A method for fluidizing and uniformly coating quartz sand using a fluidized bed

Abstract

The present invention relates to a method for fluidizing and uniformly coating quartz sand by using a fluidized bed, wherein quartz sand is added to the bottom of the fluidized bed through a feed hopper; a gas at a certain temperature is blown in from an air inlet pipe to fluidize the quartz sand and spray phenolic resin through a first atomizing nozzle; at the same time, a urotropine aqueous solution is sprayed through a second atomizing nozzle, and calcium stearate powder is sprayed through a powder spraying head; under the action of the airflow, the quartz sand coated with the phenolic resin continues to move upward until the upper baffle, then changes the direction and speed of movement to enter the side area of ​​the fluidized bed, and passes through the urotropine aqueous solution spray cooling area and the calcium stearate spraying area in turn to prevent the quartz sand from agglomerating; finally, the coated quartz sand product is collected through a sand box. The method realizes the fluidized coating of quartz sand through a fluidized bed, and the coating is more uniform. The phenolic resin is sprayed through an atomizing nozzle, which reduces the consumption of resin and reduces the production cost, and combined with a water cooling method, the production cycle is short.

Description

Technical Field

[0001] The invention belongs to the technical field of coating processing of quartz sand for casting, and particularly relates to a method for fluidizing and uniformly coating quartz sand by utilizing a fluidized bed. Background Art

[0002] Casting is one of the most common means to obtain blanks or finished parts, and is applicable to most metal materials. Therefore, castings produced by casting technology can be widely used in defense and military, aerospace, machinery manufacturing, automobile manufacturing, petrochemical, engineering construction and other fields. With the development of social economy, the progress of science and technology, the rapid development of machinery industry, the requirements for the structure and mechanical properties of castings have been greatly improved, and the requirements for the appearance quality and dimensional accuracy of castings have also become higher and higher. The coated sand casting process came into being. The sand core has good strength and disintegration. The castings produced by coated sand have high dimensional accuracy, good surface quality and high production efficiency.

[0003] The coated sand mainly uses high-quality selected natural quartz sand as the raw sand, thermoplastic phenolic resin, hexamethylenetetramine and reinforcing agent as raw materials. The product has suitable strength performance; good fluidity, the sand mold and sand core produced have clear outlines and dense structure, and can produce complex sand cores; the surface quality of the sand mold (core) is good; the collapsibility is good, and the casting is easy to clean. According to different technical requirements, the proportion can be appropriately adjusted in terms of curing speed, demolding, fluidity, collapsibility, casting surface finish, storage, etc. At present, coated quartz sand is one of the best modeling materials for casting related parts of mechanical equipment such as valves, pump bodies, automobile cylinder bodies, cylinder heads, intake manifolds, etc. The preparation processes of coated sand mainly include cold coating, warm coating, and hot coating. Among them, the hot coating has a good coating effect and is suitable for mass production. At present, the production of coated sand almost all adopts the hot coating method. The thermal coating process is to heat the raw sand to a certain temperature, then mix and stir with phenolic resin, urotropine aqueous solution and calcium stearate respectively, and then cool, crush and screen naturally. This method is relatively complicated and requires the use of special sand mixing equipment to mix various raw materials.

[0004] The main deficiencies of the existing technology are: 1. For the mixing of coated sand, various raw materials are mostly put into a mixing barrel according to a certain proportion and mixed by mechanical stirring. This kind of mixing method has a large power load, and insufficient stirring leads to uneven coating. 2. After the coated sand is coated, it adopts a natural cooling method, which has a long production cycle. Summary of the invention

[0005] In view of the above problems existing in the prior art, the technical problem to be solved by the present invention is: how to provide a method for producing coated sand with uniform coating and short production cycle.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for fluidizing quartz sand and uniformly coating it by using a fluidized bed, wherein the fluidized bed comprises the following structure:

[0007] It comprises a fluidized bed shell and a feed hopper, wherein an air inlet pipe is arranged at the bottom of the fluidized bed shell, and two vertically arranged walls are arranged inside the fluidized bed shell, and a pipeline is arranged inside each of the walls, and a plurality of No. 1 atomizing nozzles are installed on each wall, and the plurality of No. 1 atomizing nozzles are connected to the pipelines in the corresponding walls;

[0008] The feed hopper comprises a feed hopper and a feed pipe which are interconnected, wherein the feed hopper is located outside the top of the fluidized bed shell, the feed pipe is located between two walls, and the discharge port at the bottom end of the feed pipe is close to the inner bottom wall of the fluidized bed shell;

[0009] A baffle plate with an inverted triangle longitudinal section is fixedly mounted on the feeding pipe, the baffle plate is located above the wall, and the diameter of the top of the baffle plate is greater than the distance between the two walls;

[0010] An air distribution plate is provided in the fluidized bed shell, and a discharge port is provided at the bottom of the fluidized bed shell. The air distribution plate and the air inlet pipe are both located between the two walls. The air distribution plate is close to the inner bottom wall of the fluidized bed shell, and a plurality of blowing holes are provided on the air distribution plate. The discharge port is located between the wall and the inner vertical wall of the fluidized bed shell. A sand box is provided on the outer side of the bottom of the fluidized bed shell, and a sand inlet on the top of the sand box is connected to the discharge port.

[0011] A plurality of No. 2 atomizing nozzles and a plurality of powder spraying heads are arranged on the inner vertical wall of the fluidized bed shell, the No. 2 atomizing nozzle is lower in vertical direction than the top of each wall, and the powder spraying head is lower in vertical direction than the No. 2 atomizing nozzle;

[0012] The method for uniform film coating using the fluidized bed comprises the following steps:

[0013] S1: adding quartz sand to the bottom of the fluidized bed through a feed hopper;

[0014] S2: Blowing gas with a temperature of 80-150°C from the air inlet pipe, the gas enters the fluidized bed to fluidize the quartz sand, and adding the diluted silane solution from the funnel into the fluidized bed along with the quartz sand raw material. The gas temperature can be selected to be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C;

[0015] S3: After 5-8 seconds, a phenolic resin having a temperature of 80-150°C is sprayed through a No. 1 atomizing nozzle. The temperature of the phenolic resin can be selected to be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C;

[0016] S4: At the same time, the urotropine aqueous solution is sprayed through the second atomizing nozzle, and the calcium stearate powder is sprayed through the powder spraying head;

[0017] S5: Under the action of the airflow, the quartz sand coated with phenolic resin continues to move upward until it reaches the upper baffle. After the quartz sand collides with the baffle, the movement direction and speed are changed. The coated quartz sand enters the side area of ​​the fluidized bed, loses the effect of the airflow, and falls under the action of gravity. When passing through the spraying area of ​​the urotropine aqueous solution, the phenolic resin on the surface of the coated quartz sand solidifies and cools. The coated quartz sand passes through the calcium stearate spraying area to prevent the coated quartz sand from agglomerating.

[0018] S6: The finished coated quartz sand enters the sand box below the fluidized bed from the discharge port and is collected.

[0019] As an optimization, the gas in S2 is blown into the air inlet pipe at a speed of 1.0-10.0 m / s. The gas speed can be selected as 1.0 m / s, 2.0 m / s, 3.0 m / s, 4.0 m / s, 5.0 m / s, 6.0 m / s, 7.0 m / s, 8.0 m / s, 9.0 m / s or 10.0 m / s. The appropriate blowing speed and flow rate are calculated based on the weight of the material added in the fluidized bed to make the quartz sand reach a fluidized state. When the gas flow rate is greater than 10.0 m / s, the quartz sand will move violently, causing violent collisions and affecting the coating effect. It also affects the movement trajectory of the quartz sand after coating, and even causes the coated sand to block the filter; when the gas flow rate is less than 1.0 m / s, it will affect the fluidization state of the quartz sand, thereby affecting the coating effect, and will also affect the movement trajectory of the quartz sand after coating, such as being unable to reach the side area to complete the solidification cooling step.

[0020] As an optimization, the silane in S2 is diluted 3-6 times, and the dilution can be selected to be 3 times, 4 times, 5 times or 6 times. Silane is used in the traditional coated sand preparation process to avoid quartz sand agglomeration and increase fluidity. Because this patent adopts fluidized uniform coating technology, quartz sand is distributed in the fluidized bed space in a fluidized state, so the silane concentration can be reduced, effectively reducing the production cost.

[0021] As an optimization, the ratio of the mass (kg) of quartz sand to the volume (ml) of silane in S2 is 2.5 to 5:1. When the mass (kg) of quartz sand to the volume (ml) of silane is more than 5:1, it means that too little silane is added, which may cause the coated sand to agglomerate and deteriorate in fluidity. When the mass (kg) of quartz sand to the volume (ml) of silane is less than 2.5:1, too much silane is added, which is not conducive to improving the bonding force between the phenolic resin and the quartz sand interface, and affects the phenolic resin coating effect on the surface of the quartz sand.

[0022] As an optimization, the droplet size of the phenolic resin in S3 is 2-10 μm, and the droplet size of the phenolic resin can be selected to be 2 μm, 4 μm, 5 μm, 8 μm or 10 μm. This droplet size can make the droplets of phenolic resin evenly sprayed on the surface of quartz sand to achieve a uniform coating effect.

[0023] As an optimization, the flow rate of the phenolic resin in S3 is 200-2500 cm 3 / min. This flow range combined with the movement state of quartz sand can achieve better coating effect.

[0024] As an optimization, the ratio of water to hexamine in S4 is 3: 1. This ratio can make the hexamine aqueous solution have a good solidification and cooling effect on the coated quartz sand.

[0025] As an optimization, the S4 urotropine aqueous solution urotropine aqueous solution is 150-2500 cm 3 / min flow rate is sprayed from the second atomizing nozzle. This flow range is set in combination with the movement state of the quartz sand after coating to ensure that the urotropine aqueous solution can be sprayed on the surface of the quartz sand after coating to promote the solidification of the phenolic resin on the surface of the quartz sand.

[0026] As an optimization, the droplet size of the S4 urotropine aqueous solution is 50-100 μm, and the droplet size of the urotropine aqueous solution can be 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm. This droplet size can make the urotropine aqueous solution evenly sprayed on the surface of the retroperitoneal quartz sand, so that the coated quartz sand can be better cooled and solidified.

[0027] Compared with the prior art, the present invention has at least the following advantages:

[0028] The method of the present invention uses a fluidized bed to fluidize the quartz sand for more uniform coating. The quartz sand surface is coated by atomizing phenolic resin through a nozzle, which reduces resin consumption and production costs, and uses water cooling to improve production efficiency.

[0029] The present invention proposes to fluidize and uniformly coat quartz sand in a fluidized bed, fluidize the quartz sand by blowing hot air into the fluidized bed, spray liquid phenolic resin into the fluidized quartz sand through an atomizing nozzle for coating, fully mix the resin droplets with the quartz sand and form a film on the surface of the quartz sand, spray a methenamine aqueous solution on the coated quartz sand surface to solidify the resin coating and cool it, and finally spray calcium stearate powder on the cured coated quartz sand surface to prevent the quartz sand from agglomerating after the coating, improve the fluidity of the coated sand and the demoulding property of the sand mold. Compared with the mechanical stirring method, this method can reduce electricity costs and resin consumption, and can be water-cooled, shorten the production cycle, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the fluidized bed device of the present invention.

[0031] In the figure, fluidized bed shell -1, filter -2, baffle -3, No. 2 atomizing nozzle -4, No. 1 atomizing nozzle -5, coated sand -6, quartz sand -7, air distribution plate -8, air inlet pipe -9, sand box -10, feed hopper -11, feed pipe -12, wall -13, powder spray head -14. DETAILED DESCRIPTION

[0032] The present invention is described in further detail below.

[0033] In the present invention, "front", "rear", "left", "right", "up", and "down" all refer to Figure 1 The direction in which 'front' refers to the Figure 1 In the figure, the back is facing outward relative to the paper surface. Figure 1 The center faces inward relative to the paper.

[0034] Example: See Figure 1 , a method for fluidizing quartz sand and uniformly coating it using a fluidized bed, wherein the fluidized bed comprises the following structure:

[0035] It includes a fluidized bed shell 1 and a feed funnel. The bottom of the fluidized bed shell 1 is provided with an air inlet pipe 9, and also includes a feed funnel; the fluidized bed shell 1 has two vertically arranged walls 13, each of the walls 13 is provided with a pipeline, and each wall 13 is installed with multiple No. 1 atomizing nozzles 5, and the multiple No. 1 atomizing nozzles 5 are connected to the pipelines in the corresponding walls 13.

[0036] The feed funnel includes a feed hopper 11 and a feed pipe 12 which are interconnected. The feed hopper 11 is located on the outside of the top of the fluidized bed shell 1, and the feed pipe 12 is located between two walls 13, and the discharge port at the bottom end of the feed pipe 12 is close to the inner bottom wall of the fluidized bed shell 1; in specific implementation, the feed pipe 12 passes through the filter 2 in the fluidized bed shell 1 and extends downward until it is close to the inner bottom wall of the fluidized bed shell 1.

[0037] A baffle plate 3 with an inverted triangle longitudinal section is fixedly mounted on the feeding pipe 12 . The baffle plate 3 is located above the wall 13 , and the diameter of the top of the baffle plate 3 is greater than the distance between the two walls 13 .

[0038] An air distribution plate 8 is provided in the fluidized bed shell 1, and a discharge port is provided at the bottom of the fluidized bed shell 1. The air distribution plate 8 and the air inlet pipe 9 are both located between two walls 13. The air distribution plate 8 is close to the inner bottom wall of the fluidized bed shell 1. The air distribution plate 8 has multiple blowing holes. The discharge port is located between the wall 13 and the inner vertical wall of the fluidized bed shell 1. A sand box 10 is provided on the outside of the bottom of the fluidized bed shell 1, and the sand inlet at the top of the sand box 10 is connected to the discharge port.

[0039] By arranging the air distribution plate 8, the gas blown into the bottom of the fluidized bed through the air inlet pipe 9 is evenly dispersed, which is more conducive to fluidizing the quartz sand arranged at the bottom of the fluidized bed.

[0040] A plurality of No. 2 atomizing nozzles 4 and a plurality of powder spraying heads 14 are provided on the inner vertical wall of the fluidized bed shell 1 . The No. 2 atomizing nozzles 4 are vertically lower than the top of each wall 13 , and the powder spraying heads 14 are vertically lower than the No. 2 atomizing nozzles 4 .

[0041] In a specific implementation, the plurality of No. 1 atomizing nozzles 5 are symmetrically distributed with the feed pipe 12 as the axis. In a specific implementation, the plurality of No. 1 atomizing nozzles 5 are located at the portion of the feed pipe 12 close to the baffle 3. This is because after the feed pipe 12 delivers the quartz sand to the bottom of the fluidized bed, the hot air blows up the quartz sand. Due to the effect of the air distribution plate 8, the blown up quartz sand is basically evenly distributed outside the feed pipe 12. Therefore, the plurality of No. 1 atomizing nozzles 5 are symmetrically distributed with the feed pipe 12 as the axis, which can make the phenolic resin and the quartz sand more evenly mixed.

[0042] In specific implementation, the plurality of No. 2 atomizing nozzles 4 are symmetrically distributed with the feed pipe 12 as the axis, and the No. 2 atomizing nozzle 4 is higher in the vertical direction than the No. 1 atomizing nozzle 5. Under the action of the airflow, the quartz sand coated with phenolic resin continues to move upward until it reaches the upper baffle 3, and then changes the direction and speed of movement to enter the area between the air inlet pipe and the inner vertical wall of the fluidized bed shell 1, i.e., the cooling area. At this time, the quartz sand coated with phenolic resin is sprayed and cooled by the urotropine aqueous solution sprayed from the No. 2 atomizing nozzle 4. Since the coated quartz sand enters the side area of ​​the fluidized bed, it loses the effect of the airflow and will immediately fall due to the action of gravity. Therefore, in order to extend the cooling time of the coated quartz sand and also to ensure the cooling effect, the No. 2 atomizing nozzle 4 is higher in the vertical direction than the No. 1 atomizing nozzle 5, so that the coated quartz sand is immediately cooled as soon as it enters the side area of ​​the fluidized bed.

[0043] The method for uniform film coating using the fluidized bed comprises the following steps:

[0044] S1: 50-500 kg of quartz sand 7 is added into the fluidized bed through the feed hopper 11 and then fed into the bottom of the fluidized bed through the feed pipe 12.

[0045] S2: Blow gas with a temperature of 80-150°C from the air inlet pipe 9, the gas enters the fluidized bed, fluidizes the quartz sand, dilutes 10-200ml of silane to 30~600ml of silane solution, and adds the quartz sand raw material from the funnel into the fluidized bed. The gas is blown into the air inlet pipe at a speed of 1.0-10.0 m / s.

[0046] S3: After 5-8 seconds, a phenolic resin at a temperature of 80-150°C is sprayed through a first atomizing nozzle 5; the droplet size of the phenolic resin is 2-10 μm, and the flow rate is 200-2500 cm 3 / min.

[0047] S4: At the same time, the urotropine aqueous solution is sprayed out through the second atomizing nozzle 4, and the calcium stearate powder is sprayed out through the powder spraying head 14; the ratio of water to urotropine is 3:1, and the flow rate of the urotropine aqueous solution is 150-2500 cm 3 / min, the droplet size of the urotropine aqueous solution is 50-100μm.

[0048] S5: Under the action of the airflow, the fluidized quartz sand moves upward, and passes through the liquid phenolic resin area sprayed by the first atomizing nozzle 5, so that the quartz sand and the phenolic resin micro-droplets are fully mixed and evenly coated on the surface of the quartz sand. Then, under the action of the airflow, the quartz sand coated with the phenolic resin continues to move upward until it reaches the upper baffle 3. After the coated quartz sand collides with the baffle, the moving direction and speed are changed, and it enters the side area of ​​the fluidized bed, that is, the area between the air inlet pipe and the inner vertical wall of the fluidized bed shell 1. The coated quartz sand enters the side area of ​​the fluidized bed, loses the effect of the airflow, and falls under the action of gravity. When passing through the hexamethylenetetramine aqueous solution spraying area, the phenolic resin on the surface of the coated quartz sand is solidified and cooled; the solidified coated quartz sand continues to fall under the action of gravity, passes through the calcium stearate spraying area, prevents the coated quartz sand from agglomerating, and improves the fluidity of the coated sand and the demoulding property of the sand mold.

[0049] S6: The finished coated quartz sand product enters the sand box 10 below the fluidized bed from the discharge port and is collected.

[0050] The method of the present invention allows gas at 80-150° C. to pass through the quartz sand bed from bottom to top through the air blowing hole, so that the quartz sand 7 is in a suspended motion state, and the liquid phenolic resin is sprayed through the first atomizing nozzle 5, so that the phenolic resin micro-droplets are fully mixed with the quartz sand 7 and coated on the surface of the quartz sand 7. The second atomizing nozzle 4 sprays the urotropine aqueous solution on the surface of the coated quartz sand to cool and solidify the resin coating, and finally the coated sand 6 is collected through the sand box 10, and the spray cooling method is adopted to save the production cycle.

[0051] The method of the present invention is not limited to the mixing of quartz sand and phenolic resin, but is also applicable to other mixing methods involving solid-gas mixing and solid-liquid mixing.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for fluidizing quartz sand and uniformly coating it using a fluidized bed, characterized in that: The structure of the fluidized bed is: It comprises a fluidized bed shell (1) and a feed hopper, wherein an air inlet pipe (9) is provided at the bottom of the fluidized bed shell (1), and the fluidized bed shell (1) has two vertically arranged walls (13), each of which is provided with a pipeline, and each of which is provided with a plurality of atomizing nozzles (5), and the plurality of atomizing nozzles (5) are connected to the pipelines in the corresponding walls (13); The feed hopper comprises a feed hopper (11) and a feed pipe (12) which are interconnected, wherein the feed hopper (11) is located outside the top of the fluidized bed shell (1), the feed pipe (12) is located between two walls (13), and the discharge port at the bottom end of the feed pipe (12) is close to the inner bottom wall of the fluidized bed shell (1); A baffle plate (3) having an inverted triangular longitudinal section is fixedly mounted on the feed pipe (12); the baffle plate (3) is located above the wall (13), and the diameter of the top of the baffle plate (3) is greater than the distance between the two walls (13); An air distribution plate (8) is provided inside the fluidized bed shell (1), and a discharge port is provided at the bottom of the fluidized bed shell (1). The air distribution plate (8) and the air inlet pipe (9) are both located between two walls (13), the air distribution plate (8) is close to the inner bottom wall of the fluidized bed shell (1), and a plurality of air blowing holes are provided on the air distribution plate (8). The discharge port is located between the wall (13) and the inner vertical wall of the fluidized bed shell (1), and a sand box (10) is provided on the outer side of the bottom of the fluidized bed shell (1), and the sand inlet at the top of the sand box (10) is connected to the discharge port; A plurality of atomizing nozzles (4) and a plurality of powder spraying heads (14) are provided on the inner vertical wall of the fluidized bed shell (1); the atomizing nozzles (4) are lower in vertical height than the top of each wall (13); and the powder spraying heads (14) are lower in vertical height than the atomizing nozzles (4); The method for uniform film coating using the fluidized bed comprises the following steps: S1: adding quartz sand to the bottom of the fluidized bed through a feed hopper (11); S2: Blowing gas at a temperature of 80-150°C from the gas inlet pipe (9), the gas enters the fluidized bed, fluidizes the quartz sand, and adds the diluted silane solution from the feed funnel into the fluidized bed along with the quartz sand; The silane is diluted 3-6 times; The mass ratio of the quartz sand to the volume of silane is 2.5-5:1, wherein the mass unit of the quartz sand is kg, and the volume unit of the silane is ml; S3: After 5-8 seconds, the phenolic resin at a temperature of 80-150° C. is sprayed out through the atomizing nozzle (5); S4: At the same time, the urotropine aqueous solution is sprayed out through the atomizing nozzle (4), and the calcium stearate powder is sprayed out through the powder spraying head (14); wherein the ratio of water to urotropine is 3:1; S5: Under the action of the airflow, the quartz sand coated with phenolic resin continues to move upward until it reaches the upper baffle (3). After the quartz sand collides with the baffle, the direction and speed of movement change. The coated quartz sand enters the side area of ​​the fluidized bed, loses the action of the airflow, and falls under the action of gravity. When passing through the area where the urotropine aqueous solution is sprayed, the phenolic resin on the surface of the coated quartz sand solidifies and cools. The coated quartz sand passes through the area where the calcium stearate is sprayed, thereby preventing the coated quartz sand from agglomerating. S6: The finished coated quartz sand enters the sand box (10) below the fluidized bed from the discharge port and is collected.

2. The method for fluidizing and uniformly coating quartz sand using a fluidized bed as claimed in claim 1, characterized in that: The gas in S2 is blown into the air inlet pipe at a speed of 1.0-10.0 m / s.

3. The method for fluidizing and uniformly coating quartz sand using a fluidized bed as claimed in claim 2, characterized in that: The droplet size of the phenolic resin in S3 is 2-10 μm.

4. The method for fluidizing and uniformly coating quartz sand using a fluidized bed as claimed in claim 3, characterized in that: The flow rate of the phenolic resin in S3 is 200-2500cm 3 / min.

5. The method for fluidizing and uniformly coating quartz sand using a fluidized bed as claimed in claim 4, characterized in that: The urotropine aqueous solution in S4 is 150-2500cm 3 / min flow rate is sprayed out from the atomizing nozzle (4).

6. The method for fluidizing and uniformly coating quartz sand using a fluidized bed as claimed in claim 5, characterized in that: The droplet size of the urotropine aqueous solution in S4 is 50-100 μm.

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