Suspension control of casting coatings

Suspensibility refers to the ability of coating to resist stratification and precipitation of solid refractory powder. On the premise of ensuring other properties, the higher the suspensibility, the better. Good suspension, uniform coating, no flow, simple operation, easy drying, high strength and no cracking after drying. There are many factors that affect the suspensibility of coatings, such as carrier, aggregate, suspending agent, binder and various additives. The influence of coating components on the suspensibility belongs to static control. The field adjustment is dynamic control. There are three main factors that affect the suspensibility of the coating during use

(1) Control the amount of carrier to ensure that the density meets the process requirements, so as to avoid too low powder, the polymer adsorbed on the particle surface can not overlap with other particles to form a network structure, resulting in poor suspension of the coating;

(2) It should be avoided that the material level in the trough is too low, and the material liquid composition is not uniform due to too large drop in the circulation process;

(3) The equipment control should be strengthened, the material tank should be cleaned regularly according to the process requirements, and the new coating should be replaced to keep the material liquid composition in the tank uniform.

In 2019, in the process of dipping the side core of 35K cylinder block, due to the air leakage of circulating pump and the blockage of intake and exhaust pipes, the coating composition in the whole material tank is uneven, the concentration of the upper part of the liquid level is low, the density is difficult to meet the process requirements, the coating thickness is too thin, and many bubbles of different sizes gather on the liquid level, leaving traces of bubble burst after drying, It leads to many point defects on the corresponding parts of the cylinder block (as shown in the figure). On the contrary, when the concentration at the bottom of the coating tank is too high, the coating will accumulate in the water jacket core and the sand core of the cylinder hole. It can be seen from this case that the selection of coatings with good suspension property is only static control, on the one hand, and on the other hand, it also needs on-site dynamic control. Only by organically combining the two, can the material liquid in the tank be uniform and stable during the use of coatings. It is necessary to check the coating pump and clean the air inlet and exhaust pipes regularly to ensure that the coating is in good circulation in the production process, which is the basis of dynamic control of suspension.

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