Centrifugal casting method for small butterfly valve castings

Abstract

This invention discloses a centrifugal casting method for small butterfly valve castings. The casting cavity includes a box body with horizontal or vertical parting, and a gating ring core, a valve inner core, a valve outer core, and a rod core assembled inside the box body. The lower surface of the valve inner core is fitted with the inner core groove of the bottom plate, and a horizontal runner is provided on its upper surface. An inner cavity is provided between the outer surface of the valve outer core and the inner wall of the cylinder. The rod core is assembled in the branch pipe cavity of the support plate core. The gating ring core compacts the valve inner core and the valve outer core, with a gating point at the center and the top surface compacted by a pressure iron. After the box body is assembled, the two semicircular parts of the rod core fix the outer ends of the rod core, and the two semicircular parts of the support plate core fix the support plate core. This invention improves the process yield of butterfly valve castings and eliminates casting cracks.

Description

Technical Field

[0001] This invention is applied in the casting field and relates to the casting production of butterfly valve castings, specifically a centrifugal casting method for butterfly valve castings. Background Technology

[0002] Butterfly valves are essential components of pipelines, and while they come in various sizes, shapes, and materials, their overall shape is circular. Currently, cast steel butterfly valves are mostly produced using sand gravity casting, with the riser and gating system accounting for a large proportion of the valve's weight. This results in a yield rate of less than 60%, and casting defects such as surface porosity and inclusions exist, leading to significant labor-intensive rework and high production costs in terms of labor, energy, and materials. This application aims to reduce the production cost of cast steel butterfly valves by employing a centrifugal process to improve yield, avoid porosity and inclusions, and increase production efficiency.

[0003] CN119282058A discloses a semi-centrifugal casting method for large barrel-shaped castings. The method involves creating a casting channel in the middle of a sand core, with an enlarged hidden riser at the bottom of the channel. The sand core is fabricated using a water glass + carbon dioxide blowing hardening process. A mesh steel skeleton is constructed inside the sand core, and venting ropes are designed for casting. The surface of the sand core and the inside of the outer mold are coated with a paint, and the mold is positioned and assembled. Centrifugal casting is then performed according to the process, and slow pouring occurs when the calculated process weight is reached. The shortcomings of this method are: 1) the feeding riser is located at the bottom, which does not conform to the principle of gravity feeding, resulting in poor feeding effect; 2) centrifugal force is not utilized for feeding; 3) the use of a sprue and hidden riser leads to a low process yield.

[0004] Several patent applications for valve bodies or valve shells, including CN106734950A (casting process method for hollow valve body cast steel parts), CN103433434A (casting method for flat gate valve body), CN114632912A (casting process method for gate valve body of pipeline valve), CN102463326A (casting mold and casting process of valve shell for marine diesel engine exhaust valve), CN114643339A (casting method for ball valve body), and CN103056325A (casting method for cast steel parts of exhaust valve shell), do not use centrifugal casting process for production. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a centrifugal casting method for small butterfly valve castings, which utilizes the principle of layered solidification, centrifugal force and gravity feeding to improve the process yield; prevents cracks from the perspective of shrinkage and sand core collapse and retreat; and ensures the butterfly valve casting is formed from multiple perspectives such as venting and dynamic balance.

[0006] The technical solution adopted in this invention is as follows: The centrifugal casting method for small butterfly valve castings provided by this invention includes a casting cavity comprising a positioning and assembly box and a sand core assembled within the box. The box is formed by vertical parting of a half-mold or horizontal parting of upper and lower molds, with the parting surface passing through the center of the support plate and the support pipe. The box is composed of a base plate and a cylinder. The box is positioned and fixedly assembled on the rotating platform of a centrifuge. The sand core includes a gating ring core, a valve body core, a valve body core, and a rod core. On both sides of the cylinder at the parting surface, semicircles of the rod core and semicircles of the support plate are machined from the outside in. After the box is positioned and assembled, two semicircles of the rod core at corresponding positions cooperate to fix the outer ends of the rod core, and two semicircles of the support plate cooperate to form a support plate cavity. The outer surface of the valve body core forms the inner surface of the butterfly valve casting, its lower surface is assembled with the inner core groove on the base plate, and its upper surface is provided with a horizontal sprue, which cooperates with the upper main plate cavity for feeding molten steel to the upper main plate. The valve body outer core includes a support disc core, which is positioned by the inner wall of the cylinder. Its inner surface is formed with the circumferential outer surface of the butterfly valve, and an inner cavity is provided between the outer surface and the inner wall of the cylinder to provide space for the valve body outer core to collapse and retract. The rod core is assembled in the branch cavity of the support disc core, and the inner end of the rod core is fixed by the valve body inner core. The gate ring core is positioned and assembled by the inner wall of the box, compacting the valve body inner core and the valve body outer core, with a gate in the center and the top surface compacted by a pressure iron. In this way, the pressure iron can prevent the sand core inside the box from floating due to the buoyancy of the molten steel.

[0007] Furthermore, the inner wall of the cylinder is machined with an inner groove, or the outer surface of the valve body is machined with an outer groove, and the inner groove, the outer groove, or both together form the inner cavity. The inner cavity is transverse or longitudinal, and avoids the circumferential or axial reinforcing ribs on the outer surface of the valve body, having sufficient thickness and strength to resist the centrifugal force of molten steel.

[0008] Furthermore, a lower cavity is provided at the lower center of the valve body core; or a conical central hole is machined at the center of the base plate. The lower cavity or central hole provides space for the collapse and retraction of the valve body core.

[0009] Furthermore, to enhance the collapse and yielding of the core, a core end cavity is machined on the outer side of the core semicircle.

[0010] Furthermore, a sprue recess is provided at the center of the upper surface of the valve body core (8) to prevent molten steel from splashing during pouring. Vent holes with vertical ventilation are provided on the sprue ring core, or a venting rope is provided to enhance cavity venting.

[0011] Furthermore, if there is a weight difference between the two support plates and the support pipes, dynamic balance can be controlled by increasing the weight of the housing and / or by reducing the centrifugal speed; or by using the same support plate core and machining it after casting; or by adding a dark cavity in a relatively small support plate cavity position. The dark cavity is an annular cavity or a cavity evenly distributed around the circumference, which is cleaned out after casting.

[0012] Furthermore, a coating 1-2 mm thick is sprayed onto the inner wall of the mold that comes into contact with the molten steel to increase the service life of the metal mold. Before pouring, the temperature of the mold body is not lower than 120°C to prevent free water from remaining within the coating. During pouring, the centrifuge speed is not lower than 10G to enhance centrifugal force compensation. After pouring, the gate is covered with a heat-insulating agent to prevent radiative heat loss from the molten steel. From the start of pouring, water is sprayed to cool the metal mold body and strengthen layered solidification.

[0013] Furthermore, the assembly steps of the casting cavity are as follows: 1) The outer core of the valve body is assembled into a half mold or lower mold, with the support plate semicircle positioning and matching the support plate core; 2) The inner core of the valve body is positioned and assembled with the inner core groove, so that the blind hole on the inner core of the valve body corresponds to the semicircle of the support plate; 3) A rod core is inserted into the branch tube cavity for fixation; 4) Another half mold or upper mold is positioned and assembled, and the two half molds or upper and lower molds are tightened; 5) The gate ring core is positioned and assembled by the inner wall of the box, compacting the outer core of the valve body and the inner core of the valve body, and the pressure iron is used to fix and compact the gate ring core to form a casting mold; 6) The casting mold is placed on the rotating platform of the centrifuge, positioned by the positioning groove or central hole of the bottom plate, and the connecting parts are fixedly connected.

[0014] The beneficial effects of this invention are: this invention greatly improves the yield of butterfly valve castings and reduces production costs. Butterfly valves made using this process have no casting cracks, high valve body density, and significantly improved mechanical properties. Attached Figure Description

[0015] Figure 1 These are schematic diagrams of the butterfly valve castings for Examples 1 and 2. Figure 2 This is a schematic front view of the casting cavity in Example 1, and also... Figure 3 BB cross-sectional diagram; Figure 3 for Figure 2 A partial sectional view of AA; Figure 4 This is a schematic front view of the semi-mold structure in Example 1; Figure 5 for Figure 4 A top-down view; Figure 6 This is a schematic front view of the valve body core structure of Example 1; Figure 7 for Figure 6 A top-down view; Figure 8 This is a schematic diagram of the casting cavity in Example 2; Figure 9 This is a schematic diagram of the casting cavity in Example 3; Figure 10This is a schematic diagram of the lower mold in Example 3; Figure 11 for Figure 10 A top-down view; Figure 12 This is a schematic diagram of the parting surface sealing structure; In the diagram: 1-Main panel, 2-Branch panel, 3-Branch pipe, 4-Valve body; 6-Pressure iron, 7-Gating ring core, 8-Valve body core, 9-Horizontal runner, 10-Gating, 11-Vent hole, 12-Bolt, 13-Support core, 14-Left half mold, 15-Bar core, 16-Core end cavity, 17-Connector, 18-Positioning groove, 19-Valve body core, 20-Inner cavity, 21-Fastener, 22-Positioning pin, 23-Right half mold, 24-Upper mold, 25-Lower mold, 26-Gating brick, 27-Gating socket, 28-Lower cavity, 29-Central hole; 41-Core end half cavity, 42-Rock core half circle, 43-Support plate half circle, 45-Inner groove, 46-Inner core groove, 47-Pass through, 48-Annular groove, 49-Bottom plate, 50-Outer groove, 51-Branch cavity. Detailed Implementation

[0016] The "small butterfly valve casting" described in this invention refers to butterfly valve castings with a diameter not exceeding DN800. Centrifugal casting metal molds are divided into horizontal and vertical parting types; Examples 1 and 3 are vertical parting types, while Examples 2 and 4 are horizontal parting types. This invention elucidates the centrifugal casting process for butterfly valve castings from the perspectives of resin sand core collapse and retreat, prevention of core drift, gas venting during pouring, layered solidification and feeding of molten steel, as-cast shrinkage, and dynamic balancing. Example

[0017] This embodiment uses the appendix Figure 1 The butterfly valve casting shown is used as an example for illustration. The support plate and branch pipe of this product are symmetrical.

[0018] The casting cavity in this embodiment is shown in the attached figure. Figure 2 and attached Figure 3 As shown, a two-part mold is used for vertical parting, including a metal box body for positioning and assembly, and a resin sand core assembled inside the box body. The left half mold 14 and the right half mold 23 are positioned and assembled into a barrel-shaped metal box body by positioning pins 22. Fasteners 21 secure the left and right half molds together. The parting surface is a vertical surface passing through the center of the support plate and the support pipe, which facilitates the assembly of the box after the sand core is assembled and the opening of the butterfly valve casting. In this embodiment, there are four sand cores: the gate ring core 7, the valve body core 8, the valve body core 19, and the rod core 15.

[0019] In this embodiment, the left half-mold 14 and the right half-mold 23 have a symmetrical structure, and the structure of the half-mold is shown in the attached figure. Figure 4 and attached Figure 5As shown, the mold is semi-cylindrical, consisting of a semi-circular base plate 49 and a semi-annular cylindrical body, with the parting line passing through the annular center of the cylindrical body. Mounting plates are provided on both sides of the parting line, with through holes machined on the mounting plates for securing the left and right half-molds together using fasteners 21. Positioning pins 22 are provided on the mounting plates for positioning and assembling the left and right half-molds. An annular groove 48 is machined on the top surface of the cylindrical body, used to limit and fix the end of the bolt 12. A through-hole 47 communicates with the annular groove, allowing the bolt end to slide into the groove. The structure of the through-hole 47 and annular groove 48 can be referenced from the platforms used to fix workpieces on milling machines and planers. A through-hole is machined on the outer edge of the base plate for installing a connector 17, which is used to fix the mold to the rotating platform of the centrifuge. An inner groove 45 is machined on the inner wall of the cylindrical body, which mates with the outer groove 50 on the outer core of the valve body to form an inner cavity 20. A positioning groove 18 is machined at the center of the lower surface of the base plate. This positioning groove is used to position the mold on the centrifuge, ensuring the concentricity of the mold and the centrifuge during integrated rotation. An inner core groove 46 is machined on the upper surface of the base plate. This inner core groove mates with the lower end of the valve body core 8, allowing for quick and easy positioning and assembly of the valve body core. On the cylinders on both sides of the parting surface, core end semi-cavities 41, rod core semi-circles 42, and support plate semi-circles 43 are machined from the outside in. After the left and right half molds are positioned and assembled, the two core end semi-cavities 41 at corresponding positions mate to form a core end cavity 16, the two rod core semi-circles 42 mate together to fix the outer end of the rod core 15, and the two support plate semi-circles 43 mate to form the forming cavity of the support plate 2, i.e., the support plate cavity.

[0020] The gating ring 7 is a ring-shaped integral sand core, assembled and compacted on top of the valve body core 8 and the valve body core 19. The gating ring 7 is positioned by the inner wall of the casting box and assembled tightly against it. Vent holes 11 or vent ropes should be provided on the gating ring to facilitate venting of the mold cavity. A gating gate 10 is located in the middle of the gating ring to receive molten steel during pouring. The top surface of the gating ring is stabilized by a pressure iron 6 to prevent the gating ring, valve body core 8, and valve body core 19 from floating due to the buoyancy of the molten steel. The pressure iron 6 is fixed to the top surface of the casting box with bolts 12. When the gating ring 7 collapses, although the outer surface of the ring is constrained by the inner wall of the casting box, the upper pressure iron is not a completely closed ring, allowing the collapse of the gating ring to move upwards and retract.

[0021] The valve body core 8 is an annular integral sand core, assembled in the center of the housing and positioned by the inner core groove 46. A horizontal sprue 9 is provided on its upper surface, connecting to the casting cavity. This horizontal sprue 9 mates with the upper main plate cavity, used for feeding molten steel to the upper main plate. A gating socket 27 should be added to the bottom of the gating gate 10, which mates with and connects to the horizontal sprue. During pouring, the molten steel in the gating socket acts as a buffer, preventing splashing and evenly distributing the molten steel to the radial horizontal sprue. A lower cavity 28 is provided in the lower center of the valve body core to facilitate the collapse and retraction of the valve body core.

[0022] The valve body core 19 is a ring-shaped integral sand core, the structure of which is shown in the attached figure. Figure 6 and attached Figure 7 As shown, the device includes two symmetrical support cores 13, which are used to form the support plate and branch pipe. The flat end of the support core extends beyond the outer cylindrical surface of the valve body outer core, and this flat end mates with the support plate semicircle 43 of the housing to form the support plate cavity. The inner hole of the support core 13 is the branch pipe cavity 51, which forms the outer surface of the branch pipe. An outer groove 50 is provided on the outer cylindrical surface of the valve body outer core, which mates with the inner groove 45 of the half mold to form an inner cavity 20. This inner cavity 20 provides space for the valve body outer core to collapse. When the valve body and main plate solidify, cool, and shrink, the valve body outer core collapses into this inner cavity, creating a clearance and freeing up space for the main plate to shrink freely, thus avoiding the formation of casting shrinkage cracks due to obstructed shrinkage. The outer surface of the valve body outer core 19 is fitted tightly against the inner wall of the housing and positioned by the inner wall of the housing. Its inner surface is used to form the circumferential outer surface of the butterfly valve. The top surface of the valve body core is pressed and fixed by the gate ring core 7, and the outer circular surface of the support core is fixed by the housing, together with the gate ring core, to prevent the valve body core from floating.

[0023] The core 15 is a simple cylindrical sand core used to form the inner hole of the branch pipe. Its inner end is fitted into the blind hole of the support core 13 and fixed by the valve body core. Its outer end is fitted with the semicircular cores 42 of the two half-molds and fixed by the housing to prevent core drift. The inner end of the core can collapse and retract with the collapse of the valve body core. To facilitate the collapse and retraction of the outer end of the core, a core end cavity 16 is provided on the housing. If the core size is small and its collapse and retraction do not affect the forming of the branch pipe, the core end cavity may not be provided.

[0024] In this embodiment, the centrifugal casting mold is assembled at the assembly station. The inner wall of the box that comes into contact with the molten steel is coated with a layer of paint, such as the support plate cavity and the lower main plate cavity. The valve body outer core 19 is moved into a half-mold and fitted tightly against the inner wall of the half-mold. The support plate core 13 is positioned and fitted with the support plate semicircle 43. The valve body inner core 8 is positioned and assembled with the inner core groove on the bottom plate of the half-mold, so that the blind hole corresponds to the support plate semicircle. The rod core 15 is inserted into the branch pipe cavity 51 and fixed with the blind hole and the rod core semicircle 42. Then, the other half-mold is positioned and moved by the positioning pin 22 to assemble the box, and the two half-molds are fixed into a box body with fasteners 21. A gating ring core 7 is assembled on top of the valve body outer core and the valve body inner core. The gating ring core is positioned and assembled by the inner wall of the box body and fixed and compacted with a pressure iron 6 and bolts 12. The assembled mold is placed on the rotating platform of the centrifuge, positioned by the positioning groove 18, and fixedly connected by the connecting piece 17. The mold rotates at high speed on the centrifuge's rotating platform. Molten steel enters the gating socket from the gate and then flows into the mold through the runner. Air in the mold cavity is expelled through the sand core assembly gaps, vents, and runner under the pressure of gravity and centrifugal force, preventing defects caused by poor venting. After solidification, the mold is separated from the centrifuge and cooled at the cooling station. The centrifuge can then proceed to the next mold installation and pouring. After cooling, the mold is opened at the unpacking and sand removal station, the butterfly valve casting is removed, the metal mold is cleaned and coated, and then transferred to the assembly station for reassembly of the sand core, initiating the production of the next butterfly valve.

[0025] In this embodiment, the butterfly valve is small in size, with a relatively small outer diameter of the mold, facilitating the pouring and ladle operation of molten steel. Molten steel can be poured directly from the gating gate. After centrifugal pouring, the molten steel in the support plate cavity is rapidly cooled by the metal casing, while the molten steel in the valve body and branch pipe cavities solidifies more slowly, creating a layered solidification temperature difference from the outer support plate to the inner valve body. The direction of this layered solidification feeding is consistent with the direction of the centrifugal force, and the centrifugal force generated by the centrifugal rotation enhances the horizontal feeding of molten steel from the inside out. The molten steel in the lower main plate of the butterfly valve is rapidly cooled by the bottom plate, resulting in a faster solidification rate. The molten steel in the upper main plate cavity does not directly contact the metal casing, resulting in slower solidification and creating a cooling temperature gradient from bottom to top, i.e., layered solidification from bottom to top. This solidification direction is consistent with the direction of gravity feeding of the molten steel. The sprue is large, and the molten steel inside cools more slowly than the valve body, providing feeding for the valve body and upper main plate. Its feeding direction is consistent with the direction of the centrifugal force. The gating gate is covered with a heat-insulating agent to prevent the molten steel inside from dissipating heat outwards, resulting in the slowest cooling rate and effectively enhancing the feeding effect on the sprue. In other words, this embodiment utilizes the metal box to rapidly cool the molten steel, achieving solidification and feeding in the direction of centrifugal force and gravity, thus strengthening the feeding effect. Compared to sand gravity casting, this embodiment eliminates the feeding risers on the support plate and lower main plate, and also eliminates the sprue, improving the process yield.

[0026] To allow for free shrinkage during butterfly valve molding, this embodiment provides space for the sand core to collapse and recoil, such as the inner cavity, lower cavity, and core end cavity, preventing casting shrinkage cracks caused by insufficient space for the sand core to recoil. Regarding dynamic balancing, the support plate and support pipe in this embodiment are symmetrical, eliminating any dynamic imbalance issues. For venting, the gate and vent are directly connected to the outside, ensuring smooth venting. Example

[0027] Example 1 uses a vertical parting line, while this example uses a horizontal parting line for the upper and lower molds. The casting cavity is shown in the attached figure. Figure 8 As shown. The parting surface is designed for a stop sealing method and also serves as an auxiliary positioning function. The casting cavity includes a positioning and assembly box and sand cores assembled inside the box. The upper mold 24 and lower mold 25 are positioned and assembled into a barrel-shaped box by positioning pins 22, and fasteners 21 secure the upper and lower molds together. The parting surface is a horizontal plane passing through the center of the support plate and the support pipe. The sand cores in this embodiment are similar to those in embodiment 1, with four sand cores: the gate ring core 7, the valve body core 8, the valve body core 19, and the rod core 15. Compared with embodiment 1, the most significant difference is the different box closing direction.

[0028] This embodiment provides another structural form of the inner cavity 20, but the inner cavity must not affect the forming of the support plate and the assembly of the core.

[0029] In this embodiment, the upper mold 24 is tubular, and the lower mold 25 is basin-shaped. The structure of the upper mold 24 can be referred to the attached diagram. Figure 4 The upper part, the lower mold 25 structure can be referred to in the appendix of embodiment 3. Figure 10 and attached Figure 11 .

[0030] This embodiment presents an alternative casting method. The gating brick 26 is fixed by a support, with its lower opening aligned with the gating gate 10 and the gating socket 27. Molten steel enters vertically from the gating brick into the gating socket and then flows into the mold through the sprue 9. This casting method avoids molten steel flowing onto the mold and causing steel spillage, making it safer than Embodiment 1. The molten steel feeding, layered solidification, and sand core collapse and retreat are the same as in Embodiment 1 in this embodiment, and the cooling, mold opening, and sand removal operations after casting are also the same as in Embodiment 1.

[0031] The centrifugal casting assembly steps in this embodiment are similar to those in Embodiment 1, performed at the assembly station, with a coating sprayed onto the inner wall of the box that comes into contact with the molten steel. Then, the valve body core 19 is assembled into the lower mold, tightly against the inner wall of the box, with the support plate semicircle 43 positioning and engaging with the support plate core 13. The valve body core 8 is positioned and assembled with the inner core groove 46 on the upper surface of the base plate, so that the blind hole of the valve body core corresponds to the rod core semicircle 42. The rod core is inserted into the branch pipe cavity 51, and fixed using the blind hole of the valve body core and the rod core semicircle. The positioning pin 22 guides and positions the upper mold assembly; after the upper and lower molds are assembled, they are fixed with fasteners 21. The sprue ring core 7 is positioned downwards from the inner wall of the box, compacting the valve body core and the valve body core, and finally, the sprue ring core is fixed and compacted with a pressure iron to form the casting mold. The casting mold is hoisted and placed on the rotating platform of the centrifuge, positioned by the positioning groove on the lower surface of the base plate engaging with the rotating platform, and fixedly connected by the connector 17. The centrifuge is then started for centrifugal casting. Example

[0032] In the above embodiments, the branch pipe and the support disc have the same specifications. In this embodiment, the butterfly valve has one large and one small support disc.

[0033] The casting cavity in this embodiment is shown in the attached figure. Figure 9 As shown, a horizontal parting pattern is adopted, similar to the structure of Example 2, including a box body for positioning and assembly and a sand core assembled inside the box body. The metal box body is assembled into a barrel shape by positioning and assembly of upper and lower molds, and fasteners 21 are fastened into one piece. The parting surface is a horizontal plane passing through the center of the support plate and the branch pipe. The sand core is still the gate ring core 7, the valve body core 8, the valve body core 19, and the rod core 15.

[0034] The lower half of the mold in this embodiment is as shown in the attached figure. Figure 10 and attached Figure 11 As shown, the mold is basin-shaped, consisting of a circular base plate 49 and an annular cylinder. On the symmetrical sides of the cylinder at the parting line, semicircular core 42 and semicircular support plate 43 are machined from the outside in. After the upper and lower molds are positioned and assembled, the two semicircular core 42 at corresponding positions cooperate to fix the outer end of the core, and the two semicircular support plate 43 cooperate to form the support plate cavity. A conical central hole 29 is machined in the center of the base plate. The central hole has a smaller upper diameter and a larger lower diameter, effectively combining the functions of the positioning groove 18 and the lower cavity 28. Its conical slope provides positioning, and its through hole serves as a clearance space for the valve body core to disintegrate. Furthermore, this central hole facilitates the disintegration and cleaning of the valve body core inside the housing, allowing for direct cleaning and quick unpacking.

[0035] Another difference between this embodiment and the previous embodiment lies in the shape of the valve body core. It is still an annular integral sand core, positioned and assembled by the inner wall of the housing. However, there are no annular supports at the top and bottom. The bottom surface is positioned and assembled by the annular stepped surface of the housing. The molten steel in the lower main plate cavity has increased contact surface with the metal mold, increasing the cooling capacity of the molten steel in the lower main plate cavity and helping to strengthen gravity and centrifugal force compensation. The upper surface is still compacted by the gating ring core 7, but the outer circumference of the upper main plate is formed by the gating ring core.

[0036] The mold assembly, pouring, and unpacking operations in this embodiment are the same as in Embodiment 2. The biggest difference from Embodiment 2 lies in the dynamic balance issue, as shown in the attached... Figure 9 A comparison of the left and right sides reveals that the left plate is larger than the right plate, and the two support plates and support pipes are of different sizes, causing asymmetry between the box and the sand core. During the centrifugal casting process, as the molten steel fills the mold, the center of rotation of the dynamic balance will move from the side of the smaller support plate before casting to the side of the larger support plate. When the centrifugal force is large, it will cause vibration of the centrifuge. Therefore, the present invention adopts the following method to solve the problem of unstable dynamic balance: 1) For cases where the two branch pipes are identical but the two support plates are different in size, both support plates use the casting cavity of the larger support plate, which is dynamically balanced and stable. After unpacking, the larger support plate is machined to the size of the smaller support plate.

[0037] 2) For cases where the weight difference between the two support plates and pipes is small, if the weight difference is no more than 10% of the weight of the smaller support plate and pipe, the weight of the chamber can be increased to increase its centrifugal inertia and reduce the difference in centrifugal inertia between the two support plates. Although this method cannot strictly control dynamic balance, it can prevent centrifugal vibration, ensure the use of the centrifuge equipment, and avoid affecting centrifugal casting. When the weight ratio is closer to the upper limit, dynamic balance can also be controlled by appropriately lowering the centrifuge speed to avoid vibration.

[0038] 3) For cases where the weight difference between the two support plates and support pipes is significant, if the weight difference is greater than 10% of the weight of the smaller support plate and support pipe, a hidden cavity can be added at the support plate cavity location of the smaller support plate. The connection between the hidden cavity and the support plate cavity is similar to that of a hidden riser. This is beneficial for both pre-pouring mold centrifugal balance and pouring centrifugal balance. The portion formed by the hidden cavity can be removed in a subsequent cleaning process. The hidden cavity can be annular or consist of multiple small cavities evenly distributed around the circumference. However, the position and dimensions of the hidden cavity should be verified and simulated using computer software dynamic balancing, or the empirical data from section 2) above should be used to ensure that the weight difference does not exceed 10%, and should ideally be adjusted to below 5%. Example

[0039] The casting cavity in Example 3 can also be vertically parted, as shown in the structure of Example 1. The assembly method and pouring of the casting cavity in this example are the same as in Example 1, and the solution to the dynamic balance problem is the same as in Example 3.

[0040] It should be noted that: 1) In the above embodiments, the inner groove of the inner wall of the metal mold and the outer groove of the outer surface of the valve body together form the inner cavity for the outer core to collapse and yield. Alternatively, the inner groove or the outer groove can be provided separately, as long as the groove space meets the requirements for the outer core to collapse and yield, as shown in Appendix of Embodiment 3. Figure 10 The lower mold does not have an internal groove; instead, it utilizes the external groove of the valve body to provide clearance.

[0041] 2) In the above embodiments, the inner cavity is transverse, but it can also be set longitudinally, as long as the number and space meet the requirements for the outer core to collapse and retreat. For some butterfly valves, the outer surface of the valve body is provided with circumferential or axial reinforcing ribs. The position of the inner cavity should avoid the formed cavities of these reinforcing ribs, so that the outer core of the valve body has sufficient thickness and strength to withstand the centrifugal force of molten steel.

[0042] 3) The sand core in this invention can be a whole sand core or it can be assembled from multiple small sand cores.

[0043] 4) To increase the strength of the sand core and resist the gravity and centrifugal force of the molten steel, core reinforcement can be embedded inside the sand core. This includes using steel bars, mesh skeletons, etc., which are existing technologies. Other existing technologies include sand core spraying coatings and refractory mortar sealing assembly, but these are not shown in the accompanying drawings or described in detail in the embodiments.

[0044] 5) To avoid exposed steel at the parting line, an additional... Figure 12 The sealing configurations shown are: a stop seal at the top, a convex groove seal in the middle, and a double-groove clamping block seal at the bottom. Examples 2 and 3 illustrate conventional forms of horizontal parting surface stop seals. These sealing structures are prior art; for simplicity, other sealing configurations are not shown in the figures.

[0045] 6) If the thickness of the main plate is very large relative to the valve body wall thickness (this special case accounts for a very small percentage of products), meaning that the molten steel in the valve body solidifies before the molten steel in the lower main plate, and the molten steel in the valve body cannot compensate for the shrinkage of the lower main plate, multiple evenly distributed symmetrical hidden risers can be set at the bottom of the valve body core, or horizontal runners can be set at both the top and bottom to compensate for the shrinkage of the molten steel in the lower main plate. Setting hidden risers and adding horizontal runners at the bottom are both existing technologies and no additional embodiments are provided.

[0046] 7) Even without centrifugal force, the casting cavity of this embodiment can achieve static gravity forming of the butterfly valve, but risers are needed at the positions of the support plate and the lower main plate for feeding. This invention uses centrifugal casting, which enhances the feeding effect of centrifugal force, which is beneficial for obtaining dense castings. Molten steel is poured into the rotating casting cavity, resulting in good temperature uniformity and smooth venting. The support plate and the lower main plate do not use risers, reducing the number of risers and eliminating the need for a sprue, thus improving the process yield. Furthermore, slag inclusions move towards the inner surface of the valve body under the action of centrifugal force, preventing casting defects such as slag inclusions and porosity on the outer surface. The centrifugal speed of this invention is not less than 10G; otherwise, centrifugal feeding will be imperfect. When there is no dynamic balance problem, the centrifugal speed can be increased to over 30G to enhance the effect of centrifugal force.

[0047] 8) To enhance the layered solidification from the outside in and from the bottom up, a rapid cooling method of spraying water to cool the box should be adopted from the beginning of molten steel pouring.

[0048] 9) To avoid cold-blocking or cold-shut defects, a coating with a thickness of 1-2 mm is sprayed onto the surface of the casting cavity in the mold box. The coating temperature (mold box temperature) before casting should not be lower than 120℃ to avoid free water in the coating and prevent porosity. In addition, the coating helps to improve the service life of the metal mold.

[0049] 10) The casting cavity and the rotating platform are detachably fixedly connected by connectors, as shown in the attached diagram, using bolts and nuts. This connection method is common and falls under existing technology. Bolts, fasteners, and connectors are used to achieve detachment and fixed connection; any substitutions within the scope of existing technology are equivalent.

[0050] 11) In the above embodiments, the inner cavity is a closed structure, mainly for safety considerations. If the valve body can ensure safety, the inner cavity can be open, communicating with the outside. This structure facilitates faster unpacking and sand removal. It allows for quick unpacking along with the central hole in the bottom plate, and the residual heat from casting can be used for water-cooling treatment of the stainless steel.

[0051] 12) In this invention, the assembly and positioning of the inner wall of the cylinder can be done directly using the inner wall or through other components, but the reference for assembly and positioning is the inner wall of the cylinder.

[0052] 13) This invention is applicable to small butterfly valve castings with a specification less than DN1000. For large butterfly valve castings with a specification greater than DN1200, the difficulty of center gate alignment with the ladle increases, safety decreases, the length of the horizontal runner increases, and the cooling of molten steel increases. It is not recommended to apply it to large butterfly valve castings. However, this invention does not exclude the possibility of application to large butterfly valve castings when molten steel is guided or when a gate brick is used.

[0053] This invention increases the yield rate from less than 60% in sand casting to over 87%, saving not only raw materials and melting costs but also significantly reducing molding sand usage and labor, resulting in a 40% reduction in production costs. Low-alloy steel and stainless steel butterfly valves manufactured using this process are free of casting shrinkage cracks and have no casting defects such as slag inclusions, porosity, or cold shuts on their outer surfaces. The butterfly valves cast using this invention utilize centrifugal force feeding, resulting in a higher density than those produced by gravity casting, and their mechanical properties are significantly improved after heat treatment.

Claims

1. A centrifugal casting method for a small butterfly valve casting, characterized in that: The casting cavity includes a positioning and assembly box and a sand core assembled inside the box; the box is formed by vertical parting of the half mold or horizontal parting of the upper and lower molds, with the parting surface passing through the center of the support plate and the support pipe; the box is composed of a bottom plate and a cylinder; the box is positioned and fixedly assembled on the rotating platform of the centrifuge; the sand core includes a gate ring core (7), a valve body core (8), a valve body core (19), and a rod core (15). On both sides of the parting surface, a core semicircle (42) and a support plate semicircle (43) are machined from the outside to the inside; after the box body is positioned and assembled, the two core semicircles (42) at the corresponding positions cooperate to fix the outer end of the core (15), and the two support plate semicircles (43) cooperate to form a support plate cavity; The outer surface of the valve body core (8) forms the inner surface of the butterfly valve casting, the lower surface is assembled with the inner core groove (46) on the bottom plate, and the upper surface is provided with a horizontal sprue. The valve body core (19) includes a support core (13). The valve body core (19) is positioned by the inner wall of the cylinder. Its inner surface is formed with the outer circumferential surface of the butterfly valve. An inner cavity (20) is provided between the outer surface and the inner wall of the cylinder. The rod core (15) is assembled in the branch cavity (51) of the support plate core (13), and the inner end of the rod core (15) is fixed by the valve body core (8); The gate ring (7) is positioned and assembled by the inner wall of the box, compacting the inner core (8) and outer core (19) of the valve body, with a gate set in the center, and the top surface is compacted by a pressure iron (6).

2. The centrifugal casting method for a small butterfly valve casting according to claim 1, characterized in that: The inner wall of the cylinder is machined with an inner groove, or the outer surface of the valve body (19) is machined with an outer groove, and the inner groove, or the outer groove, or both together form the inner cavity (20).

3. The centrifugal casting method for a small butterfly valve casting according to claim 2, characterized in that: The inner cavity (20) is transverse or longitudinal, and the inner cavity (20) avoids the circumferential or axial reinforcing ribs on the outer surface of the valve body.

4. The centrifugal casting method for a small butterfly valve casting according to claim 1, characterized in that: The lower center of the valve body core (8) is provided with a lower cavity (28); or a conical central hole (29) is machined in the center of the base plate.

5. The centrifugal casting method for a small butterfly valve casting according to claim 1, characterized in that: On the outer side of the core semicircle (42), the core end semi-cavity (41) is machined.

6. The centrifugal casting method for a small butterfly valve casting according to claim 1, characterized in that: A gate socket is provided at the center of the upper surface of the valve body core (8); an air outlet hole for vertical ventilation is provided on the gate ring core (7), or a breathable rope is provided.

7. The centrifugal casting method for a small butterfly valve casting according to claim 1, characterized in that: If there is a weight difference between the two support plates and the support pipes, dynamic balance can be controlled by increasing the weight of the box and / or by reducing the centrifugal speed; or by using the same support plate core and machining it after casting; or by adding a dark cavity in the relatively small support plate cavity position.

8. The centrifugal casting method for a small butterfly valve casting according to claim 7, characterized in that: The dark cavity is an annular cavity or a cavity evenly distributed around the circumference.

9. The centrifugal casting method for a small butterfly valve casting according to claim 1, characterized in that: The inner wall of the box that comes into contact with the molten steel is coated with a coating of 1-2 mm thickness; before pouring, the temperature of the box is not lower than 120°C; during pouring, the speed of the centrifuge is not lower than 10G; after pouring, the gate is covered with a heat-insulating agent; from the start of pouring, water is sprayed to cool the box.

10. The centrifugal casting method for a small butterfly valve casting according to claim 1, characterized in that: The assembly steps of the casting cavity are as follows: 1) The valve body core (19) is assembled into a half mold or lower mold with the inner wall of the box, and the support plate semicircle (43) is positioned and matched with the support plate core (13); 2) The valve body core (8) is positioned and assembled with the inner core groove (46), so that the blind hole of the valve body core (8) corresponds to the support plate semicircle (43); 3) The rod core (15) is inserted into the branch tube cavity (51) and fixed; 4) The other half mold or upper mold is positioned and assembled, and the two half molds or upper and lower molds are tightened; 5) The gate ring core (7) is positioned and assembled by the inner wall of the box, and the valve body core (19) and valve body core (8) are compacted. The pressure iron (6) is used to fix and compact the gate ring core (7) to form a casting mold; 6) The casting mold is placed on the rotating platform of the centrifuge and positioned by the positioning groove (18) or the middle hole (29) of the bottom plate, and the connecting parts are fixedly connected.

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