A process for manufacturing a box casting for oil machinery

Abstract

The application discloses a kind of box castings process manufacturing methods for petroleum machinery, belong to casting manufacturing technical field.The box castings are integrally cast top drive box, including box body and integrated suspension body.The method includes: casting process design, adopt three box molding and the position of suspension body main stress part is in upper box;Directly above it is set up clear riser, and the dark riser with exhaust hole is set up on the thick part of the two sides of box top;Cold iron is set below the thickened skirt of box opening, and deformation resisting rib is set at box opening;Adopt ceramic sand and modified sodium silicate sand mold, electric arc furnace and LF furnace double connection smelting, bottom pouring and heat treatment including normalizing, quenching and tempering.The application effectively solves the problem of shrinkage porosity in thick part, deformation of thin wall opening and unqualified internal quality of key position in integrally casting due to large wall thickness difference, so that the casting has high density, small deformation, excellent comprehensive mechanical properties, and the flaw detection of key position meets high standard requirements.

Description

Technical Field

[0001] This invention relates to a manufacturing process for a housing casting for petroleum machinery, belonging to the technical field of casting manufacturing. Background Technology

[0002] As the core power unit of modern drilling equipment, the top drive system in oilfields directly affects the safety and efficiency of deep well, ultra-deep well, and complex trajectory well operations. In this system, the housing and suspension body, as the main load-bearing components, must not only withstand the rated load, dynamic torque, and frequent impacts transmitted by the drill string, but also maintain good toughness reserves under low-temperature conditions to meet the structural integrity requirements of API Spec 8C at 1.5 times the rated load. Given its complex internal structure integrating gear transmission mechanisms, drilling fluid channels, and high-precision bearing housings, forging is difficult to achieve due to material flowability and geometric constraints. Therefore, the industry generally uses sand casting to manufacture such castings. Traditional solutions are mostly based on water glass sand or resin sand systems, formed by separate casting followed by welding. While this solves the forming difficulties caused by structural complexity to some extent, it also introduces potential risks to service reliability.

[0003] Although the welding process of split casting can avoid the solidification control problem in integral casting, the welded joint area inevitably forms microstructure discontinuity and residual stress concentration. Under the long-term action of combined loads (tension, bending and torque coupling), fatigue cracks are easily induced, which significantly weakens the structural load-bearing capacity and makes it difficult to pass the strength verification specified by API Spec 8C.

[0004] Even when attempting to eliminate welds through integral casting, severe metallurgical quality control challenges remain: the significant differences in casting wall thickness (from 30mm thin-walled boxes to 150mm thick flanges) result in extremely uneven heat distribution during solidification, making thicker areas such as bearing seats and flange roots prone to volumetric defects like shrinkage cavities and porosity; while the box opening area, due to its thinner wall thickness (30–50mm), is prone to irreversible deformation during solidification shrinkage and subsequent heat treatment, severely affecting assembly sealing and dimensional accuracy.

[0005] As the suspension lugs are key load-bearing nodes, their internal quality must meet the GB / T 7233.1-2023 ultrasonic flaw detection level 1 standard. However, the existing sand casting process has systematic deficiencies in feeding path design, temperature field control, and molten steel purity control, which often results in this area failing to meet the standard due to microscopic porosity or inclusions. Furthermore, because the standard prohibits welding repairs on major load-bearing parts, the scrap rate remains high.

[0006] Based on this, the existing two-box molding method has limited adaptability to complex spatial structures, making it difficult to achieve effective feeding and venting in the high-point area of ​​the suspended body; conventional bottom-pouring or top-pouring casting systems also fail to take into account both the stability of filling and the sequential solidification requirements of thick parts; in addition, the smelting process lacks precision in controlling the content of harmful elements and gases such as sulfur and phosphorus, which further exacerbates the tendency for hot cracking and the probability of internal defects.

[0007] Therefore, how to achieve source suppression of defects such as shrinkage cavities, porosity, deformation and cracking through systematic reconstruction of the casting process while ensuring the integrated molding of the housing and suspension body, and meeting multiple stringent requirements of high strength, high toughness and high flaw detection level, has become a key challenge and a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a manufacturing method for a box casting for petroleum machinery. This method solves the problems of shrinkage cavities and porosity in thick parts, deformation at thin-walled openings, and difficulty in meeting high-standard flaw detection requirements for the internal quality of key stress-bearing parts during the integral casting of petroleum top drive box castings due to large differences in wall thickness.

[0009] The technical problem to be solved by this invention is achieved by the following technical solution:

[0010] A method for manufacturing a housing casting for petroleum machinery, the housing casting comprising a housing body and an integrated suspension body, the housing body having an opening at its bottom, and a skirt with a cross-sectional dimension larger than the housing wall thickness at the opening, comprising the following steps:

[0011] Casting process design: A three-box molding is adopted to form the mold, and the main stress-bearing parts of the suspension body are set in the upper box area;

[0012] An exposed riser is provided directly above the main stress-bearing part of the suspension body, and a concealed riser is provided above the thick parts on both sides of the main body of the box. A vent is provided at the top of the concealed riser.

[0013] A chill is installed below the skirt of the opening;

[0014] Mold making: Design and manufacture molds according to casting processes;

[0015] Molding and assembly: Using sand casting technology, three boxes are shaped and assembled using molds to form a casting mold;

[0016] Smelting and casting: Smelting molten steel and casting it into the mold using a bottom-pouring system;

[0017] Post-processing: The following steps are performed sequentially: unpacking and sand removal, followed by heat treatment.

[0018] Finishing and Inspection: Finishing the castings and inspecting their surface and internal quality.

[0019] The present invention is further configured such that: in the casting process design, the suspension body is provided with a lug for connection, a chill is provided at the bottom of the lug portion, and an exhaust hole is provided at the top of the lug portion.

[0020] The present invention is further configured such that, in the casting process design, the ingate of the bottom-pouring gating system is provided at least once at the bottom of the thick parts on both sides of the box body.

[0021] The present invention is further configured such that: in the casting process design, a tie rod is designed at the opening of the box, the tie rod is set along the width direction of the box body and connected to the two sides with smaller wall thickness at the opening of the box.

[0022] The present invention is further configured such that: the sand casting uses ceramic sand as the raw sand and modified water glass as the binder.

[0023] The present invention is further configured such that: the smelting adopts a dual-process of electric arc furnace and LF refining furnace, specifically including:

[0024] Material preparation: steel plate material ≥70%, recycled material ≤30%, carbon is prepared with carbon raiser, and lime is placed at the bottom of the furnace;

[0025] Electric arc furnace smelting control: melting temperature is 1540-1560℃, carbon content is 0.50-0.60%, carbon content of melt is 0.30-0.45%, carbon content of tapped steel is 0.10-0.15%, phosphorus content of tapped steel is ≤0.015%, sulfur content is ≤0.012%, and tapping temperature is 1620-1650℃;

[0026] LF refining furnace control: Maximum power supply for 8-10 minutes, argon flow rate before slag whitening 8-12 NL / min, tapping temperature 1580-1590℃.

[0027] The present invention is further configured such that the heat treatment comprises, in sequence:

[0028] Normalizing: Temperature is 900±10℃, hold for 7-9 hours and then air cool;

[0029] Quenching: The temperature is 900±10℃, and the temperature is held for 3.5-4.5 hours before water cooling;

[0030] Tempering: The temperature is 540±40℃, and the temperature is maintained for 8-10 hours before water cooling.

[0031] The present invention is further configured such that: the material of the box casting is high-strength low-alloy steel, and its chemical composition, by mass percentage, includes:

[0032] C: 0.17-0.22%, Mn: 0.80-1.20%, Si≤0.60%, Cr: 0.40-0.90%, Mo: 0.40-0.70%, Ni: 0.60-1.00%, P≤0.015%, S≤0.02%, balance being Fe and unavoidable impurities.

[0033] The present invention is further configured such that the quality inspection step includes:

[0034] Surface quality inspection: Magnetic particle testing is performed on all detectable surfaces of the casting using the wet magnetic particle method with a magnetic suspension concentration of 10-20 mL / L.

[0035] Internal quality inspection: Ultrasonic testing is performed on the base of the suspension lugs, the flange mating surface, and the end face of the housing.

[0036] The present invention is further configured such that: in the casting process design, the skirt at the opening is an inner skirt, and the ratio of its cross-sectional thickness to the wall thickness of the main body of the box is (1.5-2.5):1.

[0037] The beneficial effects of this invention are:

[0038] By combining the three-box design, targeted risers, and chill design, the traditional problems of shrinkage porosity in thick sections and deformation in thin-walled areas are effectively solved. This ensures that the internal quality of the castings consistently meets high-level flaw detection requirements, significantly reducing the scrap rate caused by internal defects. The optimized process integrates the production of the box body and the suspension body, shortening the production cycle by approximately 50% and greatly improving production efficiency. At the same time, it reduces subsequent welding and straightening processes, lowering overall manufacturing costs.

[0039] By combining integral casting with precision-controlled heat treatment, the uniformity and stability of the mechanical properties of all parts of the casting are ensured. Its strength, toughness, and low-temperature impact resistance consistently meet the highest standards required in the petroleum machinery industry, enhancing the product's market competitiveness. Furthermore, the use of a green molding material system combining ceramic sand and modified water glass improves the surface quality and dimensional accuracy of the casting, and enables the efficient recycling of used sand, aligning with the trend of environmentally friendly production. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a box structure made by split casting in the prior art.

[0041] Figure 2 This is a schematic diagram of a suspension structure made by split casting in the existing technology.

[0042] Figure 3 This is a schematic diagram of the existing technology for the process of casting a box in parts.

[0043] Figure 4 This is a schematic diagram of the existing technology for the process of casting a suspension body in a split-body manner.

[0044] Figure 5 This is a schematic diagram of the overall process scheme of the present invention.

[0045] Figure 6 This is a schematic diagram of the chill in the process scheme of this invention.

[0046] Figure 7 This is a schematic diagram of the riser in the process scheme of this invention.

[0047] Figure 8 This is a schematic diagram of the casting system in the process scheme of the present invention.

[0048] Figure 9 This is a schematic diagram of the tie rod in the process scheme of the present invention.

[0049] Figure 10 This is a mold flow analysis diagram of the process scheme of the present invention.

[0050] Figure 11 This is a temperature field distribution diagram of the process scheme of the present invention.

[0051] Figure 12 This is a schematic diagram of the heat treatment process of the present invention. Detailed Implementation

[0052] To facilitate a clear understanding of the technical means, creative features, objectives, and effects of this invention, the invention will be further described below in conjunction with specific illustrations.

[0053] Core components such as top drive housings and suspension systems for petroleum machinery form the "skeleton" of drilling equipment and must simultaneously meet the requirements of high strength, high toughness, high sealing performance, and complex structural integration (integrated gear trains, drilling fluid channels, bearing housings, etc.).

[0054] Traditionally, tank castings for oilfield top drives are produced by separate casting followed by welding, such as... Figures 1-2 The diagram shown is a schematic of the split casting structure.

[0055] like Figures 3-4 As shown, the traditional casting process is as follows: the box opening faces downwards, and the suspension joint faces upwards, both being two-box designs; metal smelting uses a medium-frequency furnace or an electric arc furnace; heat treatment includes normalizing and tempering; water glass or resin sand molds are used.

[0056] When the box body and the suspension body are cast separately: due to the complex structure of the box body, the large number of related dimensions, the high requirements for core positioning, and the easy deformation during cooling solidification and heat treatment;

[0057] The suspension lugs have high requirements for internal quality and dimensional accuracy, and ultrasonic testing (UT) needs to meet the Class 1 standard in GB / T7233.1-2023.

[0058] Traditional processes use separate casting and welding, which can easily lead to stress concentration at the welded joints. Under combined loads (tension, bending, and torque), cracks are likely to occur, making it impossible to meet the strength requirement of 1.5 times the rated load in API Spec 8C standard, resulting in a shorter service life.

[0059] When attempting integral casting, due to the complex structure of the casting and the large differences in wall thickness (30-150mm), shrinkage cavities and porosity are easily generated in thick parts (such as bearing seats and flanges), and deformation is easily generated at thin-walled openings (such as box openings). The internal quality is difficult to meet the Level 1 flaw detection standard in GB / T 7233.1-2023.

[0060] This invention provides a manufacturing method for a box-shaped casting for petroleum machinery, comprising the following steps: casting process design, mold making, molding and box assembly, smelting and pouring, unpacking and sand removal, normalizing, hot cutting of risers and gating gates, tempering, shot blasting, first inspection, rough machining, external dimensions / UT / MT (self-inspection), finishing (defect handling), quenching and tempering, mechanical property testing, external dimensions / UT / MT (final inspection), shot blasting, and shipping.

[0061] like Figures 5-9 As shown, the casting process design is as follows: The box casting includes the box body and the integrated suspension body. The bottom of the box body has an opening, and a skirt with a cross-sectional dimension larger than the box body wall thickness is provided at the opening. The skirt is an inner skirt, and the ratio of its cross-sectional thickness to the box body wall thickness is (1.5-2.5):1. In this embodiment, the typical wall thickness of the box body is 30mm. The skirt cross-section is designed as a 50mm×50mm rectangle. The appropriately thickened skirt acts as a local reinforcing rib, improving the structural rigidity and deformation resistance of the opening edge.

[0062] The box casting adopts a three-box molding scheme to form the mold, specifically dividing the mold into an upper box, a middle box, and a lower box. The main stress-bearing parts of the suspension (i.e., the areas bearing the main tensile and bending loads, such as the lifting lugs and nearby thick connecting parts) are located in the upper box area, while the main body of the box is located in the lower box area. The parting lines of the upper and middle boxes are located at the main stress-bearing parts of the suspension, while the parting lines of the middle and lower boxes are located at the connection points between the suspension and the main body of the box.

[0063] An exposed riser is installed directly above the main stress-bearing part of the suspension body. The top of the exposed riser is exposed outside the mold cavity. It is used to feed liquid metal into the thick hot section during the later stage of casting solidification to prevent shrinkage cavities and porosity. A concealed riser is installed above the thick parts on both sides of the main body of the box. The top of the concealed riser is not exposed above the upper surface of the mold cavity. It is equipped with a vent hole at the top to discharge gas in the mold cavity and assist in feeding.

[0064] Chills are installed below the skirt of the box opening. The chills are located at the thin-walled part of the skirt, and several are evenly distributed along the length of the main body of the box. The chills are metal quenching blocks, usually made of cast iron or steel. Their function is to accelerate the cooling rate of this area, reduce the solidification time difference with the surrounding thin-walled areas, refine the grains, and guide the solidification sequence.

[0065] The suspension body is equipped with ear plates for connection, with chills at the bottom of the ear plate section and vents at the top. A chill is placed below the root of the ear plate section (i.e., the cavity position in the mold corresponding to the bottom of the ear plate). It fits tightly into the sand mold to strongly absorb heat in this area, accelerating cooling, refining grains, and altering the solidification sequence, facilitating the sequential solidification of the molten metal from below towards the riser. Vents at the top of the ear plate section of the suspension body allow gas accumulated in this dead zone within the mold cavity during pouring to escape, ensuring complete filling of the molten metal and preventing porosity or incomplete filling defects.

[0066] Because the wall thickness of the opening area at the bottom of the box is relatively thin and it is a free end, it is very easy to "open" deformation during the solidification and shrinkage process of the casting and the subsequent high-temperature heat treatment process due to uneven internal and external cooling and phase transformation stress. That is, the opening size becomes larger or warping occurs, which seriously affects the assembly accuracy and sealing of other components.

[0067] Therefore, tie rods are designed at the opening, with the tie rods installed along the width of the casting and connecting the two sides of the opening where the wall thickness is smaller. During the solidification and cooling process of the casting, the tie rods provide mechanical tension and constraint to the two sides of the thin wall of the opening, limiting the amplitude and direction of its free contraction, thereby effectively preventing opening deformation.

[0068] The thick sections on both sides of the mold box are critical hot spots. Improper gating system design, uneven molten metal filling, or insufficient feeding in these areas can lead to cold shuts, incomplete filling, or severe shrinkage cavities. For bottom-pouring gating systems, at least one guillotine should be installed at the bottom of each of the thick sections on both sides of the mold box. The two guillotunes should be aligned with the bottom of the cavities on the left and right sides of the mold box, respectively, to introduce molten steel. The cross-sectional area of ​​the guillotunes is calculated to ensure a stable molten steel filling speed and prevent erosion of the sand mold.

[0069] Bottom pouring allows molten steel to rise gradually from the bottom of the mold cavity, which facilitates the upward discharge of gas from the mold cavity through the riser and vent. At the same time, it ensures that the molten steel that enters the mold cavity first and has a relatively low temperature is located at the bottom of the thick part, forming a temperature field with the hot molten steel at the riser above, which is conducive to sequential solidification and enhances the feeding effect of the riser.

[0070] like Figure 10 As shown in the figure, the filling rate reaches 98.0%-98.9%, approaching a fully filled state, indicating that the bottom-pouring casting system of this embodiment of the invention achieves stable and sufficient filling of the mold with molten steel. The bottom-pouring method can avoid molten steel splashing and slag entrapment, and at the same time, the venting design of the high-point vent holes reduces the occurrence of defects such as incomplete filling of the mold cavity and porosity.

[0071] The filling process takes about 3.5 hours. Considering the complex structure of the casting with different wall thicknesses (30-150mm), this filling speed matches the process requirements, ensuring sufficient feeding of thick parts (bearing seats, flanges) while avoiding turbulence defects caused by excessive filling in thin-walled parts.

[0072] like Figure 11 As shown in the figure, the liquidus temperature (Tlig=1516℃) and solidus temperature (Tsol=1430℃) are marked, clearly illustrating the solidification range of molten steel from liquid to solid. The temperature gradient (124℃-1580℃) in different parts of the casting conforms to the "sequential solidification" design principle. Thick parts (such as load-bearing parts of the suspension body and bearing housings) have higher temperatures, while thin-walled parts (box opening and skirt) have lower temperatures, ensuring that thick parts can receive continuous feeding through the risers.

[0073] Mold making: Based on the casting process design drawings described above, the corresponding mold is made. The mold material can be wood, plastic, or metal. In this embodiment, a plastic mold is used because it has the advantages of dimensional stability and high surface finish. In practical applications, other materials can also be selected for the mold, and this embodiment does not limit this choice.

[0074] Molding and Assembly: Sand casting is employed, using molds to create upper, middle, and lower sand molds. These three molds are then accurately assembled according to positioning marks to form a complete casting cavity. Ceramic sand is used as the raw sand in sand casting, and modified water glass is used as a binder.

[0075] Ceramic sand is a spherical artificial sand particle made primarily from high-alumina bauxite through melting in an electric arc furnace and high-pressure air blowing. Its main mineral components are Al₂O₃ and SiO₂, with a particle size range of 0.020 mm to 3.350 mm. It exhibits high sphericity (≥0.9), a smooth surface, a much lower coefficient of thermal expansion than quartz sand, and a refractoriness exceeding 1790℃. In practical applications, other types of sand particles can also be selected for molding materials; this application does not limit this selection.

[0076] Modified water glass is an inorganic binder that has undergone physical or chemical modification of traditional water glass (sodium silicate aqueous solution). Its chemical formula is R₂O·nSiO₂ (where R represents Na, K, etc.), and it appears as a colorless or slightly colored transparent viscous liquid. The modified water glass retains its rapid hardening characteristic at room temperature when reacting with CO₂ or ester-based hardeners, while also improving its collapsibility and the regeneration performance of old sand.

[0077] Sand molds using ceramic sand and modified water glass result in high surface finish on castings, improved dimensional accuracy, and significantly reduced labor intensity for sand removal. Furthermore, this material combination is environmentally friendly and recyclable, reducing production costs and solid waste emissions.

[0078] Smelting and Casting: The smelting process produces qualified molten steel. A bottom-pouring casting system is used to pour the molten steel into the mold. The smelting process employs a dual-process combining an electric arc furnace and an LF refining furnace, specifically including:

[0079] Material preparation: High-quality scrap steel and pig iron are used as furnace charge, with steel plate material accounting for ≥70% and recycled material (internal return material) accounting for ≤30%.

[0080] The chemical composition of the housing casting material is shown in the table below:

[0081]

[0082] The material of the box casting is high-strength low-alloy steel, and its chemical composition, expressed as a percentage by mass, is shown in the table above. The residual element Cu content should not exceed 0.30%; the target value is a reference value for calculating the alloy content; the chemical composition of the casting must be retested after unpacking and must meet the standard range.

[0083] To precisely control the final carbon content, carbon raisers (such as graphite raisers) are used in the furnace. 1000-1200 kg of lime is placed at the bottom of the electric arc furnace for early slag formation and dephosphorization.

[0084] Electric Arc Furnace Smelting Control: The prepared charge is added to the electric arc furnace for melting. The melting point temperature (i.e., the temperature of the molten steel after all the charge has melted) is controlled at 1540-1560℃. The carbon content (i.e., the expected carbon content after the charge has melted) is controlled at 0.50-0.60%. After melting and analysis, the carbon content of the melt is controlled at 0.30-0.45%. After decarburization during the oxidation period, the carbon content (C1) of the tapped steel is controlled at 0.10-0.15%. At tapping, the phosphorus content (P) is ≤0.015%, and the sulfur content (S) is ≤0.012%. The molten steel is tapped after meeting the requirements, with the tapping temperature controlled at 1620-1650℃.

[0085] LF Refining Furnace Control: Molten steel from the electric arc furnace is transferred to the LF (Ladle Furnace) refining furnace. Maximum power is supplied for 8-10 minutes to rapidly increase the steel temperature and promote slag-steel reaction. Before the slag turns white (indicating good reducing properties), argon gas is blown in through the permeable bricks at the bottom of the ladle for stirring, with the argon flow rate controlled at 8-12 NL / min. When the molten steel temperature reaches 1580-1590℃ and the chemical composition is sampled, analyzed, and adjusted to meet standards, the steel can be tapped for casting. During the refining process, deoxidizers (such as aluminum granules and calcium silicate powder) and slag-forming materials (lime and fluorite) are continuously added to ensure the formation of highly fluid white slag, achieving deep desulfurization, deoxidation, and adsorption of inclusions.

[0086] The electric arc furnace completes the initial smelting, primarily for rapid melting and dephosphorization. The LF furnace then undertakes the refining task. Under a reducing atmosphere, precise temperature control via electric arc heating, argon stirring to promote compositional homogenization and inclusion flotation, and deep desulfurization and deoxidation via white slag refining result in high-purity, precisely composed, and temperature-uniform molten steel. This dual-smelting process stably controls the content of harmful elements P and S in the steel at extremely low levels, significantly improving the purity of the molten steel. This provides a fundamental metallurgical guarantee for castings to achieve excellent mechanical properties, especially meeting the low-temperature toughness requirement of -20℃ impact energy Akv ≥ 46J.

[0087] Post-processing: After casting is completed and the casting has fully solidified and cooled, the casting is removed from the mold and then cleaned of molding sand and oxide scale from the surface and internal cavity using methods such as vibration sand removal and shot blasting. The casting is then subjected to heat treatment.

[0088] Because the wall thickness of the unibody casting is uneven, the thick-walled areas have poor hardenability, and the core is prone to developing a soft phase structure with insufficient strength; the thin-walled areas cool too quickly, resulting in high quenching stress and easy deformation and cracking. A sophisticated heat treatment process is needed to balance strength and toughness and control deformation.

[0089] like Figure 12 As shown, the heat treatment includes the following steps in sequence:

[0090] Normalizing: The cleaned casting is placed in a bogie-type resistance furnace and heated to 900±10℃. The holding time is determined according to the maximum wall thickness of the casting (e.g., 150mm). In this embodiment, the holding time is 7-9 hours to ensure that the core of the casting also reaches the phase transformation temperature. After holding, the casting is removed from the furnace and air-cooled. The purpose of normalizing is to refine the coarse grains formed during casting, homogenize the microstructure, eliminate internal stress, and prepare the microstructure for subsequent quenching.

[0091] Quenching: After normalizing, the casting is reheated to 900±10℃, with a shorter holding time than normalizing, approximately 3.5-4.5 hours, to ensure uniform austenitization. After holding, the casting is quickly removed and immersed in a circulating cooling water bath for quenching. Quenching transforms austenite into high-strength martensite.

[0092] Tempering: The quenched castings are immediately (or as soon as possible) placed in a tempering furnace, heated to 540±40℃, held for 8-10 hours, and then water-cooled. The purpose of tempering is to eliminate quenching stress, transform unstable martensite into tempered sorbite, and significantly improve the plasticity and toughness of the material while maintaining high strength.

[0093] This heat treatment effectively solves the problem of balancing strength and toughness in castings with uneven wall thickness, resulting in uniform and stable mechanical properties of the overall casting, fully meeting the requirements. Figure 5 The technical requirements shown ensure the safe operation of the castings under complex loads.

[0094] Finishing and Inspection: The cleaned castings undergo finishing processes, including cutting up and downgates, grinding burrs and flash, and welding to repair surface defects within permissible limits. Then, a comprehensive surface and internal quality inspection is performed on the castings according to standards.

[0095] The quality inspection steps include:

[0096] Surface quality inspection: Magnetic particle testing (MT) is performed on all detectable surfaces of the casting (i.e., the outer and inner surfaces accessible to the probe). A wet magnetic particle method is used, where fluorescent magnetic powder is suspended in water or oil to create a magnetic suspension. The concentration of the magnetic suspension is controlled at 10-20 mL / L of magnetic powder precipitate per liter of carrier liquid. During testing, the casting is magnetized by electromagnetic flux or by using a magnetic yoke, then the magnetic suspension is sprayed on, and the presence of magnetic traces is observed under ultraviolet light. The testing standard must meet the Class 2 requirements of GB / T 9444-2007.

[0097] Internal quality inspection: Ultrasonic testing (UT) is performed on critical stress areas such as the base of the suspension lugs, flange mating surfaces, and end faces of the housing. A pulse-echo ultrasonic flaw detector is used, with appropriate probes (such as straight probes and angle probes) and coupling agents selected, and the inspection is conducted according to the specified scanning path and sensitivity. Ultrasonic testing must meet the Class 2 requirements of GB / T 7233.1-2023, with the suspension lugs, as particularly important components, requiring a Class 1 standard.

[0098] Through systematic non-destructive testing, the surface and internal quality of castings can be comprehensively and accurately assessed, ensuring that all defects are within the allowable range of standards. This provides a reliable quality basis for the safe use of castings and reduces the risk of product failure during service.

[0099] This invention utilizes a systematic casting, metallurgical, and post-processing technology to achieve integrated molding and high-performance control of complex petroleum machinery housing castings. A three-box molding scheme is employed for rational parting, with key load-bearing components located in the upper box for feeding purposes. Exposed and concealed risers are carefully arranged above thicker sections for molten metal feeding, while chills are placed in thin-walled areas, such as below the mold opening, to regulate solidification sequence and prevent deformation. Venting holes are designed at key points such as lifting lugs to ensure complete filling.

[0100] In the molding stage, spherical ceramic sand and modified water glass binder are used to prepare sand molds with high dimensional accuracy and good collapsibility. In the smelting stage, a dual process of electric arc furnace and LF refining furnace is adopted. Through strict process control, high purity and precise composition of molten steel are obtained, and a bottom pouring system is used to fill the mold smoothly.

[0101] After solidification, the casting undergoes sand removal and a multi-stage heat treatment process, including normalizing, quenching, and tempering, to balance the differences in microstructure and stress caused by uneven wall thickness, ultimately achieving a uniform strength and toughness balance. Finally, comprehensive finishing and non-destructive testing ensure that the surface and internal quality of the casting meets stringent technical standards, thus completing the entire manufacturing process from design to finished product.

[0102] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention, all of which fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a housing casting for petroleum machinery, the housing casting comprising a housing body and an integrated suspension body, the housing body having an opening at its bottom, and a skirt with a cross-sectional dimension larger than the housing wall thickness at the opening, characterized in that... Includes the following steps: Casting process design: A three-box molding is adopted to form the mold, and the main stress-bearing parts of the suspension body are set in the upper box area; An exposed riser is provided directly above the main stress-bearing part of the suspension body, and a concealed riser is provided above the thick parts on both sides of the main body of the box. A vent is provided at the top of the concealed riser. A chill is installed below the skirt of the opening; Mold making: Design and manufacture molds according to casting processes; Molding and assembly: Using sand casting technology, three boxes are shaped and assembled using molds to form a casting mold; Smelting and casting: Smelting molten steel and casting it into the mold using a bottom-pouring system; Post-processing: The following steps are performed sequentially: unpacking and sand removal, followed by heat treatment; Finishing and Inspection: Finishing the castings and inspecting their surface and internal quality.

2. The method according to claim 1, characterized in that, In the casting process design, a tie rod is designed at the opening of the box. The tie rod is set along the width direction of the box body and connects the two sides with smaller wall thickness at the opening.

3. The method according to claim 1, characterized in that, In the casting process design, the ingate of the bottom-pouring gating system is provided at least once at the bottom of the thick parts on both sides of the box body.

4. The method according to claim 1, characterized in that, In the casting process design, the suspension body is provided with ear plates for connection, chills are provided at the bottom of the ear plate portion, and vent holes are provided at the top of the ear plate portion.

5. The method according to claim 1, characterized in that, The sand casting uses ceramic sand as the raw sand and modified water glass as the binder.

6. The method according to claim 1, characterized in that, The smelting process employs a dual-process combining an electric arc furnace and an LF refining furnace, specifically including: Material preparation: steel plate material ≥70%, recycled material ≤30%, carbon is prepared with carbon raiser, and lime is placed at the bottom of the furnace; Electric arc furnace smelting control: melting temperature is 1540-1560℃, carbon content is 0.50-0.60%, carbon content of melt is 0.30-0.45%, carbon content of tapped steel is 0.10-0.15%, phosphorus content of tapped steel is ≤0.015%, sulfur content is ≤0.012%, and tapping temperature is 1620-1650℃; LF refining furnace control: Maximum power supply for 8-10 minutes, argon flow rate before slag whitening 8-12 NL / min, tapping temperature 1580-1590℃.

7. The method according to claim 1, characterized in that, The heat treatment includes, in sequence: Normalizing: Temperature is 900±10℃, hold for 7-9 hours and then air cool; Quenching: The temperature is 900±10℃, and the temperature is held for 3.5-4.5 hours before water cooling; Tempering: The temperature is 540±40℃, and the temperature is maintained for 8-10 hours before water cooling.

8. The method according to claim 1, characterized in that, The material of the box casting is high-strength low-alloy steel, and its chemical composition by mass percentage includes: C: 0.17-0.22%, Mn: 0.80-1.20%, Si≤0.60%, Cr: 0.40-0.90%, Mo: 0.40-0.70%, Ni: 0.60-1.00%, P≤0.015%, S≤0.02%, balance being Fe and unavoidable impurities.

9. The method according to claim 1, characterized in that, The quality inspection steps include: Surface quality inspection: Magnetic particle testing is performed on all detectable surfaces of the casting using the wet magnetic particle method with a magnetic suspension concentration of 10-20 mL / L. Internal quality inspection: Ultrasonic testing is performed on the base of the suspension lugs, the flange mating surface, and the end face of the housing.

10. The method according to claim 1, characterized in that, In the casting process design, the skirt at the opening is an inner skirt, and the ratio of its cross-sectional thickness to the wall thickness of the main body of the box is (1.5-2.5):1.

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