Factors leading to mechanical sand sticking of castings

The factors that lead to the mechanical sand sticking of castings are: 1. The particle size of the molding sand and core sand is too coarse, the mud content and ash content of the molding sand are too low, the gap between the mold (sand core) is large, and the metal penetration resistance is small.
The factors that cause mechanical sand sticking of castings are:

1. The particle size of the molding sand and core sand is too coarse, the mud content and ash content of the molding sand are too low, the gap of the mold (sand core) is large, and the metal penetration resistance is small. The particle size of the workshop molding sand is 50/100 or 100/50, and the average fineness is between 50 and 57. The particle size of the coated sand is 50/100 or 100/50, and the average fineness is between 49 and 55. The original sand is thicker than the original sand used in the general wet molding process, and the air permeability of the molding sand is between 130 and 170. However, the mud content and ash content of the molding sand are too low, and the gap of the molding sand cannot be filled, which will also affect the gap of the molding sand. At the same time, in addition to the production of clutch housings, the workshop also produces cylinder blocks and cylinder heads. The performance of molding sand is affected by product conversion.

2. The compactness of sand mold and sand core is low or uneven, and local looseness. The molding mold is complex, and the pits and corners are not easy to be compacted; improper selection of molding equipment parameters, low molding pressure; poor sand fluidity, difficult to fill and other factors may cause the sand mold to be low in compactness. The low compactness of the sand core may be caused by the poor exhaust effect of the core box and the low sand injection pressure during the core making process.

3. The coating quality of the mold and core is poor, the coating thickness is uneven, and the coating peels off. The sand mold in the workshop is sprayed with alcohol-based paint. Because the upper mold is close to the parting surface and the sand mold has low compactness, it is easy to cause sand collapse after spraying and drying. Therefore, in the original process, the upper mold is less sprayed and the parts that are prone to sand collapse are not sprayed. The sand core is composed of 1# and 2# sand cores. During the core making process, the 1# sand core is brushed with water-based paint as a whole, and the 2# is partially brushed. The sand core is used to preheat and dry the paint. The process of spraying and brushing It is possible that the operation is not in place, resulting in missed coating and sand sticking.

4. The pouring temperature is high, the fluidity is good, the surface tension is low, and the metal hydrodynamic pressure is large. Due to the thin-walled parts of the shell casting, the wall thickness of the thinnest part is 8mm. In order to avoid cold insulation waste in castings, the pouring temperature is higher in the original process.

5. The content of pulverized coal in the molding sand is low, and the quality of pulverized coal is poor. The most important molding sand addition for wet casting to prevent sand sticking and improve the surface finish of castings is pulverized coal. The quality of pulverized coal affects the sand resistance of molding sand. The effective pulverized coal content of workshop molding sand is between 3.5% and 4%. The air volume of molding sand is between 17~20ml/g.

6. The height of the upper box or the pouring cup is too high, and the hydrostatic pressure of the metal is large; the pouring system and the riser are not set properly, which will cause the local overheating of the mold and castings and cause sand sticking.

The factors that lead to the explosion and sticking of the casting sand include high mud content and high moisture content in the molding sand; high pulverized coal content and large gas generation; poor ventilation conditions of the sand mold; too fast pouring speed; , the gas generation of the sand core is larger than that of the resin sand core, and at the same time, the curing degree of the sand core affects its gas generation; in addition, the gas generation of the coating on the surface of the sand core is also larger, and the sand core is too hot. The core is cracked, so it needs to be brushed after the sand core is properly cooled, and the coating cannot be guaranteed to dry.

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