Large steel casting 3D printing sand mold pouring system and molding method

Abstract

The invention relates to a large steel casting 3D printing sand mold pouring system and a molding method, belongs to the technical field of casting, and solves the problems that a sand mold pouring system prepared by an existing molding method is not resistant to high-temperature erosion, sand molding sand is easy to fall off and is involved into a casting to form casting defects and the like. The invention discloses a modeling method of a large steel casting 3D printing sand mold pouring system. The modeling method comprises the following steps that 1, a three-dimensional model of a sand mold is established, specifically, the three-dimensional model of the whole sand mold in which the position of a pouring gate in the pouring system and a ceramic tile pipe reserved gap are reserved is established; 2, 3D printing is carried out; 3, the outer surface of the ceramic tile pipe is coated with high-temperature-resistant epoxy resin glue, and the ceramic tile pipe is horizontally placed at the reserved position of the sand mold and completely cured; step 4, shaping; step 5, pouring; step 6, unboxing and cleaning; and step 7, finishing and flaw detection. The sand mold 3D printing is applied to the large casting with the net weight exceeding 30 tons, the production period is shortened, the cost is reduced, and the precision and quality of the large casting are improved.

Description

Technical Field

[0001] This invention relates to the field of casting technology, and in particular to a 3D printing sand casting system and molding method for large cast steel parts. Background Technology

[0002] The manufacturing of large cast steel parts is a fundamental industry in national equipment manufacturing, and its development level is an important indicator of a country's comprehensive national strength. Large cast steel parts are widely used in power plants, petrochemicals, metallurgy, shipbuilding, and other equipment manufacturing industries. Their manufacturing directly affects the quality, safety, and progress of key national projects, and is of great significance to the national economy and people's livelihood. The gating system is a crucial component of the casting process design for large cast steel parts. The gating system is the channel that guides molten metal into the mold cavity. It consists of the pouring cup, sprue, runner, and ingate, and directly impacts the quality and yield of large cast steel parts.

[0003] Traditional casting methods mainly use refractory bricks or ceramic brick tubes as the gating system, which has the advantages of high refractoriness, light weight and low gas content, and is usually used for sand casting.

[0004] Sand mold 3D printing technology, as an emerging manufacturing technology, is based on digital design and constructs sand molds layer by layer through printing. It has unique advantages, which can not only shorten the production cycle and reduce costs, but also improve the precision and quality of castings. For small and medium-sized castings, which are small in size and tonnage, have short pouring times, and are exposed to high-temperature molten steel for a short period of time, sand mold gating systems can meet the manufacturing requirements. Currently, small and medium-sized cast steel parts (net weight below 20 tons) can basically achieve fully intelligent casting throughout the entire process.

[0005] However, for large cast steel parts with a net weight of more than 20 tons, due to their large size and tonnage, the gating system is subjected to long-term corrosion by high-temperature molten steel. If the 3D printed sand mold gating system is still used, the molding sand is very likely to fall off and be caught in the casting, resulting in casting defects. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a 3D printing sand casting system and molding method for large cast steel parts, in order to solve at least one of the problems of existing molding methods for sand casting systems being unable to withstand high-temperature corrosion, and the molding sand easily falling off and being caught in the casting to form casting defects.

[0007] On one hand, embodiments of the present invention provide a modeling method for a 3D printing sand casting system for large cast steel parts, comprising the following steps:

[0008] Step 1: Create a 3D model of the sand mold: Create a 3D model of the overall sand mold that includes the reserved positions of the gating channels in the pouring system and the reserved gaps between the ceramic brick pipes;

[0009] Step 2: Import the 3D model of the integral sand mold into the 3D printer, and perform 3D printing, sand cleaning, coating, drying, and model assembly;

[0010] Step 3: Apply high-temperature resistant epoxy resin adhesive that has been powdered at temperatures above 800℃ to the outer surface of the ceramic tile tube, and place it horizontally in the reserved inner gating position of the sand mold. The high-temperature resistant epoxy resin adhesive will be fully cured at room temperature for 24 hours.

[0011] Step 4, Shaping: Lead out the ceramic brick tubes that were placed horizontally in the sand mold in Step 3, and connect them to the horizontal and vertical sprues on the outside of the sand mold in sequence to form the entire casting system;

[0012] Step 5, Pouring: The refined molten steel is poured through the refining bottom ladle in sequence through the straight sprue, the horizontal sprue, and the ingate. After pouring, a covering agent is sprinkled into the riser.

[0013] Step 6: Cleaning the riser: Clean the riser when the temperature at the root of the riser drops below 300℃.

[0014] Step 7: Finishing and flaw detection. Grind the surface of the casting to the roughness required for flaw detection and then perform ultrasonic flaw detection.

[0015] Furthermore, the modeling method includes the following steps before establishing the three-dimensional model of the sand mold:

[0016] S1. Use 3D software to create a 3D model of the casting, design the casting process, and combine the casting process design principles and casting characteristics to design the riser position and size, and determine the weight of the molten steel in the casting.

[0017] S2. Design the gating system: Set the size of the sprue based on the weight of the molten steel in the casting and the rising speed of the molten steel during filling; determine the size of the sprue, runner and ingate of the gating system based on the ratio of the total cross-sectional area of ​​the sprue to the total cross-sectional area of ​​the sprue, the total cross-sectional area of ​​the runner, and the total cross-sectional area of ​​the ingate.

[0018] Specifically, the riser size in step S1 is determined using the modular method, wherein the casting module M 铸 = Casting volume / Casting surface area, riser modulus M 冒 =kM 铸 Where k is the safety factor, with a value ranging from 1 to 1.25, and M... 铸 M 冒 The unit is cm; the volume of the casting is in cm³. 3 The surface area of ​​the casting is measured in cm². 2 .

[0019] Preferably, in step S2, the ratio of the total cross-sectional area of ​​the sprue to the total cross-sectional area of ​​the gating system to the total cross-sectional area of ​​the sprue to the total cross-sectional area of ​​the inlet is 1:(1.8~2):(1.8~2):(2.0~2.5).

[0020] It should be noted that after the casting system described in step 4 is formed, the area around the sand mold is filled with furan resin quartz sand.

[0021] For example, the covering agent in step 5 is carbonized rice husk.

[0022] On the other hand, embodiments of the present invention also provide a 3D printing sand casting system for large cast steel parts, which is prepared using the aforementioned molding method.

[0023] Specifically, the gating system includes a sprue, a runner, and an ingate; the sprue and runner are located outside the 3D printed sand mold and connected to the ingate located inside the sand mold; there is a gap between the ingate and the sand mold, and the gap is filled with high-temperature resistant epoxy resin.

[0024] Preferably, the material of the inner gating system is a ceramic brick tube.

[0025] Furthermore, the gap between the 3D printed sand mold and the ingate is 0.8-1.2mm.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0027] 1. The present invention provides a modeling method for a 3D printing sand mold casting system for large cast steel parts weighing over 20 tons. When establishing the three-dimensional model of the sand mold, the position of the gating channel of the casting system is reserved. After the overall sand mold is manufactured, ceramic brick pipes are used as the gating channel and placed horizontally in the reserved position of the sand mold. This greatly improves the high temperature resistance and corrosion resistance of the casting system, avoids the problem of molding sand falling off and being caught in the casting due to the long casting process, and meets the requirements for long-term casting of large cast steel parts.

[0028] 2. This invention applies high-temperature resistant epoxy resin to the outer surface of the ceramic brick tube before it is laid horizontally in the reserved position of the sand mold, filling the gap between the ceramic brick tube and the sand mold; this effectively avoids the problem of the ceramic brick tube breaking and being caught in the casting due to the pressure of high-temperature molten steel during the casting process, ensuring good overall quality of the casting and a high pass rate for flaw detection.

[0029] 3. This invention addresses the characteristics of ceramic brick tubes and high-temperature resistant epoxy resin adhesives that pulverize at high temperatures. By reserving the position of the pouring system and designing reasonable gaps while designing the three-dimensional sand mold model, it ensures that the ceramic brick tubes are arranged inside the 3D printed sand mold according to the designed pouring channel position and size, and that they will not break during the pouring process.

[0030] 4. The castings produced using the 3D printing sand casting system of this invention, with a net weight exceeding 30 tons, exhibit good overall quality. They passed flaw detection on the first attempt, with no internal defects found due to damage to the casting system. The flaw detection results showed that individual defects were less than 40 cm². 2 / 1000cm 2 The cumulative area of ​​defects is less than 300cm² 2 / 1000cm 2 .

[0031] 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

[0032] 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.

[0033] Figure 1 This is a schematic diagram of the structure of a large cast steel pad according to an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the design of a large cast steel shim casting and gating system according to an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the ingate structure of a large cast steel shim in an embodiment of the present invention;

[0036] Figure 4 This is an internal image of a large cast steel shim casting, Comparative Example 1 of the present invention.

[0037] Figure 5 This is an internal image of the large cast steel pad casting, which is a comparative example of the present invention.

[0038] Figure label:

[0039] 1- Cast steel shim; 2- 3D printed sand mold; 3- Riser; 4- 3D printed sand mold horizontal ceramic brick tube inlet; 5- Ceramic brick tube inlet connected to 3D printed sand mold horizontal ceramic brick tube; 6- Horizontal sprue; 7- Vertical sprue; 8- Steel ladle; 9- Bottom surface of casting. Detailed Implementation

[0040] 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.

[0041] Sand mold 3D printing technology, as an emerging manufacturing technology, is suitable for small and medium-sized castings with small size and tonnage, short pouring time, and short exposure of the gating system to high-temperature molten steel. A sand mold gating system can meet the manufacturing requirements. However, for large cast steel parts weighing over 20 tons, due to their large size and tonnage, the gating system is exposed to high-temperature molten steel for extended periods. Using a 3D printed sand mold gating system in this case is prone to sand detachment and entrapment into the casting, leading to casting defects. Refractory bricks or ceramic brick tubes are often used as gating systems in traditional sand casting due to their high refractoriness, light weight, and low gas content. However, the outer surface of ceramic brick tubes is not smooth, and their outer diameter has errors. Since 3D printing is a monolithic sand molding process, placing ceramic brick tubes directly into the formed 3D printed sand mold can lead to size mismatches. Furthermore, the high temperature and pressure of the molten steel during pouring, along with the long pouring time, can cause the ceramic brick tubes to break, resulting in internal defects in the casting.

[0042] On one hand, a specific embodiment of the present invention discloses a modeling method for a 3D printing sand casting system for large cast steel parts, comprising the following steps:

[0043] Step 1: Create a 3D model of the sand mold: Create a 3D model of the overall sand mold that includes the location and gaps of the gating system's runners;

[0044] Step 2: Import the 3D model of the integral sand mold into the 3D printer, and perform 3D printing, sand cleaning, coating, drying, and model assembly;

[0045] Step 3: Apply high-temperature resistant epoxy resin adhesive that has been powdered at temperatures above 800℃ to the outer surface of the ceramic tile tube, and place it horizontally in the reserved position of the sand mold. Use a scraper to remove the excess high-temperature resistant epoxy resin adhesive that overflows from both ends. The high-temperature resistant epoxy resin adhesive will be fully cured at room temperature for 24 hours. After curing, the ceramic tile tube should not move when pulled.

[0046] Step 4, Shaping: Lead out the ceramic brick tubes that were placed in the sand mold in Step 3, and connect them to the horizontal and vertical sprues on the outside of the sand mold in sequence to form the entire casting system. Then fill the area around the sand mold with furan resin quartz sand to prepare for casting.

[0047] Step 5, Pouring: The refined molten steel is poured through the straight gating channel, horizontal gating channel, and inner gating channel in sequence using a refining bottom ladle. After pouring, carbonized rice husk covering agent is sprinkled into the riser.

[0048] Step 6: Cleaning the riser: Clean the riser when the temperature at the root of the riser drops below 300℃.

[0049] Step 7: Finishing and flaw detection. Grind the surface of the casting to the roughness required for flaw detection and then perform ultrasonic flaw detection.

[0050] It should be noted that before establishing the three-dimensional model of the sand mold in step 1, the following steps are also included:

[0051] S1. Use 3D software to create a 3D model of the casting, design the casting process, and combine the casting process design principles and casting characteristics to design the riser position and size, and determine the weight of the molten steel in the casting.

[0052] S2. Design the gating system: Set the size of the sprue based on the weight of the molten steel in the casting and the rising speed of the molten steel during filling; determine the size of the sprue, runner and ingate of the gating system based on the ratio of the total cross-sectional area of ​​the sprue to the total cross-sectional area of ​​the sprue, the total cross-sectional area of ​​the runner, and the total cross-sectional area of ​​the ingate.

[0053] Furthermore, in step S1, the riser size is determined using the modular method, where the casting module M... 铸 = Casting volume / Casting surface area, riser modulus M 冒 =kM 铸 Where k is the safety factor, with a value ranging from 1 to 1.25. Based on the casting handbook, the safety factor for this casting is selected as 1.25; M 铸 M 冒 The unit is cm; the volume of the casting is in cm³. 3 The surface area of ​​the casting is measured in cm². 2 .

[0054] In one possible design, the casting is a cast steel pad. In step 1, the casting is equipped with a riser located at the center of the upper surface of the casting. The riser must ensure that the hot spot is fed back and that the feeding distance is guaranteed. Therefore, the riser is designed to be located at the center of the upper surface of the casting.

[0055] Preferably, the design of the gating system in step S2 is mainly related to the size of the ladle openings in the refining bottom ladle. The size of the ladle openings mainly affects the flow rate of molten steel poured per second, i.e., the pouring time of the molten steel. If the pouring time is too fast, the molten steel cannot rise steadily, resulting in incomplete pouring or splashing of molten steel. If the pouring time is too slow, the temperature of the molten steel decreases, leading to an excessively low temperature at the riser, which is not conducive to the feeding of the riser. Therefore, it is necessary to select an appropriate pouring time, i.e., an appropriate flow rate of molten steel. The formula for calculating the flow rate of molten steel is: q=(Q·V) / (n·H), where: q is the flow rate of molten steel, in kg / s; Q is the weight of the molten steel in the casting, in t; V is the rising speed of the molten steel during filling, in mm / s; n is the number of ladle openings, in units; and H is the height of the casting, in mm.

[0056] The size of the ladle is derived from the steel flow rate q and the steel flow velocity, and then the size of the gating system is determined by the size of the ladle; that is, the total cross-sectional area of ​​the ladle: the total cross-sectional area of ​​the sprue: the total cross-sectional area of ​​the gating runner: the total cross-sectional area of ​​the inlet = 1:(1.8~2):(1.8~2):(2.0~2.5);

[0057] In one possible design, the ratio of total cross-sectional area of ​​the sprue to total cross-sectional area of ​​the gating system to total cross-sectional area of ​​the runner to total cross-sectional area of ​​the inlet is 1:1.8:1.8:2.5.

[0058] Preferably, in step S2, a side-entry ingate is used, with the ingate 300mm from the bottom surface of the casting. The side-entry method is more convenient for laying the ceramic brick tube of the ingate horizontally than other methods. At the same time, in order to facilitate the smooth rise of molten steel and reduce the scouring of the cavity by molten steel, the height of the ingate should be lower than the parting surface of the casting.

[0059] The location and length of the ingate are designed reasonably according to the weight of the casting blank and the complexity of the casting shape. This facilitates the horizontal placement of ceramic brick tubes in the 3D printed sand mold, more effectively maintains the temperature of the molten metal during the flow process, avoids cold isolation and secondary solidification problems, reduces the generation of eddies and cavitation, ensures uniform solidification and quality of the casting, and improves the operability in the molding process.

[0060] Furthermore, in step 1, the optimal gap for the reserved inlet of the sand mold was verified to be 0.8-1.2mm;

[0061] If the reserved gap is less than 0.8mm, the ceramic tile tube may not be able to be inserted into the reserved inner gating channel. The high-temperature resistant epoxy resin will pulverize after being exposed to high-temperature molten steel, which will increase the gap between the ceramic tile tube and the sand mold. When the reserved gap is greater than 1.2mm, the increased gap between the ceramic tile tube and the sand mold will cause excessive pressure during long-term pouring, which may easily cause the ceramic tile tube to break.

[0062] Furthermore, the high-temperature resistant epoxy resin adhesive in step 3 is mainly composed of epoxy resin, curing agent and various fillers, and can be completely cured at room temperature in 24 hours.

[0063] In one possible design, the high-temperature resistant epoxy resin adhesive comprises bisphenol A type epoxy resin, methyltetrahydrophthalic anhydride, triphenylethylphosphonium bromide, propylene glycol, γ-methacryloyloxypropyltrimethoxysilane, and silicon dioxide.

[0064] High-temperature resistant epoxy resin adhesive can withstand temperatures above 800℃, but because it contains resin and curing agent, it will still produce gas and pulverize after being corroded by high temperature, which will increase the gap between the ceramic tile tube and the sand mold.

[0065] It should be noted that in step 4, the ceramic brick tubes used in step 3, which are placed horizontally inside the sand mold, are led out and connected to the horizontal and vertical runners outside the sand mold. The ceramic brick tubes are for casting and are connected in the form of a male and female joint. One end of the tube is designed with a flange (male joint) and the other end is designed with a groove (female joint) to achieve a tight connection between the tubes.

[0066] Preferably, in step 4, filling the area around the sand mold with furan resin quartz sand can enhance the bonding force between the quartz sand particles, allowing the sand mold to maintain its shape and structure during the casting process, preventing the sand mold from collapsing due to the impact and pressure of the molten metal, enabling the sand mold to withstand the high temperature of the molten metal, and reducing the wear of the sand mold.

[0067] Furthermore, in step 5, the covering agent mainly consists of carbonized rice husks, which serve to insulate the riser, slow down the solidification rate of the riser, and increase the riser's shrinkage efficiency.

[0068] It is worth noting that in step 6, before the cleaning of the riser root, the cleaning should be carried out after the temperature drops below 300°C to prevent premature cleaning from causing thermal cracks.

[0069] Furthermore, the flaw detection requires that the area of ​​a single defect be less than 40 cm². 2 / 1000cm 2 The cumulative area of ​​defects is less than 300cm² 2 / 1000cm 2 .

[0070] On the other hand, a specific embodiment of the present invention also discloses a 3D printing sand mold casting system for large cast steel parts, including a sprue, a gating system and an ingate; the sprue and gating system are located outside the 3D printing sand mold and connected to the ingate located inside the sand mold; there is a gap between the ingate and the sand mold, and the gap is filled with high-temperature resistant epoxy resin.

[0071] Furthermore, the material of the inner gating system is a ceramic brick tube.

[0072] The sprue and runner are located outside the 3D-printed sand mold, but they need to be surrounded by external sand. Ceramic brick tubes, as a casting system, have the advantages of high refractoriness, light weight, and low gas content.

[0073] It should be noted that the gap between the 3D printed sand mold and the inlet is filled with high-temperature resistant epoxy resin to ensure that the ceramic tile tube does not move and to prevent the ceramic tile tube from breaking due to high temperature and pressure.

[0074] Specifically, the large cast steel component is a cast steel shim with a net weight exceeding 30 tons.

[0075] In summary, the modeling method of the 3D printing sand mold casting system for large cast steel parts weighing over 20 tons of the present invention reserves the position of the gating system's inner runner when the three-dimensional sand mold model is established. After the overall sand mold is manufactured, ceramic brick tubes are used as the inner runners and placed horizontally in the reserved position of the sand mold. This greatly improves the high temperature resistance and corrosion resistance of the casting system, avoids the problem of molding sand falling off and being caught in the casting due to the long casting process, and meets the usage requirements of long-term casting of large cast steel parts. In view of the characteristics of ceramic brick tubes and high-temperature resistant epoxy resin adhesive that powder at high temperatures, the position of the gating system is reserved and a reasonable gap is designed when designing the three-dimensional sand mold model. This ensures that the ceramic brick tubes are arranged inside the 3D printed sand mold according to the designed gating position and size, and the high-temperature resistant epoxy resin adhesive is applied to the outer surface of the ceramic brick tubes to ensure that they will not break during the casting process.

[0076] The following describes the 3D printing sand casting system and molding method for large cast steel parts of the present invention with reference to specific embodiments.

[0077] Example 1

[0078] This embodiment provides a 3D printing sand casting system and molding method for large cast steel parts.

[0079] In this embodiment, the large cast steel component is a cast steel shim 1, with outline dimensions of 2700×1350×1200mm. For specific structure and dimensions, please refer to [link / reference needed]. Figure 1 , Figure 2 The casting has a net weight of 34.2 tons and a liquid weight of 69.4 tons.

[0080] A method for creating a 3D printed sand casting system for large cast steel parts, including the following steps:

[0081] Step 1: Design the three-dimensional model and casting process of cast steel pad 1. Based on the casting process design principles and casting characteristics, design the position and size of riser 3.

[0082] (1) Riser design: The riser must ensure feeding at the hot spot and also guarantee the feeding distance. Therefore, the riser is designed at the center of the upper surface of the casting; then, according to M 铸 = Casting volume / Casting surface area determines the casting modulus to be 24.5 cm²; through the riser, the modulus M 冒 (cm)=1.25M 铸 The riser modulus was calculated to be 30.625 cm, and then based on M... 冒 = Riser volume / riser surface area determines the riser size to be φ1700mm × 2000mm (height);

[0083] (2) Numerical simulation: Numerical simulation of the temperature field and shrinkage porosity trend during the solidification process of the designed casting process is carried out. The casting process is adjusted through simulation results to ensure that there are no defects such as shrinkage porosity and structural shrinkage in the casting, and that the temperature field of the casting is uniform, so as to achieve sequential solidification of the casting first and the riser later.

[0084] Step 2: Design the casting system: Based on the steel flow rate formula, the ladle bore size for the shim casting is calculated to be φ100mm. Then, based on the ratio of the cross-sectional areas of the casting system (total cross-sectional area of ​​the bore: total cross-sectional area of ​​the sprue: total cross-sectional area of ​​each layer of the gating runner: total cross-sectional area of ​​each layer of the inlet = 1:1.8:1.8:2.5), the dimensions of each part of the casting system are determined. The sprue diameter is φ140mm, the gating runner diameter is φ140mm, and the inlet is set with entry from both sides of the shim, with an inlet diameter of φ60mm. To ensure the ceramic tile tubes are horizontally placed within the sand mold, the shim uses a side-entry inlet. Figure 3 As shown, the height of the ingate from the bottom surface 9 of the casting is 300mm. Lowering the height of the ingate facilitates the smooth rise of molten steel and reduces the scouring of the mold cavity by the molten steel.

[0085] Step 3: Establish a 3D model of the overall sand mold, including the location and gap of the inlet gate in the gating system. Using castings, risers, and the gating system as tools, calculate the difference between the overall sand mold and the model to create a 3D model of the entire sand mold. The 3D model of the overall sand mold needs to design the location of the inlet gate and the gap between the ceramic brick tube and the sand mold. For the 3D printed sand mold, the horizontal ceramic brick tube inlet gate 4 is selected as φ60mm, corresponding to an inner diameter of φ60mm and an outer diameter of φ74mm. The gap between the ceramic brick tube and the sand mold is selected as 1mm. The designed reserved position size of the sand mold gating system is φ76mm.

[0086] Step 4: Import the 3D model of the overall sand mold into the 3D printer, and perform 3D printing, sand cleaning, coating, drying, and model assembly.

[0087] Step 5: Apply high-temperature resistant epoxy resin to the outer surface of the φ60mm ceramic tube. Place the coated ceramic tube horizontally in the reserved position of the 3D printed sand mold 2. Use a scraper to remove the excess high-temperature resistant epoxy resin from both ends. The high-temperature resistant epoxy resin will be fully cured at room temperature for 24 hours. After curing, the ceramic tube should not move when pulled.

[0088] Step 6, Shaping: Connect the inner gating system of the 3D printed sand mold to the φ60mm ceramic brick tube to form the entire gating system, including the straight gating 7, the horizontal gating 6, the inner gating system 4 of the horizontal ceramic brick tube of the 3D printed sand mold, and the inner gating system 5 of the ceramic brick tube connected to the horizontal ceramic brick tube of the 3D printed sand mold. Then fill the area around the sand mold with furan resin quartz sand to prepare for the pouring.

[0089] Step 7, Casting: The smelting method adopts refining. The casting temperature is controlled at 1545-1560℃. The ladle has 8 holes with a diameter of φ90mm. During casting, pay attention to the casting situation and close the ladle holes in time. After casting is completed, sprinkle carbonized rice husk covering agent into the riser.

[0090] Step 8: Cleaning and Unpacking: When the temperature at the riser root drops to 300℃, unpack the casting. First, remove the loose sand from the top of the casting to expose the lifting shaft. Remove as much dry sand as possible from around the casting. Use a special steel rope to hold the lifting shaft and lift slowly. During lifting, ensure that multiple ropes are under tension simultaneously; do not allow only one or two ropes to bear the load, otherwise the casting will deform significantly or even break. Handle the casting gently during lifting and sand removal to avoid collisions. After cleaning, remove the riser using flame cutting. After riser removal, tempering is required to relieve stress and prevent cold cracking of the casting.

[0091] Step 9: Finishing and flaw detection. Grind the surface of the pad to the required roughness for flaw detection, and then perform ultrasonic flaw detection. Use the longitudinal wave vertical reflection method, and select a longitudinal wave straight probe.

[0092] Flaw detection shall be performed in accordance with CCH70-4 standard, and the flaw detection level shall be performed according to ultrasonic flaw detection level 4, which requires that the area of ​​a single defect be less than 40 cm². 2 / 1000cm 2 The cumulative area of ​​defects is less than 300cm² 2 / 1000cm 2 The specific flaw detection conditions and results are shown in Table 1.

[0093] The cast steel pad casting produced by the 3D printing sand casting system molding method for large cast steel parts in this embodiment has good overall quality, and the flaw detection requirements are strict and the flaw detection is qualified on the first attempt.

[0094] Comparative Example 1

[0095] Based on Example 1, a method for modeling a 3D printing sand mold casting system for large cast steel parts is provided, the difference being that ceramic brick tubes are not used as the casting system in steps 3 to 6, but sand mold ingate is used as the casting system, and the size of the sand mold ingate is φ60mm.

[0096] After the insulation is poured, fine finishing and flaw detection are carried out. The specific flaw detection results are shown in Table 1.

[0097] An overall dissection of the cast steel shim revealed a large number of inclusions inside the casting. Composition analysis showed that the inclusions were mainly composed of O, Si, and Al, indicating a sand inclusion defect. The inclusion details are shown in Table 2. This indicates that due to the high pouring temperature and long pouring time, the sand mold gating system was subjected to prolonged erosion by the high-temperature molten steel, causing the sand mold to collapse rapidly. This resulted in the sand falling off and being incorporated into the casting, forming a casting defect and causing the casting to exceed the flaw detection standards.

[0098] Comparative Example 2

[0099] The modeling method of a large cast steel 3D printing sand casting system is the same as that in Example 1, except that the gap between the ceramic brick tube and the sand mold is selected to be 3mm in step 3, and the reserved position size of the designed sand casting system is φ80mm.

[0100] After the insulation is poured, fine finishing and flaw detection are carried out. The specific flaw detection results are shown in Table 1.

[0101] An overall dissection of the cast steel shim revealed a small number of inclusions inside the casting. Composition analysis showed that these inclusions were mainly composed of O, Al, Zr, and N, which should be the main components of the ceramic brick pipe. The inclusion details are shown in Table 2. This indicates that the high-temperature resistant epoxy resin will pulverize after being exposed to high-temperature molten steel, leading to an increase in the gap between the ceramic brick pipe and the sand mold. Excessive pressure during long-term pouring caused the ceramic brick pipe to break, forming a casting defect and resulting in the casting failing the flaw detection test.

[0102] Comparative Example 3

[0103] The modeling method of a large cast steel 3D printing sand casting system is the same as that in Example 1. The difference is that in step 3, the gap between the ceramic brick tube and the sand mold is selected to be 0.5mm, and the reserved position size of the designed sand casting system is φ75mm. At this time, because the surface of the ceramic brick tube is not smooth and the gap is too small, it cannot be laid flat in the reserved position.

[0104] Table 1. Flaw detection conditions and results for the examples and comparative examples.

[0105]

[0106] Table 2. Types of inclusions in Comparative Examples 1 and 2

[0107] serial number Morphology of inclusions Inclusion composition Comparative Example 1 like Figure 4 As shown O, Si, Al Comparative Example 2 like Figure 5 As shown O, Al, Si, Zr, N

[0108] As can be seen from Tables 1 and 2, compared with Example 1, Comparative Example 1, using a sand mold ingate as the gating system, resulted in the detachment and entrapment of molding sand into the casting, forming casting defects and causing the casting to exceed the flaw detection standards. Compared with Example 1, Comparative Example 2 had an excessively large gap between the ceramic brick tube and the sand mold. Under long-term high-pressure pouring, the high-temperature epoxy resin powdered, further increasing the gap between the ceramic brick tube and the sand mold, causing the ceramic brick tube to break during the pouring process, forming casting defects and causing the casting to exceed the flaw detection standards. Compared with Example 1, Comparative Example 3 had an excessively small gap between the ceramic brick tube and the sand mold. Due to the uneven surface of the ceramic brick tube and other errors, the ceramic brick tube could not be placed.

[0109] In summary, the modeling method of the 3D printing sand mold casting system for large cast steel parts weighing over 20 tons of the present invention reserves the position of the gating system's inner runner when the three-dimensional sand mold model is established. After the overall sand mold is manufactured, ceramic brick tubes are used as the inner runners and placed horizontally in the reserved position of the sand mold. This greatly improves the high temperature resistance and corrosion resistance of the casting system, avoids the problem of molding sand falling off and being caught in the casting due to the long casting process, and meets the usage requirements of long-term casting of large cast steel parts. In view of the characteristics of ceramic brick tubes and high-temperature resistant epoxy resin adhesive that powder at high temperatures, the position of the gating system is reserved and a reasonable gap is designed when designing the three-dimensional sand mold model. This ensures that the ceramic brick tubes are arranged inside the 3D printed sand mold according to the designed gating position and size, and the high-temperature resistant epoxy resin adhesive is applied to the outer surface of the ceramic brick tubes to ensure that they will not break during the casting process.

[0110] 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 molding method for a 3D printed sand casting system for a large steel casting, characterized in that: The steps include: Step 1, establish a three-dimensional model of the sand mold: establish a three-dimensional model of the overall sand mold with the location of the pouring channel in the pouring system and the reserved gap of the ceramic brick tube; Step 2: Import the three-dimensional model of the whole sand mold into the 3D printer for 3D printing, sand cleaning, coating, drying and molding; Step 3: Apply high temperature resistant epoxy resin glue powdered at a temperature of more than 800°C to the outer surface of the ceramic brick tube, and place it horizontally at the reserved inner runner position of the sand mold. The high temperature resistant epoxy resin glue is completely cured at room temperature for 24 hours; Step 4, molding: lead out the ceramic brick tube placed horizontally in the sand mold in step 3, and connect the horizontal runner and the vertical runner outside the sand mold in sequence to form the entire pouring system; Step 5, pouring: pour the refined molten steel through the sprue, runner and inner pouring channel in sequence with a refining bottom ladle, and sprinkle a covering agent into the riser after the pouring is completed; Step 6: Box cleaning: When the temperature at the root of the riser drops below 300℃, box cleaning is performed; Step 7: Finishing inspection: Grind the casting surface to a roughness that meets the requirements for inspection and perform ultrasonic inspection.

2. The molding method according to claim 1, characterized in that: Before building the three-dimensional model of the sand mold, the following steps are also included: S1. Use 3D software to build a 3D model of the casting, design the casting process, combine the casting process design principles and casting characteristics, design the riser position and size, and determine the weight of the molten steel of the casting; S2. Design the pouring system: set the size of the hole according to the weight of the molten steel of the casting and the rising speed of the molten steel when filling the mold; determine the sizes of the sprue, runner and inner runner of the pouring system according to the proportional relationship between the total cross-sectional area of ​​the hole: the total cross-sectional area of ​​the sprue: the total cross-sectional area of ​​the runner: the total cross-sectional area of ​​the inner water inlet.

3. The molding method according to claim 2, characterized in that: The riser size in step S1 is determined by the modulus method: the casting modulus M 铸 = casting volume / casting surface area, riser modulus M 冒 =kM 铸 , where k is the safety factor, and its value range is 1-1.25, M 铸 、M 冒 The unit is cm, the casting volume unit is cm 3 , casting surface area unit is cm 2 .

4. The molding method according to claim 2, characterized in that: The total cross-sectional area of ​​the package hole in step S2: the total cross-sectional area of ​​the straight runner: the total cross-sectional area of ​​the horizontal runner: the total cross-sectional area of ​​the inner nozzle = 1: (1.8 ~ 2): (1.8 ~ 2): (2.0 ~ 2.5).

5. The molding method according to claim 1, characterized in that: After the pouring system described in step 4 is formed, the surrounding of the sand mold is filled with furan resin quartz sand.

6. The molding method according to claim 1, characterized in that: The covering agent in step 5 is carbonized rice husk.

7. A large steel casting 3D printing sand casting system, characterized in that: The product is prepared by the molding method described in any one of claims 1 to 6.

8. The pouring system according to claim 7, characterized in that: It includes a straight runner, a cross runner and an ingrate; the straight runner and the cross runner are located outside the 3D printing sand mold and are connected to the ingrate located inside the sand mold; there is a gap between the ingrate and the sand mold, and the gap is filled with high-temperature resistant epoxy resin glue.

9. The pouring system according to claim 8, characterized in that: The ingrate material is a ceramic brick tube.

10. The pouring system according to claim 8, characterized in that: The gap between the 3D printing sand mold and the inner runner is 0.8-1.2 mm.

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