Method for treating core head of ceramic core of directional solidification hollow turbine blade

Abstract

The invention relates to the technical field of aeronautical part manufacturing, and particularly discloses a directional solidification hollow turbine blade ceramic core head treatment method which comprises the following steps: S1, respectively measuring the thermal expansion rates of a ceramic core and a mold shell which are slowly heated from room temperature to 1550 DEG C, and calculating the amount of a gap which needs to be reserved between the mold shell and the ceramic core when the mold shell is heated to a pouring temperature; s2, a method for limiting the ceramic core in the mold shell and freely expanding / shrinking the ceramic core is given, namely, a counter bore structure is arranged on the ceramic core, the surface of the ceramic core is pre-filled with a coating and a wax sheet, and a gap between the ceramic core and the mold shell is formed; and S3, a crystal growth channel is arranged in a gap between the mold shell and the ceramic core head, and mixed crystals are prevented from being formed in the gap between the ceramic core and the mold shell. The method not only thoroughly solves the problem of disordered crystal grains of the core head at the fixed end of the directional solidification hollow blade, but also can keep the function of fixing the relative position of the ceramic core in the mold shell by the core head at the fixed end, and has a remarkable effect on improving the production qualification rate of the directional solidification hollow turbine blade.

Description

Technical Field

[0001] The invention relates to the technical field of aviation parts manufacturing, in particular to a method for processing a core head of a directional solidified hollow turbine blade ceramic core. Background Art

[0002] Turbine blades are the core hot end components of aircraft engines and industrial gas turbines, and have the characteristics of high quality requirements, high technical difficulty, high manufacturing cost, technical development cost and long production process. The temperature bearing capacity of turbine blades determines the inlet temperature of the turbine, which is of great significance to the fuel efficiency and thrust ratio of aircraft engines and industrial gas turbines.

[0003] There are two main ways to improve the temperature bearing capacity of aircraft engine turbine blades: 1) Use directional solidification high-temperature alloys and directional solidification technology to prepare a directional solidification structure in which the entire blade is composed of one grain; 2) Make the turbine blade into a hollow structure with a complex structure so that it can be cooled by advanced air cooling technology. That is, directional solidification hollow turbine blades have become an indispensable key hot end component of advanced aircraft engines.

[0004] The manufacturing process of directional solidification hollow turbine blades is near-net-mold investment casting. The process principle is: the ceramic core is embedded in the metal mold, and the wax mold with the built-in ceramic core is made by injection molding. The ceramic shell is cast on the surface of the wax mold, and then the wax mold is melted to obtain the shell with the built-in ceramic core. The molten metal is melted and poured into the ceramic shell. After the molten metal is cooled, the ceramic shell is broken and removed, and the internal ceramic core is removed by alkali boiling to obtain a hollow turbine blade.

[0005] However, since the ceramic core matrix is ​​usually made of quartz glass (SiO2), and the mold shell used for directional solidification turbine blade precision casting is capacitor corundum (Al2O3), there is a 1% to 1.5% difference in thermal expansion between the two materials. Figure 2 As shown, the consequences are:

[0006] (1) During the cooling process of the shell firing process, the shrinkage of the alumina shell is greater than the shrinkage of the silica-based core, especially in the length direction, and the ceramic core is broken by the shrinkage pressure of the alumina shell;

[0007] (2) During the mold shell heating process in the pouring process, the expansion of the alumina mold shell is greater than the expansion of the silica-based core, and a gap appears between the ceramic core head and the mold shell. When the molten metal is poured into the mold shell, the ceramic core is impacted by the molten metal and shifts its position, resulting in excessive wall thickness of the casting;

[0008] (3) In particular, for directional solidification blades, when the ceramic core head and the mold shell are not completely fitted together, the molten metal enters the gap after pouring. Since the grains of the directional solidification blade are first solidified by the crystallization section or crystal selector at the bottom of the mold shell (crystallizer), and the grains grow along a certain direction, if the molten metal solidifies and grows independently of the grains, such as the molten metal in the gap of the core head at the bottom of the blade, the grains of the blade body will no longer have the characteristics of single crystals or columnar crystals with a straight orientation, which will reduce the high-temperature mechanical properties of the blade. Summary of the invention

[0009] The object of the present invention is to provide a method for processing a core head of a directional solidified hollow turbine blade ceramic core to solve the problems raised in the above-mentioned background technology.

[0010] To achieve the above object, the present invention provides the following technical solution: a method for processing a ceramic core head of a directional solidified hollow turbine blade, comprising the following steps:

[0011] S1: Calculate the gap between the mold shell and the ceramic core when the temperature rises to the pouring temperature;

[0012] S2: pre-fill the coating into the gap between the ceramic core and the mold shell;

[0013] S3: Arrange the crystal growth channel between the mold shell and the ceramic core head.

[0014] Preferably, the thermal expansion rate of the ceramic core and the mold shell is measured separately, and the thermal expansion rate is slowly heated from room temperature to 1550° C. to obtain a thermal expansion rate curve between the ceramic core and the mold shell, with a value of 1.2%.

[0015] Preferably, the calculation formula for the gap in the width direction is: (ceramic core width×1.2%) / 2.

[0016] Preferably, the calculation formula for the gap in the thickness direction is: (ceramic core thickness×1.2%) / 2.

[0017] Preferably, the calculation formula of the gap in the length direction is: ceramic core length×1.2%.

[0018] Preferably, when the ceramic core is limited, a countersunk hole structure is provided on the ceramic core, one end of the core head in the length direction of the ceramic core is fixed in the mold shell, and a gap in the length direction is provided on the other end surface.

[0019] Preferably, paint is applied on the surface of the ceramic core, with a thickness of 0.04 to 0.06 mm each time. After each application of the paint, it is dried naturally for 5 to 10 minutes before the next layer is applied.

[0020] Preferably, the shell calcining temperature ranges from 800 to 1100°C.

[0021] Preferably, the number of times of painting is the calculated gap volume divided by 0.05.

[0022] Preferably, the crystal growth channel at the fixed end of the ceramic core head is made of a round rod-shaped wax with a diameter of 3 to 5 mm, and is connected to the crystal selector or the crystal starting section. The crystal growth channel at the fixed end of the non-ceramic core head is made of a wax sheet with a thickness of 2 to 3 mm and a width of 3 to 5 mm. The crystal growth channels are arranged along the periphery of the side and bottom surfaces of the ceramic core head.

[0023] The present invention has at least the following beneficial effects:

[0024] 1. This solution not only completely solves the problem of messy grains in the fixed end core head of directional solidification hollow blades, but also retains the function of the fixed end core head to fix the relative position of the ceramic core in the mold shell, which has a significant effect on improving the production qualification rate of directional solidification hollow turbine blades. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the ceramic core head of the present invention;

[0026] Figure 2 It is a schematic diagram of the linear expansion rate of the silicon oxide-based ceramic core and the aluminum oxide mold shell of the present invention;

[0027] Figure 3 It is a schematic diagram of a directionally solidified hollow turbine blade mold shell of the present invention;

[0028] Figure 4 It is a schematic diagram of the gap between the ceramic core head and the mold shell of the present invention;

[0029] Figure 5 This is a schematic diagram of the core head area of ​​the paint brush of the present invention;

[0030] Figure 6 This is a schematic diagram of the core head area where the coating needs to be removed according to the present invention;

[0031] Figure 7 It is a schematic diagram of the arrangement of the crystal growth channel of the present invention;

[0032] Figure 8 It is a schematic diagram of the arrangement of the crystal growth channel at the fixed end of the crescent-shaped core head of the present invention. DETAILED DESCRIPTION

[0033] 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.

[0034] Embodiment 1

[0035] See also Figure 1 - Figure 8 , a method for processing a ceramic core head of a directional solidified hollow turbine blade, comprising:

[0036] Step 1: Measure the thermal expansion coefficient of the ceramic core and mold shell;

[0037] The thermal expansion coefficients of the silicon oxide-based ceramic core and the alumina ceramic shell were measured respectively, and were slowly heated from room temperature to 1550°C to obtain the thermal expansion coefficient curves between the silicon oxide-based core and the alumina shell, as shown in FIG. Figure 2 As shown, there is a difference of 1% to 1.5% in thermal expansion rate between the two materials. In this embodiment, the value can be 1% or 1.3%, preferably 1.2%, as shown below.

[0038] Step 2: Calculate the gap between the core and the head:

[0039] According to the difference in thermal expansion coefficient between the ceramic core and the mold shell, as well as the core head size, the maximum gap between the mold shell and the core is calculated when the temperature rises to the pouring temperature. The core head length (W), thickness (T) and length (L) directions are as follows: Figure 4 As shown, the gap amount is calculated respectively, and the calculation formula is:

[0040] (1) Gap in width direction: (core width × 1.2%) / 2

[0041] For example, if the width of the ceramic core is 30 mm, the single-side gap in the width direction of the core head is 30×1.2% / 2=0.18 mm.

[0042] (2) Gap in thickness direction: (ceramic core thickness × 1.2%) / 2

[0043] (3) Gap in length direction: Ceramic core length × 1.2%

[0044] For example, if the length of the ceramic core is 150 mm, the gap at the end surface of the core head is 150×1.2%=1.8 mm.

[0045] Note: In order to ensure the positioning of the ceramic core in the length direction, one end of the core head in the length direction of the ceramic core is fixed in the mold shell (this is achieved by designing a countersunk hole structure on the ceramic core, such as Figure 4 As shown), the longitudinal gap is applied entirely on the other end face, as Figure 4 shown.

[0046] Step 3: Prepare gap pre-filling paint for gaps with a thickness of less than 0.2 mm:

[0047] Formula: Stir 500 ml of nitro lacquer (in accordance with BG / T25271-2010) and 500 ml of acetone until fully dissolved and mixed, then add 30-50 g of malachite green powder (analytical grade) and continue stirring for at least 30 minutes.

[0048] The coating is similar to paint and is green and viscous. After each coating is prepared, use a brush to apply 3 layers on the surface of the ceramic core and measure the coating thickness as a reference for the subsequent production of the free end gap. If the thickness of each coating layer is too small, for example, less than 0.03mm, then appropriately increase the nitro varnish to increase the viscosity of the coating; if the thickness of each coating layer is too large, it means that the coating is too viscous, and add an appropriate proportion of acetone to reduce the viscosity of the coating.

[0049] Step 4: Pre-filling the gap between the ceramic core and the mold shell:

[0050] The so-called method for reserving a gap between the ceramic core head and the mold shell is to adhere or apply certain materials, such as nail polish, wax flakes or the coating of the present invention, to the surface of a specified area of ​​the ceramic core before making the shell. These materials can be burned out during the firing process of the mold shell, thereby reserving a gap between the ceramic core and the mold shell.

[0051] The pre-filling material for the gap between the ceramic core and the mold shell must meet the following characteristics:

[0052] a) The thickness is controllable, such as nail polish or paint. The thickness of each application on the ceramic core surface is uniform and controllable to ensure the accuracy of the reserved gap;

[0053] b) The pre-filling material has good adhesion to the ceramic core and the shell slurry. Otherwise, during the slurry dipping and sand pouring operations in the shell making process, the pre-filling material will peel off from the surface of the ceramic core, or the slurry will not be able to adhere to the surface of the pre-filling material, which will lead to the failure of the reserved gap.

[0054] c) The prefilled material can be fully burned out during the shell firing. The shell firing temperature is usually in the range of 800-1100°C, so the prefilled material must be fully burned out within this temperature range, otherwise it will remain inside the casting and cause the casting to be scrapped.

[0055] In the traditional turbine blade precision casting industry, nail polish, scotch tape and other materials are usually used to make gaps with a thickness of less than 0.2mm. The disadvantage of nail polish is that the material is transparent and it is impossible to quickly distinguish whether there is a leak or misoperation, and the adhesion between scotch tape and the mold shell slurry is poor.

[0056] The coating prepared by the present invention is a blue paint raw material, has good adhesion to both the ceramic core and the mold shell slurry, the coating is clearly discernible, and the risk of missing brushing can be effectively avoided. The thickness of each brushing is 0.04-0.06mm.

[0057] (1) Figure 5 As shown, the side surface of the ceramic core head is coated with the paint prepared in step 3. The number of coating times is the gap amount calculated in step 1 divided by 0.05. The actual gap amount and the calculated gap amount are allowed to fluctuate within the range of 0 to 0.05 mm, that is, it is better to apply one more layer than to reduce the gap amount.

[0058] After each coat of paint, allow it to dry naturally for 5 to 10 minutes before applying the next coat.

[0059] (2) Figure 5 As shown, wax paper is bonded to the end surface of the core head (usually the end surface of the free end of the core head in the length direction), and the thickness of the wax paper is the same as the gap amount in the length direction.

[0060] Step 5: Figure 6 As shown, the paint of the six circular hole areas on the four sides of the fixed end core head is removed, and the diameter of the circular hole is: after the paint of the circular hole area on the front and back of the fixed end is removed, the mold shell contacts the core to ensure that the ceramic core will not drift in both the front and back directions, which is beneficial to the control of the wall thickness of the final casting. In particular, when the blade has an exhaust edge core head, a circular hole is also required on the back of the basin of the exhaust edge core head to further restrict the drift of the ceramic core on the back of the basin, which is beneficial to the control of the wall thickness of the casting.

[0061] Step 6: Arrangement of the crystal growth channel between the mold shell and the ceramic core head gap:

[0062] Figure 7 The red arrows indicate the crystal growth channels. The crystal growth channel at position A is made of round wax with a diameter of 3 to 5 mm and is connected to the crystal selector or crystal starting section. The crystal growth channels at other positions are made of wax sheets with a thickness of 2 to 3 mm and a width of 3 to 5 mm. Figure 7 The red line frame in the figure is the boundary of the ceramic core.

[0063] Explanation: The cross section of the ceramic core is usually irregular, and the crystal growth channel layout is different from Figure 7 The scheme shown is similar to that shown in FIG. 1 , and can be arranged along the periphery of the side and bottom surfaces of the core head, such as Figure 8 And the size of the crystal growth channel can be appropriately adjusted according to the size of the ceramic core.

[0064] The present invention not only completely solves the problem of disordered grains in the fixed end core head of the directional solidification hollow blade, but also retains the function of the fixed end core head to fix the relative position of the ceramic core in the mold shell, which has a significant effect on improving the production qualification rate of the directional solidification hollow turbine blade.

[0065] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0066] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for processing a directional solidified hollow turbine blade ceramic core head, characterized in that: include: S1: Calculate the gap between the mold shell and the ceramic core when the temperature rises to the pouring temperature; S2: pre-fill the coating into the gap between the ceramic core and the mold shell; S3: Arrange the crystal growth channel between the mold shell and the ceramic core head; The crystal growth channel at the fixed end of the ceramic core head is made of a round rod-shaped wax with a diameter of 3 to 5 mm, which is connected to the crystal selector or the crystal starting section. The crystal growth channel at the fixed end of the non-ceramic core head is made of a wax sheet with a thickness of 2 to 3 mm and a width of 3 to 5 mm. The crystal growth channels are arranged along the periphery of the side and bottom surfaces of the ceramic core head.

2. A method for processing a directional solidification hollow turbine blade ceramic core head according to claim 1, characterized in that: The thermal expansion coefficients of the ceramic core and the mold shell were measured separately, and they were slowly heated from room temperature to 1550° C., a thermal expansion coefficient curve between the ceramic core and the mold shell was obtained, and the upper limit value of the thermal expansion coefficient was taken.

3. A method for processing a directional solidification hollow turbine blade ceramic core head according to claim 2, characterized in that: The calculation formula for the gap in the width direction is: (ceramic core thickness × φ) / 2, φ range is 1% to 1.3%; The calculation formula of the gap in the thickness direction is: (ceramic core thickness × φ) / 2; The calculation formula for the gap in the length direction is: (ceramic core thickness × φ) / 2.

4. A method for processing a directional solidification hollow turbine blade ceramic core head according to claim 3, characterized in that: The φ is 1.2%.

5. The method for processing a directional solidification hollow turbine blade ceramic core head according to claim 3, characterized in that: When the ceramic core is limited, a countersunk hole structure is arranged on the ceramic core, one end of the core head in the length direction of the ceramic core is fixed in the mold shell, and a gap in the length direction is arranged on the other end face.

6. The method for processing a directional solidification hollow turbine blade ceramic core head according to claim 3, characterized in that: Paint the surface of the ceramic core with a thickness of 0.04 to 0.06 mm each time. After each application of paint, let it dry naturally for 5 to 10 minutes before applying the next layer.

7. A method for processing a directional solidification hollow turbine blade ceramic core head according to claim 6, characterized in that: The mold shell baking temperature ranges from 800 to 1100°C.

8. A method for processing a directional solidification hollow turbine blade ceramic core head according to claim 7, characterized in that: The number of times to apply paint is the calculated gap volume divided by 0.05.

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