Casting method for large inline multi-cylinder compressor blocks

Abstract

The application discloses a casting method for a large-scale inline multi-cylinder compressor body, which takes wet sand as a molding material and HT300 as a casting material, and sequentially comprises the following steps: S10, printing a simulation model and testing pouring by adopting a 3D printing casting cavity mode, including printing a casting outer cavity and an inner cavity; S20, hierarchical exhaust sand mold construction, including independent exhaust design of the inner cavity and exhaust needle and riser design of the outer cavity; S30, balanced feeding, calculating a thermal section modulus M of each region of the compressor body by a simulation software, and opening a heat preservation riser in a side wall of a region with a thermal section modulus M greater than or equal to 1.2 cm; a semicircular hole is symmetrically designed on a side close to each other between an adjacent group of cylinder hole cores and regions between the cylinder hole cores, a semicircular cold iron is arranged in the semicircular hole, and an exhaust gap is arranged between a straight line part of the semicircular cold iron and a straight line side wall of the semicircular hole; S40, process control, including sequentially performing sand mold pretreatment, smelting and pouring, cooling and box opening and post-treatment, and the casting has low cost and high quality.

Description

Technical Field

[0001] This invention relates to the field of compressor manufacturing technology, and in particular to a casting method for the housing of a large inline multi-cylinder compressor. Background Technology

[0002] Large inline multi-cylinder compressors generally refer to compressors with a single unit weight ≥200kg, ≥6 cylinders (inline layout), and cylinder bore diameter ≥80mm. Typical models include the H88 series, H90 series, and C610 series. They are commonly used in industrial refrigeration, HVAC (heating, ventilation and air conditioning), chemical process cooling, data center cooling, and other fields.

[0003] The compressor body of a large inline multi-cylinder compressor is a key load-bearing component, characterized by its large size. Not only are the internal oil passages and air passages densely interwoven and the cavity structure complex, but the wall thickness also varies significantly, with the maximum wall thickness reaching 110mm and the minimum wall thickness (such as the bottom of the crankcase) being only 12mm. At the same time, the hot spots such as the cylinder block joints are large in volume and have a slow cooling rate. After casting, the dimensional tolerance of key parts must be ≤±0.08mm and the coaxiality of the cylinder bore must be ≤0.04mm. It also needs to withstand a working pressure of ≥3.0Mpa, which means that there are strict requirements for the density, airtightness and dimensional stability of the casting.

[0004] In the existing technology, in order to meet the quality requirements of large inline multi-cylinder compressor bodies made of HT300 material, the industry mostly adopts high-end casting processes such as resin sand and lost foam casting. However, there are obvious drawbacks: the raw material cost of resin sand is more than 30% higher than that of wet foam sand, the molding and drying process is complicated, and the production efficiency is reduced by 35%; the lost foam casting process has high requirements for the precision of the foam pattern and is prone to carbon defects, which is not compatible with HT300 material. The production cost and technical threshold are both high, which is not conducive to large-scale industrialization.

[0005] Therefore, there is an urgent need to develop a casting method specifically for large inline multi-cylinder compressor bodies to balance high quality and economy. Summary of the Invention

[0006] This application provides a casting method for large inline multi-cylinder compressor bodies. While maintaining the advantages of low cost and high efficiency of wet molding sand, it can also adapt to the casting characteristics of HT300 material, so that the casting quality meets the stringent requirements of large compressor bodies and achieves a balance between high quality and economy in large-scale production.

[0007] This application provides a casting method for a large inline multi-cylinder compressor body. The casting method uses wet molding sand as the molding material and HT300 as the casting material, and includes the following steps in sequence: S10, a printed simulation model, is used for experimental casting by printing casting cavities. It includes printing the outer and inner cavities of the casting. The outer cavity is formed by an upper sand mold and a lower sand mold, while the inner cavity is a sand core, consisting of a motor chamber, a crankshaft chamber, a cooling chamber, and a cylinder bore chamber. By measuring and inspecting, the deformation law of the casting and the risk area of ​​sand flushing are guided. In the subsequent mold design, the design size is adjusted according to the deformation law of the casting. S20, graded venting sand mold construction, including independent venting design for the inner cavity and venting pin and riser design for the outer cavity. The independent venting design for the inner cavity involves designing cavities for the thick areas of the motor chamber and crankshaft chamber. Sand core venting structures are respectively opened in the cavities, the cooling chamber, and the cylinder bore chamber. The sand core venting structures, in conjunction with the sand core venting pins, independently discharge the gas generated by the sand core into the casting cavity. The thick areas refer to the areas where the wall thickness of the chamber sand core is ≥50mm. For the design of the venting pin and riser for the outer cavity, 3-4 liquid replenishment risers are set on the side of the crankcase and the side of the motor case, respectively. An outer cavity venting pin is set at the top of the outer cavity to independently discharge the gas generated by the outer cavity. The top of the liquid replenishment riser is connected to the outside atmosphere, and the height of the liquid replenishment riser exceeds the height of the casting. S30, balanced feeding, the thermal modulus M of each region of the compressor body is calculated by simulation software, and the sidewalls of several regions with thermal modulus M≥1.2cm are opened with heat insulation risers; the regions between adjacent sets of cylinder cores and cylinder cores are symmetrically designed with semi-circular holes on the side that are close to each other, and semi-circular chills are set in the semi-circular holes, wherein the arc-shaped parts of the two semi-circular chills are close to each other, and an exhaust gap is provided between the straight part of the semi-circular chill and the straight sidewall of the semi-circular hole; S40, process control, includes sequential sand mold pretreatment, smelting and pouring, cooling and unpacking, and post-treatment. Sand mold pretreatment maintains the deep moisture content of the sand mold at 3.4%-4.2%. The carbon equivalent of the HT300 gray cast iron used in smelting is 3.2%-3.6%, and the smelting temperature is 1480-1530℃. Before pouring, nitrogen is used for degassing to reduce the gas content of the molten metal to ≤0.035%. The unpacking temperature is ≤360℃. Post-treatment includes shot blasting and artificial aging. A medium-strength shot blasting machine is used for the first shot blasting to remove sand, oxide scale, and gating residue from the sand mold surface. After aging, a second shot blasting is performed, using a heat treatment aging furnace at 520-580℃.

[0008] In one possible implementation, in step S10, the moisture-proof molding sand printing formula for the outer cavity is: Silica sand, 100%, wherein the silica sand is 70 / 140 mesh, containing ≥90% silicon and <0.2% mud; Modified bentonite, 0.8%-1.5%; Starch-based binder, 0.5%-1.0%; Curing aid, 0.2%-0.4%; Moisture control agent, 0.1%-0.2%; Lubricant / disintegrating agent, 0.1%-0.2%; The total binder phase is less than 3%.

[0009] In one possible implementation, in step S10, the anti-coating sand printing formula for the inner cavity is: Silica sand, 100%, wherein the silica sand is 70 / 140 mesh or 100 / 200 mesh, and contains ≥98% silicon; Phenolic resin, 1.8%-2.5%; Curing aid, 0.4%-0.8%; Curing accelerator, 0.1%-0.3%; High-temperature stabilizing agent, 0.1%-0.2%; Dispersant, 0.2%-0.4%; Flow aid, 0.1%-0.2%.

[0010] In one possible implementation, in step S30, the insulating riser is opened on the sidewall of 3-5 regions where the thermal modulus M ≥ 1.2 cm, and the volume ratio of the insulating riser to the thermal section volume is 1.7-2.3:1.

[0011] In one possible implementation, in step S30, the inner cavity of the cylinder bore core is the cylinder bore cavity, and the cylinder bore core is made of chromite coated sand with a particle size of 70 / 140 mesh.

[0012] In one possible implementation, the exhaust gap is 2-3 mm, and the distance between the arcuate portion of the semicircular chill and the inner wall of the cylinder bore core is 5-10 mm.

[0013] In one possible implementation, in step S40, the sand mold pretreatment is as follows: the sand mold is heated in a sand mold heating furnace at 68-72°C, and the moisture content of the deep layer of the sand mold is measured every 10-20 minutes until the moisture content of the deep layer of the sand mold is maintained at 3.4%-4.2% and then the heating is stopped. The compactness of the sand mold is 1.7-1.8 g / cm³.

[0014] In one possible implementation, in step S40, the chemical composition of HT300 gray cast iron is controlled as follows: C: 2.9%-3.1%, Si: 1.8%-2.0%, Mn: 0.7%-1.0%, P≤0.05%, S: 0.05%-0.10%, Cr: 0.30%-0.35%, Sn: 0.07%-0.08%, Cu: 0.80%-0.85%, with the balance being Fe.

[0015] In one possible implementation, in step S40, a composite casting method of center pouring + side pouring is adopted. At the same time, a three-stage purification and filtration method of slag-blocking dam → slag-collecting needle → honeycomb filter screen is adopted during the casting process. First, the dam body is used for coarse filtration and preliminary interception of large slag pieces; then, the slag-collecting needle is used to adsorb and capture fine inclusions; finally, the honeycomb screen is used for final fine filtration and rectification. The filling speed is 0.5-1.0 m / s, the casting temperature is 1390-1420℃, and the initial filling speed is 1.0 m / s. For every 10 mm increase in the casting wall thickness, the filling speed decreases by 0.1 m / s until it is maintained at a minimum of 0.5 m / s.

[0016] In one possible implementation, in step S40, during the first shot blasting process, for a 200-250kg compressor body, the shot blasting time is 0.5 hours, and for a 250-300kg compressor body, the shot blasting time is 0.6-0.7 hours, with a shot diameter of 1.4-1.6mm and a shot blasting intensity of 0.18-0.32MPa; during the second shot blasting process, the shot diameter is 0.6-0.8mm and the shot blasting intensity is 0.5-0.7MPa.

[0017] Beneficial effects: Compared with the prior art, the casting method for large inline multi-cylinder compressor bodies provided in this application is based on wet sand molding and HT300 material. Through the combination of printing simulation, graded venting, balanced feeding and precise process control, it can ensure cost and performance advantages when casting large inline multi-cylinder compressor bodies. The defect rates such as porosity, shrinkage cavities, sand holes and slag inclusions are significantly reduced. The tolerances of key dimensions and cylinder bore coaxiality are significantly improved, and the mechanical properties are more stable.

[0018] These and other objects, features and advantages of the present invention will become fully apparent from the following detailed description. Attached Figure Description

[0019] Figure 1 A cross-sectional structural schematic diagram of the wet-mold sand mold of the large inline multi-cylinder compressor body of this application is shown.

[0020] Figure 2 A partial structural schematic diagram and corresponding cross-sectional schematic diagram of the cylinder bore core in this application are shown.

[0021] Figure 3 A schematic flowchart of the casting method for the housing of a large inline multi-cylinder compressor according to this application is shown. Detailed Implementation

[0022] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0023] Those skilled in the art should understand that, in the disclosure of this specification, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0024] Unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will also be understood that terms, such as those defined in commonly used dictionaries, shall be interpreted as having a meaning consistent with their meaning in the context of the relevant art and shall not be interpreted as having an idealized or overly formal meaning unless expressly so defined herein.

[0025] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0026] Large inline multi-cylinder compressors generally refer to compressors with a single unit weight ≥200kg, ≥6 cylinders (inline layout), and cylinder bore diameter ≥80mm. Typical models include the H88 series, H90 series, and C610 series, which are commonly used in industrial refrigeration, chemical process cooling, data center cooling, and other fields.

[0027] HT300 gray cast iron is a preferred material for the body of large inline multi-cylinder compressors due to its good casting performance, mechanical strength and wear resistance. However, HT300 material has poorer fluidity than ductile iron, and the requirements for controlling the casting process parameters are higher.

[0028] Tide-molded sand has low raw material cost, short molding cycle, high production efficiency, and is suitable for large-scale production. It can also be used as a process for casting compressor bodies. However, when applied to large inline multi-cylinder compressor bodies made of HT300 material, the following prominent technical bottlenecks exist due to limitations in process characteristics, material characteristics, and large-scale structure: 1. Severe gas defects: Large inline multi-cylinder compressors have large volumes and complex cavities. The moisture content of the molding sand is typically 3%-5%. During casting, the moisture evaporates rapidly, generating a large amount of water vapor. In addition, the sand core inside the cavity produces a huge amount of gas, while the exhaust channels are long and obstructed. Water vapor and molten metal are trapped and cannot be discharged in time, forming defects such as pores and pinholes. The defect rate is as high as 13%-20%, which directly leads to unqualified air tightness and a pressure test leakage rate of over 12%. At the same time, HT300 material has poor fluidity and is prone to air entrapment during the filling process, further aggravating gas defects. 2. Shrinkage cavities and porosity are difficult to control: The hot spot area has a large volume and slow cooling rate. The solidification shrinkage characteristics of HT300 material lead to higher feeding requirements. Conventional riser feeding paths are long and have low feeding efficiency. Insufficient feeding fluid leads to frequent shrinkage cavities and porosity in hot spot areas such as the bottom of the crankcase and the cylinder block joint, affecting the strength and sealing of the casting. 3. Insufficient dimensional accuracy and stability: The sand mold dimensions of the large inline multi-cylinder machine body are large, and the wet compressive strength of the mold sand is only 0.18-0.25MPa. The impact force of the molten metal during pouring is large, which easily leads to mold wall deformation and sand mold displacement. The uneven solidification shrinkage of HT300 material, combined with sand mold deformation, results in frequent dimensional deviations in key parts and cylinder bore coaxiality deviations, with an assembly qualification rate of less than 78%. 4. High risk of sand holes and slag inclusions: The high temperature resistance of the mold sand is limited (refractory ≤1400℃), and sand particles are prone to falling off when washed by molten metal at 1380-1430℃; HT300 material has poor fluidity, and slag inclusions are difficult to float, resulting in a sand hole and slag inclusion defect rate of 9%-11%, which affects the processing quality and sealing performance.

[0029] 5. Coarse crystal grain size in cylinder bore: Slow cooling in the cylinder bore aggregation area and significant inoculation decay lead to excessive eutectic length, resulting in high roughness after cylinder bore machining and reducing the service life of the machine body.

[0030] To address one or more of the aforementioned technical problems, a casting method for the housing of a large inline multi-cylinder compressor is proposed. The aforementioned technical problems mainly include gas defects, shrinkage cavities, dimensional deformation, sand inclusions, and slag inclusions.

[0031] refer to Figures 1 to 3This application provides a casting method for a large inline multi-cylinder compressor body, wherein the casting method uses wet molding sand as the molding material and HT300 as the casting material, and includes the following steps in sequence: S10, printing a simulation model, S20, constructing a graded exhaust sand mold, S30, equalizing feeding, and S40, process control.

[0032] For S10, a simulation model was printed, and the casting cavity was tested using 3D printing. This included printing an outer cavity 10 and an inner cavity 20. The outer cavity was formed by an upper sand mold 11 and a lower sand mold 12, while the inner cavity was a sand core consisting of a motor chamber, a crankshaft chamber, a cooling chamber, and a cylinder bore chamber. By measuring the direction and size of the casting deformation, checking the location and characteristics of sand holes in the casting, and identifying the sand filling risk zone, the deformation law of the casting and the sand flushing risk zone were guided. Subsequently, in the mold design, the design size was adjusted according to the deformation law of the casting, the flow rate of molten iron in the sand filling risk zone was slowed down, and the risk of sand holes and slag inclusions was reduced.

[0033] As a preferred option, the moisture-proof molding sand printing formula for the outer cavity is: Silica sand, 100%, wherein the silica sand is 70 / 140 mesh, containing ≥90% silicon and <0.2% mud; Modified bentonite, 0.8%-1.5%, wherein the modified bentonite is in powder form and has undergone activation treatment; Starch-based binder, 0.5%-1.0%, wherein the starch-based binder can be gelatinized corn starch, which has the characteristic of low gas evolution; Curing aid, 0.2%-0.4%, wherein the curing aid may be hexamethylenetetramine; Moisture control agent, 0.1%-0.2%, wherein the moisture control agent may be fumed silica; Lubricant / dispersant, 0.1%-0.2%, wherein the lubricant / dispersant may be calcium stearate; The total binder phase was less than 3%. Therefore, the wet strength and collapsibility of tumbled sand were simulated by compounding bentonite and starch.

[0034] Furthermore, Table 1 below provides specific examples of printing simulation for the molded cavity damp sand formula: Table 1 External cavity printing process: In a sand mixer, add silica sand and bentonite sequentially and mix for 3 minutes → add starch and mix for 1-2 minutes → add urotropine and mix for 1-2 minutes → add calcium stearate and mix for 1-2 minutes → add fumed silica and mix for 1-2 minutes. Then discharge the material (temperature below 40℃); sieve through a 40-60 mesh screen (to remove lumps); let it stand for 0.5-1 hour to mature. Next, feed the matured sand into a binder jet printer to print the external cavity. After printing, let it stand for 4-8 hours to cure.

[0035] As a preferred option, the anti-coating sand printing formula for the inner cavity is: Silica sand, 100%, wherein the silica sand is 70 / 140 mesh or 100 / 200 mesh, and contains ≥98% silicon; Phenolic resin, 1.8%-2.5%, wherein the phenolic resin is thermosetting and can be powder or atomized liquid; Curing aid, 0.4%-0.8%, wherein the curing aid may be hexamethylenetetramine; Curing accelerator, 0.1%-0.3%, wherein the curing accelerator may be PTSA; High-temperature stabilizing agent, 0.1%-0.2%, wherein the high-temperature stabilizing agent can be nano-alumina; Dispersant, 0.2%-0.4%, wherein the dispersant can be starch powder; Flow aid, 0.1%-0.2%, wherein the flow aid may be fumed silica. This results in an internal cavity formulation with strength close to that of a hot core box, with tensile strength reaching 2.0-3.5 MPa, high hardness (Shore C 70-95), and low gas evolution (≤10 ml / g).

[0036] Furthermore, Table 2 below provides specific examples of printing simulations for the internal cavity simulated coated sand formula: Table 2 Internal cavity printing process: Add silica sand and nano-alumina to the sand mixer sequentially and dry-mix for 2 minutes → add phenolic resin and mix for 2-3 minutes → add hexamethylenetetramine and mix for 1-2 minutes → add PTSA and mix for 1-2 minutes → add starch and mix for 1-2 minutes → add fumed silica and mix for 1-2 minutes. Then discharge the material (temperature below 40℃); sieve through a 40-60 mesh screen (to remove lumps); let it stand and mature for 0.5-1 hour. Then, feed the matured sand into a binder jet printer to print the outer cavity. After printing, let it stand and cure for 4-8 hours.

[0037] Assembly: Assemble the printed outer and inner cavities; Pouring: Pouring molten HT300 iron, cooling, and cleaning; Measurement: Deformation location and size of castings, summarizing patterns, and identifying sand-filling risk areas by inspecting the location characteristics of sand holes in castings; Mold design: Adjust the design size according to the deformation law of the printed simulation casting, and reduce the risk of sand inclusions and slag inclusions by adjusting the size of the flow channel system to slow down the flow rate of molten iron in the sand-filling risk zone.

[0038] The core physical properties of the simulated molded sand and coated sand conform to the physical change range of molded sand and coated sand under normal conditions. Therefore, to intuitively reflect the purpose of our experiment, the molded sand of Example 1, which has low wet compressive strength and large deformation, was used for external cavity printing to highlight the defects of sand filling and slag inclusion in the flow channel system. The coated sand of Example 4, which has high tensile strength and large gas generation, was used for internal cavity printing to highlight the deformation law of the casting.

[0039] Specifically, for S20, a graded venting sand mold construction includes an independent venting design for the inner cavity and an venting pin and riser design for the outer cavity. The independent venting design for the inner cavity involves designing cavities for the thick areas of the motor chamber and crankshaft chamber. Simultaneously, sand core venting structures, such as vent holes or vent gaps, are respectively opened in the cavities, the cooling chamber, and the cylinder bore chamber. These sand core venting structures, in conjunction with the sand core venting pins, independently discharge the gas generated from the sand core into the casting cavity. The thick areas refer to regions with a sand core wall thickness ≥ 50mm. Regarding the design of the outer cavity venting pins and risers, 3- Four liquid replenishment risers 110 are provided, and external cavity venting pins (such as 3-8) are set on the top of the external cavity 10 to independently discharge the gas generated in the external cavity 10. The top of the liquid replenishment riser 110 is connected to the outside atmosphere, and the height of the liquid replenishment riser 110 exceeds the height of the casting, thereby realizing an efficient and zoned venting strategy. This can ensure that the gas is discharged quickly and reduce the heat dissipation of the molten metal in the liquid replenishment riser 110, which can effectively improve the feeding effect. Preferably, the height of the liquid replenishment riser 110 exceeds the height of the casting by 100-150mm, and the volume of the excess part is greater than 2%-3% of the volume of the casting to ensure the liquid replenishment efficiency. Specifically, for S30, balanced compression is achieved by using simulation software (such as Magma / Procast) to calculate the thermal modulus M (thermal modulus = thermal modulus volume / heat dissipation surface area) of each region of the compressor body. Insulation risers 120 are opened on the side walls of several regions where the thermal modulus M ≥ 1.2 cm (typical locations such as the bottom sides of the crankcase, the middle joint of the cylinder block, and the connection between the motor cavity and the crankshaft cavity). Semicircular holes 201 are symmetrically designed on the side of adjacent sets of cylinder bore cores 21 and the regions between cylinder bore cores 21 that are close to each other. At the same time, semicircular chills 22 are set in the semicircular holes 201. Taking the H88 series inline eight-cylinder compressor body as an example, it has a total of eight, that is, four sets of cylinder bore cores 21. Two semicircular holes 201 are symmetrically designed in the region between two cylinder bore cores 21 in each set. The arc-shaped portions of the two semi-circular chills 22 are close to each other, following the principle of highlighting the hot spot in the chill shape. At the same time, an exhaust gap is provided between the straight portion of the semi-circular chill 22 and the straight sidewall of the semi-circular hole 201, which can improve the cooling rate of specific parts, achieve uniform cooling in the cylinder bore area, effectively control the coarseness of the cylinder bore grains, and thus ensure that the cylinder bore meets the surface roughness requirements (Ra0.2-0.4μm) after machining. For S40, process control includes sequential sand mold pretreatment, melting and casting, cooling and unpacking, and post-treatment. Sand mold pretreatment maintains the deep moisture content of the sand mold at 3.4%-4.2%, ensuring a sand mold compactness of 1.7-1.8 g / cm³, preventing overheating and cracking, and preventing displacement of large, inline multi-cylinder sand molds during casting to guarantee dimensional accuracy. This also addresses the stability requirements of the sand mold due to uneven solidification shrinkage of HT300 material. The deep layer of the sand mold refers to the inner wall of the outer cavity or the area near the inner cavity (…). For example, in the inner wall area (1-3mm), the carbon equivalent of the HT300 gray cast iron used in the smelting is 3.2%-3.6%, thus balancing good fluidity and strength, and adapting to the casting and filling requirements of large inline multi-cylinder engines. The smelting temperature is 1480-1530℃ to ensure that the material is fully melted and the composition is uniform, avoiding overheating that leads to coarse grains. In addition, nitrogen is used for degassing before casting to reduce the gas content of the molten metal to ≤0.035%, thereby reducing internal porosity defects and adapting to the gas sensitivity of HT300 material. Features include an opening temperature ≤360℃, and cooling time adjusted based on the machine weight. For example, for a 200-250kg machine, the cooling time is 7 hours, and for a 250-300kg machine, the cooling time is 8-9 hours, significantly longer than the conventional 5-6 hours, to avoid rapid cooling cracks. It is adapted to the stress characteristics of HT300 material, ensuring stable casting structure and reducing internal stress. Post-treatment includes shot blasting and artificial aging. First, a medium-strength shot blasting machine is used for a single shot blasting treatment to remove surface sand from the mold. Adhesive sand, oxide scale, and gating remnants are removed by a second shot blasting treatment after aging to remove any attachments that were not identified and removed during the first shot blasting. A heat treatment aging furnace is used at 520-580℃, with a heating rate of 45℃ / h and a cooling rate of 38℃ / h. The holding time is adjusted to 3-5 hours based on the casting stress test results. Existing technologies use natural aging or low-temperature aging at 450-500℃. This improvement eliminates casting internal stress, stabilizes dimensional accuracy, and prevents deformation during subsequent processing or use. Finishing: Honing of cylinder bores and crankshaft bores, checking dimensional tolerances of key parts to be ±0.05mm and cylinder bore coaxiality to be 0.03mm.

[0040] In some embodiments, in step S30, the insulating riser 120 is opened on the sidewall of 3-5 areas with a thermal section modulus M ≥ 1.2 cm. At the same time, the volume ratio (or modulus volume) of the insulating riser 120 to the volume ratio (or thermal section modulus) of the thermal section is 1.7-2.3:1 to ensure sufficient shrinkage liquid, avoid shrinkage defects caused by the solidification lag of large thermal sections in large inline multi-cylinder engines, and give full play to the self-compensating shrinkage characteristics of HT300 material.

[0041] In some embodiments, in step S30, the inner cavity of the cylinder bore core 21 is the cylinder bore cavity, and the cylinder bore core 21 is made of chromite coated sand with a particle size of 70 / 140 mesh.

[0042] In some embodiments, the exhaust gap is 2-3 mm. The distance between the arcuate portion of the semi-circular chill 22 and the inner wall of the cylinder bore core 21 is 5-10 mm.

[0043] In some embodiments, in step S40, the sand mold pretreatment is as follows: the sand mold is heated in a sand mold heating furnace at 68-72°C, and the moisture content of the deep layer of the sand mold is measured every 10-20 minutes until the moisture content of the deep layer of the sand mold is maintained at 3.4%-4.2%, and the heating is stopped to ensure that the compactness of the sand mold is 1.7-1.8 g / cm³, to avoid overheating and cracking of the sand mold; to prevent the large inline multi-cylinder sand mold from shifting during pouring, to ensure dimensional accuracy, and to meet the requirements of the uneven solidification shrinkage of HT300 material on the stability of the sand mold.

[0044] In some embodiments, in step S40, the chemical composition of HT300 gray cast iron is controlled as follows: C: 2.9%-3.1%, Si: 1.8%-2.0%, Mn: 0.7%-1.0%, P≤0.05%, S: 0.05%-0.10%, Cr: 0.30%-0.35%, Sn: 0.07%-0.08%, Cu: 0.80%-0.85%, with the balance being Fe.

[0045] For example, the chemical composition (mass percentage) of HT300 is as follows: C: 2.9%, Si: 1.9%, Mn: 0.82%, P: 0.03%, S: 0.08%, Cr: 0.3%, Sn: 0.1%, Cu: 0.8%, Fe: balance; Carbon equivalent: 3.5%; Melting temperature: 1500℃, nitrogen degassing for 6 minutes; Pouring parameters: Pouring temperature 1400℃, filling speed 0.7m / s, pouring time 23 seconds.

[0046] In some embodiments, in step S40, a composite casting method of center pouring + side pouring is adopted. At the same time, a three-stage purification and filtration method of slag-blocking dam → slag-collecting needle → honeycomb filter screen is adopted during the casting process. That is, the dam body is used for coarse filtration and preliminary interception of large slag pieces; then the slag-collecting needle is used to adsorb and capture small inclusions; finally, the honeycomb screen is used for final fine filtration and rectification. The filling speed is 0.5-1.0 m / s, the casting temperature is 1390-1420℃, and the initial filling speed is 1.0 m / s. For every 10 mm increase in casting wall thickness, the filling speed decreases by 0.1 m / s until it is maintained at a minimum of 0.5 m / s, forming a linkage control based on wall thickness.

[0047] Center gating (also called bottom gating or intermediate injection): The main channel (sprue) of the gating system is located in the middle or bottom of the mold, and the molten metal smoothly enters the cavity from the lower middle or bottom of the casting. Side gating (also called top gating or side injection): The ingate of the gating system is located on the side or top of the casting, and the molten metal flows in from the side or top of the cavity. Combining the two forms a multi-level, multi-entry composite gating system. The core purpose of this composite design is to "maximize strengths and minimize weaknesses" to achieve precise control over the molten metal filling process. The synergistic effect after the composite system is as follows: In the initial stage of filling, the center gating system acts as the main force, smoothly filling the lower half of the cavity. At the same time or shortly thereafter, the side gating / top gating system begins to work, like "paratroopers," quickly filling the upper area and corners, and merging with the molten metal rising from the bottom. This approach allows for: significantly shortening the overall filling time, which is particularly beneficial for thin-walled castings; creating a more uniform temperature field throughout the mold cavity, reducing defects caused by excessive temperature differences; and balancing stability and efficiency, improving casting success rate while ensuring the internal quality of the casting. This significantly reduces defects such as porosity, inclusions, cold shuts, and incomplete pouring. It is particularly suitable for castings of large inline multi-cylinder compressor bodies with complex structures, large differences in wall thickness, and stringent quality requirements, boasting a high success rate. Furthermore, by adjusting the cross-sectional area of ​​different inlets, baffles, or pouring time, the flow rate and direction of the molten metal can be precisely controlled, offering good flexibility. It also helps establish an ideal temperature gradient, enabling the use of risers to achieve a dense casting structure and improve feeding.

[0048] In some embodiments, in step S40, during the primary shot blasting process, a chain-type shot blasting machine can be used. For a 200-250kg compressor body, the shot blasting time is 0.5 hours, and for a 250-300kg compressor body, the shot blasting time is 0.6-0.7 hours. The shot diameter is 1.4-1.6mm, and the shot blasting intensity is 0.18-0.32MPa, to avoid damaging the surface of the casting. During the secondary shot blasting process, a handheld shot blasting machine can be used. The shot diameter is 0.6-0.8mm, and the shot blasting intensity is 0.5-0.7MPa.

[0049] Regarding the large inline multi-cylinder compressor housing obtained by casting using the casting method for large inline multi-cylinder compressor housings provided in this application: Regarding the porosity / shrinkage cavity defect rate, according to GB / T 1348-2019 (gray cast iron parts), ultrasonic testing (UT) + metallographic analysis showed that the defect area ratio was ≤0.5%. Regarding the defect rate of sand inclusions, according to GB / T 1348-2019, the test was conducted by visual observation and magnification (10x) and the result was: the number of defects ≤ 3 / ㎡; Regarding dimensional accuracy, according to GB / T 1958-2017 (Technical Specifications for Geometric Measurements of Products), the coordinate measuring machine test results show that the tolerance of key parts is ≤ ±0.07mm, and the coaxiality of the cylinder bore is ≤0.035mm. In terms of mechanical properties, tests were conducted according to GB / T 228.1-2010 (tensile strength) and GB / T 231.1-2018 (hardness), and the results showed that the tensile strength was ≥320MPa and the hardness was HB200-220. Regarding air tightness, tests conducted according to GB / T 25747-2010 (Test Method for Air Tightness of Castings) showed that there was no leakage after holding a pressure of 16MPa for 60 minutes. Regarding the cylinder bore roughness, according to GB / T 3505-2009 (Surface Roughness Terminology), the roughness was measured by a roughness tester and found to be Ra0.2-0.4μm.

[0050] Comparative Example 1: Conventional Tide Sand Casting Process (Pre-existing Technology); Process parameters: conventional mold sand formula (3-4% bentonite, 3-5% moisture content), single-gating system, ordinary riser for feeding, natural cooling for 6 hours, and natural aging.

[0051] Test results: Porosity defect rate 15%, shrinkage cavity and porosity defect rate 12%, sand hole and slag inclusion defect rate 10%, critical dimension tolerance ±0.12mm, cylinder bore coaxiality 0.06mm, air tightness pressure test leakage rate 13%, tensile strength 280MPa.

[0052] Comparative Example 2: Resin Sand Casting Process (Existing High-End Process) Process parameters: Resin sand formulation (resin 3-3.5%), drying temperature 180℃ / 2 hours, conventional shrinkage compensation, cooling for 8 hours, artificial aging (500℃ / 3 hours).

[0053] Test results: Porosity defect rate 2.5%, shrinkage and porosity defect rate 1.8%, sand hole and slag inclusion defect rate 1.5%, critical dimension tolerance ±0.06mm, cylinder bore coaxiality 0.035mm, air tightness with no leakage, tensile strength 310MPa; however, the raw material cost is 32% higher than that of wet molding sand, and the production efficiency is 35% lower.

[0054] Therefore, the core advantages of the technical solution of this application compared to the comparative example are as follows: 1. Superior Defect Control: Compared with Comparative Example 1, the defect rates of porosity, shrinkage cavities, shrinkage porosity, sand holes and slag inclusions were reduced by 95%, 97%, and 97% respectively, and the airtightness fully met the standards; compared with Comparative Example 2, the defect rates were further reduced by 68%, 78%, and 80%.

[0055] 2. Higher dimensional accuracy: Key dimensional tolerances and cylinder bore coaxiality are better than Comparative Example 1 (improved by more than 50%), and slightly better than Comparative Example 2, meeting the assembly requirements of large compressor bodies.

[0056] 3. Superior economic efficiency: It maintains the low-cost advantage of wet molding sand (raw material cost is 32% lower than that of Comparative Example 2), and the production efficiency is 35% higher than that of Comparative Example 2, making it suitable for large-scale production; at the same time, it avoids the scrap loss caused by the high defect rate of Comparative Example 1.

[0057] 4. Enhanced material adaptability: Specifically optimized to address the issues of poor fluidity and uneven solidification shrinkage of HT300 material, resulting in stable mechanical properties (tensile strength ≥320MPa), superior to Comparative Example 1 and comparable to Comparative Example 2, but at a lower cost.

[0058] Those skilled in the art should understand that the embodiments of the present invention described above and shown in the accompanying drawings are merely examples and do not limit the invention. The advantages of the present invention have been fully and effectively realized. The functional and structural principles of the present invention have been demonstrated and explained in the embodiments; any variations or modifications can be made to the implementation of the present invention without departing from these principles.

Claims

1. A casting method for the housing of a large inline multi-cylinder compressor, characterized in that, The casting method uses molded sand as the molding material and HT300 as the casting material, and includes the following steps in sequence: S10, a printed simulation model, is used for experimental casting by printing casting cavities. It includes printing the outer and inner cavities of the casting. The outer cavity is formed by an upper sand mold and a lower sand mold, while the inner cavity is a sand core, consisting of a motor chamber, a crankshaft chamber, a cooling chamber, and a cylinder bore chamber. By measuring and inspecting, the deformation law of the casting and the risk area of ​​sand flushing are guided. In the subsequent mold design, the design size is adjusted according to the deformation law of the casting. S20, graded venting sand mold construction, including independent venting design for the inner cavity and venting pin and riser design for the outer cavity. The independent venting design for the inner cavity involves designing cavities for the thick areas of the motor chamber and crankshaft chamber. Sand core venting structures are respectively opened in the cavities, the cooling chamber, and the cylinder bore chamber. The sand core venting structures, in conjunction with the sand core venting pins, independently discharge the gas generated by the sand core into the casting cavity. The thick areas refer to the areas where the wall thickness of the chamber sand core is ≥50mm. For the design of the venting pin and riser for the outer cavity, 3-4 liquid replenishment risers are set on the side of the crankcase and the side of the motor case, respectively. An outer cavity venting pin is set at the top of the outer cavity to independently discharge the gas generated by the outer cavity. The top of the liquid replenishment riser is connected to the outside atmosphere, and the height of the liquid replenishment riser exceeds the height of the casting. S30, balanced feeding, the thermal modulus M of each region of the compressor body is calculated by simulation software, and the sidewalls of several regions with thermal modulus M≥1.2cm are opened with heat insulation risers; the regions between adjacent sets of cylinder cores and cylinder cores are symmetrically designed with semi-circular holes on the side that are close to each other, and semi-circular chills are set in the semi-circular holes, wherein the arc-shaped parts of the two semi-circular chills are close to each other, and an exhaust gap is provided between the straight part of the semi-circular chill and the straight sidewall of the semi-circular hole; S40, process control, includes sequential sand mold pretreatment, smelting and pouring, cooling and unpacking, and post-treatment. Sand mold pretreatment maintains the deep moisture content of the sand mold at 3.4%-4.2%. The carbon equivalent of the HT300 gray cast iron used in smelting is 3.2%-3.6%, and the smelting temperature is 1480-1530℃. Before pouring, nitrogen is used for degassing to reduce the gas content of the molten metal to ≤0.035%. The unpacking temperature is ≤360℃. Post-treatment includes shot blasting and artificial aging. A medium-strength shot blasting machine is used for the first shot blasting to remove sand, oxide scale, and gating residue from the sand mold surface. After aging, a second shot blasting is performed, using a heat treatment aging furnace at 520-580℃.

2. The casting method for a large inline multi-cylinder compressor body as described in claim 1, characterized in that, In step S10, the moisture-proof molding sand printing formula for the outer cavity is as follows: Silica sand, 100%, wherein the silica sand is 70 / 140 mesh, containing ≥90% silicon and <0.2% mud; Modified bentonite, 0.8%-1.5%; Starch-based binder, 0.5%-1.0%; Curing aid, 0.2%-0.4%; Moisture control agent, 0.1%-0.2%; Lubricant / disintegrating agent, 0.1%-0.2%; The total binder phase is less than 3%.

3. The casting method for a large inline multi-cylinder compressor body as described in claim 2, characterized in that, In step S10, the anti-coating sand printing formula for the inner cavity is: Silica sand, 100%, wherein the silica sand is 70 / 140 mesh or 100 / 200 mesh, and contains ≥98% silicon; Phenolic resin, 1.8%-2.5%; Curing aid, 0.4%-0.8%; Curing accelerator, 0.1%-0.3%; High-temperature stabilizing agent, 0.1%-0.2%; Dispersant, 0.2%-0.4%; Flow aid, 0.1%-0.2%.

4. The casting method for a large inline multi-cylinder compressor body as described in claim 1, characterized in that, In step S30, the insulating riser is opened on the sidewall of 3-5 regions where the thermal section modulus M≥1.2cm, and the volume ratio of the insulating riser to the thermal section volume is 1.7-2.3:

1.

5. The casting method for a large inline multi-cylinder compressor body as described in claim 1, characterized in that, In step S30, the inner cavity of the cylinder bore core is the cylinder bore cavity, and the cylinder bore core is made of chromite coated sand with a particle size of 70 / 140 mesh.

6. The casting method for a large inline multi-cylinder compressor body as described in claim 5, characterized in that, The exhaust clearance is 2-3mm, and the distance between the arc-shaped part of the semi-circular chill and the inner wall of the cylinder bore core is 5-10mm.

7. The casting method for a large inline multi-cylinder compressor body as described in claim 1, characterized in that, In step S40, the sand mold pretreatment is as follows: the sand mold is heated in a sand mold heating furnace at 68-72℃, and the moisture content of the deep layer of the sand mold is measured every 10-20 minutes until the moisture content of the deep layer of the sand mold is maintained at 3.4%-4.2% and then the heating is stopped. The compactness of the sand mold is 1.7-1.8g / cm³.

8. The casting method for a large inline multi-cylinder compressor body as described in claim 1, characterized in that, In step S40, the chemical composition of HT300 gray cast iron is controlled as follows: C: 2.9%-3.1%, Si: 1.8%-2.0%, Mn: 0.7%-1.0%, P≤0.05%, S: 0.05%-0.10%, Cr: 0.30%-0.35%, Sn: 0.07%-0.08%, Cu: 0.80%-0.85%, with the balance being Fe.

9. The casting method for a large inline multi-cylinder compressor body as described in claim 1, characterized in that, In step S40, a composite casting method of center pouring + side pouring is adopted. At the same time, a three-stage purification and filtration method of slag-blocking dam → slag-collecting needle → honeycomb filter screen is adopted during the casting process. The filling speed is 0.5-1.0m / s, the casting temperature is 1390-1420℃, and the initial filling speed is 1.0m / s. For every 10mm increase in the casting wall thickness, the filling speed is reduced by 0.1m / s until it is maintained at a minimum of 0.5m / s.

10. The casting method for a large inline multi-cylinder compressor body as described in claim 1, characterized in that, In step S40, during the first shot blasting process, for a 200-250kg compressor body, the shot blasting time is 0.5 hours, and for a 250-300kg compressor body, the shot blasting time is 0.6-0.7 hours. The shot diameter is 1.4-1.6mm, and the shot blasting intensity is 0.18-0.32MPa. During the second shot blasting process, the shot diameter is 0.6-0.8mm, and the shot blasting intensity is 0.5-0.7MPa.

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