Internal thread casting method in large casting

In recent years, with the deepening of China’s industrialization and the promulgation of a series of policies and regulations to encourage and support large castings, the output growth of large castings has accelerated. With the improvement of process technology and equipment level of China’s casting enterprises, the product quality of large castings in China has been steadily improved. Especially in automobile, internal combustion engine, machine tool, power generation equipment, electric power, rail transit and other industrial fields, a number of large-scale and professional casting enterprises with high quality level have been formed. The independent manufacturing capacity of key large castings has been further improved. The dimensional accuracy, surface quality and internal quality of some large castings have reached the international advanced level, and the export grade of large castings has been greatly improved.

Taking a large casting as an example, this paper expounds the casting method based on the internal thread in the large casting, reduces the cost of post-processing, and verifies the feasibility of the casting method.

Fig. 1 is a three-dimensional diagram of the large-scale casting. The weight of the casting is about 500kg. If the three threaded holes are processed into threads after casting, it will bring a lot of waste of human and material resources. Therefore, combined with the characteristics of large-scale castings, a casting process suitable for such large-scale castings with internal threads is designed by using divergent design thinking.

First, the spare parts as shown in Fig. 2 are processed.

In the process of large-scale casting mold design, the hexagonal hole as shown in Figure 3 should be designed first. The shape of the hole is consistent with the shape of the spare part.

The internal thread on the side needs to be solved by the lower core. The shape of the core is shown in Figure 4.

In the molding process of large castings, screw the spare parts in Figure 2 together with the bolts of M16 (the experimental results show that the extension length should not be less than 80mm) and put them into the reserved hexagonal hole on the mold, so that the internal thread will remain in the sand mold cavity during molding. The same method is used for core modeling. Reserve hexagonal holes on the core box, screw the spare parts in Figure 2 and the bolts of M16 together, put them into the reserved hexagonal holes on the core box, open the mold and take out the core, as shown in Figure 4, then put the core into the lower sand box, close the upper and lower sand boxes, and the modeling process is over.

After the casting of large castings is completed, shot blasting, cleaning, and then screw out the M16 bolts to complete the casting of the whole large castings.

There is a key point in this method, that is, the design of the parts in Figure 2 should prevent both channeling and rotation, so we design it into a hexagonal shape with grooves in the middle. The hexagonal shape prevents rotation and the middle groove prevents channeling, and then M16 bolts. If the sand mold hardness is relatively high, ordinary bolts can be used. If the sand mold hardness is high enough, Then use the T-bolt as shown in Figure 5 to ensure the strength of spare parts in the sand mold.

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