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Precautions for brushing lost foam coatings

2023-10-17

The lost foam coating should be applied on the surface of the lost foam, and the traditional sand casting coating should be applied on the prepared casting surface. The coating methods are very different, and the technical standards are also different. There are many ways to apply foam coatings, such as brushing, dipping, showering, spraying, or dipping. Generally speaking, the appearance roughness and dimensional accuracy of lost foam castings depend on the quality of the castings, and the thickness of the coating does not affect the castings specifications. The rough coating layer not only does not affect the surface roughness of the casting but is also beneficial for improving the air permeability.

The brushing method is done by hand with a brush. The performance requirements of this method are not as strict as that of coating or impregnation, but the requirements for the operator's skills and experience are higher. When brushed, the thickness uniformity of the paint is not as good as spraying or dipping, but the effect is quite satisfactory. For lost foam casting equipment with complex structures and shapes, it is best to choose brushing. Because when painting, some "blind areas" are often not sprayed; and dipping is often difficult to discharge the deposited paint in some grooves.

The main disadvantages of painting are its high labor intensity and low production efficiency. It is only suitable for repairing operations or when the volume is large, and it cannot be soaked or sprayed to complete single-piece production.

Knowledge expansion:

The role of the lost foam coating is to support and maintain the foam model, prevent liquid metal from entering the sand and sticky sand, absorb the split goods, make the split gas pass through the coating to keep the foam model from evaporating, and keep the heat of the liquid metal from releasing quickly. Therefore, the use of lost foam coatings can reduce the accuracy of the surface roughness of castings. Reduce or prevent defects such as sand sticking, sand holes, pores, metal infiltration, cold protection, non-pouring, and carbon deposits in castings.

The modeling material commonly used in lost foam coatings is generally dry quartz sand. When the foam pattern is replaced by liquid metal, a large amount of gas generated by thermal splitting of high-quality carbon steel castings can be discharged through the open space between the dry sand for forging. However, the liquid metal easily enters the open space between the dry sand under the influence of negative pressure, resulting in mechanical sand sticking. In order to prevent mechanical sand sticking, the exterior of the fading model is coated with refractory paint.

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