A rear bearing casing casting method and a special composite core thereof

Abstract

The present invention is a method for casting a rear-bearing casing and a special composite core thereof, and specifically relates to the field of rear-bearing casing manufacturing. A method for casting a rear-bearing casing adopts a gravity casting process design scheme, uses a special composite core, utilizes a medium-frequency induction furnace for smelting and pouring, and inert gas protection pouring to achieve precision casting of the rear-bearing casing; the special composite core is composed of an inner ring sand mold, an outer ring sand mold, and a rectifier support plate core connected in a mortise and tenon manner. The present invention can effectively ensure the accuracy of the shape and size of the casting, improve the overall dimensional accuracy of the casting, has low production cost, has strong practicality and promotion value, and is easy to realize engineering application.

Description

Technical Field

[0001] The invention belongs to the field of rear-bearing casing manufacturing, and in particular relates to a rear-bearing casing casting method and a special composite core thereof. Background Art

[0002] Gas turbine is an efficient and environmentally friendly energy equipment, and the rear bearing casing is an important supporting component of the gas turbine. The main body of the rear bearing casing is a multi-layer thin-walled rotary structure and a hollow rectifier support plate structure. It is a typical double-layer annular frame structure with large outline dimensions. The internal and external flow channels are local auxiliary fastening functional structures of non-machined surfaces. It mainly carries and connects the three major parts of the gas turbine: the compressor, combustion chamber and air-permeable turbine. Among them, the multi-layer thin-walled rotary structure is mainly used to support key components such as compressor bearings, intake pipes, and gearboxes. The hollow rectifier support plate structure is mainly used to connect the hub and the outer shell. There are oil supply and return oil pipelines inside. The hollow rectifier support plate is a non-machining key part, and the wall thickness of the support plate is only 5mm, which is very prone to defects such as cold shut and air holes. The mechanical properties, internal and external quality and forming accuracy of the multi-layer thin-walled rotary structure and hollow support plate structure of the rear bearing casing are important guarantees for the service effect of the gas turbine. However, large-area equal-wall thickness structures are extremely unfavorable to the solidification sequence. Ordinary sand casting makes it difficult to control sand inclusions, slag inclusions and surface pore defects that occur during the casting process, and it is difficult to meet the requirements of internal quality, surface quality, dimensional accuracy, etc. for the rear-bearing casing. Summary of the invention

[0003] The purpose of the present invention is to provide a casting method for a rear bearing casing and a special composite core thereof.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] A method for casting a rear-bearing casing adopts a gravity casting process design scheme, uses a special composite core, utilizes a medium-frequency induction furnace for smelting and pouring, and performs inert gas protection pouring to achieve precision casting of the rear-bearing casing; the special composite core is composed of an inner ring sand mold, an outer ring sand mold and a rectifier support plate core connected by mortise and tenon joints; the rear-bearing casing consists of an inner ring, an outer ring and a rectifier support plate; a test mounting seat is provided on the outer ring, wherein the rectifier support plate is a hollow variable curved surface structure and the wall thickness of the rectifier support plate is 5 mm; the rectifier support plate inner cavity is a hollow portion inside the rectifier support plate.

[0006] Furthermore, the rear bearing receiver is made of ZG07Cr20Ni10G, the inner ring wall thickness and the outer ring wall thickness are both 18mm, and the inner ring shape and the outer ring shape are both cylindrical.

[0007] Further, the gravity casting process is as follows: a machining allowance is placed on the inner ring machining surface at an increment of 0.55 times the inner ring wall thickness; a machining allowance is placed on the outer ring machining surface at an increment of 0.55 times the outer ring wall thickness; the inner ring upper end surface mounting edge is axially incremented by 0.66 times the inner ring wall thickness, radially incremented by 0.88 times the inner ring wall thickness, and a waist-shaped riser is provided; the outer ring upper end surface mounting edge is axially incremented by 0.66 times the outer ring wall thickness, radially incremented by 0.88 times the outer ring wall thickness, and a waist-shaped riser is provided; the inner and outer ring lower end surface mounting edges are both provided with anti-gravity shrinkage systems; a chill is provided on the test mounting seat, and exhaust holes are provided on the inner ring sand mold, the outer ring sand mold and the rectifier support plate core.

[0008] Furthermore, the inert gas is argon with a purity of 99%, and the inert gas is introduced from the top cover plate, vertically from the bottom, and obliquely around, and the pouring temperature is 1590°C.

[0009] Furthermore, the composite core specially used for casting the rear-bearing casing is formed by combining an inner ring sand mold, an outer ring sand mold and a rectifier support plate core by using mortise and tenon joints. The inner ring sand mold and the outer ring sand mold are manufactured by layered 3D printing additive manufacturing. The inner ring sand mold and the outer ring sand mold are divided into layers. The inner ring sand mold, the outer ring sand mold and the rectifier support plate core are pre-arranged with sand mold guide holes, core assembly guide pins and lifting holes. The sand mold manufactured by 3D printing additive manufacturing uses 3D printing resin sand as molding sand, modified furan resin as a binder, and toluenesulfonic acid as a curing agent. The inner ring sand mold and the outer ring sand mold are printed layer by layer by inkjet.

[0010] Furthermore, the rectifying support plate core is a composite material core of a metal support frame and a non-metallic material.

[0011] Furthermore, the metal is cast iron or low-carbon martensitic stainless steel, the metal support skeleton is in the form of a cylinder, a cuboid or a triangular prism, and the central structure of the metal support skeleton is a hollow grid connection.

[0012] Furthermore, the non-metal is potassium silicate sand, which is filled into the metal support skeleton and then slurry-coated and baked to shape after the entire skeleton is hardened.

[0013] Furthermore, the mortise and tenon type mortise and tenon is one of a convex square tenon, a round tenon, a double-layer convex tenon, a dovetail tenon or a tongue and groove tenon; the inner ring sand mold and the outer ring sand mold are respectively provided with mortise type grooves, tenon type convex heads are provided at both ends of the rectifier support plate core, and the rectifier support plate core is placed in the inner cavity of the rectifier support plate.

[0014] Beneficial effects of the present invention:

[0015] (1) The casting method of the rear bearing casing of the present invention adopts a combination of light and dark heat-insulating risers and chillers to achieve riser partition solidification and shrinkage compensation, thereby ensuring the internal quality and structural density of the rear bearing casing casting; an anti-gravity shrinkage compensation system, chillers and exhaust holes are adopted to ensure the forming quality and surface quality;

[0016] (2) The special composite core of the present invention adopts two types of castings, namely, inner ring sand mold, outer ring sand mold and composite support plate core, which are manufactured by 3D printing additive manufacturing, and a combination of mortise and tenon joints of the two types of castings. The combined connection method can ensure that the core heads at both ends of the support plate core are accurately positioned and firmly fixed to the inner ring sand mold and the outer ring sand mold, prevent the support plate core from shifting during the filling process, and ensure the quality and dimensional accuracy of thin-wall filling. It can effectively ensure the accuracy of the shape and size of the casting and improve the overall dimensional accuracy of the casting.

[0017] (3) The support plate core of the composite core specially used in the present invention is a composite of a metal skeleton and potassium (K2O·mSiO2) water glass sand. The support plate core composite core has better strength than a sand mold, is beneficial for long-distance thin-wall filling, and is suitable for precision casting of multi-level thin-walled rotating structures of rear-bearing casings, equal-wall-thickness and large-scale thin-walled complex steel components. It has low production cost, strong practicality and promotion value, and is easy to realize engineering application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall structure of the rear-bearing casing casting.

[0019] Figure 2 Schematic diagram of the rectifier support plate structure.

[0020] Figure 3 Schematic diagram of a sand mold for 3D printing additive manufacturing.

[0021] Figure 4 Schematic diagram of the rectifier support plate core.

[0022] Figure numerals: 1. inner ring, 2. outer ring, 3. rectifier support plate, 4. test mounting seat, 6. inner cavity of rectifier support plate, 7. inner ring sand mold, 8. outer ring sand mold, 9. exhaust hole, 10. sand mold guide hole, 11. core assembly guide pin, 12. lifting clamp hole, 13. rectifier support plate core. DETAILED DESCRIPTION

[0023] The preparation method of the present invention will be described in detail below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0024] Example 1

[0025] A method for casting a rear-bearing casing adopts a gravity casting process design, uses a special composite core, utilizes a medium-frequency induction furnace for melting and pouring, and uses an inert gas to protect the pouring, so as to achieve precision casting of the rear-bearing casing.

[0026] The overall structure of the rear bearing casing casting is as follows Figure 1 As shown, the schematic diagram of the rectifier support plate structure is as follows Figure 2 As shown. The maximum outer dimension of the rear bearing casing is φ1300mm. The rear bearing casing is made of ZG07Cr20Ni10G. The rear bearing casing is composed of an inner ring 1, an outer ring 2 and a rectifier support plate 3. A test mounting seat 4 is provided on the outer ring 2, wherein the rectifier support plate 3 is a hollow variable curved surface structure with a wall thickness of 5mm. The rectifier support plate inner cavity 6 is the hollow part inside the rectifier support plate 3. The wall thickness of the inner ring 1 and the wall thickness of the outer ring 2 are both 18mm. The shape of the inner ring 1 and the shape of the outer ring 2 are both cylindrical.

[0027] 1) Process design: The machining allowance of the inner ring 1 and the outer ring 2 of the rear bearing casing casting is designed to be 10mm at the starting point, so as to form a sequential solidification direction; the axial increment of the upper end surface mounting edge of the inner ring 1 and the outer ring 2 is 12mm, and the radial increment of the casting is 16mm, and waist-shaped risers are respectively provided; the lower mounting edge of the inner ring 1 and the outer ring 2 is provided with an anti-gravity shrinkage system, that is, reverse shrinkage is performed through the runner; the test mounting seat 4 is provided with a chill, and the inner ring sand mold 7, the outer ring sand mold 8 and the rectifier support plate core 13 are all provided with exhaust holes 9.

[0028] 2) Preparation of composite cores: The rear bearing casing casting is divided into layers according to modules, and 3D printing additive sand molds are used. There are 2 sand cores at the bottom of the first layer, 5 sand cores at the second layer, 6 sand cores at the third layer, and 2 sand cores at the fourth layer. The inner ring sand mold 7 and the outer ring sand mold 8 are pre-set with sand mold guide holes 10, core assembly guide pins 11 and lifting holes 12 on the rectifying support plate core 13; the rectifying support plate core 13 is a composite material core of a metal support skeleton and non-metal. The metal support skeleton is made of a cylinder, and the central structure of the metal skeleton is a hollow grid connection. The metal is low-carbon martensitic stainless steel, and the non-metal is potassium water glass sand. The potassium water glass sand is filled into the metal support skeleton, and the whole is hardened and then slurry is applied and baked to finalize the shape. There are 12 rectifying support plate cores 13 in total. The sand mold manufactured by 3D printing additive manufacturing is shown as follows Figure 3 shown.

[0029] 3) Core combination: Schematic diagram of the rectifier support plate core is as follows Figure 4As shown. The special composite core is composed of an inner ring sand mold 7, an outer ring sand mold 8 and a rectifying support plate core 13 connected by mortise and tenon joints. The inner ring sand mold 7 and the outer ring sand mold 8 are divided into layers; the sand mold manufactured by 3D printing additive manufacturing uses 3D printing resin sand as molding sand, modified furan resin as a binder, and toluenesulfonic acid as a curing agent, and the inner ring sand mold 7 and the outer ring sand mold 8 are printed by inkjet layer by layer. Combined positioning is performed based on the sand mold guide hole 10, the core assembly guide pin 11 and the convex square tenon connector. The inner ring sand mold 7 and the outer ring sand mold 8 are respectively provided with mortise grooves, and tenon convex heads are provided at both ends of the rectifying support plate core 6. The mortise and tenon joint method adopted is a convex square tenon; the rectifying support plate core 13 is placed in the inner cavity 6 of the rectifying support plate.

[0030] 4) Melting and pouring: Use medium frequency induction furnace for melting, argon atmosphere with purity of 99% for protection pouring, the top cover is used as the entry method, and the pouring temperature is 1590℃.

[0031] Compared with conventional casting methods, the overall composition and performance indicators of the rear bearing casing casting cast by the casting method of the present invention meet or exceed the requirements of the HB5430-2011 standard, and the internal quality and surface quality of the casting meet the relevant requirements of Class II castings in the HB5430-2011 standard; the casting flow surface type value is ±0.5 mm, and the dimensional accuracy reaches above CT10 level of the HB6103-2004 standard.

[0032] Matters not covered by the present invention are known technologies.

[0033] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for casting a rear bearing casing, characterized in that: A gravity casting process design is adopted, a special composite core is used, a medium frequency induction furnace is used for smelting and pouring, and an inert gas protection pouring is used to achieve precision casting of a rear bearing casing; the special composite core is composed of an inner ring sand mold (7), an outer ring sand mold (8) and a rectifier support plate core (13) connected by mortise and tenon joints, the rear bearing casing is composed of an inner ring (1), an outer ring (2) and a rectifier support plate (3), the outer ring (2) is provided with a test mounting seat (4), wherein the rectifier support plate (3) is a hollow variable curved surface structure with a wall thickness of 5 mm, and the rectifier support plate inner cavity (6) is a hollow part inside the rectifier support plate (3); the inner ring sand mold (7) and the outer ring sand mold (8) are manufactured by layered 3D printing additive manufacturing; the inner ring sand mold (7) and the outer ring sand mold (8) are divided into layers, and the inner ring sand mold (7), the outer ring sand mold (8) and the rectifying support plate core (13) are all pre-arranged with sand mold guide holes (10), core assembly guide pins (11) and lifting clamp holes (12); the sand mold manufactured by 3D printing additive manufacturing uses 3D printing resin sand as molding sand, modified furan resin as binder, and toluenesulfonic acid as curing agent, and prints the inner ring sand mold (7) and the outer ring sand mold (8) by inkjet layer by layer; the rectifying support plate core (13) is a composite material core of a metal support skeleton and non-metal; the metal is cast iron, low-carbon martensitic stainless steel, the metal support skeleton is a form of a cylinder, a cuboid or a triangular prism, and the central structure of the metal support skeleton is a hollow grid connection; the non-metal is potassium water glass sand, which is filled into the metal support skeleton, and the whole is hardened and then slurry is applied and baked to fix the shape.

2. The method for casting a rear bearing casing according to claim 1, characterized in that: The rear bearing casing is made of ZG07Cr20Ni10G, the wall thickness of the inner ring (1) and the wall thickness of the outer ring (2) are both 18 mm, and the shapes of the inner ring (1) and the outer ring (2) are both cylindrical.

3. The casting method of the rear bearing casing according to claim 1, characterized in that: The gravity casting process is as follows: a machining allowance is placed on the machining surface of the inner ring (1) at an increment of 0.55 times the inner ring wall thickness; a machining allowance is placed on the machining surface of the outer ring (2) at an increment of 0.55 times the outer ring wall thickness; an upper end surface mounting edge of the inner ring (1) is axially incremented at 0.66 times the inner ring wall thickness and radially incremented at 0.88 times the inner ring wall thickness, and a waist-shaped riser is provided; an upper end surface mounting edge of the outer ring (2) is axially incremented at 0.66 times the outer ring wall thickness and radially incremented at 0.88 times the outer ring wall thickness, and a waist-shaped riser is provided; an anti-gravity shrinkage compensation system is provided on the lower end surface mounting edges of the inner ring (1) and the outer ring (2); a chill is provided on the test mounting seat (4), and exhaust holes (9) are provided on the inner ring sand mold (7), the outer ring sand mold (8) and the rectifier support plate core (13).

4. The casting method of the rear bearing casing according to claim 1, characterized in that: The inert gas is argon with a purity of 99%. The inert gas is introduced from the top cover plate, vertically and obliquely from the bottom, and the pouring temperature is 1590°C.

5. The casting method of the rear bearing casing according to claim 1, characterized in that: The mortise and tenon joint method is one of a convex square tenon, a round tenon, a double-layer convex tenon, a dovetail tenon or a tongue-and-groove tenon; the inner ring sand mold (7) and the outer ring sand mold (8) are respectively provided with mortise-type grooves, tenon-type protrusions are provided at both ends of the rectifying support plate core (13), and the rectifying support plate core (13) is placed in the rectifying support plate inner cavity (6).

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