A large-scale cast steel 3D printing sand mold pouring system and molding method

Abstract

The present application relates to a kind of large steel casting 3D printing sand mould pouring system and molding method, belong to the field of foundry technology, solve the sand mould pouring system prepared by the existing molding method is not resistant to high temperature erosion, sand mould sand is easy to fall off, form casting defects such as being rolled into casting.The molding method of a kind of large steel casting 3D printing sand mould pouring system, including the following steps: step 1, establish the three-dimensional model of sand mould: establish the three-dimensional model of the whole sand mould with the position of the gate in the pouring system and the ceramic brick pipe reserved gap is reserved;Step 2, 3D printing is carried out;Step 3, the outer surface of ceramic brick pipe is smeared with high-temperature resistant epoxy resin glue, and is laid in the sand mould reserved position, and is completely solidified;Step 4, molding;Step 5, pouring;Step 6, box cleaning;Step 7, finishing inspection.The sand mould 3D printing is applied to large casting with net weight exceeding 30 tons, shortens production cycle, reduces cost, and improves the precision and quality of large casting.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of casting, in particular to a 3D printing sand mold pouring system for large steel castings and a molding method. BACKGROUND

[0002] The manufacturing industry of large steel castings is a basic industry of national equipment manufacturing, and its development level is an important indicator to measure the comprehensive national power of a country. Large steel castings are widely used in power stations, petrochemical industry, metallurgy, shipbuilding and other equipment and equipment manufacturing industry, and their manufacturing is directly related to the quality, safety and progress of national key projects, which is of great significance to the people's livelihood. The pouring system is an important part of the design of the casting process of large steel castings. The pouring system is a channel in the sand mold that guides the liquid metal into the mold cavity. The pouring system is composed of a pouring cup, a straight runner, a cross runner and an inner gate, and the pouring system directly affects the quality and yield of large steel castings.

[0003] The traditional casting method mainly uses refractory bricks or ceramic brick pipes as the pouring system, which has the advantages of high refractoriness, light weight and low gas content, and is usually used for sand casting.

[0004] Sand 3D printing technology, as a new manufacturing technology, is based on digital design and builds sand molds through layer-by-layer printing, which has unique advantages. This technology not only shortens the production cycle and reduces costs, but also improves the precision and quality of castings. For small and medium-sized castings, the size and tonnage are small, the pouring time is short, and the pouring system is eroded by high-temperature molten steel for a short time. The sand mold pouring system can meet the manufacturing requirements. At present, small and medium-sized steel castings (net weight less than 20 tons) can basically realize full-process intelligent casting.

[0005] However, large steel castings with a net weight of more than 20 tons have large size and tonnage, and the pouring system is eroded by high-temperature molten steel for a long time. If the 3D printing sand mold pouring system is still used, the sand mold is easy to fall off and be rolled into the casting, resulting in casting defects. SUMMARY

[0006] In view of the above analysis, the embodiments of the present application aim to provide a 3D printing sand mold pouring system for large steel castings and a molding method, which can solve at least one of the problems of the existing molding method, such as the sand mold pouring system not being resistant to high-temperature erosion, the sand mold being easy to fall off and being rolled into the casting to form casting defects, etc.

[0007] In one aspect, the embodiments of the present application provide a molding method for a 3D printing sand mold pouring system for large steel castings, comprising the following steps:

[0008] Step 1, establishing a three-dimensional model of the sand mold: establishing a three-dimensional model of the overall sand mold with a reserved position of the inner gate of the pouring system and a reserved gap of the ceramic brick pipe;

[0009] Step 2, import the three-dimensional model of the whole sand mold into the 3D printer, and perform 3D printing, sand cleaning, coating, drying, and mold assembly;

[0010] Step 3, apply high-temperature resistant epoxy resin glue above 800℃ to the outer surface of the ceramic brick pipe, and place it in the inner runner position reserved in the sand mold. The high-temperature resistant epoxy resin glue is completely cured at room temperature for 24 hours;

[0011] Step 4, molding: the ceramic brick pipe placed in the sand mold in step 3 is pulled out and connected to the cross runner and straight runner outside the sand mold in sequence to form the entire pouring system;

[0012] Step 5, pouring: the refined molten steel is poured through the straight runner, cross runner, and inner runner in sequence using a refining bottom hole package. After pouring is completed, covering agent is poured into the riser;

[0013] Step 6, box striking and cleaning: when the temperature at the root of the riser drops below 300℃, the box is struck and cleaned;

[0014] Step 7, finishing and flaw detection, polishing the surface of the casting to meet the roughness of flaw detection, and performing ultrasonic flaw detection.

[0015] Further, the molding method further comprises the following steps before establishing the three-dimensional model of the sand mold:

[0016] S1, a three-dimensional model of the casting is established using three-dimensional software, a casting process is designed, the riser position and size are designed in combination with the casting process design principles and the characteristics of the casting, and the weight of the casting molten steel is determined;

[0017] S2, design the pouring system: set the package hole size according to the weight of the casting molten steel and the rising speed of the casting molten steel when filling; determine the sizes of the straight runner, cross runner, and inner runner of the pouring system according to the proportional relationship of the total cross-sectional area of the package hole, the total cross-sectional area of the straight runner, the total cross-sectional area of the cross runner, and the total cross-sectional area of the inner runner.

[0018] Specifically, the riser size in step S1 is determined by modulus method, wherein the casting modulus M 铸 = casting volume / casting surface area, the riser modulus M 冒 =kM 铸 , wherein k is a safety factor, and its value range is 1-1.25, M 铸 , M 冒 are in units of cm, the casting volume is in units of cm 3 , and the casting surface area is in units of cm 2 .

[0019] Preferably, the total sectional area of the runner system in step S2: the total sectional area of the sprue: the total sectional area of the runner: the total sectional area of the inner gate = 1: (1.8-2): (1.8-2): (2.0-2.5).

[0020] It should be noted that after the formation of the runner system in step 4, the sand mold around is filled with furan resin quartz sand.

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

[0022] In another aspect, the embodiment of the present application also provides a 3D printing sand mold runner system for large steel castings, which is prepared by using the molding method.

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

[0024] Preferably, the material of the inner gate is a ceramic brick pipe.

[0025] Further, the gap between the 3D printing sand mold and the inner gate is 0.8-1.2 mm.

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

[0027] 1. The molding method of the 3D printing sand mold runner system for large steel castings above 20 tons in the present application reserves the position of the inner gate of the runner system when the three-dimensional model of the sand mold is established, and after the completion of the whole sand mold manufacturing, a ceramic brick pipe is used as the inner gate and is laid horizontally in the reserved position of the sand mold, which greatly improves the high-temperature resistance and corrosion resistance of the runner system, avoids the problems of sand falling off and rolling into the casting caused by long pouring time of the runner system, and meets the use requirements of long-time pouring of large steel castings.

[0028] 2. The present application coats high-temperature-resistant epoxy resin glue on the outer surface of the ceramic brick pipe before laying it horizontally in the reserved position of the sand mold, and fills the gap between the ceramic brick pipe and the sand mold, which effectively avoids the problem of the ceramic brick pipe being broken and rolled into the casting due to high-temperature steel water pressure during pouring, and ensures good overall quality of the casting and high flaw detection qualification rate.

[0029] 3. The present application reserves the position of the runner system and designs a reasonable gap in the design of the three-dimensional model of the sand mold, which ensures that the ceramic brick pipe is arranged inside the 3D printing sand mold according to the designed runner position and size, and will not be broken during pouring.

[0030] 4. The large steel casting pad with a net weight of more than 30 tons produced by the large steel casting 3D printing sand mold pouring system molding method of the present invention has good overall quality and is qualified in one flaw detection. No defects are found in the casting due to damage to the pouring system. The flaw detection results show that the single area defect is less than 40cm 2 / 1000cm 2 , the cumulative area of ​​defects is less than 300cm 2 / 1000cm 2 .

[0031] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

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

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

[0035] Figure 3 This is a schematic diagram of the ingrate structure of a large cast steel pad according to an embodiment of the present invention;

[0036] Figure 4 This is a picture of the interior of a large cast steel pad casting in Comparative Example 1 of the present invention;

[0037] Figure 5 This is a picture of the interior of the large cast steel pad casting of comparative example 2 of the present invention.

[0038] Reference numerals:

[0039] 1-cast steel pad; 2-3D printed sand mold; 3-riser; 4-introduction channel of horizontal ceramic brick tube in 3D printed sand mold; 5-introduction channel of ceramic brick tube connected to horizontal ceramic brick tube in 3D printed sand mold; 6-horizontal runner; 7-sprue; 8-ladle; 9-bottom surface of casting. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0041] The sand 3D printing technology is a new manufacturing technology, which can meet the manufacturing requirements for small and medium-sized castings with small size and tonnage, short pouring time, and short erosion time of the pouring system by high-temperature molten steel, and can meet the manufacturing requirements by using the sand mold sprue for the pouring system. However, for large cast steel pieces with large size and tonnage, the pouring system is eroded by high-temperature molten steel for a long time, and the 3D printing sand mold pouring system is prone to sand falling off and being rolled into the castings, thereby forming casting defects. The refractory brick or ceramic brick pipe is often used as the pouring system in the traditional sand mold casting method due to high refractoriness, light weight, and small gas content. However, the outer surface of the ceramic brick pipe is not smooth, and there is an error in the outer diameter. The 3D printing is an integral molding process, and if the ceramic brick pipe is directly placed in the 3D printing sand mold after molding, the size is difficult to match, and factors such as the temperature and pressure of the molten steel during pouring and the long pouring time can cause the ceramic brick pipe to break, thereby causing internal defects of the castings.

[0042] In one aspect, a specific embodiment of the present application discloses a molding method of a 3D printing sand mold pouring system for large cast steel pieces, comprising the following steps:

[0043] Step 1: establishing a three-dimensional model of the sand mold: establishing a three-dimensional model of the whole sand mold with a position and a gap of the inner sprue of the pouring system reserved;

[0044] Step 2: importing the three-dimensional model of the whole sand mold into a 3D printer, and performing 3D printing, sand cleaning, application, drying, and molding;

[0045] Step 3: smearing the outer surface of the ceramic brick pipe with high-temperature powdered high-temperature resistant epoxy resin glue above 800 DEG C, and placing the ceramic brick pipe in the reserved position of the sand mold, and removing the high-temperature resistant epoxy resin glue overflowing from the two side end faces by using a scraper; the high-temperature resistant epoxy resin glue is completely solidified at room temperature for 24 hours, and the ceramic brick pipe does not move after being pulled after solidification;

[0046] Step 4: molding: leading out the ceramic brick pipe placed in the sand mold in step 3, and sequentially connecting the cross sprue and the straight sprue outside the sand mold to form the whole pouring system, and filling the surrounding of the sand mold with furan resin quartz sand to make preparation before pouring;

[0047] Step 5: pouring: pouring the refined molten steel through the straight sprue, the cross sprue, and the inner sprue in sequence by using a refining bottom leakage package, and pouring the carbonized rice husk covering agent into the riser after the pouring is completed;

[0048] Step 6: box striking and cleaning: the box is struck and cleaned when the temperature at the riser root is reduced to below 300 DEG C;

[0049] Step 7: finishing and flaw detection, polishing the surface of the castings to meet the roughness of the flaw detection, and performing ultrasonic flaw detection.

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

[0051] S1, using three-dimensional software to establish a three-dimensional model of the casting, designing the casting process, combining the casting process design principles and the characteristics of the casting, designing the riser position and size, determining the casting steel weight;

[0052] S2, design the pouring system: according to the casting steel weight and the rising speed of the casting steel when filling, set the size of the ladle hole; according to the proportional relationship of the total cross-sectional area of the ladle hole, the total cross-sectional area of the straight runner, the total cross-sectional area of the cross runner and the total cross-sectional area of the inner gate, determine the size of the straight runner, cross runner and inner gate of the pouring system.

[0053] Further, in step S1, the modulus method is used to determine the size of the riser, wherein the casting modulus M 铸 = casting volume / casting surface area, the riser modulus M 冒 =kM 铸 , wherein k is a safety factor, the value range is 1-1.25, and the casting safety factor is selected as 1.25 according to the casting manual; M 铸 , M 冒 unit is cm, the casting volume unit is cm 3 , and the casting surface area unit is cm 2 .

[0054] In one possible design, the casting is a cast steel pad iron, and in step 1, the casting is provided with one riser, which is located at the center of the upper surface of the casting. The riser not only ensures that the hot spot is properly filled, but also ensures that the filling distance is sufficient. Therefore, the riser is designed at the center of the upper surface of the casting.

[0055] Preferably, the pouring system design in step S2 is mainly related to the size of the ladle hole of the refining bottom leakage ladle, and the size of the ladle hole mainly affects the steel liquid flow rate per second of the ladle, that is, the pouring time of the molten steel; if the pouring time is too fast, the molten steel cannot rise smoothly, and the pouring may not be full or the molten steel may splash; if the pouring time is too slow, the temperature of the molten steel decreases, which leads to too low temperature of the riser, which is not conducive to the filling of the riser; therefore, it is necessary to select appropriate pouring time, that is, appropriate steel liquid flow rate, and the calculation formula of the steel liquid flow rate is: q=(Q·V) / (n·H), wherein: q is the steel liquid flow rate, unit is kg / s; Q is the steel weight of the casting, unit is t; V is the rising speed of the molten steel when filling, unit is mm / s; n is the number of ladle holes, unit is pieces; H is the height of the casting, unit is mm;

[0056] According to the steel liquid flow rate q and the molten steel flow rate, the size of the ladle hole is determined, and then the size of the pouring system is determined according to the size of the ladle hole; that is, the total cross-sectional area of the ladle hole, the total cross-sectional area of the straight runner, the total cross-sectional area of the cross runner and the total cross-sectional area of the inner gate = 1:(1.8-2):(1.8-2):(2.0-2.5);

[0057] In one possible design, the total cross-sectional area of the bushing: the total cross-sectional area of the sprue: the total cross-sectional area of the runner: the total cross-sectional area of the inner nozzle = 1:1.8:1.8:2.5.

[0058] Preferably, in step S2, a side entry inner nozzle is used, the inner nozzle is 300 mm away from the bottom surface of the casting, and the side entry is more convenient for laying the inner nozzle ceramic brick pipe than other ways; at the same time, in order to facilitate the horizontal stable rise of the steel, and reduce the erosion of the molten steel to the cavity, the height of the inner nozzle should be lower than the middle surface of the casting;

[0059] According to the weight of the casting blank and the complexity of the shape of the casting, the position and length of the inner nozzle are reasonably designed, which is convenient for laying the ceramic brick pipe in the 3D printed sand mold, more effectively maintains the temperature of the metal liquid in the flowing process, avoids cold isolation and secondary solidification problems, reduces the generation of eddy current and air pocket, ensures the uniform solidification and quality of the casting, and improves the operability in the molding process.

[0060] Further, in step 1, it is verified that the optimal gap of the sand mold reserved inner nozzle position is 0.8-1.2 mm;

[0061] If the reserved gap is less than 0.8 mm, the ceramic brick pipe may not be inserted into the reserved inner nozzle; after the high-temperature steel, the high-temperature epoxy resin glue will powder, resulting in an increased gap between the ceramic brick pipe and the sand mold; when the reserved gap is greater than 1.2 mm, due to the increased gap between the ceramic brick pipe and the sand mold, the pressure is too large during long pouring, which is easy to break the ceramic brick pipe.

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

[0063] In one possible design, the composition of the high-temperature epoxy resin glue includes bisphenol A type epoxy resin, methyl tetrahydrophthalic anhydride, triphenyl ethyl phosphonium bromide, propylene glycol, gamma-methacryloxypropyl trimethoxysilane, and silicon oxide.

[0064] The high-temperature epoxy resin glue can withstand a high temperature of 800℃ or above, but due to the presence of resin and curing agent, after high-temperature erosion, the high-temperature epoxy resin glue will still produce gas and powder, which will increase the gap between the ceramic brick pipe and the sand mold.

[0065] It should be noted that in step 4, the ceramic brick pipe laid in the sand mold in step 3 is connected to the horizontal runner and the vertical runner outside the sand mold, the ceramic brick pipe is special for casting, and is connected in the form of a child and a mother, one end of the pipe is designed with a flange (child), and the other end is designed with a groove (mother), to realize the tight connection between the pipes.

[0066] Preferably, the quartz sand in step 4 is filled around the sand mold to enhance the bonding force between the quartz sand particles, so that the sand mold can maintain its shape and structure during casting, prevent the impact and pressure of the molten metal from causing the sand mold to collapse, enable the sand mold to withstand the high temperature of the molten metal, and reduce the wear of the sand mold.

[0067] Further, in step 5, the components of the covering agent are mainly carbonized rice husks, which play the role of a heat-insulating riser to slow down the solidification speed of the riser and increase the feeding efficiency of the riser.

[0068] Notably, in step 6, the sand mold is cleaned before the temperature of the riser root drops to below 300°C to prevent the premature cleaning of the sand mold from causing thermal cracks.

[0069] Further, the flaw detection requires that the single area defect be less than 40 cm 2 / 1000 cm 2 , and the cumulative area defect be less than 300 cm 2 / 1000 cm 2 .

[0070] In another aspect, one specific embodiment of the present application further discloses a 3D-printed sand mold casting system for large steel castings, which comprises a sprue, a runner, and an ingate; the sprue and the runner are located outside the 3D-printed sand mold and are connected to the ingate located inside the sand mold; a gap exists between the ingate and the sand mold, and the gap is filled with high-temperature-resistant epoxy resin glue.

[0071] Further, the ingate is made of a ceramic brick pipe.

[0072] The sprue and the runner are located outside the 3D-printed sand mold, but are surrounded by external sand; the ceramic brick pipe as a casting system has the advantages of high refractoriness, light weight, and low air content.

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

[0074] Specifically, the large steel casting is a steel pad iron with a net weight of more than 30 tons.

[0075] In summary, the molding method of the 3D printing sand mold pouring system for large steel castings over 20 tons of the application reserves the position of the pouring system inner runner when the sand mold three-dimensional model is established, and after the overall sand mold is manufactured, the ceramic brick pipe is used as the inner runner and is laid horizontally in the sand mold reserved position, which greatly improves the high temperature resistance and corrosion resistance of the pouring system, avoids the problems of sand falling off and rolling into the casting caused by long pouring process time of the pouring system, and meets the use requirements of long time pouring of large steel castings; according to the characteristics of the ceramic brick pipe and the high temperature pulverization of the high temperature resistant epoxy resin glue, the pouring system position is reserved and a reasonable gap is designed when the sand mold three-dimensional model is designed, so as to ensure that the ceramic brick pipe is arranged in the 3D printing sand mold according to the designed runner position and size, and the high temperature resistant epoxy resin glue is applied on the outer surface of the ceramic brick pipe, so as to ensure that the ceramic brick pipe will not be broken during pouring.

[0076] The 3D printing sand mold pouring system and the molding method for large steel castings of the application will be described below in combination with specific embodiments.

[0077] Embodiment 1

[0078] The embodiment provides a 3D printing sand mold pouring system and a molding method for large steel castings.

[0079] The large steel casting of the embodiment is a steel pad iron 1, and the contour size thereof is 2700*1350*1200mm, and the specific structure and size thereof are shown in Figure 1 、 Figure 2 The net weight of the casting is 34.2 tons, and the liquid weight is 69.4 tons.

[0080] The molding method of the 3D printing sand mold pouring system for large steel castings comprises the following steps:

[0081] Step 1, three-dimensional model of the steel pad iron 1 and casting process design, combining with the casting process design principle and the characteristics of the casting, the position and size of the riser 3 are designed;

[0082] (1) Riser design: the riser should not only ensure that the hot section is obtained, but also ensure the distance of the shrinkage, so the riser is designed at the center of the upper surface of the casting; then according to M 铸 = the volume of the casting / the surface area of the casting, the modulus of the casting is determined as 24.5cm; through the riser modulus M 冒 (cm) = 1.25M 铸 The modulus of the riser is calculated as 30.625cm, and then according to M 冒 = the volume of the riser / the surface area of the riser, the size of the riser is determined as φ1700mm*2000mm(high);

[0083] (2) Numerical simulation: numerical simulation of the temperature field and shrinkage tendency during solidification of the designed casting process, adjusting the casting process through the simulation results to ensure that the casting has no shrinkage and microstructure shrinkage defects, the temperature field of the casting is uniform, and the sequential solidification of the casting is realized.

[0084] Step 2, design the pouring system: according to the calculation of the steel flow formula, the ladle hole size of the pad iron pouring is φ100mm, and according to the sectional area ratio of the pouring system (the total sectional area of the ladle hole: the total sectional area of the straight runner: the total sectional area of each layer of the cross runner: the total sectional area of each layer of the inner nozzle = 1:1.8:1.8:2.5), the size of each part of the pouring system is determined, the diameter of the straight runner is φ140mm, the diameter of the cross runner is φ140mm, the inner nozzle is set to enter the two sides of the pad iron, and the inner runner is φ60mm in diameter; in order to make the ceramic brick pipe lie in the sand mold, the pad iron adopts side-in type inner runner, as shown in Figure 3 , the height of the inner runner from the bottom surface 9 of the casting is 300mm, reducing the height of the inner runner facilitates the stable upward of the steel level and reduces the erosion of the molten steel to the mold cavity.

[0085] Step 3, establish the three-dimensional model of the overall sand mold with the position and gap of the inner nozzle of the pouring system. The three-dimensional model of the overall sand mold is established by taking the difference between the complete sand mold and the tool of the casting, the riser and the pouring system, the position of the inner nozzle and the gap between the ceramic brick pipe and the sand mold are designed in the three-dimensional model of the overall sand mold, the 3D printed sand mold is selected as φ60mm, the corresponding ceramic brick pipe inner diameter is φ60mm, the outer diameter is φ74mm, the gap between the ceramic brick pipe and the sand mold is 1mm, and the size of the designed sand mold pouring system reserved position is φ76mm.

[0086] Step 4, import the three-dimensional model of the overall sand mold into the 3D printer, and perform 3D printing, sand cleaning, application, drying and molding.

[0087] Step 5, smear the outer surface of the φ60mm ceramic brick pipe with high-temperature resistant epoxy resin glue, lay the ceramic brick pipe smeared with glue in the reserved position of the 3D printed sand mold 2, and remove the high-temperature resistant epoxy resin glue overflowing from the two side end faces with a scraper; the high-temperature resistant epoxy resin glue is completely cured at room temperature for 24 hours, and the ceramic brick pipe does not move after curing.

[0088] Step 6, molding: use the φ60mm ceramic brick pipe to connect the inner nozzle of the 3D printed sand mold, form the entire pouring system, including the straight runner 7, the cross runner 6, the 3D printed sand mold lying ceramic brick pipe inner nozzle 4, the entire pouring of the ceramic brick pipe inner nozzle 5 connected with the 3D printed sand mold lying ceramic brick pipe, and fill the sand mold around with furan resin quartz sand to prepare for pouring.

[0089] Step 7, pouring: the refining method is used in the smelting method, the pouring temperature is controlled to be 1545-1560℃, the ladle 8 package hole is φ90mm, the pouring is observed, the package hole is closed in time, and the carbonized rice husk covering agent is poured into the riser after the pouring is completed.

[0090] Step 8, box cleaning: the box is knocked out when the riser root temperature drops to 300℃, the loose sand on the upper part of the casting is removed first, the hanging shaft is exposed, as much dry sand around the casting as possible is removed, the hanging shaft is hung slowly by using a special steel rope, and multiple ropes are ensured to be stressed simultaneously during the lifting, and the situation that only one or two ropes are stressed cannot occur, otherwise the casting will be deformed greatly or even broken. The casting is carried lightly during the lifting and the shakeout process to avoid collision. The riser is removed by using the flame cutting method after the cleaning, and the riser is removed and needs to be tempered to remove stress to prevent the casting from being cold cracked.

[0091] Step 9, finishing and flaw detection, the surface of the pad iron is polished to meet the roughness of the flaw detection, and the ultrasonic flaw detection is performed. The longitudinal wave vertical reflection method is used, and the longitudinal wave straight probe is selected.

[0092] The flaw detection is performed according to the CCH70-4 standard, the flaw detection level is performed according to the ultrasonic flaw detection level 4, that is, the single area defect is required to be less than 40cm 2 / 1000cm 2 , and the cumulative area defect is required to be less than 300cm 2 / 1000cm 2 . The specific flaw detection condition and the flaw detection result are shown in Table 1.

[0093] The casting steel pad iron casting produced by the molding method of the 3D printing sand mold pouring system of the large cast steel part has good overall quality, the flaw detection requirement is strict, and the flaw detection is qualified at one time.

[0094] Comparative example 1

[0095] On the basis of example 1, the molding method of the 3D printing sand mold pouring system of the large cast steel part is different from that in example 1 in that the ceramic brick pipe is not used as the pouring system in steps 3-6, and the sand mold sprue is used as the pouring system, and the size of the sand mold sprue is φ60mm.

[0096] The finishing flaw detection is performed after the pouring heat preservation, and the specific flaw detection result is shown in Table 1.

[0097] The cast steel pad iron is dissected as a whole, a large amount of inclusions exist in the casting, the inclusions are mainly O, Si and Al, which should be the casting sand inclusion defects, the inclusions are shown in Table 2, and it is indicated that due to the high pouring temperature and long pouring time, the sand mold pouring system is eroded by the high-temperature molten steel for a long time, the sand mold is sharply collapsed, the sand mold is dropped and rolled into the casting, the casting defects are formed, and the casting flaw detection is out of standard.

[0098] Comparative Example 2

[0099] The molding method of the 3D printing sand mold pouring system for a large steel casting is the same as that of Embodiment 1, except that the gap between the ceramic brick pipe and the sand mold is 3 mm in step 3, and the size of the reserved position of the designed sand mold pouring system is φ80 mm.

[0100] After pouring and heat preservation, finishing and flaw detection are performed, and the specific flaw detection results are shown in Table 1.

[0101] The steel casting pad iron is dissected as a whole, and it is found that there are a small amount of inclusions in the casting. The inclusions are mainly O, Al, Zr and N, which are the main components of the ceramic brick pipe. The inclusions are shown in Table 2, which shows that the high-temperature resistant epoxy resin glue will powder after the high-temperature molten steel, resulting in an increase in the gap between the ceramic brick pipe and the sand mold. When pouring for a long time, the pressure is too large, the ceramic brick pipe is broken, casting defects are formed, and the casting flaw detection is out of standard.

[0102] Comparative Example 3

[0103] The molding method of the 3D printing sand mold pouring system for a large steel casting is the same as that of Embodiment 1, except that the gap between the ceramic brick pipe and the sand mold is 0.5 mm in step 3, and the size of the reserved position of the designed sand mold pouring system is φ75 mm. At this time, the ceramic brick pipe cannot be placed in the reserved position due to the small gap and the non-smooth surface of the ceramic brick pipe.

[0104] Table 1: Flaw detection conditions and results of examples and comparative examples

[0105]

[0106] Table 2: Inclusion types of Comparative Example 1 and Comparative Example 2

[0107] Number Inclusion morphology Inclusion composition Comparative Example 1 As Figure 4 shown O, Si, Al Comparative Example 2 As Figure 5 shown O, Al, Si, Zr, N

[0108] As can be seen from Tables 1 and 2, compared with Embodiment 1, Comparative Example 1 uses a sand mold ingate as a pouring system, resulting in the falling of the sand mold, the rolling of the casting, the formation of casting defects, and the out-of-standard flaw detection of the casting. Comparative Example 2 has a too large gap between the ceramic brick pipe and the sand mold. Under the condition of long-time pouring with large pressure, the high-temperature resistant epoxy resin glue is powdered, the gap between the ceramic brick pipe and the sand mold is further increased, the ceramic brick pipe is broken during pouring, casting defects are formed, and the flaw detection of the casting is out of standard. Comparative Example 3 has a too small gap between the ceramic brick pipe and the sand mold. Due to the non-smooth surface of the ceramic brick pipe and errors, the ceramic brick pipe cannot be placed.

[0109] In summary, the molding method of the 20 tons or more large steel casting 3D printing sand mold pouring system reserves the position of the inner runner in the sand mold three-dimensional model establishment, and after the completion of the whole sand mold manufacturing, the ceramic brick pipe is used as the inner runner and is laid in the sand mold reserved position, which greatly improves the high temperature resistance and corrosion resistance of the pouring system, avoids the problems of sand falling off and rolling into the casting caused by long pouring process time, and meets the use requirements of long time pouring of large steel castings; according to the characteristics of the ceramic brick pipe and the high temperature pulverization of the high temperature resistant epoxy resin glue, the pouring system position is reserved and the reasonable gap is designed in the design of the sand mold three-dimensional model, so that the ceramic brick pipe is arranged in the 3D printing sand mold according to the designed runner position and size, and the high temperature resistant epoxy resin glue is applied on the outer surface of the ceramic brick pipe, so that the ceramic brick pipe will not be broken during pouring.

[0110] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A molding method of a 3D printing sand mold casting system for large steel castings, characterized in that, it is suitable for large steel castings with a net weight of more than 20 tons; the casting system comprises a sprue, a runner and an ingate; the sprue and the runner are located outside the 3D printing sand mold and are connected to the ingate located inside the sand mold; a side-entry ingate is adopted, and the height of the ingate is lower than the parting surface of the casting; the molding method of the casting system comprises the following steps: S1, establishing a three-dimensional model of the casting by using three-dimensional software, designing the casting process, combining the casting process design principles and the characteristics of the casting, designing the position and size of the riser, and determining the weight of the molten steel of the casting; S2, designing the casting system: setting the size of the ladle hole according to the weight of the molten steel of the casting and the rising speed of the molten steel when filling the casting; determining the size of the sprue, the runner and the ingate according to the proportional relationship of the total cross-sectional area of the ladle hole, 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; the total cross-sectional area of the ladle hole, 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 = 1:(1.8-2):(1.8-2):(2.0-2.5); Step 1, establishing a three-dimensional model of the overall sand mold with a reserved position of the ingate of the casting system and a reserved gap of the ceramic brick pipe; Step 2, importing the three-dimensional model of the overall sand mold into a 3D printer for 3D printing, sand cleaning, application, drying, and molding; Step 3, smearing the outer surface of the ceramic brick pipe with high-temperature powdered high-temperature resistant epoxy resin glue above 800℃, and laying it in the reserved ingate position of the sand mold, and the high-temperature resistant epoxy resin glue is completely cured at room temperature for 24 hours; there is a gap between the ingate and the sand mold, and the gap is filled with high-temperature resistant epoxy resin glue; the gap between the 3D printing sand mold and the ingate is 0.8-1.2mm; Step 4, molding: leading out the ceramic brick pipe laid in the sand mold in step 3, and sequentially connecting the runner and the sprue outside the sand mold to form the entire casting system; Step 5, pouring: pouring the refined molten steel through the sprue, the runner and the ingate in sequence with a refining bottom pouring ladle, and then pouring covering agent into the riser after pouring is completed; Step 6, box breaking and cleaning: breaking the box and cleaning when the temperature at the root of the riser is below 300℃; Step 7, finishing and flaw detection, polishing the surface of the casting to meet the roughness of the flaw detection, and performing ultrasonic flaw detection.

2. The molding method according to claim 1, wherein The riser size in step S1 is determined using the modulus method: casting modulus M 铸 = casting volume / casting surface area, riser modulus M 冒 = kM 铸 where k is a safety factor, having a value in the range 1-1.25, M 铸 , M 冒 are in cm, the casting volume is in cm 3 , and the casting surface area is in cm 2 .

3. The molding method according to claim 1, wherein In step 4, the casting system is formed, and the surrounding sand mold is filled with furan resin quartz sand.

4. The molding method according to claim 1, wherein In step 5, the covering agent is carbonized rice husk.

5. A large steel casting 3D printed sand mold pouring system, characterized by, Prepared by the molding method of any one of claims 1-4.

6. The gating system of claim 5, wherein, comprises a sprue, a runner and an ingate; the sprue and the runner are located outside the 3D printing sand mold and are 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 glue.

7. The gating system of claim 6, wherein, The material of the ingate is a ceramic brick pipe.

8. The gating system of claim 6, wherein, The gap between the 3D printing sand mold and the ingate is 0.8-1.2mm.

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