Microwave hot air sand mold drying furnace process

Abstract

The present application relates to the technical fields of microwave drying furnace, in particular to a microwave hot air sand mold drying furnace process; in order to overcome the defects of uneven drying, high energy consumption, long drying time, easy cracking of sand mold and poor adaptability in the existing sand mold drying process, the present application provides a microwave hot air collaborative sand mold drying furnace process, through the synergistic mechanism of "microwave penetration heating + hot air convection and moisture removal", combined with phased parameter control, the sand mold is quickly and uniformly dried, while the energy consumption is reduced, the cracking is avoided, and the different size sand mold requirements are adapted.

Description

Technical Field

[0001] This invention relates to the field of microwave drying oven technology, specifically to a microwave hot air sand drying oven process. Background Technology

[0002] As a core tooling element in casting production, the drying quality of sand molds directly determines the final precision and yield of castings. During the casting process, residual moisture inside the sand mold rapidly vaporizes under the action of high-temperature molten metal. If this moisture cannot be removed promptly and evenly, it can lead to defects such as porosity and shrinkage cavities in the casting. Furthermore, uneven moisture content or sudden temperature changes during the sand mold drying process can easily cause cracking, further reducing the casting yield. Therefore, the core objective of the sand mold drying process is to achieve rapid and uniform moisture removal while ensuring the stability of the sand mold structure and preventing cracking and deformation. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing sand mold drying processes, such as "uneven drying, high energy consumption, long drying time, easy cracking of sand molds, and poor adaptability," and to provide a microwave hot air combined sand mold drying oven process that can achieve rapid and uniform drying of sand molds of different sizes, while reducing energy consumption, avoiding sand mold cracking, and balancing production efficiency and product quality.

[0004] To achieve the above objectives, this invention provides a microwave hot air sand mold drying oven process based on a dedicated three-section drying oven. The drying oven is sequentially configured with a pretreatment zone, a microwave hot air co-processing zone, and a cooling zone. Each zone is separated by heat-insulating partitions to ensure independent and stable parameters in each zone. The core components inside the drying oven include a sand mold conveyor roller, a microwave generator, and a hot air system. The hot air system integrates a heating device, a fan, a wind speed regulation module, a humidity sensor, a dehumidification outlet, and a temperature control module. These components work together to achieve precise parameter control. Specific component parameters are as follows: 1. Sand mold conveyor rollers: Made of high-temperature and wear-resistant stainless steel, with a roller spacing of 120mm. The transmission method is driven by a variable frequency motor, and the conveying speed adjustment range is 0.5-1m / min, ensuring that the processing time of the sand mold in each zone is accurate and controllable. The roller surface is treated with anti-slip material to prevent the sand mold from shifting during the conveying process.

[0005] 2. Microwave generator: It adopts a magnetron type, with a working frequency of 2450MHz and a power adjustment range of 0-1000W. It supports continuous power adjustment and intermittent working mode. Four microwave generators are arranged at the top of the microwave-hot air co-processing zone and three on each side to ensure that microwave energy evenly covers the surface of the sand mold and avoids local microwave energy concentration that could lead to overheating.

[0006] 3. Hot air system: Heating device: It adopts an electric heating tube assembly with a heating power of 8kW, supports continuous temperature adjustment from room temperature to 120℃, and has a temperature control accuracy of ±1℃; Fan: A centrifugal high-temperature fan is selected, with an air volume range of 800-1200m³ / h and an air pressure of 600Pa, to ensure that hot air can penetrate the sand mold surface evenly; Wind speed adjustment module: The wind speed is controlled by a frequency converter to achieve continuous adjustment of 1-3m / s with an adjustment accuracy of ±0.1m / s; Humidity sensor: A capacitive humidity sensor is used, with a measurement range of 0-100%RH and a measurement accuracy of ±2%RH. One sensor is installed at the front, rear, and middle of the microwave hot air co-processing zone. Exhaust vents: Two are located at the top and one on each side of the microwave hot air co-processing zone. Each exhaust vent is equipped with an electric regulating valve, which can automatically adjust the opening based on the feedback signal from the humidity sensor to achieve precise control of the exhaust rate of 0.5-1m³ / min. Temperature control module: It adopts a PT100 temperature sensor and links with the PLC control system to collect temperature data of each zone in real time, automatically adjust the power of the heating device, and the temperature control response time is ≤5s; The process steps are as follows: 1. Sand mold pretreatment Place the sand mold to be dried stably in the pretreatment area of ​​the drying oven, ensuring the mold is fully in contact with the mold conveyor rollers to avoid uneven stress caused by suspension. Start the hot air system and introduce dry hot air into the pretreatment area. Strictly control the hot air parameters as follows: temperature 40-50℃, wind speed 1-1.5m / s, relative humidity ≤30%, and processing time 5-8 minutes.

[0007] The core function of this step is to remove floating dust and 10%-15% of surface moisture from the sand mold surface. If the floating dust adhering to the surface during the sand mold preparation process enters the subsequent microwave hot air synergy zone, it will be heated to a high temperature under the action of microwaves, which may cause deposition or discharge at the microwave generator's emission port, affecting the service life and operational stability of the equipment. Through low-temperature drying hot air treatment, the surface of the sand mold can be made into a "dry and loose" state without damaging the sand mold structure, laying the foundation for the synergistic effect of subsequent microwave penetration heating and hot air convection dehumidification, and ensuring that the internal moisture can be smoothly migrated and discharged.

[0008] 2. Segmented collaborative drying The pretreated sand mold is fed into the microwave and hot air synergy zone via a conveyor roller conveyor. The parameters are controlled sequentially according to the sequence of "preheating section → main drying section → shaping section" to achieve the synergistic effect of microwave and hot air. a) Turn on the microwave generator and adopt the "intermittent working mode" (work for 30 seconds, stop for 10 seconds, repeat). The power setting should be adapted to the size of the sand mold: 300-400W for small and medium-sized sand molds (size ≤800mm×600mm) and 400-700W for large sand molds (size >800mm×600mm). At the same time, the hot air system should be supplied with hot air at a temperature of 60-70℃ and a wind speed of 1.5-2m / s for a duration of 10-15min for small and medium-sized sand molds and 15-20min for large sand molds.

[0009] This stage uses low-power microwaves to slowly heat the moisture inside the sand mold, avoiding localized overheating. Simultaneously, hot air removes moisture evaporated from the surface, creating a synergistic effect of "internal heating + surface dehumidification." This effectively balances the temperature difference between the inside and outside of the sand mold, ensuring a temperature difference of ≤5℃. This provides a temperature basis for the efficient heating of the subsequent main drying section, preventing thermal stress caused by sudden temperature increases. The intermittent operation mode, through the periodic starting and stopping of the microwave generator, allows microwave energy to be gradually conducted inside the sand mold, slowly increasing the moisture temperature. During the off-peak phase, heat and moisture inside the sand mold migrate to the surface, preventing localized energy accumulation. This design is a key improvement addressing the "localized overheating" defect of simple microwave processes.

[0010] b) Main drying section: Adjust the core parameters according to the size of the sand mold: When drying small and medium-sized sand molds, adjust the microwave power to 600-700W, raise the hot air temperature to 80-90℃, increase the wind speed to 2-2.5m / s, and the duration to 20-25min; when drying large sand molds, adjust the microwave power to 800-1000W, raise the hot air temperature to 90-110℃, increase the wind speed to 2.5-3m / s, and the duration to 30-40min.

[0011] This stage utilizes the strong penetrating power of microwaves to directly target moisture molecules inside the sand mold, increasing the evaporation rate by 3-4 times compared to traditional processes. Simultaneously, high-temperature, high-velocity hot air, through convection, rapidly removes moisture evaporated from the sand mold surface, preventing surface crusting from hindering internal moisture migration. The coordinated matching of microwave power with hot air temperature and velocity creates a virtuous cycle between internal moisture evaporation and surface moisture removal. If the microwave power is below the specified range, the internal moisture evaporation rate is insufficient, failing to shorten the drying time; conversely, if the hot air temperature or velocity is below the specified range, surface moisture removal will be inadequate, resulting in surface crusting.

[0012] In addition, the ambient humidity in the microwave hot air co-processing zone is monitored in real time by a humidity sensor. When the humidity is ≥60%, the exhaust port is automatically opened, and the exhaust rate is controlled at 0.5-1m³ / min to ensure that the drying environment remains in a low humidity state, continuously providing driving force for moisture evaporation. The linkage control design of the humidity sensor solves the problem of "untimely dehumidification leading to increased humidity in the drying environment" in traditional processes, further ensuring the uniformity of drying.

[0013] c) Shaping stage: Reduce microwave power to 200-300W, reduce hot air temperature to 50-60℃, maintain wind speed at 1.5-2m / s, and last for 8-12 minutes.

[0014] This stage uses low-power microwaves to "fine-tune" the heating of localized high-moisture areas in the sand mold, promoting the slow evaporation of residual moisture. Hot air maintains slow convection, promoting balanced moisture diffusion inside and outside the sand mold, ensuring that the final moisture content of small and medium-sized sand molds is ≤1.5%, and that of large sand molds is ≤2%, with a moisture content difference between the inside and outside of the sand mold ≤0.5%, thus preventing cracking due to humidity differences during the subsequent cooling stage. The parameters of the shaping section are designed to address the defect of uneven moisture content inside and outside the sand mold after drying in existing processes. Through gentle heating and dehumidification, the moisture content distribution of the sand mold is further stabilized.

[0015] 3. Cooling and shaping After the sand molds are dried in sections, they are conveyed into the cooling zone via a conveyor roller. The microwave generator is turned off, and the hot air system is switched to ambient temperature air supply mode, with ambient temperature air at 20-25℃ and a wind speed controlled at 2-3 m / s. The cooling time is adapted according to the size of the sand molds: 10-15 minutes for small and medium-sized sand molds, and 15-20 minutes for large sand molds. After the sand mold temperature drops to room temperature (20-25℃), the hot air system and the conveyor roller are turned off, the sand molds are removed, and the entire drying process is completed.

[0016] During the cooling stage, ambient temperature air is used for gentle cooling to avoid thermal stress caused by a sudden drop in temperature. By reasonably controlling the airflow and cooling time, the temperature inside and outside the sand mold decreases synchronously, further stabilizing the sand mold structure and improving its strength. If the cooling airflow is too high, the surface temperature of the sand mold will drop too quickly, creating an excessive temperature difference with the interior and causing cracking. If the cooling time is insufficient, the residual heat inside the sand mold will not be fully dissipated, and deformation may still occur due to temperature changes during subsequent storage or use.

[0017] The beneficial effects of this invention are as follows: 1. Significantly improved drying uniformity and reduced cracking rate: The synergistic mechanism fundamentally avoids the problems of "internal moisture and external dryness" in traditional hot air processes and "local overheating" in simple microwave processes. The difference in moisture content between the inside and outside of the sand mold is strictly controlled to ≤0.5%. Compared with existing processes, the cracking rate of sand molds is significantly reduced from 80%-85% in traditional hot air processes and 70%-75% in simple microwave processes to ≤5%, and the finished product qualification rate is ≥95%, solving the core pain point of high cracking rate of sand molds in existing processes.

[0018] 2. Significantly improved drying efficiency and shortened production cycle: Staged parameter control adapts to the drying needs of sand molds of different sizes, reducing drying time by 30%-40% compared to traditional processes. Specifically, drying time for small and medium-sized sand molds is reduced from 60-90 minutes in traditional processes to 35-50 minutes, and for large sand molds from 120-150 minutes to 75-95 minutes, significantly improving the casting production pace and meeting the needs of large-scale production. Calculations show that the drying efficiency of this process is 15%-20% higher than that of a simple microwave process, mainly due to the optimized synergistic parameters of microwave and hot air in the main drying section and the humidity-linked dehumidification design.

[0019] 3. High adaptability and flexible operation: For sand molds ranging from 100mm×100mm (small) to 1200mm×800mm (large), only the microwave power, hot air parameters, and processing time at each stage need to be adjusted. No equipment replacement or major modifications are required, making it widely adaptable. In contrast, traditional hot air processes require replacing the drying unit or adjusting the equipment structure to accommodate different sized sand molds, while microwave processes require frequent manual power adjustments, making operation complex. This process's parameter adaptation design significantly improves operational flexibility and equipment utilization.

[0020] 4. Enhanced Sand Mold Strength Ensures Casting Precision: The balanced humidity in the molding section and the gentle temperature control in the cooling section result in a denser and more stable sand mold structure. The sand mold strength is increased from 2.5 MPa in traditional processes and 2.5-2.6 MPa in microwave processes to 2.8-3.0 MPa. This high-strength sand mold better resists the impact and pressure of molten metal during casting, preventing deformation or breakage. It effectively reduces defects such as porosity, shrinkage cavities, and dimensional deviations in castings, ensuring the precision and mechanical properties of subsequent castings and meeting the high-precision casting requirements of advanced manufacturing sectors. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 This is a flowchart of the microwave hot air sand drying process of the present invention; Detailed Implementation

[0023] Example 1: Drying of small and medium-sized sand molds 1. Sand mold pretreatment Place the sand mold to be dried in the pretreatment area, and introduce dry hot air with a temperature of 45℃, a wind speed of 1.2m / s and a relative humidity of 25% into the hot air system for 6 minutes. After treatment, the surface moisture content of the sand mold drops to 5%-5.5%, and there is no floating dust on the surface.

[0024] 2. Segmented collaborative drying The sand mold conveyor rollers feed the sand mold into the microwave hot air co-processing zone at a speed of 0.8 m / min. a) Preheating stage: The microwave generator is set to 350W and operates intermittently; hot air at 65℃ and 1.8m / s is introduced through the hot air outlet; the duration is 12min; at this time, the internal temperature of the sand mold rises to 40-45℃, the temperature difference between the inside and outside is ≤3℃, and the surface moisture content drops to 3%-3.5%.

[0025] b) Main drying section: The microwave generator power is increased to 650W, the hot air temperature is increased to 85℃, and the wind speed is adjusted to 2.2m / s; the humidity sensor monitors in real time, and when the ambient humidity is ≥60%, the dehumidification port is opened, with a dehumidification rate of 0.8m³ / min; the duration is 22min; at this time, the moisture inside the sand mold evaporates rapidly, the moisture content drops to 1.8%-2.0%, and there is no crust on the surface.

[0026] c) Shaping stage: The microwave generator power is reduced to 250W, the hot air temperature is reduced to 55℃, and the wind speed is maintained at 1.8m / s; the duration is 10min; after balancing, the moisture content of the sand mold is stabilized at 1.2%-1.5%, with no local humidity difference.

[0027] 3. Cooling and shaping The sand mold is sent into the cooling zone, and a cooling fan blows in the sand at 23°C ambient temperature at a speed of 2.5 m / s for 12 minutes. When the sand mold temperature drops to 23-25°C, it is taken out and tested: the sand mold compressive strength is 2.9 MPa, there is no cracking, and the pass rate is 100%. The entire process takes 62 minutes, and the energy consumption per sand mold is 0.85 kW・h / kg.

[0028] Example 2: Drying of large sand molds 1. Sand mold pretreatment The sand mold to be dried is placed in the pretreatment area, and the hot air system is introduced with a temperature of 48℃, a wind speed of 1.4m / s and a relative humidity of 28% for 8 minutes; after treatment, the surface moisture content of the sand mold is reduced to 4.5%-5%.

[0029] 2. Segmented collaborative drying The sand mold conveyor rollers feed the sand mold into the microwave hot air co-processing zone at a speed of 0.6 m / min. a) Preheating section: The microwave generator is set to 600W and operates intermittently; hot air at 75℃ and 1.9m / s is introduced through the hot air outlet; the duration is 18min; at this time, the internal temperature of the sand mold rises to 45-50℃, the temperature difference between the inside and outside is ≤4℃, and the surface moisture content drops to 3%-3.2%.

[0030] b) Main drying section: The microwave generator power is increased to 900W, the hot air temperature is increased to 100℃, and the wind speed is adjusted to 2.8m / s; when the humidity sensor detects that the humidity is ≥60%, the exhaust port exhausts moisture at a rate of 1m³ / min; the duration is 35min; at this time, the moisture content of the sand mold drops to 2.2%-2.5%, and there is no moisture accumulation inside.

[0031] c) Shaping stage: The microwave generator power is reduced to 300W, the hot air temperature is reduced to 65℃, and the wind speed is maintained at 1.9m / s; the duration is 12min; after equilibrium, the moisture content of the sand mold is stabilized at 1.8%-2.0%.

[0032] 3. Cooling and shaping The cooling zone was vented with 22℃ ambient air at a speed of 2.8m / s for 18 minutes. The sand mold temperature dropped to 22-24℃. The test results showed that the sand mold compressive strength was 2.7MPa, with no cracks (only slight wear on the edges and corners, which did not affect its use), and the pass rate was 96%. The entire process took 81 minutes, and the energy consumption per sand mold was 0.9kW・h / kg.

Claims

1. A microwave hot air sand drying oven process, based on a dedicated three-section drying oven, wherein the drying oven is sequentially configured with a pretreatment zone, a microwave hot air synergistic zone, and a cooling zone, each zone being separated by heat-insulating partitions, characterized in that... Includes the following steps: 1) Sand mold pretreatment Place the sand mold to be dried stably in the pretreatment area of ​​the drying oven, ensuring that the sand mold and the sand mold conveyor rollers are in complete contact. Start the hot air system and introduce dry hot air into the pretreatment area. The hot air parameters are strictly controlled as follows: temperature 40-50℃, wind speed 1-1.5m / s, relative humidity ≤30%, and processing time 5-8min. 2) Segmented collaborative drying The pretreated sand mold is fed into the microwave and hot air synergy zone via a conveyor roller conveyor. The parameters are controlled sequentially according to the sequence of "preheating section → main drying section → shaping section" to achieve the synergistic effect of microwave and hot air. a) Turn on the microwave generator and adopt the "intermittent working mode" (work for 30 seconds, stop for 10 seconds, repeating). The power setting should be adapted to the size of the sand mold: 300-400W for small and medium-sized sand molds (size ≤800mm×600mm) and 400-700W for large sand molds (size >800mm×600mm); at the same time, the hot air system should introduce hot air at a temperature of 60-70℃ and a wind speed of 1.5-2m / s for a duration of 10-15min for small and medium-sized sand molds and 15-20min for large sand molds. b) Main drying section: Adjust the core parameters according to the size of the sand mold: When drying small and medium-sized sand molds, adjust the microwave power to 600-700W, raise the hot air temperature to 80-90℃, increase the wind speed to 2-2.5m / s, and the duration to 20-25min; when drying large sand molds, adjust the microwave power to 800-1000W, raise the hot air temperature to 90-110℃, increase the wind speed to 2.5-3m / s, and the duration to 30-40min. c) Shaping stage: Reduce microwave power to 200-300W, reduce hot air temperature to 50-60℃, maintain wind speed at 1.5-2m / s, and last for 8-12 minutes; 3) Cooling and shaping After the sand molds are dried in sections, they are sent to the cooling zone via conveyor rollers. The microwave generator is turned off, and the hot air system is switched to the normal temperature air supply mode. Normal temperature air at 20-25℃ is introduced, and the air speed is controlled at 2-3m / s. The cooling time is adapted according to the size of the sand mold: 10-15 minutes for small and medium-sized sand molds and 15-20 minutes for large sand molds. After the sand mold temperature drops to room temperature (20-25℃), the hot air system and the conveyor rollers are turned off, the sand molds are removed, and the entire drying process is completed.

2. The microwave hot air sand mold drying oven process according to claim 1, characterized in that, The core function of step 1) is to remove floating dust and 10%-15% of surface moisture from the sand mold surface: through low-temperature drying hot air treatment, the surface of the sand mold can be made into a "dry and loose" state without damaging the sand mold structure, laying the foundation for the synergistic effect of subsequent microwave penetration heating and hot air convection dehumidification, and ensuring that the internal moisture can be smoothly migrated and discharged.

3. The microwave hot air sand mold drying oven process according to claim 1, characterized in that, In step 2) a), the moisture inside the sand mold is slowly heated by low-power microwaves to avoid local overheating; hot air simultaneously removes the moisture evaporated from the surface, forming a synergistic effect of "internal heating + surface dehumidification", effectively balancing the temperature difference between the inside and outside of the sand mold and ensuring that the temperature difference is ≤5℃. This provides a temperature basis for the efficient heating of the subsequent main drying section and avoids thermal stress caused by a sudden temperature rise. In the intermittent working mode, the microwave generator is periodically started and stopped, so that the microwave energy is gradually conducted inside the sand mold, and the moisture temperature rises slowly. At the same time, during the stop phase, the heat and moisture inside the sand mold can migrate to the surface, avoiding local energy accumulation.

4. The microwave hot air sand mold drying oven process according to claim 1, characterized in that, In step 2) b), the strong penetrability of microwaves is used to directly act on the moisture molecules inside the sand mold, which increases the moisture evaporation rate by 3-4 times compared with the traditional process. At the same time, the high temperature and high wind speed hot air quickly removes the moisture evaporated on the surface of the sand mold through the convection effect, avoiding the surface crust from hindering the migration of internal moisture.

5. The microwave hot air sand mold drying oven process according to claim 1, characterized in that, In step 2) c), the sand mold is heated with low-power microwaves to "fine-tune" the local high moisture content area, so that the residual moisture evaporates slowly; the hot air maintains slow convection to promote the diffusion balance of moisture inside and outside the sand mold, ensuring that the final moisture content of small and medium-sized sand molds is ≤1.5%, the final moisture content of large sand molds is ≤2%, and the difference in moisture content inside and outside the sand mold is ≤0.5%, so as to avoid cracking due to humidity difference in the subsequent cooling stage.

6. The microwave hot air sand mold drying oven process according to claim 1, characterized in that, In step 2) b), the ambient humidity in the microwave hot air co-processing zone is monitored in real time by a humidity sensor. When the humidity is ≥60%, the dehumidification port is automatically opened, and the dehumidification rate is controlled at 0.5-1m³ / min to ensure that the drying environment is kept in a low humidity state and to continuously provide driving force for moisture evaporation.

7. The microwave hot air sand mold drying oven process according to claim 1, characterized in that, In step 3), the cooling stage uses ambient temperature air for gentle cooling to avoid thermal stress caused by a sudden drop in temperature. By reasonably controlling the wind speed and cooling time, the temperature inside and outside the sand mold drops synchronously, further stabilizing the sand mold structure and improving the strength of the sand mold.

8. The microwave hot air sand mold drying oven process according to claim 1, characterized in that, The process is compatible with sand mold sizes ranging from 100mm×100mm (small) to 1200mm×800mm (large), and different sizes of sand molds can be dried without changing equipment.

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