CN-122007367-A - Railway wagon swing bolster casting method based on directional solidification

CN122007367ACN 122007367 ACN122007367 ACN 122007367ACN-122007367-A

Abstract

The application relates to the field of railway vehicle part manufacturing, discloses a railway wagon swing bolster casting method based on directional solidification, and aims to solve the problems of low feeding efficiency, easiness in shrinkage cavity and crack caused by special European subtype swing bolster wall thickness distribution. The casting mold is cast in the position with the heart disc face downward and the bottom face A area upward, a built-in shrinkage compensating bag with the modulus 1.15-1.25 times that of the heart disc is arranged in the center of the heart disc, an easy-cutting heat-insulating riser is arranged at a discrete hot joint, a partition chill is embedded between adjacent risers to physically isolate a thermal field, and a stepped bottom casting system comprising a sawtooth sand collecting bag and an inner runner riser is used for filling. Through the technical scheme, the directional solidification and zoning accurate feeding can be realized, shrinkage cavity shrinkage porosity caused by thermal field interference is eliminated, the yield is increased to more than 75%, and the reliability of castings is obviously enhanced.

Inventors

CHEN ZUHUA
DONG ZHONGYOU
LIU XIANGDONG
DING SHOULI
CHEN CHUNYU
ZHOU TIAN
YANG XINYI

Assignees

中车长江铜陵车辆有限公司

Dates

Publication Date: 20260512
Application Date: 20260213

Claims (7)

1. The railway wagon swing bolster casting method based on directional solidification is characterized by comprising the following engineering implementation steps: Firstly, constructing a gravity pose guide system, namely defining casting poses of a swing bolster casting mould in a gravity field in a way that a heart disc (2) faces downwards and a bottom surface A area (4) faces upwards, so that the heart disc (2) serving as the maximum hot joint of a full casting is positioned at the lowest horizontal plane of the casting mould, and constructing a first condensation frontal surface at the heart disc (2) at the lowest end of the casting by utilizing the initial static pressure gradient of molten metal in the filling process and the chilling effect of bottom molding sand, thereby constructing a directional solidification reference thermal field from bottom to top; Secondly, arranging a built-in center feeding system, namely arranging a built-in center feeding bag (3) which is integrally formed with the structure of the center plate (2) in the geometric center area of the corresponding center plate (2) in the inner cavity of the swing bolster, wherein the built-in center feeding bag (3) is arranged in an inner cavity sand core (16), the effective volume of the built-in center feeding bag is calibrated according to the geometric modulus of a center plate heat section, the modulus M Shrink bag of the built-in center feeding bag (3) and the heat section modulus M Heart disk of the center plate (2) meet that 1.15 multiplied by M Heart disk ≤M Shrink bag ≤1.25×M Heart disk , and the direct molten metal compensation of a shrinkage pore of the center plate core area is realized by shortening the feeding distance and delaying the cooling rate of metal liquid in the feeding bag by utilizing the thermal barrier effect of the inner cavity sand core (16); Thirdly, constructing a partition independent compensation system, namely, independently arranging an easy-cutting heat-preserving riser (5) at discrete geometrical turning points at the top and the side direction of the swing bolster casting (1), namely, a bottom surface A area (4), the middle part of an inclined plane and the inner side of a terminal plane, wherein the easy-cutting heat-preserving riser (5) is covered by a riser sleeve (6) made of heating heat-preserving materials, and the supply capacity of each partition heat after the solidification of a main structure is maintained through oxidation-reduction reaction generated by the contact of the riser sleeve (6) and molten metal; Then, constructing a thermal field physical isolation system, namely embedding a partition chill (7) with a high heat storage coefficient into a wall thickness transition region between any two adjacent easy-to-cut heat-insulating risers (5), constructing a physical low-temperature region between two adjacent feeding action regions through the partition chill (7), blocking a heat conduction path to eliminate cross interference of feeding channels, and guiding the solidification front to be in lamellar propulsion vertical to the wall surface of the casting; Finally, filling is carried out through a stepped bottom pouring type pouring system, namely molten metal sequentially passes through a pouring cup (10), a cross runner (11), a sawtooth sand collecting bag (12), an inner runner (13) and an inner runner riser (14), enters a cavity in a laminar flow state, and realizes densification molding of castings under the synergistic effect of the systems; implementation details of the in-house central feeding system include: The inner cavity sand core (16) is formed by high-strength resin sand, a layer of zircon powder coating with the thickness of 0.5-1.0 mm is sprayed on the surface of the inner cavity sand core (16) corresponding to the inner core disc shrinkage fit (3), and the refractoriness of the zircon powder coating is not lower than 1750 ℃, so that the high-refractoriness and chemical inertness of the zircon powder coating are utilized to prevent high-temperature molten metal from generating physical or chemical sintering in the inner core disc shrinkage fit (3) due to long-time hot infiltration, ensure that the inner cavity surface of a casting is kept flat after the inner core disc shrinkage fit (3) completes the feeding task of core hot joints of the core disc (2), and force shrinkage cavity risk points in the core disc (2) to migrate to the inner core disc shrinkage fit (3); The sawtooth sand collecting bag (12) in the stepped bottom pouring system is arranged at a connecting node of the transverse pouring gate (11) and the internal pouring gate (13), the internal cavity of the sawtooth sand collecting bag is of a continuous sawtooth structure with an included angle of 45-60 degrees, and the effective volume of the sawtooth sand collecting bag (12) is set to be 1.5-2.5 times of the total volume of the transverse pouring gate (11); The non-metallic inclusion, oxide film and scouring sand in the molten metal are captured and retained on the leeward surface of the root of the sawtooth by utilizing the non-uniform distribution of the local turbulence, centrifugal force and pressure field caused by the instantaneous change of flow velocity generated when the fluid passes through the nonlinear sawtooth boundary, so as to ensure the metallurgical purity of the molten metal entering the cavity; The isolating chill (7) generates a thermal break effect in an original continuous thermal field through physical contact with the surface of the swing bolster casting (1), plays a role of a thermal flow blocking valve, enables feeding hydrodynamic paths of each easy-to-cut thermal insulation riser (5) to be limited in a preset geometric range, avoids overlapping of isotherms of different areas through a physical extremely-low temperature area forcibly manufactured, and ensures that solidification processes of thermal units of each area of the casting are not interfered with each other.
2. The railway wagon swing bolster casting method based on directional solidification according to claim 1, wherein the riser bush (6) in the partition independent compensation system adopts a multi-component composite structure, and comprises, by weight, 15% -25% of aluminum powder, 10% -15% of ferric oxide powder, 20% -30% of expanded perlite, 15% -20% of hollow microspheres, 10% -15% of refractory fibers and the balance of binders; The aluminum powder and the ferric oxide powder are used as a heat release agent, the aluminum thermal reaction is excited to release latent heat after the aluminum powder and the ferric oxide powder are contacted with molten metal, and the expanded perlite, the hollow microsphere and the refractory fiber are used as heat insulation aggregate, so that the heat conductivity coefficient of the riser sleeve (6) after the reaction is maintained between 0.15 and 0.25W/m.K, a plurality of mutually independent controlled heat sinks are formed on the top surface and the inclined surface area of the variable-wall thickness casting, and the accurate point-to-point compensation of the heat joint at the discrete geometric turning point is realized.
3. The method for casting the railway wagon swing bolster based on directional solidification according to claim 1, wherein the isolating chill (7) in the thermal field physical isolation system is made of chromite sand or alloy steel, and the heat storage coefficient b of the material is not lower than 2000J/(m2.K.s 1/2 ).
4. The railway wagon swing bolster casting method based on directional solidification according to claim 1, wherein an easy-cutting sheet (8) with the thickness of 3mm to 6mm is integrally arranged between the root of the easy-cutting thermal-insulation riser (5) and the swing bolster casting (1) body, the easy-cutting sheet (8) is made of ceramic materials, and is subjected to preheating treatment before installation and is coated with a graphite powder layer on the surface; The method is characterized in that a circular overflowing hole (9) is formed in the geometric center of the easy-to-cut sheet (8), the diameter of the overflowing hole (9) is set to be 35-45% of the diameter of the root of a riser, the throttling effect of the overflowing hole (9) is utilized to stabilize the flow rate of molten metal in a filling stage, a constant pressure head gradient is maintained in a feeding stage, and microscopic stress generated by the difference of thermal expansion coefficients of ceramic materials and cast steel materials is generated in a subsequent cleaning process, and the stress concentration is induced by matching with mechanical impact load, so that the riser and a casting substrate are subjected to brittle fracture stripping at the neck position of the overflowing hole (9).
5. A railway wagon swing bolster casting method based on directional solidification according to claim 6, wherein the ingate (13) is connected with an ingate riser (14) arranged at the bottom edge of the casting in a tangential direction, and the cross-sectional area of the ingate riser (14) is set to be 1.8 to 2.2 times of the cross-sectional area of the ingate (13); The sudden expansion effect of the sectional area is utilized to reduce the Reynolds number of the molten metal entering the region of the heart plate (2), the flow state is converted into a stable laminar flow from a high-energy turbulent flow, the phenomena of metal splashing and gas rolling of the region of the heart plate (2) in the initial stage of filling are eliminated, and the stable heat gradient distribution is formed at the bottom of the heart plate (2) by matching with the gravity pose guide system.
6. The method for casting the railway wagon swing bolster based on directional solidification according to any one of claims 1 to 5, wherein the swing bolster casting (1) adopts low-alloy high-strength cast steel, and comprises the following chemical components, by mass, 0.20% -0.25% of carbon, 1.30% -1.60% of manganese, 0.40% -0.60% of silicon, less than or equal to 0.30% of chromium, less than or equal to 0.30% of nickel, less than or equal to 0.30% of copper, less than or equal to 0.020% of phosphorus, less than or equal to 0.020% of sulfur, and the balance of iron, wherein the casting temperature is controlled to be 1540 ℃ to 1570 ℃, the casting speed is calibrated to be 15kg/s to 25kg/s, and the control is carried out by the partition of the system in the solidification process, so that the Niyama criterion value Ny of all key stress sections of the swing bolster casting (1) is always kept above 0.1, wherein Ny=G% G represents the local temperature gradient of the solidification front, Represents the cooling rate to ensure the continuous opening of interdendritic feed channels and to prevent microcosmic shrinkage porosity.
7. The method for casting a railway wagon swing bolster based on directional solidification according to claim 1, further comprising the steps of stress control and post-treatment: A plurality of groups of anti-cracking strips (15) are symmetrically arranged at side frame guide grooves and stress corners of the swing bolster casting (1), the anti-cracking strips (15) are in strip-shaped trapezoid bulges, the height of each anti-cracking strip is set to be 15-20% of the thickness of the casting at the position, the arrangement direction of each anti-cracking strip (15) is parallel to a main tensile stress track at the position, shrinkage load caused by temperature difference gradient is absorbed through locally improving section modulus, and the defect of thermal cracking is eliminated; Normalizing and tempering the swing bolster casting (1) after casting, wherein the normalizing heating temperature is 890-920 ℃, the heat preservation time is not less than 3.5 hours, then air cooling is carried out, the tempering heating temperature is 580-620 ℃, the heat preservation time is not less than 4 hours, and the impact toughness Akv average value of the casting in the environment of minus 60 ℃ is not less than 40J through the cooperative refinement of a heat treatment process and a directional solidification structure, and the ultrasonic flaw detection qualification rate of a core disc area reaches two stages or more.

Description

Railway wagon swing bolster casting method based on directional solidification Technical Field The invention belongs to the field of railway vehicle part manufacturing, and particularly relates to a railway wagon swing bolster casting method based on directional solidification Background The railway freight is used as the backbone strength of a modern comprehensive transportation system, and plays an irreplaceable strategic supporting role in the process of guaranteeing the stability of a global logistics supply chain and promoting regional economy integration. Along with the continuous increase of heavy load, high frequency and cross-border intermodal demands, the manufacturing quality and service life of the swing bolster serving as a key bearing part of a truck bogie have become core indexes for measuring the railway freight safety level. The swing bolster bears complex alternating load and random impact in the operation process, and the compactness of the internal tissues of the swing bolster is directly related to the fatigue strength and fracture resistance of the components. In the global track traffic system, the structural design of the swing bolster presents remarkable regional characteristics due to the differences of line conditions, axle weight standards and service environments. Specifically, the swing bolster structure adopted in European Asia regions (such as 1520mm gage regions of Russia and the like) has fundamental logic divergence from the general design of domestic, european and eastern Asia regions, wherein the European standard swing bolster is generally provided with a special built-in shrinkage pocket on the back surface of an inner cavity heart plate, and the wall thickness of the lower part of the European standard swing bolster shows gradient distribution gradually thinned from a middle plane region to inclined planes at two sides to ends. On the contrary, the back of the heart disk of the main stream swing bolster in China and Europe and America is not provided with a shrinkage-reducing bag, and the wall thickness distribution rule of the main stream swing bolster is shown as that the junction fillet between the end head and the inclined surface is the thickest, and the inclined surfaces on two sides are gradually thinned. This complete reversal of the wall thickness gradient profile makes conventional casting process logic, in the face of the euro-asian standard bolster, a serious technical suitability challenge. In existing foundry practice, technicians have attempted to improve upon the production of European standard bolsters by a variety of process means. For example, the prior art scheme, such as the patent publication CN105195682a, proposes a downward facing molding orientation of the heart plate for the russian standard bolster, and matches the side gating system and arranges feeding heads at the longitudinal positions of the lower web and heart plate in an attempt to eliminate internal shrinkage porosity while satisfying a specific geometry. In addition, there are also technical schemes such as CN102554135A, focusing on avoiding the flash and the cloak generated by the combination of the traditional multiple sand cores through the integrated integral sand core structure, aiming at improving the surface precision and the dimensional stability of the casting. These prior art techniques do address some of the surface layer geometry problems during certain historical periods and under certain application environments and improve the yield of castings to some extent. However, the above solution, when viewed from the standpoint of the deep thermophysical solidification characteristics and the feeding mechanism of the large-section castings, still presents inherent limitations that are difficult to overcome when dealing with the special hot junction distribution of the "heavy middle, light end" type of euro-type bolster. For this reason, the existing process system is expected to enhance the local feeding capacity or optimize the sand core forming precision for the treatment of casting defects, and neglect the coupling interference effect of the whole thermal field of the casting in the dynamic evolution process. In the European standard swing bolster, the central disk area forms a main heat joint with extremely high energy density and complex geometric shape due to the built-in compression bag. Under conventional multi-riser feeding logic, a series of feeding systems are typically required for a process design to be arranged longitudinally along the casting in order to cover the multiple hot spots distributed throughout the machine. However, this simple, discrete "additive" design tends to cause the pressure gradients between the different feed regions to overlap during actual solidification, such that the flow of molten metal within the feed channel exhibits a non-linear turbulence. Due to the lack of effective blocking of the heat conduction paths between adjacent heat node