Investment precision casting process for large hollow blade

Abstract

The investment precision casting process comprises the following steps that firstly, a hollow workpiece wax mold is prepared, a water-soluble core is prefabricated, the two ends of the water-soluble core are clamped through a blade body mold, a plurality of supporting points used for supporting the water-soluble core are arranged on the portion, located on the inner side of a cavity, of the blade body mold, and the water-soluble core is supported by the supporting points; wax is injected into the cavity, and a wax mold with a water-soluble core is obtained; 2, a hollow workpiece wax mold is extracted, the water-soluble core is hydrolyzed, and the hollow workpiece wax mold is obtained; 3, wax mold inner cavity mold core preparation and shell manufacturing are conducted, specifically, the surface of the wax mold in the step 2 is dip-coated with multiple layers of slurry and powder, blowing drying is conducted to form the shell, semi-self-hardening refractory slurry is poured into the shell, and a hard mold core is formed to resist erosion and acting force of molten steel during pouring; 4, dewaxing, smelting and casting; and 5, cleaning and shaping a casting and carrying out a subsequent heat treatment process, so that a formed workpiece is obtained. And sixthly, the performance quality inspection procedure is conducted on the formed workpiece in the fifth step.

Description

Technical Field

[0001] The invention relates to the field of investment casting, and in particular to an investment casting process for a large hollow blade. Background Art

[0002] Investment casting, also known as lost wax casting, is a hot working process in which refractory materials are coated on the surface of the wax mold, the wax is melted, and then calcined at high temperature to obtain a shell of a certain size and structure, and then the molten metal is injected into the shell, and the corresponding casting is obtained after cleaning. The process includes wax injection, grouping, shell making, melting and pouring, cleaning and other processes. Investment casting has been widely used in aerospace, nuclear power, automobile, medical equipment and other industries.

[0003] Steam turbine blades with special-shaped curved hollow structures are one of the core components of gas turbines, with large dimensions and high dimensional accuracy. In the precision casting shell making process, this kind of special-shaped hollow structure castings are currently mainly made by ceramic core technology. However, due to the super-long special-shaped curved structure of the corresponding ceramic core, it is very easy to deform during the production and sintering of the ceramic core, and the price is expensive. Most domestic manufacturers have the ability to produce such super-large ceramic cores, so the existing ceramic core manufacturing process for special-shaped curved hollow castings has limitations.

[0004] Therefore, how to provide a stable and reliable investment casting process for manufacturing large hollow blades with high workpiece precision is an urgent problem to be solved by technical personnel in this field. Summary of the invention

[0005] In view of this, the present invention provides a precision investment casting process for large hollow blades, which can ensure the uniform wall thickness of the wax mold. The wax mold inner cavity core has sufficient strength to withstand the stress during dewaxing roasting and pouring without generating cracks and deformation, thereby ensuring the accuracy requirements of the workpiece size.

[0006] In order to achieve the above-mentioned object, the present invention adopts the following technical scheme: A large hollow blade investment casting process, which comprises the following steps: Step 1: preparing a hollow workpiece wax mold

[0007] First, a water-soluble core is made according to the outer contour shape of the hollow workpiece to be formed, and the two ends of the water-soluble core are clamped by the blade main body mold, so that a cavity of the wax mold to be formed is formed inside the blade main body mold and outside the water-soluble core, wherein the blade main body mold is located on the inner side of the cavity and is provided with a plurality of support points for supporting the water-soluble core, and wax is injected into the cavity to obtain a wax mold with a water-soluble core;

[0008] Step 2: Extraction of hollow workpiece wax model

[0009] The wax model with the water-soluble core obtained in step 1 is placed in a clean water tank, and the water-soluble core is hydrolyzed to obtain a hollow workpiece wax model;

[0010] Step 3: Preparation of wax mold core and shell making

[0011] In step 2, the surface of the wax mold is dipped with multiple layers of slurry and powder, and the mold shell is dried by blowing, and the mold shell is moistened with silica sol, and semi-self-hardening refractory slurry is poured into the mold shell, and ceramic core rods are inserted at both ends of the mold shell for sealing. In the subsequent high-temperature roasting state, the semi-self-hardening refractory slurry forms a hard core to resist the erosion and force of the molten steel during pouring;

[0012] Step 4: Dewaxing and Melting and Casting

[0013] On the basis of step 3, the shell is placed in a steam dewaxing kettle to melt and remove the wax mold of the blade and the wax mold of the pouring system to obtain a cavity shell, and the charge is prepared and smelted to obtain molten steel to be poured. After the shell is roasted, the molten steel is poured to obtain a casting;

[0014] Step 5: Casting cleaning and shaping and subsequent heat treatment process to obtain the molded workpiece;

[0015] Step 6: Perform a performance quality inspection on the molded workpiece in step 5.

[0016] The beneficial technical effect of the present invention is: when using a water-soluble core to make a wax mold, compared with the traditional method of using the two ends of the blade mold to position the water-soluble core, the present invention adds multiple support points in the mold cavity to prevent the water-soluble core from being easily subjected to force during the wax injection process, causing the water-soluble core to break, deviate, etc., thereby affecting the uniformity of the wax mold wall thickness, and then hydrolyze the water-soluble core, and apply a coating on the surface of the wax mold to form a mold shell. Filling the mold shell with semi-self-hardening refractory slurry can form a hard core after roasting to withstand the force of the mold shell during dewaxing or pouring. The smelting of the molten steel is protected by argon gas, the purpose of which is to separate the air and the molten alloy, prevent the alloy liquid from inhaling air, prevent the alloy elements from oxidizing and burning, and reduce the alloy liquid's tendency to inhale air, thereby improving the alloy's smelting quality and casting quality. The casting process using this scheme makes the workpiece molding high in precision and stable and reliable.

[0017] Preferably, in the step 1, the water-soluble core is cast by a water-soluble core mold, and the water-soluble core mold has a water-soluble core casting cavity inside.

[0018] The resulting technical effect is that the water-soluble core is used as the core of the wax model, and the wax model is formed on this basis.

[0019] Preferably, in step one, the blade main body mold includes an upper mold and a lower mold, and after the upper mold and the lower mold are combined, a plurality of support points are provided on the inner side of the corresponding cavity, and the support points support and position the body of the water-soluble core, and the upper mold and the lower mold are provided with positioning grooves near the end of the cavity to position the end of the water-soluble core.

[0020] The resulting technical effect is: the blade main body mold is composed of an upper mold and a lower mold, and a locking mechanism is required to lock it when the mold is closed. During specific implementation, the two end faces of the water-soluble core coincide with the positioning groove table, and the body of the water-soluble core is supported by multiple support points to avoid breakage, displacement, and other phenomena caused by the water-soluble core being subjected to force during the wax injection process.

[0021] Preferably, in the step 1, the blade main body mold is removed after wax injection, and the wax mold holes formed at the supporting points need to be filled and repaired with liquid wax.

[0022] The resulting technical effect is that after removing the blade main body mold, wax mold holes will remain at the supporting points, which need to be filled and repaired with liquid wax to ensure the integrity of the wax mold surface.

[0023] Preferably, in step 2, the obtained wax model of the hollow workpiece is trimmed to remove the parting line, and then 3D scanned, and the wax model is manually corrected again according to the scanning results, so as to obtain a complete wax model of the hollow workpiece.

[0024] The resulting technical effect is that the obtained hollow workpiece wax mold is finely trimmed to obtain a precise shell blank.

[0025] Preferably, in the step three, a first layer of zircon powder slurry is dip-coated on the surface of the wax mold, a second layer of 100 mesh zircon sand is coated, each layer is dried for 48 hours, a third layer of mullite powder is dip-coated, a fourth layer of 30-60 mesh mullite sand is coated, a fifth layer of mullite powder is dip-coated, a sixth layer of 16-30 mesh mullite sand is coated, and the wax mold is dried by air, with each layer drying for 24 hours.

[0026] The resulting technical effect is that this step forms a shell on the surface of the wax mold, and the shell provides a mold cavity for the final casting of the workpiece.

[0027] Preferably, in the step three, the semi-self-hardening refractory slurry is composed of self-hardening slurry and zircon powder slurry in a weight ratio of 2:1, wherein the self-hardening slurry is composed of magnesium oxide, diammonium dihydrogen phosphate, quartz and silica sol in a weight ratio of 1:1:8:2, and the zircon powder slurry is composed of zircon powder and silica sol in a weight ratio of 3:1; the semi-self-hardening refractory slurry solidifies within 4 hours.

[0028] The resulting technical effect is that the semi-self-hardening refractory slurry has a certain fluidity and becomes a hard entity after high-temperature sintering, thereby providing the mold shell with an inner core support foundation during pouring.

[0029] Preferably, in step 4, when the charge is smelted, an argon hood is covered on the medium frequency furnace, the argon hood is connected to an external argon source and forms an inert gas protective layer on the surface of the molten steel, thereby reducing the air absorption tendency of the alloy liquid and improving the smelting quality of the alloy.

[0030] The resulting technical effect is: the protective layer formed by argon gas can prevent the alloy liquid from contacting with the external air, prevent the oxidation and burning of the alloy elements, and reduce the air absorption tendency of the alloy liquid, thereby improving the smelting quality of the alloy and the quality of the casting.

[0031] Preferably, in step 4, the pouring system is assembled before pouring the molten steel, the inner gate is set at the hot node of the hollow workpiece, and then the pouring system such as the vertical intersection and the horizontal runner is assembled, and after the molten steel is poured, the mold shell buckle cover is taken to prevent oxidation.

[0032] The resulting technical effect is: the inner gate is set at the hot spot of the hollow workpiece, and then the pouring system such as the vertical runner and the horizontal runner is assembled to achieve the sequential solidification of the molten steel from the casting to the pouring riser during pouring and cooling, thereby avoiding the tendency of shrinkage holes in the casting.

[0033] Preferably, in step five, the heat treatment process of the hollow workpiece is annealing, quenching and tempering.

[0034] The resulting technical effect is that the workpiece meets the performance requirements after heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of a blade casting of a large hollow blade in an investment casting process of the present invention;

[0036] Figure 2 This is a blade mold structure diagram of a large hollow blade investment precision casting process of the present invention;

[0037] Figure 3 It is a schematic diagram of positioning a water-soluble core on a blade mold in a precision investment casting process of a large hollow blade of the present invention;

[0038] Figure 4 It is a diagram showing the pressing state of a water-soluble core wax mold of a large hollow blade investment precision casting process of the present invention;

[0039] Figure 5 A schematic diagram of a wax mold with a water-soluble core for a large hollow blade investment casting process of the present invention;

[0040] Figure 6 It is a schematic diagram of a hollow workpiece wax mold of a large hollow blade investment precision casting process of the present invention;

[0041] Figure 7 It is a schematic diagram of filling the core inside the mold shell in the investment casting process of a large hollow blade of the present invention;

[0042] Figure 8 The present invention is a schematic diagram of a melting device for a large hollow blade investment casting process.

[0043] 1 blade casting, 2 water-soluble core, 3 blade main body mold, 31 upper mold, 32 lower mold, 33 positioning groove table, 34 support point, 4 wax mold, 5 manual slurry layer, 6 ceramic core rod, 7 semi-self-hardening refractory slurry, 8 argon gas bottle, 9 medium frequency furnace, 10 argon gas hood, 11 argon gas protective layer, 12 molten steel. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] See the attached Figures 1 to 8 According to an embodiment of the present invention, a large hollow blade investment casting process is used to manufacture a blade casting 1, which includes the following steps: Step 1: Prepare a hollow blade wax mold

[0046] First, a water-soluble core 2 is made according to the outer contour shape of the hollow workpiece to be formed, and the two ends of the water-soluble core 2 are clamped and fixed by the blade main body mold 3, so that the inside of the blade main body mold 3 and the outside of the water-soluble core 2 form a cavity of the wax mold to be formed, wherein the blade main body mold 3 is provided with a plurality of support points 34 for supporting the water-soluble core on the inner side of the cavity, and the plurality of support points 34 are evenly arranged. When wax is injected into the cavity, the center of the water-soluble core can be prevented from being offset or broken due to the arrangement of the plurality of support points, thereby obtaining a wax mold with a water-soluble core;

[0047] Step 2: Extraction of hollow workpiece wax model

[0048] The wax model with the water-soluble core obtained in step 1 is placed in a clean water tank, and the water-soluble core is hydrolyzed to obtain a hollow leaf wax model;

[0049] Step 3: Preparation of wax mold core and shell making

[0050] In step 2, the surface of the wax mold 4 is dipped with multiple layers of slurry and powder, and the mold shell is dried by blowing, and the mold shell is moistened with silica sol, and semi-self-hardening refractory slurry 7 is poured into the mold shell, and ceramic core rods 6 are inserted at both ends of the mold shell for sealing. In the subsequent high-temperature roasting state, the semi-self-hardening refractory slurry forms a hard core to resist the erosion and force of the molten steel during pouring;

[0051] Step 4: Dewaxing and Melting and Casting

[0052] On the basis of step 3, the shell is placed in a steam dewaxing kettle to melt and remove the wax mold of the blade and the wax mold of the pouring system to obtain a cavity shell, and the charge is prepared and smelted to obtain molten steel to be poured. After the shell is roasted, the molten steel is poured;

[0053] Step 5: Casting cleaning and shaping and subsequent heat treatment process to obtain the molded workpiece;

[0054] Step 6: Perform a performance quality inspection on the molded workpiece in step 5.

[0055] During specific implementation, in step 1, the water-soluble core 2 is cast by a water-soluble core mold, and the interior of the water-soluble core mold has a water-soluble core casting cavity, so as to obtain a water-soluble core model.

[0056] In step one, the blade main body mold 3 includes an upper mold 31 and a lower mold 32. After the upper mold 31 and the lower mold 32 are molded together, multiple support points 34 are provided on the inner side of the corresponding cavity. The support points 34 support and position the body of the water-soluble core 2. The upper mold 31 and the lower mold 32 are provided with a positioning groove 33 near the end of the cavity to position the end of the water-soluble core.

[0057] In step one, after wax injection, the blade main body mold is removed, and the wax mold holes formed at the supporting points need to be filled and repaired with liquid wax to ensure that the surface of the wax mold main body is complete and smooth.

[0058] In a specific implementation, in step 2, the obtained wax model of the hollow workpiece is trimmed to remove the parting line, and then 3D scanned, and the wax model is manually corrected again according to the scanning results, so as to obtain a complete wax model of the hollow workpiece.

[0059] In step 3, the first layer of zircon powder slurry is dipped on the surface of the wax mold, the second layer is coated with 100 mesh zircon sand, each layer is dried for 48 hours, the third layer is dipped with mullite powder, the fourth layer is coated with 30-60 mesh mullite sand, the fifth layer is dipped with mullite powder, the sixth layer is coated with 16-30 mesh mullite sand, and air drying is performed, and each layer is dried for 24 hours. The seventh and eighth layers are dipped with mullite powder and coated with 16-30 mesh mullite sand to strengthen the shell strength and the support strength at both ends of the core.

[0060] In step three, the semi-self-hardening refractory slurry 7 is composed of self-hardening slurry and zircon powder slurry in a weight ratio of 2:1, wherein the self-hardening slurry is composed of magnesium oxide, diammonium phosphate, quartz, and silica sol in a weight ratio of 1:1:8:2, and the zircon powder slurry is composed of zircon powder and silica sol in a weight ratio of 3:1; the semi-self-hardening refractory slurry solidifies within 4 hours, and the core strength value is relatively high after 8 hours.

[0061] When pouring the semi-self-hardening refractory slurry, first insert the ceramic core rod 6 at the small end of the long hole of the shell, and use the glue to smear the gap tightly, then pour the special semi-self-hardening refractory slurry 7 into the hole, and finally insert the ceramic core rod 6 at the big end of the long hole, and then use the glue to smear the gap tightly. Inserting the ceramic core rods at both ends of the inner hole of the shell can improve the support strength of the hollow blade core. Pouring the semi-self-hardening refractory slurry with a certain fluidity into the shell hole can fill the inside of the hollow blade core. Under the subsequent high-temperature roasting state, a hard core with sufficient strength is formed to resist the erosion and force of the molten steel during pouring. This process is mainly to strengthen the strength and density of the 750mm inner cavity core of the blade, and avoid the core crispness and fracture defects caused by the shell during the dewaxing or pouring process.

[0062] In step 4, when melting the charge, new 12Cr13 rods are used as charge for melting in a medium frequency furnace. An argon hood 10 is covered on the medium frequency furnace 9. The argon hood 10 is connected to an external argon bottle 8 and forms an argon protective layer 11 on the surface of the molten steel to reduce the air absorption tendency of the molten steel 12 and improve the smelting quality of the alloy.

[0063] In step 4, the pouring system is assembled before pouring the molten steel, the inner gate is set at the hot spot of the hollow workpiece, and then the pouring system such as the vertical intersection and the horizontal runner is assembled. The shell is fired at 1120°C for 80 minutes, and the molten steel is poured. At the same time, anti-oxidation measures are taken by covering the shell after pouring.

[0064] Then the casting is cleaned and reshaped. The casting goes through processes such as removing the pouring head, alkali blasting and sand removal, shot blasting, welding, and trimming. After softening and annealing, the casting is corrected.

[0065] In step 5, the heat treatment process of the hollow workpiece is annealing, quenching and tempering. The annealing process is kept at 860±20℃ for 4 hours, and the cooling method is furnace cooling. The quenching process is kept at 1000±10℃ for 2 hours, and the cooling method is oil cooling. The tempering process is kept at 730±20℃ for 7 hours, and the cooling method is furnace cooling.

[0066] Finally, the hollow blade castings after heat treatment are subjected to dimensional inspection, mechanical property inspection, metallographic structure inspection, magnetic particle inspection, etc.

[0067] Mechanical properties testing

[0068]

[0069] Metallographic structure inspection

[0070]

[0071] Magnetic particle inspection

[0072]

[0073] Dimension detection (3D scanning)

[0074] After 3D scanning inspection, the deformation degree of the blade is within 1.5mm and less than 2.5mm, and the casting can meet the machining requirements well.

[0075] The invention discloses a large hollow blade investment casting process, which is stable and reliable, and the casting quality meets the standard requirements of the steam turbine industry, and the finished product rate and qualified rate of the castings reach a relatively high level in the precision casting industry. At the same time, the environmental protection, production safety and the impact of new materials and new processes on occupational health of the products are fully considered, and the materials and processes used meet the relevant national laws and regulations and the relevant requirements of the company.

[0076] The water-soluble wax core is used to support precise positioning, effectively ensuring the dimensional accuracy of the blade wax mold wall thickness and other dimensions;

[0077] The strength of the shell and core is ensured by auxiliary ceramic core rod and pouring semi-self-hardening slurry;

[0078] By taking the measure of covering the furnace top with inert gas protection, the quality of 12cr13 molten steel and castings is improved.

[0079] As for the device and the method of use disclosed in the embodiment, since they correspond to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0080] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A process for precision investment casting of large hollow blades, characterized in that: The following steps are involved: Step 1: Prepare the hollow workpiece wax model First, a water-soluble core is made according to the outer contour shape of the hollow workpiece to be formed, and the two ends of the water-soluble core are clamped by the blade main body mold, so that a cavity of the wax mold to be formed is formed inside the blade main body mold and outside the water-soluble core, wherein the blade main body mold is located on the inner side of the cavity and is provided with a plurality of support points for supporting the water-soluble core, and wax is injected into the cavity to obtain a wax mold with a water-soluble core; Step 2: Extraction of hollow workpiece wax model The wax model with the water-soluble core obtained in step 1 is placed in a clean water tank, and the water-soluble core is hydrolyzed to obtain a hollow workpiece wax model; Step 3: Preparation of wax mold core and shell making In step 2, the surface of the wax mold is dipped with multiple layers of slurry and powder, and the mold shell is dried by blowing, and the mold shell is moistened with silica sol, and semi-self-hardening refractory slurry is poured into the mold shell, and ceramic core rods are inserted at both ends of the mold shell for sealing. In the subsequent high-temperature roasting state, the semi-self-hardening refractory slurry forms a hard core to resist the erosion and force of the molten steel during pouring; Step 4: Dewaxing and Melting and Casting On the basis of step 3, the shell is placed in a steam dewaxing kettle to melt and remove the wax mold of the blade and the wax mold of the pouring system to obtain a cavity shell, and the charge is prepared and smelted to obtain molten steel to be poured. After the shell is roasted, the molten steel is poured to obtain a casting; Step 5: Casting cleaning and shaping and subsequent heat treatment process to obtain the molded workpiece; Step 6: Perform a performance quality inspection on the molded workpiece in step 5.

2. The investment casting process for large hollow blades according to claim 1 is characterized in that: In the step 1, the water-soluble core is cast by a water-soluble core mold, and the water-soluble core mold has a water-soluble core casting cavity inside.

3. The investment casting process for large hollow blades according to claim 1 is characterized in that: In the step one, the blade main body mold includes an upper mold and a lower mold. After the upper mold and the lower mold are closed, multiple support points are provided on the inner side of the corresponding cavity. The support points support and position the body of the water-soluble core. The upper mold and the lower mold are provided with positioning grooves near the end of the cavity to position the end of the water-soluble core.

4. The investment casting process for large hollow blades according to claim 1 is characterized in that: In the step 1, after wax injection, the blade main body mold is removed, and the wax mold holes formed at the supporting points need to be filled and repaired with liquid wax.

5. The investment casting process for large hollow blades according to claim 1 is characterized in that: In the step 2, the obtained wax model of the hollow workpiece is trimmed to remove the parting line, and then 3D scanned, and the wax model is manually corrected again according to the scanning results, so as to obtain a complete wax model of the hollow workpiece.

6. The investment casting process for large hollow blades according to claim 1 is characterized in that: In the step three, the first layer of zircon powder slurry is dip-coated on the surface of the wax mold, the second layer is coated with 100 mesh zircon sand, each layer is dried for 48 hours, the third layer is dip-coated with mullite powder, the fourth layer is coated with 30-60 mesh mullite sand, the fifth layer is dip-coated with mullite powder, the sixth layer is coated with 16-30 mesh mullite sand, and the wax mold is dried with air, and each layer is dried for 24 hours.

7. The investment casting process for large hollow blades according to claim 1, characterized in that: In the step three, the semi-self-hardening refractory slurry is composed of self-hardening slurry and zircon powder slurry in a weight ratio of 2:1, wherein the self-hardening slurry is composed of magnesium oxide, diammonium dihydrogen phosphate, quartz, and silica sol in a weight ratio of 1:1:8:2, and the zircon powder slurry is composed of zircon powder and silica sol in a weight ratio of 3:1; the semi-self-hardening refractory slurry solidifies within 4 hours.

8. The investment casting process for large hollow blades according to claim 1, characterized in that: In the step 4, when the charge is smelted, an argon hood is covered on the medium frequency furnace, the argon hood is connected to an external argon source and forms an inert gas protective layer on the surface of the molten steel, thereby reducing the gas absorption tendency of the alloy liquid and improving the smelting quality of the alloy.

9. The investment casting process for large hollow blades according to claim 1, characterized in that: In the step 4, the pouring system is assembled before the molten steel is poured, the inner gate is set at the hot spot of the hollow workpiece, and then the vertical intersection and cross runner pouring systems are assembled. After the molten steel is poured, the mold shell buckle cover is taken to prevent oxidation.

10. The investment casting process for large hollow blades according to claim 1, characterized in that: In the step 5, the heat treatment process of the hollow workpiece is annealing, quenching and tempering.

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