A method for manufacturing a turbine mold shell with grain refinement for investment casting

Abstract

The present invention discloses a method for manufacturing a turbine mold shell with refined grains for investment casting, comprising the steps of preparing a coating, the coating comprising a surface coating, a transition coating, and a back coating; applying the surface coating; applying the transition coating; applying the back coating; dewaxing the mold shell; and sealing the inner and outer edges of the pouring nozzle. This investment casting silica sol mold shell manufacturing process reinforces the granular filler bonded to the inner and outer edges of the pouring nozzle by adding an inner and outer slurry sealing process to the pouring nozzle, preventing the granular filler on the pouring nozzle from falling into the mold shell. The mold shell coating is divided into three different coatings, and the surface coating uses a finer-grained cobalt aluminate powder additive, thereby increasing the smoothness of the mold shell surface layer, making the surface layer more dense, resulting in a mold shell with refined grains on the inner surface, thereby making the cast turbine casting a fine-grained casting with a smoother surface and higher precision.

Description

Technical Field

[0001] The present invention relates to the field of turbine refined mold shell manufacturing, and in particular to a method for manufacturing a turbine mold shell with refined grains for investment casting. Background Art

[0002] Turbine engines are widely used in aerospace, marine, and other fields. Therefore, the manufacture of turbine rotors is of paramount importance. Traditional machining is extremely difficult due to the complex surface structure and small inter-blade clearances of turbine blades. Investment casting, however, allows for the integral molding of micro-turbines. Furthermore, investment casting surpasses other casting methods in terms of part precision and surface roughness. Turbines used in aerospace and marine engines place higher demands on the surface smoothness of turbine blades. Consequently, the investment casting process places increased demands on the mold shell, particularly the surface grain refinement of the mold shell.

[0003] Investment casting, also known as lost wax casting, includes processes such as wax pressing, wax trimming, tree formation, slurry dipping, wax melting, pouring molten metal, and post-processing. Traditional lost wax casting technology uses wax to make a wax mold of the part to be cast, and then coats the wax mold with slurry. After the mold shell is dried, it is placed in hot water to melt the internal wax mold. The mold shell with the melted wax mold is taken out and then baked into a ceramic mold. Once baked. Generally, a pouring port is left when making the mold shell, and then molten metal is poured from the pouring port. After cooling, the required part is made. The investment casting process is very complex and has many process parameters. Traditional investment casting methods have a high rate of product defects in the production of thin-walled complex workpieces such as turbines. Among them, the more common problem is that the sand grains used to shape the mold shell on the edge of the mold shell pouring port easily fall off and enter the mold shell, thereby affecting product quality.

[0004] In light of the above, this application proposes a method for manufacturing turbine shells for investment casting with refined grains to address these issues. This application utilizes investment casting to address the complex, thin-walled blade structures of micro-turbines. A fine-grained shell is formed on the inner surface of the shell, improving the surface quality of the turbine casting and producing fine-grained turbine castings. Summary of the Invention

[0005] The purpose of the present invention is to solve the above technical problems and provide a method for manufacturing a turbine mold shell for investment casting with grain refinement.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: a method for manufacturing a turbine mold shell for investment casting by grain refinement, comprising the following steps:

[0007] (1) Preparation of coating, wherein the coating comprises a top coating, a transition coating, and a back coating;

[0008] (2) Surface coating: clean the wax model with cleaning liquid, and then coat the surface layer after the cleaning liquid is completely removed. Use the slurry dipping method to evenly coat the surface of the wax model with the surface coating;

[0009] (3) Apply the transition layer. After the topcoat is dry, apply the transition layer of paint. Place the slurry-coated formwork in a sand spreader at an angle of 45° upwards, then turn it left and right to apply sand layer by layer.

[0010] (4) Back coating: After the transition layer coating is dry, take the back coating and gradually put the slurry-coated formwork into the sand spreader at an angle of 45 degrees upwards, then turn it left and right and spread sand layer by layer;

[0011] (5) Dewaxing the mold shell. After the mold shell is dried, the mold is dewaxed, the mold pouring mouth is placed downward, and the mold is sent to the dewaxing kettle to remove the wax in the mold shell;

[0012] (6) Seal the inside and outside edges of the pouring gate with the pouring gate facing downward and immerse the mold into the back layer coating so that the inside and outside edges of the pouring gate are evenly coated with the coating. After drying, a pouring gate protective layer is formed;

[0013] (7) Firing: Place the mold shell with the pouring port downward and send it into the roasting furnace. The roasting temperature is 950°C and the roasting time is 1.5-2 hours to obtain the finished mold shell.

[0014] Furthermore, the components of the surface coating include, by weight, 300-400 parts of silica sol, 500-800 parts of cobalt aluminate powder, 1-2 parts of wetting agent, 1-2 parts of defoaming agent, and 3-5 parts of graphene dispersion; the cobalt aluminate powder is 325 mesh and has a particle size of 35-50 μm.

[0015] Furthermore, graphene is added to at least the surface layer of the coating, and the graphene particle size is less than 10 μm.

[0016] Furthermore, the graphene dispersion is prepared by mixing graphene slurry, dispersant and distilled water and stirring them evenly to form a graphene mixture, and then dispersing the mixture for 10-30 minutes using mechanical stirring and ultrasonic dispersion to form a graphene dispersion, wherein the dispersant is polyoxyethylene nonylphenyl ether.

[0017] Furthermore, the components of the transition layer coating include 300-400 parts by weight of silica sol and 350-600 parts of zircon powder.

[0018] Furthermore, the components of the back layer coating include 300-400 parts by weight of silica sol and 350-600 parts of zircon sand.

[0019] Furthermore, fireproof materials are added to the surface coating, transition layer coating and back layer coating, and the fireproof materials are one or a combination of two or more of silicon oxide powder, zirconium oxide powder, aluminum oxide powder or magnesium oxide powder.

[0020] Furthermore, the defoaming agent is one of polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanolamine ether or polydimethylsiloxane.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the investment casting silica sol mold manufacturing process reinforces the granular fillers bonded inside and outside the pouring mouth by adding an inner and outer edge sealing process to the pouring mouth, thereby preventing the granular fillers on the pouring mouth from falling off into the mold; the coating of the mold is divided into three different coatings, and the surface coating adopts cobalt aluminate powder additives with finer particle size, thereby increasing the smoothness of the mold surface layer, making the surface of the surface layer more dense to obtain a mold with refined inner surface grains, so that the cast turbine casting forms a fine-grained casting with a smoother surface and higher precision; graphene additives are added to the surface layer, because graphene has high strength, high toughness, good durability, good filling effect, large specific surface area and its unique two-dimensional honeycomb lattice structure, so that the surface layer can be smoother, and the crack resistance and mechanical strength of the surface layer can be effectively improved. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0023] Example 1:

[0024] A method for manufacturing a turbine mold shell for investment casting by grain refinement comprises the following steps:

[0025] (1) Preparation of coatings, including surface coatings, transition coatings, and back coatings; the surface coating will be in direct contact with the molten metal and should not react with the molten metal and its oxides, and form a flat, dense, solid and smooth shell surface to ensure that the casting surface is smooth, with clear contours and no surface defects. The back coating requires high strength and high deformation resistance to ensure that the shell has good mechanical properties during casting. The transition coating is to better combine the surface and back coatings.

[0026] The components in the surface coating include 300-400 parts of silica sol, 500-800 parts of cobalt aluminate powder, 1-2 parts of wetting agent and 1-2 parts of defoaming agent by weight; the cobalt aluminate powder is 325 mesh and has a particle size of 35-50 μm.

[0027] The components in the transition layer coating include 300-400 parts of silica sol and 350-600 parts of zircon powder by weight, and the zircon powder has a mesh size of 70-120.

[0028] The components in the back layer coating include 300-400 parts of silica sol, 50-100 parts of zircon powder and 350-600 parts of zircon sand in parts by weight, and the zircon sand has a mesh size of 20-50.

[0029] Silica sol is a high-quality water-based binder for investment casting and is used for each of the above shell layers. Silica sol can be easily formulated into high-quality coatings with a high powder-to-liquid ratio and good coating stability. Shells made with silica sol do not require chemical hardening, and the shell manufacturing process is air-free.

[0030] Fireproof materials can be optionally added to the surface coating, transition coating and back coating. The fireproof materials are one or a combination of two or more of silicon oxide powder, zirconium oxide powder, aluminum oxide powder or magnesium oxide powder.

[0031] When preparing the coating, first add the silica sol into the mixing barrel, and add the wetting agent in proportion. Refractory materials can be added optionally, and the lumps are broken up. Then stir for about 1 hour, add the defoamer to the coating, continue stirring for 2 hours, and observe whether there are bubbles in the coating. If bubbles exist, the defoamer must be added, but the total amount should not exceed 0.4%. The defoamer is one of polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanolamine ether or polydimethylsiloxane.

[0032] The preparation method for the transition layer coating is similar to that for the back and top layers. The corresponding components are uniformly mixed. During coating preparation, the various ingredients must be thoroughly mixed, maintain a uniform density, and remain moist. To ensure uniformity, refractory materials must be thoroughly mixed with the binder to ensure optimal performance. During the coating preparation process, the ratio of the coating components, the order in which they are added, the use of a paint mixer, and the duration of the mixing time are all key factors that influence the final performance of the coating.

[0033] (2) Surface coating: clean the wax model with a cleaning liquid, which is a mixture of ZF-301 emulsified water cleaning agent and tap water in a ratio of 1:1. Clean the wax model; after the cleaning liquid is completely removed, perform surface coating; use a slurry dipping method to evenly coat the surface of the wax model with a surface coating; when dipping, tilt the wax model downward at 45° and immerse it in the surface coating, rotate the wax model, and then observe whether there are bubbles or unevenly covered parts on the surface of the wax model. If there are bubbles, pierce them with an air gun and use a fine brush to evenly coat the uncovered parts. Then hang the module on the bracket and wait for subsequent transition layer coating and sanding.

[0034] (3) coating the transition layer. After the topcoat is dry, dip the transition layer coating in it. Dip the mold shell processed and dried in step (2) into the silica sol. Then, gradually put the mold shell after the slurry into the sand spreader at an angle of 45 degrees upward. Then, turn it left and right and spread sand layer by layer. The sand spread on the transition layer is coal gangue powder or kaolin clinker. The particle size of the sand spread in this step is 30-60 mesh. The transition layer can be repeatedly coated as needed.

[0035] (4) Back layer coating: After the transition layer coating is dry, take the back layer coating, and gradually put the mold shell after slurry coating into the sand spreader at an angle of 45 degrees upward, and then turn it left and right to spread sand layer by layer. The coating method in this step is the same as step (3), but the particle size of the zircon powder and coal gangue powder components of the back layer is 16-30 mesh;

[0036] (5) Dewaxing the mold shell. After the mold shell is dried, the mold is dewaxed, the mold pouring mouth is placed downward, and the mold is sent to the dewaxing kettle to remove the wax in the mold shell;

[0037] (6) Seal the inner and outer edges of the pouring port with mortar, immerse the pouring port of the mold downward into the back layer coating, so that the inner and outer edges of the pouring port are evenly coated with coating, and form a pouring port protective layer after drying; the pouring port of the mold is the weak link of the entire mold, which is easy to be bumped and cause slag to fall off during the subsequent processing. It is not easy to detect the slag falling into the mold. Once the processing continues, the cast workpiece will definitely have defects. Sealing the pouring port in this step can greatly improve the strength of the pouring port edge, strengthen the fixation of the sand particles in the back layer, and improve the smoothness, thereby avoiding the occurrence of slag.

[0038] (7) Firing: Place the mold shell with the pouring port downward and send it into the roasting furnace. The roasting temperature is 950°C and the roasting time is 1.5-2 hours to obtain the finished mold shell.

[0039] In this embodiment, the integrity of the pouring gate is maintained by adding inner and outer sealing slurries to the edge of the pouring gate. Secondly, the surface layer of silica sol and cobalt aluminate powder used can form a fine-grained mold shell. During pouring, the casting can be well attached to the surface of the wax mold, and the mold shell is formed more accurately.

[0040] Example 2:

[0041] The manufacturing method of this embodiment is generally similar to that of the embodiment, except that in this embodiment, graphene is added to the coating. The coating is modified and optimized by utilizing graphene's unique two-dimensional honeycomb lattice structure, which provides a large specific surface area, high strength, high toughness, good durability, and excellent filling effect. Specifically, at least the topcoat of the coating contains graphene, and the graphene particle size is less than 10 μm. In this embodiment, taking the addition of graphene to the topcoat as an example, the components of the topcoat include, by weight, 300-400 parts of silica sol, 500-800 parts of zircon powder, 1-2 parts of a wetting agent, 1-2 parts of a defoaming agent, and 3-5 parts of a graphene dispersion.

[0042] The graphene dispersion liquid preparation method comprises mixing and stirring a graphene slurry, a dispersant, and distilled water to form a graphene mixed liquid, and then dispersing the mixture for 10-30 minutes using mechanical stirring and ultrasonic dispersion to form the graphene dispersion liquid, wherein the dispersant is polyoxyethylene nonylphenyl ether. When preparing the topcoat, the graphene dispersion liquid is prepared separately, and the other components are prepared together, and then the two components are mixed evenly. In actual use, stirring and ultrasonic dispersion can be used to evenly mix the two components, thereby preparing the topcoat coating in this embodiment.

[0043] Furthermore, the coating methods of each layer of coating, as well as the dewaxing and baking methods are all the same. It can be understood that this embodiment can also use a slurry sealing process inside and outside the edge of the pouring gate.

[0044] Since the overall size of the turbine engine turbine rotor is small, the blade thickness is thin, the thinnest part is only 1.3mm, and the structure is very complex and twisted, the surface roughness is required to be 3.2μm; therefore, the precision requirements of the mold shell are very high, especially the requirements for the surface layer are more stringent. Experiments have shown that in this embodiment, the process of adding graphene dispersion to the surface layer coating can make the surface of the surface layer more delicate and smooth, and the characteristics of the two-dimensional plane of graphene can be used to fill the gaps inside the surface layer coating. Its microscopically smooth two-dimensional plane can improve the smoothness of the layer after the coating dries on a macro scale, thereby improving the surface finish of the cast turbine and meeting the roughness requirements.

[0045] Comparative Example:

[0046] This example, used as a comparison with Example 1, follows the same overall mold manufacturing process, differing in that the slurry seals on the inner and outer edges of the pouring nozzles are removed. Experiments have shown that this comparative example achieves a surface layer smoothness and fineness comparable to Example 1, but the pouring nozzle edges exhibit greater granularity and brittleness. This makes it easy for the pouring nozzles of the molds to collide with each other during operations such as stockpiling, resulting in slag and other issues, which can lead to an increased rate of defective castings.

[0047] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for manufacturing a turbine mold shell for investment casting by grain refinement, characterized in that: The following steps are involved: (1) Preparation of coating, wherein the coating comprises a topcoat coating, a transition layer coating, and a backcoat coating; the components of the topcoat coating comprise, by weight, 300-400 parts of silica sol, 500-800 parts of cobalt aluminate powder, 1-2 parts of a wetting agent, 1-2 parts of a defoaming agent, and 3-5 parts of a graphene dispersion; the cobalt aluminate powder is 325 mesh and has a particle size of 35-50 μm; (2) Surface coating: clean the wax model with cleaning liquid, and then coat the surface after the cleaning liquid is completely removed. Use the slurry dipping method to evenly coat the surface of the wax model with the surface coating; (3) Apply the transition layer. After the topcoat is dry, take the transition layer coating and gradually put the slurry-coated formwork into the sand spreader at an angle of 45 degrees upwards. Then turn it left and right and spread sand layer by layer. (4) Back coating: After the transition layer coating is dry, take the back coating and gradually put the mold shell after slurry coating into the sand spreader at an angle of 45 degrees upwards, then turn it left and right and spread sand layer by layer; (5) Dewaxing the mold shell. After the mold shell is dried, the mold is dewaxed. The mold pouring mouth is placed downward and sent into the dewaxing kettle to remove the wax in the mold shell. (6) Seal the inside and outside of the pouring gate edge with slurry, immerse the pouring gate of the mold shell downward into the back layer coating, so that the inside and outside of the pouring gate edge are evenly stained with coating, and a pouring gate protective layer is formed after drying; (7) Firing: Place the mold shell with the pouring port downward and send it into the roasting furnace. The roasting temperature is 950℃ and the roasting time is 1.5-2h to obtain the finished mold shell.

2. The method for manufacturing a turbine mold shell for investment casting by grain refinement according to claim 1, characterized in that: The graphene dispersion liquid preparation method comprises the following steps: mixing graphene slurry, a dispersant and distilled water and stirring them uniformly to form a graphene mixed liquid; and dispersing the mixed liquid by mechanical stirring and ultrasonic dispersion for 10-30 minutes to form a graphene dispersion liquid, wherein the dispersant is polyoxyethylene nonylphenyl ether.

3. The method for manufacturing a turbine mold shell for investment casting by grain refinement according to claim 1, characterized in that: The components in the transition layer coating include 300-400 parts by weight of silica sol and 350-600 parts of zircon powder.

4. The method for manufacturing a turbine mold shell for investment casting by grain refinement according to claim 1, characterized in that: The components in the back layer coating include 300-400 parts by weight of silica sol and 350-600 parts of zircon sand.

5. The method for manufacturing a turbine mold shell for investment casting by grain refinement according to claim 1, characterized in that: Fireproof materials are also added to the surface coating, transition layer coating and back layer coating. The fireproof materials are one or a combination of two or more of silicon oxide powder, zirconium oxide powder, aluminum oxide powder or magnesium oxide powder.

6. The method for manufacturing a turbine mold shell for investment casting by grain refinement according to claim 1, characterized in that: The defoaming agent is one of polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropanolamine ether or polydimethylsiloxane.