Wax part, shell and shell preparation method for investment casting

Abstract

The present invention provides a method for preparing a mold shell for investment casting, comprising a wax part preparation step and a shell layer preparation step, wherein the wax part preparation step is performed before the shell layer preparation step, and the wax part preparation step comprises a raised portion preparation step, wherein raised portions are prepared on the surface of the wax part, and at least some of the raised portions are uniformly distributed in a plane or arc surface area of ​​the wax part surface, and the plane or arc surface area occupied by a single raised portion is 40-400 cm 2 At the same time, the present invention provides corresponding investment casting shells and investment casting wax parts. The present invention solves the technical difficulties such as drill steel, low-density inclusions and steel leakage caused by poor quality of the shell surface layer of oversized precision castings with no allowance.

Description

Technical Field

[0001] The present invention relates to a wax piece, a mold shell and a method for preparing the mold shell for investment precision casting, and in particular to a wax piece, a mold shell and a method for preparing the mold shell for investment precision casting for preparing super-large gas turbine turbine blades. Background Art

[0002] Turbine blades are the core components of advanced gas turbines. As the power of advanced gas turbines continues to increase, their size has also continued to increase. For example, the radial height of the last-stage rotor and stator blades of a certain gas turbine has reached over 700mm, making blade manufacturing extremely difficult.

[0003] One of the key technical difficulties that makes the production of oversized turbine blades difficult is the difficulty in preparing high-quality oversized molds for precision casting without allowances. Since oversized blades often have structural characteristics of large flat surfaces or large curved surfaces, cracks are very likely to occur on the surface layer at the large flat surfaces or large curved surfaces during the mold preparation process. In addition, the oversized blades themselves are heavy, and the weight of the master alloy used for a single pour is even greater. The ceramic mold is subjected to great pressure during the high-temperature pouring process. Especially when the quality of the mold surface is poor, at the very least, drill steel will appear on the surface of the casting or the mold surface will fall off, causing low-density inclusions inside the casting, resulting in the scrapping of the casting. At worst, it will directly lead to mold rupture and steel leakage during the pouring process, seriously affecting the production qualification rate of the blades. Therefore, how to control the quality of the mold surface layer of large flat surfaces or large curved surfaces castings is an urgent problem to be solved.

[0004] Patent CN110405134A discloses a high-strength composite fiber ceramic mold shell and its preparation method, which belongs to the field of investment precision casting. It specifically changes the back layer slurry composition and uses coating and mechanical spraying processes to make the slurry coating more uniform, solves the problem of uneven slurry mixing, and saves stirring time. At the same time, the mechanical spraying process effectively overcomes the problem of glass fiber agglomeration leading to reduced mold shell strength, greatly increases the amount of glass fiber that can be added to the mold shell, enhances the mold shell strength and air permeability, reduces the mold shell thickness, reduces the slurry coating and drying time, shortens the production cycle, and thus improves the strength and heat dissipation of the mold shell for precision casting, thereby improving the casting qualification rate and production efficiency.

[0005] Patent CN101891444A discloses a reinforcing coating for investment casting, comprising a binder, a refractory material, aluminum dihydrogen phosphate, and an appropriate amount of solvent. The binder is water glass with a density between 1.32 and 1.34; the weight ratio of the refractory material to the binder is 1.20-1.50:1; and the weight of the aluminum dihydrogen phosphate is 0.6-1.2% of the binder weight. Using this reinforcing coating to form the mold shell reinforcement layer in investment casting can reduce costs while improving the mold shell's strength, thereby increasing the mold shell manufacturing success rate and reducing casting bulging and sparking.

[0006] However, the above patent discloses a solution of improving the shell material to increase the shell strength, which cannot completely solve the problems encountered in preparing large flat or large curved castings. Summary of the Invention

[0007] The main purpose of the present invention is to provide a wax part, a mold shell and a method for preparing the mold shell for investment precision casting, so as to solve the problems in the prior art.

[0008] In order to achieve the above-mentioned object, according to one aspect of the present invention, a method for preparing a mold shell for investment casting is provided, comprising a wax part preparation step and a shell layer preparation step, wherein the wax part preparation step is performed before the shell layer preparation step, and wherein the wax part preparation step comprises a raised portion preparation step, wherein in the raised portion preparation step, raised portions are prepared on the wax part surface of the wax part, and at least part of the raised portions are uniformly distributed in the plane or arc surface area of ​​the wax part surface, and the plane or arc surface area occupied by a single raised portion is 40-400 cm 2 .

[0009] Furthermore, the plane or arc surface area of ​​the wax piece surface is a large plane or large arc surface area, and the area of ​​the large plane or large arc surface area is greater than 400 cm 2 .

[0010] Furthermore, in the wax piece preparation step, before the convex portion preparation step, a wax piece surface finishing step is also included, in which the surface of the wax piece is finished and leveled.

[0011] Furthermore, in the wax part preparation step, after the protrusion preparation step, a protrusion reinforcement step is also included. In the protrusion reinforcement step, liquid wax is applied between the protrusion and the surface of the wax part to eliminate the gap between the protrusion and the surface of the wax part.

[0012] Furthermore, in the wax piece preparation step, after the convex portion reinforcement step, a surface cleaning step is also included, in which the surface of the wax piece connected to the convex portion is cleaned with clean water.

[0013] Furthermore, the protrusion is a wax protrusion.

[0014] Furthermore, in the protrusion preparation step, a wax stick is used to prepare the wax protrusion.

[0015] Furthermore, the diameter of the wax stick is 3-5 mm, and the length of the wax stick is 3-5 mm.

[0016] Furthermore, in the step of preparing the raised portion, a tool is used to place the wax stick.

[0017] Furthermore, the tooling includes a positioning part and a working part, the positioning part is used to abut a position outside the large plane or large arc area on the wax part, the working part has openings, at least part of the openings are evenly distributed on the working part, the openings accommodate the wax sticks, and the openings correspond one-to-one to the points where the wax sticks are placed.

[0018] Furthermore, in the step of preparing the raised portion, two or more toolings are used simultaneously on one wax piece.

[0019] Furthermore, the working portion includes spaced-apart sunken portions, and the sunken portions and the openings are located at different positions on the working portion.

[0020] Furthermore, the shell layer preparation step includes a surface layer preparation step, a transition layer preparation step and a reinforcement layer preparation step performed sequentially, and the surface layer preparation step, the transition layer preparation step and the reinforcement layer preparation step all include a slurry coating step, a sand sprinkling step and a drying step performed sequentially.

[0021] Furthermore, the shell layer preparation step also includes the sealing layer preparation step, which is performed after the reinforcement layer preparation step. The sealing layer preparation step includes a slurry coating step and a drying step.

[0022] Furthermore, in the slurry coating step of the surface layer preparation step, the wax piece is immersed in a mixed solution of a grain refiner and a binder.

[0023] Furthermore, in the sand spraying step of the surface layer preparation step, the wax piece is taken out from the mixed solution and then sand sprayed using a refractory material.

[0024] Furthermore, the refractory material is 20-80 mesh corundum sand.

[0025] Furthermore, in the drying step of the surface layer preparation step, the wax piece is dried for 20-30 hours in an environment with a temperature of 18-24° C. and a humidity of 40-60%.

[0026] Furthermore, the preparation method is used for preparing turbine blades for a gas turbine, the wax part has a first direction and a second direction, the first direction is the longitudinal axis direction of the turbine blade, the second direction is a direction perpendicular to the longitudinal axis direction and located within the large plane or large arc surface area, the raised portions are distributed in a rectangular lattice along the first and second directions, and satisfy the following relationship:

[0027] 0.6*(D1 / D2) <L1 / L2<1.2*(D1 / D2);

[0028] Wherein L1 is the distance between the two most adjacent protrusions in the first direction, L2 is the distance between the two most adjacent protrusions in the second direction, D1 is the maximum length of the large plane or large arc surface area in the first direction, and D2 is the maximum length of the large plane or large arc surface area in the second direction.

[0029] Furthermore, the distribution of the protrusions on the large plane or large arc surface area also satisfies the following relationship:

[0030] L gap >0.3*MIN(L1,L2)

[0031] Among them L gap is the distance between the raised portion and the edge of the large plane or large arc area, and MIN(L1, L2) is the smaller one of L1 and L2.

[0032] According to another aspect of the present invention, there is provided a mold shell for investment casting, comprising a plurality of shell layers formed of a refractory material and a binder, wherein the mold shell inner surface comprises a recessed portion, at least part of which is evenly distributed in a plane or arc surface area of ​​the inner surface of the mold shell, and the plane or arc surface area occupied by a single recessed portion is 40-400 cm 2 .

[0033] Furthermore, the plane or arc surface area of ​​the inner surface of the shell is a large plane or large arc surface area, and the area of ​​the large plane or large arc surface area is greater than 400 cm 2 .

[0034] Furthermore, the recessed portion is a cylindrical recessed portion, the diameter of the recessed portion is 3-5 mm, and the depth of the recessed portion is 3-5 mm.

[0035] According to another aspect of the present invention, a wax piece for investment casting is provided, wherein the wax piece is used to prepare a mold shell for investment casting, and is characterized in that the wax piece surface includes raised portions, at least some of which are evenly distributed in a plane or arc surface area of ​​the wax piece surface, and the plane or arc surface area occupied by a single raised portion is 40-400 cm 2 .

[0036] Furthermore, the plane or arc surface area of ​​the wax piece surface is a large plane or large arc surface area, and the area of ​​the large plane or large arc surface area is greater than 400 cm 2 .

[0037] Furthermore, the protrusion is a cylindrical wax protrusion.

[0038] Furthermore, the diameter of the wax protrusion is 3-5 mm, and the length of the wax protrusion is 3-5 mm.

[0039] By applying the technical solution of the present invention, the following beneficial effects can be achieved:

[0040] 1. The present invention reduces the drastic shrinkage of local areas of the surface layer during the drying process by placing raised portions on large flat or large arc-shaped areas of large-sized wax parts, improves the uniformity of the overall drying shrinkage of the surface layer, and thus improves the quality of the surface layer, completely solving the technical difficulties such as steel drilling, low-density inclusions, and steel leakage caused by poor quality of the shell surface of ultra-large-sized precision castings with no allowance.

[0041] 2. The raised portion of the present invention can be of smaller size, which has less impact on the metallurgical quality of the casting and is less likely to produce defects such as shrinkage and surface holes, thereby greatly improving the product qualification rate of the precision casting blank without allowance.

[0042] 3. The raised portion of the present invention can be of smaller size and does not require extensive grinding during subsequent processing, thereby significantly improving the production efficiency of precision casting blanks without allowance.

[0043] 4. The raised portions in the present invention are evenly distributed on the surface of the flat or curved area, which improves the uniformity of shrinkage of the surface layer, but does not affect the shrinkage of the casting, will not cause cracks in the thin-walled area of ​​the casting, and will not cause a large difference between the actual shrinkage rate of the casting and the designed theoretical shrinkage rate to cause dimensional deviation.

[0044] 5. The present invention specifies a numerical range for the area of ​​the plane or arc surface occupied by a single raised portion. Only within this numerical range can a good technical effect be achieved. If the area occupied by a single raised portion is too small or the number of raised portions is too large, the shell will become locally thicker, resulting in local shrinkage of the casting ultimately cast using the shell. If the area occupied by a single raised portion is too large, it will not effectively reduce the drastic shrinkage of the local area of ​​the surface layer during the drying process, nor will it effectively improve the uniformity of the overall drying shrinkage of the surface layer, nor will it completely solve the problems of drill steel, low-density inclusions, and steel leakage caused by the poor quality of the shell surface layer of oversized precision castings with no allowance. In addition, the numerical range of the area of ​​the plane or arc surface occupied by a single raised portion specified in the present invention achieves a good coordination effect with the size of the raised portion itself, thereby improving the quality of the product obtained by investment casting.

[0045] 6. The present invention uses a special tooling to place the protrusions. This is because during the solidification process of the casting, the protrusions will solidify before other positions. When the protrusions are unevenly distributed, cracks may occur on the surface of the casting. Using the tooling of the present invention to place the protrusions can make the distribution of the protrusions more uniform and reasonable, thereby obtaining better product quality. At the same time, the processing efficiency is also improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0047] Figure 1 It shows the overall flow chart of the method for preparing a mold shell for investment casting according to the present invention;

[0048] Figure 2 A flowchart showing the steps of preparing a wax part in the method for preparing a mold shell for investment casting according to the present invention is shown;

[0049] Figure 3 A flow chart showing the steps of preparing a shell layer of a method for preparing a mold shell for investment casting according to the present invention;

[0050] Figure 4 A schematic diagram of a wax piece for investment casting according to the present invention is shown;

[0051] Figure 5 A schematic diagram of a tooling used in a method for preparing a mold shell for investment casting according to the present invention is shown; Figure 6 The effect diagrams of Example 4 and Example 5 and Comparative Example 1 and Comparative Example 2 prepared according to the method for preparing a mold shell for investment precision casting of the present invention are shown;

[0052] Figure 7 The graph shows the relationship between the crack length and the area occupied by a single protrusion obtained according to the embodiment of the present invention and the comparative example.

[0053] The above drawings include the following reference numerals:

[0054] 1. Wax part, 2. Flat or curved area, 3. Raised part, 4. Tooling, 5. Positioning part, 6. Working part, 7. Opening, 8. Sinking part. DETAILED DESCRIPTION

[0055] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0056] The present invention is further described in detail below with reference to specific examples. These examples should not be construed as limiting the scope of protection claimed in the present invention.

[0057] Example 1

[0058] As attached Figure 1-5 As shown, a method for preparing a mold shell for investment casting, the specific preparation steps include:

[0059] S1, wax part preparation step;

[0060] Wax parts preparation steps Figure 2 As shown, the specific steps include:

[0061] S101, preparing a wax part with a large flat surface or a large curved surface area;

[0062] S102, a wax part surface finishing step, in which the surface of the wax part is finished and leveled;

[0063] S103, a convex portion preparation step, in which convex portions are prepared on the wax surface of the wax piece, at least part of which is evenly distributed on the plane or arc surface area of ​​the wax surface, and the plane or arc surface area occupied by a single convex portion is 40-400 cm 2 Preferably, the plane or arc surface area occupied by a single protrusion is 180-300 cm 2 The plane or arc surface area of ​​the wax piece surface is a large plane or a large arc surface area, and the area of ​​the large plane or the large arc surface area is greater than 400cm 2 ;

[0064] S104, a step of reinforcing the raised portion, in which liquid wax is applied between the raised portion and the surface of the wax part to eliminate gaps between the raised portion and the surface of the wax part. This ensures that the raised portion is firmly connected to the wax part and eliminates gaps to prevent subsequent materials from entering between the raised portion and the wax part and affecting subsequent processing quality.

[0065] S105, a surface cleaning step, in which the surface of the wax piece connected to the protrusion is cleaned with clean water;

[0066] S2, shell preparation step,

[0067] The shell preparation steps are as follows Figure 3 As shown, the specific steps include:

[0068] S201, a surface layer preparation step, which includes a slurry coating step, a sand spraying step, and a drying step performed sequentially.

[0069] In the slurry coating step of the surface layer preparation step, the wax piece is immersed in a mixed solution of a grain refiner and a binder. Preferably, the binder is silica sol.

[0070] In the sand rinsing step of the surface layer preparation step, the wax piece is taken out from the mixed solution and then sand rinsing is performed using a refractory material, the refractory material being 20-80 mesh corundum sand, preferably, the corundum sand has a mesh number of 60 mesh.

[0071] In the drying step of the surface layer preparation step, the wax piece is dried for 20-30 hours in an environment with a temperature of 18-24° C. and a humidity of 40-60%. Preferably, the temperature is 20° C., the humidity is 50%, and the drying time is 24 hours.

[0072] S202, a transition layer preparation step, wherein the transition layer preparation step includes a slurry coating step, a sand spraying step, and a drying step performed sequentially.

[0073] In the slurry coating step of the transition layer preparation step, the preform is completely immersed in the slurry and taken out after 2 to 10 seconds.

[0074] In the sand sprinkling step of the transition layer preparation step, the transition layer sand is evenly sprinkled on the surface of the prefabricated part that has been soaked in the slurry.

[0075] In the drying step of the transition layer preparation step, the sand-sprayed prefabricated part is hung on a drying rack for 20 to 30 hours.

[0076] S203, reinforcement layer preparation step; the reinforcement layer preparation step includes a slurry coating step, a sand spraying step and a drying step performed sequentially,

[0077] In the slurry coating step of the reinforcement layer preparation step, the prefabricated part with the transition layer prepared is completely immersed in the slurry and taken out after 2 to 10 seconds.

[0078] In the sand sprinkling step of the reinforcement layer preparation step, the reinforcement layer sand is evenly sprinkled on the surface of the prefabricated part that has been soaked in the slurry.

[0079] In the drying step of the reinforcement layer preparation step, the sand-sprayed prefabricated part is hung on a drying rack for 20 to 30 hours.

[0080] S204, the sealing layer preparation step, the sealing layer preparation step includes a slurry coating step and a drying step,

[0081] In the slurry coating step of the sealing layer preparation step, the prefabricated part after the reinforcement layer preparation is completely immersed in the slurry and taken out after 2 to 10 seconds.

[0082] In the drying step of the sealing layer preparation step, the prefabricated part soaked in slurry is hung on a drying rack for 20 to 30 hours.

[0083] S3, dewaxing step, opens the wax outlet of the mold shell after slurry sealing, places it in a dewaxing kettle, and dewaxes for 15 to 30 minutes.

[0084] S4, a firing step, placing the dewaxed shell in a shell firing furnace and firing for 3 to 8 hours.

[0085] The term "uniform distribution" means that the distances between adjacent protrusions are the same in any direction in the plane or arc surface area. Figure 4 As shown, the wax surface of the wax piece 1 has a first direction and a second direction, and the spacing between adjacent protrusions 3 in the first direction is the same, and the spacing between adjacent protrusions 3 in the second direction is also the same; however, the present invention does not require that the spacing in these two directions be consistent. Figure 4 As shown in , the pitch of the protrusions in the first direction is greater than the pitch of the protrusions in the second direction.

[0086] In another preferred embodiment, the distribution of the protrusions is adapted to the shape of the large flat surface or large arc surface area, that is, Figure 4 As shown in , the first direction is the longitudinal axis direction of the blade, the second direction is the direction perpendicular to the longitudinal axis direction of the blade and located in the large plane or large arc surface area, the raised portions are distributed in a rectangular lattice along the first direction and the second direction, the distance between the two most adjacent raised portions in the first direction is the first distance L1, and the distance between the two most adjacent raised portions in the second direction is the second distance L2, and the first distance L1 and the second distance L2 satisfy the following relationship:

[0087] 0.6*(D1 / D2) <L1 / L2<1.2*(D1 / D2)

[0088] And the distance L between the protrusion and the edge of the large flat surface or large arc area is gap Greater than 0.3 times the smaller of L1 and L2, that is, the distance L between the protrusion and the edge of the large plane or large arc area gap >0.3*MIN(L1,L2),

[0089] Wherein D1 is the maximum length of the large plane or large arc surface area in the first direction, and D2 is the maximum length of the large plane or large arc surface area in the second direction.

[0090] When the raised portions adopt the above distribution pattern, the distribution of the raised portions can be adapted to the shape of the large plane or large arc surface area, thereby achieving a uniform surface quality control effect, especially ensuring the surface quality at the corners of the large plane or large arc surface area.

[0091] Furthermore, the protrusion is a wax protrusion;

[0092] Furthermore, in the step of preparing the protrusions, a wax stick is used to prepare the wax protrusions;

[0093] Furthermore, the diameter of the wax stick is 3-5 mm, preferably 4 mm, and the length of the wax stick is 3-5 mm, preferably 4 mm.

[0094] However, the protrusions may be in a form other than the wax stick, such as a spherical wax structure, an ellipsoidal wax structure, a prismatic wax structure, a cubic wax structure, and the like.

[0095] Furthermore, in the step of preparing the raised portion, a tool 4 is used to place the wax stick.

[0096] Furthermore, the tooling 4 includes a positioning portion 5 and a working portion 6. The positioning portion 5 is used to abut against a position outside the large flat or large curved area on the wax piece. The positioning portion 5 can relatively fix the position of the tooling 4 on the wax piece to ensure the quality and efficiency of the subsequent placement of the wax stick. The working portion 6 has openings 7, at least some of which are evenly distributed on the working portion 6. The openings 7 accommodate the wax sticks, and the openings 7 correspond one-to-one with the points where the wax sticks are placed. The wax sticks can be placed on the wax piece through the openings 7.

[0097] Furthermore, in the step of preparing the raised portion, two or more toolings are used simultaneously on one wax piece.

[0098] Furthermore, the working portion 6 includes spaced-apart sunken portions 8, which are located at different positions from the openings 7 on the working portion 6. The sunken portions 8 can reduce the material used in the tooling, lower manufacturing costs, reduce the weight of the tooling, and prevent the tooling from sticking to the wax piece, facilitating removal of the tooling after the wax stick is placed.

[0099] Example 2

[0100] A mold shell for investment casting, comprising a plurality of shell layers formed of a refractory material and a binder, characterized in that the inner surface of the mold shell comprises recessed portions, at least some of which are evenly distributed in a plane or arc surface area of ​​the inner surface of the mold shell, and the plane or arc surface area occupied by a single recessed portion is 40-400 cm2 .

[0101] Furthermore, the plane or arc surface area of ​​the inner surface of the shell is a large plane or large arc surface area, and the area of ​​the large plane or large arc surface area is greater than 400 cm 2 .

[0102] Furthermore, the recessed portion is a cylindrical recessed portion, the diameter of the recessed portion is 3-5 mm, preferably, the diameter of the recessed portion is 4 mm, the depth of the recessed portion is 3-5 mm, preferably, the depth of the recessed portion is 4 mm.

[0103] Example 3

[0104] like Figure 4 As shown, a wax piece 1 for investment casting is used to prepare a mold shell for investment casting, characterized in that the wax piece surface includes raised portions 3, and the raised portions are spaced apart in a plane or arc surface area 2 on the surface of the wax piece, and the plane or arc surface area occupied by a single raised portion 3 is 40-400 cm 2 .

[0105] Furthermore, the plane or arc surface area 2 on the surface of the wax piece is a large plane or large arc surface area, and the area of ​​the large plane or large arc surface area is greater than 400 cm 2 .

[0106] Furthermore, the protrusion 3 is a cylindrical wax protrusion.

[0107] Furthermore, the diameter of the wax protrusion is 3-5 mm, preferably, the diameter of the wax protrusion is 4 mm, and the length of the wax protrusion is 3-5 mm, preferably, the length of the wax protrusion is 4 mm.

[0108] Example 4

[0109] A method for preparing a mold shell for investment casting uses a wax piece with a size of 400 mm × 400 mm × 10 mm. The wax piece is a large flat surface. The wax rods used to prepare the raised portion have a diameter of 3 mm and a height of 4 mm. The wax rods are evenly distributed and connected to the large flat surface of the wax piece. A total of four wax rods are connected, and the area of ​​the large flat surface occupied by each wax rod is 400 cm. 2 The other shell preparation technical features are the same as those in Example 1. The surface layer is prepared as shown in the attached Figure 6 (a) As can be seen in the figure, there is no crack on the surface layer of the shell, and the quality is good.

[0110] Example 5

[0111] A method for preparing a mold shell for investment casting uses a wax piece with a size of 400 mm × 400 mm × 10 mm. The wax piece is a large flat surface. The wax rods used to prepare the raised portion have a diameter of 3 mm and a height of 4 mm. The wax rods are evenly distributed and connected to the large flat surface of the wax piece. A total of 9 wax rods are connected, and the area of ​​the large flat surface occupied by each wax rod is approximately 180 cm. 2 The other shell preparation technical features are the same as those in Example 1. The shell surface layer is prepared as shown in the attached Figure 6 (b) As can be seen in the figure, there are no cracks on the surface of the shell, and the quality is good.

[0112] Example 6

[0113] A method for preparing a mold shell for investment casting uses a wax piece with a size of 400 mm × 400 mm × 10 mm. The wax piece is a large flat surface. The wax rods used to prepare the raised portion have a diameter of 3 mm and a height of 4 mm. The wax rods are evenly distributed and connected to the large flat surface of the wax piece. A total of 40 wax rods are connected, and the area of ​​the large flat surface occupied by each wax rod is 40 cm. 2 The other technical features of the shell preparation are the same as those in Example 1. The surface layer obtained has no cracks and is of good quality.

[0114] Comparative Example 1

[0115] A method for preparing a mold shell for investment casting uses a wax piece with a size of 400 mm × 400 mm × 10 mm. The wax piece is a large flat surface. The wax rod used to prepare the raised portion has a diameter of 3 mm and a height of 4 mm. The wax rod is connected to the large flat surface of the wax piece. A total of one wax rod is connected, and the area of ​​the large flat surface occupied by a single wax rod is 1600 cm. 2 The other shell preparation technical features are the same as those in Example 1. The shell surface layer is prepared as shown in the attached Figure 6 (c) In the figure, it can be seen that there are serious cracks on the surface layer of the shell (the enlarged image of the crack site (white frame) is (e)). The cracks in the surface layer will directly affect the quality of subsequent shell preparation and will have an extremely adverse effect on the later casting process.

[0116] Comparative Example 2

[0117] A method for preparing a mold shell for investment casting uses a wax piece with a size of 400 mm × 400 mm × 10 mm. The wax piece is a large flat surface. The wax rod used to prepare the raised portion has a diameter of 3 mm and a height of 4 mm. The wax rod is connected to the large flat surface of the wax piece. A total of two wax rods are connected, and the area of ​​the large flat surface occupied by each wax rod is 800 cm. 2 The other shell preparation technical features are the same as those in Example 1. The shell surface layer is prepared as shown in the attached Figure 6(d) In the figure, it can be seen that there are serious cracks on the surface layer of the shell (the crack part (white frame) is enlarged in (f)). The cracks in the surface layer will directly affect the quality of subsequent shell preparation and will have an extremely adverse effect on the later casting process.

[0118] Figure 7 This is the relationship between the crack length and the area occupied by a single protrusion in the embodiment of the present invention and the comparative example, where the dotted line is the fitting curve. It can be seen that within the numerical range defined by the present invention, that is, the plane or arc surface area occupied by a single protrusion is 40-400 cm 2 The shell surface quality is good, and there will be no casting problems caused by shell size changes, achieving a good investment casting effect. Under certain specific processing conditions, the plane or arc surface area occupied by a single protrusion is 180-400cm 2 On the basis of ensuring the quality of the shell surface layer, the number of protrusions is reduced as little as possible, further ensuring the casting manufacturing effect, while also reducing the processing difficulty and improving production efficiency.

[0119] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0120] 1. The present invention reduces the drastic shrinkage of local areas of the surface layer during the drying process by placing raised portions on large flat or large arc-shaped areas of large-sized wax parts, improves the uniformity of the overall drying shrinkage of the surface layer, and thus improves the quality of the surface layer, completely solving the technical difficulties such as steel drilling, low-density inclusions, and steel leakage caused by poor quality of the shell surface of ultra-large-sized precision castings with no allowance.

[0121] 2. The raised portion of the present invention can be of smaller size, which has less impact on the metallurgical quality of the casting and is less likely to produce defects such as shrinkage and surface holes, thereby greatly improving the product qualification rate of the precision casting blank without allowance.

[0122] 3. The raised portion of the present invention can be of smaller size and does not require extensive grinding during subsequent processing, thereby significantly improving the production efficiency of precision casting blanks without allowance.

[0123] 4. The raised portions in the present invention are evenly distributed on the surface of the flat or curved area, which improves the uniformity of shrinkage of the surface layer, but does not affect the shrinkage of the casting, will not cause cracks in the thin-walled area of ​​the casting, and will not cause a large difference between the actual shrinkage rate of the casting and the designed theoretical shrinkage rate to cause dimensional deviation.

[0124] 5. The present invention stipulates the numerical range of the plane or arc surface area occupied by a single protrusion. Only within this numerical range can better technical effects be achieved. If the area occupied by a single protrusion is too small or the number of protrusions is too large, it will cause the mold shell to become locally thicker, resulting in local shrinkage of the casting finally cast using the mold shell; if the area occupied by a single protrusion is too large, it cannot effectively reduce the drastic shrinkage of the local area of ​​the surface layer during the drying process, cannot effectively improve the overall drying shrinkage uniformity of the surface layer, and cannot completely solve the problems of drill steel, low-density inclusions and steel leakage caused by poor quality of the mold shell surface layer of oversized precision castings with no allowance.

[0125] 6. The present invention uses a special tooling to place the protrusions. This is because during the solidification process of the casting, the protrusions will solidify before other positions. When the protrusions are unevenly distributed, cracks may occur on the surface of the casting. Using the tooling of the present invention to place the protrusions can make the distribution of the protrusions more uniform and reasonable, thereby obtaining better product quality. At the same time, the processing efficiency is also improved.

[0126] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a mold shell for investment casting, comprising a wax part preparation step and a shell layer preparation step, wherein the wax part preparation step is performed before the shell layer preparation step, and is characterized in that: The wax piece preparation step includes a convex portion preparation step, in which convex portions are prepared on the wax piece surface of the wax piece, at least some of the convex portions are evenly distributed on the plane or arc surface area of ​​the wax piece surface, and the plane or arc surface area occupied by a single convex portion is 40-400 cm 2 The plane or arc surface area of ​​the wax piece surface is a large plane or large arc surface area, and the area of ​​the large plane or large arc surface area is greater than 400cm 2 ; The preparation method is used for preparing a gas turbine blade. The wax part has a first direction and a second direction. The first direction is the longitudinal axis direction of the turbine blade. The second direction is a direction perpendicular to the longitudinal axis direction and located within the large plane or large arc surface area. The raised portions are distributed in a rectangular lattice along the first and second directions and satisfy the following relationship: 0.6*(D1 / D2) <L1 / L2<1.2*(D1 / D2); Wherein L1 is the distance between the two most adjacent protrusions in the first direction, L2 is the distance between the two most adjacent protrusions in the second direction, D1 is the maximum length of the large flat surface or large arc surface area in the first direction, and D2 is the maximum length of the large flat surface or large arc surface area in the second direction; The distribution of the protrusions on the large plane or large arc surface area also satisfies the following relationship: <h2 style=";text-align:left;direction:ltr">L<h2 style=";text-align:left;direction:ltr"> gap <h2 style=";text-align:left;direction:ltr"> >0.3*MIN(L1,L2) Among them L gap is the distance between the raised portion and the edge of the large plane or large arc area, and MIN(L1, L2) is the smaller one of L1 and L2.

2. The method for preparing a mold shell for investment casting according to claim 1, wherein: In the wax piece preparation step, before the convex portion preparation step, a wax piece surface finishing step is also included, in which the surface of the wax piece is finished and leveled.

3. The method for preparing a mold shell for investment casting according to claim 1, wherein: In the wax part preparation step, after the convex part preparation step, a convex part reinforcement step is also included. In the convex part reinforcement step, liquid wax is applied between the convex part and the surface of the wax part to eliminate the gap between the convex part and the surface of the wax part.

4. The method for preparing a mold shell for investment casting according to claim 3, wherein: In the wax piece preparation step, after the convex portion reinforcement step, a surface cleaning step is also included. In the surface cleaning step, the surface of the wax piece connected to the convex portion is cleaned with clean water.

5. The method for preparing a mold shell for investment casting according to any one of claims 1 to 4, characterized in that: The raised portion is a waxy raised portion.

6. The method for preparing a mold shell for investment casting according to claim 5, wherein: In the protrusion preparation step, a wax stick is used to prepare the wax protrusions.

7. The method for preparing a shell mold for investment casting according to claim 6, wherein: The diameter of the wax stick is 3-5 mm, and the length of the wax stick is 3-5 mm.

8. The method for preparing a mold shell for investment casting according to claim 7, wherein: In the step of preparing the raised portion, a tool is used to place the wax stick.

9. The method for preparing a mold shell for investment casting according to claim 8, wherein: The tooling includes a positioning part and a working part. The positioning part is used to abut against a position outside the plane or curved surface area on the wax part. The working part has openings, at least some of which are evenly distributed on the working part. The openings accommodate the wax sticks, and the openings correspond one-to-one to the points where the wax sticks are placed.

10. The method for preparing a mold shell for investment casting according to claim 9, wherein: In the step of preparing the raised portion, two or more toolings are used simultaneously on one wax piece.

11. The method for preparing a shell mold for investment casting according to claim 9, wherein: The working portion includes spaced-apart sinking portions, and the sinking portions and the openings are located at different positions on the working portion.

12. The method for preparing a shell mold for investment casting according to any one of claims 1 to 4, characterized in that: The shell layer preparation step includes a surface layer preparation step, a transition layer preparation step and a reinforcement layer preparation step which are carried out in sequence. The surface layer preparation step, the transition layer preparation step and the reinforcement layer preparation step all include a slurry coating step, a sand sprinkling step and a drying step which are carried out in sequence.

13. The method for preparing a shell mold for investment casting according to claim 12, wherein: The shell layer preparation step also includes a sealing layer preparation step, which is performed after the reinforcement layer preparation step. The sealing layer preparation step includes a slurry coating step and a drying step.

14. The method for preparing a shell mold for investment casting according to claim 13, wherein: In the slurry coating step of the surface layer preparation step, the wax piece is immersed in a mixed solution of a grain refiner and a binder.

15. The method for preparing a shell mold for investment casting according to claim 14, wherein: In the sand spraying step of the surface layer preparation step, the wax piece is taken out from the mixed solution and then sand sprayed using a refractory material.

16. The method for preparing a shell mold for investment casting according to claim 15, wherein: The refractory material is 20-80 mesh corundum sand.

17. The method for preparing a shell mold for investment casting according to claim 16, wherein: In the drying step of the surface layer preparation step, the wax piece is dried for 20-30 hours in an environment with a temperature of 18-24° C. and a humidity of 40-60%.

18. A mold shell for investment casting, comprising a plurality of shell layers formed of a refractory material and a binder, characterized in that: The inner surface of the shell includes recessed portions, at least some of which are evenly distributed in the plane or arc surface area of ​​the inner surface of the shell, and the plane or arc surface area occupied by a single recessed portion is 40-400 cm 2 The plane or arc surface area of ​​the inner surface of the shell is a large plane or large arc surface area, and the area of ​​the large plane or large arc surface area is greater than 400cm 2 ; The mold shell for investment casting is prepared using the method for preparing the mold shell for investment casting described in claim 1.

19. The shell mold for investment casting according to claim 18, wherein: The recessed portion is a cylindrical recessed portion with a diameter of 3-5 mm and a depth of 3-5 mm.

20. A wax piece for investment casting, wherein the wax piece is used to prepare a mold shell for investment casting, characterized in that: The wax surface of the wax piece includes raised portions, at least some of which are evenly distributed on the plane or arc surface of the wax piece, and the plane or arc surface area occupied by a single raised portion is 40-400 cm 2 The plane or arc surface area of ​​the wax piece surface is a large plane or large arc surface area, and the area of ​​the large plane or large arc surface area is greater than 400cm 2 ; The wax piece has a first direction and a second direction, the first direction being the longitudinal axis direction of the turbine blade, and the second direction being a direction perpendicular to the longitudinal axis direction and located within the large plane or large arc surface area, and the raised portions are distributed in a rectangular lattice along the first direction and the second direction and satisfy the following relationship: 0.6*(D1 / D2) <L1 / L2<1.2*(D1 / D2); Wherein L1 is the distance between the two most adjacent protrusions in the first direction, L2 is the distance between the two most adjacent protrusions in the second direction, D1 is the maximum length of the large flat surface or large arc surface area in the first direction, and D2 is the maximum length of the large flat surface or large arc surface area in the second direction; The distribution of the protrusions on the large plane or large arc surface area also satisfies the following relationship: <h2 style=";text-align:left;direction:ltr">L<h2 style=";text-align:left;direction:ltr"> gap <h2 style=";text-align:left;direction:ltr"> >0.3*MIN(L1,L2) Among them L gap is the distance between the raised portion and the edge of the large plane or large arc area, and MIN(L1, L2) is the smaller one of L1 and L2.

21. The wax piece for investment casting according to claim 20, wherein: The raised portion is a cylindrical waxy raised portion.

22. The wax piece for investment casting according to claim 21, wherein: The diameter of the waxy protrusion is 3-5 mm, and the length of the waxy protrusion is 3-5 mm.

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