A process for forming the inner cavity of a large-sized hollow guide blade and controlling the wall thickness

Abstract

The present invention relates to the technical field of investment casting, and specifically to a process method for inner cavity molding and wall thickness control of large-sized hollow guide vanes. When designing a wax mold, the structure and size of the inner cavity on the air inlet side are molded by a mold, and are designed as a mold block structure; the structure and size of the inner cavity on the exhaust side are molded by a semi-structural ceramic core, and are designed as a semi-structural ceramic core mold. The prepared semi-structural ceramic core and the wax mold blocks are combined to form the inner cavity of the entire guide vane, and the wax mold and the mold blocks are used to ensure the wall thickness and inner cavity size on the air inlet side of the guide vane. The small size of the semi-structural ceramic core is used to reduce the shrinkage difference between the shell-ceramic core and the alloy liquid-ceramic core, which has a significant optimization effect on the difficult problems of looseness, cracks, inclusions, etc. of large-sized guide vanes, and at the same time solves the problem of wall thickness size of large-sized guide vanes.

Description

Technical Field

[0001] The invention relates to the technical field of investment casting, in particular to a process method for inner cavity molding and wall thickness size control of a large-sized hollow guide blade. Background Art

[0002] With the continuous increase in gas turbine power and operating temperature, the demand for large-sized hollow guide blades (technical parameters: length 150-1000mm, width 100-500mm, height 100-500mm, diagonal length 250-1500mm) is also increasing. However, in the actual preparation process of large-sized hollow guide blades, defects such as stress cracks, core eccentricity, core leakage, uneven wall thickness, recrystallization and inclusions have always been the main problems limiting the qualified rate of blade production, which need to be solved urgently. Summary of the invention

[0003] In order to solve the problems encountered in the production of the above-mentioned hollow guide blades, the purpose of the present invention is to provide a process method for inner cavity molding and wall thickness control of large-size hollow guide blades. The inner cavity size on the air inlet side is formed by a mold and designed as a solid block structure, and the inner cavity size on the exhaust side is formed by a semi-structural ceramic core. It is mainly suitable for hollow guide blades with a relatively complex inner cavity structure, a transparent inner cavity and a width ≥20mm.

[0004] The technical solution of the present invention is:

[0005] A process method for inner cavity molding and wall thickness control of a large-sized hollow guide blade. When designing a wax mold, the structure and size of the inner cavity on the air inlet side are formed by mold forming, and the inner cavity on the air inlet side is designed as a solid wax mold block structure; the structure and size of the inner cavity on the exhaust side are formed by a semi-structural ceramic core, and the inner cavity on the exhaust side is designed as a ceramic core mold.

[0006] The method for forming the inner cavity of a large-sized hollow guide blade and controlling the wall thickness dimension comprises the following steps: after pressing and sintering a semi-structural ceramic core forming the inner cavity of an exhaust side, the semi-structural ceramic core is placed in a wax mold for wax mold pressing. After the pressing, the inner cavity structure of the hollow guide blade consists of an air intake side mold block and an exhaust side semi-structural ceramic core. After taking out the wax mold block forming the inner cavity of the air intake side, the hollow guide blade wax mold is used for wax mold assembly and shell preparation.

[0007] The method for forming the inner cavity of a large-sized hollow guide blade and controlling the wall thickness dimension is as follows: before the wax mold is assembled, the exhaust edge of the semi-structural ceramic core is set as a free end, and is painted, pasted with wax paper or waxed; the wide and thick part of the other end of the semi-structural ceramic core is set as a fixed end, and the fixed end of the semi-structural ceramic core corresponds to the wax mold block, and is connected by staggered or plug-in methods.

[0008] The large-size hollow guide blade inner cavity molding and wall thickness size control process method adopts a hollow guide blade molded by a wax mold, and the inner cavity channel of the wax mold of the air inlet side of the hollow guide blade can be dried normally when preparing the shell.

[0009] The large-size hollow guide blade inner cavity molding and wall thickness size control process method has a transparent inner cavity channel of the hollow guide blade with a width of ≥20mm, and the inner cavity on the air inlet side can be made into wax mold blocks.

[0010] The method for forming the inner cavity and controlling the wall thickness of a large-sized hollow guide blade comprises the following steps: when preparing a shell, the inner cavity on the air inlet side of the hollow guide blade wax mold is a hollow, transparent structure, and the shell slurry is applied and dried. The shell is used to form the inner cavity on the air inlet side of the hollow guide blade; then, the shell for forming the inner cavity on the air inlet side is used to fix the semi-structural ceramic core for forming the inner cavity on the exhaust side, so as to form the entire inner cavity of the hollow guide blade.

[0011] The design concept of the present invention is:

[0012] When designing the wax mold, the inner cavity size on the air inlet side is formed by the mold, and is designed as a solid block structure, and the inner cavity size on the exhaust side is formed by the semi-structural ceramic core. When pressing the wax mold, the semi-structural ceramic core and the wax mold mold block on the air inlet side are combined together to press the wax mold to form the entire wax mold inner cavity. The wax mold with the semi-structural ceramic core and the air inlet side inner cavity mold block after pressing is then removed from the wax mold. The inner cavity mold block of the wax mold air inlet side is then taken out and the wax mold is combined and the shell is prepared. Finally, the inner cavity on the air inlet side is formed by the shell, and the entire inner cavity of the guide vane is formed by fixing the semi-structural ceramic core on the exhaust side with the inner cavity shell on the air inlet side. Compared with the inner cavity of the guide blade formed by the conventional integral structure ceramic core, the inner cavity of the guide blade formed by the present invention can not only reduce the casting stress caused by the shrinkage difference between the ceramic core and the molten metal, but also shorten the distance from the fixed end to the free end of the ceramic core, thereby greatly improving the wall thickness of the blade after casting, reducing the recrystallization tendency of the single crystal blade and the crack tendency of the equiaxed crystal blade; at the same time, due to the shrinkage difference between the shell and the ceramic core, reducing the size of the ceramic core can reduce the probability of core breakage and core leakage, and effectively reduce the core production cost, improve the metallurgical quality of the guide blade caused by the wall thickness and core breakage problems, and improve the blade production qualification rate.

[0013] The present invention has the following advantages and beneficial effects:

[0014] 1. The present invention adopts a semi-structural ceramic core, which reduces the difficulty of producing the ceramic core and saves the core production cost.

[0015] 2. The present invention utilizes a wax mold to form the inner cavity on one side of the air inlet side of the guide vane, which can ensure the accuracy and consistency of the blade wall thickness and solve the problem of difficult process control of the wall thickness of large-sized hollow guide vanes.

[0016] 3. The present invention is easy to operate, avoiding the problem of easy deformation of large-sized ceramic cores, and at the same time reducing the probability of a series of metallurgical problems and dimensional problems caused by the shrinkage differences between the shell-core and the metal-core. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the hollow guide blade of the present invention.

[0018] Figure 2 It is a schematic diagram of the inner cavity structure of the hollow guide blade of the present invention.

[0019] Figure 3 It is a schematic diagram of the combined structure of the wax mold blocks of the inner cavity on one side of the air inlet side and the semi-structural ceramic core of the inner cavity on the exhaust side of the present invention.

[0020] Figure 4 This is a schematic diagram of the block composition of the inner cavity wax mold on one side of the air inlet side of the present invention.

[0021] In the figure, 1 is the inner cavity on one side of the air inlet side, 2 is the inner cavity on one side of the exhaust side, 3 is the wax mold block, 4 is the semi-structural ceramic core, 5 is the wax mold positioning structure, 6 is the staggered connection structure, 7 is the back of the blade, 8 is the blade basin, 9 is the screw hole one, and 10 is the screw hole two. DETAILED DESCRIPTION

[0022] In the specific implementation process, when designing the wax mold, the present invention uses a mold to shape the inner cavity size on the air inlet side, and designs it as a solid block structure, and the inner cavity size on the exhaust side is formed by a semi-structural ceramic core. When pressing the wax mold, the semi-structural ceramic core and the wax mold mold block on the air inlet side are combined together to press the wax mold to shape the entire wax mold inner cavity, and then the wax mold with the semi-structural ceramic core and the air inlet side inner cavity mold block after pressing is taken out from the wax mold mold, and then the inner cavity mold block of the wax mold air inlet side is taken out to carry out wax mold assembly and shell preparation. Finally, the inner cavity on the air inlet side is formed by a shell, and the entire inner cavity of the guide blade is formed by using the inner cavity shell on the air inlet side to fix the semi-structural ceramic core on the exhaust side.

[0023] like Figure 1 As shown, the outer structure of the hollow guide blade is that the blade size is relatively large, the inner cavity is transparent, and the width of the inner cavity channel is ≥20mm.

[0024] like Figure 2As shown, the inner cavity structure of the hollow guide blade is composed of the entire inner cavity of the hollow guide blade, namely, an inner cavity 1 on the air inlet side and an inner cavity 2 on the exhaust side. The size of the inner cavity 1 on the air inlet side is formed by a mold, and is designed as a wax mold block 3, and the size of the inner cavity 2 on the exhaust side is formed by a semi-structural ceramic core 4. The wax mold block 3 is used to form the inner cavity 1 on the air inlet side of the hollow guide blade, and the semi-structural ceramic core 4 is used to form the inner cavity 2 on the exhaust side of the hollow guide blade. The two ends of the wax mold block 3 are designed to form a wax mold positioning structure 5. When pressing the wax mold of the hollow guide blade, the wax mold block 3 is placed in the wax mold mold, and the wax mold mold block 3 used for forming the inner cavity 1 on the air inlet side is fixed in the wax mold mold by relying on the wax mold mold positioning structure 5, and the staggered connection structure 6 between the wax mold block 3 and the semi-structural ceramic core 4 used for forming the inner cavity 2 on the exhaust side is used to combine and connect them into the entire inner cavity structure ( Figure 3 ), after assembling, the mold is closed, and the wax mold is pressed according to the specified process. Among them, the wax mold block 3 and the semi-structural ceramic core 4 can be connected by means of dislocation, insertion, etc. The "semi-structure" of the semi-structural ceramic core means that the ceramic core used to form the complete inner cavity of the blade is an integral structural ceramic core, and the ceramic core used to form a partial inner cavity (or half of the inner cavity) of the blade is a semi-structural ceramic core. The functions of the semi-structural ceramic core are: 1) When the integral structural ceramic core is used to form the inner cavity of a large-sized guide blade, the core size is large and the shrinkage size of the core is difficult to control. At the same time, the shrinkage difference of the material between the shell and the core is large, resulting in serious deviations in the wall thickness of the cast guide blade body. The use of a semi-structural core can solve the problem of deviations in the wall thickness of large-sized guide blades; 2) The use of a semi-structural ceramic core can reduce the shrinkage difference between the alloy liquid and the ceramic core, and reduce the tendency of the guide blade to produce cracks and inclusion defects; 3) The uniform inner cavity wall thickness is conducive to the control of the loose defects of the guide blade and the consistency of metallurgical quality; 4) Compared with conventional integral ceramic cores, the semi-structural ceramic core has less heat storage during the casting process, which is conducive to reducing or eliminating the loose defects of the blade.

[0025] like Figure 4As shown, the wax mold block 3 made of metal material is composed of blocks ① to ⑦, the portion corresponding to the air inlet edge of the hollow guide blade is block ⑦, the portions corresponding to the blade back 7 of the hollow guide blade are blocks ③ and ④, and the two ends of block ③ are respectively butted with a portion of block ⑦ and block ④; the portions corresponding to the blade basin 8 of the hollow guide blade are blocks ⑤ and ⑥, and the two ends of block ⑤ are respectively butted with a portion of block ⑦ and block ⑥, and block ① is arranged between block ③ and block ⑤, and block ④ is arranged between block 4 and block 5. Block ② is set between block ⑥, and the two ends of block ① are respectively connected with block ⑦ and block ②. The area of ​​the end where block ① connects with block ⑦ is smaller than the area of ​​the end where block ① connects with block ②. The end where block 1 connects with block ⑦ is plug-in matched, and the end where block 1 connects with block ② is in close contact with the end face of block ②, a part of the end face of block ④, and a part of the end face of block ⑥ respectively. The area of ​​the end where block ② contacts with block 1 is larger than the area of ​​the other end, so as to facilitate the removal of block ②. In addition, block ① is provided with an M8mm screw hole 9 for installing a screw to remove block ①; block ② is provided with an M8mm screw hole 2 10 for installing a screw to remove block ②.

[0026] After the wax mold is pressed, the wax mold containing the wax mold block 3 is taken out from the mold, and the wax mold block 3 is taken out in the order of ① to ⑦ in the composition of the wax mold block 3. The remaining wax mold containing the semi-structural ceramic core is used to prepare the shell. Before preparing the shell, the semi-structural ceramic core 4 needs to be processed with a fixed end and a free end. The side of the semi-structural ceramic core 4 close to the air inlet edge is used as the fixed end connected to the wax mold block 3. The fixed end of the semi-structural ceramic core 4 corresponds to the wax mold block 3 and can be connected by means of dislocation, insertion, etc. The semi-structural ceramic core 4 corresponds to the exhaust edge of the hollow guide blade as the free end. The free end of the semi-structural ceramic core can be designed by methods such as pasting wax paper, painting or waxing. After completing the design of the fixed end and free end of the semi-structural ceramic core, the wax mold is assembled and the shell is prepared.

[0027] When preparing the shell, the inner cavity 1 on the air inlet side of the hollow guide vane wax mold is a hollow, transparent structure, and its inner cavity width is ≥20 mm, so the shell slurry coating and drying operations can be carried out normally, and the shell is used to form the inner cavity 1 on the air inlet side of the hollow guide vane. Then, the shell that forms the inner cavity 1 on the air inlet side is used to fix the semi-structural ceramic core 4 that forms the inner cavity 2 on the exhaust side to form the entire inner cavity of the hollow guide vane.

[0028] The hollow guide vane prepared by the method of the present invention has an inner cavity 1 on the air inlet side with dimensions and wall thickness that are guaranteed by the mold, while the inner cavity 2 on the exhaust side adopts a semi-structural ceramic core with greatly reduced dimensions, thereby reducing the shrinkage differences between the shell-ceramic core and the alloy liquid-ceramic core, and having a particularly significant optimization effect on difficult problems such as wall thickness, cracks, inclusions, and looseness of the hollow guide vane.

[0029] Below, the present invention is further described in detail by examples.

[0030] Example 1

[0031] In this embodiment, an equiaxed hollow guide blade is prepared. This blade is relatively large in size: 200 mm in length, 195 mm in width, 266 mm in height, and 395 mm in diagonal length. Using conventional integral ceramic cores to prepare castings is prone to defects such as cracks, inclusions, eccentricity, core leakage, and wall thickness size tolerance. The core channel of the blade inner cavity is measured to be transparent, with a width of 36 mm; the inner cavity structure and size on the side of the air inlet side can be guaranteed by the mold, and shell molding is adopted; the inner cavity structure on the side of the exhaust side is complex and the size is small, and semi-structural ceramic core molding is used. When designing the mold, the overall inner cavity of the guide blade is divided into two design molds, the exhaust side and the air inlet side. The inner cavity block on the side of the air inlet side is made into a wax mold block structure, and the inner cavity block on the side of the exhaust side is made into a semi-structural ceramic core mold. The wax mold block and the semi-structural ceramic core are set with a staggered combination structure. When pressing the wax mold, the semi-structural ceramic core prepared in advance and the wax mold block fixed in the wax mold are staggered to form the overall inner cavity of the guide blade for wax mold pressing. After the wax mold is pressed, the mold blocks are taken out in order. During the taking-out process, the wax mold blocks are strictly prohibited from scratching the inner cavity wall of the wax mold. The side of the semi-structural ceramic core close to the air inlet side is used as the fixed end, and the exhaust side is used as the free end. The shell is prepared to form a part of the inner cavity shell at the position of the air inlet side where the original wax mold block is located. The hollow guide vane is prepared by fixing the semi-structural ceramic core with the inner cavity shell.

[0032] The shell is dewaxed, roasted, and pre-burned with cotton before pouring. The cast blades are then cleaned, sandblasted, and cored. After inspection, the blade profile dimensions are qualified, the wall thickness is uniform, the inner cavity surface roughness is 1.56μm, the core rate reaches 100%, and the qualified rate of wall thickness reaches 100%.

[0033] The results of the embodiments show that the present invention adopts a wax mold to ensure the wall thickness of the guide vane on the air inlet side, and after adopting a semi-structural ceramic core, the volume of the overall ceramic core in the conventional method is reduced, and the qualified rate of the guide vane wall thickness is greatly improved. At the same time, the shrinkage difference between the shell-ceramic core and the alloy liquid-ceramic core is reduced, which has a significant optimization effect on difficult problems such as looseness, cracks, inclusions, etc., and greatly solves the problem of difficult control of wall thickness.

Claims

1. A large-size hollow guide blade inner cavity forming and wall thickness size control process method, characterized in that: When designing the wax mold, the structure and size of the inner cavity on the air inlet side are formed by the mold, and the inner cavity on the air inlet side is designed as a solid wax mold block structure; the structure and size of the inner cavity on the exhaust side are formed by a semi-structural ceramic core; After the semi-structural ceramic core of the inner cavity on the exhaust side is pressed and sintered, the semi-structural ceramic core is placed in a wax mold for wax mold pressing. The inner cavity structure of the hollow guide vane after pressing is composed of an air intake side mold block and an exhaust side semi-structural ceramic core. After the wax mold block of the inner cavity on the air intake side is taken out, the hollow guide vane wax mold is used for wax mold assembly and shell preparation. The inner cavity of the hollow guide vane is transparent and has a width of ≥20 mm, and the inner cavity on the air inlet side can be made into wax mold blocks; The wax mold blocks are composed of blocks ① to ⑦, the portion corresponding to the air inlet side of the hollow guide blade is block ⑦, the portions corresponding to the back of the hollow guide blade are blocks ③ and ④, and both ends of block ③ are butted against a portion of block ⑦ and block ④ respectively; The portions corresponding to the blade basin of the hollow guide blade are blocks ⑤ and ⑥, the two ends of block ⑤ are respectively butted with a portion of blocks ⑦ and ⑥, block ① is arranged between blocks ③ and ⑤, block ② is arranged between blocks ④ and ⑥, the two ends of block ① are respectively butted with blocks ⑦ and ②, the area of ​​one end where block ① butts with block ⑦ is smaller than the area of ​​one end where block ① butts with block ②, the one end where block ① butts with block ⑦ is plug-in matched, the one end where block 1 butts with block ② is respectively in close contact with the end face of block ②, a portion of the end face of block ④, and a portion of the end face of block ⑥, the area of ​​one end where block ② contacts block 1 is larger than the area of ​​the other end, so as to facilitate the removal of block ②; a screw hole 1 is provided on block ① for installing a screw rod to remove block ①; a screw hole 2 is provided on block ② for installing a screw rod to remove block ②.

2. The process for inner cavity forming and wall thickness control of large-sized hollow guide blades according to claim 1, characterized in that: Before the wax mold is assembled, the exhaust edge of the semi-structural ceramic core is set as a free end, painted, pasted with wax paper or waxed.

3. The process for inner cavity forming and wall thickness control of large-sized hollow guide blades according to claim 1, characterized in that: The hollow guide vane is formed by a wax mold, and the inner cavity channel of the wax mold of the air inlet side of the hollow guide vane can be dried normally when preparing the shell.

4. The process for inner cavity forming and wall thickness control of large-sized hollow guide blades according to claim 1, characterized in that: When preparing the shell, the inner cavity on the air inlet side of the hollow guide vane wax mold is a hollow and transparent structure, and the shell slurry is applied and dried, and the shell is used to shape the inner cavity on the air inlet side of the hollow guide vane. The shell for shaping the inner cavity on the air inlet side is then used to fix the semi-structural ceramic core for shaping the inner cavity on the exhaust side to shape the entire inner cavity of the hollow guide vane.

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