Study on casting technology of Chinese steel casting parts

Casting process is a process scheme to ensure that steel casting parts have complete shape, clear outline and no internal casting defects. Reasonable design of casting process parameters is the key to obtain high-quality defect free steel casting parts. For steel casting parts of different materials, the casting process schemes are different. Even for the same steel casting parts, the process schemes are not exactly the same. Especially for large steel casting parts, due to large quality, great difference in casting wall thickness and long solidification time, it is easy to cause shrinkage, porosity, casting stress, deformation, crack and low dimensional accuracy of casting surface. Therefore, Chinese foundry workers have carried out a lot of casting process research and development of casting process simulation software around eliminating casting defects and improving steel casting quality, and applied the existing casting simulation software to new product development and existing process optimization design.

With the help of these software, technicians simulate and analyze the flow field, temperature field and stress field of the casting in the forming process in advance before compiling the casting process, so as to predict the possible defects of the casting. According to the simulation results, the casting process is optimized and the final process scheme is determined.

For example, before the casting process design of bridge cable clamp steel casting parts, first carefully analyze the structural form of cable clamp casting, then preliminarily calculate the process parameters of pouring system, determine the position and size of pouring and riser and the rising speed of steel liquid level, and then further optimize the process scheme through solidification simulation prediction, determine the final casting process scheme and organize production, After inspection, the cable clamp steel casting parts produced by the optimized casting process are of good quality, without internal casting defects, and all meet the product requirements. Z1451 stand is the main casting of six high cold rolling mill. Based on the analysis of casting structure and with the help of computer simulation software, the researchers determined the casting process of using internal and external chill and thermal insulation riser, and determined the position, quantity and size of gating system, internal and external chill and riser. The actual production shows that the frame produced by this casting process fully meets the design requirements.

In view of the problems existing in the casting process of large guide vane steel casting parts with typical structure, the casting solidification process is numerically simulated through mathematical modeling, the reasonable temperature field distribution is established, the temperature gradient field required for sequential solidification is determined, the casting process parameters are optimized, and the problems of shrinkage cavity and porosity are solved. The actual production shows that there are no defects in the casting, Meet delivery requirements.

The original casting process of steel casting frame was numerically simulated by casting simulation software, the temperature field and flow field in the casting filling process were analyzed, and the causes of shrinkage defects were predicted. The shrinkage defects of castings were eliminated by using the optimized process of increasing cold iron and increasing the cooling rate of thick and large parts. When the researchers designed the casting process of dual phase stainless steel impeller for nuclear power, the casting process of impeller was simulated by ProCAST software. The location of shrinkage porosity, porosity and slag inclusion defects was predicted by calculating the temperature field and velocity field during solidification. The process scheme was optimized, the defects such as shrinkage porosity, porosity and slag inclusion in the casting were eliminated, and the quality of the casting was improved. As a key component in the runner of hydraulic turbine, the lower ring has a large diameter (inch 4586mm) and thin wall thickness (60mm). It is not conducive to feeding during casting solidification, and is prone to deformation, shrinkage cavity, shrinkage porosity and other casting defects. According to the structural characteristics of the lower ring, the casting process with 6 gate annular arrangement and 16 insulation gates on the top of the lower ring is adopted. The process scheme is reasonable through the simulation and prediction of Huazhu CAE solidification simulation software. The production inspection shows that the casting meets the quality requirements.

Rudder hanging arm is the key part of supporting and hanging rudder structure of large ships. The maximum outline dimension of casting blank is 10795 mm × 6 948 mm × 2000mm, unit weight of more than 1700t (300000 tons) and 7000mm × 4400 mm × 1500 mm, unit weight about 50 t (120000 tons). Due to the impact of seawater, the casting needs to bear large variable load, which requires it to have excellent internal quality and comprehensive mechanical properties. In order to obtain high-quality cast parts of rudder arm steel, the overall casting process is optimized and calculated based on the full analysis of rudder arm casting structure before casting, and it is determined to adopt pit core assembly modeling and multiple sand composite core making (chromite sand is used as surface sand) , the gating system adopts two layers of inner nozzle, the second layer of gate is set on the riser to ensure good temperature gradient, the riser adopts thermal insulation open riser, the riser is added inside the shaft hole to increase the feeding channel, and the external chill is placed at the bottom of the thick part of the rudder arm shaft hole and between the riser to increase the chilling effect and ensure the sequential solidification of castings. The production results show that the rudder arm steel casting parts The structure is compact, the performance is excellent, and meets the requirements of LR standard. The casting process yield is 60%.

The lower half of the steam turbine cylinder block is an important part of the engine block group, and the maximum contour dimension of the casting is 6000 mm × 3000 mm × 2000 mm, net weight 48 T, main wall thickness 70 ~ 150 mm, complex casting structure and difficult process design and manufacturing. In order to obtain high-quality castings, after analyzing the casting structure, the process scheme of two-layer transverse sprue with ring riser and placing external cold iron at thick hot joints is adopted to create good conditions for sequential solidification and feeding of castings. It is confirmed by production inspection that the steel casts zero parts The stainless steel pump shell of the stripper bottom pump has complex structure and large wall thickness difference, which is very easy to produce cracks and slag inclusion defects. In order to obtain an excellent stainless steel pump shell, the researchers determined the corresponding design according to the causes of shrinkage, cracks and slag inclusion after analyzing the product structure, quality requirements, materials and service conditions Scheme: the runner drainage groove is adopted at the thin-wall part to avoid local overheating of the body, and the large flow bottom injection gating system is adopted to ensure stable mold filling of liquid steel and avoid secondary oxidation slag inclusion of liquid steel. The shrinkage defects at the intersection of castings are eliminated through the combined use of risers, subsidies and cold iron. It can be seen that the solidification simulation prediction results are used to optimize the design of casting process parameters and eliminate non-uniformity Remarkable results have been achieved in casting defects such as shrinkage cavity and porosity in steel casting parts of the same material and different sizes.

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