A method for preparing a zirconium acetate surface layer shell for precision investment casting of titanium alloys

Abstract

The application provides a zirconium acetate surface layer shell preparation method for titanium alloy investment precision casting, and comprises the following steps: S1, taking zirconium acetate binder and anti-resolvent, adding adhesion aid and deionized water under stirring, and stirring uniformly to obtain a surface layer binder; S2, mixing the surface layer binder with surface layer refractory powder, adding a wetting agent, and uniformly dispersing the material to obtain a surface layer coating; S3, defoaming the surface layer coating under vacuum negative pressure; S4, under vacuum negative pressure, uniformly dipping a wax mold in the surface layer coating, maintaining pressure for 60-300s, then performing sand spraying and drying on the dipped wax mold to obtain a surface layer shell; S5, opening the wax removal hole of the surface layer shell, and performing staged hot steam dewaxing; and S6, baking the dewaxed surface layer shell to obtain a shell. The application can effectively inhibit resolvent of the zirconium sol surface layer, improve the surface layer compactness, and obviously improve the resolvent, peeling and falling of the zirconium gel surface layer shell process in titanium alloy investment precision casting.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of investment precision casting, in particular to a preparation method of a zirconium acetate surface layer shell for titanium alloy investment precision casting. BACKGROUND

[0002] Titanium alloy can be used as an important material for high-end equipment manufacturing structural parts due to small density, high specific strength, corrosion resistance, and non-magneticity. Due to the physical and chemical and metallurgical characteristics of titanium, the forming method and molding material of titanium alloy structural parts are special. For example, titanium alloy has high activity and is easy to oxidize, and is easy to chemically react with the shell material in a molten state, so that an oxygen-rich alpha brittle layer is formed on the surface of the casting, affecting the mechanical properties.

[0003] The prior art often uses zirconium sol (zirconium acetate) as a surface layer binder, but the applicant finds in actual production and manufacturing that the prepared shell is prone to have general high-temperature thermal stability, the surface layer is prone to be dissolved back, and peeling or even falling off occurs, which on the one hand causes the solvent to penetrate after the slurry is coated, resulting in softening and sponging of the surface layer coating, and on the other hand causes poor compactness of the coating, and it is difficult to meet the demand of the surface layer strength of complex structural castings. SUMMARY

[0004] Therefore, the application aims to provide a preparation method of a zirconium acetate surface layer shell for titanium alloy investment precision casting to solve the problems that the prepared shell has a surface layer prone to be dissolved back, peeling or even falling off.

[0005] To achieve the above-mentioned purposes, the technical scheme of the application is as follows:

[0006] A preparation method of a zirconium acetate surface layer shell for titanium alloy investment precision casting, comprising the following steps: S1, taking zirconium acetate binder and anti-dissolution inhibitor, adding adhesion aid and deionized water under stirring conditions, stirring uniformly to obtain a surface layer binder; S2, mixing the surface layer binder with surface layer refractory powder, adding a wetting agent after first-stage stirring for 40-60 min, and second-stage stirring to uniformly disperse the material to obtain a surface layer coating; S3, vacuum negative pressure defoaming the surface layer coating; S4, uniformly dipping the wax mold in the pretreated surface layer coating under vacuum negative pressure, and after pressure maintaining for 60-300 s, sequentially performing sand spraying and drying on the dipped wax mold to obtain a surface layer shell; S5, opening the wax removal hole of the surface layer shell and performing staged hot steam dewaxing; the staged hot steam dewaxing comprises a first-stage high-temperature high-pressure rapid dewaxing process and a second-stage low-temperature low-pressure slow dewaxing process; and S6, baking the dewaxed surface layer shell to obtain a shell for pouring.

[0007] Further, in step S1, the surface layer binder comprises zirconium acetate binder 35-75 parts by weight, anti-resolvent inhibitor 25-45 parts by weight, 1-3% mass concentration of adhesion promoter aqueous solution 1-5 parts, deionized water 1-15 parts; the anti-resolvent inhibitor is a rare earth salt substance.

[0008] Further, the rare earth salt substance comprises at least one of yttrium nitrate and yttrium carbonate.

[0009] Further, the adhesion promoter comprises polyvinyl alcohol.

[0010] Further, in step S2, the weight ratio of the surface layer binder to the surface layer refractory powder is 1.5-3.5:1, the wetting agent is JFC wetting agent, and the addition amount of the JFC wetting agent accounts for 0.03-0.15% of the total weight of the surface layer coating.

[0011] Further, in step S2, during the second-stage stirring process, when the flow cup viscosity of the material at room temperature is 18-25 s, the material is uniformly dispersed.

[0012] Further, in step S3, the vacuum negative pressure defoaming process is to maintain the pressure for 30-120 s under a vacuum degree of-0.06 to-0.08 MPa.

[0013] Further, in step S4, the vacuum degree of the vacuum negative pressure state is-0.08 to-0.1 MPa.

[0014] Further, in step S4, the surface layer sand material for sanding comprises at least one of yttrium oxide sand, zirconium oxide sand and composite aluminum zirconium sand, and the mesh size is 60-120 mesh.

[0015] Further, in step S5, the high-temperature high-pressure rapid dewaxing process is to dewax at a temperature of 165-175 DEG C and a pressure of 0.65-0.75 MPa for 2-3 minutes; and the low-temperature low-pressure slow dewaxing process is to dewax at a temperature of 95-105 DEG C and a pressure of 0.25-0.35 MPa for 10-15 minutes.

[0016] Compared with the prior art, the preparation method of the zirconium acetate surface layer shell for titanium alloy investment precision casting has the following advantages:

[0017] Compared with the existing preparation process of the zirconium acetate surface layer shell, the preparation method of the zirconium acetate surface layer shell for titanium alloy investment precision casting can effectively inhibit the resolvent of the zirconium sol surface layer, improve the surface layer density, and obviously improve the resolvent, peeling and falling of the zirconium sol surface layer shell process in the titanium alloy investment precision casting. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the application illustrated in the drawings are presented to aid in the understanding of the present application and are not intended to limit the application in its application to such specific embodiments.

[0019] Figure 1 A physical photo of the shell prepared for Comparative Example 1;

[0020] Figure 2 A physical photo of the shell prepared by a zirconium acetate surface layer shell preparation method for titanium alloy investment precision casting according to the embodiment of the application (Example 1). DETAILED DESCRIPTION

[0021] The detailed description set forth below in connection with the appended drawings describes exemplary aspects of the application and is not intended to represent the only embodiments or compositions in which the application might be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the application. However, it will be apparent to those skilled in the art that the application can be practiced without these specific details.

[0022] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0023] The application will be described in greater detail with reference to the drawings, in which:

[0024] In order to solve the problems of the shell prepared by the prior art, such as easy dissolution, peeling and even falling off of the surface layer, the present application provides a zirconium acetate surface layer shell preparation method for titanium alloy investment precision casting, which comprises the following steps:

[0025] S1, preparation of a surface layer binder: taking zirconium acetate binder and anti-dissolution inhibitor, adding adhesion aid and deionized water under stirring, and stirring uniformly to obtain the surface layer binder; wherein the anti-dissolution inhibitor is a rare earth salt substance;

[0026] Preferably, the rare earth salt substance comprises at least one of yttrium nitrate and yttrium carbonate, and the adhesion aid comprises polyvinyl alcohol.

[0027] Thus, compared with the prior art of using zirconium acetate alone as a surface layer binder, the application can form yttrium-zirconium solid solution with the addition of yttrium nitrate and yttrium carbonate as anti-resolvent inhibitors, which can effectively improve the high-temperature thermal stability and reduce the concentration of acetate, thereby improving the anti-resolvent resistance of conventional zirconium sol, and improving the stability and durability of the colloid. Meanwhile, the addition of polyvinyl alcohol as an adhesion promoter is beneficial to the film formation of the coating, improves the surface layer density, and further improves the anti-resolvent resistance.

[0028] The stirring speed in step S1 is 50-100 r / min, and the stirring time is 20-60 min.

[0029] S2, preparation of the surface layer coating: the surface layer binder is mixed with the surface layer refractory powder, and after first-stage stirring for 40-60 min, JFC wetting agent is added for second-stage stirring, and the material is uniformly dispersed to obtain the surface layer coating;

[0030] The weight ratio of the surface layer binder to the surface layer refractory powder is 1.5-3.5:1, and the addition amount of the JFC wetting agent accounts for 0.03-0.15% of the total weight of the surface layer coating.

[0031] The surface layer refractory powder comprises yttrium oxide powder, and the yttrium oxide powder is preferably 325# yttrium oxide ceramic powder; the stirring speed of the first-stage stirring and the second-stage stirring is both 50-100 r / min; during the second-stage stirring, when the flow cup viscosity of the material at room temperature is 18-25 s, the material is uniformly dispersed, so that the uniformity of the material dispersion can be accurately determined without being affected by the difference in the specific component ratio, thereby improving the production efficiency.

[0032] S3, surface layer coating pretreatment: vacuum negative pressure defoaming is performed on the surface layer coating;

[0033] The vacuum negative pressure defoaming can be performed by placing a container containing the surface layer slurry into a conventional vacuum negative pressure sealing device. The process of the vacuum negative pressure defoaming is to maintain the pressure for 30-120 s under a vacuum degree of -0.06 to -0.08 MPa.

[0034] S4, surface layer shell preparation: the wax mold is uniformly immersed in the pretreated surface layer coating under a vacuum negative pressure state, and after pressure maintaining for 60-300 s, the immersed wax mold is sequentially subjected to sand spraying and drying to obtain the surface layer shell.

[0035] The vacuum degree of the vacuum negative pressure state is -0.08 to -0.1 MPa, and after pressure maintaining for 60-300 s, the vacuum negative pressure immersion of the wax piece can be completed, further removing the small bubbles in the slurry and balancing the viscosity of the slurry.

[0036] Therefore, the surface layer shell is prepared by the two-stage vacuum treatment process of vacuum negative pressure defoaming (pretreatment) of the surface layer coating in step S3 and vacuum negative pressure state impregnation in step S4, which can effectively remove the micro-bubbles in the slurry, prevent the micro-bubbles from entering the coating (i.e. the surface layer shell), help to further improve the surface layer density, and ensure the mechanical properties of the final shell.

[0037] In addition, in step S4, for individual special cases where the wax mold cannot be impregnated by the slurry, the corresponding part can be coated by the conventional coating method. The sand can be sprayed on the impregnated wax mold by the rain shower type sand spraying method. The surface layer sand for the sand spraying includes at least one of yttria sand, zirconia sand and composite aluminum zirconium sand, and the mesh size is 60-120 mesh. The drying process is carried out in a constant temperature and humidity workshop, the drying time is 8-12 hours, the temperature is 23±2℃, and the relative humidity is 45-65%.

[0038] S5, shell dewaxing: opening the wax discharge hole of the surface layer shell, and performing phased hot steam dewaxing; the phased hot steam dewaxing includes a first-stage high-temperature high-pressure rapid dewaxing process and a second-stage low-temperature low-pressure slow dewaxing process.

[0039] The wax discharge hole can be opened by a file, and the mold shell main runner is placed downward on the dewaxing car and pushed into the dewaxing kettle for the phased hot steam dewaxing.

[0040] Specifically, the high-temperature high-pressure rapid dewaxing process is: the dewaxing temperature is 165-175℃, the pressure is 0.65-0.75MPa, and the time is 2-3 minutes, so as to realize rapid softening of the wax mold and reduce the output of high-temperature high-pressure steam, avoiding the impact of high-temperature high-pressure steam on the surface layer.

[0041] The low-temperature low-pressure slow dewaxing process is: the dewaxing temperature is 95-105℃, the pressure is 0.25-0.35MPa, and the time is 10-15 minutes, so as to weaken the impact of the hot steam and uniformly and gently exhaust.

[0042] Compared with the existing conventional hot steam dewaxing process (dewaxing temperature 165-175℃, pressure 0.65-0.75MPa, dewaxing time 7-15min, and only one hot steam dewaxing is performed), the present application forms a gradient dewaxing process of "temperature and pressure gradient reduction and dewaxing time gradient increase" through staged hot steam dewaxing, after ensuring the rapid softening of the wax mold, the output of a large amount of high-temperature and high-pressure hot steam is avoided as much as possible, and then the hot steam can be output and exhausted more gently at a lower dewaxing temperature and pressure, so as to avoid the hot steam impact causing the surface layer to dissolve back and fall off or the surface layer to crack. That is, through the staged hot steam dewaxing, not only the normal dewaxing can be ensured, but also the instantaneous output amount, impact strength and impact time of the high-temperature and high-pressure hot steam are effectively reduced, and the surface layer dissolution back and fall off and the surface layer cracking of the mold shell after dewaxing in the prior art can be significantly improved.

[0043] In addition, after dewaxing, the surrounding of the dewaxing hole of the mold shell and the small sprue part can be reinforced by mortar, and the mold is dried for not less than 12 hours under the fan. Since the existing technology can be used, no further description is given.

[0044] S6, mold shell baking: baking the surface layer mold shell after dewaxing, and obtaining the mold shell for pouring after baking. The process of baking is that the surface layer mold shell is heated to 1000-1100℃ and then is kept for 3-6h.

[0045] The mold shell prepared by the method can be used for pouring and cleaning to obtain a titanium alloy casting blank. Since the pouring and cleaning processes can refer to the existing technology, no further description is given.

[0046] Example 1

[0047] The zirconium acetate surface layer mold shell for precision investment casting of titanium alloy prepared by the method is used for mold shell preparation, and the specific process is as follows:

[0048] S1, preparation of surface layer binder: zirconium acetate binder, anti-dissolution inhibitor, adhesion aid, deionized water are added under stirring conditions, and the surface layer binder is obtained after stirring uniformly; wherein the anti-dissolution inhibitor is a rare earth salt substance; wherein the surface layer binder includes 55 parts of zirconium acetate binder, 35 parts of anti-dissolution inhibitor, 3 parts of 2% mass concentration adhesion aid aqueous solution, and 8 parts of deionized water; preferably, the rare earth salt substance is yttrium carbonate, and the adhesion aid is polyvinyl alcohol;

[0049] S2, preparation of the surface layer coating: the surface layer binder is mixed with the surface layer refractory powder, after first stage stirring for 50 min, JFC wetting agent is added, and second stage stirring is performed, and the material is uniformly dispersed to obtain the surface layer coating; wherein the weight ratio of the surface layer binder to the surface layer refractory powder is 2.5:1, and the addition amount of the JFC wetting agent accounts for 0.10% of the total weight of the surface layer coating;

[0050] S3, surface layer coating pretreatment: vacuum negative pressure defoaming is performed on the surface layer coating; wherein the process of vacuum negative pressure defoaming is to keep the pressure in the range of -0.06~-0.08 MPa for 80 s;

[0051] S4, surface layer shell preparation: the wax mold is uniformly dipped in the pretreated surface layer coating in a vacuum negative pressure state, and after pressure keeping for 200 s, the dipped wax mold is sequentially subjected to sand spraying and drying to obtain the surface layer shell; wherein the vacuum degree of the vacuum negative pressure state is kept in the range of -0.08~-0.1 MPa, the surface layer sand used for sand spraying is zirconia sand with a mesh size in the range of 60~120 meshes. The drying process is carried out in a constant temperature and humidity workshop, the drying time is 10 hours, the temperature is kept in the range of 23±2℃, and the relative humidity is kept in the range of 45~65%;

[0052] S5, shell dewaxing: the dewaxing hole of the surface layer shell is opened, and phased hot steam dewaxing is performed; the phased hot steam dewaxing includes a first stage high-temperature high-pressure rapid dewaxing process and a second stage low-temperature low-pressure slow dewaxing process; wherein the high-temperature high-pressure rapid dewaxing process is: dewaxing temperature 173℃, pressure 0.7 MPa, dewaxing time 2 min; the low-temperature low-pressure slow dewaxing process is: dewaxing temperature 102℃, pressure 0.3 MPa, dewaxing time 14 min;

[0053] S6, shell baking: the dewaxed surface layer shell is baked, and the shell for pouring is obtained after baking. wherein the process of baking is: the surface layer shell is heated to 1000℃~1100℃ and kept for 5h.

[0054] The shell prepared in Example 1 is photographed, as shown in the accompanying Figure 2 figure.

[0055] Comparative Example 1

[0056] Most of the preparation contents of Comparative Example 1 are the same as those of Example 1. The difference between the two is:

[0057] The step S3 of the example 1 is not performed for the comparative example 1; during the preparation of the face layer shell in the step S4, the wax mold is immersed in the face layer coating obtained in the step S2 under the normal temperature and pressure in the normal environment, and the uniform impregnation is performed. That is, compared with the steps S3 and S4 of the example 1, the comparative example 1 does not perform any vacuum negative pressure operation.

[0058] In addition, the shell dewaxing process of the comparative example 1 adopts the existing conventional hot steam dewaxing process, that is, only one hot steam dewaxing process is performed, wherein the dewaxing temperature is 173 DEG C, the pressure is 0.7 MPa, and the dewaxing time is 13 minutes.

[0059] On this basis, the remaining preparation operations of the comparative example 1 are consistent with those of the example 1.

[0060] The shell prepared in the comparative example 1 is photographed, as shown in the accompanying drawings. Figure 1

[0061] The shell prepared in the present application and the shell prepared in the prior art are observed and compared, the face layer resolubility of the shell prepared in the present application is less than 5%, and the shell surface is free of peeling and falling off; the face layer resolubility of the shell prepared in the prior art is greater than 20%, and the shell surface has peeling and falling off, which can be referred to the accompanying drawings of the present application. Figure 1 2

[0062] In summary, the present application proposes a preparation method of a zirconium acetate face layer shell for titanium alloy investment precision casting. Compared with the existing preparation process of the zirconium acetate face layer shell, the present application can effectively inhibit the resolubility of the zirconium sol face layer, improve the denseness of the face layer, and obviously improve the resolubility, peeling and falling off of the zirconium sol face layer shell process in the titanium alloy investment precision casting by optimizing the formulation of the zirconium sol face layer, the high-temperature hot steam dewaxing technology and the calcination process.

[0063] Compared with the prior art in which only zirconium acetate is used as the face layer binder, the present application can form a yttrium-zirconium solid solution with the zirconium acetate by optimizing the formulation of the face layer binder and adding rare earth salt substances as the anti-resolubility inhibitor, especially the addition of yttrium nitrate and yttrium carbonate, which can effectively improve the high-temperature stability on the one hand and reduce the concentration of acetate on the other hand, improve the anti-resolubility of the conventional zirconium sol, and improve the stability and durability of the colloid. At the same time, the addition of polyvinyl alcohol as the adhesion promoter is beneficial to the film formation of the coating, improves the denseness of the face layer, and further improves the anti-resolubility.

[0064] ​​​The present application can effectively remove the tiny bubbles in the slurry, prevent the tiny bubbles from entering the coating (i.e. the surface layer shell), help to further improve the surface layer density, and ensure the mechanical properties of the final shell.

[0065] Meanwhile, compared with the conventional single hot steam dewaxing process, the present application forms a gradient dewaxing process of "temperature and pressure gradient reduction and dewaxing time length gradient increase" through staged hot steam dewaxing. After ensuring the rapid softening of the wax mold, the output of a large amount of high-temperature and high-pressure hot steam is avoided as much as possible, and then the hot steam can be output and exhausted more gently at a lower dewaxing temperature and pressure, so as to avoid the face layer from being dissolved and falling off or the face layer from being cracked due to the impact of the hot steam. That is, through the staged hot steam dewaxing, the present application not only can ensure the normal dewaxing, but also effectively reduces the instantaneous output amount, impact strength and impact time of the high-temperature and high-pressure hot steam, and can significantly improve the situation of the face layer being dissolved and falling off or the face layer being cracked after the shell is dewaxed in the prior art.

[0066] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing a zirconium acetate face coat shell for precision investment casting of a titanium alloy, characterized by, The method comprises: S1, taking zirconium acetate binder, anti-resolution inhibitor, adding adhesion promoter, deionized water under stirring condition, stirring uniformly to obtain surface layer binder; S2, mixing the surface layer binder with surface layer refractory powder, after first stage stirring for 40-60 min, adding wetting agent, second stage stirring, material dispersion uniformity to obtain surface layer coating; S3, vacuum negative pressure defoaming for the surface layer coating; S4, under vacuum negative pressure condition, uniformly dipping wax mold in pretreated surface layer coating, pressure maintaining for 60-300 s, then sequentially performing sand spraying and drying for the dipped wax mold to obtain surface layer shell; S5, opening the wax removal hole of the surface layer shell, and performing staged hot steam dewaxing; the staged hot steam dewaxing comprises high-temperature high-pressure rapid dewaxing process in the first stage and low-temperature low-pressure slow dewaxing process in the second stage; S6, baking the dewaxed surface layer shell to obtain a shell for pouring; The anti-resolution inhibitor is a rare earth salt, and the rare earth salt comprises at least one of yttrium nitrate and yttrium carbonate; in step S5, the high-temperature high-pressure rapid dewaxing process is that the dewaxing temperature is 165-175 DEG C, the pressure is 0.65-0.75 MPa, and the time is 2-3 min; the low-temperature low-pressure slow dewaxing process is that the dewaxing temperature is 95-105 DEG C, the pressure is 0.25-0.35 MPa, and the time is 10-15 min.

2. A method for preparing a zirconium acetate face coat shell for precision investment casting of titanium alloys according to claim 1, characterized in that, In step S1, the surface layer binder comprises zirconium acetate binder 35-75 parts, anti-resolution inhibitor 25-45 parts, 1-3% mass concentration adhesion promoter aqueous solution 1-5 parts, and deionized water 1-15 parts by weight.

3. The method of claim 2, wherein the zirconium acetate face coat is prepared by mixing 0.5 to 1.5 parts by weight of zirconium acetate, 0.5 to 1.5 parts by weight of a binder, 0.5 to 1.5 parts by weight of a solvent, and 0.5 to 1.5 parts by weight of a dispersant. The adhesion promoter comprises polyvinyl alcohol.

4. The method of claim 1, wherein the zirconium acetate face coat is prepared by mixing 0.5 to 1.5 parts by weight of zirconium acetate, 0.5 to 1.5 parts by weight of a binder, 0.5 to 1.5 parts by weight of a solvent, and 0.5 to 1.5 parts by weight of a dispersant. In step S2, the weight ratio of the surface layer binder to the surface layer refractory powder is 1.5-3.5:1, the wetting agent is JFC wetting agent, and the addition amount of the JFC wetting agent accounts for 0.03-0.15% of the total weight of the surface layer coating.

5. The method of claim 1, wherein the method is characterized by: In step S2, during the second stage stirring, when the flow cup viscosity of the material at room temperature is 18-25 s, the material is uniformly dispersed.

6. A method of preparing a zirconium acetate facecoat shell for precision investment casting of a titanium alloy, according to claim 1, characterized by, In step S3, the process of vacuum negative pressure defoaming is pressure maintaining for 30-120 s under vacuum degree of-0.06 to-0.08 MPa.

7. The method of claim 1, wherein the method is characterized by: In step S4, the vacuum degree of the vacuum negative pressure condition is-0.08 to-0.1 MPa.

8. The method of claim 1, wherein the method is characterized by: In step S4, the surface layer sand used for sand spraying comprises at least one of yttria sand, zirconia sand and composite aluminum zirconium sand, and the mesh size is 60-120 mesh.

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