter of the inner chamber opening (202). When the tube wrapping sleeve (41) contacts the inner wall of the conical shell (2) and contacts the outer wall of the device housing (1), the air guide tube (42) is coaxial with the outer chamber opening (203) and the inner chamber opening (202), respectively.

6. The method for preparing a low-odor anti-shelling coated sand according to claim 5, characterized in that: The conical interlayer (21) comprises a cylindrical section (211) fixedly connected to (22), a conical section (212) fixedly connected between the cylindrical section (211) and the outer wall of the equipment housing (1), and a redirecting layer (213) fixedly connected to the outer surface of the conical section (212); the cylindrical section (211) is a hard structure, the conical section (212) is an elastic structure, the redirecting layer (213) is a flexible sealing structure, and the redirecting layer (213) is filled with a non-Newtonian fluid; a plurality of aeration holes are drilled on the inner wall of the lower conical surface of the conical housing (2), each of the aeration holes is provided with a one-way sealing unit, and the plurality of aeration holes are communicated with the open bin (501).

7. The method for preparing low-odor anti-shelling coated sand according to claim 6, characterized in that: The one-way sealing unit comprises a hard ball (5) fixedly connected to the cylindrical segment (211), and a breathable protective layer (6) fixedly connected to the middle of one end of the hard ball (5) facing the axis of the device housing (1), the outer edge of the breathable protective layer (6) being fixedly connected to the inner wall of the device housing (1), and the hard ball (5) fixedly passes through the conical segment (212) and extends into the direction-changing layer (213).

8. The method for preparing low-odor anti-shelling coated sand according to claim 7, characterized in that: The inner wall of the aeration hole is an arc-shaped structure that fits the surface of the hard ball (5) in the hole, and the maximum span of the aeration hole is smaller than the diameter of the hard ball (5) in the hole. The air-permeable protective layer (6) is made of a flexible porous material.

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