Novel shell mold precoated sand manufacturing process

Abstract

The invention is applied to the technical field of precoated sand, and discloses a novel shell mold precoated sand manufacturing process which comprises the following steps: S1, crude sand treatment, S2, precoated sand preparation, S3, stirring and S4, finished product packaging. According to the novel shell mold precoated sand manufacturing process, in the aspect of liquidity, an accurate hot mixing process is adopted, the heating temperature is strictly controlled within a specific range, crude sand and resin are mixed in a proper temperature environment, it is ensured that the crude sand and the resin can be fully and evenly blended, and the fluidity of the shell mold precoated sand is improved. According to the precoated sand, a foundation is laid for good flowability of the precoated sand, the self-lubricating lubricant in a specific proportion is added, so that the precoated sand can smoothly flow when filling a mold cavity, and the precoated sand can be rapidly and completely filled in place according to the shape of a mold no matter for a complex mold internal structure or a thin-wall and fine-texture area; and the molding quality of the sand mold is greatly improved, and the sand mold defects caused by insufficient fluidity are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of coated sand, in particular to a novel process for producing shell-shaped coated sand. Background Art

[0002] In the foundry field, the performance of coated sand plays a vital role in the quality and production efficiency of castings. However, the existing coated sand technology has many shortcomings. The current coated sand generally has the problem of poor fluidity. In the casting process, the poor fluidity makes it difficult for the coated sand to evenly fill the mold cavity, especially for some molds with complex structures, thin walls and fine textures. The coated sand cannot fully reach every corner, resulting in incomplete sand mold molding and difficulty in ensuring dimensional accuracy, which seriously affects the final shape and quality of the casting, increases the scrap rate and subsequent processing costs. Its slow polymerization speed is also a major drawback. The slow polymerization speed prolongs the curing time of the sand mold, reduces the production cycle, and limits the casting production. The production capacity of the production line, in large-scale production, this not only leads to a large waste of energy, but also increases the equipment occupancy time, reduces the overall production efficiency, and cannot meet the needs of modern efficient and fast production. In addition, the existing coated sand has poor surface finish. After the casting is formed, the surface quality of the sand mold is directly reflected on the surface of the casting. Due to the surface defects of the coated sand, the surface of the casting is rough and the smoothness does not meet the requirements. Additional post-processing processes such as grinding and polishing are required, which not only consumes manpower, material resources and time, but also may affect the dimensional accuracy of the casting during the grinding process, reduce the consistency and stability of the product, and limit the application of castings in industries with high requirements on surface quality, such as automotive parts, precision machinery and other fields. Summary of the invention

[0003] The purpose of the present invention is to provide a novel process for producing shell-type coated sand to solve the problems of poor fluidity, slow polymerization speed and poor surface gloss proposed in the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides the following technical solution: a novel shell-shaped coated sand production process, comprising the following steps:

[0005] S1. Raw sand processing: The raw sand is fed by a bucket elevator and roasted at a heating temperature of 870-890°C for 1 hour to improve the refractoriness of the raw sand.

[0006] S2. Preparation of coated sand: After the roasted raw sand is cooled for 3-5 hours, it is transported to the sand storage. 300 kg of the sand in the sand storage enters the hot mixing drum for heating. After the temperature reaches the required level, it enters the sand mixer for mixing. 4.5-5 kg ​​of No. 1 resin and 2.5-3 kg of No. 2 resin are added to the sand mixer.

[0007] S3, stirring: stirring for 1-3 minutes to melt the resin and evenly cover the surface of the original sand. The speed of the sand mixer during the stirring process is 300rpm, and then add curing agent and lubricant for coating. After stirring for 1-3 minutes, the material is discharged into the crusher and cooled and vibrated after crushing.

[0008] S4. Finished product packaging: The finished product warehouse is packed in ton bags. Humidity testing is required before packaging to ensure product quality and storage stability.

[0009] Preferably, during the raw sand roasting process, the heating temperature rise rate of the raw sand is 10°C / min, and the stability of the heating rate is controlled at ±1°C / min, to ensure that the raw sand is fully roasted without damaging the raw sand structure.

[0010] Preferably, the heating temperature of the hot mixing drum is controlled at 140° C. with an error range of ±3° C. to ensure that the raw sand and the resin can be fully and evenly mixed.

[0011] Preferably, the weight ratio of resin No. 1 to resin No. 2 is 3.5:2.8, ensuring the bonding and molding properties of the coated sand.

[0012] Preferably, the added amount of the curing agent is 0.3% of the weight of the original sand, and the curing agent is a composite curing agent formed by mixing an organic amine curing agent and a metal oxide curing agent in a ratio of 2:1, and the organic amine curing agent in the composite curing agent is a mixture of ethylenediamine and diethylenetriamine, and the molar ratio of ethylenediamine to diethylenetriamine is 1:1.5.

[0013] Preferably, the amount of the lubricant added is 0.2% of the weight of the original sand, and the lubricant is a mixture of nano graphite powder with self-lubricating properties and organic silicone oil in a ratio of 1:3.

[0014] Preferably, the crushing particle size of the crusher is controlled at 0.1-0.8 mm, and during the cooling and shaking screen process, the vibration frequency of the shaking screen is 15-20 Hz and the amplitude is 3-5 mm.

[0015] Preferably, the packaging humidity is lower than 3%, and a desiccant bag is added inside the packaging material, and the desiccant bag uses a montmorillonite desiccant with a high moisture absorption capacity.

[0016] Compared with the prior art, the invention has the following beneficial effects: the new shell-shaped coated sand production process:

[0017] 1. In terms of fluidity, the new shell-type coated sand production process adopts a precise hot mixing process. In the hot mixing barrel, the heating temperature is strictly controlled within a specific range, so that the raw sand and the resin are mixed under a suitable temperature environment to ensure that the two can fully and evenly blend with each other, laying the foundation for the good fluidity of the coated sand. At the same time, a specific proportion of self-lubricating lubricant is added, which is carefully formulated from nanographite powder and silicone oil. The addition of this lubricant effectively reduces the friction resistance between the coated sand particles, so that the coated sand can flow smoothly when filling the mold cavity. Whether it is facing a complex internal structure of the mold, or a thin-walled, fine-textured area, it can be quickly and completely filled in place according to the shape of the mold, greatly improving the molding quality of the sand mold, reducing sand mold defects caused by insufficient fluidity, and thus reducing the scrap rate;

[0018] 2. For the problem of slow polymerization speed, this process adopts an innovative composite curing agent system, which is a mixture of an organic amine curing agent and a metal oxide curing agent in a specific ratio, wherein the organic amine curing agent is a combination of ethylenediamine and diethylenetriamine in a specific molar ratio. By precisely controlling the ratio and dosage of this composite curing agent, the curing reaction mechanism of the coated sand is optimized. During the stirring and coating process of the coated sand, the curing agent can quickly and evenly react with the original sand and resin, significantly accelerating the start and progress of the polymerization reaction. In actual casting scenarios, this technical means greatly shortens the curing time of the sand mold, accelerates the production rhythm that was originally limited by slow polymerization, and significantly improves the production capacity of the casting production line. At the same time, the energy consumption in the curing process is reduced, the equipment utilization efficiency is improved, and the equipment waiting time is reduced, which comprehensively improves the efficiency and economy of casting production and meets the requirements of modern industrial efficient production.

[0019] 3. In solving the defect of poor surface gloss, this process starts from the core links of raw sand processing and coated sand preparation. When processing raw sand, bucket elevator is used for feeding and roasting, and the heating temperature, roasting time and heating rate are accurately set and strictly controlled. High-temperature roasting can effectively remove impurities in the raw sand, and at the same time optimize the crystal structure of the raw sand, improve its refractoriness, and provide high-quality basic materials for the subsequent good molding and surface quality of coated sand. In the preparation stage of coated sand, specific No. 1 resin and No. 2 resin are selected, and the weight ratio of the two is accurately controlled within the appropriate range. Then, through a strict and standardized stirring process, it is ensured that the resin is evenly coated on the surface of the raw sand to form a dense and uniform coating layer. The fine technical means of the whole process from raw sand to coated sand preparation work together to make the surface of the sand mold made of coated sand more dense and smooth. After the casting is formed, its surface finish is significantly improved, and a large amount of post-processing processes such as grinding and polishing are not required. DETAILED DESCRIPTION

[0020] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The present invention provides a technical solution: a novel process for producing shell-shaped coated sand.

[0022] Example:

[0023] 1. Raw sand processing:

[0024] High-quality natural silica sand is selected as the raw sand, and the raw sand is transported to the roasting furnace through a bucket elevator. The heating temperature is set to 880℃, the heating temperature rise rate is stably controlled at 10℃ / min, and the fluctuation range of the heating rate is within ±1℃ / min. The roasting is carried out for 1 hour. After the roasting is completed, the raw sand is cooled in a natural environment for 4 hours and then transported to the sand warehouse for storage.

[0025] 2. Preparation of coated sand:

[0026] 300 kg of cooled raw sand is quantitatively taken out from the sand storage and transported into the hot mixing drum. The heating temperature of the hot mixing drum is set to 140°C, and the error is controlled within the range of ±3°C. When the raw sand reaches the set temperature in the hot mixing drum, it is transferred to the sand mixer for mixing.

[0027] Add 4.8 kg of No. 1 resin and 2.8 kg of No. 2 resin into the sand mixer.

[0028] 3. Stirring:

[0029] Stir at 300rpm for 2 minutes to fully melt the resin and evenly cover the surface of the original sand. Then add the curing agent, the amount of which is 0.3% of the weight of the original sand, and then add the lubricant, the amount of which is 0.2% of the weight of the original sand. After stirring for another 2 minutes, the mixed coated sand is discharged into the crusher.

[0030] 4. Crushing and cooling vibration screen:

[0031] The crusher crushes the coated sand to a particle size between 0.1-0.8mm. The crushed coated sand enters the cooling and vibrating screening equipment. During the cooling and vibrating screening process, the vibration frequency of the vibrating screen is set to 18Hz and the amplitude is 4mm. Cooling and screening are carried out to remove unqualified large particles and fine powder.

[0032] 5. Finished product packaging:

[0033] The finished coated sand after cooling and vibration screening is transported to the finished product warehouse for discharge and packed in ton bags. Before packaging, the coated sand is tested for humidity using a professional humidity testing instrument to ensure that the packaging humidity is less than 3%, and a montmorillonite desiccant bag with high moisture absorption capacity is added inside the packaging material to ensure product quality and storage stability.

[0034] The new shell-type coated sand produced by the above embodiment shows good fluidity in actual casting applications, can quickly fill complex mold cavities, and significantly accelerates the polymerization speed, greatly shortening the sand mold production cycle. In addition, the surface finish of the produced casting is high, which effectively reduces the post-processing process, improves production efficiency and product quality, and verifies the feasibility and superiority of the new shell-type coated sand production process.

[0035] Example Test data on fluidity, polymerization speed and surface gloss:

[0036] 1. Liquidity test:

[0037] Using a standard coated sand fluidity test device, the coated sand prepared in the embodiment was poured into the funnel of the test device. It was allowed to fall freely at a fixed height of -200 mm, and its flow length was measured. After multiple tests, the average flow length reached 250 mm, while the average flow length of traditional coated sand under the same test conditions was only 180 mm, indicating that the fluidity of the coated sand in this embodiment is significantly improved compared with traditional products, and can better meet the filling requirements of complex mold cavities.

[0038] 2. Aggregation speed test:

[0039] Using a special coated sand curing time tester, under a set temperature of 220°C and a humidity of 50%, the coated sand of the embodiment was tested from the beginning of mixing the curing agent to reaching the demolding strength, which was set to the time when the compressive strength reached 1.5 MPa. After repeated tests, the average curing time was 60 seconds, while the average curing time of traditional coated sand under the same test conditions was as long as 120 seconds. This fully demonstrates that the polymerization speed of the coated sand of the present invention is greatly improved, which can effectively shorten the sand mold making cycle and improve production efficiency.

[0040] 3. Surface light inspection:

[0041] A surface roughness measuring instrument was used to measure the surface of the casting made of the coated sand in the embodiment. The measurements were taken at multiple typical parts of the casting, such as the flat surface and the curved surface, and the average value was taken. The results showed that the average surface roughness Ra value of the casting was 6.5 μm, while the average surface roughness Ra value of the casting made of the traditional coated sand was 12 μm. At the same time, through visual inspection, the surface gloss of the casting made of the coated sand in this embodiment was significantly better than that of the casting made of the traditional coated sand, which reduced the amount of post-processing steps such as grinding and polishing required due to surface quality problems by about 40%, effectively improving the appearance quality and production efficiency of the product.

[0042] These test data intuitively prove from quantitative and qualitative perspectives that the new shell-type coated sand production process has significant advantages and good application effects compared with traditional processes in terms of fluidity, polymerization speed and surface finish.

[0043] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and do not limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A new shell-type coated sand production process, characterized by: The steps include: S1. Raw sand processing: The raw sand is fed by a bucket elevator and roasted at a heating temperature of 870-890°C for 1 hour to improve the refractoriness of the raw sand. S2. Preparation of coated sand: After the roasted raw sand is cooled for 3-5 hours, it is transported to the sand storage. 300 kg of the sand in the sand storage enters the hot mixing drum for heating. After the temperature reaches the required level, it enters the sand mixer for mixing. 4.5-5 kg ​​of No. 1 resin and 2.5-3 kg of No. 2 resin are added to the sand mixer. S3, stirring: stirring for 1-3 minutes to melt the resin and evenly cover the surface of the original sand. The speed of the sand mixer during the stirring process is 300rpm, and then add curing agent and lubricant for coating. After stirring for 1-3 minutes, the material is discharged into the crusher and cooled and vibrated after crushing. S4. Finished product packaging: The finished product warehouse is packed in ton bags. Humidity testing is required before packaging to ensure product quality and storage stability.

2. A novel shell-type coated sand production process according to claim 1, characterized in that: During the raw sand roasting process, the heating temperature rise rate of the raw sand is 10°C / min, and the stability of the heating rate is controlled at ±1°C / min, ensuring that the raw sand is fully roasted without damaging the raw sand structure.

3. The novel shell-type coated sand production process according to claim 1 is characterized in that: The heating temperature of the hot mixing drum is controlled at 140°C with an error range of ±3°C to ensure that the raw sand and the resin can be fully and evenly mixed.

4. The novel shell-type coated sand production process according to claim 1 is characterized in that: The weight ratio of the No. 1 resin to the No. 2 resin is 3.5:2.8, which ensures the bonding performance and molding performance of the coated sand.

5. The novel shell-type coated sand production process according to claim 1 is characterized in that: The added amount of the curing agent is 0.3% of the weight of the original sand, and the curing agent is a composite curing agent formed by mixing an organic amine curing agent and a metal oxide curing agent in a ratio of 2:

1. The organic amine curing agent in the composite curing agent is a mixture of ethylenediamine and diethylenetriamine, and the molar ratio of ethylenediamine to diethylenetriamine is 1:1.

5.

6. The novel shell-type coated sand production process according to claim 1 is characterized in that: The added amount of the lubricant is 0.2% of the weight of the original sand, and the lubricant is a mixture of nano graphite powder with self-lubricating properties and organic silicone oil in a ratio of 1:

3.

7. The novel shell-type coated sand production process according to claim 1 is characterized in that: The crushing particle size of the crusher is controlled at 0.1-0.8 mm. During the cooling and shaking screen process, the vibration frequency of the shaking screen is 15-20 Hz and the amplitude is 3-5 mm.

8. The novel shell-type coated sand production process according to claim 1 is characterized by: The packaging humidity is lower than 3%, and a desiccant bag is added inside the packaging material, wherein the desiccant bag adopts a montmorillonite desiccant with a high moisture absorption capacity.