A method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings

Abstract

The present invention relates to a method for solving the problems of columnar crystals and coarse grains in equiaxed crystal castings. The present invention includes using a wax press to press a casting wax mold according to the shape of the casting; designing a grain improvement process structure, the cross-sectional shape of the grain improvement process structure is an isosceles triangle structure, and vertically bonding the grain improvement process structure to the surface of the casting wax mold; combining the casting wax mold into a wax mold module; coating the surface of the wax mold module with slurry so that the surface of the casting wax mold is in full contact with the surface coating, and then taking out the casting wax mold and evenly spraying sand on the surface of the casting wax mold through a sand spreader; after drying the wax mold module, dewaxing it with high-pressure steam to obtain a casting mold shell; roasting the casting mold shell, and then pouring the alloy after removing the residual wax. When solving the problems of columnar crystals and large grains, the present invention can use this method to avoid the problem of grain out-of-tolerance, and at the same time, after using this method, the casting process parameter window can be widened without causing the problems of columnar crystals and large grains.

Description

Technical Field

[0001] The invention relates to the technical field of investment casting, in particular to a method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings. Background Art

[0002] In investment casting, the surface grain refinement of traditional equiaxed crystal castings is usually achieved by adding a required proportion of cobalt aluminate to the surface slurry prepared by the mold shell as a catalyst for grain refinement, thereby refining the surface grains of the castings during the process from liquid to solidification of the alloy. However, due to the different structures and requirements of various castings, the alloy parts used in aviation, aerospace, and gas turbine engines have high-temperature alloy precision castings whose grain standards have requirements for columnar crystals and maximum grain size, such as turbine blades, casings, guide vanes, etc., involving various alloy grades (such as: M247, K417, K438, K403, K452, K465, Rene80, etc.). Similar castings will inevitably have a problem of disparity in wall thickness at the beginning of structural design, because of the disparity in wall thickness, which leads to the formation of columnar crystals or large grains. Refining grains with existing surface refiners can no longer meet the surface grain requirements of the local structural change position of the casting. In addition, due to the differences in casting structure and wall thickness, columnar grains grow on the surface of the casting and local grains are too large. Summary of the invention

[0003] To this end, the technical problem to be solved by the present invention is to overcome the problem in the prior art that grain refinement by surface refiner cannot meet the surface grain requirements of local positions of the casting and the problem of columnar grains growing on the surface of the casting and large local grains.

[0004] In order to solve the above technical problems, the present invention provides a method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings, comprising the following steps:

[0005] S1: Use wax pressing machine to press the casting wax mold according to the shape of the casting;

[0006] S2: designing a grain improvement process structure, wherein the cross-sectional shape of the grain improvement process structure is an isosceles triangle structure, and vertically bonding the grain improvement process structure to the surface of the casting wax mold;

[0007] S3: combining the casting wax molds into a wax mold set;

[0008] S4: coating the wax mold module with slurry to make the surface of the casting wax mold fully contact with the surface coating, then taking out the casting wax mold and evenly spraying sand on the surface of the casting wax mold through a sand spreader;

[0009] S5: After the wax mold assembly is dried, it is dewaxed with high-pressure steam to obtain a casting mold shell;

[0010] S6: The casting mold shell is baked to remove the residual wax and then the alloy is poured.

[0011] In one embodiment of the present invention, in step S2, the base width of the isosceles triangle structure is 1-5 mm, the height is 1-5 mm, and the three corners are rounded by 0.2-1 mm respectively.

[0012] In one embodiment of the present invention, in step S2, the grain improvement process structure is pressed and molded using blue wax or medium-temperature wax without filler.

[0013] In one embodiment of the present invention, in step S4, the slurry is a silica sol-zircon powder refined slurry with a surface layer containing 4.6-7.2% cobalt aluminate.

[0014] In one embodiment of the present invention, in step S4, 8 to 12 layers of sand are poured onto the surface of the casting wax mold.

[0015] In one embodiment of the present invention, in step S6, the casting shell mold is calcined to 950-1180°C.

[0016] In one embodiment of the present invention, in step S6, the pouring temperature of the alloy is 1460-1540°C.

[0017] In one embodiment of the present invention, in step S6, a three-chamber vacuum furnace is used to cast the alloy.

[0018] In one embodiment of the present invention, in step S6, thermal insulation cotton is used to insulate the runner and the casting mold shell as a whole to slow down the heat dissipation of the alloy and form gradient cooling.

[0019] The above technical solution of the present invention has the following advantages compared with the prior art:

[0020] The method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings described in the present invention can be used to avoid the problem of grain out-of-tolerance when solving the problem of columnar crystals and coarse grains. At the same time, after using this method, the casting process parameter window can be widened without causing the problem of columnar crystals and coarse grains.

[0021] By adjusting the process structure at a specific position of the casting, rapid crystallization can be formed at the position where the process structure is adjusted, thereby controlling the growth of columnar crystals and the problem of large grains. The process structure can change with the structure of the casting and has a wide range of applications. Due to the characteristics of the process structure, the grains on the surface of the casting after the process structure is removed will not be different from the surrounding grains. During the casting process, the process structure does not have high requirements on the range of casting parameters. When designing the casting process parameters, it is temporarily unnecessary to consider the influence of the casting parameters on the local grains. The process parameters are designed only for other metallurgical problems, eliminating the variables that the casting parameters affect the grains, which helps the success rate of research and development. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein

[0023] Figure 1 It is a schematic diagram of the wax model structure of the present invention.

[0024] Figure 2 It is a schematic diagram of the surface of the wax mold in which the grain optimization process structure of the present invention is bonded.

[0025] Figure 3 It is a schematic diagram of the grain optimization process structure. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0027] Reference Figures 1 to 3 As shown, a method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings of the present invention comprises the following steps:

[0028] S1: Use wax pressing machine to press the casting wax mold according to the shape of the casting;

[0029] S2: designing a grain improvement process structure, wherein the cross-sectional shape of the grain improvement process structure is an isosceles triangle structure, and vertically bonding the grain improvement process structure to the surface of the casting wax mold;

[0030] S3: combining the casting wax molds into a wax mold set;

[0031] S4: coating the wax mold module with slurry to make the surface of the casting wax mold fully contact with the surface coating, then taking out the casting wax mold and evenly spraying sand on the surface of the casting wax mold through a sand spreader;

[0032] S5: After the wax mold assembly is dried, it is dewaxed with high-pressure steam to obtain a casting mold shell;

[0033] S6: The casting mold shell is baked to remove the residual wax and then the alloy is poured.

[0034] Specifically, in step S2, the base width of the isosceles triangle structure is 1 to 5 mm, the height is 1 to 5 mm, and the three corners are rounded by 0.2 to 1 mm. The width of the triangle base is narrow, the contact area with the surface of the part is small, and the volume of the entire triangle is small, which will not cause other fluorescence and radiation defects of the part. At the same time, because the rounding of the triangle is pointed, the alloy will crystallize and cool quickly here after pouring, avoiding coarse grains and columnar crystals. In this embodiment, the isosceles triangle structure preferably has a base width of 1 mm, a height of 1.5 mm, and three angles are rounded by R0.2 mm. Figure 2 shown.

[0035] Specifically, in step S2, the grain improvement process structure is pressed and formed using blue wax or medium-temperature wax without fillers.

[0036] Specifically, in step S4, the slurry is a silica sol-zircon powder refined slurry with a surface layer containing 4.6-7.2% cobalt aluminate.

[0037] Specifically, in step S4, 8 to 12 layers of sand are poured onto the surface of the casting wax mold.

[0038] Specifically, in step S6, the casting shell mold is calcined to 950-1180°C.

[0039] Specifically, in step S6, the pouring temperature of the alloy is 1460-1540°C.

[0040] Specifically, in step S6, a three-chamber vacuum furnace is used to cast the alloy.

[0041] Specifically, in step S6, thermal insulation cotton is used to insulate the runner and the casting mold shell as a whole to slow down the heat dissipation of the alloy and form gradient cooling.

[0042] In this embodiment, according to the part structure combined with columnar crystals and the position of oversized grains, the grain optimization process structure is bonded to the surface of the wax mold (the area with large thickness difference and mutation of the tenon root of the casting, and the use parts are, for example, the inlet and outlet edges of the casting, the root of the tenon and the thickness mutation area of ​​the blade crown, and the edge plate transition area of ​​the guide vane) using bonding wax according to the requirements of the casting process design. The bonding position is 2-3mm at the beginning of the columnar crystal, and is bonded to the surface of the wax mold in a direction approximately perpendicular to the columnar crystal. The runner and the local casting and the entire module are insulated by using insulation cotton to slow down the heat dissipation of the alloy and form gradient cooling at the same time. A three-chamber vacuum furnace is used to complete the casting of high-temperature alloy turbine blades, guide blades and other castings. During the casting, the cooling characteristics of the grain-improved process structure are used. The alloy at the rounded position of the process structure will start to crystallize at the first time, and quickly form partial quenching crystals, thereby blocking the growth of columnar crystals and the problem of oversized grains, and forming surface grains with uniform grains.

[0043] The present invention adjusts the process structure at a specific position of the casting so that rapid crystallization is formed at the position where the process structure is adjusted, thereby controlling the growth of columnar crystals and the problem of large grains; the process structure can change with the structure of the casting and has a wide range of applications; due to the characteristics of the process structure, the grains on the surface of the casting after the process structure is removed will not be different from the surrounding grains; during the casting process, the process structure does not have high requirements on the range of casting parameters, and when designing the casting process parameters, it is temporarily unnecessary to consider the influence of the casting parameters on the local grains, and the process parameters are only designed for other metallurgical problems, eliminating the variables that the casting parameters affect the grains, which helps the success rate of research and development.

[0044] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings, characterized in that: The steps include: S1: Use wax pressing machine to press the casting wax mold according to the shape of the casting; S2: designing a grain improvement process structure, wherein the cross-sectional shape of the grain improvement process structure is an isosceles triangle structure, and vertically bonding the grain improvement process structure to the surface of the casting wax mold; S3: combining the casting wax molds into a wax mold set; S4: coating the wax mold module with slurry to make the surface of the casting wax mold fully contact with the surface coating, then taking out the casting wax mold and evenly spraying sand on the surface of the casting wax mold through a sand spreader; S5: After the wax mold assembly is dried, it is dewaxed with high-pressure steam to obtain a casting mold shell; S6: calcining the casting mold shell, removing the residual wax and then pouring the alloy; In step S2, the base width of the isosceles triangle structure is 1 to 5 mm, the height is 1 to 5 mm, and the three corners are rounded by 0.2 to 1 mm respectively; In step S2, the grain improvement process structure is pressed and formed using blue wax or medium-temperature wax without fillers.

2. A method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings according to claim 1, characterized in that: In step S4, the slurry is a silica sol-zircon powder refined slurry with a surface layer containing 4.6-7.2% cobalt aluminate.

3. A method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings according to claim 1, characterized in that: In step S4, 8 to 12 layers of sand are poured onto the surface of the casting wax mold.

4. A method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings according to claim 1, characterized in that: In step S6, the casting shell mold is calcined to 950-1180°C.

5. A method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings according to claim 1, characterized in that: In step S6, the pouring temperature of the alloy is 1460-1540°C.

6. A method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings according to claim 1, characterized in that: In step S6, a three-chamber vacuum furnace is used to cast the alloy.

7. A method for solving the problem of columnar crystals and coarse grains in equiaxed crystal castings according to claim 1, characterized in that: In step S6, thermal insulation cotton is used to insulate the runner and the casting mold shell as a whole to slow down the heat dissipation of the alloy and form gradient cooling.

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