A casting system and casting method for a high-voltage outer cylinder of a 1,000 kW nuclear power unit

Abstract

This invention relates to a casting system and method for a high-pressure outer cylinder of a megawatt-class nuclear power unit, belonging to the field of nuclear power equipment casting technology. It solves the problems of slag easily entering the mold cavity and unstable molten steel filling leading to poor internal quality of castings during existing casting of large high-pressure outer cylinders. The method includes a mold casting system and a separate riser-point casting system. The casting system employs a first and second straight runner, with a slag collection trough at the bottom. The horizontal runner consists of two layers, and the inner runner is evenly distributed along the circumference of the casting. The riser-point casting system is located within the riser core, with the pouring cup positioned between the two pouring cups of the mold casting system. During casting, the mold casting system pours first. When the molten steel reaches the designated height, the ladle orifice is closed, and the ladle is moved to align the ladle orifice with the pouring cup of the riser-point casting system. The riser is then replenished through the riser-point casting system. This achieves slag isolation during high-flow-rate filling, ensuring stable and clean molten steel filling of the mold cavity, thus improving the quality of large nuclear power high-pressure outer cylinder castings.

Description

Technical Field

[0001] This invention relates to the field of nuclear power equipment casting technology, and in particular to a high-pressure outer cylinder casting system and casting method for a megawatt nuclear power unit. Background Technology

[0002] The high-pressure outer cylinder is a core pressure-bearing component of the conventional island turbine in a nuclear power unit. Operating under the long-term scouring of high-temperature, high-pressure steam, the quality of its internal casting directly determines the safety and service life of the equipment. Currently, such large, thick-walled castings are typically produced using integral sand casting technology.

[0003] The gating system is the channel that guides molten metal into the mold cavity, and its design has a decisive impact on the internal quality of the casting. An ideal gating system should ensure that the molten metal fills the mold cavity smoothly, cleanly, and continuously, and should have good slag-blocking and venting capabilities. In the existing technology, for the casting of large high-pressure outer cylinders, open or semi-open bottom-pouring systems are usually used, and attention is paid to the calculation of the number and cross-sectional area of ​​the ingates.

[0004] However, these solutions are still insufficient when facing more stringent quality requirements. For example, they are prone to slag inclusion defects; they are also prone to turbulence, air entrapment, and secondary oxidation, which affect the internal purity and solidification quality of the casting. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a high-pressure outer cylinder casting system and casting method for a megawatt nuclear power unit, in order to at least solve one of the problems in the prior art where steel slag easily enters the mold cavity at the end of casting and the riser replenishment process may interfere with the sequential solidification of the casting.

[0006] On the one hand, embodiments of the present invention provide a casting system for casting the high-pressure outer cylinder of a megawatt nuclear power unit, including a mold casting system and a riser spot casting system that are physically separated in space and have no direct or indirect connection with any channel for the flow of molten steel.

[0007] The casting system is used to deliver molten metal to the casting cavity, and includes: a slow-flow sprue and a second sprue arranged in parallel, a slag collection trough located at the bottom of the slow-flow sprue and the second sprue, an upper sprue and a lower sprue connected to the sprue, and multiple sets of ingates connected to the upper sprue and the lower sprue and arranged circumferentially along the casting cavity. The riser casting system is used to independently deliver molten metal into the riser cavity, and includes: a riser pouring cup, a riser sprue connected to the riser pouring cup, a riser gating system connected to the riser sprue, and multiple sets of riser insprues connected to the riser gating system and embedded in the sand core along the circumference of the riser cavity; The riser and pouring cup are positioned on the horizontal projection plane along the line connecting the centers of the two pouring cups of the casting system, and the three are symmetrically distributed.

[0008] Furthermore, each pouring layer of the casting system satisfies the following total cross-sectional area ratio: ∑A 包 :∑A 直 :∑A 横 :∑A 内 =1.0:(1.8-2.0):(1.8-2.0):(2.0-2.5), Where, ∑A 包 Let A be the total cross-sectional area of ​​the casting ladle orifice. 直 Let A be the total cross-sectional area of ​​the second straight gating system. 横 The total cross-sectional area of ​​the upper or lower horizontal runner is ∑A. 内 The total cross-sectional area of ​​all ingates that are connected to the corresponding layer in the upper or lower horizontal runner.

[0009] Furthermore, the slag collection trough has an annular structure with an inner diameter larger than the outer diameter of the direct casting channel, and a trough depth of 100-150mm.

[0010] Furthermore, the lower horizontal runner is connected to the bottom sprue area of ​​the casting cavity through the corresponding ingate to achieve bottom pouring; the upper horizontal runner is connected to the flange area of ​​the casting cavity through the corresponding ingate.

[0011] Furthermore, in the riser-point pouring system, the total cross-sectional area of ​​the riser direct pouring channel is 1.8-2.0 times the total cross-sectional area of ​​the pouring ladle orifice used for pouring to the riser.

[0012] Furthermore, the gating channels in both the casting system and the riser gating system are made of standard circular ceramic refractory brick pipes and are connected by refractory connectors.

[0013] On the other hand, the present invention proposes a casting method for the high-pressure outer cylinder of a megawatt nuclear power unit using the casting system described above, comprising the following steps: S1. Construct a three-dimensional model of the casting based on the high-pressure outer cylinder drawings, and determine the casting process parameters, including machining amount, correction amount, expansion rate and preset liquid level rise speed. S2. Calculate the required total pouring flow rate based on the weight of the casting blank, the height of the mold, and the preset liquid level rise rate. S3. At least two pouring ladles are used to simultaneously pour molten steel into the casting cavity through the mold pouring system. S4. When the molten steel level rises to a designated position below the predetermined height of the riser, stop pouring through the casting system. S5. Move at least one of the casting ladles so that its orifice is aligned with the riser pouring cup of the riser spot pouring system, and pour molten steel into the riser cavity through the riser spot pouring system to achieve physical isolation between the molten steel and the casting cavity at the end of the pouring process.

[0014] Furthermore, in step S5, the total switching time from stopping the mold pouring to starting the riser replenishment pouring is controlled to be completed within 10-20 seconds.

[0015] Furthermore, two casting ladles, one large and one small, are used; the large casting ladle carries all the molten steel used for the riser spot pouring in step S5 and part of the molten steel used for mold pouring; when switching casting, it is only necessary to move the trolley carrying the large casting ladle laterally so that its ladle hole is aligned with the riser pouring cup.

[0016] Furthermore, in step S2, the preset liquid level rise rate ranges from 10-15 mm / s; the total pouring flow rate Q is calculated according to the formula Q=G. 毛 ×V / H 铸 Calculate, where G 毛 V is the weight of the blank, V is the speed at which the liquid level rises, and H is the weight of the blank. 铸 This refers to the height of the mold.

[0017] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1) This invention completely separates the casting pouring path from the riser replenishment path through an independently set riser-based pouring system that is not connected to the mold pouring system. At the end of the pouring process, when the slag layer at the bottom of the ladle is easily entrained into the casting cavity with the molten steel, closing the ladle orifice and switching to the independent riser-based pouring system guides the slag-containing molten steel to the riser cavity, rather than the casting cavity. This operation provides dual isolation in terms of spatial path and pouring sequence, solving the industry problem of unavoidable slag entering the casting cavity at the end of large-scale multi-ladle combined pouring, and reducing the slag inclusion defect rate in castings.

[0018] 2) This invention employs a combined design in the casting system of "slow-flowing sprue and second sprue (double sprue) buffer + bottom slag collection trough + upper and lower two-layer horizontal runners for diversion + circumferentially distributed ingate bottom pouring". The double sprue and slag collection trough work together to reduce the initial impact force of the molten steel and collect early slag; the two-layer horizontal runners further disperse the flow rate of the molten steel; the circumferentially distributed ingate bottom pouring allows the molten steel to rise synchronously and smoothly from multiple positions at the bottom of the cavity. These structural features work synergistically to achieve high flow rate, low flow velocity, and clean filling. It reduces turbulence and splashing, facilitates the floating and removal of gas and small inclusions, improves the purity of the filling molten steel, and lays the foundation for obtaining a dense and uniform solidification structure in the casting.

[0019] 3) This invention simplifies the high-risk operation of casting changeover by placing the pouring cup of the riser-point casting system in the middle of the two pouring cups of the mold casting system, combined with a large and small ladle design. When a changeover is required, only a unidirectional horizontal movement of the trolley of the large ladle is needed to quickly and accurately align the ladle orifice with the pouring cup of the riser-point casting system, eliminating the need for complex multi-dimensional adjustments. This not only shortens the casting changeover time and avoids steel temperature drops or operational errors caused by alignment difficulties, but also improves the reliability, safety, and repeatability of ultra-large, multi-ladle collaborative casting processes.

[0020] 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

[0021] 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.

[0022] Figure 1a This is a top view of the upper half of the high-pressure outer cylinder casting system. Figure 1b This is a side view of the gating system for the upper half of the high-pressure outer cylinder mold. Figure 2 A three-dimensional structural diagram of the upper half of the high-pressure outer cylinder casting; Figure 3 A schematic diagram of the gating system layout for the first layer (left) and second layer (right) of the upper half of the high-pressure outer cylinder mold; Figure 4 This is a three-dimensional structural diagram of the lower half of the high-pressure outer cylinder casting. Figure 5a A top view showing the overall layout of the gating system and riser point gating system for the lower half of the high-pressure outer cylinder mold; Figure 5b A side view of the overall layout of the gating system and riser point gating system for the lower half of the high-pressure outer cylinder mold; Figure 6 A schematic diagram of the gating system layout for the first layer (left) and the second layer (right) of the lower half of the high-pressure outer cylinder mold; Figure 7 This is a diagram showing the locations of non-compliant points in the upper half of the inner cavity during UT testing, as shown in Example 1. Figure 8 This is a diagram showing the locations of non-compliant points in the lower half of the inner cavity during UT testing, as shown in Example 2. Figure 9 This is a diagram showing the locations of non-compliant UT tests in the upper half of the inner cavity of Comparative Example 1. Figure 10 This is a diagram showing the locations of non-compliant points in the lower half of the inner cavity during UT testing, as shown in Comparative Example 2.

[0023] Figure label: 1. Slow-flow sprue; 2. Slag collection trough; 3. Second sprue; 4. Lower horizontal sprue; 5. Upper horizontal sprue; 6. Ingate; 7. Mold pouring cup; 8. Riser pouring cup; 9. Riser sprue; 10. Riser horizontal sprue; 11. Riser ingate; 12. Riser cavity; 13. Lower cavity of high-pressure outer cylinder; 14. Upper cavity of high-pressure outer cylinder. Detailed Implementation

[0024] 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.

[0025] During the project, it was discovered that in the sand gravity casting of large nuclear power plant high-pressure outer cylinders, during the later stages of pouring, as the liquid level in the ladle drops, the slag accumulated at the bottom (such as deoxidation products and corroded refractory materials) easily enters the casting cavity with the molten steel, forming inclusions that are difficult to clean. Simultaneously, traditional single-gating systems struggle to simultaneously meet the demands of high flow rates and stable low-flow-rate filling, contributing to turbulence, air entrapment, and secondary oxidation, thus affecting the internal purity and solidification quality of the casting.

[0026] To address the aforementioned issues, this embodiment provides a gating system and method for casting high-pressure outer cylinders of megawatt nuclear power units, which completely separates the clean filling of the casting cavity from the slag-containing feeding of the riser cavity 12 in terms of spatial path and pouring sequence.

[0027] A specific embodiment of the present invention discloses a casting system for casting the high-pressure outer cylinder of a megawatt nuclear power unit, including a mold casting system and a riser spot casting system that are physically separated in space and have no direct or indirect connection with any channel for the flow of molten steel. The casting system is used to deliver molten metal to the casting cavity, including: a slow-flow sprue 1 and a second sprue 3 arranged in parallel, a slag collection trough 2 located at the bottom junction of the slow-flow sprue 1 and the second sprue 3, an upper horizontal sprue 5 and a lower horizontal sprue 4 connected to the sprue, and multiple sets of ingates 6 connected to the upper horizontal sprue 5 and the lower horizontal sprue 4 and arranged circumferentially along the casting cavity; The riser casting system is used to independently deliver molten metal to the riser cavity 12, and includes: a riser pouring cup 8, a riser sprue 9 connected to the riser pouring cup 8, a riser gating 10 connected to the riser sprue 9, and multiple sets of riser ingates 11 connected to the riser gating 10 and embedded in the sand core circumferentially along the riser cavity 12; The riser and pouring cup 8 is positioned on the horizontal projection plane along the line connecting the centers of the two pouring cups 7 of the casting system.

[0028] like Figures 1a to 6 As shown, the casting system consists of a high-pressure outer cylinder upper half casting system, a high-pressure outer cylinder lower half casting system, and a high-pressure outer cylinder upper half riser spot casting system and a high-pressure outer cylinder lower half riser spot casting system, which are respectively used in conjunction with the two half casting systems. All casting systems and corresponding riser spot casting systems are functionally independent, physically separated and without flow channel connections.

[0029] The physical separation and lack of flow channel connection means that the two systems do not share any molten steel flow pipes or cavities in three-dimensional space. They are independent molten steel introduction channels, ensuring that the molten steel flowing from the ladle follows two completely isolated paths when entering the casting cavity and the riser cavity 12. This structural design allows the high-slag-content molten steel at the end of the pouring process to be completely directed to the riser cavity 12, without entering and contaminating the already filled casting cavity.

[0030] For the upper and lower halves of the high-pressure outer cylinder casting structure, the dual systems are adapted and integrated separately: the upper half casting system and the matching upper half riser spot casting system are correspondingly integrated. Figure 1a , 1b and Figure 3 The layout shown is suitable for the forming of the upper half of the high-pressure outer cylinder casting; the lower half of the high-pressure outer cylinder casting system and the matching lower half riser spot casting system correspond to... Figure 5a , 5b and Figure 6 The layout shown is adapted for the forming of the lower half of the high-pressure outer cylinder casting, with both subsystems arranged together in the sand mold structure of the corresponding mold. Through this spatial layout design and the double-ladle staged pouring process, uniform filling of the casting cavity and directional feeding of the riser cavity 12 are achieved.

[0031] Specifically, the lower half of the high-pressure outer cylinder casting system is used to deliver molten metal to the lower cavity 13 of the high-pressure outer cylinder, and is the main channel for achieving clean and stable filling. For example... Figure 5a , 5b and Figure 6As shown in the figure, it includes: a slow pouring sprue 1 and a second sprue 3 arranged in parallel, a slag trap 2 provided at the bottom of both, an upper layer runner 5 and a lower layer runner 4 connected to the slow pouring sprue 1 and the second sprue 3, and multiple groups of mold inner runners 6 respectively connected to the upper layer runner 5 and the lower layer runner 4 and arranged circumferentially along the lower cavity 13 of the high-pressure outer cylinder.

[0032] Among them, the middle upper part of the slow pouring sprue 1 is connected to the upper layer runner 5, and the middle lower part is connected to the lower layer runner 4; the lower layer runner 4 is connected to the bottom horseback area of the lower cavity 13 of the high-pressure outer cylinder through the corresponding mold inner runner 6 to achieve bottom pouring; the upper layer runner 5 is connected to the flange area of the lower cavity 13 of the high-pressure outer cylinder through the corresponding mold inner runner 6. One ends of multiple groups of mold inner runners 6 are respectively connected to the lower layer runner 4 and the upper layer runner 5, and the other ends are directly connected to key parts such as the flange and barrel body of the lower cavity 13 of the high-pressure outer cylinder to ensure the smooth and orderly filling process of the molten metal. The slag trap 2 of this mold pouring system is of a ring structure, its inner diameter is larger than the outer diameter of the sprue, and the depth of the trough body is 100 - 150 mm; each pouring layer satisfies the total cross-sectional area ratio relationship: ∑A 包 :∑A 直 :∑A 横 :∑A 内 = 1.0:(1.8 - 2.0):(1.8 - 2.0):(2.0 - 2.5).

[0033] The structural composition, sprue design form, position connection relationship and dimensional parameters of the pouring system for the upper half mold of the high-pressure outer cylinder are completely the same as those of the pouring system for the lower half mold of the high-pressure outer cylinder, and only corresponding adaptation adjustments are made according to the size specifications of the upper half casting of the high-pressure outer cylinder. Its supporting upper half riser gating system also has the same structure as the lower half riser gating system and is adapted to the feeding requirements of the riser cavity 12 of the upper half casting.

[0034] Specifically, the lower half riser gating system supporting the pouring system for the lower half mold of the high-pressure outer cylinder is used to independently convey molten metal to the riser cavity 12, and it is a dedicated channel for receiving the late-stage slag-containing molten steel, achieving feeding and isolating the slag, and there is no intersection of any runners with the mold pouring system. This system includes: a riser pouring cup 8, a riser sprue 9 connected to the riser pouring cup 8, a riser runner 10 connected to the bottom of the riser sprue 9, and multiple groups of riser inner runners 11 connected to the riser runner 10 and buried inside the sand core along the circumference of the riser cavity 12. One ends of multiple groups of riser inner runners 11 are connected to the riser runner 10, and the other ends are connected to the riser cavity 12 to ensure the feeding effect of the thick and large parts of the casting; the total cross-sectional area of the riser sprue 9 is 1.8 - 2.0 times the total cross-sectional area of the pouring ladle holes for riser gating.

[0035] The upper riser gating system, which is matched with the upper half casting mold gating system of the high-pressure outer cylinder, has the same structure, gating design, position connection relationship and dimensional parameters as the lower riser gating system, and is adapted to the feeding requirements of the upper half casting riser cavity 12.

[0036] Combination Figure 5a As seen in the top view, the riser and pouring cup 8 of the lower half riser gating system of the high-pressure outer cylinder is positioned on the horizontal projection plane along the center line connecting the two casting pouring cups 7 of the lower half casting system, and the three are symmetrically distributed: specifically, they are collinear on the horizontal projection plane (i.e., coincident with the center line connecting the two casting pouring cups 7), and the horizontal distances from the riser and pouring cup 8 to the two casting pouring cups 7 are equal, forming an axisymmetric structure with the riser and pouring cup 8 as the center of symmetry. This layout can shorten the pouring ladle switching path, ensure rapid alignment, and improve operational reliability.

[0037] Similarly, the riser and pouring cup 8 of the upper half riser point pouring system of the high-pressure outer cylinder and the two pouring cups 7 of the matching upper half casting system are also symmetrically distributed as described above.

[0038] Specifically, the riser pouring cup 8 of the riser point pouring system is located horizontally between the two mold pouring cups 7. This layout can shorten the metal molten material transport path during double-ladle pouring, improve the synchronization of mold filling, and facilitate the rapid and precise pouring switching operation of this invention. When switching is required, the pouring ladle only needs to be moved horizontally along the direction of the center line to quickly align.

[0039] During implementation, the upper and lower halves of the high-pressure outer cylinder casting system are responsible for guiding clean molten steel into the corresponding upper and lower casting cavities, respectively. Taking the casting of the lower half of the high-pressure outer cylinder casting as an example: the molten steel flows out of the ladle through the ladle hole and first enters two parallel sprues (slow-flow sprue 1 and the second sprue 3), where the initial impact force is dispersed. When the molten steel flows to the annular slag collection trough 2 at the bottom, due to the change in flow direction and the decrease in flow velocity, the refractory material debris and slag generated in the early scouring, due to their lower density, settle and accumulate here, achieving primary purification of the molten steel. Subsequently, the purified molten steel is divided into two streams, which enter the upper horizontal sprue 5 and the lower horizontal sprue 4, respectively, where the flow rate is further evenly distributed. Finally, the molten steel is injected synchronously from multiple points at the bottom of the mold cavity at a low speed through dozens of ingates 6 that are evenly arranged around the bottom of the casting, achieving an ideal high-flow-rate, bottom-pouring, and stable filling mode, avoiding turbulence and splashing; the pouring process of the upper half of the high-pressure outer cylinder casting is completely consistent with that of the lower half of the casting.

[0040] After the upper and lower halves of the high-pressure outer cylinder castings are poured and cooled to the specified temperature through their respective gating systems, the two halves are first subjected to sand removal to remove auxiliary structures such as gating channels and risers. Then, the surface and interior of the castings are subjected to UT (ultrasonic) / RT (radiological) non-destructive testing and dimensional inspection to remove unqualified products. The two halves of the castings that pass the inspection are aligned together using special tooling fixtures to ensure that the mating surfaces fit tightly. Then, the joints of the two halves of the castings are welded together using welding technology. After welding, post-weld heat treatment is performed to eliminate welding stress. Finally, the whole is machined, subjected to overall non-destructive testing and performance testing to complete the overall forming of the high-pressure outer cylinder of the megawatt nuclear power unit.

[0041] Compared to the simple bottom-pouring systems in existing technologies, the pouring system provided by this invention utilizes a multi-stage structure of double sprues for buffering, slag collection trough 2 for purification, double-layer horizontal runners for diversion, and circumferential bottom pouring. This multi-stage structure significantly reduces the flow velocity and disturbance of molten steel within the mold cavity while meeting the requirements for rapid filling of large flow rates. The double sprues and slag collection trough 2 constitute the first-level unit, reducing the initial impact kinetic energy of the molten steel and intercepting early slag. The double-layer horizontal runners serve as the second-level unit, uniformly dispersing the molten steel and preventing localized overflow. The circumferentially distributed bottom-pouring ingates serve as the third-level unit, allowing the molten steel to rise synchronously and slowly from multiple positions at the bottom of the mold cavity. This three-stage series structure works synergistically, enabling the molten steel to fill the mold smoothly in a near-static pressure manner, greatly reducing turbulence, air entrapment, secondary oxidation, and erosion of the molding sand, thereby improving the purity and density of the internal structure of the casting.

[0042] Furthermore, each pouring layer of the casting system satisfies the following total cross-sectional area ratio: ∑A 包 :∑A 直 :∑A 横 :∑A 内 =1.0:(1.8-2.0):(1.8-2.0):(2.0-2.5), Where, ∑A 包 Let A be the total cross-sectional area of ​​the casting ladle orifice. 直 Let A be the total cross-sectional area of ​​the second straight gating channel 3. 横 The total cross-sectional area of ​​the upper horizontal gating 5 or the lower horizontal gating 4 is ∑A. 内 The total cross-sectional area of ​​all ingates 6 that are connected to the corresponding layer in the upper or lower horizontal runner 4.

[0043] Preferably, the total cross-sectional area of ​​the slow-casting straight-sprue 1 is the same as the total cross-sectional area of ​​the second straight-sprue 3.

[0044] This proportional relationship is set based on the fluid dynamics principle of the open gating system. For each gating layer, the flow cross-sectional area gradually increases from the sprue to the ingate. This is conducive to the smooth filling of the gating channel with molten steel and keeping the outlet flow velocity of the ingate within a reasonable range. If the total cross-sectional area of ​​the ingate is too small, the outlet flow velocity will be too high and turbulence will be easily caused. If it is too large, it may lead to insufficient filling pressure in the later stage of casting and cold shut.

[0045] In the specific design, the following calculations need to be performed for the upper and lower casting layers respectively: First, according to the large-orifice outflow theory formula (Where, q is the flow rate of molten steel through the ladle orifice, μ is the flow coefficient, usually taken as 0.8-0.9, A is the cross-sectional area of ​​the ladle orifice, g is the acceleration due to gravity, and h is the hydrostatic head height of the liquid surface inside the ladle.) Calculate the unit flow rate q of the selected orifice specification; then, based on the total pouring flow rate Q obtained in step S2, determine the required number of orifices n (n=Q / q, round up the calculation result), and obtain the total cross-sectional area of ​​the system's orifices ∑A. 包 .

[0046] Next, a layered design is implemented: for each pouring layer (upper or lower), the aforementioned proportional relationship (∑A) is followed. 包 :∑A 直 :∑A 横 :∑A 内 =1.0:(1.8-2.0):(1.8-2.0):(2.0-2.5)), with the total cross-sectional area of ​​the system's aperture ∑A 包 Using the base area (i.e., "1.0" in the scale), calculate the total cross-sectional area (∑A) of the direct gating system required for this layer. 直 ), total cross-sectional area of ​​the horizontal gating (∑A) 横 ) and the total cross-sectional area of ​​the ingate (∑A 内 ).

[0047] Wherein, the total cross-sectional area of ​​the straight gating channel (∑A) 直 This is the target cross-sectional area of ​​the single second straight gating channel 3 corresponding to this layer.

[0048] Finally, based on the common specifications of standardized circular ceramic refractory brick pipes (such as Φ60, Φ80, Φ100, Φ120, Φ140mm), the specific pipe diameter and arrangement quantity of each pouring channel are determined for each layer, thereby completing the quantitative design of the pouring system.

[0049] Furthermore, the slag collection trough 2 is an annular structure, located at the bottom intersection of the slow-casting sprue 1 and the second sprue 3, used to collect refractory material debris and molten slag generated during the initial pouring stage. The annular structure allows the flow direction of the molten steel to change gradually after flowing down from the two sprues, which facilitates the accumulation of the lighter molten slag towards the center and top of the annular trough under the action of centrifugal force and buoyancy. The inner diameter of the slag collection trough 2 is slightly larger than the outer diameter of the sprue, and the trough depth is designed to be 100-150mm. This depth provides sufficient space for slag collection, effectively collecting the large amount of molten slag and refractory material particles generated during the initial pouring stage due to the impact of the ladle nozzle opening or early scouring, thereby preventing these early impurities from entering the subsequent horizontal gating system and achieving primary purification of the molten steel.

[0050] Furthermore, the lower horizontal sprue 4 is connected to the bottom sprue area of ​​the casting cavity via the corresponding ingate 6, achieving bottom pouring; the upper horizontal sprue 5 is connected to the vicinity of the flange area of ​​the casting cavity via the corresponding ingate 6. This layered introduction method allows molten steel to be smoothly injected from the bottom of the cavity first, forming a stable rising front. For tall, high-pressure outer cylinder castings, the flange area is usually thicker and has obvious hot spots. The upper horizontal sprue 5 replenishes molten steel to this area in the middle and later stages of filling, which not only ensures full filling of this area and avoids cold shuts, but also uses the higher temperature of the molten steel in the later stages to provide some thermal compensation for the hot spots. This design helps to optimize the temperature distribution of the casting in the height direction, promotes sequential solidification from bottom to top, and avoids local overheating or solidification defects.

[0051] Furthermore, in the riser spot casting system, the total cross-sectional area of ​​the riser sprue 9 is designed to be 1.8-2.0 times the total cross-sectional area of ​​the pouring ladle orifice used for spot casting to the riser. This ensures that the replenished molten steel can enter the riser runner 10 at a lower flow rate and then flow out smoothly through the pre-embedded ingate. The controlled flow rate avoids splashing that might occur if the molten steel directly impacts the bottom of the riser cavity 12, or localized remelting of the already partially solidified casting surface below, thus maintaining an ideal sequential solidification temperature field and improving the riser's feeding efficiency.

[0052] Based on the structural design of the upper and lower halves of the high-pressure outer cylinder casting system and the matching riser spot casting system, this embodiment provides a casting method for the high-pressure outer cylinder of a megawatt nuclear power unit, including the following steps: S1. Construct the casting model and determine casting process parameters: Construct a 3D model of the casting based on the high-pressure outer cylinder drawings (e.g., using UG software), and define the upper half of the high-pressure outer cylinder (…). Figure 2 ), lower half ( Figure 4 The overall structural form of the casting process is determined, including the machining amount, the correction amount, the expansion rate, and the preset liquid level rise speed V.

[0053] S2. Calculate the pouring flow rate requirement: Based on the aforementioned three-dimensional model, process parameters, and mold height H... 铸 Calculate the blank weight G of the casting. 毛 The casting time T and the required total casting flow rate Q are given, where the formula for calculating the total casting flow rate Q is: Q = G 毛 ×V / H 铸 .

[0054] S3. At least two pouring ladles are used, with molten steel in large and small ladles, and molten steel is poured into the casting cavity simultaneously through the casting pouring system.

[0055] S4. When the molten steel level rises to a designated position below the predetermined height of the riser, stop pouring through the casting system.

[0056] S5. Move at least one of the casting ladles so that its orifice is aligned with the riser pouring cup 8 of the riser spot pouring system, and pour molten steel into the riser cavity 12 through the riser spot pouring system to achieve physical isolation between the molten steel and the casting cavity at the end of the pouring process.

[0057] This method employs a two-stage casting process: the first stage (steps S3-S4) utilizes a mold gating system to cleanly fill the casting cavity; the second stage (S5) utilizes an independent riser spot gating system to replenish the slag-containing cavity 12. The two stages are completely separated in time and space.

[0058] In implementation, the process design is first completed according to steps S1 and S2. During the molding stage, a casting gating system consisting of standard ceramic tubes is laid in the sand box strictly according to the design drawings, and the inner sprue of the riser gating system is pre-embedded when making the riser sand core. During the S3 pouring operation, a double-ladle (usually one large and one small) pouring is used. The ladles of the two pouring ladles simultaneously pour into the two casting gating cups 7 of the casting gating system, allowing the molten steel to smoothly fill the casting cavity through the aforementioned multi-stage buffer and diversion structure. Next, in S4, by observing the preset cavity liquid level mark or estimating by calculation time, when the molten steel level rises to a certain height (e.g., 300-600mm) from the bottom of the riser, all ladle orifices are quickly closed, ending the first stage. At this point, the large pouring ladle, carrying all or most of the molten steel used for replenishment, only needs its crane to make simple lateral movements to accurately align one ladle orifice with the riser gating cup 8 located precisely in the middle of the two casting gating cups 7. By opening the riser orifice, molten steel can be poured into the riser cavity 12 through an independent riser spot pouring system until the riser is full, thus completing the second stage, S5.

[0059] Compared to the traditional method in which all molten steel (including the clean and slag-containing stages) is injected through the same system and the replenishment flows through the hot spot area of ​​the casting, this method re-engineers the process, shifting the most risky final stage of slag-containing molten steel pouring from the casting cavity to the riser cavity 12. This design not only eliminates the possibility of final-stage slag entering the casting but also avoids interference from the already formed solidification front of the casting caused by the replenishment of high-temperature molten steel. The method uses a diversion process based on the cleanliness of the molten steel: clean molten steel is dedicated to casting body forming, while slag-containing risk molten steel is dedicated to riser feeding. This makes the previously difficult-to-completely avoidable final-stage slag inclusion defects controllable and avoidable, significantly improving the stability and reliability of the casting's internal quality.

[0060] Furthermore, in S5, the total switching time from stopping mold pouring to starting riser replenishment is controlled within 10-20 seconds. This time control takes into account the temperature drop and solidification characteristics of molten steel during the pouring of large castings. Excessive switching time would cause the temperature of the replenished molten steel to drop too much, resulting in poor fluidity, affecting the feeding effect, and potentially even causing crust formation in the runner. This method makes this rapid switching possible through layout and operational design.

[0061] Furthermore, in step S1, the preset liquid level rise speed V ranges from 10 to 15 mm / s. A speed that is too low (<10 mm / s) may cause the temperature at the molten steel front to drop too quickly, resulting in cold shuts or incomplete filling defects in thin-walled or complex structures; a speed that is too high (>15 mm / s) can easily lead to turbulent filling and severe air entrapment. For castings with large variations in wall thickness, such as high-pressure outer cylinders, fine adjustments can be made within the overall value range according to the characteristics of different areas. For example, a lower value (e.g., 10-12 mm / s) can be used for thicker parts, and a higher value (e.g., 13-15 mm / s) can be used for relatively thin-walled areas, or optimization can be achieved through computer solidification simulation.

[0062] Furthermore, in step S2, the total pouring flow rate Q is calculated according to the formula Q=G 毛 ×V / H 铸 Calculate, where G 毛 V is the weight of the blank, V is the speed at which the liquid level rises, and H is the weight of the blank. 铸 This refers to the height of the mold.

[0063] Furthermore, in step S3, two pouring ladles, one large and one small, are used. The large ladle carries all the molten steel used for the riser pouring in step S5, as well as part of the molten steel used for mold pouring. The small ladle carries the remaining molten steel used for mold pouring. When switching pouring ladles, only the trolley carrying the large ladle needs to be moved laterally to align its ladle opening with the riser pouring cup 8. This design, with its separate large and small ladles, simplifies the complex switching operation that requires coordinating two ladles into a unidirectional operation that only requires moving one ladle. This allows the operator to complete the alignment quickly and accurately, greatly reducing the risk of misoperation and minimizing the switching time, thereby maintaining the temperature and fluidity of the replenished molten steel and ensuring the feeding effect and process repeatability.

[0064] It should be noted that in step S4, the designated position is typically 300-600mm above the bottom of the riser. This range is chosen because: if the process stops too early (too far), shrinkage cavities may form at the top of the casting due to shrinkage, and the excessive amount of molten steel added later through the riser system could negatively impact the solidification of the top of the casting; if the process stops too late (too short), slag-containing molten steel may have already begun to enter the top of the casting cavity, negating the purpose of isolation. The 300-600mm range ensures that the casting body is completely filled with clean molten steel while also reserving sufficient molten steel for feeding into the riser.

[0065] This invention achieves effective control of defects such as shrinkage cavities and porosity in the high-pressure outer cylinder castings of megawatt-class nuclear power units by completely separating the casting system and the riser casting system in terms of function and space, combined with a two-ladle, staged casting process. The independently set riser casting system, with its centrally located pouring cup, allows the pouring ladle to quickly switch flow channels through simple unidirectional movement, thereby precisely guiding the slag-containing molten steel into the riser. The entire system can guide the molten steel to the casting cavity and riser cavity 12 according to the cleanliness of the molten steel, ensuring a smooth filling process while completely isolating the slag and molten steel.

[0066] 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.

[0067] Example 1 This example is used to cast the upper half of the high-pressure outer cylinder of a 1,000 kW nuclear power unit. The model structure is shown below. Figure 2 The main dimensions are 6880mm×5050mm×2345mm, and the net weight of the casting is 93 tons.

[0068] like Figure 1a , 1b and Figure 3As shown, the gating system of the present invention is provided with a physically independent mold gating system and a riser gating system that are not connected by flow channels.

[0069] The casting system includes a slow-flow sprue, a second sprue, a slag collection trough, an upper runner, a lower runner, and circumferentially distributed ingates. The slag collection trough is an annular structure with an inner diameter of Φ180mm and a depth of 200mm. The lower runner connects to the bottom saddle area of ​​the upper cavity of the high-pressure outer cylinder; the upper runner connects to the flange area, forming a filling method combining bottom and center pouring.

[0070] The riser gating system includes a riser gating cup, a riser sprue, a riser runner, and circumferentially distributed riser ingates.

[0071] All gating channels are composed of standard circular ceramic refractory brick pipes and refractory connectors (such as tees and reducing tees), with the joints sealed with high-temperature tape.

[0072] The specific pouring method is as follows: S1. Construct the casting model and determine the casting process parameters: Complete the 3D model based on the drawings. Determine the machining allowance as 30mm, the correction allowance as 15mm, the expansion rate as 1%, and the preset liquid level rise speed as V = 10 mm / s.

[0073] S2. Calculate the pouring flow rate requirement: Based on the model and process parameters, calculate the weight G of the casting blank. 毛 =125 tons. Casting height H 铸 =2400mm (including machining allowance). Calculate the casting time T=H 铸 / V=2400 / 10=240s. Calculate the total flow rate required for casting pouring: Q=G 毛 / T=125,000 / 240≈521kg / s. The total weight of the molten steel required is approximately 240 tons.

[0074] S3. Two casting ladles, one large and one small, are used. The large ladle holds 148 tons of molten steel (including all spot-cast steel), and the small ladle holds 92 tons. Casting is performed simultaneously through a mold-casting system, using a double-ladle, four-hole casting method. Based on the total flow rate Q = 521 kg / s and the theoretical outflow from the large hole, an 80mm diameter ladle hole is selected (corresponding to a single-hole flow rate qladle of approximately 150 kg / s). Therefore, the required number of ladle holes is n = Q / q. 包 =521 / 150≈3.47, rounded down to 4 holes. ∑A 包 =4×π×40 2 ≈ 20096 mm². Based on the proportion ∑A 包 :∑A 直 :∑A 横 :∑A 内A layered design is performed using the ratio 1:1.9:1.9:2.2. The target cross-sectional area required for each pouring layer is calculated as follows: ∑A 直 ≈38182mm², ∑A 横 ≈38182 mm², ∑A 内 ≈44211 mm².

[0075] Accordingly, in the casting system, Φ120mm ceramic tubes are selected as the first and second sprues (4 tubes) and as the tubes for the gating system; Φ60mm ceramic tubes are selected as the ingate, with 16 ingates per layer, for a total of 32 ingates across the two layers.

[0076] The riser-point gating system uses 12 Φ60mm ceramic tubes as the ingate, evenly embedded inside the riser core. Its sprue uses Φ110mm ceramic tubes, with a cross-sectional area approximately 1.89 times that of a single 80mm sprue used for point gating. The riser pouring cup (minimum diameter Φ110mm) of this riser-point gating system is located precisely in the middle of the pouring cups (minimum diameter Φ120mm) of the two casting systems. The gating systems are connected via refractory tees, reducing tees, and other fittings, with the connections sealed using high-temperature tape.

[0077] S4. When the molten steel level rises to 300mm from the bottom of the riser, quickly close all the ladle holes and stop casting.

[0078] S5. Move the trolley of the large bale laterally only, so that one of its bale holes is aligned with the riser cup, and perform replenishment pouring. The total switching time is controlled within 15 seconds until the riser is full.

[0079] The final casting was tested by UT and found to have excellent internal quality, very few inclusion defects, and a first-pass yield significantly higher than that of the traditional single casting process (see Comparative Example 1).

[0080] Example 2 This example is used to cast the lower half of the high-voltage outer cylinder of a 1,000 kW nuclear power unit (model shown). Figure 4 (Dimensions: 8506×5050×2605mm, Net Weight: 111 tons) Its casting system, layout, and operation steps are basically the same as those of Example 1, with the only difference being: S1. When constructing the casting model and determining the casting process parameters, the preset liquid level rise speed V=13mm / s; the slag collection tank depth is 200mm.

[0081] S2. Calculate the pouring flow rate requirement: Weight of the casting blank (G) 毛 =153 tons. Casting height H 铸 =2650mm. Calculations yield T=204s, Q=750 kg / s. The total weight of molten steel required is approximately 300 tons, using a double-ladle casting method.

[0082] S3. Two casting ladles, one large and one small, are used. The large ladle holds 165 tons, and the small ladle holds 135 tons. Casting is performed simultaneously through a mold-based gating system, using a double-ladle, four-hole combined casting method. The ladle orifice diameter is selected as 100mm (single-hole flow rate approximately 195kg / s). ∑A 包 =4×π×50² ≈31400 mm². The cross-sectional area ratio ∑A for each casting layer. 包 :∑A 直 :∑A 横 :∑A 内 A layered design is performed using a ratio of 1:2:2:2.5. The target cross-sectional area required for each pouring layer is calculated as follows: ∑A 直 ≈∑A 横 ≈62800 mm², ∑A 内 ≈78500 mm².

[0083] Accordingly, in the casting system, Φ140mm ceramic tubes are selected as the first and second sprues and the gating system; Φ80mm ceramic tubes are selected as the ingate, with 20 ingates arranged in each layer, for a total of 40 ingates. Figure 5a , 5b , Figure 6 Arrangement.

[0084] The riser-spotting system uses 12 Φ60mm ceramic tubes for the ingate. The sprue uses Φ140mm ceramic tubes. Spot casting uses a single Φ100mm orifice in a large ladle, and the sprue cross-sectional area is approximately 1.96 times the orifice cross-sectional area. The pouring cup is centrally located.

[0085] S4. When the molten steel level rises to 565mm from the bottom of the riser, stop casting.

[0086] S5. Move the ladle laterally for replenishment, and control the total switching time from stopping the mold pouring to starting the riser replenishment within 10 seconds.

[0087] The final casting was of good quality and passed non-destructive testing, effectively preventing steel slag from entering the casting cavity at the end of the process.

[0088] Comparative Example 1 A traditional single-gating system (without an independent riser point casting system, without a double-layer horizontal sprue, and without a double vertical sprue bottom slag collection trough) is used to cast the upper half of the high-pressure outer cylinder as described in Example 1. All molten steel (including the final stage) enters the mold cavity and riser through the same system.

[0089] As a result, UT testing of the castings revealed multiple point-like slag inclusions, significantly increasing the finishing time.

[0090] Comparative Example 2 The invention employs a dual-system structure, but the riser and pouring cup are not positioned on the center line connecting the two casting pouring cups; instead, they are positioned on the side. The pouring is performed as described in Example 2 for the lower half of the high-pressure outer cylinder.

[0091] As a result, during the casting switching, the crane needed to move the ladle and rotate it simultaneously to align it, with a switching time of up to 50 seconds. This caused a significant drop in the temperature of the molten steel being poured, and the riser feeding effect was not as good as in Example 2.

[0092] Characterization results and analysis The final castings of the above embodiments and comparative examples were subjected to comprehensive UT nondestructive testing. The distribution of non-conforming points is as follows: Figures 7-10 As shown, the key data is summarized in Table 1.

[0093] Table 1

[0094] From the comparison data in Table 1 and Figure 7-10 The defect distribution shows that Examples 1 and 2, employing the complete process of this invention, have significantly fewer defects detected by UT (11 and 3 respectively) than Comparative Example 1 (29 defects) with a traditional single casting system and Comparative Example 2 (22 defects) with improper riser and pouring cup positions. Furthermore, Examples 1 and 2 benefit from optimized riser and pouring cup positions, resulting in convenient and short casting switching (<15 seconds), effectively ensuring the temperature of the replenished molten steel. This contrasts sharply with Comparative Example 2, which suffers from difficult switching, leading to a longer switching time (~50 seconds) and a significant temperature drop. This fully demonstrates the comprehensive advantages of the process of this invention in reducing slag inclusions and ensuring the effectiveness of riser feeding.

[0095] In summary, this invention forms a complete, efficient, and reliable casting solution for large-scale nuclear power high-pressure outer cylinders. While ensuring high internal quality of the castings, it also improves the safety and efficiency of production operations, and has significant industrial application value.

[0096] 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 system for casting the high-pressure outer cylinder of a 1,000 kW nuclear power unit, characterized in that, This includes mold casting systems and riser spot casting systems that are physically separated in space and have no direct or indirect connection to any channel for the flow of molten steel; The casting system is used to deliver molten metal to the casting cavity, including: a slow-flow sprue (1) and a second sprue (3) arranged in parallel, a slag collection trough (2) located at the bottom intersection of the slow-flow sprue (1) and the second sprue (3), an upper horizontal sprue (5) and a lower horizontal sprue (4) connected to the sprue, and multiple sets of ingates (6) connected to the upper horizontal sprue (5) and the lower horizontal sprue (4) and arranged circumferentially along the casting cavity; The riser casting system is used to independently deliver molten metal to the riser cavity (12), and includes: a riser pouring cup (8), a riser sprue (9) connected to the riser pouring cup (8), a riser gating system (10) connected to the riser sprue (9), and multiple sets of riser ingates (11) connected to the riser gating system (10) and embedded in the sand core circumferentially along the riser cavity (12); The riser pouring cup (8) is located on the horizontal projection plane on the line connecting the centers of the two pouring cups (7) of the casting system, and the three are symmetrically distributed.

2. The casting system according to claim 1, characterized in that, Each pouring layer of the casting system satisfies the following total cross-sectional area ratio: ∑A 包 :∑A 直 :∑A 横 :∑A 内 =1.0:(1.8-2.0):(1.8-2.0):(2.0-2.5), Where, ∑A 包 Let A be the total cross-sectional area of ​​the casting ladle orifice. 直 The total cross-sectional area of ​​the second straight gating channel (3) is ∑A. 横 The total cross-sectional area of ​​the upper horizontal gating (5) or the lower horizontal gating (4) is ∑A. 内 The total cross-sectional area of ​​all ingates (6) that are connected to the corresponding layer in the upper horizontal runner (5) or the lower horizontal runner (4).

3. The casting system according to claim 1, characterized in that, The slag collection trough (2) is a ring structure with an inner diameter larger than the outer diameter of the direct casting channel and a trough depth of 100-150mm.

4. The casting system according to claim 1, characterized in that, The lower horizontal runner (4) is connected to the bottom back area of ​​the casting cavity through the corresponding mold ingate (6) to achieve bottom pouring; the upper horizontal runner (5) is connected to the flange area of ​​the casting cavity through the corresponding mold ingate (6).

5. The casting system according to claim 1, characterized in that, In the riser spot pouring system, the total cross-sectional area of ​​the riser direct pouring channel (9) is 1.8-2.0 times the total cross-sectional area of ​​the pouring pot hole used for spot pouring to the riser.

6. The casting system according to claim 1, characterized in that, Both the casting system and the riser casting system use standard circular ceramic refractory brick pipes for their gating channels, which are connected by refractory connectors.

7. A method for casting the high-pressure outer cylinder of a megawatt nuclear power unit using the casting system described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Construct a three-dimensional model of the casting based on the high-pressure outer cylinder drawings, and determine the casting process parameters, including machining amount, correction amount, expansion rate and preset liquid level rise speed. S2. Calculate the required total pouring flow rate based on the weight of the casting blank, the height of the mold, and the preset liquid level rise rate. S3. At least two pouring ladles are used to simultaneously pour molten steel into the casting cavity through the mold pouring system. S4. When the molten steel level rises to a designated position below the predetermined height of the riser, stop pouring through the casting system. S5. Move at least one of the casting ladles so that its orifice is aligned with the riser pouring cup (8) of the riser pouring system, and pour molten steel into the riser cavity (12) through the riser pouring system to achieve physical isolation between the molten steel and the casting cavity at the end of the pouring process.

8. The casting method according to claim 7, characterized in that, In step S5, the total switching time from stopping the mold pouring to starting the riser replenishment pouring is controlled to be completed within 10-20 seconds.

9. The casting method according to claim 7, characterized in that, Two casting ladles, one large and one small, are used. The large casting ladle carries all the molten steel used for the riser pouring in step S5 and part of the molten steel used for casting in the mold. When switching casting, it is only necessary to move the trolley carrying the large casting ladle laterally so that its ladle hole is aligned with the riser pouring cup (8).

10. The casting method according to claim 7, characterized in that, In step S2, the preset liquid level rise rate ranges from 10 to 15 mm / s; the total pouring flow rate Q is calculated according to the formula Q=G. 毛 ×V / H 铸 Calculate, where G 毛 V is the weight of the blank, and H is the speed at which the liquid level rises. 铸 This refers to the height of the mold.

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