A method for stripping a rare earth oxide core-shell structure ceramic core

Abstract

This invention provides a method for removing the core of a rare earth oxide core-shell ceramic core. The method includes the following steps: Step 1, preparation of the core removal solution; Step 2, preparation of the core removal solution; Step 3, assisted core removal; Step 4, neutralization and cleaning with alkaline solution; Step 5, assisted core removal; Step 6, neutralization and cleaning with acid solution; Step 7, repeating steps 3-6 more than twice until the ceramic core inside the titanium alloy casting is completely disintegrated and removed, resulting in a titanium alloy casting with the core removed. The core removal method of this invention has the following advantages and effects: (1) the required raw materials are inexpensive; (2) the chemicals used in the core removal process are less toxic; (3) the core removal process is simple, the core removal efficiency is high, and the core removal time is short, which can be completed within 24h-36h; (4) the removal process can be carried out under normal pressure and will not cause damage, wear, or other adverse conditions to the titanium alloy casting, which is beneficial to improving the integrity of the titanium alloy casting.

Description

Technical Field

[0001] This invention relates to the field of ceramic core removal technology, specifically a method for removing rare earth oxide core-shell structure ceramic cores. Background Technology

[0002] With the increasing demand for improved aero-engine performance, the inlet temperature of the turbine has approached or even exceeded the melting point of the turbine blade material, necessitating air cooling. Currently, ceramic cores are commonly used to form the complex internal structure of high-temperature alloy air-cooled hollow turbine blades during casting. After the turbine blades are cooled and formed, the internal ceramic cores need to be removed to create air channels. However, ceramic cores possess high mechanical strength and stability, hardly reacting with acid or alkali solutions at room temperature, and their complex structures often require multiple removal processes. This not only prolongs processing time but also increases damage to the titanium alloy castings, significantly limiting the production efficiency and yield of high-temperature alloy hollow turbine blades.

[0003] To overcome the aforementioned difficulties, there are three main methods in the existing technology. The first method involves immersing the titanium alloy casting containing the ceramic core in molten fluoride salt. Since the fluoride salt dissolves in water, it can detach from the ceramic core. High-pressure water jetting can further accelerate the core removal process. However, this method is only suitable for alloy castings with simple structures and may damage the titanium alloy casting. The second method uses molten KOH or NaOH to remove the core from the titanium alloy casting. For example, Chinese patent (publication number 101229975A) uses boiling water treatment combined with molten alkaline reaction for core removal. This method can achieve relatively rapid core removal, but the loss to the titanium alloy casting cannot be ignored. The third method uses a high-concentration alkaline solution accompanied by ultrasound or heating for core removal. For example, Chinese patent (publication number CN103752810A) discloses a pressure stirring core removal method, where the core removal solution is KOH, NaOH, or a mixture of both. High temperature and alternating pressure increases and decreases cause the alkaline solution to boil and the reaction products in the blade cavity to be discharged. Although this process causes less damage to titanium alloy castings, it is time-consuming, results in incomplete core removal, and is inefficient. Overall, while the above methods can remove the core, they suffer from complex processes, excessive resource consumption, and the potential to damage the castings.

[0004] With the development of high-temperature titanium alloy turbine casting technology, mullite rare earth oxide core-shell ceramic cores have been developed to suppress the influence of ceramic cores on casting performance. This further increases the difficulty of core removal. The fundamental issue in improving the core removal efficiency of ceramic cores lies in improving the permeability of the core-removing fluid to the ceramic core, its reaction performance with the ceramic core, and the renewal rate of the reaction interface. Currently, some experience has been accumulated in the application and research of core-removing fluid formulations, core-removing processes, and equipment. However, problems remain, such as the penetration of the core-removing fluid, the renewal rate of the reaction interface, the need for a high-pressure environment, and the difficulty in controlling equipment process parameters. Furthermore, the removal of core-shell structure ceramic cores also requires consideration of the shell removal method, for which no relevant reports or patents have been published. Therefore, it is essential to explore other safer and more efficient core-shell structure ceramic core removal methods. Summary of the Invention

[0005] The purpose of this invention is to provide a method for removing the core of a rare earth oxide core-shell structure ceramic core, so as to solve the technical problems in the background art.

[0006] To achieve the aforementioned objectives, the present invention provides the following technical solution:

[0007] A method for removing the core from a rare earth oxide core-shell structured ceramic core, the method comprising the following steps:

[0008] Step 1, Preparation of the shelling solution: The shelling solution contains the following chemical components: 7-9 mol / L nitric acid, 0.03-0.05 mol / L penetrant, and 0.03-0.05 mol / L additives;

[0009] Step 2, Preparation of the stripping solution: The stripping solution contains the following chemical components: 10-16 mol / L NaOH, KOH or a mixture thereof, 0.05-0.1 mol / L penetrant and 0.05-0.1 mol / L additives;

[0010] Step 3, Assisted Descrapping: Place the titanium alloy casting containing the ceramic core into the descrapping liquid of Step 1, heat the descrapping liquid to a temperature of 70℃-95℃, and intermittently apply ultrasonic waves to accelerate the interface reaction rate based on cavitation and oscillation, while promoting the diffusion of reactants and the dissolution of rare earth oxide shells.

[0011] Step 4, neutralization and cleaning with alkaline solution: After placing the titanium alloy casting from Step 3 in a 0.01 mol / L NaOH solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0012] Step 5, Assisted core removal: Place the titanium alloy casting from Step 4 into the core removal liquid from Step 2. The core removal liquid temperature is 80℃-100℃, and ultrasonic waves are applied intermittently.

[0013] Step 6, neutralization and cleaning of acid solution: After placing the titanium alloy casting from step 5 in a 0.01 mol / L citric acid solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0014] Step 7: Repeat steps 3-6 more than twice until the ceramic core inside the titanium alloy casting is completely disintegrated and removed, resulting in a titanium alloy casting with the core removed.

[0015] Furthermore, the penetrant in step 1 comprises one or more of disodium EDTA, sodium dodecyl sulfonate, and OEP-70.

[0016] Furthermore, the auxiliary agent in step 1 includes one or more of citric acid, oxalic acid, and ethylenediaminetetraacetic acid.

[0017] Furthermore, the penetrant in step 2 comprises one or more of disodium EDTA, sodium dodecyl sulfonate, and OEP-70.

[0018] Furthermore, the auxiliary agent in step 2 includes one or both of NaF and KF.

[0019] Furthermore, the ultrasonic frequency in steps 3 and 5 is 40000Hz and the power is 500W.

[0020] Compared with the prior art, the core removal method of the present invention has the following advantages and effects:

[0021] (1) The required raw materials are inexpensive, and the chemicals used in the decoking process are inexpensive and readily available, thus reducing the cost of decoking;

[0022] (2) The chemicals used in the core stripping process have low toxicity, which reduces environmental pollution and improves operational safety;

[0023] (3) The core removal process is simple, the core removal efficiency is high, and the core removal time is short, which can be completed within 24h-36h;

[0024] (4) The removal process can be carried out under normal pressure and will not cause damage or wear to the titanium alloy castings, which is beneficial to improving the integrity of the titanium alloy castings. Attached Figure Description

[0025] Figure 1 : Flowchart of the present invention. Detailed Implementation

[0026] The following is in conjunction with the appendix Figure 1The flowchart and specific embodiments of the core removal method shown herein provide a further detailed description of the present invention, but the content and implementation of the present invention are not limited thereto.

[0027] Example 1:

[0028] Step 1, Preparation of the shelling solution: The shelling solution contains the following chemical components: 9 mol / L nitric acid, 0.05 mol / L penetrant, and 0.05 mol / L auxiliary agent. The penetrant consists of 0.02 mol / L disodium EDTA, 0.01 mol / L sodium dodecyl sulfate, and 0.02 mol / L LOEP-70; the auxiliary agent consists of 0.03 mol / L citric acid, 0.01 mol / L oxalic acid, and 0.01 mol / L ethylenediaminetetraacetic acid.

[0029] Step 2, Preparation of the stripping solution: The stripping solution contains the following chemical components: 8 mol / L NaOH, 8 mol / L KOH, 0.1 mol / L penetrant, and 0.1 mol / L additives. The penetrant used is 0.05 mol / L disodium EDTA, 0.03 mol / L sodium dodecyl sulfate, and 0.02 mol / L LOEP-70; the additives used are 0.05 mol / L NaF and 0.05 mol / L KF.

[0030] Step 3, Assisted Descrapping: Place the titanium alloy casting containing the ceramic core into the acidic descrapping solution of step (1), heat the descrapping solution and raise the temperature to 95°C, maintain for 10 hours, and intermittently apply ultrasonic waves, wherein the ultrasonic frequency is 40000Hz and the power is 500W, based on cavitation and oscillation to accelerate the interface reaction rate, while promoting the diffusion of reactants and the dissolution of rare earth oxide shells.

[0031] Step 4, neutralization and cleaning with alkaline solution: After placing the titanium alloy casting from Step 3 in a 0.01 mol / L NaOH solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0032] Step 5, Assisted core removal: The titanium alloy casting treated in Step 4 is placed into the alkaline core removal solution in Step 2, the core removal solution is heated to 100°C and maintained for 12 hours, and ultrasonic waves are applied intermittently, with a frequency of 40000Hz and a power of 500W. Based on its cavitation and oscillation effects, the interface reaction rate is accelerated and the diffusion of reactants is promoted, thereby causing the mullite core to be pulverized and detached, achieving the purpose of removing the ceramic core;

[0033] Step 6, neutralization and cleaning of acid solution: After placing the titanium alloy casting from step 5 in a 0.01 mol / L citric acid solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0034] Step 7: Repeat steps 3-6 twice until the ceramic core inside the titanium alloy casting is completely disintegrated and removed, resulting in a titanium alloy casting with the core removed.

[0035] X-ray examination revealed no residue inside the cavity of the titanium alloy casting, indicating that the core removal was successful.

[0036] Example 2:

[0037] Step 1, Preparation of the shelling solution: The shelling solution contains the following chemical components: 7 mol / L nitric acid, 0.03 mol / L penetrant, and 0.03 mol / L auxiliary agent. The penetrant consists of 0.01 mol / L disodium EDTA, 0.01 mol / L sodium dodecyl sulfate, and 0.01 mol / L LOEP-70; the auxiliary agent consists of 0.01 mol / L citric acid, 0.01 mol / L oxalic acid, and 0.01 mol / L ethylenediaminetetraacetic acid.

[0038] Step 2, Preparation of the stripping solution: The stripping solution contains the following chemical components: 10 mol / L NaOH, 0.05 mol / L penetrant, and 0.05 mol / L additives. The penetrant used is 0.03 mol / L disodium EDTA and 0.02 mol / L sodium dodecyl sulfate, and the additives are 0.03 mol / L NaF and 0.02 mol / L KF.

[0039] Step 3, assisted descraping: The titanium alloy casting containing the ceramic core is placed in the acidic descraping solution of step (1), the descraping solution is heated and the temperature is raised to 85°C and maintained for 10 hours. Ultrasonic waves are applied intermittently, with an ultrasonic frequency of 40000Hz and a power of 500W. Based on cavitation and oscillation, the interface reaction rate is accelerated, and the diffusion of reactants and dissolution of rare earth oxide shells are promoted.

[0040] Step 4, neutralization and cleaning with alkaline solution: After placing the titanium alloy casting from Step 3 in a 0.01 mol / L NaOH solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0041] Step 5, Assisted core removal: The titanium alloy casting treated in Step 4 is placed into the alkaline core removal solution in Step 2, the core removal solution is heated to 80°C and maintained for 12 hours, and ultrasonic waves are applied intermittently, with a frequency of 40000Hz and a power of 500W. Based on its cavitation and oscillation effects, the interface reaction rate is accelerated and the diffusion of reactants is promoted, thereby causing the mullite core to be pulverized and detached, achieving the purpose of removing the ceramic core;

[0042] Step 6, neutralization and cleaning of acid solution: After placing the titanium alloy casting from step 5 in a 0.01 mol / L citric acid solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0043] Step 7: Repeat steps 3-6 three times until the ceramic core inside the titanium alloy casting is completely disintegrated and removed, resulting in a titanium alloy casting with the core removed.

[0044] X-ray examination revealed no residue inside the cavity of the titanium alloy casting, indicating that the core removal was successful.

[0045] Example 3

[0046] Step 1, Preparation of the shelling solution: The shelling solution contains the following chemical components: 8 mol / L nitric acid, 0.05 mol / L penetrant, and 0.05 mol / L auxiliary agent. The penetrant used is 0.05 mol / L disodium EDTA, and the auxiliary agent is 0.05 mol / L citric acid.

[0047] Step 2, Preparation of the stripping solution: The stripping solution contains the following chemical components: 5 mol / L NaOH, 6 mol / L KOH, 0.1 mol / L penetrant, and 0.1 mol / L additive. The penetrant used is 0.1 mol / L disodium EDTA, and the additive is 0.1 mol / L KF.

[0048] Step 3, Assisted Descrapping: Place the titanium alloy casting containing the ceramic core into the acidic descrapping solution of step (1), heat the descrapping solution and raise the temperature to 95°C, maintain for 10 hours, and intermittently apply ultrasonic waves, wherein the ultrasonic frequency is 40000Hz and the power is 500W, based on cavitation and oscillation to accelerate the interface reaction rate, while promoting the diffusion of reactants and the dissolution of rare earth oxide shells.

[0049] Step 4, neutralization and cleaning with alkaline solution: After placing the titanium alloy casting from Step 3 in a 0.01 mol / L NaOH solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0050] Step 5, Assisted core removal: The titanium alloy casting treated in Step 4 is placed into the alkaline core removal solution in Step 2, the core removal solution is heated to 100°C and maintained for 15 hours, and ultrasonic waves are applied intermittently, with a frequency of 40000Hz and a power of 500W. Based on its cavitation and oscillation effects, the interface reaction rate is accelerated and the diffusion of reactants is promoted, thereby causing the mullite core to be pulverized and detached, achieving the purpose of removing the ceramic core;

[0051] Step 6, neutralization and cleaning of acid solution: After placing the titanium alloy casting from step 5 in a 0.01 mol / L citric acid solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0052] Step 7: Repeat steps 3-6 three times until the ceramic core inside the titanium alloy casting is completely disintegrated and removed, resulting in a titanium alloy casting with the core removed.

[0053] X-ray examination revealed no residue inside the cavity of the titanium alloy casting, indicating that the core removal was successful.

[0054] Example 4

[0055] Step 1, Preparation of the shelling solution: The shelling solution contains the following chemical components: 9 mol / L nitric acid, 0.05 mol / L penetrant, and 0.05 mol / L auxiliary agent. The penetrant consists of 0.02 mol / L disodium EDTA, 0.01 mol / L sodium dodecyl sulfate, and 0.02 mol / L LOEP-70; the auxiliary agent consists of 0.03 mol / L citric acid, 0.01 mol / L oxalic acid, and 0.01 mol / L ethylenediaminetetraacetic acid.

[0056] Step 2, Preparation of the stripping solution: The stripping solution contains the following chemical components: 8 mol / L NaOH, 8 mol / L KOH, 0.1 mol / L penetrant, and 0.1 mol / L additives. The penetrant used is 0.05 mol / L disodium EDTA, 0.03 mol / L sodium dodecyl sulfate, and 0.02 mol / L LOEP-70; the additives used are 0.05 mol / L NaF and 0.05 mol / L KF.

[0057] Step 3, Assisted Descrapping: Place the titanium alloy casting containing the ceramic core into the acidic descrapping solution of step (1), heat the descrapping solution and raise the temperature to 95°C, maintain for 10 hours, and intermittently apply ultrasonic waves, wherein the ultrasonic frequency is 40000Hz and the power is 500W, based on cavitation and oscillation to accelerate the interface reaction rate, while promoting the diffusion of reactants and the dissolution of rare earth oxide shells.

[0058] Step 4, neutralization and cleaning with alkaline solution: After placing the titanium alloy casting from Step 3 in a 0.01 mol / L NaOH solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0059] Step 5, Assisted core removal: The titanium alloy casting treated in Step 4 is placed into the alkaline core removal solution in Step 2, the core removal solution is heated to 95°C and maintained for 12 hours, and ultrasonic waves are applied intermittently, with a frequency of 40000Hz and a power of 500W. Based on its cavitation and oscillation effects, the interface reaction rate is accelerated and the diffusion of reactants is promoted, thereby causing the mullite core to be pulverized and detached, achieving the purpose of removing the ceramic core;

[0060] Step 6, neutralization and cleaning of acid solution: After placing the titanium alloy casting from step 5 in a 0.01 mol / L citric acid solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0061] Step 7: Repeat steps 3-6 twice until the ceramic core inside the titanium alloy casting is completely disintegrated and removed, resulting in a titanium alloy casting with the core removed.

[0062] X-ray examination revealed no residue inside the cavity of the titanium alloy casting, indicating that the core removal was successful.

[0063] Example 5

[0064] Step 1, Preparation of the shelling solution: The shelling solution contains the following chemical components: 9 mol / L nitric acid, 0.05 mol / L penetrant, and 0.05 mol / L auxiliary agent. The penetrant used is 0.02 mol / L disodium EDTA and 0.03 mol / L LOEP-70, and the auxiliary agent used is 0.03 mol / L citric acid and 0.02 mol / L oxalic acid.

[0065] Step 2, Preparation of the stripping solution: The stripping solution contains the following chemical components: 16 mol / L KOH, 0.1 mol / L penetrant, and 0.1 mol / L additive. The penetrant used is 0.05 mol / L disodium EDTA and 0.05 mol / L LOEP-70, and the additive is 0.1 mol / L NaF.

[0066] Step 3, assisted descraping: The titanium alloy casting containing the ceramic core is placed in the acidic descraping solution of step (1), the descraping solution is heated and the temperature is raised to 90°C and maintained for 10 hours. Ultrasonic waves are applied intermittently, with an ultrasonic frequency of 40000Hz and a power of 500W. Based on cavitation and oscillation, the interface reaction rate is accelerated, and the diffusion of reactants and the dissolution of rare earth oxide shells are promoted.

[0067] Step 4, neutralization and cleaning with alkaline solution: After placing the titanium alloy casting from Step 3 in a 0.01 mol / L NaOH solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0068] Step 5, Assisted core removal: The titanium alloy casting treated in Step 4 is placed into the alkaline core removal solution in Step 2, the core removal solution is heated to 80°C and maintained for 10 hours, and ultrasonic waves are applied intermittently, with a frequency of 40000Hz and a power of 500W. Based on its cavitation and oscillation effects, the interface reaction rate is accelerated and the diffusion of reactants is promoted, thereby causing the mullite core to be pulverized and detached, achieving the purpose of removing the ceramic core;

[0069] Step 6, neutralization and cleaning of acid solution: After placing the titanium alloy casting from step 5 in a 0.01 mol / L citric acid solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes.

[0070] Step 7: Repeat steps 3-6 twice until the ceramic core inside the titanium alloy casting is completely disintegrated and removed, resulting in a titanium alloy casting with the core removed.

[0071] X-ray examination revealed no residue inside the cavity of the titanium alloy casting, indicating that the core removal was successful.

[0072] Compared with the prior art, the core removal method of the present invention has the following advantages and effects:

[0073] (1) The required raw materials are inexpensive, and the chemicals used in the decoking process are inexpensive and readily available, thus reducing the cost of decoking;

[0074] (2) The chemicals used in the core stripping process have low toxicity, which reduces environmental pollution and improves operational safety;

[0075] (3) The core removal process is simple, the core removal efficiency is high, and the core removal time is short, which can be completed within 24h-36h;

[0076] (4) The removal process can be carried out under normal pressure and will not cause damage or wear to the titanium alloy castings, which is beneficial to improving the integrity of the titanium alloy castings.

[0077] It will be apparent to those skilled in the art that the present invention is not limited to the details of the foregoing exemplary embodiments, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for removing the core from a rare earth oxide core-shell structured ceramic core, characterized in that, The method includes the following steps: Step 1, Preparation of the shelling solution: The shelling solution contains the following chemical components: 7-9 mol / L nitric acid, 0.03-0.05 mol / L penetrant, and 0.03-0.05 mol / L additives; Step 2, Preparation of the stripping solution: The stripping solution contains the following chemical components: 10-16 mol / L NaOH, KOH or a mixture thereof, 0.05-0.1 mol / L penetrant and 0.05-0.1 mol / L additives; Step 3, Assisted Descrapping: Place the titanium alloy casting containing the ceramic core into the descrapping liquid of Step 1, heat the descrapping liquid to a temperature of 70℃-95℃, and intermittently apply ultrasonic waves to accelerate the interface reaction rate based on cavitation and oscillation, while promoting the diffusion of reactants and the dissolution of rare earth oxide shells. Step 4, neutralization and cleaning with alkaline solution: After placing the titanium alloy casting from Step 3 in a 0.01 mol / L NaOH solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes. Step 5, Assisted core removal: Place the titanium alloy casting from Step 4 into the core removal liquid from Step 2. The core removal liquid temperature is 80℃-100℃, and ultrasonic waves are applied intermittently. Step 6, neutralization and cleaning of acid solution: After placing the titanium alloy casting from step 5 in a 0.01 mol / L citric acid solution with compressed air stirring for 10 minutes, remove the titanium alloy casting and rinse it in clean water for 5 minutes. Step 7: Repeat steps 3-6 more than twice until the ceramic core inside the titanium alloy casting is completely disintegrated and removed, resulting in a titanium alloy casting with the core removed.

2. The method for removing the core from a rare earth oxide core-shell structure ceramic core according to claim 1, characterized in that: The penetrant in step 1 comprises one or more of disodium EDTA, sodium dodecyl sulfonate, and OEP-70.

3. The method for removing the core from a rare earth oxide core-shell structure ceramic core according to claim 1, characterized in that: The auxiliary agent in step 1 includes one or more of citric acid, oxalic acid, and ethylenediaminetetraacetic acid.

4. The method for removing the core from a rare earth oxide core-shell structure ceramic core according to claim 1, characterized in that: The penetrant in step 2 comprises one or more of disodium EDTA, sodium dodecyl sulfonate, and OEP-70.

5. The method for removing the core from a rare earth oxide core-shell structure ceramic core according to claim 1, characterized in that: The auxiliary agent in step 2 includes one or both of NaF and KF.

6. The method for removing the core from a rare earth oxide core-shell structure ceramic core according to claim 1, characterized in that: The ultrasonic frequency in steps 3 and 5 is 40000Hz and the power is 500W.

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