Lost foam casting technology is widely used in the foundry industry because of its advantages of small investment, low energy consumption, good working environment, high production efficiency and less pollution emission, especially in the production of large quantities, high precision and complex structure castings. However, the lost foam casting technology, like other casting technologies, has certain limitations, such as the slag inclusion problem of lost foam casting is one of the main problems with lost foam production for a long time. In the process of using EPC to produce batch brake shells in yto (Luoyang) Foundry Co., Ltd., serious slag inclusion occurred in the castings, resulting in the scrap of castings, with the scrap rate as high as 40%, which affected the production progress and increased the cost. Therefore, it is an important means to reduce the cost to prevent slag inclusion and ensure mass production.
Brake housing (as shown in Figure 1) has simple structure and large demand. Material: HT250, weight: 14.5kg, the upper and lower end faces and inner circle of the casting are required to be fully processed, and the defects such as slag inclusion and air hole are not allowed. The slag inclusion defects of the upper and lower end faces and inner circle frequently appear after the EPC production, leading to scrap, and the rejection rate is as high as 40%. The cost of the casting is increased, which seriously affects the production of the casting.
The slag inclusion defects of the casting are mainly distributed on the upper and lower end faces and the inner circular wall, with irregular morphology and unidentified inclusions, with a depth of about 2mm, as shown in Fig. 2 and 3.
The conclusions are as follows
(1) The slag inclusion defect is caused by lost foam casting coating;
(2) The fire resistance of lost foam casting coating used by foundry company is slightly lower.
Improvement measures:
(1) Reduce the pouring temperature to 1420 ℃ ± 10℃；
(2) Replace the coating and use high quality lost foam casting coating;
(3) properly increase the specific gravity of foam beads, and obtain a high surface finish and small gap between the beads when the white mold is formed, which can reduce the penetration of the coating when coating the coating and reduce the slag inclusion.