Casting process for effectively eliminating shrinkage porosity of rail bearing surface of top plate of rail damper

Abstract

The invention relates to the technical field of metal casting, in particular to a casting process for effectively eliminating shrinkage porosity of a rail bearing surface of a top plate of a rail shock absorber, which comprises four steps of burdening, smelting, molten iron treatment and casting molding, and comprises the following steps: accurately controlling the raw material ratio, standing for 10-13 minutes at the high temperature of 1510-1540 DEG C by adopting a medium-frequency induction furnace, and then cooling to the room temperature; according to the method, the graphite expansion is effectively utilized to counteract the shrinkage of the molten iron, the precipitation of primary graphite is inhibited, the shrinkage porosity defect of the rail bearing surface is thoroughly eliminated, the reject ratio is reduced to zero, and the production cost is reduced. And the fatigue strength and the use safety of the casting are greatly improved, and the method is suitable for high-quality casting of the subway track shock absorber top plate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal casting, in particular to a casting process for effectively eliminating shrinkage of a rail bearing surface of a rail shock absorber top plate. BACKGROUND

[0002] The top plate of the urban subway rail line rubber shock absorber is not allowed to have shrinkage defects on the rail bearing surface (the rail bearing surface is frequently subjected to alternating stress under tension and compression, which may cause shrinkage or stress concentration, casting fatigue fracture, and serious consequences such as subway derailment), and the shrinkage cannot be effectively compensated due to the limitation of the design structure of the top plate. In the conventional case, the casting engineer usually chooses to eliminate shrinkage by cold iron chilling, but the cold iron process increases the manufacturing cost (sand bag iron or sand core assembly cold iron), and is prone to cause quality problems such as subcutaneous porosity (cold iron rust generates porosity) and carbide (cold iron contact surface molten iron chilling generates carbide), which affects the service life and safety of the casting. Therefore, there is an urgent need for a casting process that can effectively eliminate shrinkage without introducing other defects. SUMMARY

[0003] The purpose of the present application is to provide a casting process for effectively eliminating shrinkage of a rail bearing surface of a rail shock absorber top plate, which significantly improves the casting quality and reduces the defect rate by optimizing the molten iron refining process and local cooling measures.

[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 effectively eliminating shrinkage of a rail bearing surface of a rail shock absorber top plate, comprising the following steps: S1, batching: according to mass percentage, 10-15% of pig iron, 20-25% of scrap steel, 60-70% of returned material, and adding a carbon content ≥99% carbon additive; S2, smelting: smelting is carried out by using a medium frequency induction furnace, and the feeding sequence is pig iron, carbon additive, scrap steel, and returned material in turn; after the smelting temperature reaches 1420-1440℃, power is turned off and slag is removed, and after sampling and detecting carbon and alloy components, auxiliary materials are added, and smelting is continued to 1510-1540℃, and high-temperature standing is carried out at this temperature for 10-13 minutes; S3, molten iron treatment: 2.1kg of inoculant with a particle size of 1-3mm, 2.1kg of inoculant with a particle size of 3-8mm and 7.7kg of lanthanide spheroidizing agent are placed in the spheroidizing treatment chamber of the molten iron ladle; 700±15kg of molten iron is poured into the molten iron ladle for spheroidizing treatment, and after the treatment is completed, slag is removed, and the surface of the molten iron is cleaned; S4, pouring and forming: the molten iron treated in step S3 is poured into the sand mold to solidify and form, and cooling needles are arranged at the rail bearing surface hot spot area of the top plate casting to accelerate cooling of the area.

[0005] Preferably, the scrap steel is briquetted scrap steel.

[0006] Preferably, in step S2, the smelting adopts a 6T medium-frequency induction furnace, and the power supply power is 2200-2500KW.

[0007] Preferably, in step S3, the spheroidization reaction is completed by using a ladle to transfer the molten iron from the electric furnace to the pouring machine.

[0008] Preferably, the cooling needle is made of cast iron.

[0009] The beneficial effects of the present application are as follows: the present application realizes the densification of the rail bearing surface and the complete elimination of the shrinkage by refining the molten iron and optimizing the graphite process, combined with the synergistic effect of setting the cooling needle in the hot spot area. Specifically, the process promotes the uniform precipitation and concentrated crystallization of graphite by controlling the smelting temperature, standing time and spheroidization treatment, which effectively compensates for the volume shrinkage during the solidification process of the molten iron, while inhibiting the premature precipitation of primary graphite and avoiding the shrinkage tendency in the paste solidification stage. Finally, the graphite ball grade of the rail bearing surface of the casting is significantly improved, and the shrinkage defect rate is reduced to zero, which not only improves the fatigue strength and reliability of the product, but also greatly reduces the subsequent processing and quality inspection cost, and has significant economic benefits and application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0010] Fig. 1 is the casting process flowchart of the present application; Fig. 2 is the top plate casting of the present application; Fig. 3 is the sand mold of the present application.

[0011] Marked as follows: 1, top plate casting; 2, rail bearing surface; 3, cooling needle; 4, sand mold; 5, cross gate; 6, ingate; 7, riser. DETAILED DESCRIPTION

[0012] The present application will be further described in conjunction with the drawings and specific embodiments. The embodiments of the present application are given for the purpose of illustration and description, and are not exhaustive or limit the present application to the disclosed form. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are chosen and described in order to better illustrate the principles and practical application of the present application, and to enable those of ordinary skill in the art to understand the present application in order to design various embodiments with various modifications suitable for specific purposes.

[0013] As shown in Figs. 1-3 , the present application provides a casting process for effectively eliminating the shrinkage of the rail bearing surface of the top plate of the rail shock absorber, comprising the following steps: S1, batching: by mass percentage, pig iron 10-15%, scrap steel 20-25%, return material 60-70%, and adding carbon content ≥99% carbon additive. The scrap steel is briquetted scrap steel, which has high bulk density and less surface oxidation, can significantly improve the smelting efficiency and the stability of molten iron composition.

[0014] S2, smelting: using a 6T medium frequency induction furnace for smelting, the power supply power is 2200-2500KW. The feeding sequence is pig iron, carbon additive, scrap steel, and return material in turn; this sequence is conducive to the rapid dissolution and absorption of the carbon additive in the high-temperature molten iron. After the smelting temperature reaches 1420-1440℃, the power is turned off and the slag is removed, the carbon and alloy components are sampled and detected, and then the auxiliary materials are added, and the smelting is continued to 1510-1540℃, and the temperature is kept for 10-13 minutes to ensure that the carbon and heterogeneous nuclei are fully dissolved, laying a foundation for subsequent graphitization.

[0015] S3, molten iron treatment: placing 2.1kg of inoculant with a particle size of 1-3mm, 2.1kg of inoculant with a particle size of 3-8mm and 7.7kg of lanthanide spheroidizing agent in the spheroidizing treatment chamber of the iron ladle; pouring 700±15kg of molten iron into the iron ladle, and using the process of transferring the iron ladle from the electric furnace to the pouring machine to complete the spheroidizing reaction. After spheroidizing treatment, the slag is removed, and the surface of the molten iron is cleaned to prevent the molten slag from being mixed into the casting to cause slag inclusion defects.

[0016] S4, pouring and forming: pouring the molten iron treated in step S3 into the sand mold 4 shown in Fig. 3 The sand mold 4 includes a cavity forming the shape of the top plate casting 1, and a pouring system communicating with the cavity, the pouring system including a cross runner 5 and an inner runner 6, the molten iron is introduced into the cavity smoothly through the inner runner 5, effectively preventing turbulence, air entrapment and sand flushing problems during pouring, and a riser 7 is arranged at the top hot spot area of the casting for feeding and venting the casting. On this basis, in order to further enhance the cooling effect of the rail bearing surface area and prevent shrinkage from occurring in this area, a plurality of cooling needles 3 made of cast iron are arranged in the rail bearing surface 2 hot spot area of the top plate casting 1 (usually located at the bolt hole or wall thickness mutation), which significantly increases the heat exchange area and heat conduction capacity of this area, accelerates the cooling and solidification speed of the hot spot area, and makes it realize sequential solidification or simultaneous solidification with the surrounding area, thereby fundamentally eliminating the shrinkage defects caused by hot spots.

[0017] The present application realizes the densification of the rail bearing surface organization and the complete elimination of the shrinkage by refining the molten iron and optimizing the graphite process, combined with the synergistic effect of setting cooling needles in the hot spot area. Specifically, the process promotes the uniform precipitation and concentrated crystallization of graphite by controlling the smelting temperature, standing time and spheroidizing treatment, which is beneficial to the effective compensation of the volume shrinkage during the solidification process of molten iron by the expansion of graphite, while inhibiting the premature precipitation of primary graphite and avoiding the shrinkage tendency in the pasty solidification stage. Finally, the graphite ball grade of the rail bearing surface of the casting is significantly improved, and the shrinkage defect rate is reduced to zero, which not only improves the fatigue strength and reliability of the product, but also greatly reduces the subsequent processing and quality inspection cost, and has significant economic benefits and application prospect.

[0018] In summary, the present application forms a set of casting process system with significant synergistic effect through the above-mentioned precise component control, high-temperature smelting and standing process, composite inoculation and spheroidizing treatment, reasonable pouring system and targeted cooling needle chilling measures, finally ensures the denseness of the rail bearing surface organization of the rail shock absorber top plate, realizes the complete elimination of the shrinkage defect, and provides a feasible process guarantee for the high-quality and high-reliability casting of the rail shock absorber top plate.

Claims

1. A foundry process effective to eliminate rail pad railhead pad shrinkage of rail pad railhead pads of rail dampers, characterized by: The method comprises the following steps: S1, batching: 10-15% of pig iron, 20-25% of scrap steel, 60-70% of returned material, and a carbon additive with a carbon content of ≥99% by mass percentage; S2, smelting: using a medium-frequency induction furnace for smelting, the feeding sequence is pig iron, carbon additive, scrap steel, and returned material; after the smelting temperature reaches 1420-1440℃, power is cut off and slag is removed, after sampling and detecting carbon and alloy components, auxiliary materials are added, and smelting is continued until 1510-1540℃, and high-temperature standing is performed at the temperature for 10-13 minutes; S3, hot metal treatment: placing 2.1 kg of inoculant with a particle size of 1-3 mm, 2.1 kg of inoculant with a particle size of 3-8 mm, and 7.7 kg of lanthanide spheroidizing agent in the spheroidizing treatment chamber of a hot metal ladle; pouring 700±15 kg of hot metal into the hot metal ladle for spheroidizing treatment, and after the treatment, slag is removed and the surface of the hot metal is cleaned; S4, casting: pouring the hot metal treated in step S3 into a sand mold (4) for solidification and molding, and arranging a cooling needle (3) in the hot spot area of the rail surface (2) of the top plate casting (1) to accelerate cooling of the area.

2. The casting process substantially eliminating the porosity of the rail bearing surface of the top plate of the rail damper of claim 1, wherein: The scrap steel is briquetted scrap steel.

3. The casting process substantially eliminating the porosity of the rail bearing surface of the top plate of the rail damper of claim 1, wherein: In step S2, the smelting uses a 6T medium-frequency induction furnace with a power of 2200-2500 KW.

4. The casting process substantially eliminating the porosity of the rail bearing surface of the top plate of the rail damper of claim 1, wherein: In step S3, the spheroidizing reaction is completed during the process of transferring the hot metal ladle from the electric furnace to the casting machine.

5. The casting process substantially eliminating the porosity of the rail seating surface of the top plate of the rail damper of claim 1, wherein: The cooling needle (3) is made of cast iron.

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