Forming method of duplex stainless steel propeller

Abstract

The invention discloses a forming method of a duplex stainless steel propeller, which is specifically implemented according to the following steps: step 1, designing a casting process of the duplex stainless steel propeller, and designing a sand mold used by the casting process by adopting three-dimensional modeling software; 2, a designed sand mold is formed through the 3D printing technology, then the printed sand mold is detected and trimmed, then the sand mold is assembled and put into a sand box, the periphery of the sand box is filled with molding sand, and a mold cavity needed by propeller forming can be obtained; 3, the duplex stainless steel molten metal is injected into the cavity, and a complete propeller casting is obtained; and 4, the propeller casting obtained in the step 3 is subjected to heat treatment, and the final propeller casting is obtained. According to the method, the method that the sand mold is printed in a 3D mode, the cavity is formed, and then metal is poured for integral forming is adopted, so that the problems of sand falling, difficult forming and low strength existing in the existing technology that a resin model is printed in a 3D mode and then sand casting or metal propellers are directly printed in a 3D mode are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of marine parts manufacturing methods and relates to a forming method of a duplex stainless steel propeller. Background Art

[0002] The propeller is the core component of the ship's propulsion system, and its strength and corrosion resistance directly affect the ship's propulsion efficiency and navigation performance. With the rapid development of marine engineering and shipbuilding industry, higher requirements are placed on the material properties and manufacturing process of propellers; especially for high-performance ships, such as high-speed yachts, military ships, etc., the corrosion resistance, strength and weight of propellers are more stringent. Although traditional propeller materials such as manganese bronze and nickel-aluminum bronze have certain strength and corrosion resistance, their strength and corrosion resistance can no longer meet the needs of modern large ships and special ships in harsh marine environments such as high salinity and high flow rates. The strength of duplex stainless steel is much higher than that of traditional manganese bronze and nickel-aluminum bronze, and its toughness and corrosion resistance are good, making it extremely suitable for manufacturing high-performance propellers.

[0003] At present, the manufacturing of duplex stainless steel propellers mainly adopts the method of split forging followed by welding and integral casting. The method of split forging followed by welding is to forge the duplex stainless steel material into the general shape of the hub and blades respectively, assemble and weld them, and then process them into the required shape. This method has disadvantages such as low material utilization, poor isotropy, long manufacturing cycle, and high cost. In particular, there is the problem of intergranular corrosion at the weld, which poses a great safety hazard to the operation of the propeller. The integral casting method is a method of directly molding the blades and the hub together by casting, additive manufacturing, etc., which can effectively avoid the problems of low material utilization, poor isotropy, long manufacturing cycle, high cost, and intergranular corrosion at the weld caused by the split molding method. The Chinese patent "A method for manufacturing propellers by 3D printing" (application date: July 20, 2016, application number: 201610579419.6, publication number: CN106166599A, publication date: November 30, 2016) discloses a method for manufacturing marine propellers by 3D printing, wherein a photosensitive resin is used to make a model that is completely consistent with the appearance of the propeller, and then the resin model is placed in a sand box, and the resin model is taken out after the sand is filled and solidified, thereby obtaining the cavity required for casting the propeller, and then the solid metal is melted and poured into the cavity to obtain the propeller casting. Although this method can quickly print out the propeller model, since the propeller blades are curved, it is very easy to cause sand to fall off due to loose sand filling, forming sand inclusion defects and causing the product to be scrapped, and how to take the resin model of the curved blade out of the solidified sand mold without destroying the sand mold is difficult, which is very challenging for the workers' operating level. The patent has not yet been published. The Chinese patent "A 3D additive manufacturing method for casting marine propellers" (application date: December 30, 2017, application number: 201711493691.3, publication number: CN107999770A, publication date: May 8, 2018) discloses a 3D additive manufacturing method for marine propellers, which is prepared by mixing titanium alloy, cobalt-chromium alloy, stainless steel, aluminum, ceramic powder and copper alloy in a certain proportion, then spreading the powder layer by layer, bonding the layers with glue, and accumulating layer by layer to form the required propeller. Although this method has a high material utilization rate, metallurgical bonding is not achieved between the printed layers, and the glue evaporates after post-processing, forming a large number of pore-like defects inside, resulting in a low strength of the overall propeller, which cannot meet the performance requirements of high-speed or large ships for propellers. Summary of the invention

[0004] The purpose of the present invention is to provide an integral forming method for a duplex stainless steel propeller, which adopts a method of 3D printing a sand mold and forming a cavity and then pouring metal for integral forming, thereby solving the problems of sand falling, difficult forming and low strength existing in the existing technology of 3D printing a resin model and then sand casting or 3D direct printing a metal propeller.

[0005] The technical solution adopted by the present invention is a forming method of a duplex stainless steel propeller, which is specifically implemented according to the following steps:

[0006] Step 1, designing a casting process for a duplex stainless steel propeller, and using 3D modeling software to design a sand mold used in the casting process;

[0007] Step 2, using 3D printing technology to form the designed sand mold, then inspecting and trimming the printed sand mold, and then assembling it into a sand box and filling it with molding sand around it to obtain the cavity required for molding the propeller;

[0008] Step 3, injecting duplex stainless steel molten metal into the mold cavity to obtain a complete propeller casting;

[0009] Step 4, heat treating the propeller casting obtained in step 3 to obtain a final propeller casting.

[0010] The present invention is also characterized in that:

[0011] The casting process in step 1 is specifically as follows:

[0012] Austenite and ferrite matrix duplex stainless steel is selected, and the scale is selected according to the structural characteristics of the propeller casting, with a scale range of 1.0-2.5%; a parting surface is set, and the blades are separated from the facet surface; a semi-closed casting system is used, ΣF 直 :ΣF 横 :ΣF 内 =(1.0-1.2):(0.8-0.9):1.0, where ΣF 直 ,ΣF 横 ,ΣF 内 They respectively refer to the cumulative cross-sectional areas of the sprue, runner and ingates in the pouring system. The pouring method is bottom pouring, and a circular cross-section ceramic pouring pipe is used to inject the molten metal from the bottom surface of the propeller shaft. The diameter of the ingates is 1 / 2-1 / 3 of the diameter of the propeller shaft; the diameter of the riser is selected to be 1.2-1.6 times the diameter of the hot pitch circle of the propeller shaft, the height of the riser is 1.1-1.7 times the diameter of the riser, and the riser is placed on the top surface of the propeller shaft; the machining allowance of the propeller is placed according to the size of the propeller, and the machining allowance value can meet the machining requirements.

[0013] In step 1, 3D modeling software is used to design the sand mold, specifically: the propeller is divided into upper and lower molds along the center dividing surface of the blade, and a radial core head is added. The size of the core head is 100-300mm larger than the outline size of the propeller. A positioning groove is set in the central part of the bottom surface of the core head. The positioning groove adopts a truncated cone-shaped male and female pin hole matching form, and the vertical projection area of ​​the positioning groove is 1 / 8-1 / 6 of the bottom surface area of ​​the sand mold; the upper sand cover and the lower sand cover of the sand mold are designed, and the edges of the upper sand cover and the lower sand cover of the sand mold are flush with the outer edge of the blade sand mold.

[0014] In step 2, the 3D printing technology is used to form the designed sand mold. Specifically, the three-dimensional model data of the sand mold, the upper sand cover of the sand mold, and the lower sand cover of the sand mold obtained by mold separation are sliced ​​and processed, and the processed data is imported into the control system of the sand mold printer. The molding sand uniformly mixed with the resin binder and the curing agent is sent to the array nozzle device. The nozzle device is under the control of the computer. The nozzle's squeezing and pushing device densely accumulates the molding sand particles within the sand mold layered cross-sectional contour range to form a sand mold structure, and loosely accumulates the molding sand particles outside the sand mold layered cross-sectional contour range to form a support structure, and prints the designed sand mold layer by layer.

[0015] In step 2, the printed sand mold is inspected and repaired as follows: a scanner is used to collect surface data points of the printed sand mold, the scanning data is fitted and compared with the 3D model for printing using Geomagic Qualify software, and the parts of the sand mold with out-of-tolerance dimensions are repaired to control the sand mold dimension deviation within "nominal dimension ±0.3mm";

[0016] The filling of molding sand in step 2 is specifically as follows: spraying alcohol-based zircon powder coating on the active surface of the sand mold, drying the coating, adding a sand box with a sand intake of 100-200mm, placing the assembled sand mold and runner in the sand box, and filling back sand around it; after the lower box sand mold is made and solidified, the box is turned over, the riser, sprue and gate cup are placed, and back sand is filled. After the back sand is hardened, the cavity is baked with a hot air blower.

[0017] When sand mold printing is performed in step 2, the weight ratio of the molding sand, the resin binder and the curing agent is 100: (1.5-3): (0.5-1);

[0018] In step 2, the hot air blower is used to bake the cavity by heating the hot air blower to 150-200° C. and sending hot air into the cavity through a pipe until the surface of the cavity is dry.

[0019] Step 3 is as follows:

[0020] A medium frequency furnace is used to melt austenite and ferrite matrix duplex stainless steel to obtain duplex stainless steel liquid. After the duplex stainless steel metal is liquefied and the alloy elements are adjusted to the required composition range, the duplex stainless steel liquid is transferred from the medium frequency furnace to the AOD furnace, and refined by AOD argon oxygen decarburization. High-purity nitrogen is blown into the molten metal in the AOD furnace for many times. The nitrogen element is fully homogenized and alloyed in the metal liquid through gas stirring. After the nitrogen content meets the requirements, it is taken out of the furnace for pouring, and the propeller casting is cleaned after cooling and solidification to obtain a complete propeller casting.

[0021] In step 3, the purity of the high-purity nitrogen is 99.99-99.9999%. The high-purity nitrogen is introduced into the duplex stainless steel molten metal through a heat-resistant tube. After the nitrogen content meets the requirements, the duplex stainless steel molten metal is taken out of the furnace at 1640-1660° C. and poured at 1600-1620° C.

[0022] Step 4 is as follows:

[0023] Weld anti-deformation ribs on the blades of the propeller casting obtained in step 3, and then heat the propeller casting to 1145-1155°C in a box-type resistance furnace. The insulation time is δ(mm) / 20(mm)+2 hours of the casting wall thickness, so that the alloy elements are fully dissolved in the austenite and ferrite. After the insulation is completed, the furnace is cooled to 1065-1075°C, and the casting is taken out of the furnace and quickly cooled in 35-45°C water. After cooling, the anti-deformation ribs are removed.

[0024] The anti-deformation reinforcement in step 4 is arranged in both circumferential and axial directions. The circumferential direction uses globe-like latitude reinforcements to horizontally surround the propeller blade tip and are welded to the edge of the blade tip. A circle of reinforcement is set every 150-200mm in height; one end of the axial reinforcement is welded to the side of the propeller shaft, and the other end is welded to the central area of ​​the top surface of the blade to prevent the blade from bending downward due to heat softening. Each blade needs to have an axial reinforcement welded to it.

[0025] The beneficial effects of the present invention are:

[0026] (1) The present invention directly forms the required propeller cavity by 3D printing sand molds, which can effectively avoid the problems of loose filling and difficulty in removing the resin model caused by printing the resin propeller model and then filling the sand mold, and the difficulty in forming the propeller cavity. At the same time, with the help of laser scanning detection means, it can ensure that the dimensional accuracy of the sand mold is highly consistent with the required propeller model, and the product consistency and accuracy are significantly improved.

[0027] (2) The propeller forming method of the present invention can directly form the propeller into an integral casting, and with the addition of certain heat treatment and anti-deformation measures, can effectively avoid the problems of low overall strength of the propeller caused by non-metallurgical bonding between layers and loose internal structure caused by direct printing of alloy powder. The overall structure is dense and the strength is high.

[0028] (3) The present invention can significantly improve the production efficiency of propellers. The use of 3D printed sand molds can reduce molding time and improve the yield rate. Compared with traditional casting, 3D printed sand molds have high compactness and good consistency, shortening the manufacturing cycle by 20-30% and increasing the yield rate by 10-20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the casting process structure of the duplex stainless steel propeller of the present invention;

[0030] Figure 2 This is the microstructure diagram of the duplex stainless steel propeller prepared in Example 2.

[0031] In the figure: 1. pouring cup, 2. riser sleeve, 3. upper sand cover of sand mold, 4. sand mold, 5. lower sand cover of sand mold, 6. ceramic pouring pipe, 7. back sand. DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1

[0034] The forming method of the duplex stainless steel propeller of the present invention is specifically implemented according to the following steps:

[0035] Step 1, designing a casting process for a duplex stainless steel propeller, and using 3D modeling software to design a sand mold used in the casting process;

[0036] Step 2, using 3D printing technology to form the designed sand mold, then inspecting and trimming the printed sand mold, and then assembling it into a sand box and filling it with molding sand around it to obtain the cavity required for molding the propeller;

[0037] Step 3, injecting duplex stainless steel molten metal into the mold cavity to obtain a complete propeller casting;

[0038] Step 4, heat treating the propeller casting obtained in step 3 to obtain a final propeller casting.

[0039] The casting process in step 1 is specifically as follows:

[0040] Austenite and ferrite matrix duplex stainless steel is selected, and the scale is selected according to the structural characteristics of the propeller casting, with a scale range of 1.0-2.5%; a parting surface is set, and the blades are separated from the facet surface; a semi-closed casting system is used, ΣF 直 :ΣF 横 :ΣF 内 =(1.0-1.2):(0.8-0.9):1.0, where ΣF 直 ,ΣF 横 ,ΣF 内 They refer to the cumulative cross-sectional areas of the sprue, runner and ingates in the pouring system, respectively. The pouring method is bottom pouring, such as Figure 1 As shown, a circular cross-section ceramic pouring pipe is used to inject molten metal from the bottom surface of the propeller shaft, and the inner gate diameter is 1 / 2-1 / 3 of the propeller shaft diameter; the riser diameter is selected to be 1.2-1.6 times the hot pitch circle diameter of the propeller shaft, the riser height is 1.1-1.7 times the riser diameter, and the riser is placed on the top surface of the propeller shaft; the machining allowance of the propeller is placed according to the size of the propeller, and the machining allowance value can meet the machining requirements.

[0041] In step 1, 3D modeling software (such as UG, CATIA, SolidWorks, etc.) is used to design the sand mold, specifically: the propeller is divided into upper and lower molds along the center dividing surface of the blade, and a radial core head is added. The size of the core head is 100-300mm larger than the outline size of the propeller. A positioning groove is set in the central part of the bottom surface of the core head. The positioning groove adopts a truncated cone-shaped male and female pin hole matching form, and the vertical projection area of ​​the positioning groove is 1 / 8-1 / 6 of the bottom surface area of ​​the sand mold; the upper sand cover 3 and the lower sand cover 5 of the sand mold are designed, and the edges of the upper sand cover 3 and the lower sand cover 5 of the sand mold are flush with the outer edge of the blade sand mold.

[0042] In step 2, the 3D printing technology is used to form the designed sand mold. Specifically, the three-dimensional model data of the sand mold 4, the upper sand cover 3, and the lower sand cover 5 obtained by mold separation are sliced ​​and processed, and the processed data is imported into the sand mold printer control system. The molding sand uniformly mixed with the resin binder and the curing agent is sent to the array nozzle device. The nozzle device is under the control of the computer. The nozzle's squeezing and pushing device densely accumulates the molding sand particles within the sand mold layered cross-sectional contour range to form a sand mold structure, and loosely accumulates the molding sand particles outside the sand mold layered cross-sectional contour range to form a support structure, and prints the designed sand mold layer by layer.

[0043] In step 2, the printed sand mold is inspected and repaired as follows: a scanner is used to collect surface data points of the printed sand mold, the scanning data is fitted and compared with the 3D model for printing using Geomagic Qualify software, and the parts of the sand mold with out-of-tolerance dimensions are repaired to control the sand mold dimension deviation within "nominal dimension ±0.3mm";

[0044] The filling of molding sand in step 2 is specifically as follows: spraying alcohol-based zircon powder coating on the active surface of the sand mold, drying the coating, adding a sand box with a sand intake of 100-200 mm, placing the assembled sand mold 4 and runner 6 in the sand box, and filling the surrounding with back sand 7; after the lower box sand mold is made and solidified, the box is turned over, the riser 2, the sprue 6 and the pouring cup 1 are placed, the back sand 7 is filled, and after the back sand 7 is hardened, the cavity is baked with a hot air blower.

[0045] When sand mold printing is performed in step 2, the weight ratio of the molding sand, the resin binder and the curing agent is 100: (1.5-3): (0.5-1);

[0046] In step 2, the hot air blower is used to bake the cavity by heating the hot air blower to 150-200° C. and sending hot air into the cavity through a pipe until the surface of the cavity is dry.

[0047] Step 3 is as follows:

[0048] A medium frequency furnace is used to melt austenite and ferrite matrix duplex stainless steel to obtain duplex stainless steel liquid. After the duplex stainless steel metal is liquefied and the alloy elements are adjusted to the required composition range, the duplex stainless steel liquid is transferred from the medium frequency furnace to the AOD furnace, and refined by AOD argon oxygen decarburization. High-purity nitrogen is blown into the molten metal in the AOD furnace for many times. The nitrogen element is fully homogenized and alloyed in the metal liquid through gas stirring. After the nitrogen content meets the requirements, it is taken out of the furnace for pouring, and the propeller casting is cleaned after cooling and solidification to obtain a complete propeller casting.

[0049] In step 3, the purity of the high-purity nitrogen is 99.99-99.9999%. The high-purity nitrogen is introduced into the duplex stainless steel molten metal through a heat-resistant tube. After the nitrogen content meets the requirements, the duplex stainless steel molten metal is taken out of the furnace at 1640-1660° C. and poured at 1600-1620° C.

[0050] Step 4 is as follows:

[0051] Weld anti-deformation ribs on the blades of the propeller casting obtained in step 3, and then heat the propeller casting to 1145-1155°C in a box-type resistance furnace. The insulation time is δ(mm) / 20(mm)+2 hours of the casting wall thickness, so that the alloy elements are fully dissolved in the austenite and ferrite. After the insulation is completed, the furnace is cooled to 1065-1075°C, and the casting is taken out of the furnace and quickly cooled in 35-45°C water. After cooling, the anti-deformation ribs are removed.

[0052] The anti-deformation reinforcement in step 4 is arranged in both circumferential and axial directions. The circumferential direction uses globe-like latitude reinforcements to horizontally surround the propeller blade tip and are welded to the edge of the blade tip. A circle of reinforcement is set every 150-200mm in height; one end of the axial reinforcement is welded to the side of the propeller shaft, and the other end is welded to the central area of ​​the top surface of the blade to prevent the blade from bending downward due to heat softening. Each blade needs to have an axial reinforcement welded to it.

[0053] Example 2

[0054] Based on Example 1, this example uses a certain type of 5-blade propeller as a reference example. The propeller has an overall size of Net weight 46kg, main wall thickness 20mm, maximum wall thickness 120mm, minimum wall thickness 2mm, composition (percentage content) control range: C≤0.04, Si≤2, Mn≤4, Cr 21-27, Ni 4-9, S≤0.02, P≤0.035, Mo 3-5, N 0.14-0.35.

[0055] Step 1, casting process design: the propeller is selected with a scale of 1.8%; the propeller is placed vertically, and the parting surface is set on the top surface of the propeller shaft; a bottom pouring pouring system with a filter is adopted, and the pouring system is composed of a ceramic pouring pipe 6, and the cross-sectional ratio of the pouring system is straight runner: horizontal runner: inner runner = 1.2:0.9:1; an open riser is set on the top surface of the propeller shaft, and the riser adopts an insulating riser sleeve 2, the riser diameter is 155mm, and the riser height is 1.3 times the riser diameter; the processing amount on one side is 8mm.

[0056] Step 2, sand mold design: the propeller is divided into curved surfaces along the dividing surface in the middle of the blades, and the dividing surface is used as the outer surface of the sand mold. Five sand molds 4 are obtained for the five-blade propeller. A 150mm long core head is added radially, and a truncated cone-shaped positioning groove is set on the bottom surface of the core head; the upper sand cover 3 and the lower sand cover 5 of the sand mold are designed on the upper and lower surfaces of the sand mold, and the outer contours of the upper sand cover 3 and the lower sand cover 5 of the sand mold are flush with the radial side surfaces of the sand mold.

[0057] Step 3, sand mold printing: Slice the sand mold and sand cover 3D model data obtained by parting, set the slice layer height to 0.4mm, set the print layer height to 0.4mm, and import the processed data into the sand mold printer control system. Send 0.1mm large and small sand particles uniformly mixed with curing agent and phenolic resin binder into the array nozzle device, with a weight ratio of sand: binder: curing agent = 100: 2.1: 0.7. The nozzle device is under the control of the computer, and the nozzle's squeezing and pushing device densely accumulates the sand particles within the sand mold layered cross-sectional contour to form a sand mold / core structure, and loosely accumulates the sand particles outside the sand mold layered cross-sectional contour to form a support structure; print the designed sand mold, upper and lower sand cover plates layer by layer until the sand mold printing is completed by superposition.

[0058] Step 4, sand mold inspection: Use a portable laser scanner to collect data points on the sand mold surface, use Geomagic Qualify software to fit and compare the scanned data with the 3D model for printing, repair the deformed parts of the sand mold, and control the size deviation of the sand mold within "±0.3mm".

[0059] Step 5, sand filling and molding: spray paint on the active surface of the printed sand mold, dry the paint, choose a sand box with a sand intake of 180mm, place the assembled sand mold and sand cover in the sand box, install the pouring channel, and fill the back sand 7 around; after the lower box sand mold is made and solidified, turn the box over, place the riser sleeve 2, ceramic pouring channel 6 and pouring cup 1, fill with back sand 7, and after the back sand 7 hardens, heat it to 180℃ with a hot air blower and bake the cavity for 3h.

[0060] Step 6, melting and pouring: medium frequency furnace melting, after the metal liquid is adjusted to the required composition, the molten metal is transferred to the AOD furnace, refined by AOD argon oxygen decarburization, and then 99.999% high-purity nitrogen is blown into the molten metal in the AOD furnace for 15 minutes multiple times, with the flow rate controlled at 30l / min. The nitrogen element is fully homogenized and alloyed in the molten metal through the stirring effect of the gas. After the nitrogen content meets the requirements, the metal is taken out of the furnace and poured into the casting mold; the furnace temperature is controlled at 1660℃, and the pouring temperature is 1620℃; the propeller casting is cleaned after cooling and solidification.

[0061] Step 7, heat treatment: weld a circle of annular tie bars around the propeller, and weld anti-deformation ribs between the blades and the propeller shaft in the axial direction; heat the propeller casting to 1155℃, keep it warm for 3 hours, the alloy elements are fully dissolved in the austenite, cool it to 1070℃, quickly take it out of the furnace, and then cool it in 40℃ water to inhibit the precipitation of harmful phases.

[0062] Step 8, performance test verification: randomly select one piece for performance test analysis; wire cutting to cut tensile and metallographic specimens, grind metallographic and tensile specimens; test tensile strength with a universal tensile testing machine, and observe the austenite and ferrite phase ratio with a metallographic microscope, such as Figure 2 As shown, it is the microstructure diagram of the duplex stainless steel propeller prepared in this embodiment; the microstructure of the propeller casting is austenite + ferrite, of which austenite accounts for 45%; the tensile strength Rm is 752MPa, which meets the metallographic and mechanical property requirements.

[0063] Example 3

[0064] Based on Example 1, this example uses a certain type of 3-blade propeller as a reference example. The propeller has an overall size of Net weight 38kg, main wall thickness 25mm, maximum wall thickness 80mm, minimum wall thickness 3mm, composition (percentage content) control range: C≤0.04, Si≤1.8, Mn≤3, Cr 21-25, Ni 4-7, S≤0.02, P≤0.02, Mo 3-4, N 0.15-0.35.

[0065] Step 1, casting process design: the propeller is selected with a scale of 2%; the propeller is placed vertically, and the parting surface is set on the top surface of the propeller shaft; a bottom pouring pouring system with a filter is adopted, and the pouring system is composed of a ceramic pouring pipe 6, and the cross-sectional ratio of the pouring system is straight runner: horizontal runner: inner runner = 1.1:0.9:1; an open riser is set on the top surface of the propeller shaft, and the riser adopts an insulating riser sleeve 2, the riser diameter is 150mm, and the riser height is 1.3 times the riser diameter; the processing amount on one side is 10mm.

[0066] Step 2, sand mold design: the propeller is divided into curved surfaces along the dividing surface in the middle of the blade, and the dividing surface is used as the outer surface of the sand mold. Three sand molds 4 are obtained for the three-blade propeller. A 150mm long core head is added radially, and a truncated cone-shaped positioning groove is set on the bottom surface of the core head; the upper sand cover 3 and the lower sand cover 5 of the sand mold are designed on the upper and lower surfaces of the sand mold, and the outer contours of the upper sand cover 3 and the lower sand cover 5 of the sand mold are flush with the radial side surfaces of the sand mold.

[0067] Step 3, sand mold printing: Slice the sand mold and sand cover 3D model data obtained by parting, set the slice layer height to 0.4mm, set the print layer height to 0.4mm, and import the processed data into the sand mold printer control system. Send 0.1mm large and small sand particles uniformly mixed with curing agent and phenolic resin binder into the array nozzle device, with a weight ratio of sand: binder: curing agent = 100: 2.1: 0.7. The nozzle device is under the control of the computer, and the nozzle's squeezing and pushing device densely accumulates the sand particles within the sand mold layered cross-sectional contour to form a sand mold / core structure, and loosely accumulates the sand particles outside the sand mold layered cross-sectional contour to form a support structure; print the designed sand mold, upper and lower sand cover plates layer by layer until the sand mold printing is completed by superposition.

[0068] Step 4, sand mold inspection: Use a portable laser scanner to collect data points on the sand mold surface, use Geomagic Qualify software to fit and compare the scanned data with the 3D model for printing, repair the deformed parts of the sand mold, and control the size deviation of the sand mold within "±0.3mm".

[0069] Step 5, sand filling and molding: spray paint on the active surface of the printed sand mold, dry the paint, choose a sand box with a sand intake of 180mm, place the assembled sand mold and sand cover in the sand box, install the pouring channel, and fill the back sand 7 around; after the lower box sand mold is made and solidified, turn the box over, place the riser sleeve 2, ceramic pouring channel 6 and pouring cup 1, fill with back sand 7, and after the back sand 7 hardens, heat it to 180℃ with a hot air blower and bake the cavity for 3h.

[0070] Step 6, melting and pouring: medium frequency furnace melting, after the metal liquid is adjusted to the required composition, the molten metal is transferred to the AOD furnace, refined by AOD argon oxygen decarburization, and then 99.999% high-purity nitrogen is blown into the molten metal in the AOD furnace for 15 minutes multiple times, with the flow rate controlled at 30l / min. The nitrogen element is fully homogenized and alloyed in the molten metal through the stirring effect of the gas. After the nitrogen content meets the requirements, the metal is taken out of the furnace and poured into the casting mold; the furnace temperature is controlled at 1660℃, and the pouring temperature is 1620℃; the propeller casting is cleaned after cooling and solidification.

[0071] Step 7, heat treatment: weld a circle of annular tie bars around the propeller, and weld anti-deformation ribs between the blades and the propeller shaft in the axial direction; heat the propeller casting to 1155℃, keep it warm for 3.25 hours, the alloy elements are fully dissolved in the austenite, cool it to 1070℃, quickly take it out of the furnace, and then cool it in 40℃ water to inhibit the precipitation of harmful phases.

[0072] Step 8, performance test verification: randomly select one piece for performance test analysis; cut tensile and metallographic specimens by wire cutting, grind metallographic and tensile specimens; test tensile strength by universal tensile testing machine, observe the austenite and ferrite phase ratio by metallographic microscope; the microstructure of propeller casting is austenite + ferrite, of which austenite accounts for 46%; tensile strength Rm is 755MPa, which meets the metallographic and mechanical property requirements.

Claims

1. A method for forming a duplex stainless steel propeller, characterized in that: The specific steps are as follows: Step 1, designing a casting process for a duplex stainless steel propeller, and using 3D modeling software to design a sand mold used in the casting process; Step 2, using 3D printing technology to form the designed sand mold, then inspecting and trimming the printed sand mold, and then assembling the trimmed sand mold and filling it with molding sand to obtain the cavity required for molding the propeller; Step 3, injecting duplex stainless steel molten metal into the mold cavity to obtain a complete propeller casting; Step 4, heat treating the propeller casting obtained in step 3 to obtain a final propeller casting.

2. The method for forming a duplex stainless steel propeller according to claim 1, characterized in that: The casting process in step 1 is specifically as follows: Austenite and ferrite matrix duplex stainless steel is selected, and the scale is selected according to the structural characteristics of the propeller casting, with a scale range of 1.0-2.5%; a parting surface is set, and the blades are separated from the facet surface; a semi-closed casting system is used, ΣF 直 :ΣF 横 :ΣF 内 =(1.0-1.2):(0.8-0.9):1.0, where ΣF 直 ,ΣF 横 ,ΣF 内 They respectively refer to the cumulative cross-sectional areas of the sprue, runner and ingates in the pouring system. The pouring method is bottom pouring. A circular cross-section ceramic pouring pipe (6) is used to inject molten metal from the bottom surface of the propeller shaft. The diameter of the ingates is 1 / 2-1 / 3 of the diameter of the propeller shaft. The diameter of the riser (2) is selected to be 1.2-1.6 times the diameter of the hot pitch circle of the propeller shaft. The height of the riser (2) is 1.1-1.7 times the diameter of the riser. The riser (2) is placed on the top surface of the propeller shaft. The machining allowance of the propeller is placed according to the size of the propeller. The machining allowance value can meet the machining requirements.

3. The method for forming a duplex stainless steel propeller according to claim 1, characterized in that: In the step 1, the sand mold is designed using 3D modeling software, specifically: the propeller is divided into upper and lower molds along the center dividing plane of the blade, and a radial core head is added, the size of the core head is 100-300mm larger than the outline size of the propeller, and a positioning groove is set in the central part of the bottom surface of the core head. The positioning groove adopts a truncated cone-shaped male and female pin hole matching form, and the vertical projection area of ​​the positioning groove is 1 / 8-1 / 6 of the bottom surface area of ​​the sand mold; The upper sand cover (3) and the lower sand cover (5) of the sand mold are designed, and the edges of the upper sand cover (3) and the lower sand cover (5) of the sand mold are flush with the outer edge of the blade sand mold.

4. The method for forming a duplex stainless steel propeller according to claim 2, characterized in that: The step 2 of using 3D printing technology to form the designed sand mold specifically comprises: slicing the three-dimensional model data of the sand mold, the upper sand cover (3) and the lower sand cover (5) obtained by mold separation, importing the processed data into the control system of the sand mold printer, feeding the molding sand uniformly mixed with the resin binder and the curing agent into the array nozzle device, the nozzle device is controlled by a computer, and the nozzle pushing device densely accumulates the molding sand particles within the sand mold layered cross-sectional contour range to form a sand mold structure, and loosely accumulates the molding sand particles outside the sand mold layered cross-sectional contour range to form a support structure, and prints the designed sand mold layer by layer; In step 2, the printed sand mold is inspected and repaired as follows: a scanner is used to collect data points on the surface of the printed sand mold, the scanning data is fitted and compared with the 3D model for printing using Geomagic Qualify software, and the parts of the sand mold with out-of-tolerance dimensions are repaired to control the sand mold dimension deviation within "nominal size ± 0.3 mm"; The filling of molding sand in step 2 is specifically as follows: spraying alcohol-based zircon powder coating on the active surface of the sand mold, drying the coating, adding a sand box with a sand intake of 100-200 mm, placing the assembled sand mold and runner in the sand box, and filling back sand around; turning the box over after the lower box sand mold is solidified, placing a riser, a sprue and a pouring cup, filling back sand, and baking the cavity with a hot air blower after the back sand is hardened.

5. The method for forming a duplex stainless steel propeller according to claim 5, characterized in that: When sand mold printing is performed in step 2, the weight ratio of the molding sand, the resin binder and the curing agent is 100: (1.5-3): (0.5-1); In step 2, the hot air blower is used to bake the cavity, and the hot air blower is heated to 150-200° C., and hot air is sent into the cavity through a pipeline until the surface of the cavity is dry.

6. The method for forming a duplex stainless steel propeller according to claim 1, characterized in that: The step 3 is specifically as follows: A medium frequency furnace is used to melt austenite and ferrite matrix duplex stainless steel to obtain duplex stainless steel liquid. After the duplex stainless steel metal is liquefied and the alloy elements are adjusted to the required composition range, the duplex stainless steel liquid is transferred from the medium frequency furnace to the AOD furnace, and refined by AOD argon oxygen decarburization. High-purity nitrogen is blown into the molten metal in the AOD furnace for many times. The nitrogen element is fully homogenized and alloyed in the metal liquid through gas stirring. After the nitrogen content meets the requirements, it is taken out of the furnace for pouring, and the propeller casting is cleaned after cooling and solidification to obtain a complete propeller casting.

7. The method for forming a duplex stainless steel propeller according to claim 7, characterized in that: In step 3, the purity of the high-purity nitrogen is 99.99-99.9999%. The high-purity nitrogen is introduced into the duplex stainless steel molten metal through a heat-resistant tube. After the nitrogen content meets the requirements, the duplex stainless steel molten metal is taken out of the furnace at 1640-1660° C. and poured at 1600-1620° C.

8. The method for forming a duplex stainless steel propeller according to claim 1, characterized in that: The step 4 is specifically as follows: Weld anti-deformation ribs on the blades of the propeller casting obtained in step 3, and then heat the propeller casting to 1145-1155°C in a box-type resistance furnace. The insulation time is δ(mm) / 20(mm)+2 hours of the casting wall thickness, so that the alloy elements are fully dissolved in the austenite and ferrite. After the insulation is completed, the furnace is cooled to 1065-1075°C, and the casting is taken out of the furnace and quickly cooled in 35-45°C water. After cooling, the anti-deformation ribs are removed.

9. The method for forming a duplex stainless steel propeller according to claim 8, characterized in that: The anti-deformation reinforcement in step 4 is arranged in both circumferential and axial directions. The circumferential direction uses globe-like latitude reinforcements to horizontally surround the propeller blade tip and are welded and fixed to the edge of the blade tip. A circle of reinforcement is arranged every 150-200mm in height; one end of the axial reinforcement is welded to the side of the propeller shaft, and the other end is welded to the central area of ​​the top surface of the blade to prevent the blade from bending downward due to heat softening. Each blade needs to be welded with an axial reinforcement.

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