A method for preparing a high-surface-quality titanium alloy investment casting shell

Abstract

The present invention provides a method for preparing a high-surface-quality titanium alloy investment casting shell, which relates to the technical field of investment casting and comprises the following steps: S1, wax mold cleaning; the wax mold is sequentially cleaned with a detergent solution and a cleaning solution, and the steps are repeated 1 to 3 times; S2, surface layer slurry preparation; S3, surface layer preparation; S4, back layer preparation. In step S1, the detergent solution comprises detergent, JFC wetting agent, and clean water, wherein the mass fraction of the detergent is 0.1 to 0.3%, and the mass fraction of the JFC wetting agent is 0.03% to 0.15%. The wax mold cleaning and drying method of the present invention increases the coating property of the surface layer slurry, improves the quality of the wax mold and the surface shell; the surface layer slurry of the present invention can increase the surface layer bonding strength, improve the shelling performance, and reduce the surface roughness of the casting; the vacuum slurry impregnation process of the present invention effectively promotes the surface layer slurry to fill the fine shape of the wax mold, eliminates defects in narrow slits, narrow grooves, corners, blind holes, etc., and avoids defects such as casting nodules and slag inclusions in subsequent castings.

Description

Technical Field

[0001] The present invention relates to the technical field of investment precision casting, and in particular to a method for preparing a high-surface-quality titanium alloy investment precision casting shell. Background Art

[0002] Titanium alloys have excellent properties such as low density and high specific strength. Various complex structural castings formed by the investment casting process are widely used in aviation, aerospace, navigation, chemical industry, petroleum, medicine and other fields. Investment casting can meet the requirements of dimensional accuracy while ensuring good casting formability, and is suitable for mass production of complex and nearly zero-allowance castings. The quality of shell making has a significant impact on the surface quality of the casting. The titanium alloy investment casting shell preparation process is to apply several layers of special refractory coating on the surface of the fusible mold. After drying, it forms an integral shell, and then the fusible mold is removed with hot water steam to obtain a cavity. When the casting has a semi-closed structure with narrow slits and narrow grooves, the slurry accumulates in the gaps during the conventional surface shell making process, and the sand particles form bridges, which can easily cause casting defects such as nodules and slag inclusions during pouring. For precision parts with zero allowance, eliminating such defects will result in excessive grinding, resulting in dimensional deviations, which can easily cause batch quality problems in the casting.

[0003] Publication number CN102284678A discloses a method for preparing a precision casting titanium alloy mold shell, the steps of which are as follows: 1) preparing a surface layer; 2) preparing a transition layer; 3) preparing a reinforcement layer; 4) dewaxing and sintering; the wax mold in the prior art is not processed, the surface layer slurry has poor coating properties, the surface quality of the prepared mold shell is poor, and the bonding strength of the surface layer slurry is low, the shelling performance is weak, and the surface roughness of the casting is relatively large. Summary of the Invention

[0004] In light of this, the present invention aims to provide a method for preparing high-surface-quality titanium alloy investment casting shells. This method addresses the existing problems of untreated wax patterns, poor surface slurry coating, and the resulting poor surface quality of the prepared shells. Furthermore, the surface slurry exhibits low bonding strength, weak shelling performance, and significant surface roughness in the castings.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A method for preparing a titanium alloy investment casting shell with high surface quality comprises the following steps:

[0007] S1, wax model cleaning: the wax model is cleaned with detergent solution and cleaning solution in sequence, and the steps are repeated 1 to 3 times;

[0008] S2, preparation of surface slurry;

[0009] S3, surface layer preparation;

[0010] S4. Preparation of back layer.

[0011] The arrangement increases the coating property of the surface slurry and improves the quality of the wax mold and the surface shell by repeatedly cleaning the wax mold with a cleaning agent solution and a cleaning solution during the preparation of the shell.

[0012] Furthermore, in step S1, the cleaning agent solution includes detergent, JFC wetting agent, and clean water, wherein the mass fraction of the detergent is 0.1-0.3%, and the mass fraction of the JFC wetting agent is 0.03%-0.15%.

[0013] Furthermore, in step S1, the cleaning solution is JFC wetting agent and clean water, wherein the mass fraction of the JFC wetting agent is 0.03-0.15%.

[0014] Furthermore, in step S2, the surface layer slurry adopts modified silica sol, and the modified silica sol includes diluted silica sol, PVA solution, and acid-base regulator. The mass ratio of the diluted silica sol to the PVA solution is 15~25:1, the mass fraction of PVA in the PVA solution is 10~20%, the acid-base regulator is NaOH solution and HCl solution, and the pH value of the modified silica sol is 9~10.

[0015] This setting can not only ensure the strength of the surface layer, but also reduce high-temperature interface reactions, reduce pores and pit defects on the casting surface, and improve shelling performance.

[0016] Furthermore, the mass fraction of SiO2 in the diluted silica sol is 15-20%.

[0017] Furthermore, in step S2, the specific steps are: adding yttrium oxide powder to the modified silica sol, wherein the powder-liquid mass ratio is 3.5~5.5:1, and then adding JFC wetting agent, dispersing evenly, and preparing a surface layer slurry with a flow cup viscosity of 6~12s.

[0018] The composition of the surface layer slurry in this setting can increase the surface layer bonding strength, improve the shelling performance, and reduce the surface roughness of the casting.

[0019] Furthermore, the mesh size of the yttrium oxide powder is 200-400 mesh, preferably 325 mesh.

[0020] Furthermore, the total mass ratio of the JFC wetting agent to the modified silica sol and the yttrium oxide powder is 0.03-0.15%.

[0021] Furthermore, in step S2, mechanical stirring is used for uniform dispersion at a rotation speed of 180-250 r / min.

[0022] Furthermore, the specific preparation steps of the diluted silica sol are: using ordinary silica sol, using deionized water as a solvent, diluting the silica content to 15% to 20%, adding a pH adjuster to adjust the pH to 9 to 10, and stirring for about 24 to 48 hours, wherein the pH adjuster is NaOH solution and HCl solution.

[0023] This setting can reduce high-temperature interface reactions, reduce pores and pit defects on the casting surface, and improve shelling performance.

[0024] Furthermore, the specific preparation steps of step S3 are as follows: place the wax mold in a container, pour the surface slurry of step S2 into the container, and submerge the wax mold to a certain height, which is to cover the wax mold. Place the entire container in a vacuum pump, do a good job of sealing, set a certain vacuum degree and start the vacuum equipment. When the wax mold no longer bubbles, end the vacuum treatment, manually release the negative pressure, and the liquid level of the surface slurry drops, completing the vacuum impregnation of the wax mold; then perform surface coating on other parts of the wax mold that have not been impregnated, and the coating can be done by traditional coating methods. Then, sand is sprinkled in a rain-type sanding method, and the surface sand used is one of yttrium oxide sand, zirconium oxide sand, and composite aluminum zirconium sand, with a mesh size of 60 to 120. The surface layer is dried in a constant temperature and humidity workshop, with a drying time of 8 to 12 hours, a temperature of 21 to 25°C, and a humidity not lower than 75%. For complex and fine structures such as slits, narrow grooves, micropores, or mold shells with high surface accuracy requirements, the surface layer vacuum impregnation can be repeated 1 to 2 times after drying.

[0025] This setting effectively promotes the surface slurry to fill the fine shape of the wax mold, eliminates the slurry air holding, air / bean bubble defects in narrow slits, narrow grooves, corners, blind holes, etc., and avoids defects such as casting nodules and slag inclusions in subsequent castings.

[0026] Furthermore, in step S4, a back layer slurry and a back layer sand are used in preparing the back layer, wherein the back layer slurry includes a back layer silica sol and mullite powder, the back layer silica sol is a silica sol with a SiO2 content of 30%, the mullite powder is 200 mesh mullite powder, and the back layer sand is 16~60 mesh mullite sand.

[0027] Furthermore, in step S4, the back layer includes back layer 1, back layer 2, back layer 3, and back multiple layers, and back multiple layers refers to more than three layers;

[0028] The back layer includes back layer slurry and back layer sand. The back layer slurry is made of mullite powder and back layer silica sol in a powder-liquid mass ratio of 1.0-1.5:1. The back layer sand is made of 30-60 mesh mullite sand sprinkled by hand and dried in a constant temperature and humidity workshop for 12-24 hours.

[0029] The back 2 layer includes back 2 layer slurry and back 2 layer sand. The back 2 layer slurry is made of mullite powder and back layer silica sol in a powder-liquid mass ratio of 1.5-2.0:1. The back 2 layer sand is made of hand-spread 16-30 mesh mullite sand and is dried in a constant temperature and humidity workshop for 12-24 hours.

[0030] The back 3 layer includes back 3 layer slurry and back 3 layer sand. The back 3 layer slurry is made of mullite powder and back layer silica sol according to the powder-liquid mass ratio of 2.0~2.2:1. The back 3 layer sand is made of 16~30 mesh mullite sand sprinkled by hand and dried in a constant temperature and humidity workshop for 12~24 hours.

[0031] The back multi-layer includes back multi-layer slurry and back multi-layer sand. The back multi-layer slurry is made of mullite powder and back layer silica sol according to the powder-liquid mass ratio of 2.0~2.2:1. The back multi-layer sand is made of hand-spread 16~30 mesh mullite sand and dried in a constant temperature and humidity workshop for 12~24 hours.

[0032] This setting ensures that the mold shell layers are tightly bonded, not easily delaminated, and fully dried, reducing the risks of pouring, bulging, slag falling or water leakage.

[0033] Preferably, the back layer is prepared as a multilayer with 5 to 9 layers.

[0034] Furthermore, the environment during the preparation of the backing layer is a constant temperature and humidity room with a temperature of 23-27° C. and a humidity of 45-65%.

[0035] Compared with the prior art, the method for preparing a high-surface-quality titanium alloy investment casting shell according to the present invention has the following advantages:

[0036] 1) The wax pattern cleaning and drying method of the present invention increases the coating property of the surface slurry and improves the quality of the wax pattern and the surface shell;

[0037] 2) The surface layer slurry preparation process of the present invention can increase the surface layer bonding strength, improve the shelling performance, and reduce the surface roughness of the casting;

[0038] 3) The vacuum slurry impregnation process of the present invention effectively promotes the filling of the surface slurry into the fine shape of the wax mold, eliminates the slurry holding back air and gas / bean bubble defects in narrow slits, narrow grooves, corners, blind holes, etc., and avoids defects such as casting nodules and slag inclusions in subsequent castings;

[0039] 4) The multi-layer back layer preparation process of the present invention allows the mold shell layers to be tightly bonded, not easily delaminated, and fully dried, thereby reducing the risks of pouring, such as bulging, slag dropping, or water leakage. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below.

[0041] Example 1

[0042] A method for preparing a titanium alloy investment casting shell with high surface quality comprises the following steps:

[0043] S1. Wax mold cleaning

[0044] After patching, repairing, scraping, and dusting, the wax model is qualified. It is then washed by immersing it in a cleaning solution consisting of 0.2% detergent, 0.1% JFC wetting agent, and 0.1% water. After removing any wax debris and oil, it is then rinsed three times in a 0.1% JFC wetting agent-to-water cleaning solution. The cleaned wax model is then air-dried in an environment with a humidity of 65%-75% and a temperature of 23-27°C. The dried wax model is then rinsed a second time in the aforementioned cleaning solution, and again in the same cleaning solution.

[0045] S2. Preparation of surface slurry

[0046] Specifically, the surface layer slurry adopts modified silica sol, and the modified silica sol includes diluted silica sol, PVA solution, and acid-base regulator; the acid-base regulator is NaOH solution and HCl solution, and the pH value of the modified silica sol is 9.

[0047] Specifically, the mass fraction of SiO2 in the diluted silica sol is 17%. The specific preparation steps of the diluted silica sol are: using ordinary silica sol, using deionized water as a solvent, diluting the silicon dioxide content to 17%, adding a pH adjuster to adjust the pH to 9, and stirring for about 36 hours, wherein the pH adjuster is NaOH solution and HCl solution.

[0048] Specifically, the mass ratio of the diluted silica sol to the PVA solution was 20:1, with the mass fraction of PVA in the PVA solution being 15%. The PVA solution consisted of PVA and water. 325-mesh yttrium oxide powder was added to the modified silica sol at a powder-to-liquid ratio of 4:1. JFC wetting agent was also added, with the total mass ratio of JFC wetting agent to modified silica sol and yttrium oxide powder being 0.03%. The mixture was dispersed with a mechanical stirrer at 200 rpm, resulting in a surface slurry with a flow cup viscosity of 8s at room temperature.

[0049] S3. Surface preparation

[0050] Place the wax model in a container and pour the surface slurry into the container, submerging the wax model to a certain height, which should be above the wax model. Place the entire container in a vacuum pump, seal it properly, set a certain vacuum level, and start the vacuum equipment. The vacuum level should be -0.09MPa. When the wax model stops bubbling, end the vacuum treatment. Manually release the negative pressure, and the surface slurry level will drop, completing the vacuum impregnation of the wax model. Then, apply the surface coating to the remaining parts of the wax model that have not been impregnated. Use traditional coating methods. Then, apply sand using a rain-like sanding method. The surface sand used is yttrium oxide sand with a mesh size of 60-120. The surface layer is dried in a constant temperature and humidity workshop for 10 hours at a temperature of 24°C and a humidity not lower than 75%.

[0051] For shells with complex and fine structures such as narrow slits, micropores, or high surface precision requirements, the surface layer can be vacuum impregnated twice after drying.

[0052] S4. Back layer preparation

[0053] The back layer slurry is composed of back layer silica sol and mullite powder, and the back layer sand is mullite sand.

[0054] The back layer silica sol is a silica sol with a SiO2 content of 30%, the mullite powder is 200 mesh mullite powder, and the back layer sand is 16-60 mesh mullite sand.

[0055] The back layer 1 is made of the silica sol and mullite powder with a powder-liquid mass ratio of 1.2:1 to prepare the back layer 1 slurry. The back layer 1 sand is made of 30-60 mesh mullite sand sprinkled by hand and dried in a constant temperature and humidity workshop for 12 hours.

[0056] The back 2 layer is made of the silica sol and mullite powder at a powder-liquid mass ratio of 1.7:1 to prepare the back 2 layer slurry. The back 2 layer sand is made of 16-30 mesh mullite sand sprinkled by hand and dried in a constant temperature and humidity workshop for 12 hours.

[0057] The back 3 layer is made of the silica sol and mullite powder with a powder-liquid mass ratio of 2.1:1 to prepare the back 3 layer slurry. The back 3 layer sand is made of 16-30 mesh mullite sand sprinkled by hand. The sand is dried in a constant temperature and humidity workshop for 12 hours.

[0058] For the back 3 to 5 layers, the silica sol and mullite powder are mixed at a powder-liquid mass ratio of 2.1:1 to prepare the slurry for the back 3 to 5 layers. The sand for the back 3 to 5 layers is manually spread with 16-30 mesh mullite sand. The sand is dried in a constant temperature and humidity workshop for 12 hours.

[0059] The temperature of the constant temperature and humidity room on the back layer is 23~27℃, and the humidity is 45~65%.

[0060] After preparing the backing layer, the mold shell is obtained through dewaxing, roasting, pouring, and shell cleaning. These processes all utilize conventional, existing processes and are not described in detail here. Using this mold shell, precision casting produces complex precision castings with a wall thickness of 0.7 mm. Slender slits and micropores are well-formed, free of casting defects such as titanium beads and slag inclusions.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Example 1 is that the qualified wax pattern is only cleaned in the cleaning solution, and the prepared shell is precision cast to produce a complex precision casting with a wall thickness of 0.7 mm.

[0063] Comparative Example 2

[0064] The difference between this comparative example and Example 1 is that the surface layer prepared with publication number CN102284678A is used to prepare a shell precision casting to produce a complex precision casting with a wall thickness of 0.7 mm.

[0065] Comparative Example 3

[0066] This comparative example differs from Example 1 in that the conventional process steps are as follows: wax pattern making, wax pattern trimming, and wax pattern assembly welding. The surface layer is made using conventional silica sol as the surface layer binder, 325-mesh yttrium oxide powder as the surface layer powder, and 60-80-mesh yttrium oxide sand as the surface layer sand. The coating is performed manually by pouring or dipping the slurry, without vacuum negative pressure dipping technology. The back layer reinforcement involves repeated coating and sanding, without a coordinated matching of the powder-liquid mass ratio, back layer sand, and environmental conditions. The resulting shell was used for precision casting to produce complex precision castings with a wall thickness of 0.7 mm.

[0067] Performance Testing

[0068] The complex precision castings of Example 1 and Comparative Examples 1 to 3 were tested for surface roughness, filling completeness, titanium beads, surface slag, one-time molding pass rate, and surface contamination layer thickness. 288 castings were produced in batches, and the filling completeness, surface slag, titanium beads, and one-time molding pass rate of each casting were tested. Filling completeness / %=number of fully filled pieces n / 288, surface slag / %=number of pieces with surface slag m / 288, similarly, titanium beads / %=number of pieces with titanium beads x / 288, one-time molding pass rate / %=100%-surface slag / %, and surface roughness and surface contamination layer thickness refer to the average corresponding indicators. The test results are shown in Table 1.

[0069] Table 1 Test results of casting related properties of Example 1 and Comparative Examples 1 to 3

[0070]

[0071] It can be seen from Example 1 and Comparative Example 1 in Table 1 that the wax mold of the present invention is cleaned with a cleaning solution and a cleaning solution, which can increase the coating property of the surface slurry and improve the quality of the surface shell. The precision castings obtained after casting the shell have correspondingly improved filling completeness and one-time molding pass rate, and the surface roughness, titanium beads, surface slag, and surface contamination layer thickness all reach a lower level.

[0072] It can be seen from Example 1 and Comparative Example 2 in Table 1 that the surface layer slurry of the present invention is subjected to vacuum treatment to improve the quality of the surface shell. The precision castings obtained after casting the shell have correspondingly improved filling completeness and one-time molding pass rate, and the surface roughness, titanium beads, surface slag, and surface contamination layer thickness all reach a lower level.

[0073] It can be seen from Example 1 and Comparative Example 3 in Table 1 that the traditional process not only has low filling completeness and one-time molding qualification rate, but also has high surface roughness and is not suitable for making precision castings. Compared with the traditional process, the mold shell obtained by the present invention can be used for casting precision castings, and the surface defects of the castings are fewer.

[0074] In summary, the preparation method of the mold shell of the present invention is achieved through the synergistic effect of multiple steps of wax mold cleaning, drying, surface layer slurry preparation, surface layer preparation, back layer preparation and corresponding process parameters. Compared with the traditionally prepared mold shell, the surface smoothness of the mold shell, the completeness of the detailed modeling replication, and the high one-time molding pass rate are significantly improved.

[0075] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A method for preparing a high surface quality titanium alloy investment casting shell, characterized in that: The steps include: S1, wax model cleaning: the wax model is cleaned with detergent solution and cleaning solution in sequence, and the steps are repeated 1 to 3 times; S2, preparation of surface slurry; S3, surface layer preparation; S4, back layer preparation; In step S1, the cleaning solution includes detergent, JFC wetting agent, and clean water, wherein the mass fraction of the detergent is 0.1-0.3%, and the mass fraction of the JFC wetting agent is 0.03%-0.15%; In step S1, the cleaning solution includes JFC wetting agent and clean water, and the mass fraction of JFC wetting agent is 0.03% to 0.15%; In step S4, a back layer slurry and a back layer sand are used for preparing the back layer, wherein the back layer slurry comprises a back layer silica sol and mullite powder, wherein the back layer silica sol is a silica sol with a SiO2 content of 30%, the mullite powder is 200 mesh mullite powder, and the back layer sand is 16-60 mesh mullite sand; In step S4, the back layer includes back layer 1, back layer 2, back layer 3, and back multi-layers, and back multi-layers refer to more than three layers; The back layer is specifically as follows: The back layer includes back layer slurry and back layer sand. The back layer slurry is made of mullite powder and back layer silica sol in a powder-liquid mass ratio of 1.0-1.5:

1. The back layer sand is made of 30-60 mesh mullite sand sprinkled by hand and dried in a constant temperature and humidity workshop for 12-24 hours. The back 2 layer includes back 2 layer slurry and back 2 layer sand. The back 2 layer slurry is made of mullite powder and back layer silica sol in a powder-liquid mass ratio of 1.5-2.0:

1. The back 2 layer sand is made of hand-spread 16-30 mesh mullite sand and is dried in a constant temperature and humidity workshop for 12-24 hours. The back 3 layer includes back 3 layer slurry and back 3 layer sand. The back 3 layer slurry is made of mullite powder and back layer silica sol according to the powder-liquid mass ratio of 2.0~2.2:

1. The back 3 layer sand is made of 16~30 mesh mullite sand sprinkled by hand and dried in a constant temperature and humidity workshop for 12~24 hours. The back multi-layer includes back multi-layer slurry and back multi-layer sand. The back multi-layer slurry is prepared with mullite powder and back layer silica sol according to the powder-liquid mass ratio of 2.0~2.2:

1. The back multi-layer sand is manually sprinkled with 16~30 mesh mullite sand and dried in a constant temperature and humidity workshop for 12~24 hours; the environment during the preparation of the back layer is a constant temperature and humidity room with a temperature of 23~27℃ and a humidity of 45~65%.

2. The preparation method according to claim 1, characterized in that In step S2, the surface layer slurry adopts modified silica sol, and the modified silica sol includes diluted silica sol, PVA solution, and acid-base regulator. The mass ratio of the diluted silica sol to the PVA solution is 15~25:1, the mass fraction of PVA in the PVA solution is 10~20%, the acid-base regulator is NaOH solution and HCl solution, and the pH value of the modified silica sol is 9~10.

3. The preparation method according to claim 2, characterized in that The mass fraction of SiO2 in the diluted silica sol is 15-20%.

4. The preparation method according to claim 2, characterized in that In step S2, the specific steps are: adding yttrium oxide powder to the modified silica sol, wherein the powder-liquid mass ratio is 3.5~5.5:1, and then adding JFC wetting agent, dispersing evenly, and preparing a surface layer slurry with a flow cup viscosity of 6~12s.

5. The preparation method according to claim 4, characterized in that The mesh size of yttrium oxide powder is 200~400 mesh.

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