Impeller casting processing technology

Abstract

The invention belongs to the field of metal part casting, and discloses an impeller casting processing technology which comprises the following steps: preparing foam particles; an impeller pattern is prepared, specifically, the foam particles are injected into a mold to be formed, the impeller pattern is obtained, and an exhaust channel is preset in the impeller pattern; the surface of the impeller pattern is evenly coated with fireproof paint, drying is conducted after painting is completed, and an impeller model is obtained; exhaust channel structures made of high-density foam are preset at key stress parts such as blade roots and hub connecting areas, and due to the fact that the polymer content of the exhaust channel structures is higher, bead fusion is more compact, and the rigidity of the exhaust channel structures is far better than that of matrix foam. The high-density area is just like a built-in reinforcing rib, deformation of the three-dimensional twisted thin-wall structure in the technological process is effectively restrained, it is ensured that the space angle of the blade and the geometric accuracy of the flow channel meet the requirements for dynamic balance and hydraulic performance, and the casting rejection rate caused by mold instability is reduced from the source.

Description

Technical Field

[0001] This invention belongs to the field of metal casting, and specifically relates to a casting process for impellers. Background Technology

[0002] As a core rotating component in fluid machinery such as pumps, fans, and compressors, the impeller typically consists of a hub and multiple spatially twisted blades. It has a complex geometry, significant differences in wall thickness, and high requirements for dimensional accuracy, internal density, and dynamic balance. Among various metal casting processes, lost foam casting technology has been increasingly applied to impeller manufacturing in recent years due to its advantages such as no parting line required, ability to form a closed flow channel as a single piece, low mold cost, and good surface quality. This process uses a vaporizable foam plastic pattern instead of a traditional pattern. Molten metal is poured under dry sand negative pressure conditions; the foam rapidly vaporizes and decomposes upon heating, and the molten metal then fills the space it previously occupied and solidifies. However, in practical applications, lost foam casting for impeller-type castings still faces significant challenges: Impeller blades are mostly thin-walled, three-dimensionally twisted structures. Their foam plastic patterns have low density, low elastic modulus, and severely insufficient rigidity. During handling, cluster bonding, refractory coating application, and dry sand filling and vibration compaction, they are prone to bending, collapse, or localized crushing, leading to casting contour distortion, blade angle deviation, or hub ellipticization. This severely affects hydrodynamic performance and dynamic balance stability under high-speed rotation. To improve pattern rigidity, high-density foam is often considered, but this introduces new contradictions: while high-density foam improves structural stability, it has a higher polymer content per unit volume, significantly increasing the total gas generation during pyrolysis. Furthermore, due to its dense structure and slow heat conduction, the gasification rate is reduced. This not only increases the burden on the exhaust system but may also obstruct the advance of the molten metal—if the foam fails to "give way" in time, it can easily cause filling defects such as cold shuts and incomplete pouring. Simultaneously, material costs and curing energy consumption also increase significantly, limiting economic viability.

[0003] This problem is further amplified by the unique closed flow channel structure of impellers. Impeller flow channels are usually closed or semi-closed structures with narrow internal spaces and tortuous exhaust paths. When foam is subjected to high temperatures at the leading edge of the molten metal, it decomposes instantly, generating a large amount of organic gas. If this gas cannot be discharged in time through coating pores or external extraction systems, it is very easy to accumulate at the interface between the molten metal and the foam, causing air entrapment, backflow, or pressure rebound, which in turn leads to casting defects such as subcutaneous porosity, surface wrinkles, carbon black inclusions, cold shuts, and even localized incomplete pouring. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an impeller casting process to solve the problems existing in the background art.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is an impeller casting process, comprising the following steps: Step S1: Preparation of foam particles; Step S2, Impeller pattern preparation: The foam particles are injected into a mold and shaped to obtain an impeller pattern. The impeller pattern has a pre-set exhaust channel. Step S3: Apply refractory coating evenly to the surface of the impeller pattern, and dry it after coating to obtain the impeller model; Step S4: The impeller model is buried in a sand box. The sand box is filled with sand layer by layer and compacted by vibration so that the sand body covers the model. The exhaust channel is connected to a negative pressure system. Step S5: Pour the molten metal along the gating system until the molten metal completely replaces the impeller pattern, and obtain the impeller casting after cooling.

[0006] Preferably, in step S2, the impeller foam pattern is prepared by a split molding method, including an outline pattern and a blade pattern; step S2 includes: Step S21: Provide a contour pattern forming mold and a blade pattern forming mold respectively, and inject the foam particles into the corresponding molds for foaming and molding to obtain a contour pattern and a blade pattern with internal venting channels. Step S22: Assemble the blade pattern and the outline pattern according to the preset exhaust channel alignment relationship and bond the two together to obtain an integral impeller foam pattern with a continuous exhaust channel inside.

[0007] Further, in step S21, both the outline pattern and the blade pattern are prepared using a split molding method, including a base foam portion and an embedded exhaust channel portion. The exhaust channel portion is composed of an independently prefabricated exhaust channel pattern, and the exhaust channel pattern has through-holes extending along a predetermined path inside. Step S21 includes: Step S211: Provide an exhaust channel pattern molding die, inject the foam particles into the corresponding die to foam and form an exhaust channel pattern with through holes. Step S212: Place the exhaust channel pattern in the corresponding position in the cavity of the contour pattern forming mold or the blade pattern forming mold, and then inject the foam particles into the corresponding mold for secondary foaming and molding, thereby forming an integral contour pattern or blade pattern with a continuous exhaust channel.

[0008] Furthermore, the foam particle density of the exhaust channel pattern is greater than that of the matrix pattern, making the rigidity of the exhaust channel pattern higher than that of the matrix pattern. While improving the overall pattern's resistance to deformation, the through-holes serve as gas flow channels during the casting process, achieving efficient exhaust.

[0009] Furthermore, at the interface between the exhaust channels of the outline pattern and the blade pattern, one side has an axially extending protrusion, and the other side has a matching recess. The protrusion and the recess form a plug-in positioning pair, which guides and locks the relative position of the two during assembly in step S212, ensuring that the spatial angle and outline consistency of the blade and the outline after split forming meet the casting accuracy requirements. The protrusion is the exhaust channel end part of the outline pattern or the blade pattern.

[0010] Preferably, in step S5, the casting system adopts a bottom-pouring design.

[0011] Preferably, in step S1, the foam particles are selected from EPS polystyrene or STMMA copolymer resin, and the foam particles are pre-foamed and cured.

[0012] Preferably, in step S3, the thickness of the refractory coating is 0.5 mm to 2 mm, and the refractory coating is used to prevent the penetration of molten metal and the residue of gasification products; the drying temperature of the coating is 40°C to 60°C.

[0013] Preferably, in step S4, dry quartz sand is used to fill the sand layer by layer and then vibrated to compact it.

[0014] The main technical effects of this invention are reflected in the following aspects: Traditional low-density foam, while producing little gas, has an extremely low elastic modulus, making it prone to bending or collapse during handling, coating, and sand filling, leading to distortion of the casting contour. This invention pre-designs exhaust channels composed of high-density foam in key stress-bearing areas such as the blade root and hub connection region. Due to its higher polymer content and denser bead fusion, this high-density foam exhibits significantly superior rigidity compared to the base foam. This high-density region acts like a built-in "reinforcing rib," effectively suppressing deformation of the three-dimensional tortuous thin-walled structure during the process. This ensures that the blade's spatial angle and flow channel geometry meet dynamic balance and hydraulic performance requirements, reducing the casting scrap rate caused by pattern instability at its source.

[0015] High-density foam, due to its dense structure, slow thermal conductivity, and high pyrolysis activation energy, exhibits a later vaporization initiation time compared to low-density matrix foam. During bottom-pouring casting, the molten metal progresses from bottom to top, causing the low-density matrix to rapidly vaporize and make way. Meanwhile, the high-density venting channels maintain their tubular skeletal shape during the critical window of several seconds to over ten seconds, ensuring the unobstructed flow of the through-holes during the initial filling stage when gas generation is most intense. This "delayed vaporization" characteristic allows the venting channels to guide airflow precisely when venting is most needed, preventing gas accumulation in closed channels that could lead to back pressure, air entrapment, or wrinkling defects. This achieves functional, time-controlled venting in pure foam materials without relying on heterogeneous materials such as ceramic or fiber cores.

[0016] To address the issues of angular deviation and channel misalignment that easily occur during the bonding process of split-molded impellers, this invention designs the exhaust channel end with a complementary boss and slot structure. During assembly, the protrusions embed into the recesses, automatically constraining the relative positions of the blades and the outline pattern in the radial and circumferential directions, while ensuring strict coaxial connection between the two exhaust channel sections, eliminating exhaust path interruptions caused by manual misalignment. This structure combines a functional exhaust channel with a mechanical positioning function, eliminating the need for additional positioning fixtures, simplifying the clustering process, and improving assembly repeatability and production efficiency. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0018] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, so as to make the technical solution of the present invention easier to understand and master. In the embodiments, it should be understood that the terms "middle," "upper," "lower," "top," "right side," "left end," "above," "back," "center," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, unless otherwise specified in this specific embodiment, the connection or fixing method between components can be achieved by bolt fixing, pin fixing, or pin connection commonly used in the prior art, etc., and therefore will not be described in detail in this embodiment.

[0019] The impeller casting process provided by this invention is mainly applicable to the manufacture of metal impeller castings with closed flow channel structures in pumps, fans, and compressors, but it is not limited to this. For other thin-walled rotating castings with complex geometries and high requirements for contour accuracy and internal density (such as turbine housings, guide vanes, propellers, etc.), the technical solution of this invention can also be applied when using the lost foam casting process to solve the common problems of insufficient pattern rigidity and difficulty in venting.

[0020] Furthermore, as is common knowledge in this industry, the EPS (polystyrene) or STMMA (styrene-methyl methacrylate copolymer) foam particles used in lost foam casting must undergo pre-foaming, curing, and molding processes to obtain the foam pattern; during the dry sand negative pressure molding process, quartz sand is used for filling and vibration compaction; refractory coatings are usually formulated from zircon powder, silica sol, or water-based binders and applied to the pattern surface by dip coating or spraying. The above material selection, equipment configuration, and basic process steps are all standard technical methods in the field of lost foam casting, therefore their specific composition, working principle, and equipment structure will not be elaborated further.

[0021] Example 1 This embodiment provides an impeller casting process that aims to systematically solve the contradiction between insufficient rigidity of foam patterns and difficulty in venting in the prior art. It is especially suitable for the manufacture of impellers for pumps or fans with complex structures, closed flow channels, and significant differences in wall thickness.

[0022] In traditional lost foam casting, impeller blades, due to their thin walls and three-dimensional twisted shape, typically use low-density EPS or STMMA materials for their foam patterns. While this reduces gas generation, it results in extremely poor rigidity. During handling, coating, sand filling, and vibration processes, they are prone to bending, collapse, or localized crushing, leading to distorted casting contours, blade angle deviations, and severely impacting dynamic balance and hydraulic performance. Simply increasing the overall foam density to enhance rigidity, however, leads to increased polymer content, higher total pyrolysis gas volume, and decreased gasification rate. This not only increases the venting burden but also easily causes filling defects such as cold shuts and incomplete filling, while simultaneously increasing material costs and curing energy consumption. It is difficult to balance economic efficiency with process stability.

[0023] To address the aforementioned technical bottlenecks, this embodiment proposes an integrated process solution combining "rigid reinforcement, efficient exhaust, and precise assembly." Its core improvement lies in: using a combination of split molding and a high-density embedded exhaust channel structure to locally enhance rigidity in key stress areas. Simultaneously, this channel serves directly as a functional exhaust path, and its geometric features enable self-positioning assembly of the split components. See also... Figure 1 Specifically, it includes the following steps: Step S1: Preparation of foam particles. The foam particles are selected from EPS polystyrene or STMMA copolymer resin, and the foam particles are pre-foamed and cured.

[0024] Step S2, Impeller pattern preparation: The foam particles are injected into a mold and shaped to obtain an impeller pattern. The impeller pattern has a pre-set exhaust channel. Step S21: The impeller pattern is no longer prepared by integral foaming or simple split bonding. Instead, the impeller foam pattern is prepared by split molding, including contour pattern and blade pattern. Contour pattern molding mold and blade pattern molding mold are provided respectively. The foam particles are injected into the corresponding molds for foaming and molding to obtain contour pattern and blade pattern with internal exhaust channels. The contour pattern and blade pattern are prepared by split molding, including a base foam part and an embedded exhaust channel part. The exhaust channel part is composed of an independently prefabricated exhaust channel pattern. The exhaust channel pattern has through-holes extending along a predetermined path inside. Step S211: Provide an exhaust channel pattern molding mold, inject the foam particles into the corresponding mold for foaming and molding to obtain an exhaust channel pattern with through holes; the exhaust channel is not a simple opening, but is composed of an independently prefabricated high-density foam core - that is, the exhaust channel pattern with through holes is first foamed and molded using a special mold.

[0025] Step S212: Place the exhaust channel pattern in the corresponding position in the cavity of the contour pattern forming mold or the blade pattern forming mold, and then inject the foam particles into the corresponding mold for secondary foaming and molding, thereby forming a contour pattern or blade pattern with an embedded continuous exhaust channel. This design not only forms a "rigid skeleton" in easily deformable parts such as the blade root and hub connection area, which significantly improves the bending and torsional resistance, but also, because the channel retains a through hole, it naturally becomes the main channel for gas flow during casting, effectively guiding the pyrolysis gas to be discharged along the predetermined path and avoiding accumulation in the closed flow channel.

[0026] Preferably, the foam particle density of the exhaust channel pattern is greater than that of the matrix pattern, resulting in higher rigidity of the exhaust channel pattern compared to the matrix pattern. While enhancing the overall pattern's resistance to deformation, the through-holes act as gas flow channels during casting, achieving efficient venting. Under the same molten metal temperature, the high-density region has a higher vaporization initiation temperature and a slower pyrolysis rate, maintaining structural integrity for a longer period during the initial casting stage. This difference is cleverly utilized: as the high-temperature molten metal fills from the bottom and pyrolyzes the foam layer by layer, the low-density matrix rapidly vaporizes and makes way, while the high-density exhaust channel, due to delayed vaporization, maintains its tubular skeleton shape during the critical filling window of several seconds to over ten seconds. This effectively maintains the geometry and permeability of the through-holes, providing a stable, low-resistance exhaust path for the large amount of organic gas generated during pyrolysis. Only after the molten metal front has passed this region does the high-density channel gradually and completely vaporize, at which point most of the gas has been successfully discharged, avoiding back pressure, air entrapment, or wrinkling defects caused by gas accumulation in closed channels. Therefore, the high-density exhaust channel not only acts as a local reinforcing rib to improve the rigidity of the pattern, but also achieves the "dynamic shape-preserving exhaust" function through its controllable delayed gasification characteristics; that is, the channel remains unobstructed during the filling stage when exhaust is most needed, and disappears naturally after filling is completed without leaving any residue.

[0027] Furthermore, at the interface between the exhaust channels of the outline pattern and the blade pattern, one side has an axially extending protrusion, and the other side has a matching recess. The protrusion and the recess form a plug-in positioning pair, which guides and locks the relative position of the two during assembly in step S212, ensuring that the spatial angle and outline consistency of the blade and the outline after split forming meet the casting accuracy requirements. The protrusion is the exhaust channel end portion of the outline pattern or the blade pattern. For example, the end of the outline pattern has an axially extending boss, and the end of the blade pattern has a matching recessed slot. During assembly, the boss is inserted into the slot, which not only automatically achieves precise radial and circumferential positioning, ensuring that the blade spatial installation angle error is controlled within ±0.5°, but also ensures that the two exhaust channels are strictly coaxially connected, preventing exhaust blockage caused by misalignment. This structure has both mechanical positioning and functional connection functions, replacing the traditional method of relying on external tooling or manual visual alignment, greatly improving assembly efficiency and repeatability.

[0028] Step S22: Assemble the blade pattern and the outline pattern according to the preset exhaust channel alignment relationship and bond the two together to obtain an integral impeller foam pattern with a continuous exhaust channel inside.

[0029] Step S3: Apply refractory coating evenly to the surface of the impeller pattern, and dry it after application to obtain the impeller model; the thickness of the refractory coating is 0.5 mm to 2 mm, and the refractory coating is used to prevent the penetration of molten metal and the residue of gasification products; the drying temperature of the coating is 40℃ to 60℃.

[0030] Step S4: The impeller model is buried in a sand box. The sand box is filled with sand layer by layer and compacted by vibration so that the sand body covers the model. The exhaust port of the exhaust channel is connected to a negative pressure system. Dry quartz sand is used to fill the sand layer by layer and compact it by vibration.

[0031] Step S5: Pour the molten metal along the gating system until the molten metal completely replaces the impeller pattern. After cooling, the impeller casting is obtained. The gating system adopts a bottom pouring design.

[0032] Of course, the above are just typical examples of the present invention. In addition, the present invention may have many other specific embodiments. All technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed by the present invention.

Claims

1. A casting and machining process for an impeller, characterized in that, Includes the following steps: Step S1: Preparation of foam particles; Step S2, Impeller pattern preparation: The foam particles are injected into a mold and shaped to obtain an impeller pattern. The impeller pattern has a pre-set exhaust channel. Step S3: Apply refractory coating evenly to the surface of the impeller pattern, and dry it after coating to obtain the impeller model; Step S4: The impeller model is buried in a sand box. The sand box is filled with sand layer by layer and compacted by vibration so that the sand body covers the model. The exhaust channel is connected to a negative pressure system. Step S5: Pour the molten metal along the gating system until the molten metal completely replaces the impeller pattern, and obtain the impeller casting after cooling.

2. The impeller casting process as described in claim 1, characterized in that, In step S2, the impeller foam pattern is prepared using a split molding method, including an outline pattern and a blade pattern; step S2 includes: Step S21: Provide a contour pattern forming mold and a blade pattern forming mold respectively, and inject the foam particles into the corresponding molds for foaming and molding to obtain a contour pattern and a blade pattern with internal venting channels. Step S22: Assemble the blade pattern and the outline pattern according to the preset exhaust channel alignment relationship and bond the two together to obtain an integral impeller foam pattern with a continuous exhaust channel inside.

3. The impeller casting process as described in claim 2, characterized in that: In step S21, both the outline pattern and the blade pattern are prepared using a split molding method, including a base foam portion and an embedded exhaust channel portion. The exhaust channel portion is composed of an independently prefabricated exhaust channel pattern, and the exhaust channel pattern has through-holes extending along a predetermined path inside. Step S21 includes: Step S211: Provide an exhaust channel pattern molding die, inject the foam particles into the corresponding die to foam and form an exhaust channel pattern with through holes. Step S212: Place the exhaust channel pattern in the corresponding position in the cavity of the contour pattern forming mold or the blade pattern forming mold, and then inject the foam particles into the corresponding mold for secondary foaming and molding, thereby forming an integral contour pattern or blade pattern with a continuous exhaust channel.

4. The impeller casting process as described in claim 3, characterized in that: The density of the foam particles in the exhaust channel pattern is greater than that in the matrix pattern, making the rigidity of the exhaust channel pattern higher than that of the matrix pattern. While improving the overall pattern's resistance to deformation, the through-holes serve as gas flow channels during the casting process, achieving efficient exhaust.

5. The impeller casting process as described in claim 3 or 4, characterized in that: At the interface between the exhaust channels of the outline pattern and the blade pattern, one side has an axially extending protrusion and the other side has a matching recess. The protrusion and the recess form a plug-in positioning pair, which guides and locks the relative position of the two during assembly in step S212, ensuring that the spatial angle and outline consistency of the blade and the outline after split forming meet the casting accuracy requirements. The protrusion is the exhaust channel end part of the outline pattern or the blade pattern.

6. The impeller casting process as described in claim 1, characterized in that: In step S5, the gating system adopts a bottom-pouring design.

7. The impeller casting process as described in claim 1, characterized in that: In step S1, the foam particles are selected from EPS polystyrene or STMMA copolymer resin, and the foam particles are pre-foamed and cured.

8. The impeller casting process as described in claim 1, characterized in that: In step S3, the thickness of the refractory coating is 0.5 mm to 2 mm. The refractory coating is used to prevent the penetration of molten metal and the residue of gasification products. The drying temperature of the coating is 40°C to 60°C.

9. The impeller casting process as described in claim 1, characterized in that: In step S4, dry quartz sand is used to fill the sand layer by layer and then vibrated to compact it.

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