Large turbine working blade narrow groove shell manufacturing method

Abstract

The invention discloses a narrow groove shell making method for a large turbine working blade, relates to the technical field of narrow groove shell making methods for large turbine working blades, and aims to solve the problem of narrow groove shell making defects. The narrow groove shell making method comprises the following steps of structural analysis and ceramic core design; a module is manufactured through precise assembly, strict size inspection is conducted on the manufactured ceramic core and the manufactured main body wax mold, and the ceramic core and the wax mold are assembled into the module; shell making, wherein the module is subjected to dip-coating, sanding and drying according to the standard investment casting shell making process; and post-treatment is conducted, specifically, the dried module is roasted and dewaxed to be manufactured into a shell, and whether the dewaxed shell meets the standard or not is checked. According to the scheme, the restriction of limited space such as a narrow groove structure in the investment casting industry is eliminated through the ceramic core structure, the problem of restricting the quality of the shell is fundamentally eliminated, and through the design of the positioning connector, the shell anchoring and the reserved gap, the quality of the shell is greatly improved. The free end of the ceramic core is effectively positioned, and the structural stability of the module in the shell manufacturing process is enhanced.

Description

Technical Field

[0001] This invention relates to the technical field of a method for manufacturing a narrow-slot shell for a large turbine working blade, specifically a method for manufacturing a narrow-slot shell for a large turbine working blade. Background Technology

[0002] In investment casting, the creation of shells with narrow, deep groove structures (high aspect ratio) is a serious challenge. The core difficulty lies in achieving uniform penetration and coverage of the coating, effective removal of air bubbles, dense filling of sand particles, and uniform drainage of moisture within the confined space.

[0003] Due to its high viscosity and surface tension, the coating is difficult to completely wet the bottom and sidewalls of the tank, easily leading to coating defects. Air bubbles become trapped due to obstructed venting paths, creating cavities and weak points. During sand application, sand particles struggle to penetrate the tank bottom, accumulating and bridging at the inlet, resulting in localized insufficient strength. During drying, solvent / moisture evaporation inside the tank is hindered and occurs much slower than in the outer areas, triggering severe shrinkage stress and easily causing coating cracking or peeling. During dewaxing, the molten wax expands due to heat, but the drainage channels are narrow, and internal pressure easily cracks the insufficiently strengthened shell.

[0004] Traditional shell-making processes often employ methods such as optimizing materials and process parameters. These include using low-viscosity, high-wetting coatings; using extremely fine sand supplemented with fluidized sand spreading or vibration to promote penetration and filling; and using vibration and directional adjustment during dip coating to drive away air bubbles. Enhanced venting and drying control are also crucial: precisely regulating the temperature and humidity of the drying environment, strengthening directional airflow, and adding process vents when necessary. Strict dewaxing management is essential: employing slow heating and extended heat preservation strategies to reduce internal pressure. While these methods are common in ensuring the integrity of such structural shells, their effectiveness is not consistent, and numerous shell defects still occur.

[0005] For example, the patent with patent number 202011069730.9 in the prior art also uses ceramic core as filler to eliminate the difficulty of making shells in confined space, but it does not take into account the stability of the connection between the ceramic core and the shell and the accuracy of the positioning. At the same time, different materials expand differently when heated. If no corresponding solutions are adopted, the shell qualification rate will not be much higher than that of the traditional shell making process. Summary of the Invention

[0006] To address the aforementioned problems, specifically those raised in the background section, this invention proposes a method for fabricating a narrow-slot shell for large turbine blades, comprising the following steps: S100: Structural Analysis and Ceramic Core Design; S110: The structural analysis includes analyzing the three-dimensional model of the casting to identify confined spaces, which include all narrow grooves or deep cavities with a depth-to-width ratio greater than a set threshold, where the coating is difficult to cover evenly and sand is difficult to fill. S120: The ceramic core design includes designing the filler, positioning interface, and shell anchoring; S121: The filling material is a ceramic core that is negatively matched with the shape of the confined space. The ceramic core can be assembled with the wax model of the blade body to fill the confined space. A reserved gap between the ceramic core and the wax model is set on the filling material. S122: The positioning interface is located on the contact surface adjacent to the wax model of the ceramic core and the blade body; S123: The shell anchor is set on the outer surface of the ceramic core exposed inside the shell; S200: Precision assembly into modules. Strict dimensional inspection is carried out on the manufactured ceramic core and main body wax model. The ceramic core and wax model are assembled into modules to ensure the accurate position of the free end of the main body ceramic core. Wax or special sealant is used to seal the joint between the ceramic core and the wax model to prevent the paint from seeping into the reserved gap during shell making. S300: Shell making, the module is dipped, sanded and dried according to the standard investment casting shell making process; S400: Post-processing, the dried module is baked and dewaxed to form a shell. The shell after dewaxing is inspected to see if it meets the standard. If it meets the standard, the shell enters the casting process.

[0007] A further feature of the present invention is that the shell anchoring is provided as an annular groove, a grid-like pit, or a roughened textured area.

[0008] A further feature of the present invention is that the positioning interface is a groove provided on the solid part of the ceramic core.

[0009] A further provision of the present invention is that the post-processing also includes a judgment step for shells with abnormal internal structures after inspection, to determine whether the abnormality can be eliminated by repair and polishing. If it can be eliminated, the shells are then processed and the casting process begins. If they cannot be repaired or polished, the shells are then destroyed to recover the sand and ceramic cores.

[0010] A further provision of the present invention is that the reserved gap on one side is the sum of thermal expansion, assembly tolerance compensation and process safety margin. Assuming that the thermal expansion (mm) is ΔL, the relevant length of the component at room temperature (mm) is L0, the coefficient of thermal expansion of the material ( / °C) is α, and the temperature change (°C) is ΔT, then the formula for calculating the thermal expansion (mm) ΔL is: ΔL = L0 × α × ΔT.

[0011] The beneficial technical effects of this invention are as follows: This solution eliminates the constraints of limited space, such as narrow-slot structures, in the investment casting industry through the ceramic core structure, thus eliminating the problem of restricting shell quality from the root. Through the design of positioning interface, shell anchoring, and reserved gap, the free end of the ceramic core is effectively positioned and the structural stability of the module during the shell making process is enhanced, which greatly reduces the difficulty of making shells of this type of structure. Ultimately, the shell qualification rate of this type of structure is increased from 10%-15% in the traditional shell making process to 90%, achieving a leap in technical effect. Attached Figure Description

[0012] Figure 1 An example diagram of a narrow groove structure at the tip of a blade is shown.

[0013] Figure 2 It shows Figure 1 A schematic diagram of the ceramic core structure corresponding to the narrow groove structure.

[0014] The attached diagram shows: 1. Positioning point of ceramic core at the leaf tip; 2. Corresponding structure of the ceramic core at the leaf tip; 3. Positioning groove of the ceramic core. Detailed Implementation

[0015] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0016] This invention proposes a method for manufacturing a narrow-slot shell for large turbine blades. This method is applicable to various casting structures with narrow and deep slots, deep cavities, high ribs, etc., which are difficult to guarantee quality through conventional coating and sanding. The specific steps are as follows: Step 1: Structural Analysis and Ceramic Core Design 1. Identify target structure: Analyze the three-dimensional model of the casting to identify confined spaces, including all narrow grooves or deep cavities where the aspect ratio is greater than the set threshold, the coating is difficult to cover evenly, and the sand is difficult to fill; 2. Design of ceramic core structure: 2.1 Infill Material: Design a ceramic core that negatively matches the shape of the target confined space to fill the confined space, and set and design the reserved gap between the ceramic core and the wax model; 2.2 Positioning Interface Design: On the contact surface between the ceramic core and the wax model of the blade body (the wax model of the non-confined space part), a positioning interface is set at the contact point between the ceramic core and the main body wax model, based on the material expansion coefficient and process temperature. 2.3 Shell Anchoring Design: On the outer surface of the ceramic core exposed inside the shell (i.e., the outer surface of the part of the ceramic core that contacts the wax model), annular grooves, grid-like pits, or roughened texture areas are set to increase the bonding force between the ceramic core and the wax model and the shell.

[0017] Step 2: Precision assembly into modules 1. Parts Inspection: Strict dimensional inspection is carried out on the manufactured ceramic cores and main body wax models; 2. Assembly and Positioning: Assemble the ceramic core and wax model into a module (the reserved gaps are naturally formed in this step through size design) to ensure the accurate position of the free end of the main ceramic core; 3. Sealing treatment: Use wax or special sealant to seal the joint between the ceramic core and the wax mold to prevent the paint from seeping into the reserved gap during shell making.

[0018] Step 3: Shell Making 1. The module is dipped, sanded and dried according to the standard investment casting shell making process. Since the difficult-to-handle narrow and deep cavities are eliminated, problems such as paint penetration, air bubble removal, sand filling and drying uniformity are fundamentally improved. 2. Anchoring effect: During the dip coating process, the coating will fully flow into the positioning grooves on the surface of the ceramic core. After drying and curing, it forms a mechanical lock, making the shell strength in this area significantly higher than that of the planar bond.

[0019] Step 4: Post-processing 1. Dewaxing and firing: The dried mold is fired to dewax. Since the confined space is supported by the ceramic core and the reserved gap buffers the thermal stress, the risk of wax expansion damaging the shell during dewaxing is greatly reduced. 2. Inspection and Repair: Inspect whether the interior of the dewaxed shell meets the standards. Shells that meet the standards enter the casting process. For shells with abnormal internal structures, determine whether the abnormalities can be eliminated by repair and polishing. If so, proceed to the repair process and then enter the casting process. If they cannot be repaired or polished, proceed to the destruction process and recover the sand and ceramic core.

[0020] Calculation method for reserved gap: I. Design Principles 1. Functional principle: The primary purpose of the gap is positioning, ensuring that the free end of the ceramic core is accurately and stably positioned during module assembly and subsequent shell making, preventing shaking or sinking.

[0021] 2. Thermal matching principle: Space must be reserved for dimensional changes caused by the different coefficients of thermal expansion of the wax, ceramic core, and shell materials during the dewaxing (150°C) and firing (1000°C) processes to prevent thermal stress accumulation from causing cracks in the ceramic core or shell.

[0022] 3. Process Feasibility Principle: The gap size should facilitate assembly operations and be effectively sealed by subsequent wax sealing to prevent paint seepage during shell making.

[0023] II. Specific Calculation and Design Steps Step 1: Determine the datum dimensions and fit relationships. Target position measurement: Precisely measure the theoretical assembly gap that naturally forms after the wax model and ceramic core are assembled in a confined area. This gap is the starting point for the design.

[0024] Clearly define the mating objects: The gap is located between the inner cavity of the wax model and the ceramic core, that is, between the ceramic core and the free end of the wax model that needs to be supported and positioned by it.

[0025] Step 2: Calculate the thermal expansion compensation amount Calculation formula (simplified): ΔL = L0 × α × ΔT.

[0026] ΔL: Thermal expansion (mm); L0: The relevant length (mm) of the component at room temperature, such as the length from the ceramic core fixing point to the free end; α: Coefficient of thermal expansion of the material ( / °C). The α value of ceramic core (silicon-based) and shell refractory materials needs to be obtained from the material handbook. ΔT: Temperature change (°C), such as from 20°C to dewaxing temperature (150°C) or calcination temperature (1000°C); Calculation example: Assuming the free end length of the ceramic core is L0 = 50 mm, and the ceramic core material α = 6.0 × 10⁻⁶ mm, then... -6 / °C, calculate the expansion during the dewaxing process (ΔT=130°C): ΔL_ceramic = 50 × 6.0e-6 × 130 ≈ 0.039mm.

[0027] The expansion of the shell in the same direction must also be considered. If both are made of the same material and expand in the same direction, the relative expansion may be small; if the materials are different or expansion is restricted, the difference must be calculated.

[0028] Design value: The thermal compensation portion of the single-sided reserved gap should be greater than the calculated maximum relative thermal expansion ΔL, and usually multiplied by a safety factor (1.5-2.0).

[0029] Step 3: Determine the gap value comprehensively. The final unilateral reserved gap δ consists of the following parts: δ = (Thermal expansion compensation) + (Assembly tolerance compensation) + (Process safety margin) Thermal expansion compensation: As mentioned above, to ensure that it does not jam at high temperatures.

[0030] Assembly tolerance compensation: This takes into account the manufacturing tolerances and assembly errors of the ceramic core to ensure smooth insertion without interference. This is typically determined based on the dimensional accuracy grade of the part (CT4-CT6).

[0031] Process safety margin: An empirically added value to account for unforeseen minor deformations or stresses.

[0032] Step 4: Typical Value Range and Verification Experience range: In investment casting, the process clearance used for positioning and buffering is typically designed to be between 0.1 mm and 0.5 mm on one side. For large turbine blades, due to the larger component size and more complex thermal processes, the clearance tends to be at the upper middle of this range (0.2-0.4 mm).

[0033] Verification method: Room temperature assembly verification: Use feeler gauges or precision measuring tools to confirm that the gaps are uniform and meet the design values ​​after assembly.

[0034] Process simulation: Thermal-structural coupling simulation was performed using finite element analysis (FEA) software to verify whether the gap was sufficient to release stress and avoid excessive contact pressure under the dewaxing and calcination temperature fields.

[0035] Process testing: By producing a small number of modules and going through the complete shell making, dewaxing, and firing process, check whether there are cracks in the ceramic core and whether the shell is crushed or cracked, and optimize the gap value in reverse.

[0036] In summary, the reserved gap is a functional design feature, not a manufacturing error. Its core function is to position the free end and buffer thermal stress. Simultaneously, calculations must be based on specific material thermophysical parameters and precise process temperature curves, not just experience. The final value must balance thermal expansion, manufacturing precision, and process reliability. In this scheme, the gap design complements the positioning groove on the outside of the ceramic core. The positioning groove solves the radial locking problem between the shell and the ceramic core, while the gap solves the axial positioning and stress buffering problems within the module.

[0037] Although the invention has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0038] In the description of this invention, terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate direction or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. These are used merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0040] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to those processes, articles, or apparatus / devices.

[0041] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for manufacturing a narrow slot shell for a large turbine working blade, characterized in that: Includes the following steps: S100: Structural Analysis and Ceramic Core Design; S110: The structural analysis includes analyzing the three-dimensional model of the casting to identify confined spaces, which include all narrow grooves or deep cavities with a depth-to-width ratio greater than a set threshold, where the coating is difficult to cover evenly and sand is difficult to fill. S120: The ceramic core design includes designing the filler, positioning interface, and shell anchoring; S121: The filling material is a ceramic core that is negatively matched with the shape of the confined space. The ceramic core can be assembled with the wax model of the blade body to fill the confined space. A reserved gap between the ceramic core and the wax model is set on the filling material. S122: The positioning interface is located on the contact surface adjacent to the wax model of the ceramic core and the blade body; S123: The shell anchor is set on the outer surface of the ceramic core exposed inside the shell; S200: Precision assembly into modules. Strict dimensional inspection is carried out on the manufactured ceramic core and main body wax model. The ceramic core and wax model are assembled into modules to ensure the accurate position of the free end of the main body ceramic core. Wax or special sealant is used to seal the joint between the ceramic core and the wax model to prevent the paint from seeping into the reserved gap during shell making. S3 00: Shell making: The module is dipped, sanded, and dried according to the standard investment casting shell making process; S400: Post-processing, the dried module is baked and dewaxed to form a shell. The shell after dewaxing is inspected to see if it meets the standard. If it meets the standard, the shell enters the casting process.

2. The method for manufacturing a narrow slot shell for a large turbine working blade according to claim 1, characterized in that: The shell anchoring is configured as an annular groove, a grid-like pit, or a roughened textured area.

3. The method for manufacturing a narrow slot shell for a large turbine working blade according to claim 1, characterized in that: The positioning interface is a groove set on the solid part of the ceramic core.

4. The method for manufacturing a narrow slot shell for a large turbine working blade according to claim 1, characterized in that: The post-processing also includes a judgment step for shells with abnormal internal structures after inspection, to determine whether the abnormality can be eliminated by repair and polishing. If it can be eliminated, the shells are then repaired and enter the casting stage. If they cannot be repaired or polished, the shells are destroyed and the sand and ceramic cores are recycled.

5. The method for manufacturing a narrow slot shell for a large turbine working blade according to claim 1, characterized in that: The reserved gap on one side is the sum of thermal expansion, assembly tolerance compensation and process safety margin. Assuming the thermal expansion (mm) is ΔL, the relevant length of the component at room temperature (mm) is L0, the coefficient of thermal expansion of the material ( / °C) is α, and the temperature change (°C) is ΔT, then the formula for calculating the thermal expansion (mm) ΔL is: ΔL=L0×α×ΔT.

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