Framework type internal chill for thick and large casting

Abstract

The invention relates to a skeleton type internal chill for a thick and large casting, belongs to the technical field of metal casting, and solves the problems that in the prior art, fusion of a traditional internal chill and a casting body is poor, the defects of inclusion and air holes are easily generated, and a solid external chill has a poor chilling effect on an ultra-thick and large part. The skeleton type internal chill comprises a hollow skeleton main body and a positioning structure, the outer contour shape of the hollow framework body is matched with the contour of a wall thickness area of a target casting in a profiling mode. The positioning structure is used for being matched with a positioning part on a casting mold core so as to fix the skeleton type internal chill at a preset position; after the framework type internal chill is fixed through the positioning structure and is closed, the hollow framework main body can be coaxially centered in a wall thickness area of a casting cavity, and a preset cooling gap is formed between the outer surface of the hollow framework main body and the surface of the cavity. And finally, the chilling effect on the wall thickness core area of the thick and large casting is remarkably enhanced, the shrinkage porosity and shrinkage cavity defects are effectively eliminated, and the internal density of the casting is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal casting, in particular to a skeleton type inner chill for thick and large castings. BACKGROUND

[0002] In the field of metal casting, especially in the casting process of thick and large castings (such as large aluminum alloy cylinders, boxes, etc.), the solidification and shrinkage control of the castings is the key to ensuring the internal quality. Due to the huge cross-sectional size of the castings, the metal liquid solidifies slowly, and it is easy to form internal defects such as shrinkage and shrinkage holes in the center area of the hot spot of the castings, which seriously affects the mechanical properties and use reliability of the castings.

[0003] In order to accelerate local solidification and improve the feeding condition, the industry widely adopts the process of setting chills in the mold. The chills are divided into external chills and internal chills. The external chills are placed on the surface of the mold or core, and the contact chilling effect is used to accelerate the solidification of the surface layer of the casting; the internal chills are directly placed in the mold cavity, and finally wrapped and fused into part of the casting body by the metal liquid.

[0004] However, although the solid external chill is simple to manufacture, its chilling effect only acts on the surface for the super-thick and large castings, and it is difficult to effectively affect the core area of the thick and large part of the casting, and it cannot fundamentally solve the center shrinkage problem. The traditional solid or simple structure internal chill often leads to poor fusion interface due to the mismatch of its contact with the casting body and shape, and new casting defects such as oxidation inclusions and pores are easily generated at the interface, which reduces the reliability of the casting, and its application is greatly limited. SUMMARY

[0005] In view of the above analysis, the embodiments of the present application aim to provide a skeleton type internal chill for thick and large castings to at least solve one of the problems of poor fusion of the internal chill with the casting and easy to produce defects in the prior art, and poor chilling effect of the external chill on the core of the thick and large area.

[0006] In one aspect, the embodiments of the present application provide a skeleton type internal chill for thick and large castings, comprising: a hollow skeleton main body, the outer contour shape of which is adaptively shaped to the contour of the thick wall area of the target casting; a positioning structure integrally formed with the hollow skeleton main body, used for cooperating with a positioning part on a casting core to fix the skeleton type internal chill at a predetermined position of the core.

[0007] Wherein, when the skeleton type internal chill is fixed on the casting core through the positioning structure thereof and the mold is closed, the hollow skeleton main body can be coaxially centered in the thick wall area of the casting cavity, and there is a first cooling gap with uniform distance between the outer surface of the hollow skeleton main body and the cavity surface; there is a cooling gap between the inner surface of the hollow skeleton main body and the outer surface of the casting core.

[0008] Further, at the axial end corresponding to the target casting, a second cooling gap exists between the end face of the hollow skeleton body and the end face of the mold cavity.

[0009] Further, the hollow skeleton body is provided with a local hollow window at the position corresponding to the hole to be machined or the structure to be avoided on the target casting.

[0010] Further, the end edges of the hollow skeleton body in the metal liquid filling direction are provided with a fillet transition structure, and the fillet radius is usually not less than 5mm.

[0011] Further, the positioning structure is composed of at least three ribs; the ribs extend radially outward from the hollow skeleton body, and the cross-sectional shape can form a clamping fit with the positioning part on the casting core.

[0012] Further, the ribs are located in the middle area of the hollow skeleton body along the axial direction.

[0013] Further, the hollow skeleton body is made of cast iron, cast steel or metal material which is the same or similar to the material of the target casting body.

[0014] Further, the hollow skeleton body is an integrally formed frame with regular or irregular hollow structure, and the structure is a single-layer cylindrical skeleton or a double-layer ring cylindrical skeleton.

[0015] The application further provides a casting device comprising the above-mentioned skeleton type inner chill, which is used for casting thick and large castings, and comprises:

[0016] a casting cavity whose profile matches the shape of the target casting; the skeleton type inner chill as described above; a core for forming the inner cavity of the casting cavity, and the core is provided with a positioning part matched with the positioning structure of the skeleton type inner chill; wherein the skeleton type inner chill is fixed on the core through the positioning structure, and is located in the thick wall area of the casting cavity.

[0017] Correspondingly, the application also provides a casting method of thick and large castings, which adopts the above-mentioned casting device.

[0018] Compared with the prior art, the application can at least achieve one of the following beneficial effects:

[0019] 1) This invention employs a hollowed-out skeleton-type internal chiller that mimics the wall thickness contour of the casting, maintaining a precisely preset gap (e.g., 15-20mm for the main body and 80-100mm for the end areas) between it and the casting cavity surface. Its outer surface, together with all cavity surfaces, forms a surrounding forced cooling and feeding channel. This design forces the molten metal to solidify simultaneously from both the cavity surface and the internal chiller surface after filling, advancing towards the center of the wall thickness. This shortens the feeding distance and transforms the traditionally difficult-to-control solidification process of thick sections into a controllable, bi-directional solidification process, eliminating shrinkage cavities and porosity defects in the casting core.

[0020] 2) The hollowed-out structure of the skeleton-type internal chill of this invention creates conditions for good fusion by increasing the contact and interweaving area with the molten metal. When made of a material similar to the casting body, combined with its relatively small cross-sectional size and large rounded corner transition design at the ends, the high-temperature molten metal can fully surround, flush, and melt through each branch of the chill. This significantly reduces the risk of poor fusion, and the molten metal can penetrate the hollowed-out areas to communicate with each other, ensuring the metallurgical bonding quality of the fusion interface and avoiding defects such as porosity and inclusions that are prone to occur in traditional internal chills.

[0021] 3) This invention achieves rapid and accurate engagement between an integrally formed positioning structure (such as multiple radial ribs) and pre-set positioning parts (such as grooves or holes) on the core, ensuring that the skeleton-type internal chill is firmly and coaxially fixed in the preset position within the complex core. This rigid connection method prevents displacement or floating during core assembly, mold assembly, or casting, ensuring the uniformity of the final cooling gap and process reproducibility. It solves the problem of difficult positioning of large and complex internal chills, and improves core assembly accuracy and production efficiency.

[0022] 4) The hollow skeleton body of this invention can be locally enlarged and hollowed out according to the subsequent machining holes or structural avoidance requirements on the target casting, avoiding interference with the final function of the casting. The overall skeleton can adopt different forms such as single-layer or double-layer cylindrical, offering flexible design. Compared with traditional solid internal chills or large external chills, this hollow skeleton design reduces the amount of metal used in the chills themselves while providing a larger heat dissipation surface area, thus reducing material costs and thermal shock to the mold cavity, and is conducive to obtaining a better as-cast microstructure.

[0023] 5) This invention combines a skeleton-type internal chill with segmented external chills (such as the first external chill on the core surface and the second external chill on the inner surface of the mold) and a matching gating system (such as slotted gating) to form a synergistic, three-dimensional cooling and feeding system. This system allows for flexible adjustment of the internal and external chill layout according to different casting shapes and wall thicknesses, resulting in high cooling intensity and overall temperature control from the casting core to the surface. This significantly enhances the operability of the process and its adaptability to castings of varying thicknesses (especially enclosed cavities).

[0024] 6) The casting system or process solution provided by this invention integrates a specially designed skeleton-type internal chill, a suitable positioning core, a segmented external chill assembly, and a matching gating system. It is a solution designed for the efficient production of high-quality, thick, and large castings. The components work together to optimize the entire filling and solidification process. This helps reduce scrap rates, improve production stability and efficiency, and is particularly suitable for the mass production of thick, large castings with high-quality requirements.

[0025] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0026] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0027] Figure 1 This is a schematic diagram of the outline structure of the target casting described in an embodiment of the present invention;

[0028] Figure 2a This is a schematic diagram of the independent structure of the single-layer skeleton-type internal chill of the present invention;

[0029] Figure 2b This is a schematic diagram of the independent structure of the double-layer skeleton internal chill of the present invention;

[0030] Figure 3 This is a schematic diagram of the gating system and the location of the casting cavity in the casting process of this invention;

[0031] Figure 4 This is a schematic diagram of the arrangement of the mold cavity, external chill and gating system in the casting process of this invention;

[0032] Figure 5 This is a schematic diagram of the process of positioning and fixing the skeleton-type internal chiller on the core according to the present invention;

[0033] Figure 5a yes Figure 5 Schematic diagram of the first external chiller laid in the lower half of the core;

[0034] Figure 5b yes Figure 5 Schematic diagram of the first external chiller laid in the upper half of the core;

[0035] Figure 5c yes Figure 5 A schematic diagram showing the arrangement of a second external chill in the mold area;

[0036] Figure 5d yes Figure 5 Schematic diagram of the positioning of the central frame type internal chiller in the casting cavity;

[0037] Figure 6 This is a cross-sectional view of the arrangement of the skeleton-type internal chills in the casting cavity.

[0038] Figure 7 yes Figure 6 Top view.

[0039] Figure label:

[0040] 1. Target casting; 2. Skeleton-type internal chill; 3. Positioning structure; 4. Core; 5. First external chill; 6. Second external chill; 7. Streamline; 8. Slit tube; 9. Positioning part; 10. Slit opening; 11. Mold. Detailed Implementation

[0041] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0042] In the field of metal casting, especially in the production of thick and large castings (such as large cylindrical and box structures), controlling internal shrinkage porosity and other defects has always been a technical challenge. Traditional processes often use external chills or simple-shaped internal chills to accelerate local solidification. However, external chills have limited cooling effect on the core of thick areas, while traditional internal chills, due to their large fusion interface with the casting and mismatched shape, are prone to causing fusion defects such as inclusions and porosity, seriously affecting the reliability and mechanical properties of the casting. To address this, this invention proposes a skeleton-type internal chill design and a matching casting process. By optimizing the chill structure and positioning method, it guides the casting to achieve sequential solidification, thereby improving the internal quality of the casting.

[0043] On one hand, a specific embodiment of the present invention provides a skeleton-type internal chill for thick castings, comprising:

[0044] The hollow skeleton body has an outer contour shape that conforms to the wall thickness region of the target casting. A positioning structure, integrally formed with the hollow skeleton body, engages with a positioning part on the casting core to fix the skeleton-type internal chill at a predetermined position on the core. When the skeleton-type internal chill is fixed to the casting core by its positioning structure and the mold is closed, the hollow skeleton body is coaxially centered within the wall thickness region of the casting cavity, and a uniform first cooling gap exists between the outer surface of the hollow skeleton body and the cavity surface. A cooling gap also exists between the inner surface of the hollow skeleton body and the outer surface of the casting core. The distance of the first cooling gap is 15mm-20mm.

[0045] Furthermore, at the axial end corresponding to the target casting, a second cooling gap exists between the end face of the hollow skeleton body and the end face of the cavity. The second cooling gap is 80mm-100mm.

[0046] The skeleton-type internal chill of this invention adopts an integrally formed frame structure, the shape of which perfectly matches the cavity surface of the target casting. This skeleton-type internal chill is not simply placed inside the cavity, but is precisely fixed to the entire contour surface of the core forming the inner cavity of the target casting through a positioning structure, and has a certain cooling gap with the outer surface of the core, forming an internal cooling system. This arrangement achieves a fundamental shift in cooling method from "discrete point cooling" to "continuous surface cooling".

[0047] Furthermore, the hollowed-out skeleton body has partial hollowed-out windows at positions corresponding to the target casting where holes need to be machined or where structural avoidance is required.

[0048] Furthermore, the hollow skeleton body has rounded corner transition structures on the end edges in the direction of molten metal filling, and the rounded corner radius is usually not less than 5mm.

[0049] Furthermore, the positioning structure consists of at least three ribs; the ribs extend radially outward from the hollow skeleton body, and their cross-sectional shape can form a snap-fit ​​with the positioning part on the casting core.

[0050] Furthermore, the ribs are located in the central region of the hollow skeleton body along its axial direction.

[0051] Furthermore, the hollowed-out skeleton body is made of cast iron, cast steel, or a metal material that is the same as or similar to the material of the target casting body.

[0052] Furthermore, the hollowed-out skeleton body is an integrally formed frame with a regular or irregular hollowed-out structure, and its structure is a single-layer cylindrical skeleton or a double-layer ring cylindrical skeleton.

[0053] Furthermore, the main body of the hollowed-out skeleton is an integrally formed grid-like frame, a radial rib frame, or a contoured frame composed of continuous curved surfaces and reinforcing ribs (for example, a ring-shaped grid frame can be used for cylindrical target castings). The integral forming design helps to ensure the strength and dimensional accuracy of the skeleton-type internal chill.

[0054] Furthermore, the wall thickness of the skeletal internal chill can be adjusted within the range of 30mm-50mm according to the target casting wall thickness and material type. The hollowing ratio (percentage of hollowed-out area to surface area) of the chill can be selected between 40% and 70%.

[0055] Furthermore, the surface of the skeleton-type internal chill can be treated with sandblasting, oxidation, or coating to adjust the heat exchange coefficient between it and the molten metal.

[0056] In practical applications, the hollowed-out skeleton body can be presented as a single-layer cylindrical structure (such as...). Figure 2a (as shown) or a double-layered annular cylindrical structure (such as...) Figure 2b (As shown) Two specific forms. The choice of which structure to use is based on a comprehensive judgment of the specific structure of the target casting, the wall thickness, and the cooling intensity required by the process.

[0057] Among them, single-layer cylindrical structures (such as Figure 2a As shown), the main body is a single-layer cylindrical hollow frame, the hollow frame as a whole is a rigid ring structure, and the cylinder wall is a regular grid-like frame. A double-layer ring-cylindrical structure (as shown) Figure 2b As shown, the main body is a double-layered ring-shaped hollow skeleton, including an inner cylinder wall, an outer cylinder wall, and vertical ribs connecting the inner and outer cylinder walls, forming a rigid ring structure as a whole.

[0058] Specifically, when the target casting wall thickness is relatively moderate, and the radial thickness required for the hollow skeleton body itself is small after meeting the preset cooling gap (usually 15mm-20mm), a single-layer cylindrical structure is preferred. This structure is the simplest, convenient to manufacture and install, and its single-layer cylindrical wall surface faces both the outer surface of the core and the inner surface of the mold, which can achieve good weight reduction while ensuring effective cooling.

[0059] For castings with extremely thick walls, complex structures, or extremely high internal density requirements, a double-layer annular structure is preferred. This structure consists of coaxially arranged inner and outer annular cylinders and connecting ribs between them, essentially creating two independent cooling interfaces within the casting cavity. This design significantly increases the heat capacity and structural stiffness of the chills, providing a more intense and uniform three-dimensional chilling effect, and is particularly suitable for guiding the sequential solidification of ultra-thick, large-section castings.

[0060] Whether it is a single-layer or double-layer structure, the core design objective and evaluation standard are consistent: after the structure is precisely fixed to the core, it is necessary to ensure that the effective cooling surface of the hollow skeleton body (the outer surface for a single layer, and the outer surface of the outer ring and the inner surface of the inner ring for a double layer) can form a designed, uniform cooling gap with the inner cavity surface and outer surface of the target casting.

[0061] In actual casting applications, the aforementioned skeleton-type internal chill does not exist independently. Its preset cooling gap and coaxial centering positioning must be achieved through a matching casting device. Therefore, the present invention further provides a casting device including the skeleton-type internal chill.

[0062] A casting apparatus for casting thick castings, comprising:

[0063] The casting cavity has a contour that matches the shape of the target casting; a skeleton-type internal chill as described above; a core for forming the inner cavity of the casting cavity, the core having a positioning part that cooperates with the positioning structure of the skeleton-type internal chill; wherein the skeleton-type internal chill is fixed to the core by its positioning structure and is located in the wall thickness area of ​​the casting cavity.

[0064] Accordingly, based on the above-described casting apparatus, the present invention also provides a casting method for thick and large castings. This method employs the casting apparatus described above. Specifically, the core steps of the method include:

[0065] S1. Preparation of skeleton-type internal chill: The skeleton body is integrally formed and its outer contour is adapted to the contour of the wall thickness area of ​​the target casting. The skeleton body is provided with axially through windows evenly distributed in the circumferential direction. The total area of ​​the windows accounts for 55%–70% of the area of ​​the skeleton side wall.

[0066] S2. Positioning and fixing: On the core forming the inner cavity of the target casting, a positioning part is provided that cooperates with the positioning structure of the skeleton-type internal chill; the skeleton-type internal chill is assembled to the positioning part through the positioning structure to coaxially fix the skeleton-type internal chill at a preset position on the core.

[0067] In this embodiment, the core is divided into two halves (upper core and lower core) along the axial direction. The positioning and fixing operation specifically includes the following steps:

[0068] (1) Assembly of the lower core: such as Figure 5a As shown, the first external chill is fully laid on the outer surface of the lower half of the core (i.e., the side corresponding to the lower half of the inner cavity of the target casting). The maximum projected size of a single chill is no more than 100mm×100mm. The spacing between adjacent chills is 8mm-10mm to ensure uniform cooling and reserve expansion space for the molding sand.

[0069] (2) Installation of skeleton-type internal chill: The positioning structure of the skeleton-type internal chill with hollow frame structure is precisely engaged with the pre-set positioning part (i.e., the matching groove on the core surface) on the lower half core to complete the initial fixation and ensure the relative position of the skeleton and the core is stable; after installation, the skeleton-type internal chill is suspended in the center outside the lower half core, and there is a pre-set gap between the skeleton-type internal chill and the outer surface of the lower half core.

[0070] (3) Assembly of the upper core: such as Figure 5b The lower end face of the upper half of the core is aligned and fastened to the upper end face of the lower half of the core to form a complete core. Then, the outer surface of the upper half of the core is fully covered with the same specification of first external chills to form a fully enclosed cooling structure for the core.

[0071] (4) Arrangement of the second external chiller: as follows Figure 5c As shown, in the mold area corresponding to the outer surface of the target casting, a second external chill of the same specification is arranged in the high-temperature area between each ingate to enhance the cooling of the key areas of the outer wall.

[0072] (5) Molding preparation: The assembled core assembly (including the skeleton-type internal chill and the first external chill) is placed into the mold (e.g., Figure 5d The gaps between the mold and the core, and between the mold and the external chill, are filled with sand and compacted to complete the overall shape;

[0073] S3. Mold Assembly and Casting: After completing the molding process including the core and the skeleton-type chill fixed thereon, the mold is assembled, that is, the upper and lower molds are accurately snapped together to form a casting cavity. Cooling gaps are pre-set between the outer surface of the skeleton-type chill and the outer surface of the core, as well as between the chill and the inner surface and end face of the mold. The hollowed-out areas of the skeleton-type chill allow molten metal to penetrate and communicate with each other. Subsequently, low-pressure casting is used to pour the molten metal through a gating system consisting of a horizontal sprue and eight slotted gating units (slot cylinder diameter not less than 70mm, slot opening width not less than 20mm). In some embodiments, the pouring temperature is controlled at 700±10℃, allowing the molten metal to smoothly fill the cavity, first filling the cooling gaps around the skeleton, then penetrating through the hollowed-out areas of the skeleton, and finally completely enveloping and fusing the skeleton-type chill into a single unit, achieving sequential solidification.

[0074] The thick castings described in this invention refer to castings whose large cross-sectional dimensions (such as wall thickness and hot spot diameter) result in slow solidification of the molten metal, making it difficult to effectively eliminate core shrinkage cavities and other defects after solidification using traditional external chills or risers alone. This invention is particularly applicable to castings with a main wall thickness of not less than 30 mm.

[0075] This invention improves upon the traditional arrangement of internal chills. In conventional processes, internal chills are typically placed randomly or empirically at localized hot spots within the mold cavity of the target casting, often as discrete metal blocks or bars. This arrangement has significant limitations: the contact area between the chill and the target casting is limited, resulting in low cooling efficiency; furthermore, the discrete chill blocks obstruct the flow of molten metal, easily creating dead zones around them, leading to poor fusion, porosity, and inclusion buildup.

[0076] In practice, the skeleton-type internal chill is integrally formed from a metal material with the same or similar composition as the target casting. Its outer contour is designed to mimic the contour of the wall thickness area of ​​the target casting, ensuring that after being positioned in the casting cavity, it maintains a preset cooling gap with the cavity surface of the target casting: in the area corresponding to the main wall thickness of the target casting, the gap between the outer surface of the skeleton-type internal chill and the outer surface of the core, as well as between the external surface of the internal chill and the inner surface of the mold, is 15mm-20mm. By reducing the gap, the chilling effect is enhanced, accelerating the solidification of the liquid metal in this area; in the area corresponding to the axial end of the target casting, or in the opening area designed for guiding feeding (e.g., the root of the riser), the gap between the end face of the skeleton-type internal chill and the end face of the cavity is 80mm-100mm, to reserve sufficient space to ensure unobstructed feeding channels and ensure efficient liquid metal feeding.

[0077] During the pouring process, the molten metal first fills the annular gaps around the skeleton-type internal chill, and then evenly penetrates into the interior through the hollowed-out areas and local hollowed-out structures of the skeleton-type internal chill, so that the skeleton-type internal chill is completely encapsulated and fused by the molten metal. Relying on the huge specific surface area of ​​the skeleton-type internal chill and the high thermal conductivity of the metal material, it can quickly absorb the heat of the thick parts of the casting, and precisely guide the casting to solidify sequentially from the inside to the outside, and from the thick areas to the feeding channels, effectively improving the density of the casting.

[0078] The skeleton-type internal chill of this invention avoids the defects of splicing multiple internal chills in traditional methods, and improves the internal cooling from a passive and localized measure to an active and systematic control method. It effectively solves the problem of shrinkage porosity and shrinkage holes in thick castings, and at the same time improves the problem of poor fusion between traditional internal chills and the casting body.

[0079] Specifically, in step S1, when preparing the skeleton-type internal chill, it is first necessary to determine the target casting (e.g., Figure 1 shown Based on the geometric contour of the wall thickness region of the aluminum alloy rotary cylinder, a monolithic hollow frame body (as shown in Figure 2) was designed and fabricated to match its shape. (Hollowed-out rotating body).

[0080] This skeleton-type internal chill is a three-dimensional spatial frame structure. Unlike the point or rod arrangement of traditional solid internal chills (such as solid round bars or blocks), its design can precisely fit the internal space of the thick area of ​​the target casting in the cavity, achieving precise and all-round coverage of the hot spot, and fundamentally solving the problem of uneven cooling in traditional methods.

[0081] The frame structure design employs a hollow form rather than a solid structure, which significantly increases the effective contact surface area with the flowing molten metal while ensuring overall structural rigidity and subsequent positioning stability. This allows the skeletonized internal chill to quickly absorb and conduct heat from the core of the casting, much like an internal radiator, thus significantly improving cooling efficiency.

[0082] To further improve the permeability and fusion quality of the molten metal into the skeleton, the sidewalls of the hollow skeleton body are provided with circumferentially distributed and axially continuous windows, the total area of ​​which accounts for 55%–70% of the sidewall area. Below 55%, the molten metal penetration resistance is high, easily leading to internal fusion cold shuts; above 70%, the skeleton's own heat capacity and strength drop sharply, the cooling effect is weakened, and localized sand erosion is prone to occur in the early stages of filling. Using a 55%–70% window area ratio ensures the skeleton's rigidity while allowing the molten metal to penetrate the skeleton uniformly and rapidly along the circumference, significantly reducing shrinkage porosity. Furthermore, the continuous windows disperse the high-temperature molten metal into multiple fine streams, reducing direct impact on the core and further reducing inclusions and porosity defects.

[0083] To ensure smooth filling of the mold with molten metal, achieve good fusion, and precisely control the cooling effect, it is necessary to strictly control the preset gap between the outer contour of the skeleton-type internal chill and the inner surface, outer surface, and axial end face of the target casting.

[0084] Specifically, in the main area with the thickest wall of the target casting, the gaps between the skeleton-type internal chill and the outer surface of the core, and between the skeleton-type internal chill and the inner surface of the mold, are both set to 15mm-20mm. This gap range ensures that the chill generates sufficient quenching effect on the high-temperature molten metal, rapidly establishing the solidification front and guiding sequential solidification; it also avoids problems such as narrow molten metal flow channels, increased filling resistance, and incomplete chill wrapping caused by gaps that are too small (<15mm), and weakened quenching effect and inability to effectively eliminate central thermal shrinkage porosity caused by gaps that are too large (>20mm).

[0085] At the axial end of the target casting, at the root of the riser, or in the opening area designed to guide feeding, the gap between the end face of the skeleton-type internal chill and the end face of the cavity is increased to 80mm-100mm to provide a smooth flow and feeding channel for the molten metal, ensuring that the thick area receives sufficient liquid metal replenishment during solidification, and avoiding the risk of new shrinkage cavities forming near the chill due to obstruction of the feeding path.

[0086] Through the aforementioned differentiated gap design, an adjustable cooling intensity gradient can be constructed inside the casting, enabling the skeleton-type internal chill to form strong cooling in the thick areas of the target casting while maintaining unobstructed flow in the feeding channel area. This strengthens the cooling effect starting from the internal contour of the casting, laying a crucial foundation for subsequent sequential solidification.

[0087] Furthermore, when preparing the skeleton-type internal chill in step S1, it is necessary to accurately analyze the structural characteristics of the target casting: for functional areas of the target casting that require subsequent machining to form holes (such as flange mounting holes) or reserve structural clearance space (such as oil passages), targeted local hollowing treatment needs to be performed at the corresponding positions of the skeleton-type internal chill. By flexibly adjusting the shape of the skeleton-type internal chill and implementing local hollowing according to the machining requirements of the target casting, interference of the chill metal with the functional areas of the target casting can be completely avoided. This not only ensures the structural integrity and core mechanical properties of the target casting body, but also avoids problems such as increased machining difficulty and excessive tool wear caused by the "hard points" of the chill during subsequent machining, significantly improving machining efficiency and extending tool life.

[0088] Meanwhile, to optimize the flow of molten metal and reduce forming defects, the edges of the hollowed-out structure of the skeletal internal chill in the direction of molten metal filling must be machined into large rounded corners. The rounded corner design effectively smooths the molten metal flow lines, reduces flow resistance, and avoids eddies, gas entrapment, or the formation of difficult-to-fill "dead corners" at sharp corners. Retaining sharp corners not only increases filling resistance but may also cause defects such as porosity and inclusions at the fusion interface between the chill and the final casting due to gas entrapment or excessively rapid local solidification. The rounded corner radius can be determined according to the chill cross-sectional dimensions, typically not less than 5mm, to ensure good flow guidance and defect prevention.

[0089] In step S2, when fixing the skeleton-type internal chill, precise positioning and stable fixation are achieved through its integrated positioning structure. This positioning structure is preferably composed of three or four transverse ribs integrally formed with the hollow skeleton body, with the ribs concentrated in the central area of ​​the chill. Correspondingly, when preparing the core to form the cavity of the target casting, positioning holes that perfectly match the position and size of the ribs must be pre-drilled. The fixing operation can be completed simply by inserting the transverse ribs into the corresponding positioning holes.

[0090] This positioning method has multiple technical advantages: First, the rib structure, which is integrally formed with the hollow skeleton body, has high strength and can reliably resist the impact of molten metal during the pouring process, effectively preventing the displacement of chills and ensuring uniform preset gaps; Second, the snap-fit ​​fixing does not require additional tooling or adhesives, making it simple to operate and highly efficient; Third, the rib cross-sectional dimensions (such as 20mm×20mm) are optimized to meet the support and positioning strength requirements, and are easy to remove mechanically after the target casting has solidified and been cleaned, leaving only slight residue and having minimal impact on the quality of the inner surface of the casting.

[0091] Preferably, the skeleton-type internal chill is fixed on the individual core before core assembly to ensure that the relative position of the chill and the core remains stable during subsequent core assembly and box assembly, and to avoid the chill shifting due to collision, handling or other operations.

[0092] To further enhance the precise control of the solidification process of the target casting and form a coordinated internal and external cooling system, this process also includes step S0: arranging segmented external chills on the outer surface of the target casting or on a large concave surface formed by the sand mold. The maximum projected size of a single external chill should not exceed 100mm × 100mm, and a gap of 8mm-10mm should be reserved between adjacent external chills.

[0093] Compared with the traditional large external chill, the segmented design has significant advantages: on the one hand, the small chill generates less thermal stress during the cooling process, which can effectively avoid mold cracking caused by excessive thermal stress; on the other hand, the reserved gap can provide buffer space for the thermal expansion of the molding sand, preventing the target casting from being squeezed due to the obstruction of expansion, thereby causing surface thermal cracking defects.

[0094] When arranging external chills: Segmented external chills (i.e., the first external chill) can be fully laid on the core surface within the inner cavity of the target casting to achieve uniform cooling of the inner cavity area; while on the outer surface of the target casting, segmented external chills need to be concentrated in the area between each ingate (i.e., the second external chill). This is because the ingate, as the inflow channel of high-temperature molten metal, has the highest temperature near the molding sand and the target casting wall, making it a weak point in the solidification of the outer wall. By focusing on arranging external chills in this area, the cooling intensity of the high-temperature zone can be specifically enhanced, balancing the solidification rate of the entire outer wall of the target casting. This works synergistically with the internal skeleton-type internal chills, ultimately constructing an ideal sequential solidification mode that "progresses gradually from the inside out, from the area between the ingates to the ingate area," thereby minimizing internal defects such as shrinkage porosity and shrinkage cavities in the formed casting.

[0095] In the pouring stage of step S3, low-pressure casting is preferably used, combined with a slit gating system. The diameter of the slit cylinder of this gating system should be no less than 70 mm, and the slit opening width should be no less than 20 mm. Low-pressure casting uses stable gas pressure to push the molten metal to rise smoothly and fill the mold, which can effectively reduce defects such as gas entrapment and oxide inclusions, and is especially suitable for target castings with both complex thin walls and thick areas (such as aluminum alloy cylinders). The slit gating system can achieve uniform and rapid filling of molten metal along the height direction of the target casting, avoiding local filling delays, and works in conjunction with the hollow structure of the skeleton-type internal chill to ensure that the molten metal fully penetrates into the interior of the chill.

[0096] The setting of the gap size is directly related to the filling quality and the shrinkage compensation effect: if the diameter of the vertical cylinder is too small or the opening is too narrow, it will result in insufficient flow of molten metal, slow filling speed, and excessively rapid temperature drop at the front edge of the molten metal, which may cause cold shut and incomplete casting defects before the skeleton-type inner chill is completely wrapped, and at the same time affect the smooth flow of the shrinkage compensation channel in the later stage; conversely, if the size is too large, although it can improve the filling efficiency, it is easy to aggravate the turbulence of molten metal, increase the risk of air entrapment, and cause molten metal waste.

[0097] For example, the following can be adopted: Figure 3 The 8 diameters shown The vertical cylinder, with a 40mm wide gap, ensures a smooth flow of molten metal while maintaining the filling speed, ensuring the cavity is filled quickly and allowing the molten metal to fully penetrate the hollowed-out area of ​​the skeleton-type internal chill, achieving good fusion between the chill and the casting body.

[0098] The casting method described above can produce a thick casting with significantly improved internal quality. The wall thickness is internally fused with the aforementioned skeleton-type chill, thereby greatly improving the density of the casting body.

[0099] Furthermore, in order to maximize and stabilize the control of the cooling and feeding processes, this invention provides a fully functional and highly integrated dedicated casting system based on the above method.

[0100] like Figure 2a and Figure 2b As shown, the system specifically includes: a mold, the inner surface of which defines the outer surface of the target casting; a core, disposed inside the mold, the outer surface of which defines the inner surface of the target casting, the core having a positioning part; and a skeleton-type internal chill, including a hollow skeleton body and a positioning structure integrally formed therewith; the positioning structure cooperates with the positioning part to coaxially fix the skeleton-type internal chill at a preset position on the core, so that the hollow skeleton body is located within the wall thickness area of ​​the casting cavity enclosed by the inner surface of the mold and the outer surface of the core.

[0101] The casting system also includes a first external chill, which is segmented and laid on the outer surface of the core; a second external chill, which is segmented and laid on the inner surface of the mold; and a slit gating system, including a sprue, a slit column, and slit openings, wherein the diameter of the slit column is not less than 70 mm, and the width of the slit opening is not less than 20 mm; wherein the ratio of the total area A1 of all slit openings to the sum of the working surface areas A2 of all external chills is A1 / A2 = 0.18 to 0.25.

[0102] The ratio A1 / A2, ranging from 0.18 to 0.25, quantifies the matching relationship between the feeding capacity of the gating system and the quenching intensity of the cooling system. If the ratio is too small (<0.18), it means that the amount of molten metal replenished through the gating gate per unit time is relatively insufficient, making it difficult to offset the rapid volume shrinkage caused by the strong quenching of the external chill, which easily leads to shrinkage porosity in the final solidification area. If the ratio is too large (>0.25), it means that the feeding flow is sufficient, but the total opening area of ​​the gating system may be too large, resulting in a decrease in the stability of mold filling. At the same time, the relative heat dissipation area of ​​the external chill is insufficient, making it difficult to establish a sufficient temperature gradient in the thick area, which is also not conducive to the formation of sequential solidification. Controlling A1 / A2 within the range of 0.18 to 0.25 can achieve the best balance between the feeding rate of the molten metal and the solidification rate under the synergistic effect of the internal and external chills, while ensuring stable mold filling. This most effectively guides the thick casting to achieve sequential solidification from the inside out, ensuring that the casting is dense and defect-free inside.

[0103] Furthermore, the gaps between the outer surface of the hollow skeleton body and the outer surface of the core, as well as between the hollow skeleton body and the inner surface of the mold, are all 15mm-20mm; in the region corresponding to the axial end of the target casting, the gap between the hollow skeleton body and the inner surface of the end of the mold is 80mm-100mm.

[0104] Furthermore, the size of the first gap zone ranges from 15mm to 20mm. This design maintains a close bidirectional distance between the chill surface and the outer surface of the core and the inner surface of the mold within the wall thickness region of the casting cavity, thereby generating a strong chilling effect in the thick area and promoting the rapid formation of the solidification front. If the first gap is less than 15mm, it may lead to excessive cooling, causing the metal near the chill to solidify prematurely, which not only increases the risk of cracking but may also hinder the flow of molten metal in the feeding channel; if it is greater than 20mm, the chilling effect is significantly weakened, making it difficult to effectively suppress shrinkage defects in the thick area and failing to achieve the purpose of core cooling.

[0105] The size range of the second gap area is 80mm-100mm. This larger axial end face gap can maintain a higher molten metal temperature at the end of the casting and in the feeding path area, ensuring that the feeding channel remains unobstructed during the solidification of the main body of the casting. This avoids the risk of the feeding path being blocked due to the gap being too small, thus forming a new shrinkage cavity near the chill, and provides sufficient liquid metal replenishment for the solidification process of thick areas.

[0106] Through the aforementioned differentiated gap design, this invention constructs an adjustable cooling intensity spatial gradient in the casting cavity, enabling the thick area to receive preferential and intense cooling, while allowing the feeding area to cool relatively slowly. This guides the molten metal to solidify sequentially from the far end of the casting to the feeding port, significantly optimizing the feeding efficiency.

[0107] Furthermore, the hollowed-out skeleton body has partially hollowed-out windows at locations on the target casting where holes (such as flange mounting holes) need to be machined (such as oil passages). To improve casting quality and process adaptability, this design completely avoids interference from chills on the functional areas of the casting, ensuring both the structural integrity and core mechanical properties of the casting body, facilitating subsequent machining positioning, and reducing the heat capacity of the chills themselves, preventing defects caused by localized overcooling of the casting cavity.

[0108] Furthermore, the hollow skeleton body has rounded corner transition structures on the end edges in the direction of molten metal filling. This rounded corner structure can effectively smooth the flow lines of molten metal, reduce the flow resistance during the filling process, reduce turbulence and gas entrainment, thereby avoiding defects such as cold shuts and porosity caused by sharp corners; at the same time, it helps to reduce stress concentration at the fusion interface between the skeleton-type chill and the casting, and improve the metallurgical bonding quality between the two.

[0109] Furthermore, the positioning structure consists of at least three transverse ribs evenly distributed along the circumference of the hollow skeleton body; the positioning part is a groove or hole formed on the core that matches the shape of the transverse ribs. This design not only ensures the stable positioning of the chill in the casting cavity and effectively resists the impact of molten metal during pouring, preventing the chill from shifting or floating and ensuring uniform preset gaps; but also facilitates the mechanical removal of the ribs after casting cleaning, leaving minimal residue and having a slight impact on the quality of the inner surface of the casting.

[0110] Furthermore, both the first and second external chills are segmented, with the maximum projected size of a single chill not exceeding 100mm × 100mm, and the spacing between adjacent chill blocks being 8mm-10mm.

[0111] Furthermore, the second external chill is concentrated in the area between each ingate on the inner surface of the mold; the first external chill is fully distributed on the outer surface of the core.

[0112] Furthermore, the slit-type gating system is a low-pressure casting gating system.

[0113] Furthermore, the hollowed-out skeleton body is a single-layer cylindrical skeleton structure or a double-layer ring cylindrical skeleton structure.

[0114] During the casting process, the skeleton-type internal chill is pre-fixed in the reserved positioning holes of the core through its positioning structure (fixation is completed before core assembly to ensure stable positioning), followed by mold assembly and pouring. After the molten metal fills the mold, the skeleton-type internal chill, as a highly efficient chiller, rapidly absorbs heat from the interior of the casting wall due to its huge specific surface area, accelerating the solidification of the surrounding metal. Because its hollow structure does not hinder the flow and feeding of the molten metal within the wall thickness, coupled with the differentiated gap design, strong cooling is achieved in the thick areas of the casting to promote sequential solidification, while the ends or feeding paths remain unobstructed to facilitate feeding.

[0115] It is through this flexible structural design that can adapt to different working conditions that the skeleton-type internal chiller of the present invention can be widely used in the production of thick and large target castings of different specifications. It can achieve the excellent effect of simultaneous cooling from both the inside and outside of the casting, shortening the feeding distance, and finally obtaining a dense casting.

[0116] The skeleton-type internal chill of this invention is not a traditional solid structure, but a meticulously designed three-dimensional spatial frame. Its core advantage lies in its adaptability to the installation scenario of casting cavities: on the one hand, the hollow structure significantly increases the effective contact surface area with the molten metal, enabling rapid absorption of heat from the casting core and enhancing convective heat transfer; on the other hand, the design of pre-reserved cooling gaps between the chill and the outer surface of the core, as well as between the chill and the inner surface and end face of the mold, ensures smooth molten metal filling while avoiding the uneven cooling problem caused by traditional internal chills being close to a single surface. Simultaneously, the frame structure itself has low flow resistance, and the large rounded corners at the ends effectively avoid dead flow zones and newly formed hot spots, demonstrating significant technological advancements and practical value compared to traditional internal chills.

[0117] Compared with the prior art, the skeleton-type internal chill provided by the present invention not only inherits the quenching effect of traditional internal chills, but also overcomes the problems of poor fusion, flow obstruction and uneven cooling caused by traditional solid chills due to its unique contour-following hollow structure, cavity-adaptive installation design and partition gap design, thereby improving the density of the internal structure of the casting.

[0118] Accordingly, the present invention provides a method for casting thick and large castings using the casting system described above. The key steps of the method include: precisely fixing the skeleton-type internal chill to the preset position of the core through its positioning structure; assembling the assembled core assembly with the mold to form a casting cavity; and pouring molten metal into the cavity through the slit gating system.

[0119] By implementing the above steps, the skeleton-type inner chill, the segmented outer chill assembly, and the slotted gating system work together to construct a three-dimensional sequential solidification control field within the mold cavity. After the molten metal fills the mold, it fully fills and encapsulates the hollow skeleton body, and under the combined quenching of the skeleton and the inner and outer chills, sequential solidification is achieved from the core of the casting wall thickness outwards, thereby obtaining a high-quality casting with a dense interior.

[0120] In summary, the skeleton-type internal chill casting process and its supporting skeleton-type internal chill and casting system provided by this invention fundamentally change the solidification control method for thick castings through contour-following skeleton structure and systematic process design. This solution transforms the traditional discrete and passive cooling mode into a system-controllable solidification control, solving long-standing technical problems such as shrinkage porosity, shrinkage cavity, and poor chill fusion in thick castings. It significantly improves the internal quality, mechanical properties, and process reliability of castings, and has significant engineering application value.

[0121] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0122] Example 1

[0123] This embodiment provides a single-layer skeleton-type internal chill for thick castings. This skeleton-type internal chill is specifically designed for casting an aluminum alloy bearing housing with a main hot spot wall thickness of 50 mm.

[0124] The skeletal chiller is made of the same ZL101A aluminum alloy as the target casting body and is integrally formed by casting. Its main body is a single-layer cylindrical hollow skeleton, the outer contour of which strictly conforms to the wall thickness region of the target bearing housing casting, forming an overall hollow shell with a complex curved surface. The hollow skeleton is a rigid ring structure with a regular grid-like frame on the cylindrical wall, and the grid members have a cross-section of 18mm × 18mm. At the center of the hollow skeleton along its axial direction, three transverse positioning ribs are integrally formed and evenly distributed circumferentially. These positioning ribs extend radially outward from the skeleton body, also with a cross-section of 18mm × 18mm, and are designed to engage with positioning grooves on the casting core.

[0125] The overall dimensions of this skeleton-type internal chill are specially designed. Once fixed to the core and assembled in the mold box via its positioning ribs, it ensures precise coaxial centering within the wall thickness region of the casting cavity. As a result, in areas corresponding to the thicker main body wall of the casting, a uniform cooling gap (denoted as H1) of 18 mm will be formed between the outer surface of the internal chill and the outer surface of the core, as well as between the internal chill and the inner surface of the mold. In the axial end region corresponding to the root of the casting riser, a larger gap of 90 mm (denoted as H2) will be formed between the end face of the internal chill and the inner end surface of the mold. This design facilitates the feeding of molten metal.

[0126] Furthermore, at the structural positions corresponding to the two symmetrical bolt holes on the target casting body, the corresponding grid areas of the hollow skeleton are specially enlarged to form dedicated avoidance windows to prevent interference with the final structure of the casting. In addition, the hollow skeleton has rounded transition structures with a radius of R10 on all end edges in all directions of molten metal filling to optimize molten metal flow and reduce eddies and air entrapment.

[0127] Example 2

[0128] This embodiment provides a specific structure for a double-layer skeleton-type internal chill used in thick castings. This skeleton-type internal chill is used in castings such as... Figure 1 The thick aluminum alloy cylinder shown has an outer diameter of φ560mm, a height of 800mm, and a wall thickness of 80mm.

[0129] The skeletal chiller is integrally cast from ZL114A aluminum alloy of the same grade as the target casting. Its main body is a double-layered, annular, hollowed-out skeleton, specifically composed of an inner cylindrical wall, an outer cylindrical wall, and numerous vertical ribs connecting the inner and outer cylindrical walls, forming a rigid annular structure with a wall thickness of approximately 50mm. The outer diameter of the inner cylindrical wall is φ430mm, and the outer diameter of the outer cylindrical wall is φ530mm. In the central region along the axial direction of the double-layered hollowed-out skeleton, four radially extending transverse positioning ribs are integrally formed. The cross-section of each positioning rib is 20mm × 20mm.

[0130] The profile dimensions of this skeleton-type internal chiller are designed to meet specific clearance requirements. Once installed, a uniform cooling gap of 15mm will be formed between the outer surface of its outer cylinder wall and the outer surface of the core, as well as between it and the inner surface of the mold, in the sidewall region of the casting cylinder. At both axial ends of the casting cylinder, an 80mm gap will be formed between its end face and the inner end face of the mold.

[0131] At the locations corresponding to the three evenly distributed φ30mm machining holes on the circumferential direction of the side of the target casting, corresponding φ45mm circular hollow clearance windows are opened on the outer cylinder wall. At the same time, all exposed edges of this skeleton-type internal chill, especially the edges of the two end faces, are cast with large rounded corners with a radius of R15.

[0132] Example 3

[0133] This embodiment provides a complete casting system specifically designed for casting the thick aluminum alloy cylindrical castings described in Embodiment 2.

[0134] The casting system mainly includes the following components:

[0135] Mold and Core: The system includes a mold and a core. The inner surface of the mold forms the outer profile (φ560mm×800mm) of the target cylindrical casting. The core has an outer diameter of φ400mm, and its outer surface forms the inner surface of the target casting. Four square positioning holes are machined at a specific height in the center of the core as positioning parts.

[0136] Skeleton-type internal chill: A double-layered annular cylindrical skeleton-type internal chill is used, as described in detail in Example 2. This internal chill is precisely engaged with the four square positioning holes on the core via its four 20mm × 20mm transverse positioning ribs, thereby achieving a reliable connection and coaxial fixation with the core. After installation, the internal chill is located at the center of the wall thickness region of the casting cavity formed by the inner surface of the mold and the outer surface of the core.

[0137] External chill assembly: The system comprises two sets of external chills. First external chill: These are segmented chills, each measuring 80mm (length) × 80mm (width) × 20mm (thickness). These chill blocks are spaced 8mm to 10mm apart, covering the entire outer surface of the core. Second external chill: These are segmented chills of the same specifications as the first external chill. They are centrally arranged on the inner surface of the mold, in the area between the ingates, avoiding direct placement below the runners.

[0138] Gating System: A slit gating system suitable for low-pressure casting is employed. This system comprises an annular sprue and eight slit gating units evenly distributed circumferentially along the mold and connected to the annular sprue. Each gating unit consists of a vertical slit cylinder and a slit opening communicating with it. The diameter of the slit cylinder is φ80mm, and the width of the slit opening is 40mm. The ratio of the total area A1 of all slit openings to the sum of the working surface areas A2 of all external chills is A1 / A2 = 0.20.

[0139] Once the casting system is assembled—that is, the skeleton-type internal chill is fixed to the core, and the core and mold are accurately aligned—a pre-set, uniform 15mm cooling gap channel is naturally formed between the surface of the skeleton-type internal chill and the outer surface of the core, as well as between the chill and the inner surface of the mold. During the subsequent pouring and solidification process, the molten metal will fill these gaps and the hollowed-out areas of the internal chill, ultimately forming a dense and complete casting.

[0140] Example 4

[0141] This embodiment employs the casting process described in this invention to cast a material as follows: Figure 1 The ZL114A aluminum alloy cylindrical target casting shown has the following design outline dimensions: (Outer diameter) × 800mm (height), wall thickness 80mm, is a typical thick and large casting.

[0142] The casting system used in this embodiment mainly includes the following parts:

[0143] The cavity portion is formed by the mold and the core, and its cavity contour matches the shape of the target casting described in this embodiment. The mold has an inner surface that defines the outer surface of the target casting; the core is located inside the mold, and its outer surface defines the inner surface of the target casting, with a positioning part on the core; the skeleton-type internal chill includes a hollow skeleton body and an integrally formed positioning structure; the positioning structure cooperates with the positioning part to coaxially fix the skeleton-type internal chill at a preset position on the core, so that the hollow skeleton body is located within the wall thickness area of ​​the casting cavity enclosed by the inner surface of the mold and the outer surface of the core; the first external chill is segmented and laid on the outer surface of the core; the second external chill is segmented and laid on the inner surface of the mold; the slit gating system includes a horizontal sprue, a slit column, and a slit opening, the slit column having a diameter of 80mm and the slit opening having a width of 25mm.

[0144] Internal chill section: This is a skeleton-type internal chill located within the thick-walled area of ​​the cavity, and it is connected and fixed to the core via a positioning structure. External chill section: This includes a first external chill laid on the surface of the core, and a second external chill laid on the casting portion forming the outer surface of the cavity. Gating system section: This is connected to the cavity and used to pour molten metal into the cavity. The ratio A1 / A2 of the total area of ​​all gaps and openings to the sum of the working surface areas of all external chills is A1 / A2 = 0.25.

[0145] The detailed structure of the skeleton-type internal chill used in this embodiment is as follows:

[0146] The skeleton-type internal chill has a double-layered ring-shaped structure, such as... Figure 2bAs shown, it is integrally cast using the same grade of material (ZL114A) as the target casting. The main body of the product is a hollow cylindrical frame adapted to the contour of the wall thickness area of ​​the target casting, consisting of inner and outer cylindrical walls and connecting stiffeners forming a rigid grid with its own thickness. The outer diameter of the outer cylindrical wall of this inner chill is designed as follows: The inner diameter of the inner cylinder wall is This results in a skeleton with a wall thickness of 50mm and a total axial length of 640mm. The skeleton's openwork structure is composed of a regular grid-like frame, with the basic size of each grid unit being approximately 80mm × 80mm. The cross-section of the skeleton members constituting the grid is 20mm × 20mm, and all connecting corners have a radius of 15mm. Three evenly distributed... The location of the machining holes, the skeleton has... A circular, openwork clearance window. The product's central section features three evenly distributed 20mm x 20mm horizontal positioning ribs, integrally molded. Figure 6 and Figure 7 As shown, this is the positioning structure. The internal chiller forms a 15mm cooling gap between the main body area (sidewall) and the outer surface of the core, and between the inner surface of the mold and the main body area. It also forms an 80mm cooling gap between the axial end area and the end face of the target casting, thus achieving differentiated cooling effects, such as... Figure 6 As shown.

[0147] The casting process is as follows:

[0148] S1. Preparation of skeleton-type internal chill: The hollow skeleton body is integrally formed according to the above product structure and size. Its outer contour is adapted to the contour of the wall thickness area of ​​the target casting. The side wall of the hollow skeleton body is provided with circumferentially distributed and axially penetrating windows. The total area of ​​all windows accounts for 60% of the total area of ​​the side wall.

[0149] S2. Fixed skeleton type internal chill: The outer diameter of the core forming the inner cavity of the target casting is... like Figure 5 As shown in the left half, three 21mm × 21mm square positioning holes (i.e., positioning parts) are made at the corresponding height positions. The three transverse positioning ribs of the skeleton-type internal chill are then inserted into the positioning holes of the core to achieve precise fixation, ensuring that the chill is coaxially centered within the wall thickness area of ​​the casting cavity. Figure 5 As shown in the right half.

[0150] S0. Step-by-step assembly and external chill arrangement:

[0151] In this embodiment, the core is divided into upper and lower halves along the axial direction. For example... Figure 5 As shown, the assembly and chills arrangement shall proceed in the following order:

[0152] (1) Assembly of the lower half: such as Figure 5aThe outer surface of the lower half core (i.e., the side corresponding to the lower half inner cavity of the target casting) is fully covered with the first external chill with a size of 80mm×80mm×20mm, and the gap between adjacent chills is kept at 9mm.

[0153] (2) Install the skeleton-type internal chill: Connect the positioning structure of the skeleton-type internal chill to the preset positioning part on the lower half core to complete its initial fixation and positioning on the lower half.

[0154] (3) Upper part assembly: Close the upper core, aligning it with the lower core and the fixed skeleton-type chill to form a complete core. Then, as... Figure 5b As shown, the outer surface of the upper core is covered with the same type of segmented first external chills in the same manner.

[0155] (4) Arrange the second external chill: such as Figure 5c and Figure 4 As shown, in the mold area corresponding to the outer surface of the target casting, in the area between each ingate, a segmented second external chill of the same specification is arranged.

[0156] This embodiment uses a low-pressure casting method, and its gating system is as follows: Figure 3 As shown, it includes a horizontal gating system and eight slotted casting units connected to it. Each unit consists of a slotted vertical tube (diameter...). It consists of a core assembly and a slit opening (40mm wide). Subsequently, the assembled core assembly (including the inner chill and the first outer chill) is lowered into the mold (e.g., ...). Figure 5d (As shown), and fill and compact the gaps between the mold and the core, as well as between the mold and the external chill, to complete the overall shape.

[0157] S3. Mold Assembly and Casting: After completing the upper and lower molds, including the assembled core, skeleton-type internal chill, and external chill, the molds are assembled (i.e., the upper and lower molds are accurately fitted together). Casting then proceeds, with the pouring temperature controlled at 700±10℃. The molten metal fills the mold cavity, completely encapsulating and fusing the skeleton-type internal chill. After solidification, the target casting is obtained.

[0158] Example 5

[0159] The difference between this embodiment and embodiment 4 is that the target casting is an aluminum alloy bearing housing with a main hot spot wall thickness of 50mm.

[0160] The skeleton-type internal chiller used in this embodiment is a single-layer cylindrical structure, such as... Figure 2aAs shown, it is cast from ZL101A aluminum alloy. Its shape is a hollowed-out grid-like square tube skeleton that mimics the contour of the 50mm wall thickness area of ​​the target casting. The overall dimensions of the skeleton are designed as follows: after fixing, the gap between the outer surface of the skeleton-type chill and the outer surface of the core, as well as between the skeleton and the inner surface of the mold, is 18mm (H1 = 18mm); at the riser root region, the gap between the skeleton end face and the end face of the target casting is 90mm (H2 = 90mm). Three evenly distributed transverse positioning ribs with a cross-section of 18mm × 18mm are integrally formed in the middle of the skeleton. After fixing, the gap between the outer surface of the single-layer cylindrical skeleton and the outer surface of the core, as well as between the skeleton and the inner surface of the mold, is 18mm (H1 = 18mm); at the top of the casting cavity, the gap between the axial end face of the single-layer cylindrical skeleton and the inner surface of the upper end of the mold (i.e., the riser root region) is 90mm (H2 = 90mm). Meanwhile, in the middle of the single-layer cylindrical skeleton, there are three transverse positioning ribs that are evenly distributed along the circumference and have a cross-sectional size of 18mm×18mm.

[0161] The casting process steps are the same as those in Example 4: the single-layer skeleton-type internal chill is fixed by the positioning groove on the core to ensure that the 18mm cooling gap in the wall thickness area of ​​the casting cavity is uniform, and then the external chill is arranged and poured.

[0162] Example 6

[0163] This embodiment is identical to Embodiment 4 in terms of the target casting and process steps. The difference lies in that the skeleton-type internal chiller is made of 304 stainless steel wire mesh welded into a contoured hollow skeleton, and the skeleton's external dimensions are consistent with those of Embodiment 4 (to ensure the formation of the same preset cooling gap). Before pouring, the stainless steel skeleton-type internal chiller is sandblasted to remove rust and preheated at 200°C to improve its fusion with the molten aluminum alloy.

[0164] Example 7

[0165] The difference between this embodiment and Embodiment 4 is that the first cooling gap between the hollow skeleton body and the outer surface of the core and the inner surface of the mold is 20mm (H1 = 20mm); the second cooling gap between the axial end of the hollow skeleton body and the inner surface of the end of the mold is 100mm (H2 = 100mm). The specific structure, materials, and fixing method of the skeleton-type internal chill to the core through the positioning structure are the same as in Embodiment 4.

[0166] Comparative Example 1

[0167] This comparative example uses a traditional process, without using any internal chills, relying solely on the same external chills as in Example 4 to rapidly cool the surface corresponding to the outer wall of the target casting. Steps S1 and S2 are omitted, and the molding, gating system, and gating parameters are the same as in Example 4.

[0168] Comparative Example 2

[0169] This comparative example uses a traditional internal chiller solution: using The ZL114A aluminum alloy solid round bars are discretely arranged in a crisscross pattern in the mold cavity. Lacking a precise positioning structure, they cannot guarantee a uniform cooling gap between the core and the outer surface of the core, or between the inner surface and end face of the mold. Furthermore, they cannot ensure a coaxial and centered position within the wall thickness area of ​​the casting cavity. The external chill, gating system, and other conditions are the same as in Example 4.

[0170] Comparative Example 3

[0171] The external shape of the skeleton-type internal chill in this comparative example is the same as that in Example 4, except that the length of the skeleton-type internal chill is 760mm, that is, the gap H2 between the axial end of the skeleton-type internal chill and the inner surface of the mold end is 20mm. The rest of the structure and process parameters are the same as those in Example 4.

[0172] Comparative Example 4

[0173] The external shape of the skeleton-type internal chill in this comparative example is the same as that in Example 4, the only difference being that the skeleton-type internal chill is designed with an outer diameter of... inner diameter That is, the gap H1 between the sidewall and the outer surface of the core, and between the inner surface of the mold, is 30mm. The remaining structure and process parameters are the same as in Example 4.

[0174] Characterization results and analysis

[0175] The castings obtained in the above embodiments and comparative examples were subjected to X-ray flaw detection (RT) to determine the internal defect level, and the tensile strength of the body specimens was tested. The results are shown in the table below:

[0176] Table 1 Results of casting performance and defect detection

[0177]

[0178] As can be seen from Table 1, the internal defect level (I-II), tensile strength (320-335MPa), and density (≥98.5%) of the castings in Examples 4-7 of the present invention are significantly better than those in the comparative examples.

[0179] Comparative Examples 1-4 all had internal defect levels of III-IV, tensile strength of only 295-305 MPa, and density of less than 96%, and none of them could reach the quality level of the present invention.

[0180] In summary, the skeleton-type internal chiller design and casting process provided by this invention solves the problems of internal shrinkage defects and poor internal chiller fusion in thick castings, especially aluminum alloy cylindrical castings, through internal cooling structure design and systematic process matching. It can stably produce high-quality castings with dense internal structure and excellent performance, and has extremely high industrial application value.

[0181] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A skeleton-type internal chill (2) for thick castings, characterized in that, include: The hollow skeleton body has an outer contour shape that is adapted to the contour of the wall thickness area of ​​the target casting (1). The positioning structure (3) is integrally formed with the hollow skeleton body and is used to cooperate with the positioning part (9) on the casting core (4) to fix the skeleton-type internal chill (2) at the predetermined position of the core (4). When the skeleton-type internal chill (2) is fixed to the casting core (4) by its positioning structure (3) and the box is closed, the hollow skeleton body can be coaxially centered in the wall thickness area of ​​the casting cavity, and there is a uniform first cooling gap between the outer surface of the hollow skeleton body and the cavity surface; there is a cooling gap between the inner surface of the hollow skeleton body and the outer surface of the casting core (4).

2. The skeleton-type internal chiller (2) according to claim 1, characterized in that, At the axial end corresponding to the target casting (1), there is a second cooling gap between the end face of the hollow skeleton body and the end face of the cavity.

3. The skeleton-type internal chiller (2) according to claim 1, characterized in that, The hollow skeleton body has a partial hollow window at the position where holes need to be machined or structural avoidance is required on the target casting (1).

4. The skeleton-type internal chiller (2) according to claim 1, characterized in that, The hollow skeleton body has rounded corner transition structures on the end edges in the direction of molten metal filling, and the radius of the rounded corners is usually not less than 5mm.

5. The skeleton-type internal chiller (2) according to claim 1, characterized in that, The positioning structure (3) consists of at least three ribs; the ribs extend radially outward from the hollow skeleton body, and their cross-sectional shape can form a snap-fit ​​with the positioning part (9) on the casting core (4).

6. The skeleton-type internal chiller (2) according to claim 5, characterized in that, The ribs are located in the central region along the axial direction of the hollow skeleton body.

7. The skeleton-type internal chill (2) according to claim 1, characterized in that, The hollowed-out skeleton body is made of cast iron, cast steel, or a metal material that is the same as or similar to the material of the target casting (1).

8. The skeleton-type internal chill (2) according to claim 1, characterized in that, The hollowed-out skeleton is a one-piece molded frame with a regular or irregular hollowed-out structure, and its structure is a single-layer cylindrical skeleton or a double-layer ring cylindrical skeleton.

9. A casting apparatus for casting thick and large castings, characterized in that, include: The casting cavity has a contour that matches the shape of the target casting (1); The skeleton-type internal chill (2) as described in any one of claims 1 to 8; The core (4) is used to form the inner cavity of the casting cavity. The core (4) is provided with a positioning part (9) that cooperates with the positioning structure (3) of the skeleton-type internal chill (2). The skeleton-type internal chiller (2) is fixed to the core (4) by its positioning structure (3) and is located in the wall thickness area of ​​the casting cavity.

10. A method for casting thick, large castings, characterized in that, The casting apparatus described in claim 9 is used.

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