Feeding theory and technology of cylinder body cast iron

As one of the key parts of the engine, the cast iron parts of the engine block have high quality requirements, and the structure of the cylinder block is more complex than that of the general castings, so it is difficult to produce, and a large number of core manufacturing technologies are concentrated. Therefore, the research on the process design of its gating and riser has always been an important guarantee for production practice. The casting process of cylinder body cast iron mainly includes feeding riser process and pouring process. On the basis of classification based on gating and riser technology, each production example is regarded as the test of casting and riser technology for cylinder block iron castings. The common rules of casting and riser technology and the process design principles under different quality are found by statistical analysis.

According to statistics, the main material of the cylinder body is gray cast iron. At present, the sequential solidification theory and proportional solidification theory are mainly applied in the casting practice of engine cylinder block.

The technological principle of sequential solidification theory is to realize the solidification from the far end of the riser to the riser, that is to say, the solidification is carried out at the place far away from the riser, then near the riser, and finally at the riser. It is the key point of the feeding and feeding process. The core point of equilibrium solidification theory is finite feeding, that is, in the process of solidification and cooling of iron castings, the shrinkage, feeding and expansion in unit time are carried out in proportion to achieve the self feeding effect of dynamic superposition of expansion and shrinkage. The main points of the technology are that the feeding riser considers the comprehensive effect of many factors (size, structure, alloy composition, casting process scheme and pouring temperature); on the basis of self feeding, the riser makes up for the deficiency of self feeding, and the feeding effect is limited; the smaller the part, the higher the feeding requirement.

The feeding technology based on different feeding theories mainly includes large riser technology, direct practical riser technology and non riser technology.

The large riser technology is the concrete embodiment of the sequential solidification theory to guide the riser process design of cylinder block iron castings, and the requirements for iron castings and casting conditions are not high. However, considering the extreme situation, the riser design of large riser is generally too large because it does not make use of the self feeding characteristics of the casting itself. Moreover, the rate of defective iron castings is high, and the cleaning work in the later stage is complicated. Direct practical riser technology belongs to small riser technology. The technological principle is that when the casting is in the liquid shrinkage stage, the riser feeding; when the liquid metal shrinkage ends or the volume expansion begins, the riser neck freezes, and through the eutectic expansion of the cast iron, the internal pressure is formed in the high-strength cavity, forcing the liquid metal to flow to the defects, so as to prevent the defects caused by vacuum in the solidification stage between the cast irons. The principle of riser free process is to use the post filling function in the pouring process. After pouring, the difference between the cooling and solidification shrinkage of the cast iron is compensated by the short-term smooth gate system and the volume expansion caused by graphite precipitation during the solidification process of molten metal. In the riser process design, there is no special riser, but it does not mean that the iron castings do not need feeding. The application requirements of riser free process are high carbon equivalent of liquid metal, strong graphitization tendency, low temperature rapid casting process and safety riser.