Manufacturing method of frozen sand mold by negative pressure coating

Abstract

The present invention provides a method for producing a frozen sand mold by negative pressure coating, the method includes the following steps: a frozen sand mold is produced, a frozen sand body is directly processed by digital control to obtain a sand mold cavity, a softened film is applied to the surface of the cavity of the sand mold coated with heat insulating paint, and at the same time, a backing film is applied to the outer surface of the sand mold to seal the sand box, the frozen sand mold is fixed in an air extraction sand box with a vacuum gas chamber, air is extracted by a vacuum pump, the film is adhered to the sand mold by vacuum suction, the box is closed to obtain the whole sand mold, and the casting is cast by pouring molten metal at room temperature or low temperature while maintaining negative pressure. This method is environmentally friendly, and the produced frozen sand mold has high strength, easy sand removal, little gas generation during the pouring process, and can produce castings with rapid metal solidification, good internal quality, high dimensional accuracy, and excellent surface quality.

Description

[Technical field]

[0001] The present invention relates to a method for producing a frozen sand mold by using a negative pressure coating. [Background technology]

[0002] The traditional foundry industry consumes a lot of energy and resources, and the manufacturing of wooden / metal mold inversion has problems such as a long mold manufacturing cycle, many production steps, high labor intensity, high product development costs, poor working environment, etc. The traditional foundry industry needs to break through and transform its processes to green, so as to promote the energy saving, emission reduction, and clean and sustainable development of the manufacturing industry. Summary of the Invention [Problem to be solved by the invention]

[0003] Frozen sand mold for casting is a new type of mold that uses water as adhesive and various sand particles as a kind of refractory aggregate. After the frozen sand body is produced by freezing water in a low-temperature environment, the frozen sand mold is quickly formed by digitalized die-free casting molding technology based on the cutting molding principle. However, during the pouring process, if the temperature of the metal liquid is too high, a large amount of water in the frozen sand mold will evaporate, the strength of the sand mold will decrease, and the cavity will be easily deformed, which is unfavorable for filling the mold with metal liquid. In addition, the surface of the cavity of the frozen sand mold will directly contact the high-temperature metal liquid, and the instantaneous water vapor will generate bubbles in the metal liquid, which will damage the surface quality of the casting and affect the mechanical performance. In serious cases, the frozen sand mold will collapse early during the pouring process. Therefore, it makes up for the shortcoming of frozen sand molds being easily collapsed during the pouring process, ensures that high-temperature metal liquid is stably filled into the cavity of the frozen sand mold, prevents the phenomenon of "collapse upon touch" during the pouring process, and makes the contour of the casting clearer, the dimensions more accurate, and reduces the amount of machining residue, which is a new direction for breakthroughs in the green foundry industry. [Means for solving the problem]

[0004] In order to solve the above problems, the present invention provides a method for manufacturing a frozen sand mold using a negative pressure coating, which makes up for the drawback that the frozen sand mold is easily collapsed during the pouring process and prevents a large amount of water vapor from being generated during the pouring process. In addition, the side wall of the sand mold is provided with an air bleed hole in advance, and the water vapor in the frozen sand mold can be quickly discharged by continuously drawing a vacuum during the molding and pouring processes, which reduces the generation of pores in the casting and the defects of pinholes, and is a new direction for the green casting industry to break through.

[0005] A method for producing a frozen sand mold by negative pressure coating, comprising the steps of: In step 1, a frozen sand mold is manufactured by digitally cutting a frozen sand body in which an appropriate amount of moisture is mixed directly in a low-temperature processing environment based on the cutting molding principle using a digitalized casting molding technology without a mold, Step 2: Fix the prepared frozen sand mold in an air extraction sand box that is suitable for the size of the sand mold, and apply a layer of heat insulating paint to the surface of the cavity; Step 3: Heating the film until it is softened and then coating it on the surface of the sand mold cavity on which the heat insulating paint is applied; Step 4: Covering the outer surface of the sand mold with a backing film to seal the sand box; In step 5, the vacuum pump is started, and the film is attached to the sand mold by the vacuum suction force, and the upper and lower boxes of the sand mold are negative pressure sealed, and the boxes are closed to obtain the entire sand mold.

[0006] Furthermore, an air bleed hole is provided in the frozen sand mold, and the air bleed hole is manufactured by embedding a metal needle in the frozen sand body in advance and removing the metal needle when the sand body initially solidifies to obtain the air bleed hole, or by machining the air bleed hole in the frozen sand body using digitally controlled drilling technology.

[0007] Furthermore, the sand box for the sand mold is an air extraction sand box with a vacuum gas chamber, and air is extracted by a vacuum pump in combination with an air extraction hole and a filtered air extraction pipe.

[0008] Furthermore, the heat insulating paint is a barrier type heat retaining heat insulating paint, and its main material is aerogel or the like.

[0009] Furthermore, during the film coating and pressure holding process, the degree of vacuum can be controlled to 0.03 to 0.04 MPa.

[0010] Furthermore, the upper and lower boxes are combined to form an entire sand mold having a sprue and a cavity. When pouring molten metal directly at room temperature or in a low-temperature environment, the sand mold is kept under negative pressure (a vacuum of 0.05 to 0.06 MPa and a large amount of bleed air) and gases such as water vapor generated during pouring are extracted in a timely manner through the bleed hole.

[0011] Moreover, the film is one of EVA plastic film, LDPE (low density polyethylene film) and polyesteramine fiber.

[0012] The film is then heated and softened by a heater to a softening temperature of about 70° C., and then laid in the cavity of a sand mold.

[0013] In addition, adhesive tape is used to attach the bonding points between the release surface and the film to prevent defects such as falling molding sand getting caught in the bonding points.

[0014] In addition, this method can not only protect the surface of the cavity of the frozen sand mold from being destroyed by the high-temperature film by applying the heat insulating paint, but also make the film adhere and stick well to the surface of the cavity at the initial stage of film coating. During the pouring of the frozen sand mold, the residue after the film evaporates and the sand mold mainly form a temporary transition shell layer to maintain the molding.

[0015] Preferably, special sand (such as brown corundum) is used instead of paint. Select brown corundum type sand of about 100 / 200 mesh, and compared with ordinary type sand of 70-100 mesh, the hardness of the obtained sand mold is higher and the fire resistance of the sand mold is improved.

[0016] Preferably, when the upper mold is manufactured, a small amount of paint is applied around the sprue to reduce flashing of the metal liquid onto the sand mold and adhesion defects of the sand. Effect of the Invention

[0017] The beneficial effects of the present invention are as follows: 1. During the pouring process, the film momentarily blocks the direct contact between the high-temperature metal liquid and the surface of the frozen sand mold cavity, and the residue after the film evaporates and the sand mold form a temporary transition shell layer to maintain the molding. At the same time, negative pressure pouring accelerates the speed of the metal liquid filling the mold, so that the metal liquid can be rapidly solidified on the surface of the cavity to form a metal shell with a certain strength, and improve the density and dimensional accuracy of the casting.

[0018] 2. The film prevents direct contact between the hot metal liquid and the ice crystal adhesion bridge in the frozen sand mold, guarantees the strength of the sand mold, and prevents a large amount of water vapor from being generated during the pouring process. In addition, by providing an air bleed hole in the side wall of the sand mold in advance and continuously drawing a vacuum during the molding and pouring process, the water vapor in the frozen sand mold can be rapidly discharged, which causes porosity in the casting and reduces pinhole defects. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a flow diagram of the process of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention will be further described below with reference to the drawings and specific embodiments, but it should be understood that the specific embodiments are for the purpose of illustrating the present invention and do not limit the scope of the present invention. Note that the terms "front", "back", "left", "right", "upper" and "lower" used in the following description refer to directions in the drawings, and the terms "inside" and "outside" refer to directions away from or away from the geometric center of a particular component, respectively.

[0021] As shown in FIG. 1, in the manufacturing method of a frozen sand mold using a negative pressure coating according to this embodiment, a frozen sand body is subjected to digital processing and molding to obtain the upper and lower boxes of the sand mold, which are then coated with a film by applying a heat insulating paint, and the cavity and outer surface of the sand mold are respectively coated with a film and a backing film by evacuating the air extraction box. The upper and lower boxes are then joined together to form an entire sand mold having a sprue, a cavity and an air extraction hole, and the sand mold is kept in a negative pressure state and molten metal is directly poured into it at room temperature or in a low temperature environment.

[0022] Specifically, it includes the following steps: Step 1: Using a digitalized die-free casting technique, a frozen sand body containing an appropriate amount of water is directly cut in a low-temperature processing environment based on the cutting molding principle to manufacture a frozen sand mold. In this embodiment, 100 mesh brown corundum is selected, and the frozen sand body contains 4% mass fraction of pure water. Metal needles are embedded in the side walls of the sand body beforehand, and the sand body is frozen in an environment of -30°C. During the initial solidification of the sand body, the metal needles are removed.

[0023] Step 2: the prepared frozen sand mold is fixed in an air extraction sand box that is suitable for the size of the sand mold, the air extraction sand box is equipped with a vacuum gas chamber, and the air extraction hole and the filtering air extraction pipe are combined to extract air by a vacuum pump, and a layer of heat insulating paint is applied to the surface of the cavity, and the main material of the heat insulating paint is aerogel, thereby protecting the cavity from heat destruction and film sticking.

[0024] Step 3: The heat-softened film is coated on the surface of the sand mold cavity. The film is an EVA plastic film, and the mass fraction of vinyl acetate (VA) in the EVA is controlled to 14% to 19%.

[0025] The film is heated and softened by a heater (softening temperature is about 70° C.), and then laid in a sand mold cavity.

[0026] Step 4: Cover the outer surface of the sand mold with a backing film and seal the sand box. Use adhesive tape to attach the joining point between the release surface and the EVA plastic film, to reduce the problem of sand being pinched by falling sand due to improper operation and the wrong box.

[0027] In step 5, the vacuum pump is started to adhere the film to the sand mold by vacuum suction, and the upper and lower boxes of the sand mold are completed. During the film coating and pressure holding process, the vacuum degree is controlled to 0.03-0.04 MPa, and after the upper and lower boxes are combined, the vacuum degree of the sand mold is controlled to 0.05-0.06 MPa during the pouring process.

[0028] As can be seen from the above description, the above embodiment of the present invention can achieve the following technical effects. This method can use special sand or other heat-resistant sand instead of heat-insulating paint. Its main principle is that the residue after the film evaporates and the sand mold form a temporary transition shell layer to maintain the molding, and the metal liquid rapidly solidifies on the surface of the cavity to form a layer of metal shell with a certain strength, thereby improving the density, dimensional accuracy, etc. of the casting. In addition, the film blocks the direct contact between the high-temperature metal liquid and the adhesion bridge of the ice crystals in the frozen sand mold, so as to protect the strength of the sand mold and prevent a large amount of water vapor from being generated during the pouring process. In combination with the constant negative pressure of the sand mold during the pouring process, the generated water vapor can be quickly discharged, accelerating the mold filling speed of the metal liquid and reducing defects such as surface porosity of the casting.

[0029] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but include technical solutions constituted by any combination of the above technical features.

Claims

1. A method for producing a frozen sand mold by negative pressure coating, comprising the steps of: The method comprises: Step 1: by using a digitalized dieless casting molding technique to apply a digitally controlled cutting technique to a sand body frozen in a low-temperature processing environment to manufacture a frozen sand mold, thereby obtaining an upper and lower box of the sand mold; Step 2: Fix the produced frozen sand mold in an air extraction sand box that is suitable for the size of the sand mold, and paint the cavity surfaces of the upper and lower box sand molds with heat insulating paint; Step 3: heating the film until it is softened, and then coating the film on the surface of the cavity of the sand mold coated with the heat insulating paint; Step 4: Covering the outer surface of the sand mold with a backing film to seal the sand box; Step 5 includes starting the vacuum pump, making the film adhere to the sand mold by vacuum suction, and closing the upper and lower boxes of the sand mold by negative pressure coating to obtain the whole sand mold; The method for manufacturing a frozen sand mold using a negative pressure coating is characterized in that the film is heated and softened by a heater, the softening temperature being 65 to 75°C, and the film is laid in a cavity of a sand mold after being cooled.

2. 2. The method for manufacturing a frozen sand mold using a negative pressure coating according to claim 1, wherein in step 1, it is necessary to provide an air bleed hole in the frozen sand mold, and the air bleed hole is manufactured by embedding a metal needle in the frozen sand body in advance and removing the metal needle when the sand body initially solidifies to obtain the air bleed hole, or by drilling the air bleed hole directly in the side wall of the sand mold using digitally controlled processing.

3. 2. The method for manufacturing a frozen sand mold using a negative pressure coating according to claim 1, wherein the sand box for the sand mold is an air extraction sand box equipped with a vacuum gas chamber, and air extraction is performed by a vacuum pump in combination with an air extraction hole and a filtered air extraction pipe.

4. 2. The method for producing a frozen sand mold by negative pressure coating according to claim 1, wherein the degree of vacuum is controlled to 0.03 to 0.04 MPa during the film coating and pressure holding process.

5. 2. The method for manufacturing a frozen sand mold by a negative pressure coating according to claim 1, wherein the heat insulating paint is a barrier type heat retaining and insulating paint.

6. The method for manufacturing a frozen sand mold using a negative pressure coating according to claim 1, characterized in that the upper box and the lower box are combined to form an entire sand mold having a sprue, a cavity and an air bleed hole, the sand mold is kept in a negative pressure state, and molten metal is directly poured in at room temperature or in a low temperature environment.

7. 2. The method for manufacturing a frozen sand mold by negative pressure coating according to claim 1, wherein the film is one of EVA plastic film, low density polyethylene film and polyesteramine fiber.

8. 2. The method for producing a frozen sand mold by negative pressure coating according to claim 1, wherein the thickness of the film is 0.1 mm.

9. 2. The method for producing a frozen sand mold by negative pressure coating according to claim 1, characterized in that an adhesive tape is used to adhere to the bonding portion between the release surface and the film.

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