A process for optimizing the surface pitting defect quality of precision cast single crystal turbine blades

Abstract

A precision casting single crystal turbine blade surface pit defect quality optimization process, different fused mullite powder, corundum powder and different specifications of silica sol mixed into slurry, matched with different mesh corundum sand or EC95 sand, after shell preparation, dewaxing, shell burning, single crystal turbine blade shell is obtained; In the stirring container, the surface layer slurry which can directly contact with the high-temperature alloy liquid is prepared, then the transition layer slurry which can possibly contact with the high-temperature alloy liquid is prepared, finally, the reinforcing layer slurry which does not directly contact with the high-temperature alloy liquid is prepared in the stirring container, and the reinforcing layer slurry is evenly coated on the outer surface of the dried shell, and then the EC95 mullite sand is evenly scattered. The advantages of the present application are: without adding other chemical components to inhibit the reaction between the main elements and the shell in the parent alloy composition, the blade composition and performance are guaranteed to meet the blade preparation requirements. The surface quality of the blade is improved, the post-grinding is reduced, and the overall working performance of the blade is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy blade casting, and in particular to a process for optimizing the quality of pitting defects on the surface of precision-cast single-crystal turbine blades. Background Technology

[0002] High-temperature alloy blades are widely used in the manufacture of gas turbines for ships and land-based industries. With continuous optimization of propulsion structures, increasing gas turbine efficiency, and rising turbine inlet temperatures, single-crystal blades require higher temperature resistance. Because single-crystal blades eliminate transverse grain boundaries during grain growth, they exhibit better resistance to high-temperature creep, thermal fatigue, oxidation, hot corrosion, and durability compared to other blades, leading to their increasingly widespread application in various fields. Single-crystal turbine blades operate in harsh environments, have complex internal structures, and require small dimensional tolerances. Therefore, during precision casting, ensuring the integrity of their single crystal structure while achieving better surface quality and higher dimensional accuracy is crucial. In precision casting, a mixture of EC95 powder and silica sol is typically used as a slurry. A wax resin is impregnated with the slurry, and then different grades of EC95 sand are applied to the surface to create the mold shell.

[0003] In the process of preparing single-crystal blades, especially in the smelting process, the high-temperature alloy liquid easily reacts with the mold shell, resulting in chemical sand adhesion on the blade surface. At the same time, under high-temperature calcination, the iron oxide contained in the refractory material in the mold shell reacts with the silicon dioxide generated by the decomposition of silica sol to form iron silicate, the reaction equation of which is shown in formula (1): 2FeO + SiO2 = 2FeO·SiO2 (1). In the molten state, it penetrates into the blade surface to form pit defects. The diameter of these defects is 0.2-2 mm and the depth is 0.05-0.1 mm, making it difficult to guarantee the blade size. If the smelting temperature is lowered, defects will not only be generated in the later solidification process, but the platinum wire supporting the core will also not melt. Therefore, it is urgent to invent a shell-making process that does not erode the blade surface at high temperatures. Summary of the Invention

[0004] In order to overcome the shortcomings and disadvantages of existing production processes, this invention aims to provide a preparation process for high-temperature alloy single-crystal turbine blade mold shells. This process can prevent the formation of iron silicate during the high-temperature casting process, which would cause corrosion to the blade surface and thus reduce the surface quality and precision of the blade. At the same time, it can also ensure that the mold shell has good strength and flexibility when combined with powder adhesives of different specifications.

[0005] This invention provides a process for optimizing the quality of pitting defects on the surface of precision-cast single-crystal turbine blades. The process is characterized by: mixing different electrofused mullite powders and corundum powders with silica sol of different specifications to form a slurry, then combining it with corundum sand or EC95 sand of different mesh sizes to prepare a shell, followed by dewaxing and shell burning to obtain a single-crystal turbine blade shell.

[0006] First, when preparing the surface slurry that will directly contact the high-temperature alloy liquid in a dedicated mixing vessel, a 320-mesh EC95 fused mullite powder with fewer impurities and S-830 silica sol are used. After uniformly coating the wax tree with this surface slurry, a layer of 100-mesh white corundum abrasive is evenly sprinkled on top. Then, when preparing the transition layer slurry that is more likely to come into contact with the high-temperature alloy liquid in a dedicated mixing vessel, another 320-mesh EC95 fused mullite powder with fewer impurities and S-10 silica sol are used. After uniformly coating the dried surface shell with silica sol of specification 80, a layer of 60-mesh white corundum sand is evenly sprinkled on top. Finally, when preparing the reinforcing layer slurry that does not directly contact the high-temperature alloy liquid in a special mixing container, a 320-mesh white corundum powder and S-1430 specification silica sol are used. After uniformly coating the dried surface-transition layer shell with the reinforcing layer slurry in several layers, EC95 mullite sand with mesh sizes of 60-46-24 is evenly sprinkled on top.

[0007] The wax trees described in this technical solution all use medium-temperature molding wax, and all wax parts are connected by welding.

[0008] In the shell-making process described in this technical solution, the powder-to-liquid mass ratio is 3.6-4.0:1, the silica sol pH value is 8-10, the shell is dried naturally for 6-16 hours, the shell weight is 2.7-3.0Kg, and the thickness is 7-11mm.

[0009] The dewaxing process described in this technical solution has a dewaxing temperature of 165-175℃, a dewaxing pressure of 0.6-0.7MPa, and a dewaxing time of 13-16min.

[0010] The shell-firing process described in this technical solution involves a shell-firing temperature of 900-1000℃ and a shell-firing duration of 2-3 hours.

[0011] Compared with the prior art, the advantages of this invention are:

[0012] The precision casting single-crystal turbine blade surface pitting defect optimization process described in this invention eliminates the need to add other chemical components to the master alloy to inhibit the reaction between the main element and the mold shell, ensuring the blade composition and performance meet the requirements for blade manufacturing. This improves the surface quality of the blade, reduces post-grinding, and guarantees the overall working performance of the blade while maintaining the dimensional accuracy of the profile. Detailed Implementation

[0013] The present invention will be further explained below with reference to specific implementation schemes, but it is not limited to the present invention. In order to make the purpose, technical solution and advantages of the present invention clearer, examples are listed below to further explain the optimized process scheme in detail.

[0014] Example 1

[0015] First, the wax parts and corresponding gating system are prepared using the bottom-pouring crystal selection method. Medium-temperature wax is used, with a wax tree height of 280mm. Each group consists of 6 wax parts. The air inlet edge of the wax part is perpendicular to the horizontal direction of the central injection pipe, ensuring the wax part is perpendicular to the longitudinal direction of the water-cooled base. After assembling the gating system, the entire module undergoes a tight casting coating and sand-sprinkling shell-making process. The surface coating is prepared by mixing 320-mesh fused mullite powder with S-830 specification silica sol at a powder-to-liquid mass ratio of 4.0:1. The silica sol pH value is 10, and 100-mesh white corundum is used as the sand. The surface shell drying time is 16 hours. The transition layer coating is prepared by mixing 320-mesh fused mullite powder from another manufacturer with S-1080 specification silica sol. The powder-to-liquid ratio was 3.8:1, the silica sol pH was 9, and 60-mesh white corundum was used as the abrasive. The drying time for the transition layer was 8 hours. The reinforcing layer coating was prepared by mixing 320-mesh white corundum powder with S-1430 silica sol at a powder-to-liquid ratio of 3.7:1. The silica sol pH was [not specified in the original text]. Four layers of the reinforcing layer were applied, each using 60-46-24-24 fused mullite sand. The drying time for each layer was 8 hours. The shell thickness was 7 mm. After the shell was prepared, dewaxing was performed at 165°C and 0.65 MPa. The shell firing temperature was 900°C for 2 hours. Finally, the fired shell was cast at 1570°C. After removing the shell, the pitting defects on the blade surface completely disappeared, and the shell no longer produced reactants that corroded the blade, thus ensuring the appearance quality and dimensional accuracy of the blade.

[0016] Example 2

[0017] First, the wax parts and corresponding gating system are prepared using the top-injection crystal selection method. Medium-temperature wax is used, with a wax tree height of 280mm. Each group consists of 6 wax parts, with the wax blades perpendicular to the horizontal direction of the injection pipe and ensuring the wax parts are longitudinally perpendicular to the water-cooled base. After assembling the gating system, the entire mold undergoes a tight casting coating and sand-sprinkling shell-making process. The surface coating is prepared by mixing 320-mesh fused mullite powder with S-830 silica sol at a powder-to-liquid mass ratio of 3.7:1. The silica sol has a pH of 10, and the sand is 100-mesh white corundum. The surface shell drying time is 16 hours. The transition layer coating is prepared by mixing 320-mesh fused mullite powder from another manufacturer with S-1080 silica sol. The powder-to-liquid ratio was 3.8:1, the silica sol pH was 9, and 60-mesh white corundum was used as the abrasive. The drying time for the transition layer was 8 hours. The reinforcing layer coating was prepared by mixing 320-mesh white corundum powder with S-1430 silica sol at a powder-to-liquid ratio of 4.0:1. The silica sol pH was [not specified in the original text]. Four layers of the reinforcing layer were applied, each using 60-46-24-24 fused mullite sand. The drying time for each layer was 8 hours. The shell thickness was 9 mm. After the shell was prepared, dewaxing was performed at 175°C and 0.75 MPa. The shell firing temperature was 950°C and the firing time was 3 hours. Finally, the fired shell was cast at 1600°C. After removing the shell, the pitting defects on the blade surface completely disappeared, and the shell no longer produced reactants that corroded the blade, thus ensuring the appearance quality and dimensional accuracy of the blade.

[0018] Matters not covered in this invention are common knowledge.

[0019] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A process for optimizing the quality of pitting defects on the surface of precision-cast single-crystal turbine blades, characterized in that: The aforementioned process for optimizing the surface pitting defects of precision-cast single-crystal turbine blades involves mixing different types of fused mullite powder, corundum powder, and silica sol of different specifications into a slurry. This slurry is then combined with corundum sand of different mesh sizes or EC95 sand to prepare a mold shell. After dewaxing and shell firing, a single-crystal turbine blade mold shell is obtained. When preparing the surface slurry that directly contacts the high-temperature alloy liquid in a stirring vessel, a 320-mesh EC95 fused mullite powder with fewer impurities and S-830 silica sol are used. This surface slurry is evenly coated onto the wax resin surface, followed by a uniform layer of 100-mesh white corundum sand. Then, in a dedicated stirring vessel, a slurry is prepared to react with the high-temperature alloy liquid. When preparing the transition layer slurry, which is more likely to come into contact with the gold liquid, another type of 320-mesh EC95 fused mullite powder with fewer impurities and S-1080 specification silica sol are used. After uniformly coating the dried surface shell with this transition layer slurry, a layer of 60-mesh white corundum sand is evenly sprinkled on top. Finally, when preparing the reinforcing layer slurry, which does not come into direct contact with the high-temperature alloy liquid, in a special mixing container, a type of 320-mesh white corundum powder and S-1430 specification silica sol are used. After uniformly coating the dried surface-transition layer shell with this reinforcing layer slurry in several layers, EC95 mullite sand with mesh sizes of 60-46-24 is evenly sprinkled on top.

2. The process for optimizing the surface pitting defects of precision-cast single-crystal turbine blades according to claim 1, characterized in that: All wax trees are made with medium-temperature molding wax, and all wax parts are connected by welding.

3. The process for optimizing the surface pitting defects of precision-cast single-crystal turbine blades according to claim 1, characterized in that: In the shell-making process, the powder-to-liquid mass ratio is 3.6-4.0:1, the silica sol pH value is 8-10, the shell is dried naturally for 6-16 hours, the shell weight is 2.7-3.0Kg, and the thickness is 7-11mm.

4. The process for optimizing the surface pitting defects of precision-cast single-crystal turbine blades according to claim 1, characterized in that: The dewaxing process involves a dewaxing temperature of 165-175℃, a dewaxing pressure of 0.6-0.7MPa, and a dewaxing time of 13-16min.

5. The process for optimizing the surface pitting defects of precision-cast single-crystal turbine blades according to claim 1, characterized in that: The shell-firing process involves a shell-firing temperature of 900-1000℃ and a firing time of 2-3 hours.