Composite sand mould for chilled sand casting and method for its production

Abstract

This invention belongs to the field of cryogenic sand casting technology, specifically relating to a composite sand mold for cryogenic sand casting and its preparation method. The preparation method includes: based on the size and shape of the casting, the structure and three-dimensional dimensions of the cryogenic sand blank; preparing cryogenic sand blanks according to a preset structure and three-dimensional dimensions; performing subtractive processing on the cryogenic sand blanks according to a preset subtractive processing procedure to obtain a sand mold; wherein the sand mold includes a cryogenic sand mold and a resin sand mold disposed on one side of it; and closing the separately prepared upper and lower sand molds to form a cavity, thereby obtaining a composite sand mold for cryogenic sand casting. The preparation method of this invention can at least improve the problem of floating sand during cryogenic sand mold blank preparation and moldless subtractive processing, while also improving the processing performance of the sand mold and increasing the gas generation during pouring.

Description

Technical Field

[0001] This invention belongs to the field of cryogenic sand casting technology, specifically relating to a composite sand mold for cryogenic sand casting and its preparation method. Background Technology

[0002] Cryogenic sand casting is a revolutionary process in the casting industry. It replaces the solidifying agent in traditional casting with pure water. Water and sand are thoroughly mixed and then frozen to obtain a cryogenic sand mold. Cryogenic sand casting can accelerate the cooling rate of castings after pouring, improve casting performance, and does not produce irritating gases during the process, making it environmentally friendly. The sand can be directly recycled after pouring without sand treatment, which can reduce production costs.

[0003] Currently, cryogenic sand casting mainly employs moldless subtractive molding. The process involves first preparing a cryogenic sand blank, then performing subtractive processing on the blank, and finally assembling the resulting cryogenic sand mold to perform cryogenic casting and obtain the corresponding casting. However, some problems exist in the preparation, subtractive processing, and pouring of cryogenic sand molds:

[0004] First, moisture loss occurs during the preparation and processing of sand blanks, resulting in surface sand on the sand mold and affecting the dimensional accuracy of the sand mold;

[0005] Secondly, frozen sand molds have poor machinability. During the sand mold processing, the cutting tools generate a lot of heat, which causes the sand mold to melt locally, and also affects the strength and size of the sand mold.

[0006] Finally, the vaporization of moisture during the sand casting process will generate a large amount of gas. Some of this gas cannot be discharged from the mold cavity, which can easily cause defects such as porosity in the casting.

[0007] Therefore, existing frozen sand casting still needs improvement. Summary of the Invention

[0008] The main objective of this invention is to propose a composite sand mold for cryogenic sand casting and its preparation method. The preparation method of this invention can at least improve the floating sand problem in the process of cryogenic sand mold blanking and moldless subtractive casting, while improving the processing performance of the sand mold and increasing the gas generation of the sand mold during pouring.

[0009] To achieve the above objectives, the present invention provides the following technical solutions.

[0010] In a first aspect, the present invention provides a method for preparing a composite sand mold for cryogenic sand casting. The method includes the following steps: designing the structure and three-dimensional dimensions of an upper cryogenic sand blank and a lower cryogenic sand blank according to the size and shape of the casting; preparing the upper cryogenic sand blank and the lower cryogenic sand blank according to the preset structure and three-dimensional dimensions; performing subtractive processing on the upper cryogenic sand blank and the lower cryogenic sand blank according to a preset subtractive processing procedure to obtain an upper sand mold and a lower sand mold; wherein, the upper sand mold includes an upper cryogenic sand mold and an upper resin sand mold disposed on one side of its surface; the lower sand mold includes a lower cryogenic sand mold and a lower resin sand mold disposed on one side of its surface; and fitting the upper sand mold and the lower sand mold together to form a cavity by the upper resin sand mold and the lower resin sand mold, thereby obtaining a composite sand mold for cryogenic sand casting.

[0011] In some embodiments of the present invention, the upper frozen sand blank includes an upper molding sand blank and an upper resin sand blank disposed on one side thereof along its thickness direction.

[0012] In some embodiments of the present invention, the preparation of the upper frozen sand blank includes: thoroughly mixing water and molding sand and pouring it into a first sand box, fully compacting it and keeping the surface flat, so that the thickness of the upper molding sand blank reaches the target thickness; thoroughly mixing resin and molding sand and continuing to pour it into the first sand box, and evenly spreading it on the surface of the upper molding sand blank, fully compacting it and keeping the surface flat, so that the thickness of the upper resin sand blank reaches the target thickness; and transferring the entire sand blank to a freezing environment for freezing to obtain the upper frozen sand blank.

[0013] In some embodiments of the present invention, the lower frozen sand blank includes a lower molding sand blank and a lower resin sand blank disposed on one side thereof along its thickness direction.

[0014] In some embodiments of the present invention, the preparation of the lower frozen sand blank includes: thoroughly mixing water and molding sand and pouring the mixture into a second sand box, fully compacting it and keeping the surface flat, so that the thickness of the lower molding sand blank reaches the target thickness; thoroughly mixing resin and molding sand and continuing to pour the mixture into the second sand box, and evenly spreading it on the surface of the lower molding sand blank, fully compacting it and keeping the surface flat, so that the thickness of the lower resin sand blank reaches the target thickness; and transferring the entire sand blank to a freezing environment for freezing to obtain the lower frozen sand blank.

[0015] In some embodiments of the present invention, the ambient temperature of the freezing environment is -15°C to -10°C.

[0016] In some embodiments of the present invention, the resin accounts for 1% to 2% of the mass of the molding sand, based on the total mass of the upper resin sand blank or the lower resin sand blank.

[0017] In some embodiments of the present invention, the moisture content of the upper molding sand blank or the lower molding sand blank is 3% to 5% of its molding sand mass.

[0018] In some embodiments of the present invention, the resin includes at least one of alkali phenolic resin and furan resin.

[0019] In some embodiments of the present invention, the upper resin sand blank of the upper frozen sand blank and the lower resin sand blank of the lower frozen sand blank are respectively subjected to subtractive processing according to a preset subtractive processing procedure, wherein the thickness of the subtractive processing is less than the thickness of the resin sand blank.

[0020] In some embodiments of the present invention, the preparation method further includes rapidly freezing the upper frozen sand blank and the lower frozen sand blank before subtractive processing.

[0021] In some embodiments of the present invention, the ambient temperature of the rapid freezing is ≤-30°C.

[0022] In some embodiments of the present invention, the shapes of the upper frozen sand blank and the lower frozen sand blank are each independently square.

[0023] In a second aspect, the present invention provides a composite sand mold for cryogenic sand casting prepared by the preparation method described in the first aspect. The composite sand mold includes an upper sand mold and a lower sand mold that cooperate with each other. The upper sand mold has an upper cryogenic sand mold and an upper resin sand mold disposed on one side thereon. The lower sand mold has a lower cryogenic sand mold and a lower resin sand mold disposed on one side thereon. The upper resin sand mold and the lower resin sand mold together form a cavity.

[0024] Compared with the prior art, the present invention achieves the following technical effects:

[0025] 1. In this invention, a combination of frozen sand mold and resin sand mold is used for preparation. The thickness of the frozen sand mold is much greater than that of the resin sand mold, and it still has the green advantages of frozen sand mold casting. At the same time, since the frozen sand mold accounts for the largest proportion, the sand mold will disintegrate after pouring and can be directly recycled. In addition, the resin sand mold layer in contact with the casting is relatively thin, and cleaning is relatively simple.

[0026] 2. In this invention, by covering the surface of the frozen sand mold with a layer of resin sand mold, the contact between the frozen sand mold and air during the freezing molding process and the subtractive processing is reduced, the moisture loss during the entire process is reduced, and the problem of floating sand in the frozen sand mold casting process is solved.

[0027] 3. In the subtractive processing of this invention, the resin sand blank is mainly processed. The resin sand blank has good processing performance, which avoids the problem of local melting of the sand mold caused by the heat generated by the tool during the subtractive processing of frozen sand mold, and ensures the overall strength of the sand mold.

[0028] 4. In this invention, the surface of the frozen sand mold after subtractive processing is a resin sand mold. During pouring, the molten iron comes into contact with the resin sand mold, which avoids a large amount of gas in the frozen sand mold from entering the casting, reducing the problem of porosity in the casting. Moreover, the frozen sand mold can still improve the cooling rate of the casting, refine the microstructure of the casting, and improve the performance of the casting.

[0029] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0030] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0031] Figure 1 This is a schematic diagram of the structure of an upper frozen sand blank according to some embodiments of the present invention;

[0032] Figure 2 This is a schematic diagram of the subtractive processing of an upper-frozen sand blank according to some embodiments of the present invention;

[0033] Figure 3 This is a schematic diagram of the structure of a composite sand mold for cryogenic sand casting according to some embodiments of the present invention.

[0034] Figure Labels

[0035] 100. Freeze the sand blank;

[0036] 110. Top-molded sand blank; 120. Top-molded resin sand blank;

[0037] 200. Composite sand mold;

[0038] 210. Upper sand mold; 220. Lower sand mold; 230. Mold cavity;

[0039] 2110, Upper frozen sand mold; 2120, Upper resin sand mold;

[0040] 2210, Lower frozen sand mold; 2220, Lower resin sand mold. Detailed Implementation

[0041] Exemplary embodiments of the present invention will now be described in more detail with reference to specific examples. It should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0043] In the description of the embodiments of the present invention, the technical terms "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0044] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0045] In the description of the embodiments of this invention, the term "and / or" is merely a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists, A and B exist simultaneously, and B exists. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0046] In the description of the embodiments of the present invention, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0047] In the description of the embodiments of the present invention, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0048] Terminology Explanation

[0049] Frozen sand mold: refers to a sand mold obtained by freezing a mixture of water and silica sand. The sand mold does not contain resin, curing agent or other components, and has the advantages of being green and environmentally friendly.

[0050] Frozen sand mold: A sand mold used for casting obtained by subtracting material from frozen sand blanks.

[0051] Resin sand mold: refers to the alkali-phenol-formaldehyde resin sand mold used in traditional casting.

[0052] Subtractive processing refers to the method of placing frozen sand blanks in processing equipment and obtaining the required sand mold shape and size through milling or other means.

[0053] To address the issue of loose sand, existing technologies have proposed a method and apparatus for directional, quantitative, in-situ deposition and remanufacturing of frozen sand mold surfaces. This method is primarily applied during the sand mold manufacturing process. It involves spraying atomized water onto the mold surface during processing and atomized resin onto the surface after processing to reduce loose sand and improve mold strength. While this method considers moisture loss during processing, significant moisture loss still occurs during the initial freezing process. If the mold size is large, the freezing time can exceed one day. The mold's contact with air in the frozen environment causes continuous sublimation of moisture. Furthermore, the timed and quantitative spraying of atomized water and resin during the freezing process can lead to locally high moisture content and increased gas generation.

[0054] This invention proposes a method for preparing composite sand molds for cryogenic sand casting, which reduces or even solves the problem of floating sand in the process of cryogenic sand mold blanking and moldless subtractive casting, while improving the processing performance of sand molds and improving the problem of excessive gas generation in sand molds during pouring.

[0055] The key to the preparation method in this invention lies in the process of first preparing a frozen sand blank, and then covering the surface of the frozen sand blank with a layer of resin sand blank, the thickness of which is greater than the maximum subtractive thickness of the sand mold. During the freezing process of the sand mold, the resin sand effectively reduces the sublimation of moisture in the bottom sand mold, thereby preventing surface floating sand. In the moldless subtractive process, because the thickness of the resin sand blank is greater than the maximum subtractive thickness of the sand mold, processing is mainly performed on the resin sand blank, and the underlying frozen sand blank is not processed. Since the processing performance of the resin sand blank is superior to that of the frozen sand blank, the sand mold does not experience moisture loss or reduced strength.

[0056] The preparation method in this invention is carried out according to the following steps.

[0057] (1) Determine the structure and three-dimensional dimensions of the frozen sand blank.

[0058] In embodiments of the present invention, the structure and three-dimensional dimensions of the upper and lower frozen sand blanks are designed according to the size and shape of the casting.

[0059] In some embodiments of the present invention, the shape of the frozen sand blank includes, but is not limited to, a square shape, which can be set according to actual needs.

[0060] In some embodiments of the present invention, the shape of the lower frozen sand blank includes, but is not limited to, a square shape, which can be set according to actual needs.

[0061] Figure 1 A cube-shaped frozen sand blank 100 is shown, the overall thickness of which is h.

[0062] See also Figure 1 As shown, the upper frozen sand blank 100 consists of two parts, including an upper molding sand blank 110 and an upper resin sand blank 120 disposed on one side of it along its thickness direction.

[0063] In some embodiments of the present invention, the thickness h1 of the upper molding sand blank 110 and the thickness h2 of the upper resin sand blank 120 are set according to actual needs, and the overall thickness h of the upper frozen sand blank 100 is satisfied as h = h1 + h2.

[0064] In some embodiments of the present invention, the lower frozen sand blank includes a lower molding sand blank and a lower resin sand blank disposed on one side thereof along its thickness direction.

[0065] In some embodiments of the present invention, the thicknesses of the upper and lower molding sand blanks are each independently greater than or equal to the thickness of the lower resin sand blank.

[0066] (2) Determine the maximum machining thickness for subtractive processing.

[0067] In an embodiment of the present invention, before the subtractive processing of the sand billet, processing simulation is used to determine the subtractive processing procedure of the frozen sand billet in advance and to determine the maximum subtractive processing thickness, such as obtaining... Figure 2 The maximum subtractive material thickness h0 shown is illustrated.

[0068] (3) Prepare frozen sand blanks.

[0069] In an embodiment of the present invention, an upper frozen sand blank and a lower frozen sand blank are prepared according to a preset structure and three-dimensional dimensions.

[0070] In some embodiments of the present invention, the preparation processes of the upper frozen sand blank and the lower frozen sand blank are the same, that is, the upper frozen sand blank and the lower frozen sand blank are prepared according to the same procedures.

[0071] In some embodiments of the present invention, the upper frozen sand blank is formed by pressing a sand blank after mixing water and molding sand, and its thickness is set to h1. The upper resin sand blank is formed by pressing a resin blank after mixing resin and molding sand, and its thickness is set to h2. The overall thickness of the upper frozen sand blank is h = h1 + h2.

[0072] In some embodiments of the present invention, the preparation of the upper frozen sand blank includes: thoroughly mixing water and molding sand and pouring it into a first sand box, fully compacting it and keeping the surface flat; when the thickness of the upper molding sand blank reaches the target thickness, such as reaching a preset thickness h1, stop adding sand and scrape the surface flat; thoroughly mixing resin and molding sand and continuing to pour it into the first sand box, and evenly spreading it on the surface of the upper molding sand blank, similarly fully compacting it and keeping the surface flat; when the thickness of the upper resin sand blank reaches the target thickness, such as reaching a preset thickness h2, and the overall thickness of the sand blank reaches h, stop adding sand and scrape the sand blank flat; and transferring the entire sand blank to a freezing environment for freezing to obtain the target upper frozen sand blank.

[0073] In some embodiments of the present invention, the preparation of the lower frozen sand blank includes: thoroughly mixing water and molding sand and pouring it into a second sand box, fully compacting it and keeping the surface flat; when the thickness of the lower molding sand blank reaches the target thickness, such as a preset thickness h1, stop adding sand and scrape the surface smooth; thoroughly mixing resin and molding sand and continuing to pour it into the second sand box, and evenly spreading it on the surface of the lower molding sand blank, similarly fully compacting it and keeping the surface smooth; when the thickness of the lower resin sand blank reaches the target thickness, such as a preset thickness h2, and the overall thickness of the sand blank reaches h, stop adding sand and scrape the sand blank smooth; and transferring the entire sand blank to a freezing environment for freezing to obtain the lower frozen sand blank.

[0074] In embodiments of the present invention, the ambient temperature of the freezing environment is within the range of -15℃ to -10℃. The ambient temperature of the freezing environment should meet the following conditions: the sand blank should possess initial strength after freezing; the tensile strength of the frozen sand blank should not be less than 0.5 MPa; and the compressive strength should be greater than 1 MPa. Based on these requirements, the ambient temperature of the freezing environment should be below -10℃. Simultaneously, to reduce energy waste during the freezing process, the ambient temperature should not be too low. Considering all factors, the ambient temperature is set within the range of -15℃ to -10℃. Exemplarily, the freezing environment temperature can be one of -15℃, -14℃, -13℃, -12℃, -11℃, and -10℃, or any value satisfying the above range. In embodiments of the present invention, the resin can be, but is not limited to, alkali-phenolic resin and furan resin.

[0075] In embodiments of the present invention, the molding sand may be, but is not limited to, silica sand.

[0076] In some embodiments of the present invention, the percentage of resin to molding sand mass is 1% to 2% based on the total mass of the resin-bonded sand blank. Exemplarily, the percentage of resin to molding sand mass can be one of 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any value satisfying the above range.

[0077] In some embodiments of the present invention, the percentage of resin to molding sand mass is 1% to 2% based on the total mass of resin in the lower resin-bonded sand blank. Exemplarily, the percentage of resin to molding sand mass can be one of 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any value satisfying the above range.

[0078] In some embodiments of the present invention, the moisture content of the upper molding sand blank is 3% to 5% of the mass of the molding sand. Exemplarily, the percentage of moisture content of the upper molding sand blank to the mass of the molding sand can be one of 3%, 3.2%, 3.4%, 3.5%, 3.6%, 3.8%, 4.2%, 4.4%, 4.5%, 4.6%, 4.8%, 5%, or any value satisfying the above range.

[0079] In some embodiments of the present invention, the moisture content of the lower molding sand blank is 3% to 5% of the mass of the molding sand. Exemplarily, the percentage of moisture content of the lower molding sand blank to the mass of the molding sand can be one of 3%, 3.2%, 3.4%, 3.5%, 3.6%, 3.8%, 4.2%, 4.4%, 4.5%, 4.6%, 4.8%, or 5%, or any value satisfying the above range.

[0080] (5) Rapid freezing of frozen sand blanks.

[0081] In an embodiment of the present invention, before the frozen sand blank, comprising an upper frozen sand blank and a lower frozen sand blank, is subjected to rapid freezing to make it ready for processing, wherein the tensile strength of the frozen sand blank should be higher than 1 MPa and the compressive strength should be higher than 2 MPa. Taking all factors into consideration, the ambient temperature for rapid freezing should be lower than -30°C, such as -50°C to -30°C.

[0082] In some embodiments of the present invention, liquid nitrogen can be used to rapidly freeze the frozen sand blank.

[0083] It is worth mentioning that, according to actual needs, the frozen sand blank can be frozen and stored before rapid freezing treatment, that is, stored in an ambient temperature of -15℃ to -10℃. When the subtractive processing is required, the frozen sand blank can be rapidly frozen. (5) Subtractive processing molding.

[0084] In an embodiment of the present invention, the frozen sand blank after freezing is transferred to a subtractive processing equipment and the subtractive processing program obtained by simulation in step (2) above is executed.

[0085] In embodiments of the present invention, the upper frozen sand blank and the lower frozen sand blank are subjected to subtractive processing according to a preset subtractive processing procedure to obtain an upper sand mold and a lower sand mold. The upper sand mold includes an upper frozen sand mold and an upper resin sand mold disposed on one side of its surface; the lower sand mold includes a lower frozen sand mold and a lower resin sand mold disposed on one side of its surface.

[0086] In embodiments of the present invention, the subtractive processing mainly targets the resin sand blank area, wherein the maximum processing thickness h0 of the subtractive processing is slightly smaller than the resin sand blank thickness h2, see [reference]. Figure 2 As shown, the remaining resin sand blank area is then formed into a resin sand mold.

[0087] In some embodiments of the present invention, the upper resin sand blank of the upper frozen sand blank and the lower resin sand blank of the lower frozen sand blank are respectively subjected to subtractive processing according to a preset subtractive processing procedure, wherein the thickness of the subtractive processing is less than the thickness of the resin sand blank.

[0088] In some embodiments of the present invention, the thicknesses of the upper frozen sand mold and the lower frozen sand mold are each independently much greater than the thicknesses of the upper resin sand mold and the lower resin sand mold. This can be understood as covering the surface of the upper frozen sand mold with a thin layer of upper resin sand mold and the surface of the lower frozen sand mold with a thin layer of lower resin sand mold.

[0089] In some embodiments of the present invention, the thickness of the upper resin sand mold can be 1mm to 5mm, for example, the thickness of the upper resin sand mold can be one of 1mm, 2mm, 3mm, 4mm, 5mm or any value satisfying the above range. The thickness of the lower resin sand mold can be 1mm to 5mm, for example, the thickness of the lower resin sand mold can be one of 1mm, 2mm, 3mm, 4mm, 5mm or any value satisfying the above range. Of course, the specific thickness of the upper and lower resin sand molds at different positions can be set according to the actual situation and is not specifically limited.

[0090] In some cases, depending on actual needs, the thickness of a certain area in the resin sand mold is 0, that is, the frozen sand mold corresponding to this part of the area is exposed and directly contacts the molten metal during casting.

[0091] (6) Sand mold assembly.

[0092] In an embodiment of the present invention, after the frozen sand blank is subjected to moldless subtractive material processing, the desired target frozen sand mold is obtained. After the upper and lower frozen sand molds are closed, a composite sand mold is obtained, which is ready for casting.

[0093] In some embodiments of the present invention, the upper sand mold and the lower sand mold are joined together to form a cavity, thereby obtaining a composite sand mold for cryogenic sand casting.

[0094] Another aspect of the present invention provides a composite sand mold for cryogenic sand casting prepared by the above-described preparation method.

[0095] join Figure 3 As shown, the composite sand mold 200 includes an upper sand mold 210 and a lower sand mold 220 that cooperate with each other. The upper sand mold 210 has an upper frozen sand mold 2110 and an upper resin sand mold 2120 disposed on one side thereon. The lower sand mold 220 has a lower frozen sand mold 2210 and a lower resin sand mold 2220 disposed on one side thereon. The upper resin sand mold 2120 and the lower resin sand mold 2220 together form a cavity 230.

[0096] In another aspect, the present invention provides a casting method, specifically based on the above-mentioned composite sand mold for cryogenic sand casting.

[0097] In an embodiment of the invention, the composite sand mold is transferred to the pouring area, where pouring and subsequent cleaning processes can be carried out.

[0098] It is worth mentioning that before being transported to the casting area, the obtained composite sand mold can be frozen and stored, that is, stored in an ambient temperature of -15℃ to -10℃. Before casting, the composite sand mold can be rapidly frozen as needed, with the rapid freezing temperature below -30℃, such as -50℃ to -30℃.

[0099] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a composite sand mold for chilled sand casting, characterized by, The preparation method includes the following steps: Based on the size and shape of the casting, the structure and three-dimensional dimensions of the upper and lower frozen sand blanks are designed respectively; The upper frozen sand blank and the lower frozen sand blank are prepared according to the preset structure and three-dimensional dimensions respectively; the upper frozen sand blank includes an upper molding sand blank and an upper resin sand blank disposed on one side along its thickness direction; the lower frozen sand blank includes a lower molding sand blank and a lower resin sand blank disposed on one side along its thickness direction. The upper frozen sand blank and the lower frozen sand blank are processed according to a preset subtractive processing procedure to obtain an upper sand mold and a lower sand mold; wherein, the upper sand mold includes an upper frozen sand mold and an upper resin sand mold disposed on one side of its surface; the lower sand mold includes a lower frozen sand mold and a lower resin sand mold disposed on one side of its surface; the upper resin sand blank of the upper frozen sand blank and the lower resin sand blank of the lower frozen sand blank are processed according to the preset subtractive processing procedure, wherein the thickness of the subtractive processing is less than the thickness of the resin sand blank; The upper sand mold and the lower sand mold are joined together to form a cavity, thus obtaining a composite sand mold for cryogenic sand casting. The preparation of the frozen sand blank includes: After thoroughly mixing water and molding sand, pour the mixture into the first sand box, compact it fully and keep the surface flat, so that the thickness of the upper molding sand blank reaches the target thickness. After thoroughly mixing the resin and molding sand, continue pouring it into the first sand box and spreading it evenly on the surface of the upper molding sand blank. Compact it fully and keep the surface flat so that the thickness of the upper resin sand blank reaches the target thickness. The sand blank is transferred as a whole to a freezing environment for freezing to obtain the frozen sand blank; The preparation of the frozen sand blank includes: After thoroughly mixing water and molding sand, pour the mixture into the second sand box, compact it fully and keep the surface flat, so that the thickness of the lower molding sand blank reaches the target thickness. After thoroughly mixing the resin and molding sand, continue pouring it into the second sand box and spreading it evenly on the surface of the lower molding sand blank. Compact it fully and keep the surface flat so that the thickness of the lower resin sand blank reaches the target thickness. The sand blank is transferred as a whole to a freezing environment for freezing to obtain the lower frozen sand blank.

2. The production method according to claim 1, wherein The ambient temperature of the freezing environment is -15℃ to -10℃.

3. The production method according to claim 1, wherein Based on the total mass of the upper resin sand blank or the lower resin sand blank, the resin accounts for 1% to 2% of the mass of the molding sand.

4. The production method according to claim 1, wherein The moisture content of the upper or lower molding sand blank is 3% to 5% of its molding sand mass.

5. The production method according to claim 1, wherein The resin includes at least one of alkali phenolic resin and furan resin.

6. The production method according to claim 1, wherein The preparation method further includes rapidly freezing the upper frozen sand blank and the lower frozen sand blank before subtractive processing.

7. The preparation method according to claim 6, characterized in that, The ambient temperature for rapid freezing is ≤-30℃.

8. The preparation method according to claim 1, characterized in that, The upper frozen sand blank and the lower frozen sand blank each have independent shapes, including square.

9. A composite sand mold for cryogenic sand casting, prepared by the method according to any one of claims 1-8, characterized in that, The composite sand mold includes an upper sand mold and a lower sand mold that cooperate with each other. The upper sand mold has an upper frozen sand mold and an upper resin sand mold disposed on one side thereon. The lower sand mold has a lower frozen sand mold and a lower resin sand mold disposed on one side thereon. The upper resin sand mold and the lower resin sand mold together form a cavity.

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