Lost foam casting technology has the advantages of wide application range, accurate size and shape of lost foam casting, smooth surface, convenient mechanized production, low production cost, free design, high production efficiency, clean production, green casting and so on. In recent years, with the deepening of the research on the principle and theory of lost foam casting by relevant scientific research institutes, the development momentum of lost foam casting industry in China is rapid. According to incomplete statistics, at present, there are more than 100 scientific research institutes engaged in lost foam casting technology research in China, and there are more than 2000 lost foam casting enterprises, with an annual output of more than 3 million tons of lost foam castings, which is still increasing. However, in order to save costs, some lost foam casting enterprises use self-made lost foam casting coatings. Because they do not pay attention to the best ratio of coating formula, the properties of lost foam casting coatings are greatly reduced. The problems of carbon deposition and wrinkle in the production of iron castings by lost foam casting technology have not been effectively solved for a long time, resulting in low yield and high cost of iron castings, which limits the rapid development of China’s lost foam casting industry. It is mainly due to the improper selection of refractory aggregate for lost foam casting coating and poor high-temperature air permeability of coating.
(1) In the lost foam casting coating with this formula, the most significant factor affecting the 24-h suspension rate and conditional viscosity of the coating is kaolin; the most significant factor affecting the coating strength is wollastonite, and the most significant factor affecting the gas evolution of the coating is talc powder. The main reason is that talc powder is a layered magnesium silicate hydrate with crystal water in its molecular structure, which is 600 ~ 900 during pouring The crystalline water is lost within the temperature range of ℃, resulting in a large amount of water vapor, which increases the gas evolution of the coating.
(2) The optimum formula of water-based lost foam casting coating for cast iron is: Bauxite 100, kaolin 40, wollastonite 20, talc powder 10, silica sol 4, PVA 1, sepiolite 4, cmc0.5, sodium dodecylbenzene sulfonate 0.1, n-octanol 0.1, Fe2O3 0.5 and appropriate amount of water.
(3) Through production test verification, it is found that the prepared water-based lost foam casting coating for cast iron has good coating performance, the surface of formed castings is smooth, and there are no lost foam casting defects such as sand sticking, porosity, carbon deposition and wrinkle skin. When lost foam castings are cleaned, most of the surface coatings of castings can collapse freely, and only a few hot spot coatings need to be gently knocked with a hammer to complete The block peels off and the coating has good overall collapsibility. It can meet the actual production needs and has excellent performance.
Therefore, bauxite is selected as the main refractory aggregate, kaolin, wollastonite and talc powder as auxiliary refractory aggregate, and the effects of kaolin, wollastonite and talc powder on the properties of water-based lost foam casting coating for cast iron are preliminarily studied. Finally, a water-based lost foam casting coating for cast iron with low cost and good process performance is developed.