Casting process for non-metal patch of large-scale high-temperature alloy casting

Abstract

The invention relates to the technical field of high-temperature alloy casting, in particular to a casting technology of a large-scale high-temperature alloy casting nonmetal patch. The casting technology comprises the following steps that a casting simulation model of a casting is built, and the position of a hot spot is determined through numerical simulation; constructing a heating core model based on the heating material characteristics and the heating patch feeding inclination 1: 5-8, and synchronously constructing the heating patch feeding inclination 1: 10 to design a metal patch model; comparing the temperature gradients of the heating core model and the metal patch model through numerical simulation; when the temperature gradient of the heating core model is larger than or equal to that of the metal subsidy model and no shrinkage porosity defect is displayed, heating core modularization parameters are stored, and otherwise, the feeding inclination parameter is iteratively adjusted until the standard is reached; manufacturing a core box and a heating core according to the modular parameters; and positioning and fixing the heating mold core in a casting mold, pouring and cooling. The non-metal patch replaces a metal patch, so that the production efficiency of the large-scale high-temperature alloy casting is improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature alloy casting, and in particular to a casting process for non-metallic patches of large high-temperature alloy castings. Background Art

[0002] Coal-fired power generation units include cylinder and valve body castings, most of which are made of ferritic steel with a Cr content of 9 to 12 wt%. The temperature parameter has developed to 630 ° C, which has reached the temperature parameter limit of this type of iron-based material. To break through the temperature parameter of 650 ° C and above, new alloy materials that are more resistant to high-temperature oxidation and corrosion are needed, such as new nickel-based and iron-nickel-based alloy materials with Ni ≥ 20 wt%.

[0003] At present, the traditional iron-based material casting process subsidy design uses metal subsidies to thicken parts to adjust the solidification temperature field of the casting, establish sequential solidification and shrinkage channels, ensure the internal quality of the product, and then remove them through hot cutting, gouging or machining. It is a mature process technology to manufacture cylinder and valve body castings based on metal subsidies and use traditional iron-based materials.

[0004] However, compared to traditional iron-based materials, new high-temperature alloys offer significant advantages in high-temperature performance for ultra-supercritical units operating at temperatures of 620°C and above. However, the following challenges exist in the manufacturing of large cylinders and valve casings: 1. High-temperature alloys have a higher alloy content than iron-based materials, and the metal shavings become non-recyclable slag after cutting, resulting in higher manufacturing costs. 2. High-temperature alloys have a large coefficient of thermal expansion and are prone to cracking. Using thermal cutting to remove the metal shavings can cause cracking in the product, resulting in high repair costs and a significant risk of scrap. 3. High-temperature alloys are austenitic materials with poor thermal conductivity, which can easily cause tool sticking during machining, making mechanical removal of the metal shavings inefficient. Currently, no effective method exists, either domestically or internationally, to effectively address these challenges in removing the metal shavings from high-temperature alloy castings.

[0005] In the existing technology, CN114951553A, CN117816937A, CN117444182A, etc. all disclose the use of heat-generating materials to make non-metallic subsidies during the casting process to replace metal subsidies and achieve the effect of falling off after casting. However, non-metallic subsidies are often used in the casting of small castings, such as pipes, fans, etc. Whether they can adapt to the casting of large castings with multiple curved surfaces and multiple hot spots is still a challenge. In particular, new alloy materials that are more resistant to high-temperature oxidation and corrosion are more likely to form casting defects due to casting hot spots. It is still challenging to use non-metallic subsidies for high-temperature alloy casting. Summary of the Invention

[0006] The present invention provides a casting process for non-metallic patches of large high-temperature alloy castings, which not only solves the problem of difficult removal of patches during casting of large high-temperature alloy castings, but also avoids new casting defects caused by replacing metal patches with non-metallic patches through sequential solidification simulation, thereby improving the production efficiency of large high-temperature alloy castings and reducing production costs.

[0007] The technical solution of the present invention to solve the above technical problems is as follows:

[0008] A casting process for non-metallic patches of large high-temperature alloy castings, comprising the following steps:

[0009] S1: Build a casting simulation model and determine the location of the hot spot through numerical simulation;

[0010] S2: Based on the characteristics of the heating material and the heating subsidy shrinkage slope of 1:5 to 8, a heating core model is constructed, and a metal subsidy model with a shrinkage slope of 1:10 is simultaneously constructed;

[0011] S3: Compare the temperature gradients of the heating core model and the metal patch model through numerical simulation; when the temperature gradient of the heating core model is greater than or equal to the metal patch model and no shrinkage defects are displayed, save the heating core modularization parameters; otherwise, iteratively adjust the heating core model parameters until they meet the standards;

[0012] S4: Make a core box according to modular parameters, fill it with heating material and shape it to prepare a heating core;

[0013] S5: Positioning the heating core to the hot-spot feeding channel in the casting mold, filling sand and drying to obtain a sand mold, and then pouring the high-temperature alloy melt;

[0014] S6: After the casting cools, the core collapses on its own and the internal density is verified by non-destructive testing.

[0015] In a specific embodiment of the present invention, the weight of the large high-temperature alloy casting is ≥5t and the wall thickness is ≥100mm.

[0016] In a specific embodiment of the present invention, the large high-temperature alloy casting is a large iron-nickel-based or nickel-based steel casting with Ni≥20wt%.

[0017] In a specific embodiment of the present invention, in step S1, the numerical simulation is based on numerical simulation software to simulate the sequential solidification process.

[0018] In a specific embodiment of the present invention, in step S2 and step S4, the maximum temperature of the heating material during combustion is ≥1500°C, the combustion duration is ≥50s, and the bulk density is 0.7-1.2g / cm 3 .

[0019] In a specific embodiment of the present invention, in step S2 and step S4, the heating core is formed by mixing and molding a heating material and a curing agent; the tensile strength after curing for 24 hours after mixing is ≥0.4 MPa; the heating material contains Al2O3 powder ≥38wt% and aluminum powder ≥20wt%; preferably, an alcohol-based paint with a thickness of ≥1mm is applied to the surface of the molded heating core.

[0020] In a specific embodiment of the present invention, the curing agent is any one or any combination of alkali phenolic resin, Piper resin, and water glass.

[0021] In a specific embodiment of the present invention, in step S5, the heating core is fixed in the sand mold by pre-embedding or core setting.

[0022] In a specific embodiment of the present invention, in step S5, the drying temperature is 100-200° C., and the drying time is 8-20 hours.

[0023] In a specific embodiment of the present invention, in step S5, the pouring temperature of the high temperature alloy is 1450-1550°C.

[0024] The beneficial effects of the present invention are as follows: 1. The present invention solves the problem that traditional metal subsidies are difficult to remove after casting large high-temperature alloy castings, improves production efficiency and saves manufacturing costs, and provides a new direction for casting process design;

[0025] 2. The present invention replaces metal filling with a heating core, thereby reducing the consumption of high-temperature alloy raw materials, reducing the removal of filler processes, reducing quality risks, and enhancing the core competitiveness of the enterprise.

[0026] 3. The present invention can be promoted and applied to all high-temperature alloy castings and steel castings, and will create higher social and economic value in future application and promotion.

[0027] 4. The heating core of the present invention can improve the casting process accuracy through numerical simulation, reduce the actual casting difference, solve the problem of insufficient adaptability of the traditional single feeding method to complex hot spots, and improve the feeding efficiency;

[0028] 5. The present invention ensures that the shrinkage feeding effect of the heating core is no less than that of the metal filling by comparing the temperature gradient and iteratively adjusting the heating core model, thereby avoiding shrinkage and shrinkage defects;

[0029] 6. The casting process of the present invention utilizes non-metallic subsidies to replace metal subsidies, combined with non-destructive testing, to comprehensively reduce material and labor costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the three-dimensional structure of an iron-nickel-based high-pressure inner cylinder model provided in a specific embodiment of the present invention;

[0031] Figure 2 A temperature gradient diagram of a metal patch provided for an embodiment of the present invention;

[0032] Figure 3 Temperature gradient diagram of non-metallic subsidies provided for specific embodiments of the present invention;

[0033] Figure 4 A three-dimensional schematic diagram of a core box for producing a heating core for a cast iron-nickel-based high-pressure inner cylinder provided in a specific embodiment of the present invention;

[0034] Figure 5 A schematic diagram of the three-dimensional structure of the heating core of the cast iron-nickel-based high-pressure inner cylinder provided in a specific embodiment of the present invention;

[0035] Figure 6 A schematic diagram of the casting mold structure of a cast iron-nickel-based high-pressure inner cylinder provided in a specific embodiment of the present invention.

[0036] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0037] 1. Iron-nickel based high pressure inner cylinder model; 2. Non-metallic patch; 3. Sand box; 4. Sand mold; 5. Cavity; 6. Riser; 7. Heating core. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0039] Casting as attached Figure 1 Taking the iron-nickel based high pressure inner cylinder as an example, a casting process for non-metallic subsidies of large high temperature alloy castings is provided, which includes the following steps:

[0040] S1: Build a casting simulation model and determine the location of the hot spot through numerical simulation;

[0041] Determining the location of the hot spot facilitates the structural design of the heating core in subsequent steps, ensuring that the heating core can improve the temperature gradient at the hot spot by adjusting the shrinkage compensation, thereby avoiding casting defects such as shrinkage and shrinkage cavities that are easily caused by the hot spot during the actual casting process. Specifically, numerical simulation is to input the casting simulation model into the numerical simulation software to simulate the sequential solidification process to determine the location of the hot spot. The sequential solidification process is based on the principle of sequential solidification. By placing risers and other process measures in thick and large areas of the casting where shrinkage cavities may occur, the areas away from the risers solidify first, followed by the areas close to the risers, and finally the risers themselves.

[0042] As attached Figure 1 As shown, after determining the hot spot position of the iron-nickel-based high-pressure inner cylinder model 1, the feeding riser is also determined simultaneously. The conventional casting process is to design a metal patch on the feeding channel side between the feeding riser and the hot spot position; this casting process is to design a non-metallic patch 2 at the same position as the metal patch. The surface structure of the non-metallic patch 2 fitting the side of the feeding channel should be the same as the surface structure of the metal patch after cutting.

[0043] S2: Based on the characteristics of the heating material and the heating subsidy shrinkage slope of 1:5 to 8, a heating core model is constructed, and a metal subsidy model with a shrinkage slope of 1:10 is simultaneously constructed;

[0044] The feeding slope refers to the inclination ratio of the cross-sectional size of the feeding channel gradually changing along the length direction. For example, a feeding slope of 1:10 means that for every 10 units of length increase, the cross-sectional width or height of the feeding channel increases by 1 unit. The heating core model and the metal patch model are designed in the numerical simulation software according to the feeding slope in the sequential solidification process, so as to realize the riser feeding slope of 1:10 to design the metal patch model, and to realize the riser feeding slope of 1:8 to design the heating core model. After the temperature gradient is tested in step S3, if the heating core model does not meet the requirements, the feeding slope of the heating patch is iteratively increased until the heating core model meets the requirements. The improvement of the temperature gradient at the hot node position is ≥ the metal subsidy model; in this way, the structural parameters of the heating core model can be quickly determined, which can reduce the design cost of replacing "metal subsidy" with "heating core" and improve efficiency; the structural parameters of the heating core model are saved, and can also provide a basis for subsequent numerical simulation of other large-scale high-temperature alloy castings of the same type; the heating core model corresponds to the number of metal subsidy models. Since large-scale high-temperature alloy castings may have multiple hot node positions through numerical simulation, each hot node position can be designed with a separate feeding riser and metal subsidy, so the heating core model needs to correspond to the metal subsidy model.

[0045] S3: Compare the temperature gradients of the heating core model and the metal patch model through numerical simulation; when the temperature gradient of the heating core model is greater than or equal to the metal patch model and no shrinkage defects are displayed, save the heating core modularization parameters; otherwise, iteratively adjust the shrinkage slope parameters until the target is met;

[0046] The metal patching model is a mature process method that improves shrinkage and shrinkage defects such as looseness and shrinkage cavities in large high-temperature alloy castings with multiple curved surfaces and multiple heat nodes by extending the feeding distance of the riser. The heating core model, on the other hand, mainly uses heat to extend the feeding time of the riser to improve defects such as looseness and shrinkage cavities. However, the heating temperature, heating duration, and strength of the heating core will affect the effectiveness of the heating core model in extending the feeding time of the riser, which can easily lead to the feeding channel being blocked due to solidification. By comparing the temperature gradients of the heating core model and the metal patching model through numerical simulation, it is possible to avoid solidification obstruction caused by insufficient feeding time of the heating core model, thereby improving the adaptability of the heating core model and the reliability of the process.

[0047] During numerical simulation comparison, a metal patch model and a heating core model were added to the casting simulation model. The location of the heating core model in the casting simulation model was the same as that of the metal patch model to eliminate the randomness caused by the different locations of the added models, reduce the error of the numerical simulation comparison, and improve the accuracy.

[0048] As attached Figure 2 、 3 As shown, the temperature gradient diagram of the sequential solidification process after the metal patch model is added is numerically simulated, and then the temperature gradient diagram of the sequential solidification process after the non-metal patch model is added is numerically simulated; according to the two temperature gradient diagrams, it is judged that the improvement effect of the heating core model on the temperature gradient of the hot node position is ≥ the improvement effect of the metal patch on the temperature gradient of the hot node position, and the heating core model satisfies the sequential solidification process after addition, then the structural parameters of the heating core model are modularly saved, otherwise it is necessary to iteratively adjust the compensation slope parameters and redesign the heating core model, and then perform numerical simulation and comparison on the redesigned heating core until the heating core meets the standards, and the structural parameters of the heating core are modularly saved.

[0049] The modular parameters of the heating core include but are not limited to the size, dimensions, and heating material of the heating core. If there are multiple heating core models, the modular parameters of each heating core model are saved separately for subsequent actual modeling, thereby achieving standardization and rapid production of large-scale high-temperature alloy castings.

[0050] During the simulation comparison process, the material of the heating core is set as a new heating material.

[0051] S4: Make a core box according to modular parameters, fill it with heating material and shape it to prepare a heating core;

[0052] In order to facilitate the molding of the heating core and to be able to remove it from the core box, the core box is designed with a core groove according to the size and dimensions of the heating core; after the molding is completed, the heating core is demoulded and removed from the core box, the size of the heating core is detected, and compared with the saved modular parameters to confirm that the size of the heating core is qualified for casting.

[0053] The modular parameters of the heating core are obtained by numerical simulation of the iron-nickel based high pressure inner cylinder model 1. The three-dimensional structure diagram of the core box is shown in the attached figure. Figure 4 The three-dimensional structure diagram of the heating core 7 prepared by filling the heating material in the core box is shown in the attached Figure 5 shown.

[0054] S5: Positioning the heating core to the hot-spot feeding channel in the casting mold, filling sand and drying to obtain a sand mold, and then pouring the high-temperature alloy melt;

[0055] The positioning of the heating core to the hot section feeding channel is the same as that of the metal patch to reduce the positioning difference that affects the casting quality of the casting.

[0056] See attached Figure 5 The casting mold shown is filled with molding sand in the sand box 3 to form a sand mold 4 required for casting the iron-nickel based high-pressure inner cylinder. The sand mold 4 has a mold cavity 5 and a riser 6. The heating core 7 obtained in step S4 is positioned to the position of the hot node shrinkage feeding channel and fixed, and then the filled sand is dried to obtain a sand mold. Finally, it is poured and solidified sequentially to obtain the iron-nickel based high-pressure inner cylinder.

[0057] S6: After the casting cools, the core collapses on its own and the internal density is verified by non-destructive testing.

[0058] As the casting solidifies after casting, the hot core collapses and falls off by itself during the boxing process, but it is still unknown whether the hot core can actually completely avoid defects in the casting due to thermal nodes. Through non-destructive testing, it is possible to actually detect whether there are defects such as shrinkage and shrinkage cavities inside the casting, and then the casting effect of the hot core can be evaluated. Of course, the results of non-destructive testing can be used as a basis for the subsequent training of the hot core model, which is beneficial to the optimization of the non-metallic compensation casting process of large high-temperature alloy castings, and can improve the efficiency and quality of large high-temperature alloy castings based on non-metallic compensation.

[0059] In some examples, the large high-temperature alloy casting has a weight of ≥5 t and a wall thickness of ≥100 mm.

[0060] In some examples, the large high-temperature alloy casting is a large iron-nickel based steel casting with Ni≥20 wt %.

[0061] In some examples, in step S1 , the numerical simulation is based on simulating a sequential solidification process using numerical simulation software.

[0062] In some examples, in step S2 and step S4, in order to ensure that the non-metallic compensation reduces the shrinkage defects caused by the hot spots, the maximum temperature of the heating material during combustion is ≥1500℃, the combustion duration is ≥50s, and the bulk density is 0.7-1.2g / cm 3 It should be noted that the combustion temperature and duration of the heating material will affect the shrinkage compensation effect during the actual casting process of large high-temperature alloy castings. Low combustion temperature and short duration can easily lead to insufficient heat generation during the entire sequential solidification process, resulting in casting defects in actual large high-temperature alloy castings due to hot spots.

[0063] In some examples, in step S2 and step S4, the heating core is formed by mixing and shaping a heating material and a curing agent;

[0064] In some examples, the ratio of the heating material to the curing agent is determined based on a tensile strength of ≥0.4 MPa after curing for 24 hours after mixing, so as to ensure the strength of the prepared heating core during the casting process and avoid casting size deviation.

[0065] In some instances, in the heating material, Al2O3 powder ≥38wt%, and aluminum powder ≥20wt%; specifically, the mass percentage of Al2O3 powder in the heating material is 38-80wt%, and the mass percentage of aluminum powder is 20-62wt%; the heating material also includes 0-42wt% of heat-generating / non-heat-generating secondary components.

[0066] In some embodiments, an alcohol-based coating having a thickness of ≥1 mm is applied to the surface of the heating core after molding.

[0067] In some examples, the curing agent is any one or any combination of alkali phenolic resin, Piper resin, and water glass.

[0068] In some instances, in step S5, the heating core is fixed in the sand mold by pre-embedding or core-down method; the heating core is exposed on the surface of the sand mold cavity, and its circumferential edge needs to be fixed during or before the sand filling process to avoid contact between its circumferential edge and the poured high-temperature alloy melt, to prevent erosion from damaging the heating core structure, to ensure the casting size of the casting, and to avoid mixing of heating materials into the casting to form adverse defects.

[0069] In some examples, in step S5, the drying temperature is 100-200° C., and the drying time is 8-20 hours.

[0070] In some examples, in step S5, the pouring temperature of the high temperature alloy is 1450-1550°C.

[0071] Through numerical simulation, the present invention can determine the structure of non-metallic subsidies quickly and at low cost, and use them to replace metal subsidies in casting large high-temperature alloy castings. On the one hand, it overcomes the problem that metal subsidies are difficult to remove. On the other hand, the non-metallic subsidies can fall off by themselves during the boxing process, thereby improving the production efficiency of large high-temperature alloy castings and saving manufacturing costs, providing a new direction for casting process design; the heating core can improve the casting process accuracy and reduce the actual casting differences through numerical simulation, solve the problem that the traditional single shrinkage feeding method has insufficient adaptability to complex hot nodes, and improve the shrinkage feeding efficiency.

Claims

1. A casting process for non-metallic patches of large high-temperature alloy castings, characterized in that: The following steps are involved: S1: Build a casting simulation model and determine the location of the hot spot through numerical simulation; S2: Based on the characteristics of the heating material and the heating subsidy shrinkage slope of 1:5 to 8, a heating core model is constructed, and a metal subsidy model with a shrinkage slope of 1:10 is simultaneously constructed; S3: Compare the temperature gradients of the heating core model and the metal patch model through numerical simulation; when the temperature gradient of the heating core model is greater than or equal to the metal patch model and no shrinkage defects are displayed, save the heating core modularization parameters; otherwise, iteratively adjust the heating core model parameters until they meet the standards; S4: Make a core box according to modular parameters, fill it with heating material and shape it to prepare a heating core; S5: Positioning the heating core to the hot-spot feeding channel in the casting mold, filling sand and drying to obtain a sand mold, and then pouring the high-temperature alloy melt; S6: After the casting cools, the core collapses on its own and the internal density is verified by non-destructive testing.

2. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 1, characterized in that: The large high-temperature alloy casting has a weight of ≥5t and a wall thickness of ≥100mm.

3. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 1, characterized in that: The large high-temperature alloy casting is a large iron-nickel-based or nickel-based steel casting with Ni≥20wt%.

4. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 1, characterized in that: Step S1, the numerical simulation is based on numerical simulation software to simulate the sequential solidification process.

5. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 1, characterized in that: In step S2 and step S4, the maximum temperature of the heating material during combustion is ≥1500°C, the combustion duration is ≥50s, and the bulk density is 0.7-1.2g / cm 3 .

6. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 1, characterized in that In steps S2 and S4, the heating core is formed by mixing and molding a heating material and a curing agent; the tensile strength after 24 hours of hardening after mixing is ≥0.4 MPa; the heating material contains Al2O3 powder ≥38wt% and aluminum powder ≥20wt%; preferably, an alcohol-based paint having a thickness of ≥1 mm is applied to the surface of the molded heating core.

7. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 6, characterized in that: The curing agent is any one or any combination of alkali phenolic resin, Piper resin, and water glass.

8. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 1, characterized in that: Step S5: The heating core is fixed in the sand mold by pre-embedding or core setting.

9. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 1, characterized in that: Step S5, the drying temperature is 100-200° C., and the drying time is 8-20 hours.

10. The casting process for non-metallic patches of large high-temperature alloy castings according to claim 1, characterized in that: Step S5: The pouring temperature of the high temperature alloy is 1450-1550°C.

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