Freezing sand mold gray scale printing forming method of hybrid phase change cold storage material

Abstract

The application discloses a freezing sand mold gray scale printing forming method of hybrid phase change cold storage material, which comprises a preparation process of the phase change cold storage material and a sand mold multi-gradient freezing printing forming process and relates to the field of sand mold casting. In the water adhesive, the mass fraction of deionized water is 73-77%, the mass fraction of the cold storage material energy storage agent NaCl is 20%, and the mass fraction of the cooling agent is 3-7%. The freezing sand mold gray scale printing forming method of the hybrid phase change cold storage material can selectively spray the water-based adhesive of the hybrid cold storage material according to the freezing sand mold corresponding to different wall thickness castings, so that the sequential solidification of large and complex castings is realized. The application is suitable for the cold storage transportation of the freezing sand mold, has high unit mass cold storage density and is suitable for industrialization and popularization.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of additive manufacturing and casting technology, and in particular relates to a method for grayscale printing of cryogenic sand molds using hybrid phase change cold storage materials. Background Technology

[0002] Sand mold 3D printing is a rapid prototyping technology primarily based on the principle of microdroplet jetting. Unlike other 3D printing technologies that print materials at room temperature or with heat, this method uses a water-based solution as a binder for sand casting. Premixed sand is frozen layer by layer into a solid state at low temperatures to maintain its shape. The frozen sand mold naturally disintegrates under the impact of the high-temperature molten material, and no strong, irritating gases are generated during the pouring process. This method does not use resin; the binder's main component is water, making it environmentally friendly and in line with modern green manufacturing principles.

[0003] The freezing temperature of cryogenic sand molds varies depending on the temperature range of high, medium, and low temperature alloys. In actual production, lower freezing temperatures mean higher energy consumption, and the mechanical properties of cryogenic sand molds initially increase and then decrease as the temperature decreases. Therefore, we must find a balance between the freezing phase transformation temperature of cryogenic sand molds and their basic casting properties. On the other hand, low-temperature cryogenic sand molds also face significant challenges during long-distance, long-term transportation. Cryogenic storage materials primarily utilize the absorption or release of heat during phase transformation to store or release energy. These materials not only have advantages such as high energy density, simple devices, and small size, but also maintain a near-constant temperature during phase transformation, allowing for temperature control of the system. Placing phase transformation materials in insulated boxes for cold chain transportation enables passive refrigerated truck compartments, allowing for small-batch, unitized, and multi-temperature zone transportation using ordinary trucks, achieving energy conservation and rational resource utilization. Given the current problems in cryogenic sand mold casting and transportation, combining phase transformation materials with cryogenic sand molds can produce gradient cryogenic sand molds, avoiding shrinkage cavities during casting and improving the overall performance of the castings. Summary of the Invention

[0004] To address the challenges of shape and performance control in cryogenic casting and the difficulties in long-distance transportation, a grayscale printing method for cryogenic sand molds using hybrid phase change cold storage materials is proposed. This method primarily solves the problem of sequential solidification of casting wall thickness, enabling high-quality long-distance transportation of cryogenic sand molds.

[0005] This invention proposes a method for cryogenic sand mold grayscale printing of hybrid phase change cold storage materials, including the preparation of phase change cold storage materials and a sand mold multi-gradient cryogenic printing process.

[0006] A grayscale printing method for cryogenic sand molds using hybrid phase change cold storage materials is disclosed. This method is applicable to the molding and core-making process for castings with significant differences in wall thickness and to the long-distance transportation of cryogenic sand molds over extended periods. The specific implementation steps are as follows: S1. The formulation design of the cold storage material for sand mold cryogenic printing is designed with a phase change temperature controlled between -15℃ and -25℃. The viscosity and surface tension of the water-based binder mixed with the phase change cold storage material meet the requirements of the array printhead.

[0007] S2. Select appropriate molding sand according to the characteristics of the casting, stir the sand material to be printed with liquid nitrogen or dry ice, and cool the premixed molding sand to a sub-zero temperature (-20℃~-40℃).

[0008] S3. In a low-temperature environment, lay a layer of pre-cooled molding sand. The control system drives the array nozzles to spray water-based adhesive as needed according to the current cross-sectional information of the sand mold, and the droplets are sprayed onto the surface of the pre-cooled molding sand.

[0009] S4. Place the digitally formed frozen sand mold in an environment exceeding -30°C to -50°C for several minutes to several hours to further reduce the temperature of the frozen sand mold.

[0010] S5. In a frozen environment, the sand mold / core unit is assembled as a whole. After assembly, it is stored in a special cold storage or transported over long distances.

[0011] Furthermore, the phase change material in the water-based adhesive can be an organic or inorganic cold storage material, can be a composite of multiple materials, or can be of different concentrations.

[0012] Furthermore, in the water-based adhesive, the main energy storage agent of the cold storage material is NaCl, and the cooling agent is one or more of GaCl2, KCl, K2CO3, NH4Br, polyvinyl alcohol, dodecane, and diethylene glycol.

[0013] Furthermore, the water-based adhesive contains 73 wt.% to 77 wt.% deionized water, 20 wt.% NaCl, and 3 wt.% to 7 wt.% cooling agent.

[0014] Furthermore, the water-based adhesive contains 73 wt% deionized water, 20 wt% NaCl, and 7 wt% cooling agent.

[0015] Furthermore, the water-based adhesive contains 77 wt.% deionized water, 20 wt.% NaCl, and 3 wt.% cooling agent.

[0016] Furthermore, the water-based adhesive contains 75 wt.% deionized water, 20 wt.% NaCl, and 5 wt.% cooling agent.

[0017] Furthermore, the surface tension of the water-based adhesive is 30–50 mN / m, and the viscosity is 2–10 mPa·s.

[0018] Furthermore, the inkjet system includes two or more ink path systems. Depending on the thickness of the casting wall, water-based adhesives with different heat storage capacities are sprayed onto the corresponding mold parts; adhesives with high heat storage capacity are sprayed on thicker wall areas, while adhesives with lower heat storage capacity are sprayed on thinner wall areas.

[0019] The beneficial effects of this invention are: (1) The water-based adhesive of the present invention has a simple composition ratio and a high cold storage density per unit mass.

[0020] (1) This solution is designed for frozen sand molds with different wall thicknesses. It can selectively spray water-based binders with different gray levels of cold storage materials under multiple gradients, so that different areas of the sand mold have different thermophysical properties, thereby achieving sequential solidification and precise control of the castings; achieving strong cold storage effect, and achieving gray printing of water binders.

[0021] (2) Multi-gradient freezing sand mold with mixed cold storage materials is suitable for long-term long-distance cold storage transportation. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for grayscale printing of a hybrid phase change cold storage material using a cryogenic sand mold. Detailed Implementation

[0023] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0024] like Figure 1 As shown, this invention provides a technical solution: A method for grayscale printing of cryogenic sand molds using hybrid phase change cold storage materials is proposed, including a preparation process for the phase change cold storage material and a multi-gradient cryogenic printing process for the sand mold. This method is applicable to the molding and core-making process for castings with significant wall thickness variations and to the long-distance transportation of cryogenic sand molds. Furthermore, all content not described in detail in this specification is prior art known to those skilled in the art.

[0025] A method for cryogenic sand mold grayscale printing of hybrid phase change cold storage materials, the specific implementation steps of which are as follows: S1. The formulation design of the cold storage material for sand mold cryogenic printing is carried out with the phase change temperature controlled between -15 ℃ and -25 ℃. Furthermore, the viscosity and surface tension of the water-based binder mixed with the phase change cold storage material meet the requirements of the array printhead.

[0026] S2. Select appropriate molding sand according to the characteristics of the casting, stir the sand material to be printed with liquid nitrogen or dry ice, and cool the premixed molding sand to a sub-zero temperature (-20 ℃~-40 ℃).

[0027] S3. In a low-temperature environment, lay a layer of pre-cooled molding sand. The control system drives the array nozzles to spray water-based adhesive as needed according to the current cross-sectional information of the sand mold, and the droplets are sprayed onto the surface of the pre-cooled molding sand.

[0028] S4. Place the digitally formed frozen sand mold in an environment exceeding -30°C to -50°C for several minutes to several hours to further reduce the temperature of the frozen sand mold.

[0029] S5. In a frozen environment, the sand mold / core unit is assembled as a whole. After assembly, it is stored in a special cold storage or transported over long distances.

[0030] The water-based binder contains 73% deionized water, 20% NaCl, 6% KCl (a cooling agent), and 1% MgSO4. The inkjet system includes two or more ink path systems. Depending on the casting wall thickness, water-based binders with different heat storage capacities are sprayed onto corresponding mold sections, thereby achieving sequential solidification of the casting.

[0031] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims

1. A method for cryogenic sand mold grayscale printing of hybrid phase change cold storage materials, characterized in that, Follow these steps: S1. Design a water-based adhesive formulation for hybrid phase change cold storage materials for sand mold cryogenic printing, with the phase change temperature controlled between -15℃ and -25℃, and the viscosity and surface tension of the water-based adhesive for hybrid phase change cold storage materials meeting the requirements of the array nozzle. S2. Select appropriate molding sand according to the characteristics of the casting, stir the sand material to be printed with liquid nitrogen, dry ice or cold air, and cool the premixed molding sand to a sub-zero temperature of -20℃ to -40℃. S3. In a low-temperature environment, a layer of pre-cooled molding sand is laid; the control system drives the array of printheads to spray water-based adhesive as needed according to the current cross-sectional information of the sand mold, and the droplets are sprayed onto the surface of the pre-cooled molding sand; the inkjet system includes two or more ink path systems; S4. Place the digitally formed frozen sand mold in an environment exceeding -30°C to -50°C for several minutes to several hours to further reduce the temperature of the frozen sand mold; S5. In a frozen environment, the sand mold / core unit is assembled as a whole. After assembly, it is stored in a special cold storage or transported over long distances. Depending on the wall thickness of the casting, water-based adhesives with different gray values ​​and heat storage capacities are sprayed on the corresponding mold parts. Thicker wall areas are sprayed with adhesives with high heat storage capacity, and thinner wall areas are sprayed with adhesives with low heat storage capacity. The water-based adhesive contains 73wt.%–77wt.% deionized water, 20wt.% NaCl, and 3wt.%–7wt.% cooling agent. The surface tension of the water-based adhesive is 30–50 mN / m, and the viscosity is 2–10 mPa·s.

2. The method for cryogenic sand mold grayscale printing of a hybrid phase change cold storage material according to claim 1, characterized in that, The cooling agent is one or more of GaCl2, KCl, K2CO3, NH4Br, polyvinyl alcohol, dodecane, and diethylene glycol.

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