A core, sand core and sand mold casting method

Abstract

The present application relates to the field of metallurgy, and particularly relates to a core bone, a sand core and a sand mold casting method. The core bone comprises a ceramic tube and a spring steel nested in the ceramic tube; along the axial direction of the ceramic tube, two end heads of the spring steel respectively exceed two ends of the ceramic tube. Thus, the core bone of the present application not only meets the high strength requirement of the sand core, reduces the deformation rate of the core bone, but also is resistant to high temperature, and has high practicability in solving the sand core deformation problem in the production of precision castings.

Description

Technical Field

[0001] This invention relates to the field of metallurgy, and specifically to a core, sand core, and sand casting method. Background Technology

[0002] Sand casting is a common casting process. After the sand cores are assembled, they are poured and cleaned to form the internal cavity of the casting. Therefore, the quality of the sand cores directly affects the quality of the casting. Slender sand cores with L / D > 15 and L > 240mm are prone to deformation or even breakage under the buoyancy of high-temperature molten metal, leading to the scrapping of the casting. Therefore, sand cores need to have sufficient strength and rigidity to resist deformation. When the raw materials themselves cannot meet the strength requirements, core reinforcement is usually placed inside the sand core during core making to improve its strength.

[0003] The core material needs to be selected based on the size of the sand core. Large and medium-sized cores are made of cast steel, cast iron, or structural steel, while small and medium-sized cores are generally made of cast iron, which has a higher coefficient of thermal expansion than the sand core. However, when the temperature of the molten metal exceeds 1400℃, the high temperature is conducted to the cast iron core, causing a decrease in strength and initiating deformation. Larger sand cores have less impact on the core, and their deformation generally does not affect the dimensions of the casting. However, for small sand cores, the wall thickness between the core and the core is only 10-20mm, resulting in significant deformation of the core when heated. For precision castings, the problem of dimensional deviations in the blank due to core deformation has always existed. Preventing the deformation of slender sand cores is a pressing issue that needs to be addressed.

[0004] Therefore, this invention is proposed. Summary of the Invention

[0005] The main objective of this invention is to provide a method for casting a core, sand core, and sand mold to solve the problems of traditional cores being unable to withstand high temperatures and being prone to deformation.

[0006] To achieve the above objectives, the present invention provides the following technical solutions.

[0007] A first aspect of the present invention provides a core comprising a ceramic tube and a spring steel nested within the ceramic tube;

[0008] Along the axial direction of the ceramic tube, the two ends of the spring steel extend beyond the two ends of the ceramic tube, respectively.

[0009] Therefore, the core of the present invention not only meets the high strength requirements of sand cores and reduces the core deformation rate, but also can withstand high temperatures. It has high practicality in solving the problem of sand core deformation in the production of precision castings, as detailed below.

[0010] Ceramic tubes have a high content of α-alumina (α-Al₂O₃), which makes them resistant to sudden heating and cooling and less prone to cracking. Their coefficient of thermal expansion is close to zero, and their dimensions remain essentially unchanged at high temperatures. While ceramics possess excellent high-temperature resistance, their lack of toughness makes them highly susceptible to breakage due to the shrinkage force and mechanical stress of molten iron during solidification. Therefore, using ceramic tubes alone as a core material is impractical. Spring steel, on the other hand, possesses excellent comprehensive properties such as high strength, heat resistance, and resistance to spring reduction. It complements ceramic tubes by leveraging their respective strengths and mitigating their weaknesses. The resulting composite core structure is regular and evenly distributed across the cross-section of the sand core, while also possessing sufficient strength and rigidity to reduce sand core deformation in precision castings.

[0011] Based on this, the material type of the ceramic tube and its dimensional differences and shape with spring steel can be further controlled to improve the casting quality.

[0012] Furthermore, the ceramic tube is a 95% corundum ceramic tube or a 99% corundum ceramic tube.

[0013] The heat resistance temperature of 95% corundum ceramic tubes is close to 1300℃, while the operating temperature of 99% corundum ceramic tubes can reach up to 1750℃. Both have relatively high heat resistance.

[0014] Furthermore, the distance between the inner wall of the ceramic tube and the outer wall of the spring steel is within 0.2 mm.

[0015] This spacing ensures that the spring steel can be inserted into the ceramic tube while limiting the radial relative movement between them. The length of the spring steel extends beyond the ceramic tube to the core head. The deformation of the spring steel at high temperature extends freely to both ends, so that the axial deformation of the spring steel will not affect the shape of the core, and at the same time, some heat can be transferred along the two ends of the spring steel.

[0016] Furthermore, the distance between the inner wall of the ceramic tube and the outer wall of the spring steel is between 0.1 mm and 0.2 mm. This distance provides better protection against deformation.

[0017] Furthermore, the ceramic tube is a round tube, and the spring steel is a cylinder.

[0018] A second aspect of the present invention provides a sand core comprising:

[0019] A sand core body having an inner cavity, wherein the inner cavity is provided with the core provided in the first aspect of the present invention;

[0020] Two core heads are respectively located at two opposite ends of the sand core body, and the two core heads are respectively connected to the two ends of the spring steel.

[0021] Similar to the principle described above, embedding a core frame in the sand core can improve its strength. Based on this, the present invention selects a ceramic tube with alumina as the main material of the core frame, and embeds spring steel inside the ceramic tube. The coefficient of thermal expansion of this combination is close to 0, and no dimensional change occurs in molten iron above 1400°C, thus controlling the deformation of the sand core.

[0022] Furthermore, the ratio of the length L of the sand core to its diameter D is ≥15.

[0023] Such slender sand cores have higher requirements for strength and deformation, and the core material of this invention can solve this problem.

[0024] Furthermore, the length L of the sand core is ≥240mm.

[0025] Furthermore, the two cores are detachably connected to the two ends of the spring steel, respectively.

[0026] The detachable connection facilitates both assembly and inspection / maintenance.

[0027] A third aspect of the present invention provides a sand casting method, comprising:

[0028] The sand core casting provided in the second aspect of the present invention is used to cast the casting.

[0029] The castings produced by sand core casting using the present invention have less deformation and higher quality.

[0030] In summary, compared with the prior art, the present invention achieves the following technical effects:

[0031] (1) The core of the present invention is a composite material, which not only meets the high strength requirements of the sand core and reduces the deformation rate of the core, but also can withstand high temperature. It has high practicality in solving the problem of sand core deformation in the production of precision castings.

[0032] (2) Controlling the distance between the ceramic tube and the spring steel can ensure that while inserting into the ceramic tube, it can also restrict the radial relative movement between the two and transmit the deformation force to both ends of the spring steel, thereby reducing the deformation of the main body.

[0033] (3) The core of the present invention is particularly suitable for slender sand cores, and the castings produced are of high quality.

[0034] 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

[0035] 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:

[0036] Figure 1 This is a partial perspective view of a sand core in the prior art;

[0037] Figure 2 A three-dimensional schematic diagram of the core provided by the present invention;

[0038] Figure 3 for Figure 2 A radial schematic diagram of the core shown;

[0039] Figure 4 A schematic diagram of the axial cross-section of the sand core provided by the present invention.

[0040] Figure label:

[0041] 11-Core head, 12-Sand core, 13-Iron core skeleton, 21-Spring steel, 22-Ceramic tube, 23-Gap, 3-Sand core body, 4-Core head. Detailed Implementation

[0042] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0043] 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.

[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 relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. 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, unless otherwise explicitly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0047] Currently, the main technologies for solving the deformation of slender sand cores in precision castings are two methods: embedding iron core reinforcement in the sand core and placing core supports.

[0048] Built-in iron core frame Figure 1 As shown, before core making, the iron core rib 13 is placed in the mold cavity of the sand core 12 and fixed with the core head 11. After the core making machine injects sand, it is cured at high temperature. This method of placing the iron core rib 13 inside the sand core 12 improves the strength of the sand core, and the weak parts of the sand core are not easy to break or crack under the buoyancy of the molten metal. The selection of the iron core rib material and size needs to be designed based on many factors such as the size and structure of the sand core, the temperature of the molten metal, and the casting method.

[0049] Core supports are auxiliary tools used to support easily deformable sand cores and remain inside the casting after pouring. They are typically made of the same material or steel, with a chrome or zinc plating. Ensure the surface is clean before use. They are placed between deformable sand cores for fixation. The deformation of the sand cores caused by the buoyancy of the molten metal provides support. The size and structure of the core supports can be flexibly selected based on the structure of the sand cores to limit the amount of deformation.

[0050] The above-mentioned method of using a core core with built-in core support and placing a core brace can prevent the deformation of slender sand cores to a certain extent, but it has limitations, as shown below.

[0051] The built-in iron core 13 has a higher coefficient of thermal expansion than the sand core 12, approximately 1.2 × 10⁻⁶. -5At high temperatures (°C), the sand core 12 will deform. For high-precision castings, the dimensional change must not exceed 1mm. The deformation of the sand core 12 can easily exceed the allowable range for precision castings. The built-in iron core frame 13 cannot effectively solve the problem of sand core deformation in precision castings. Moreover, the iron core frame 13 deforms after use, and requires correction for recycling, which increases the workload and is time-consuming and labor-intensive.

[0052] The size of the core support is difficult to determine properly. If it is too large, it not only wastes material but also leads to poor fusion between the core support surface and the casting, or local defects, making it unsuitable for leak-proof or pressure-bearing castings. If it is too small, it cannot provide sufficient strength to support the sand core, or it will melt prematurely and fail to provide support. For slender sand cores forming holes or shafts, manual placement of the core support for fixation results in a small contact area between the core support and the sand core, leading to unstable fixation. During pouring, the core support may succumb to the impact of molten iron and displace. Therefore, using core supports carries certain risks.

[0053] Therefore, embodiments of the present invention provide a core, such as Figures 2 to 4 As shown, it includes a ceramic tube 22 and a spring steel 21 nested inside the ceramic tube 22; along the axial direction of the ceramic tube 22, the two ends of the spring steel 21 extend beyond the two ends of the ceramic tube 22 respectively.

[0054] Therefore, the core of the present invention not only meets the high strength requirements of sand cores and reduces the core deformation rate, but also can withstand high temperatures. It has high practicality in solving the problem of sand core deformation in the production of precision castings, as detailed below.

[0055] The ceramic tube 22 has a high content of α-alumina (α-Al2O3), which makes it resistant to sudden heating and cooling and less prone to cracking. Its coefficient of thermal expansion is close to 0, and its dimensions remain essentially unchanged at high temperatures. Although ceramics have good high-temperature resistance, their toughness is insufficient, and the shrinkage force and mechanical stress of molten iron during solidification make them prone to breakage. Therefore, using ceramic tubes alone as core materials is not very practical. Spring steel 21, on the other hand, has excellent comprehensive properties such as high strength, heat resistance, and resistance to spring reduction. It complements the ceramic tube 22, creating a composite core structure that is regular and evenly distributed across the cross-section of the sand core. It also possesses sufficient strength and rigidity to reduce the deformation of the sand core in precision castings.

[0056] Based on this, the material type of the ceramic tube and its dimensional differences and shape with spring steel can be further controlled to improve the casting quality.

[0057] For example, in some implementations, the ceramic tube can be a 95% corundum ceramic tube or a 99% corundum ceramic tube. The heat resistance temperature of the 95% corundum ceramic tube is close to 1300℃, while the operating temperature of the 99% corundum ceramic tube can reach up to 1750℃. Both have relatively high heat resistance.

[0058] In some embodiments, the distance between the inner wall of the ceramic tube and the outer wall of the spring steel is within 0.2 mm, i.e. Figure 4 The gap 23 in the middle is controlled within 0.2mm.

[0059] This spacing ensures that the spring steel 21 can be inserted into the ceramic tube 22 while limiting the radial relative movement between the two. The length of the spring steel 21 extends beyond the ceramic tube 22 to the core head. The deformation of the spring steel 21 at high temperature extends freely to both ends. This way, the axial deformation of the spring steel 21 will not affect the shape of the core, and some heat can be transferred along the two ends of the spring steel 21.

[0060] To improve the deformation suppression effect, in some embodiments, the distance between the inner wall of the ceramic tube 22 and the outer wall of the spring steel 21 is between 0.1 mm and 0.2 mm. The shapes of the ceramic tube 22 and the spring steel 21 can be arbitrarily set in this invention. To facilitate processing and ensure uniform stress distribution on the workpiece, in some embodiments, the ceramic tube 22 is a circular tube, and the spring steel 21 is a cylinder.

[0061] The above cores are assembled into a sand core, which can be used for sand casting of castings. Specifically, the sand core includes: a sand core body 3 with an inner cavity, the inner cavity being provided with... Figure 2 The provided core; two core heads 4 are respectively located at two opposite ends of the sand core body 3, and the two core heads 4 are respectively connected to the two ends of the spring steel 21.

[0062] The core material is a ceramic tube 22 with alumina as its basic component. Spring steel 21 is embedded inside the ceramic tube 22. Based on the same principle as before, the coefficient of thermal expansion after this combination is close to 0. It does not undergo dimensional changes in molten iron above 1400℃, thus controlling the deformation of the core.

[0063] The above-mentioned beneficial effects are more pronounced for slender sand cores, for example, in some embodiments, the ratio of the length L of the sand core to its diameter D is ≥15.

[0064] Such slender sand cores have higher requirements for strength and deformation, and the core skeleton of this invention can solve this problem. Furthermore, in some embodiments, the length L of the sand core is ≥240mm, which meets the requirements of typical slender sand cores.

[0065] In some implementations, the two core ends 4 are detachably connected to the two ends of the spring steel 21, respectively. This detachable connection facilitates both assembly and inspection / maintenance.

[0066] In some embodiments, the process of producing castings using the aforementioned sand cores includes: after the sand cores are assembled, they are poured and cleaned to finally form the internal cavity shape of the casting.

[0067] Among them, casting is the process of pouring molten metal into a mold to cast and shape metal parts.

[0068] Cleaning is the process of removing the casting from the mold, removing excess parts from the body, and polishing and finishing the inner and outer surfaces of the casting.

[0069] For the same casting, using the sand core of the present invention and Figure 1 After the sand cores shown are cast, the deformation of the castings obtained by this invention is within 1 mm, or even lower, while using... Figure 1 The deformation of the casting manufactured using the sand core shown is around 2 mm. Furthermore, when the spring steel of this invention is replaced with ordinary carbon steel, the deformation of the manufactured casting is approximately 1.5 mm.

[0070] Therefore, the composite core of the present invention has lower deformation.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sand core, characterized in that, The sand core includes: A sand core body with an inner cavity, wherein a core is provided in the inner cavity; the ratio of the length L of the sand core to its diameter D is ≥15, and the length L of the sand core is ≥240mm; Two core heads are respectively located at two opposite ends of the sand core body; The core includes a ceramic tube and a spring steel nested inside the ceramic tube. Along the axial direction of the ceramic tube, the two ends of the spring steel extend beyond the two ends of the ceramic tube. The two core ends are detachably connected to the two ends of the spring steel. The ceramic tube is a 95% corundum ceramic tube or a 99% corundum ceramic tube, and the distance between the inner wall of the ceramic tube and the outer wall of the spring steel is 0.1mm to 0.2mm.

2. The sand core as described in claim 1, characterized in that, The ceramic tube is a round tube, and the spring steel is a cylinder.

3. A sand casting method, characterized in that, The sand core casting is made using the method described in claim 1 or 2.

Images