A method of forming a titanium alloy casting with an embedded fine tube

Abstract

The application discloses a forming method of a titanium alloy casting with embedded cast fine pipes, and mainly comprises the following steps: pickling and drying treatment of the fine pipes; one end of the fine pipe is blocked by a plug, and the other end is filled with refractory sand, and the filling is tamped until the inner cavity of the fine pipe is filled; the fine pipe is blocked into a sealed structure by another plug to form a fine pipe assembly; a casting mold is prepared, the fine pipe assembly is assembled with the casting mold after degassing treatment, and a mold for pouring is obtained; the mold is preheated, and then the mold is placed in a pouring furnace for smelting and pouring; and the titanium alloy casting is obtained after cleaning the mold. According to the forming method, the surface of the fine pipe is treated, and the inner cavity of the fine pipe is filled with the refractory sand, so that the deformation of the embedded cast fine pipe is reduced, the filled refractory sand is bulk filled and easy to remove, the forming quality of the product is high, and the yield is high.

Description

Technical Field

[0001] This invention relates to the field of investment casting technology for non-ferrous metals, specifically a method for forming titanium alloy castings with embedded thin tubes. Background Technology

[0002] The shapes and structures of modern aviation and aerospace equipment are becoming increasingly complex. In order to achieve lightweight and integrated design of equipment structures, products are now gradually designed as thin-walled structures with irregularly shaped cavities in the inner cavity, to replace the oil lines, air pipes and other components that were originally located on the outside.

[0003] In the aerospace field, titanium alloy castings with elongated holes are frequently used. These castings are often made using ceramic core casting. However, using ceramic cores for elongated hole casting not only makes subsequent cleaning more difficult, but also often results in problems such as the inability to remove the core or insufficient roughness of the inner wall surface of the hole after core removal, leading to product scrap. Currently, the solution to these problems in casting is to use embedded thin tubes, which integrally form the thin tube with the elongated hole into the casting to avoid the subsequent core removal process. However, in actual production, embedded thin tubes have the following problems: 1) After assembling the thin tube with the mold, during the casting process, the cooling and shrinkage pressure of the molten metal can cause the thin tube to twist and deform, and in severe cases, even block the pipeline; 2) The shape, size, and smoothness of the inner wall surface of the thin tube cannot be guaranteed, resulting in a low product yield. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for forming titanium alloy castings with inlaid thin tubes. This method involves surface treatment of the thin tube and filling the inner cavity of the thin tube with refractory sand, which reduces the deformation of the inlaid thin tube. At the same time, the refractory sand is filled in bulk, making it easy to remove, resulting in high product forming quality and high yield.

[0005] To achieve the above objectives, the specific solution adopted by the present invention is as follows: A method for forming a titanium alloy casting with an embedded thin tube mainly includes the following steps: Step 1: Prepare a thin tube and perform acid washing and drying on the thin tube; Step 2: Make two plugs that match the inner diameter of both ends of the thin tube, and degas the plugs. Step 3: Seal one end of the thin tube with one of the plugs, and fill the thin tube with refractory sand from the other end, tamping it down as you fill, until the inner cavity of the thin tube is filled. Step 4: Use another plug to seal the thin tube to form a sealed structure, thus assembling the thin tube assembly; Step 5: Prepare the mold and degas it. Step 5: Assemble the thin tube assembly with the degassed mold to obtain the casting mold; Step 6: Preheat the mold; Step 7: Place the preheated mold in the casting furnace for melting and casting; Step 8: After cleaning the mold, the titanium alloy casting is obtained.

[0006] Preferably, the pickling solution comprises 65% nitric acid, 40% hydrofluoric acid, and water, wherein the volume ratio of nitric acid to hydrofluoric acid is (1.5-2.5):1.

[0007] Preferably, in step 3, the refractory sand used is 40-90 mesh fused yttrium oxide sand or zirconium oxide sand.

[0008] Preferably, in step 3, the refractory sand is filled into the thin tube in multiple batches, with each batch reaching a depth of no more than 10 mm, and is compacted while being filled.

[0009] Preferably, the material of the plug is the same as the material of the mold.

[0010] Preferably, the mold is made of graphite.

[0011] Preferably, in step 5, the mold is placed in a vacuum furnace and vacuum degassed at 900~960°C.

[0012] Preferably, in step 6, the preheating temperature is 400~500℃, and the temperature is maintained for 1~2 hours.

[0013] Preferably, the thin tube is a titanium alloy tube with a wall thickness of 1~1.5mm.

[0014] Beneficial effects: 1) The molding method of the present invention has the following advantages: (a) Pickling the thin tube to remove the surface contaminant layer can improve the fusion effect between molten titanium and titanium tube and avoid cracks on the surface of titanium tube; (b) Filling the inside of the thin tube with compacted refractory sand can support the inner wall of the titanium tube and prevent deformation of the titanium tube caused by the cooling and shrinkage pressure of molten titanium during the casting process; (c) Filling the inside of the thin tube with refractory sand with low thermal conductivity can serve as heat preservation and prevent large temperature difference between the thin tube and molten titanium during casting, which can cause local non-fusion defects; (d) Filling the inside of the thin tube with fused yttrium oxide sand or zirconium oxide sand that is relatively inert to titanium can prevent the inner wall of the titanium tube from reacting chemically with the refractory sand under the erosion of high-temperature titanium liquid during the casting process, which would make it difficult to remove the refractory sand.

[0015] 2) The molding method of the present invention can achieve seamless or near-seamless casting of thin tubes, resulting in a smooth surface of the cast thin tube structure and a high product yield.

[0016] 3) The molding method of this invention results in a high fusion rate between the thin tube and the casting body, and high internal quality of the casting.

[0017] 4) Using the molding method of the present invention, the inner cavity of the thin tube is filled with refractory sand. The refractory sand has good collapsibility and high removal efficiency, which can significantly improve production efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cast capillary tube in this invention.

[0019] Illustration markings: 1. Titanium alloy casting, 2. Thin tube, 3. Refractory sand strip, 4. Plug. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] A method for forming a titanium alloy casting with an embedded thin tube mainly includes the following steps: Step 1: Prepare a thin tube (a titanium alloy tube with a wall thickness of 1~1.5mm), perform acid pickling on the thin tube to remove the surface contaminant layer, and then dry it; the pickling solution includes 65% nitric acid, 40% hydrofluoric acid and water, wherein the volume ratio of nitric acid to hydrofluoric acid is (1.5-2.5):1. Step 2: Make two plugs that match the inner diameter of both ends of the thin tube, and degas the plugs. Step 3: Seal one end of the thin tube with one of the plugs. To prevent the thin tube from twisting and deforming due to shrinkage during the casting process, fill the thin tube with refractory sand (40-90 mesh fused yttrium oxide sand or zirconium oxide sand, which has a low thermal conductivity and is relatively inert to molten titanium) from the other end. Fill the thin tube with refractory sand in multiple batches, with each batch not exceeding 10 mm in depth. Tamp the sand as you fill until the inner cavity of the thin tube is filled. Step 4: Use another plug to seal the thin tube to form a sealed structure, thus assembling the thin tube assembly; Step 5: Prepare the mold, the material of which is the same as that of the plug, and degas the mold. Step 5: Assemble the thin tube assembly with the degassed mold to obtain the casting mold; Step 6: Preheat the mold to 400~500℃ and keep it at that temperature for 1~2 hours. Step 7: Place the preheated mold in the casting furnace for melting and casting. Please refer to the schematic diagram after casting and melting. Figure 1 The thin tube 2 is embedded in the titanium alloy casting 1, and the thin tube 2 is sealed with a refractory sand strip 3 formed of refractory sand through the plug 4. Step 8: Clean the mold. After removing the plug, vibrate to clean the sand filling inside the thin tube to obtain the titanium alloy casting.

[0022] In detail, in step 5, the mold is made of graphite and is placed in a vacuum furnace for vacuum degassing at 900~960℃.

[0023] Example 1 The forming method for inserting 1mm thick TA2 thin tubes into ZTC4 titanium castings mainly includes the following steps: (1) Pickling the capillary tube. The pickling solution is prepared with 65% nitric acid, 40% hydrofluoric acid and water. The ratio of nitric acid to hydrofluoric acid is 1.5 to 2.5:1 (the remainder is water). Pickling the capillary tube for 3 to 8 minutes. After pickling, the capillary tube is cleaned and dried. (2) Manufacturing graphite plugs and degassing the graphite plugs; (3) Use the degassed graphite plug to block one end of the thin tube and begin filling and compacting with sand; (4) The refractory sand is fused yttrium oxide sand that has been stabilized. The sand particle size is 40-70 mesh. The yttrium oxide sand is filled into the titanium tube in multiple times. The filling depth each time does not exceed 10 mm. Each time, it is compacted until the inner cavity of the thin tube is filled. (5) Use the degassed graphite head to plug the other end of the capillary tube, and assemble it into a capillary tube assembly for later use; (6) Processing and preparing graphite molds, and degassing the graphite molds in a vacuum furnace at 900-960°C; (7) Assemble the titanium tube assembly with the vacuum-degassed graphite mold to obtain a casting mold that can be used for casting. (8) Preheat the casting mold at 450°C for 2 hours in a baking furnace; (9) The preheated casting mold is melted and poured in the titanium alloy casting furnace while it is still hot; (10) Titanium alloy castings are obtained after cleaning the casting mold.

[0024] One hundred ZTC4 titanium castings were prepared using the method of Example 1, and the prepared ZTC4 titanium castings were tested. The test results showed that, compared with castings prepared using the forming methods of the prior art, the method of the present invention resulted in a casting deformation of ±0.2 mm, an inner wall roughness higher than Ra6.3 μm, unobstructed pipeline, and a product qualification rate of over 98%. Therefore, the castings obtained by the method of the present invention have good quality.

[0025] In summary, this invention reduces the deformation of the cast tube by pickling the surface of the thin tube and filling its inner cavity with refractory sand. At the same time, the refractory sand is filled in bulk and is easy to remove, resulting in high product molding quality, high yield, and significantly improved production efficiency.

[0026] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for forming a titanium alloy casting with an embedded thin tube, characterized in that, The main steps include the following: Step 1: Prepare a thin tube, which is a titanium alloy tube with a wall thickness of 1~1.5mm. Perform acid washing and drying treatment on the thin tube. Step 2: Make two plugs that match the inner diameter of both ends of the thin tube, and degas the plugs. Step 3: Seal one end of the thin tube with one of the plugs, and fill the thin tube with refractory sand from the other end. Fill the thin tube with refractory sand in multiple times, with each filling depth not exceeding 10mm. Tamp the sand as you fill until the inner cavity of the thin tube is filled. Step 4: Use another plug to seal the thin tube to form a sealed structure, thus assembling the thin tube assembly; Step 5: Prepare the mold. Place the mold in a vacuum furnace and degas it at 900~960℃. Assemble the thin tube assembly with the degassed mold to obtain the casting mold. Step 6: Preheat the mold to 400~500℃ and keep it at that temperature for 1~2 hours. Step 7: Place the preheated mold in the casting furnace for melting and casting; Step 8: After cleaning the mold, the titanium alloy casting is obtained.

2. The forming method of a titanium alloy casting with an inlaid thin tube according to claim 1, characterized in that, The pickling solution includes 65% nitric acid, 40% hydrofluoric acid, and water, wherein the volume ratio of nitric acid to hydrofluoric acid is (1.5-2.5):

1.

3. The forming method of a titanium alloy casting with an inlaid thin tube according to claim 1, characterized in that, In step 3, the refractory sand selected is 40-90 mesh fused yttrium oxide sand or zirconium oxide sand.

4. The forming method of a titanium alloy casting with an inlaid thin tube according to claim 1, characterized in that, The plug is made of the same material as the mold.

5. The forming method of a titanium alloy casting with an inlaid thin tube according to claim 4, characterized in that, The mold is made of graphite.

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