Internal shrinkage porosity and shrinkage cavity defects of nodular iron castings are common problems in the casting industry, and how to solve them is also a major problem in the casting industry, especially for castings with high requirements for product compactness, it is more difficult to achieve perfection, and choosing a reasonable feeding process is the prerequisite to solve such problems. The feeding riser of castings is usually set at the top or side of the position where feeding is required, but where is the better effect? Starting from practice, this paper continues to explore in the process of solving the internal defects of ductile iron products, verifies the difference between the top feeding and side feeding effects in the same product, and draws a conclusion.
In line with the purpose of developing overseas markets and producing high value-added products, ZHY casting has successively developed a variety of steering gear products, with weights ranging from 15kg to 250kg (Figure 1). Due to individual differences in products, new problems continue to appear in the process of product development and urgently need to be solved.
This year, ZHY casting developed a new steering gear product. This product is a casting used in large excavators, which bears large external forces. Customers have high requirements for the internal compactness of the product, and it is not allowed to have visible shrinkage defects, that is, it meets the quality standard above level 2. The material of this product is QT500-7, and the outline size is 545 × four hundred and seventy point six × 471.9mm, the product weight is more than 81.5kg, the basic wall thickness of the product is more than 30mm, there are many isolated hot spots, and the maximum hot spot circle is υ 60 (Figure 2).
In the process design, ZHY casting combined with the previous process platform for developing this kind of products, drew lessons from the experience of ductile iron castings, and took corresponding measures. After analysis, it was verified that there were no defects in many parts that were prone to shrinkage and porosity defects, but the shrinkage and porosity defects at the largest hot spot could not be solved (Figure 2, the red circle). In order to solve this problem, we should seek new breakthroughs in the process of process improvement, Carry out process validation and application, develop strengths and circumvent weaknesses, and improve technical means.
