A combined mold for casting steel bow castings

Abstract

The present invention relates to a combination mold for casting cast steel bow column castings, which belongs to the field of casting mold technology and solves the problems in the prior art of casting cast steel bow column castings, such as a large number of sand cores, difficulty in positioning, and easy deformation, which lead to insufficient dimensional accuracy and poor casting quality. The present invention provides a combination mold for casting cast steel bow column castings, the combination mold comprising a 3D printed sand mold and a wooden master mold; wherein the 3D printed sand mold is composed of a plurality of sand mold parts, each of the sand mold parts is provided with at least one "double-row wooden comb-type" exhaust unit; wherein the wooden master mold is designed according to the overall shape of the sand mold. The number of parts of the combination mold is greatly reduced compared to traditional sand cores, thereby achieving simplified operation, accurate positioning, and reduced errors; good exhaust effect, and the casting is not prone to air holes; high precision of the inner mold surface of the sand mold, accurate casting size, and good surface quality.

Description

Technical Field

[0001] The invention relates to the technical field of casting molds, in particular to a combined mold for casting a cast steel bow column casting. Background Art

[0002] The bow is one of the most important components of a ship. It is located at the front end of the hull. Because it is located at the bow, it is the first to be impacted by the water and withstands water pressure, wave impact and external collision forces. Therefore, it has strict requirements on structure, strength, lines and life. Cast steel bows are generally slender and variable-section "rod-shaped" parts, generally reaching about 7 meters. The bows of some large ships can even reach 21 meters, and most of them have a "C"-shaped structure and a "V"-shaped cross-section. According to the manufacturing method, it can be divided into forged steel bows, cast steel bows, steel plate bows and hybrid bows. Among them, cast steel bows are widely used due to the advantages of being able to be made into more complex cross-sectional shapes and bending states.

[0003] The cast steel bow column is a typical multi-cavity thin-walled casting. The current casting method for similar castings is: first, a partial solid sample master mold and core box are made of wood, and then the master mold is struck in a sand pit. Then, according to the core setting order, the sand cores obtained by striking the molding sand are placed in the core box in sequence. Finally, the cores are assembled in a sand box or a pit to form the cavity of the cast steel bow column / multi-cavity thin-walled casting.

[0004] Existing casting technology suffers from the following drawbacks: Firstly, as ship sizes increase, the length of the cast steel bow increases, requiring more sand cores and increasing production cycles. Furthermore, the use of wooden molds increases costs, increases labor intensity, and pollutes the environment. Secondly, the core box's positioning during compaction is difficult to control, resulting in large gaps between cores and prone to deformation, which seriously affects the dimensional accuracy of the cast steel bow. Furthermore, the existing general exhaust system for sand castings is relatively simple, resulting in poor exhaust performance during the casting of cast steel bows, which can easily lead to defects such as air holes in the casting. Summary of the Invention

[0005] In view of the above analysis, an embodiment of the present invention aims to provide a combination mold for casting cast steel bow column castings, so as to solve at least one of the problems in the prior art of casting cast steel bow column castings, such as the large number of sand cores, difficult positioning, easy deformation, resulting in insufficient dimensional accuracy, poor casting quality, etc.

[0006] The present invention provides a combined mold for casting a cast steel bow column casting, the combined mold comprising a 3D printed sand mold and a wooden master mold;

[0007] The 3D printing sand mold is divided into two layers, each layer consists of multiple sand mold parts, and each sand mold part is equipped with a "double-row wooden comb" exhaust unit;

[0008] The wooden main mold is designed according to the overall shape of the sand mold and is used to pre-shape a groove for setting the sand mold in the sand box.

[0009] Specifically, the 3D printed sand mold is provided with a plurality of risers 1, including risers at the end positions and risers at the middle positions. A riser 1 is provided at each end along the length direction of the cast steel bow column casting, and the number of risers 1 at the middle position must meet a continuity of 45% to 55%; the risers 1 are provided in the upper sand mold parting.

[0010] Specifically, the cross-sectional shape of the riser 1 is one of an ellipse, a square, a rectangle or an irregular polygon; the riser 1 is further provided with a reinforcing rib plate 7 .

[0011] Specifically, the number of risers 1 in each upper sand mold is 1 to 3, and the length-to-width ratio of a single sand mold is not greater than 2.

[0012] Specifically, the "double-row comb-type" exhaust unit includes an air duct 3 and an air collecting duct 2 and an exhaust duct 4 arranged along the extending direction of the air duct 3 and respectively connected to the inner cavity of the air duct 3;

[0013] The gas during the casting process is collected through the gas collecting channel 2, enters the air guide channel 3, and is discharged to the outside of the 3D printing sand mold through the exhaust channel 4.

[0014] Specifically, there are multiple air collecting channels 2 arranged along the extending direction of the air guide channel 3, and the multiple air collecting channels 2 point to the inner cavity;

[0015] There are multiple exhaust ducts 4 arranged along the extending direction of the air guide duct 3, and the multiple exhaust ducts 4 point to the outside of the 3D printing sand mold;

[0016] There is an included angle between the air collecting duct 2 and the exhaust duct 4 , and the air collecting duct 2 and the exhaust duct 4 are arranged in a staggered manner.

[0017] Specifically, the air guide channel 3 is arranged according to the shape of the inner cavity of the sand mold;

[0018] At least one "double-row wooden comb type" exhaust unit is provided in a single sand mold.

[0019] Specifically, two "double-row wooden comb type" exhaust units are provided in each sand mold parting, and the two exhaust units are symmetrically distributed on both sides of the inner mold cavity, and the air guide 3 of each "double-row wooden comb type" exhaust unit is arranged along the length extension direction of the inner mold cavity; or, more than three "double-row wooden comb type" exhaust units are provided in each sand mold parting, and the "double-row wooden comb type" exhaust units are connected in sequence and arranged along the length extension direction of the inner mold cavity to form an overall "double-row wooden comb type" exhaust system.

[0020] Specifically, the total cross-sectional area of ​​the air collecting duct 2 in each "double-row comb-type" exhaust unit is S1, the total cross-sectional area of ​​the air guide duct 3 is S2, and the total cross-sectional area of ​​the exhaust duct 4 is S3, S1:S2:S3=(1.25~2.5):1:(2.0~3.0).

[0021] The present invention also discloses a design method for the combined mold. First, the number of risers 1 is determined according to the specific shape and heat node of the cast steel bow casting, and then the number and shape of the sand mold parting and the exhaust system design are determined to obtain a 3D printed sand mold design scheme, and then a wooden master mold is designed based on the 3D printed sand mold.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] 1. The present invention creatively adopts a combination mold of "wooden master mold + 3D printed sand mold" to cast multi-cavity thin-walled castings, especially large castings (cast steel bow column), which greatly reduces the number of sand cores, reduces the operation difficulty and improves the operation efficiency, while greatly improving the positioning accuracy and the surface quality of the cavity, thereby improving the accuracy and surface quality of the casting.

[0024] Existing 3D printing technology is mainly used for the rapid manufacture of small and medium-sized complex castings. In general sand casting, it is mainly used for small castings such as engine cylinder blocks, and medium-sized castings such as mixed-flow runners weighing more than 2 tons. It is rarely used for large steel castings. Cast steel bow columns have the characteristics of many cavities, long length, and thin wall thickness. If the sand mold is made entirely with 3D printed sand molds, the sand core forming the outer surface of the bow column also needs to be printed, which will result in long production time and high cost. The existing technology combines the traditional wooden main mold with the wooden core box sand core. Each cavity is formed by a separate sand core, resulting in a large number of sand cores and a long time to set the core.

[0025] The present invention uses 3D printed sand molds to form the complex areas of the cast steel bow, and the main mold is made of traditional wooden main mold. The combination of the two methods can greatly improve the molding efficiency of the cast steel bow, and greatly improve the positioning accuracy and casting quality.

[0026] 2. The 3D printing sand mold designed by the present invention is equipped with a "double-row wooden comb" exhaust system (composed of multiple exhaust units) with good exhaust effect. According to the characteristics of cast steel bow column with multiple cavities, long length and thin wall thickness, the present invention creatively designs a "double-row wooden comb" exhaust system composed of air collecting ducts, air guide ducts and exhaust ducts. Among them, one end of the air collecting duct is close to the inner mold cavity, which can efficiently collect the gas generated during the casting and characterization process; after the exhaust gas is collected by the air collecting duct, it enters the air guide duct set with the mold, and is finally discharged to the outside atmosphere through the exhaust duct. The exhaust efficiency of the exhaust system is significantly improved compared with the existing general exhaust system, which can reduce or even avoid the occurrence of air hole defects in castings.

[0027] Furthermore, when the cross-sectional area relationship of the gas collecting duct, the air guide duct and the exhaust duct satisfies S1:S2:S3=(1.25~2.5):1:(2.0~3.0), the exhaust effect is better, and gas congestion and poor exhaust can be avoided when a large amount of gas is discharged.

[0028] 3. The 3D printing sand mold designed by the present invention also has a reserved cavity for chiller and a through hole for fixing. In actual implementation, the chiller can be connected to the steel bar by spot welding and fixed at a preset position in the inner cavity through the through hole for fixing, thereby accelerating the solidification rate of the casting, refining the grain structure, and improving the mechanical properties of the casting during the pouring process. The chiller fixing method is simple and easy, firmly fixed and has good thermal conductivity.

[0029] 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

[0030] 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.

[0031] Figure 1 This is a schematic diagram of the cast steel bow casting structure;

[0032] Figure 2 The sand core parting process diagram of the cast steel bow casting in the prior art (34 pieces in total);

[0033] Figure 3 It is a schematic diagram of the structure of a single exhaust unit;

[0034] Figure 4 3D printing sand mold parting design drawings in Example 1 (a total of 6 pieces);

[0035] Figure 5 This is an enlarged view of parting pattern a in the 3D printed sand mold parting pattern in Example 1 (perspective rendering);

[0036] Figure 6 This is an enlarged view of parting pattern a in the 3D printed sand mold parting pattern in Example 1 (perspective line drawing);

[0037] Figure 7 Schematic diagram of the 3D printing sand mold and wooden master mold structure;

[0038] Figure 8 Schematic diagram of the overall structure of the 3D printed sand mold in Example 1 (assembled state).

[0039] Reference numerals:

[0040] 1. Riser; 2. Air collecting duct; 3. Air guide duct; 4. Exhaust duct; 5. Chill iron reserved cavity; 6. Through hole for fixing; 7. Reinforcement rib plate. DETAILED DESCRIPTION

[0041] 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.

[0042] The existing cast steel bow castings have the following problems during the casting process:

[0043] 1. During the casting process, existing cast steel bow castings use a wooden model to create a main mold and core box to form the cavity. When the bow is long, the number of sand cores increases, making the operation cumbersome, and there are many core seams, which makes it difficult to control the size. Since the cast steel bow is curved and easily deformed, the size problem may cause deformation during later processing.

[0044] 2. Currently, the use of 3D-printed sand molds for large, multi-cavity, thin-walled castings presents numerous challenges, including mold parting and design, venting, and chiller placement. Furthermore, if 3D printing is used exclusively for manufacturing, the pouring system and chiller are difficult to prefabricate into the 3D-printed sand cores, and improper handling can even lead to sparks. Furthermore, if the sand mold is entirely made with 3D-printed sand cores, the sand core for the bow's exterior surface also needs to be printed, resulting in lengthy production times and high costs.

[0045] Based on the defects of the existing technology, the researchers of this invention have conducted extensive research, theoretical analysis and experimental adjustments, and proposed a casting method for large multi-cavity thin-walled castings that combines "wooden master mold + 3D printed sand mold" (i.e., combined mold). This method achieves the efficient, high-precision and cost-controlled preparation of large multi-cavity thin-walled castings. The core of the casting method lies in the combined mold and its design.

[0046] The present invention provides a combined mold for casting a cast steel bow column casting, the combined mold comprising a 3D printed sand mold and a wooden master mold;

[0047] The 3D printing sand mold is divided into two layers, each layer consists of multiple sand mold parts, and each sand mold part is equipped with a "double-row wooden comb" exhaust unit;

[0048] The wooden main mold is designed according to the overall shape of the sand mold and is used to pre-shape a groove for setting the sand mold in the sand box.

[0049] Specifically, the cast steel bow column is a typical large multi-cavity thin-walled casting. The traditional core splitting method divides the main body cavity structure into multiple sand cores. The sand core dividing interface is generally the center dividing surface of the middle rib. In this way, the number of sand cores increases, the molding process is complicated, and it is very easy to cause dimensional deviation when the core is lowered, resulting in the problem of one side thickening and the other side being missing in the cleaning process later. It can only be refined by repair welding and carbon planing and polishing. Due to the narrow cavity space, the repair welding operation is difficult. On the other hand, large-area repair welding can easily cause deformation of the bow column body. The 3D printed sand mold (composed of multiple sand mold partings) in the combined mold designed by the present invention is significantly reduced in number compared to traditional sand cores (taking the embodiment as an example, the number is reduced from the traditional 34 sand cores to 6 sand mold partings), which effectively avoids the occurrence of the above problems.

[0050] Specifically, the 3D printed sand mold is provided with a plurality of risers 1, including risers at the end positions and risers at the middle positions. A riser 1 is provided at each end along the length direction of the cast steel bow column casting, and the number of risers 1 at the middle position must meet a continuity of 45% to 55% (the continuity of the riser is the ratio of the sum of the length of the riser root to the circumference of the wheel shape, which is called the continuity of the riser); the riser 1 is provided in the upper sand mold parting.

[0051] Furthermore, since the hot spots of different castings are closely related to the casting shape, molten steel composition, and mold cavity angle, they cannot be generalized. Computer simulation or reference to casting experience can be used to obtain hot spot information, and the number and position of risers can be determined based on the hot spot information. The principle for determining the number of risers proposed in the present invention is a universal principle and is applicable to the inner cavity / mold design of most cast steel bow castings.

[0052] Specifically, the cross-sectional shape of the riser 1 is one of an ellipse, a square, a rectangle or an irregular polygon; the riser 1 is further provided with a reinforcing rib plate 7 .

[0053] Specifically, the number of risers 1 in each upper sand mold parting is 1 to 3, and the aspect ratio of a single sand mold parting is no greater than 2. The above arrangement can not only meet the shrinkage compensation needs of the multi-cavity thin-walled casting, but also avoid the insufficient strength of the sand mold caused by too many risers. The role of the reinforcing ribs is to further improve the structural strength and avoid structural defects in the casting during the shaping and demolding process. In the specific implementation, the setting of the reinforcing ribs can refer to the existing technology. The final product will have the risers and ribs and other redundant parts removed and polished. The risers and ribs are not part of the final product.

[0054] It is worth noting that the structural dividing surface of a single sand mold parting is closely related to the shape of a specific casting. After the approximate number of sand mold partings is determined according to the number of risers, the parting surface of the sand mold parting is formed by naturally extending along the structural dividing surface of the casting. For example, the parting is divided along a rib extension surface of a multi-cavity thin-walled casting. For example, in Example 1, the d, e, and f sand mold partings are formed by naturally extending according to the shape of the protruding part, while the upper sand molds a, b, and c can be directly cut vertically because the inner cavity is a cavity and has no protruding structure. In addition, the parting surface of the upper and lower sand mold partings can be determined according to the shape of the inner cavity / casting (such as Figure 4 shown).

[0055] Furthermore, the aspect ratio of each sand mold layer is also related to the strength of the printing material used. For high-strength printing materials, the aspect ratio of each sand mold layer can be appropriately increased, for example, to 1.5-2. For low-strength materials, to prevent sand mold collapse, the aspect ratio of each sand mold layer can be appropriately reduced, for example, to 1.0-1.5. It is worth noting that unless there are special requirements for the casting material, such as appropriately reducing the material strength to achieve shear resistance, most common high-temperature resistant materials for 3D printing are suitable for aspect ratios below 2, and sand mold collapse will not occur.

[0056] For example, common high-temperature-resistant printing materials include high-temperature alloys such as nickel-based alloys and cobalt-based alloys. These alloys have extremely high creep and oxidation resistance, making them suitable for use in extremely high-temperature environments. In addition, ceramic materials such as alumina and silicon nitride are not only heat-resistant but also offer excellent electrical insulation and wear resistance. In practice, the appropriate high-temperature-resistant printing material can be selected based on factors such as casting temperature, casting surface quality requirements, and cost control.

[0057] It is worth noting that the structural dividing surface of a single sand mold parting is closely related to the shape of the specific casting. After the approximate number of sand mold partings is determined according to the number of risers, the parting surface of the sand mold parting is naturally extended along the structural dividing surface of the casting, such as the parting surface of the cast steel bow casting rib (corresponding to the gap between the protruding parts of the mold cavity) extending outward naturally (such as Figure 4 shown).

[0058] Specifically, the "double-row comb-type" exhaust unit includes an air duct 3 and an air collecting duct 2 and an exhaust duct 4 arranged along the extending direction of the air duct 3 and respectively connected to the inner cavity of the air duct 3;

[0059] The gas during the casting process is collected through the gas collecting channel 2, enters the air guide channel 3, and is discharged to the outside of the 3D printing sand mold through the exhaust channel 4.

[0060] Furthermore, the "double-row wooden comb type" exhaust system includes an air collecting duct, an air guide duct and an exhaust duct;

[0061] The air guide channel is arranged according to the shape of the inner cavity of the sand mold;

[0062] One end of the air collecting channel is connected to the air guide channel, and the other end points to the inner cavity and maintains a certain distance from the surface of the inner cavity;

[0063] One end of the exhaust duct is connected to the air guide duct, and the other end points to the outer surface of the sand mold and is connected to the atmosphere;

[0064] The interconnected air collecting duct, air guide duct and exhaust duct constitute a complete "double-row wooden comb type" exhaust unit; at least one "double-row wooden comb type" exhaust unit is provided in a single sand mold.

[0065] Specifically, one end of the gas collecting duct is close to the inner mold cavity surface, which helps collect gases generated during the pouring and solidification processes. After being collected by the gas guide duct, the gases are ultimately discharged to the outside atmosphere through the exhaust duct. It is worth noting that the gas collecting duct and the exhaust duct should not be connected to the gas guide duct at the same node. Instead, they should be staggered to avoid structural defects.

[0066] It is worth noting that after the 3D printed sand mold is assembled, if the exhaust port corresponding to the exhaust duct is located on the upper surface of the sand mold, exhaust can be achieved without additional treatment; if the exhaust port corresponding to the exhaust duct is located inside the sand box (for example, the exhaust hole of the lower sand mold parting is generally located on the side), it is necessary to directly pierce the air hole or place a hollow nylon rope during the sand placement process in the sand box to connect the exhaust hole to the external atmosphere.

[0067] Specifically, there are multiple air collecting channels 2 arranged along the extending direction of the air guide channel 3, and the multiple air collecting channels 2 point to the inner cavity;

[0068] There are multiple exhaust ducts 4 arranged along the extending direction of the air guide duct 3, and the multiple exhaust ducts 4 point to the outside of the 3D printing sand mold;

[0069] There is an included angle between the air collecting duct 2 and the exhaust duct 4 , and the air collecting duct 2 and the exhaust duct 4 are arranged in a staggered manner.

[0070] Specifically, the air guide channel 3 is arranged according to the shape of the inner cavity of the sand mold; at least one "double-row wooden comb type" exhaust unit is provided in a single sand mold.

[0071] Specifically, two "double-row wooden comb type" exhaust units are provided in each sand mold parting, and the two exhaust units are symmetrically distributed on both sides of the inner mold cavity, and the air guide 3 of each "double-row wooden comb type" exhaust unit is arranged along the length extension direction of the inner mold cavity; or, more than three "double-row wooden comb type" exhaust units are provided in each sand mold parting, and the "double-row wooden comb type" exhaust units are connected in sequence and arranged along the length extension direction of the inner mold cavity to form an overall "double-row wooden comb type" exhaust system.

[0072] Specifically, the total cross-sectional area of ​​the gas collecting duct 2 within each "double-row comb-style" exhaust unit is S1, the total cross-sectional area of ​​the air guide duct 3 is S2, and the total cross-sectional area of ​​the exhaust duct 4 is S3. S1:S2:S3 = (1.25-2.5):1:(2.0-3.0). When this relationship is met, the exhaust system achieves optimal exhaust performance, minimizing the risk of poor gas discharge. Furthermore, the total cross-sectional area of ​​the exhaust system should be limited, as this may reduce the structural strength of the sand mold.

[0073] It is worth emphasizing that in actual implementation, in order to further improve the exhaust effect, different groups of exhaust units can be connected (the specifications of the connecting air duct are the same as those of the air guide duct), so that multiple exhaust units in a single sand mold are interconnected, and the exhaust effect is improved when the gas production in the inner cavity is uneven; however, it is worth noting that during the design process, the multiple connected exhaust units still need to meet the above-mentioned cross-sectional area ratio relationship separately instead of being calculated as a whole. In addition, the connecting air duct itself can independently become a complete exhaust unit (that is, including air collecting ducts, air guide ducts and exhaust ducts) or it can be used only as a connecting air duct (including air guide ducts, which may include air collecting ducts or exhaust ducts). The specific setting can be flexibly set according to the shape of the casting / inner cavity.

[0074] Specifically, the end of the gas collecting channel close to the mold cavity is 150 to 250 mm from the inner cavity surface. The gas collecting channel is close to the inner cavity surface to more efficiently collect gas generated during the pouring process, but the end face should not be too close to the inner cavity surface to prevent molten metal from overflowing into the gas collecting channel.

[0075] Preferably, a chill reserved cavity and a fixing through hole are further provided in the sand mold parting; the chill reserved cavity is provided on the inner mold cavity surface between adjacent risers, and the chill reserved cavity is connected to the outer surface of the sand mold parting through the fixing through hole.

[0076] Specifically, the edge size of the chiller reserved cavity is 2-3mm larger than the edge of the chiller to facilitate subsequent chiller installation. The diameter of the fixing through-hole is 10-20mm, which is used to pass the fixing steel bar. The corresponding position of the fixing through-hole on the outer surface of the sand mold parting is also opened with a fixture avoidance hole with a diameter of 100-350mm and a depth of 100-150mm. In actual implementation, the sand mold / sand mold parting is first printed, and then the fixing steel bar is passed through the fixing through-hole. One end of the fixing steel bar is spot welded to the chiller, and the other end is spot welded to the fixture (such as a short steel bar or a rectangular iron sheet of appropriate thickness). This fixing method is simple, easy to use and low-cost.

[0077] Specifically, the wooden master mold's shape matches the lower half of the 3D-printed sand mold; its height is 1 / 5 to 1 / 3 the overall height of the sand mold. The wooden master mold serves to pre-press grooves in the sand box that match the sand mold, facilitating placement of the 3D-printed sand mold / sand mold parting, and improving accuracy in sand mold assembly and positioning.

[0078] Preferably, the outer surface of the sand mold parting of the lower layer is provided with a positioning slope, specifically a slope of 1:8-12, and the wooden main mold matches the outer surface of the sand mold parting of the lower layer. The role of the positioning slope is to facilitate the insertion and assembly of the 3D printing sand mold / sand mold parting, and the positioning is more accurate and stable.

[0079] The present invention also discloses a design method for the combined mold. First, the number of risers 1 is determined according to the specific shape and heat node of the cast steel bow casting, and then the number and shape of the sand mold parting and the exhaust system design are determined to obtain a 3D printed sand mold design scheme, and then a wooden master mold is designed based on the 3D printed sand mold.

[0080] The specific steps of the design method are:

[0081] S1: Determine the number of risers 1 and the number of sand mold parts according to the size and shape of the multi-cavity thin-wall casting and the thermal nodes during the casting process; the sand mold is divided into two layers, each layer of the sand mold consists of several parts;

[0082] S2: The sand mold is designed according to the number of risers 1 and the module. A "double-row wooden comb" exhaust system (composed of several exhaust units) is set inside each sand mold.

[0083] S3: Designing a wooden master mold according to the overall shape of the sand mold, wherein the wooden master mold is used to pre-shape a groove for setting the sand mold in a sand box.

[0084] The present invention also discloses a casting method for a multi-cavity thin-wall casting. The casting method adopts the casting mold combination to produce the multi-cavity thin-wall casting after shaping, pouring and demoulding.

[0085] Example 1

[0086] This embodiment provides a possible design of a combined mold for a cast steel bow column casting, as well as a design process of the combined mold and a subsequent casting process.

[0087] S1: According to the cast steel bow casting (casting shape such as Figure 1 As shown in the figure, a heat section (obtained based on computer simulation and experience) with a diameter of 300mm is set up as a waist-shaped riser. According to the riser design principle, a riser is set up at both ends of the length direction. The total length of the cast steel bow is 6014mm. According to the continuity of 50%, 6014×50%÷500=6.014≈6, so 6 waist-shaped risers with a diameter of 300mm are placed evenly in the middle position; a single sand mold parting includes 2 waist-shaped risers and the sand mold includes upper and lower layers, for a total of 6 sand mold partings (as shown in the figure). Figure 4 、 Figure 8 As shown); after the six sand molds are combined, the inner cavity is the shape of the cast steel bow casting (including auxiliary components such as risers and ribs). The upper sand mold can be divided vertically, and the lower sand mold is naturally extended along the shape segment of the protruding part (corresponding to the ribs of the cast steel bow casting) to form a cutting surface / parting surface. The aspect ratio of a single sand mold is 1.8; (as shown Figure 4 shown)

[0088] S2: After determining the number of risers, chillers should be installed between every two risers for zoned shrinkage compensation. The wall thickness of the cast steel bow is 80mm, and the thickness of the chiller should be 0.5 to 0.85 times of that, which is 40mm.

[0089] S3: The sand mold parting position should be along one side of the cavity rib as much as possible. There are 2 sand mold parting layers, and the inner cavity structure is in the sand mold parting of the lower layer. The positioning slope of each lower sand mold parting is 1:10, the height is 120mm, and there are 6 sand molds in total (3 on the upper layer and 3 on the lower layer).

[0090] S4: When printing the sand mold, a chiller cavity must be reserved. The gap between the chiller cavity and the chiller is 2mm. A 20mm hole is printed behind the chiller cavity, which goes straight to the back of the sand mold. A fixture avoidance hole with a diameter of 250mm and a depth of 150mm is reserved behind the sand mold. After the sand mold is printed, a φ12 steel bar is first passed through the small hole and spot welded to the chiller. It is then disconnected at the fixture avoidance hole and a short steel bar with a diameter of 30mm and a length of 220mm is spot welded to fix the chiller.

[0091] S5: When printing the sand mold, a "double-layer wooden comb-type" exhaust channel is directly printed. The sand intake of the air collecting channel adjacent to the active surface of the casting is 200mm. Two exhaust units are set for each block of the upper sand mold parting. The cross-section of the air collecting channel is φ6mm, and each is connected to a φ10mm air guide channel, which is connected to the external atmosphere through a φ15mm exhaust channel. The three are staggered with each other, and S1:S2:S3 in each exhaust unit is 1.8:1:2.5; the exhaust system of the lower sand mold parting (consisting of 2 exhaust units) is the same size as the upper sand mold parting, and the shape is set according to the active surface / inner mold cavity of the casting (the two exhaust units in sand molds a and c are connected by a connecting air channel); alumina ceramic material is used for 3D printing and a matching wooden master mold is prepared. The height of the wooden master mold is 1 / 5 of the total height of the sand mold;

[0092] S6: The wooden sand box of the main mold is knocked flat and turned over, the main mold is taken out, and then the 3D printed sand mold / sand mold parting mold are put into it in sequence, and then the sides of the sand mold are knocked flat with furan resin sand. The entire molding operation process takes 2 days (the molding process of the existing technology takes 7 days), and then pouring is carried out to obtain a cast steel bow column casting.

[0093] The above description is only a preferred specific 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 thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A combined mold for casting a cast steel bow column casting, characterized in that: The combined mold includes a 3D printed sand mold and a wooden master mold; The 3D printing sand mold is divided into two layers, each layer consists of multiple sand mold parts, and each sand mold part is equipped with a "double-row wooden comb" exhaust unit; The wooden main mold is designed according to the overall shape of the sand mold and is used to pre-shape a groove for setting the sand mold in the sand box; The "double-row comb-type" exhaust unit comprises an air duct (3) and a plurality of air collecting ducts (2) and exhaust ducts (4) arranged along the extending direction of the air duct (3) and respectively communicating with the inner cavity of the air duct (3); The gas during the casting process is collected through the gas collecting channel (2), enters the air guide channel (3), and is discharged to the outside of the 3D printing sand mold through the exhaust channel (4); There is an included angle between the air collecting duct (2) and the exhaust duct (4), and the air collecting duct (2) and the exhaust duct (4) are arranged in a staggered manner.

2. The combined mold according to claim 1, characterized in that: The 3D printing sand mold is provided with a plurality of risers (1), the risers including risers at end positions and risers at middle positions, wherein a riser (1) is respectively provided at both ends along the length direction of the cast steel bow column casting, and the number of risers (1) at the middle position must meet a continuity of 45-55%; the plurality of risers (1) are provided in the upper sand mold parting.

3. The combined mold according to claim 2, characterized in that: The cross-sectional shape of the plurality of risers (1) is one of an ellipse, a square, a rectangle or an irregular polygon; the plurality of risers (1) are also provided with reinforcing rib plates (7).

4. The combined mold according to claim 2, characterized in that: The number of risers (1) in each upper sand mold is 1 to 3, and the length-to-width ratio of a single sand mold is not greater than 2.

5. The combined mold according to claim 1, characterized in that: A plurality of the air collecting channels (2) point to the inner mold cavity; and a plurality of the exhaust channels (4) point to the outside of the 3D printing sand mold.

6. The combined mold according to claim 1, characterized in that: The air guide channel (3) is arranged according to the shape of the inner cavity of the sand mold; At least one "double-row wooden comb" exhaust unit is provided in a single sand mold.

7. The combined mold according to claim 6, characterized in that: Each sand mold is provided with two "double-row wooden comb type" exhaust units, the two exhaust units are symmetrically distributed on both sides of the inner mold cavity, and the air guide channel (3) of each "double-row wooden comb type" exhaust unit is arranged along the direction of the inner mold cavity; or, each sand mold is provided with three or more "double-row wooden comb type" exhaust units, the "double-row wooden comb type" exhaust units are connected in sequence, and are arranged along the direction of the inner mold cavity to form an overall "double-row wooden comb type" exhaust system.

8. The combined mold according to any one of claims 1 to 7, characterized in that: The total cross-sectional area of ​​the air collecting duct (2) in each "double-row comb-type" exhaust unit is S1, the total cross-sectional area of ​​the air guide duct (3) is S2, and the total cross-sectional area of ​​the exhaust duct (4) is S3, S1:S2:S3=(1.25-2.5):1:(2.0-3.0).

9. A method for designing a combined mold according to any one of claims 1 to 8, characterized in that: The specific steps of the design method are: S1: Determine the preset number of risers and the number of sand mold parts according to the size and shape of the cast steel bow casting and the thermal nodes during the casting process; the sand mold is divided into two layers, upper and lower, and each layer of the sand mold is composed of a number of parts; S2: Sand molds are designed based on the number of risers and modulus. A "double-row wooden comb" exhaust system is installed inside each sand mold. S3: Designing a wooden master mold according to the overall shape of the sand mold, wherein the wooden master mold is used to pre-shape a groove for setting the sand mold in a sand box.

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