Design and casting process for skeleton type internal chill of thick and large casting

Abstract

The invention relates to a framework type internal chill design and casting process for a thick and large casting, belongs to the technical field of metal casting, and solves the problems of poor internal quality and low reliability of the casting caused by the defects that shrinkage cavities and shrinkage porosity are easy to generate due to slow solidification of the thick and large casting and air holes and inclusion are easy to introduce due to poor fusion of the traditional internal chill in the prior art. The method comprises the steps that a hollow framework structure matched with the contour of a wall thickness area of a target casting in a profiling mode is prepared to serve as internal chill, and the internal chill is coaxially fixed to the preset position of a mold core; pouring is conducted after box closing, a cavity is filled with molten metal, finally, the framework type internal chill is wrapped and fused into a whole, and a part of a casting body is formed. According to the invention, through a unique skeleton type inner chill structure, in combination with optimized positioning and outer chill arrangement, a forced and uniform cooling field is formed in a casting solidification process, sequential solidification is guided, the density and the internal quality of a thick and large casting (especially an aluminum alloy cylinder) are remarkably improved, and the forming problem of the thick and large casting is solved.

Description

Technical Field

[0001] This invention relates to the field of metal casting technology, and in particular to a skeleton-type internal chill design and casting process for thick castings. Background Technology

[0002] Casting is an important method for obtaining complex structural metal parts. With the development of high-end equipment manufacturing, the demand for large, thick-walled, high-performance castings is increasing, such as large compressor cylinder blocks, hydraulic valve bodies, and aerospace frames.

[0003] In the production of thick castings (typically referring to castings with a wall thickness exceeding 50mm), the long solidification time of the molten metal makes the feeding channels prone to premature closure, leading to concentrated shrinkage cavities or diffuse shrinkage porosity in the core of the casting that are difficult to eliminate, severely impairing the mechanical properties and safety of the casting. To improve the solidification process, chill technology is widely used in the industry. External chills are applied to the surface of the mold to adjust the solidification sequence by increasing the local cooling rate; internal chills are placed directly in the mold cavity, encased in molten metal, utilizing their cold storage capacity to accelerate cooling from the inside. However, existing chill technologies have significant limitations: solid external chills have limited cooling effect on the core of ultra-thick and large cross-sections, and their large size can easily cause surface chilling defects in the casting; traditional internal chills (such as round bars and steel plates) are mechanically fused with the casting body, and the interface is prone to oxidation, resulting in unstable fusion quality, often becoming a source of inclusions and porosity, reducing the fatigue performance and reliability of the casting. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a skeleton-type internal chill design and casting process for thick castings, so as to at least solve one of the problems in the prior art: insufficient internal cooling intensity, difficulty in controlling the solidification sequence, and poor fusion quality between the internal chill and the body, which easily introduces defects.

[0005] On one hand, embodiments of the present invention provide a casting process for thick castings, including the following steps:

[0006] S1. Preparation of skeleton-type internal chill: Make an integrally formed hollow skeleton body, whose outer contour is adapted to the contour of the wall thickness area of ​​the target casting.

[0007] 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, so that after the mold is closed, the skeleton-type internal chill is coaxially and centrally positioned in the wall thickness area of ​​the casting cavity;

[0008] S3. Mold assembly and casting: After completing the molding process including the core and the skeleton-type internal chill fixed thereon, the mold assembly is performed, and then molten metal is poured in so that the molten metal fills the cavity, wraps the skeleton-type internal chill, and finally solidifies into one piece. Cooling gaps are preset between the outer surface of the skeleton-type internal chill and the outer surface of the core, as well as between the skeleton-type internal chill and the inner surface of the mold. The hollow areas of the skeleton-type internal chill allow the molten metal to penetrate and communicate with each other.

[0009] Furthermore, the preset cooling gap is set differently according to the differences in the target casting area:

[0010] In the region corresponding to the thick wall 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 chill and the inner surface of the mold, is 15mm-20mm.

[0011] In the opening area corresponding to the axial end of the target casting or for guiding feeding, the gap between the skeleton-type internal chill and the axial end face of the target casting is 80mm-100mm.

[0012] Furthermore, in step S1, according to the hole or structural avoidance requirements to be formed on the target casting, the corresponding area of ​​the skeleton-type internal chill is locally enlarged and hollowed out.

[0013] Furthermore, in step S1, the end edges of the skeleton-type internal chill in the direction of molten metal filling are provided with rounded corner transition structures.

[0014] Furthermore, in step S1, the positioning structure consists of at least three transverse ribs that are integrally formed with the skeleton-type internal chill and are evenly distributed along its circumference; correspondingly, the positioning part on the core is a groove or hole that matches the shape of the transverse ribs.

[0015] Furthermore, the process also includes step S0 before step S2: arranging a second external chill on the inner surface of the mold, and / or arranging a first external chill on the surface of the core;

[0016] The second external chill and / or the first external chill 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.

[0017] 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 surface of the core.

[0018] Furthermore, the casting in step S3 is carried out using low-pressure casting, and the casting system includes a horizontal sprue and a slit-type casting unit connected thereto. The slit-type casting unit includes a slit cylinder and a slit opening. The diameter of the slit cylinder is not less than 70 mm, and the width of the slit opening is not less than 20 mm.

[0019] Furthermore, in step S1, the skeleton-type internal chill is a single-layer cylindrical skeleton structure or a double-layer annular cylindrical skeleton structure, and its specific structure is determined according to the wall thickness of the target casting and the gap requirements.

[0020] On the other hand, embodiments of the present invention provide a thick casting prepared using the casting process described above.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] 1) The design of the skeleton-type internal chill, combined with the arrangement of the segmented external chill and the slotted gating system of this invention, constitutes a three-dimensional cooling and feeding system with synergistic internal and external effects. This solution not only has high cooling intensity, but also, by adjusting the layout of the internal and external chills, can flexibly adapt to the production needs of large target castings of various shapes and wall thicknesses (especially target castings with closed cavities), greatly enhancing the operability and versatility of the entire process.

[0023] 2) In this invention, the skeleton-type internal chill has a hollow structure. Specific cooling gaps are pre-set between its outer surface and the outer surface of the core, as well as between it and the inner surface and end face of the mold, forming a surrounding "forced cooling and feeding channel." This structure forces the molten metal to simultaneously contact the mold wall and the surface of the skeleton-type internal chill after filling, causing the solidification front to start simultaneously from the outer wall of the casting (i.e., the mold wall) and the surface of the internal skeleton-type internal chill, and to advance towards the center of the casting wall thickness. This greatly shortens the feeding distance, transforming the traditional, difficult-to-control solidification process of thick sections into a controllable, sequential solidification from the inside out, eliminating shrinkage cavities and porosity defects in the core of thick target castings.

[0024] 3) The skeleton-type internal chill of this invention features an integrally formed positioning structure (such as transverse ribs) that achieves precise and rapid snap-fit ​​fixing with the pre-drilled holes on the core. This solves the industry problem of difficult positioning and easy displacement of large and complex internal chills in the mold cavity, making the pre-casting preparation work more standardized and reliable, improving core assembly accuracy and production efficiency, and reducing reliance on operator experience.

[0025] 4) The skeleton-type internal chill of this invention creates conditions for good fusion by increasing the effective contact and interweaving area with the molten metal. When the skeleton-type internal chill is made of a material similar to or the same as the casting body, its relatively small cross-sectional size (e.g., 20mm × 20mm) and rounded corner transition design allow the high-temperature molten metal to fully surround, flush, and melt through each branch of the skeleton-type internal chill. This design reduces flow dead zones, thermal stress concentration, and the entrainment of gases and inclusions, avoiding interface defects such as porosity and inclusions that are prone to occur in traditional internal chills.

[0026] 5) Compared to traditional solid internal chills or large external chills, the hollowed-out skeleton-type internal chill design of this invention significantly reduces the amount of metal used in the chill itself while providing a larger heat dissipation surface area. This not only reduces material costs and the overall weight of the target casting, but also reduces the thermal shock to the mold cavity filling process, which is conducive to obtaining a better as-cast microstructure.

[0027] 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

[0028] 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.

[0029] Figure 1 This is a schematic diagram of the outline structure of the target casting described in an embodiment of the present invention;

[0030] Figure 2a This is a schematic diagram of the independent structure of the single-layer skeleton-type internal chill of the present invention;

[0031] Figure 2b This is a schematic diagram of the independent structure of the double-layer skeleton internal chill of the present invention;

[0032] 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;

[0033] 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;

[0034] 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;

[0035] Figure 5a yes Figure 5 Schematic diagram of the first external chiller laid in the lower half of the core;

[0036] Figure 5b yes Figure 5 Schematic diagram of the first external chiller laid in the upper half of the core;

[0037] Figure 5c yes Figure 5 A schematic diagram showing the arrangement of a second external chill in the mold area;

[0038] Figure 5d yes Figure 5 Schematic diagram of the positioning of the central frame type internal chiller in the casting cavity;

[0039] Figure 6 This is a cross-sectional view of the arrangement of the skeleton-type internal chills in the casting cavity.

[0040] Figure 7 yes Figure 6 Top view.

[0041] Figure label:

[0042] 1. Target casting (outline); 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

[0043] 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.

[0044] In the field of metal casting, especially in the production of thick aluminum alloy cylindrical castings, the large wall thickness and slow solidification rate of the castings make them prone to internal defects such as shrinkage porosity and shrinkage cavities. Traditional external chills are huge and have limited cooling effect; traditional internal chills are prone to poor fusion with the casting body, leading to problems such as porosity and inclusions, which seriously affect the performance and yield of the castings. To address this, this invention proposes a skeleton-type internal chill design and a matching casting process. By optimizing the chill structure, positioning method, and gating system, the process guides the casting to achieve sequential solidification, thereby effectively improving its internal quality.

[0045] A specific embodiment of the present invention discloses a skeleton-type internal chill casting process for thick castings, the core steps of which include:

[0046] S1. Preparation of skeleton-type internal chill: Fabricate an integrally formed hollow skeleton-type internal chill, the outer contour of which is adapted to the contour of the wall thickness area of ​​the target casting.

[0047] 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, so that after the mold is closed, the skeleton-type internal chill can be coaxially and centrally positioned in the wall thickness area of ​​the casting cavity;

[0048] 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:

[0049] (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.

[0050] (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.

[0051] (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.

[0052] (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.

[0053] (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;

[0054] 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.

[0055] Specifically, the "thick castings" mentioned in this invention refer to target 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 only traditional external chills or risers. This invention is particularly applicable to target castings with a main wall thickness of not less than 30 mm.

[0056] 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.

[0057] In contrast, the skeleton-type internal chill of this invention employs an integrally formed frame structure whose shape perfectly matches the inner cavity of the target casting. This skeleton-type internal chill is not simply placed inside the cavity, but rather precisely fixed to the entire contour surface of the core forming the inner cavity of the target casting through a positioning structure, thus forming an internal cooling system. This arrangement achieves a fundamental shift in cooling method from "discrete point cooling" to "continuous surface cooling."

[0058] During implementation, 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 specific gap with the contour of the wall thickness area of ​​the target casting: in the thickest main body area of ​​the target casting, the design gap between the skeleton-type internal chill and the outer surface of the core, the inner surface of the mold, and the end face is controlled at 15mm-20mm. By reducing the gap, the chilling effect is enhanced, accelerating the solidification of the liquid metal in this area; in the axial end of the target casting, the root of the riser, and the area where the feeding channel is located, the design gap between the skeleton-type internal chill and the axial end face of the target casting is set at 80mm-100mm to reserve sufficient space to ensure unobstructed feeding channels and ensure efficient liquid metal feeding.

[0059] 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.

[0060] 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.

[0061] 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).

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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).

[0066] 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 skeleton-type internal chill and the axial end face of the target casting 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] On the other hand, such as Figure 2a and Figure 2b As shown, a specific embodiment of the present invention discloses a casting system for thick castings, comprising: a casting cavity whose contour matches the shape of the target casting; a skeleton-type internal chill as described above, which is fixed to the core forming the inner cavity of the casting cavity by a positioning structure and located in the wall thickness region of the casting cavity; an external chill assembly, including a first external chill laid on the surface of the core and a second external chill laid on the mold portion forming the outer surface of the casting cavity; and a gating system connected to the casting cavity for pouring molten metal into the cavity.

[0080] The skeleton-type internal chill includes: a hollow skeleton body whose outer contour shape is adapted to the wall thickness area of ​​the target casting; and a positioning structure integrally formed with the hollow skeleton body for cooperating with the positioning part on the casting core.

[0081] 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.

[0082] 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.

[0083] Specifically, when the target casting has a relatively moderate wall thickness, for example, when 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 outer surface of the cylinder wall faces both the inner and outer surfaces of the target casting, which can achieve good weight reduction while ensuring effective cooling.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] Furthermore, the cooling gap is set differently according to the target casting area: in the thick main body wall area of ​​the target casting (such as the middle of the cylinder), the gap is a first size, ranging from 15mm to 20mm; in the axial end or feeding channel area of ​​the target casting (such as near the riser or gating system), the gap between the hollow skeleton body and the axial end face of the target casting is a second size, ranging from 80mm to 100mm, and the second size is larger than the first size.

[0088] 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 core of the casting and enhancing convective heat transfer; on the other hand, combined with the design of "bidirectional gaps with the inner and outer surfaces of the casting," it ensures smooth filling of the molten metal 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 with the large rounded corners at the ends, it effectively avoids flow dead zones and newly formed hot spots, demonstrating significant technological advancements and practical value compared to traditional internal chills.

[0089] The size of the first gap zone ranges from 15mm to 20mm. This design, through its close-proximity arrangement on both the inner and outer surfaces of the casting cavity, generates a strong chilling effect in thick areas, promoting rapid formation of the solidification front. If the first gap is less than 15mm, it may lead to excessive cooling, causing premature solidification of the metal near the chill, 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 thick areas and failing to achieve the purpose of core cooling.

[0090] The size range of the second gap area is 80mm-100mm. The 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, which could lead to the formation of new shrinkage cavities near the chills, and provides sufficient liquid metal replenishment for the solidification process of thick areas.

[0091] 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.

[0092] Furthermore, to improve casting quality and process adaptability, the hollowed-out skeleton body has partial hollowed-out windows at locations on the target casting where subsequent machining holes (such as flange mounting holes) or structural avoidance (such as oil passages) are required. This design completely avoids interference from chilled metal 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 chill itself, preventing defects caused by localized overcooling of the casting cavity.

[0093] Furthermore, the hollow skeleton body has rounded corner transition structures on all end edges in the direction of molten metal filling, with a radius typically not less than 5mm. This rounded corner structure effectively smooths the molten metal flow lines, reduces flow resistance during the filling process, and minimizes turbulence and gas entrainment, thereby avoiding defects such as cold shuts and porosity caused by sharp corners. Simultaneously, it helps reduce stress concentration at the fusion interface between the skeleton-type chill and the casting, improving the metallurgical bonding quality between the two.

[0094] Furthermore, the positioning structure provided on the hollow skeleton body includes at least three transverse ribs extending outward from the hollow skeleton body. These ribs are preferably located in the central region along the axial direction of the hollow skeleton body, and their cross-sectional dimensions (e.g., 20mm × 20mm) precisely match the pre-reserved positioning holes on the core (cast core), forming a snap-fit ​​fit. This design not only ensures the stable positioning of the chill in the casting cavity, effectively resisting the impact of molten metal during pouring, preventing chill displacement or floating, and ensuring uniform pre-set gaps; but also facilitates the mechanical removal of the ribs after casting cleaning, leaving minimal residue and having a slight impact on the inner surface quality of the casting.

[0095] Regarding material selection, the hollowed-out skeleton body can be made of cast iron, cast steel, or the same metal material as the casting body. Preferably, a material that is the same as or similar to the casting material is used to ensure a match in their coefficients of thermal expansion, reduce interfacial thermal stress, and promote good metallurgical bonding. For example, for aluminum alloy castings, the same aluminum alloy can be used to improve fusion, or cast iron or cast steel can be used to utilize their higher thermal conductivity to further enhance the chilling effect.

[0096] In terms of structural form, the hollow skeleton body 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, enabling it to accurately fit the casting cavity space and avoid the positioning deviation and uneven cooling problems caused by splicing multiple chills in the traditional way.

[0097] The wall thickness of the skeleton-type internal chill can be adjusted within the range of 30mm-50mm according to the target casting wall thickness and material type to ensure sufficient cooling capacity while avoiding excessive cooling, increased casting stress, or increased costs due to excessive wall thickness. The hollowing ratio (percentage of hollowed-out area to surface area) of the chill can be selected between 40% and 70%. Under the premise of ensuring structural stability, appropriately increasing the hollowing ratio is beneficial to the penetration and feeding of molten metal in the mold cavity, ensuring complete fusion between the chill and the casting body.

[0098] In addition, the surface of the skeleton-type internal chiller can be treated with sandblasting, oxidation, or coating to adjust the heat exchange coefficient between it and the molten metal, thereby further optimizing the cooling process and precisely matching the solidification requirements of the casting.

[0099] 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.

[0100] 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.

[0101] This invention also provides a casting in which any of the aforementioned skeleton-type internal chills are fused into the wall. During solidification, the casting exhibits a dense internal structure due to the directional cooling effect of the skeleton-type internal chills, significantly reducing shrinkage cavities and porosity defects. It is particularly suitable for thick-section aluminum alloy cylindrical and box-shaped structural components. The casting method involves fixing the skeleton-type internal chill to the core using a positioning structure, followed by low-pressure casting or gravity pouring after mold assembly. This is combined with a slotted gating system and segmented external chills to achieve precise control over the solidification process of thick castings.

[0102] It should be noted that, in practical applications, the specific hollowing pattern, rib layout, gap value, wall thickness and hollowing rate of the skeleton-type internal chill can be flexibly adjusted according to the specific structure and process requirements of the target casting (such as densifying the skeleton grid in areas with high cooling requirements and expanding the hollowing in critical flow areas). These adjustments are all within the scope of the present invention.

[0103] In summary, the skeleton-type internal chill casting process and its matching skeleton-type internal chill provided by this invention fundamentally change the solidification control method for thick and large castings through a contour-following skeleton structure and systematic process design. This solution transforms the traditional discrete and passive cooling mode into a systematic and controllable solidification control system, fundamentally solving long-standing technical problems such as shrinkage porosity, shrinkage cavity, and poor chill fusion in thick and large castings. It significantly improves the internal quality, mechanical properties, and process reliability of the castings, and has significant engineering application value.

[0104] 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.

[0105] Example 1

[0106] 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.

[0107] The skeletal internal 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 complex curved surfaces. The hollow skeleton is a rigid ring structure, with the cylindrical wall being a regular grid-like frame, and the grid members having a cross-section of 18mm × 18mm.

[0108] At the center of the hollow skeleton along its axial direction, there are three transverse positioning ribs that are evenly distributed circumferentially. The positioning ribs extend radially outward from the main body of the skeleton, and their cross-section is also 18mm×18mm. They are designed to engage with the positioning grooves opened on the casting core.

[0109] 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 thickest 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 surface of the mold end; this design facilitates the feeding of molten metal.

[0110] 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.

[0111] Example 2

[0112] 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 the following design outline dimension: outer diameter. Height 800mm, wall thickness 80mm.

[0113] The skeletal internal chill is integrally cast from ZL114A aluminum alloy of the same grade as the target casting. Its main body is a double-layered, ring-shaped, hollowed-out skeleton, specifically composed of an inner cylinder wall, an outer cylinder wall, and numerous vertical ribs connecting the inner and outer cylinder walls, forming a rigid ring structure with a wall thickness of approximately 50mm. The outer diameter of the inner cylinder wall is... The outer diameter of the outer cylinder wall is

[0114] In the central region along the axial direction of the double-layer hollow frame, four radially extending transverse positioning ribs are integrally formed. The cross-section of each positioning rib is 20mm × 20mm.

[0115] 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 inner surface of the casting, 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 surface of the mold end.

[0116] Three evenly distributed points on the circumferential direction corresponding to the side surface of the target casting. The location of the machining holes is correspondingly provided on the outer cylinder wall. The circular, openwork clearance window. Meanwhile, all exposed edges of the frame-type chiller, especially the edges of the two end faces, are cast with large rounded corners of radius R15.

[0117] Example 3

[0118] This embodiment provides a complete casting system specifically designed for casting the thick aluminum alloy cylindrical castings described in Embodiment 2.

[0119] The casting system mainly includes the following components:

[0120] Mold and Core: The system includes a mold and a core. The inner surface of the mold forms the outer profile of the target cylindrical casting. The outer diameter of the core is Its outer surface forms the inner surface of the target casting. At a specific height in the center of the core, four square positioning holes are machined as positioning parts.

[0121] 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.

[0122] External cooling iron assembly: The system comprises two sets of external cooling irons.

[0123] The first external chill is a segmented chill, with each segment measuring 80mm (length) × 80mm (width) × 20mm (thickness). These chill segments are spaced 8mm to 10mm apart, covering the entire outer surface of the core.

[0124] The second external chill: It is a segmented chill 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, and are avoided being placed directly below the gates.

[0125] Gating System: A slit gating system suitable for low-pressure casting is employed. This system includes an annular sprue and eight slit gating units evenly distributed along the circumference of 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 [missing information]. The width of the slit opening is 40mm.

[0126] 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.

[0127] Example 4

[0128] 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.

[0129] The casting system used in this embodiment mainly includes the following parts:

[0130] Cavity section: It is formed by the mold and the core, and its cavity contour matches the shape of the target casting described in this embodiment.

[0131] Internal coolant section: It is a skeleton-type internal coolant set in the thick area of ​​the cavity wall, which is connected and fixed to the core through a positioning structure.

[0132] External chill portion: 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.

[0133] Gating system section: Connected to the mold cavity, used to pour molten metal into the mold cavity.

[0134] The detailed structure of the skeleton-type internal chill used in this embodiment is as follows:

[0135] The skeleton-type internal chiller used in this embodiment has a double-layer ring-shaped structure, such as... Figure 2b As 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.

[0136] The casting process is as follows:

[0137] S1. Preparation of skeleton-type internal chill: Prepared according to the above product structure and dimensions.

[0138] 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.

[0139] S0. Step-by-step assembly and external chill arrangement:

[0140] 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:

[0141] (1) Assembly of the lower half: such as Figure 5a The 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.

[0142] (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.

[0143] (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.

[0144] (4) Arrange the second external chill: such as Figure 5c and Figure 4As 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.

[0145] 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.

[0146] 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.

[0147] Example 5

[0148] 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.

[0149] The skeleton-type internal chiller used in this embodiment is a single-layer cylindrical structure, such as... Figure 2a As shown, it is cast from ZL101A aluminum alloy. Its shape is a hollowed-out grid square tube frame that mimics the contour of the 50mm wall thickness area of ​​the target casting. The overall dimensions of the frame are designed such that, after fixing, the gap between its only outer surface and the inner and outer surfaces of the target casting is 18mm (H1 = 18mm), and at the riser root area, the gap between the frame 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 frame.

[0150] 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.

[0151] Example 6

[0152] 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.

[0153] Example 7

[0154] The difference between this embodiment and embodiment 4 is that the pre-set gap between the sidewall of the main body area and the inner and outer surfaces of the target casting is 20mm (H1 = 20mm); the axial end gap is 100mm (H2 = 100mm). The skeleton-type internal chill structure and fixing method remain unchanged.

[0155] Comparative Example 1

[0156] 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.

[0157] Comparative Example 2

[0158] 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, without a precise positioning structure, making it impossible to guarantee uniform gaps with the inner and outer surfaces of the target casting or to ensure a centered position in the wall thickness area of ​​the casting cavity. The external chill, gating system, and other conditions are the same as in Example 4.

[0159] Comparative Example 3

[0160] 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 and the end face of the target casting is 20mm. The rest of the structure and process parameters are the same as those in Example 4.

[0161] Comparative Example 4

[0162] 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 inner and outer surfaces of the target casting is 30mm. The remaining structure and process parameters are the same as in Example 4.

[0163] Characterization results and analysis

[0164] The castings obtained in the above embodiments and comparative examples were subjected to X-ray radiography (RT) to detect the internal defect levels, and the tensile strength of the body specimens was tested. The results are shown in the table below:

[0165] Table 1 Results of casting performance and defect detection

[0166]

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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 casting process for thick and large castings, characterized in that, Includes the following steps: S1. Preparation of skeleton-type internal chill (2): The hollow skeleton body is made as a whole, and its outer contour is adapted to the contour of the wall thickness area of ​​the target casting (1). S2. Positioning and fixing: On the core (4) that forms the inner cavity of the target casting (1), a positioning part (9) is provided that cooperates with the positioning structure (3) of the skeleton-type internal chill (2); the skeleton-type internal chill (2) is assembled to the positioning part (9) through the positioning structure (3) so as to fix the skeleton-type internal chill (2) coaxially in the preset position of the core (4), so that after the mold is closed, the skeleton-type internal chill (2) is coaxially and centrally positioned in the wall thickness area of ​​the casting cavity; S3. Mold assembly and casting: After completing the molding of the mold including the core (4) and the skeleton-type internal chill (2) fixed thereon, the mold is assembled, and then molten metal is poured to fill the cavity, wrap the skeleton-type internal chill (2) and finally solidify into one piece. Cooling gaps are preset between the outer surface of the skeleton-type internal chill (2) and the outer surface of the core (4), and between the skeleton-type internal chill (2) and the inner surface of the mold (11). The hollow area of ​​the skeleton-type internal chill (2) allows the molten metal to penetrate and communicate with each other.

2. The casting process according to claim 1, characterized in that, The preset cooling gap is set according to the differences in the target casting area: In the region corresponding to the thick wall of the target casting (1), the gap between the outer surface of the skeleton-type internal chill (2) and the outer surface of the core (4), as well as the gap between the core (4) and the inner surface of the mold (11), is 15mm-20mm. In the opening area corresponding to the axial end of the target casting (1) or for guiding feeding, the gap between the skeleton-type internal chill (2) and the axial end face of the target casting (1) is 80mm-100mm.

3. The casting process according to claim 1, characterized in that, In step S1, according to the hole or structural avoidance requirements to be formed on the target casting (1), the corresponding area of ​​the skeleton-type internal chill (2) is locally enlarged and hollowed out.

4. The casting process according to claim 1, characterized in that, In step S1, the end edges of the skeleton-type internal chill (2) in the direction of molten metal filling are provided with rounded corner transition structures.

5. The casting process according to claim 1, characterized in that, In step S1, the positioning structure (3) is at least three transverse ribs that are integrally formed with the skeleton-type internal chill (2) and are evenly distributed along its circumference; correspondingly, the positioning part (9) on the core (4) is a groove or hole that matches the shape of the transverse ribs.

6. The casting process according to claim 1, characterized in that, The process also includes step S0 before step S2: arranging a second external chill (6) on the inner surface of the mold (11) and / or arranging a first external chill (5) on the surface of the core (4); The second external chill (6) and / or the first external chill (5) 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.

7. The casting process according to claim 6, characterized in that, The second external chill (6) is concentrated in the area between each ingate on the inner surface of the mold (11); the first external chill (5) is fully covered on the surface of the core (4).

8. The casting process according to claim 1, characterized in that, The casting in step S3 is carried out by low-pressure casting, and the casting system includes a horizontal sprue (7) and a slit casting unit connected thereto. The slit casting unit includes a slit cylinder (8) and a slit opening (10). The diameter of the slit cylinder (8) is not less than 70 mm, and the width of the slit opening (10) is not less than 20 mm.

9. The casting process according to claim 1, characterized in that, In step S1, the skeleton-type internal chill (2) is a single-layer cylindrical skeleton structure or a double-layer ring cylindrical skeleton structure, and its specific structure is determined according to the wall thickness of the target casting (1) and the gap requirements.

10. A thick casting prepared using the casting process described in any one of claims 1 to 9.

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