Casting process of high-precision urban rail line rubber shock absorber casting

Abstract

The invention relates to the technical field of metal casting, in particular to a casting process of a high-precision urban rail line rubber shock absorber casting, which comprises the following steps of: designing and manufacturing a mold according to the target size of the casting and the mold shrinkage rate of 0.58%; the sand shooting pressure is controlled to be 2.2-2.4 MPa, the extrusion pressure is 12-14 MPa, the mold closing thrust is 1600 MPa, and the weight ratio of the sand mold to the molten iron is controlled to be 1.5: 1; the pouring temperature of the molten iron is controlled to be 1390-1420 DEG C, and the carbon equivalent of the molten iron in the furnace is controlled to be 4.5%; the water content of the molding sand is controlled to be 3.3-3.5%, and the compaction rate is 34-38%; according to the invention, the problem of rubber leakage in the rubber vulcanization process caused by out-of-tolerance of the size of the casting is fundamentally solved, the related complaint proportion is reduced from 2% to 0%, the production cost is effectively reduced, and the product quality is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal casting, in particular to a casting process of a high-precision urban rail line rubber shock absorber casting. BACKGROUND

[0002] The rapid development of urban rail transit puts forward higher requirements on the performance and cost of key components. As an important element in the rail line, the performance and service life of the rubber shock absorber depend largely on the quality of the metal casting as the vulcanization framework. In the production process of the shock absorber, the rubber and the metal casting are combined into one through the vulcanization process in the mold. If the dimensional accuracy of the metal casting is insufficient, especially if the key sealing surface and the matching size are out of tolerance, it will cause the rubber material to overflow from the mold gap during the vulcanization process, i.e. the rubber overflow phenomenon. The rubber overflow not only causes direct waste of rubber material, increases production cost, but also leads to an increase in product defect rate, requiring additional cleaning and rework, which seriously affects production efficiency and product qualification rate. The industry usually uses a wet sand molding machine for the production of such castings, and the conventional casting tolerance level is CT8 to CT10. However, in order to effectively prevent rubber overflow, the key width size tolerance of the casting is required to be tightened from the original 73±1mm (about CT9 level) to 73±0.5mm (corresponding to CT6 to CT7 level). This precision requirement has far exceeded the capability range of the conventional wet sand process. Therefore, there is an urgent need for a high-precision casting process that can improve the dimensional accuracy of the casting and reduce the rubber overflow phenomenon. SUMMARY

[0003] The problem to be solved by the present application is to provide a casting process for a high-precision urban rail line rubber shock absorber casting, to solve the problems of rubber overflow, rubber waste and unstable product quality caused by the insufficient dimensional accuracy of the existing wet sand casting process during the rubber vulcanization process.

[0004] In view of the deficiencies of the prior art, the technical scheme adopted by the present application to solve the technical problems is as follows: a casting process for a high-precision urban rail line rubber shock absorber casting, comprising the following steps: S1, mold design and manufacturing: mold design and manufacturing according to the target size of the casting and the mold shrinkage rate of 0.58%; S2, molding: controlling the sand injection pressure to be 2.2-2.4MPa, the extrusion pressure to be 12-14MPa, the mold closing thrust to be 1600MPa, and the weight ratio of the sand mold to the molten iron to be 1.5:1; S3, melting and pouring: controlling the pouring temperature of the molten iron to be 1390-1420℃, and controlling the carbon equivalent of the molten iron after the furnace to be 4.5%; S4, mold sand treatment: controlling the moisture content of the mold sand to be 3.3-3.5%, and the compaction rate to be 34-38%; S5, size detection: the width size of the casting is detected by using a width size stop gauge detection tool.

[0005] Preferably, in step S1, the mold shrinkage of 0.58% is determined by measuring the deviation of the actual size of the casting from the size of the mold multiple times and after statistical analysis.

[0006] Preferably, in step S2, the molding clamp plate is also subjected to heating treatment, and the molding clamp plate is cleaned once every 500 times of cavity molding is completed.

[0007] Preferably, in step S5, the width size stop gauge detection tool is customized according to the nominal size of the casting width of 73 mm and the tolerance of ±0.5 mm.

[0008] Preferably, the rubber shock absorber casting cast by the process has a width size precision of CT6 to CT7 level, and the tolerance is controlled within 73±0.5 mm.

[0009] The beneficial effects of the present application are as follows: the high-precision casting process provided by the present application brings significant technical progress and economic benefits through integrated parameter control and process optimization. First, by using a large amount of practical data to determine the accurate mold shrinkage of 0.58%, the accuracy of the mold size design is ensured from the source, laying a solid foundation for obtaining high-precision castings. Secondly, by synergistically optimizing the control of the shot pressure, extrusion pressure, mold closing thrust and the weight ratio of sand mold and molten iron during the molding stage, and combined with the regular heating and cleaning of the molding clamp plate, the size stability and surface quality of the sand mold itself are effectively guaranteed, and defects such as sand sticking are reduced. Thirdly, strict control of the smelting pouring temperature and the carbon equivalent of the molten iron ensures the good fluidity and stable shrinkage behavior of the molten iron. In combination with the fine management of the moisture content and compaction rate of the molding sand, the size fluctuation of the casting during the molding process is minimized. Finally, by introducing a customized stop gauge detection tool for full inspection, an effective quality closed-loop control is formed. Through the above means, the width size precision of the casting is successfully improved from the conventional CT8-10 level to the CT6-7 level, and the tolerance is stabilized at 73±0.5 mm. This improvement in precision directly solves the problem of rubber vulcanization runout caused by the size of the casting being out of tolerance. According to the actual production feedback, the proportion of related complaints from customers has been reduced from 2% to 0%, greatly reducing the waste of rubber material, reducing production costs, improving product qualification rate and market competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0010] Fig. 1 is the casting of the present application; Fig. 2 is the upper mold of the present application; Fig. 3 is the lower mold of the present application.

[0011] BRIEF DESCRIPTION OF DRAWINGS 1, sprue cup; 2, straight runner; 3, cross runner; 4, riser; 5, casting. DETAILED DESCRIPTION

[0012] The application will be described in further detail below with reference to the drawings and specific embodiments. The embodiments of the application are given by way of example and illustration only, and are not a limitation on the present application. Numerous modifications and variations will be apparent to those skilled in the art in light of this disclosure. The embodiment is chosen and described in order to best explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and various embodiments with various modifications as are suited to the particular use contemplated.

[0013] As shown in the drawings, the application provides a casting process for a high-precision urban rail line rubber shock absorber casting, which is characterized by fine control of the whole process of mold design, modeling, melting and pouring, sand treatment and quality detection. The specific implementation steps are as follows: Figs. 1-3 S1, mold design and manufacturing: according to the target size of the casting 5 and the mold shrinkage rate 0.58%, the mold is designed and manufactured, the mold shrinkage rate 0.58% is determined by measuring the deviation between the actual size of the casting 5 and the size of the mold many times, and after statistical analysis, the shrinkage rate value of 0.58% is not a theoretical estimate or a conventional empirical value, but an optimal value obtained by repeatedly measuring and recording the actual size of a large number of trial-produced castings and the corresponding mold size, and after systematic statistical analysis, this step is the prerequisite for ensuring that the final casting 5 size is close to the nominal size of 73mm. The gating system is the design focus of this step, which is machined integrally with the mold and mainly includes the following components: sprue cup 1, straight runner 2, cross runner 3, and riser 4. The sprue cup 1: receives molten iron from the ladle, which needs to be designed to ensure that the molten iron flows smoothly and reduces air entrapment. The straight runner 2: connects the sprue cup 1 and the cross runner 3, guiding the molten iron to flow downward. The cross runner 3: a horizontal channel that plays a role in distributing molten iron. The riser 4: is set above the hot spot of the casting 5 (such as the thick connection of the casting), its core function is to compensate, during the solidification process of the molten iron, the high-temperature molten iron stored in the riser 4 continuously supplements the casting below which is solidifying under the action of gravity, effectively eliminating the shrinkage and shrinkage defects caused by volume shrinkage, ensuring the internal density of the casting 5, and the internal density is the basis for ensuring the dimensional stability and non-deformation during subsequent processing and use.

[0014]

[0015] ​S2, molding: using a tidal film sand molding machine for molding, the control of sand pressure is 2.2-2.4 MPa, this pressure range ensures that the sand can be filled with sufficient kinetic energy to the corners of the mold cavity, avoid the filling of local loose or insufficient hardness caused by sand, thus preventing the molten iron invasion caused by sand or casting 5 size expansion. Control the extrusion pressure is 12-14 MPa, after the sand is applied in this range of compaction pressure, can make the sand mold get higher, uniform tightness (hardness), ensure that the sand mold does not deform, not collapse under the static pressure and thermal shock of molten iron, is the key to ensure the clear outline and size stability of the casting 5. Control the clamping force is 1600 MPa, this high clamping force ensures that the upper and lower sand mold is tightly combined during pouring and solidification process, effectively prevent the expansion of the box caused by the molten iron pressure, avoid the casting 5 at the parting surface produces flash or overall size out of tolerance. Control the weight ratio of sand mold and molten iron is 1.5:1, this proportion is the optimized value through the heat balance calculation and practice verification, enough sand mold quality can absorb and store the large amount of heat released by the molten iron during solidification, so that the casting 5 slowly, uniformly cooled, reduce the thermal stress and deformation caused by uneven cooling, at the same time, also help to the analysis of graphite, improve the internal quality of the casting 5. The molding plate is heated, which can significantly reduce the water condensation when the low temperature plate contacts the high temperature sand, thereby reducing the adhesion of the sand on the plate. At the same time, it is strictly stipulated that after every 500 times of molding, the molding plate must be thoroughly cleaned to remove the accumulated residual sand and dirt. This maintenance system ensures that the profile of the cavity is always clear and consistent, which is a necessary measure to maintain long-term, stable production of high-precision sand molds.

[0016] S3, smelting and pouring: control the pouring temperature of molten iron to be 1390-1420℃, this temperature range is determined by repeated tests, the temperature is lower than 1390℃, the flowability of molten iron is poor, easy to produce cold separation, pouring shortage and other defects; the temperature is higher than 1420℃, the thermal erosion of molten iron to the sand is intensified, which may lead to the sintering of the sand mold surface and the sticking of the casting 5, and the excessive temperature will increase the liquid shrinkage of the molten iron, which is not conducive to the control of size precision. Pouring in this range can ensure that the molten iron fills the cavity completely and replicates the cavity size, and the thermal shock is controllable. Control the carbon equivalent of the molten iron after the furnace to be 4.5%, the carbon equivalent is a key index to measure the casting performance and solidification characteristics of cast iron. Proper carbon equivalent ensures that the molten iron has good flowability and graphitization expansion capacity. In the late solidification stage, the precipitation of graphite will produce a certain volume expansion, which can compensate for the solidification shrinkage of cast iron, thereby reducing the tendency of shrinkage cavity and shrinkage porosity, and helping to obtain a casting 5 with more stable size and more compact internal structure. Accurate carbon equivalent control is an important internal factor for realizing high-precision size reproducibility.

[0017] S4, molding sand treatment: control the moisture content of molding sand to be 3.3-3.5%, the moisture content is the binding medium of the wet sand, if the moisture content is too low (<3.3%), the sand mold strength is insufficient, and the box is easy to collapse; if the moisture content is too high (>3.5%), a large amount of water vapor will be generated during pouring, which will easily lead to the generation of pores in the casting 5, and the wet strength of the sand mold is too high, which will make the casting 5 be damaged, so the sand mold strength and the gas generation amount should be balanced in this narrow range. Control the compaction rate to be 34-38%, the compaction rate reflects the molding performance and deformation ability of the molding sand under compaction, the molding sand in this range has the best fluidity and coating property, and can form a sand mold with uniform hardness and clear contour during molding, which is the premise of obtaining high dimensional accuracy of the casting 5 surface and contour.

[0018] S5, size detection: the width size of the casting 5 is detected by using a width size stop gauge detection tool, the detection tool is not a general gauge, but a width size stop gauge detection tool specially designed and manufactured according to the nominal size 73mm and the tolerance requirement ±0.5mm, which can quickly and accurately judge whether the product is qualified, form an effective quality feedback, and ensure the dimensional consistency of the products.

[0019] The width size precision of the rubber shock absorber casting 5 cast by the process reaches CT6 to CT7 level, and the tolerance is controlled to be 73±0.5mm. Through the fine design and strict execution of the above five steps, the process forms an organic whole. The accurate mold is the basis, the stable sand mold is the carrier, the qualified molten iron is the material, and the strict detection is the guarantee. They work together to control the mold compensation, the molding process, the solidification shrinkage, and the cooling deformation, which affect the size precision of the casting 5, in a very small fluctuation range, and finally successfully stabilize the width size precision of the casting 5 to CT6-7 level, and control the tolerance to be 73±0.5mm, so as to eliminate the rubber vulcanization running problem caused by the size out-of-tolerance of the casting 5. The actual production application shows that after adopting the process, the customer complaint rate of the vulcanization running caused by the width out-of-tolerance of the casting 5 has been reduced from the original 2% to 0%, and the economic and quality benefits are significant.

Claims

1. A casting process for a high-precision rubber vibration damper casting for urban rail lines, characterized in that: Includes the following steps: S1. Mold Design and Manufacturing: Mold design and manufacturing are carried out based on the target dimensions of the casting and the mold shrinkage rate of 0.58%. S2. Molding: Control the sand injection pressure to 2.2-2.4MPa, the extrusion pressure to 12-14MPa, the mold closing thrust to 1600MPa, and control the weight ratio of sand mold to molten iron to 1.5:

1. S3. Smelting and Casting: Control the casting temperature of molten iron to 1390-1420℃, and control the carbon equivalent of the molten iron after furnace to 4.5%; S4. Molding sand treatment: Control the moisture content of the molding sand to 3.3-3.5% and the compaction rate to 34-38%; S5. Dimension Inspection: The width dimension of casting 5 is inspected using a width dimension check gauge.

2. The casting process of the high-precision urban rail line rubber vibration damper casting according to claim 1, characterized in that: In step S1, the mold shrinkage rate of 0.58% was determined by repeatedly measuring the deviation between the actual size of the casting 5 and the mold size, and then conducting statistical analysis.

3. The casting process for the high-precision urban rail line rubber vibration damper casting according to claim 1, characterized in that: Step S2 also includes heating the molding clamp and cleaning the molding clamp after every 500 cavity moldings.

4. The casting process of the high-precision urban rail line rubber vibration damper casting according to claim 1, characterized in that: In step S5, the width dimension no-go gauge is customized according to the nominal width dimension of casting 5 of 73mm and the tolerance of ±0.5mm.

5. The casting process for the high-precision urban rail line rubber vibration damper casting according to claim 1, characterized in that: The rubber vibration damper casting 5 produced by the aforementioned process has a width dimensional accuracy of CT6 to CT7 grade, with a tolerance controlled within 73±0.5mm.

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