CN1255233C - Preparing method of low-cost oxide ceramic shell for titanium alloy precision casting - Google Patents

Abstract

The invention discloses a method for preparing an oxide ceramic mold shell for titanium alloy precision casting, which relates to a preparation process for an oxide ceramic mold shell for titanium alloy casting. After the coating of the present invention is prepared, the wax pattern of the casting is immersed in the coating for 10 to 20 minutes and taken out. When the remaining coating on the wax pattern flows evenly and no longer drips continuously, the freezing begins, and sand can be sprinkled. The graded electric fused white corundum powder is evenly sprinkled on the wax pattern coated with the coating, and the dried wax pattern coated with the surface coating is put into a high-pressure dewaxing kettle for high-pressure steam dewaxing. The invention has the following advantages: 1. Compared with the traditional ZrO ₂ , Y ₂ O ₃ and zirconium sol, the price of the surface layer binder material and shell material used is low, and the source is wide. 2. The shell is an oxide composite ceramic shell, the shell making process is simple, and the shell strength is high. 3. The material and the shell-making process can produce high-surface-quality, thin-walled complex heat-resistant titanium alloy castings.

Description

Preparation method of oxide ceramic shell for precision casting of titanium alloy

technical field

The invention relates to a preparation process of an oxide ceramic mold shell used for investment precision casting of titanium alloy.

Background technique

With the development of science and technology, the application of titanium alloys is becoming more and more extensive. From rockets and aircraft in the aerospace industry to artificial joints in the medical field, as well as in navigation, chemical industry, sports, etc., titanium alloys are famous for their excellent properties. Popular for performance. It has the characteristics of high specific strength, high specific stiffness, good corrosion resistance, and strong heat resistance, making titanium alloy one of the most promising modern structural materials. However, titanium is a very active metal element, especially at high temperature, it is easy to chemically react with other elements. The molten titanium liquid has chemical reactions with almost all refractory materials to varying degrees, which makes the casting of titanium alloys must use special molding materials and binders with high chemical stability, so as to prevent the high-temperature titanium liquid from chemically reacting with it, thereby reducing or even eliminating A contamination layer is formed on the surface of the titanium casting. The titanium alloy investment casting process is especially suitable for complex components that are mass-produced, have no machining allowance and are difficult to machine. Compared with the machining process, the production cost can be greatly reduced and the manufacturing period can be shortened. Among its various processes, the preparation process of the molten mold shell is the biggest difficulty. At present, the commonly used refractory materials for shell surfaces can be roughly divided into graphite powder, inert oxide ceramic powder (such as ZrO ₂ , Y ₂ O ₃ , etc.) and metal tungsten powder. The relatively mature graphite type (including tamped graphite type and machine-added graphite type) and the metal tungsten surface layer forming process have the disadvantages of fast heat conduction of the casting mold and defects such as cold shuts on the surface of the casting. Among them, the castings produced by the graphite type not only have a 0.1-0.15mm α pollution layer, but also have a large shrinkage rate, so they are only suitable for the production of small and medium-sized castings; the tungsten surface ceramic shell, due to its good thermal conductivity, It is difficult to cast thin castings with small wall thickness. Its process is complicated and the cost of raw materials is high, which affects the sales competitiveness of titanium alloy precision castings, and its roasting process requires a special furnace. Using the thorium oxide shell process, various large and complex titanium precision castings can be produced, but there is a problem of shell radioactivity. The shell made of fused yttrium oxide and zirconia can be used to cast thin-walled titanium castings. However, due to the high cost, it has not been widely used in production. The binder is a very critical link in the titanium alloy investment casting process, and the performance of the shell is closely related to the properties of the binder. Zirconium sol, zirconium diacetate and organic compounds of zirconium are commonly used binders in investment casting of titanium alloys. The product of this type of binder after roasting is ZrO ₂ , which is equivalent to ZrO ₂ refractory material, but there are still some problems in the strength of the mold shell, dewaxing and reaction with liquid titanium. Because ZrO ₂ , Y ₂ O ₃ and other surface layer materials and raw materials such as yttrium sol, zirconium sol, zirconium diacetate and zirconium organic compounds are expensive, the production cost of titanium alloy is too high, which affects the large scale of investment casting of titanium alloy. Mass production and popularization and application of the process.

Contents of the invention

The object of the present invention is to provide a method for preparing an oxide ceramic mold shell for titanium alloy precision casting, which has the characteristics of low raw material price, wide sources, simple shell making process and high mold shell strength. The method of the present invention is realized according to the following steps: 1. The preparation of the surface coating: add corundum powder with particle size distribution in the binder, stir while adding, and still stir for 1 hour after all the corundum powder is added, The viscosity of the paint is controlled at 80-100s (Tu-4 viscometer); 2. Preparation of the shell: After the paint is prepared, immerse the wax pattern of the casting in the paint for 10-20 minutes and take it out. When the remaining paint on the wax pattern flows When it is uniform and no longer drips continuously, the freezing starts, and sand can be sprinkled. Sprinkle the fused white corundum powder that has undergone particle size grading evenly on the wax pattern coated with paint. The sanding should be even and comprehensive, and then On this basis, paint and sand, and after each layer of paint and sand, it must be fully dried and hardened; 3. Dewaxing of the shell: put the dried wax mold coated with the surface coating Put it into a high-pressure dewaxing kettle for high-pressure steam dewaxing; 4. Put the dewaxed shell into a resistance roasting furnace for roasting, and then cool it to room temperature with the furnace. In the step 1, the particle size of the finely graded corundum powder is 200 to 300 mesh, the particle size of the fine powder is <300 mesh, the weight ratio of the coarse powder to the fine powder is 3:1.5 to 3:2.5, and the powder of the coating The liquid ratio is 2.5:1～4:1 (the weight unit of the powder is kg, and the volume unit of the binder: L); The particle size of fused white corundum powder is 100-200 mesh, and the binder used in the coating is _SiO2- based binder. The powder used for coating and sanding after the third layer is mullite, and the particle size is 20-200 mesh. The binder used in the coating is SiO ₂ series sol; the number of layers of coating, hanging and sanding is 8-10; the drying in the second step is carried out twice, first at room temperature, with a humidity of 50% and good ventilation placed in an environment of 16 to 24 hours to dry naturally, and then placed in an ammonia drying oven for 1 to 3 hours to force dry; the pressure of high-pressure steam dewaxing in step 3 is 0.4 to 0.6Mpa, and the dewaxing time is 8 to 16 minutes; the calcination in the step 4 starts from 500° C. and heats up to 1200° C. and then maintains the temperature for 2 hours. The molded shell prepared by the present invention has been subjected to a centrifugal pouring experiment in a water-cooled copper crucible vacuum induction smelting furnace. Under the condition that the centrifugal speed is 300-400 rpm and the molded shell preheating temperature is 200-400 degrees Celsius, the molded shell can withstand 1700 degrees Celsius. The filling of titanium liquid has successfully poured out a certain type of engine inlet casting, which meets the requirements of titanium alloy investment precision casting technology. The invention has the following advantages: 1. Compared with traditional ZrO ₂ , Y ₂ O ₃ and zirconium sol, the price of the surface layer binder material and shell material used is low, and the source is wide, which is beneficial to practical application. 2. The shell is an oxide composite ceramic shell, the shell making process is simple, and the shell strength is high. 3. The material and the shell making process can produce high surface quality, thin-walled complex heat-resistant titanium alloy castings, the surface roughness Ra is below 3.2 μm, and the thickness of the surface contamination layer is less than 100 μm.

Detailed ways

The steps of this embodiment are as follows: 1. Preparation of the surface coating: add corundum powder with a finely graded particle size into the binder, stir while adding, and stir for 1 hour after adding all the corundum powder. The viscosity of the paint is controlled at 80-100s (Tu-4 viscometer); 2. Preparation of the shell: After the paint is prepared, immerse the wax pattern of the casting in the paint for 10-20 minutes and take it out. When the remaining paint on the wax pattern flows When it is uniform and no longer drips continuously, the freezing starts, and the sand can be sprinkled. The fused white corundum powder that has undergone particle size grading is evenly sprinkled on the wax pattern coated with paint. The sanding should be even and comprehensive. Then paint and sand on this basis. After each layer of paint and sand, it must be fully dried and hardened; 3. Dewaxing of the shell: put the dried wax mold coated with surface coating Put it into a high-pressure dewaxing kettle for high-pressure steam dewaxing; 4. Put the dewaxed shell into a resistance roasting furnace for roasting, and then cool it to room temperature with the furnace. In the step 1, the particle size of the finely graded corundum powder is 200-300 mesh, the particle size of the fine powder is <300 mesh, the ratio of coarse powder to fine powder is 3:1.5-3:2.5, and the powder liquid of the coating The ratio is 2.5:1～4:1 (the weight unit of powder is kg, the volume unit of binder is L); The particle size of fused white corundum powder is 100-200 mesh, the binder used in the coating is SiO ₂ series binder, the powder used for coating and sanding after the third layer is mullite, the particle size is 20-200 mesh, The binder used is SiO ₂ series sol; the number of layers of coating, hanging and sanding is 8-10 layers; the drying in the second step is carried out twice, first at room temperature, with a humidity of 50%, and in a well-ventilated environment. Place it in the environment for 16-24 hours to dry naturally, and then place it in an ammonia drying oven for 1-3 hours to force dry; the pressure of high-pressure steam dewaxing in step 3 is 0.4-0.6Mpa, and the dewaxing time is 8-16 Minutes; the roasting in the step 4 starts from 500°C and heats up to 1200°C and keeps the temperature for 2 hours.

Claims (6)

1. The preparation method of the oxide ceramic mold shell for titanium alloy precision casting is characterized in that it is realized according to the following steps: 1. The preparation of the surface coating: adding the corundum with particle size distribution in the binder powder, stir while adding, and stir for 1 hour after all the corundum powder is added, the viscosity of the paint is controlled at 80-100s; 2. Preparation of the mold shell: After the paint is prepared, immerse the wax pattern of the casting in the paint for 10-20 seconds Take it out in minutes, when the remaining paint on the wax pattern flows evenly and no longer drips continuously, the freezing begins, and then sand can be sprinkled, and the fused white corundum powder that has undergone particle size grading is evenly sprinkled on the wax coated with paint. On the mold, the sanding should be even and comprehensive, and then coat and sand on this basis. After each layer of coating and sanding, it must be fully dried and hardened; 3. Dewaxing of the shell: dry Put the wax mold coated with the surface coating into a high-pressure dewaxing kettle for high-pressure steam dewaxing; 4. Put the dewaxed shell into a resistance roasting furnace for roasting, and then cool it to room temperature with the furnace . 2. The method for preparing an oxide ceramic mold shell for titanium alloy precision casting according to claim 1, characterized in that the particle size of the finely graded corundum powder in the step 1 is 200-300 mesh, The particle size of fine powder is less than 300 mesh, the weight ratio of coarse powder to fine powder is 3:1.5～3:2.5, and the powder-liquid weight-volume ratio of coating is 2.5kg:1L～4kg:1L. 3. The method for preparing an oxide ceramic mold shell for titanium alloy precision casting according to claim 1, characterized in that the electric particle size distribution used for the first and second layers of coating and sanding in said step 2 is: The particle size of fused white corundum powder is 100-200 mesh, the binder used in the coating is SiO ₂ series binder, the powder used for coating and sanding after the third layer is mullite, the particle size is 20-200 mesh, The binder used is SiO ₂ series sol; the number of layers of coating, hanging and sanding is 8-10 layers. 4. The method for preparing an oxide ceramic mold shell for titanium alloy precision casting according to claim 1, characterized in that the drying in said step 2 is carried out twice, first at room temperature with a humidity of 50 %, placed in a well-ventilated environment for 16 to 24 hours to dry naturally, and then placed in an ammonia drying oven for 1 to 3 hours to force dry. 5. The method for preparing oxide ceramic shells for titanium alloy precision casting according to claim 1, characterized in that the pressure of high-pressure steam dewaxing in the third step is 0.4-0.6Mpa, and the dewaxing time is 8 ~16 minutes. 6. The method for preparing an oxide ceramic mold shell for titanium alloy precision casting according to claim 1, characterized in that the calcination in step 4 starts from 500°C, and the temperature is kept at 2 Hour.