Source of Flange Casting Porosity and Improvement Measures

Flange castings are thin-walled gray iron castings. The production process is: resin sand boxless molding, the sand core adopts two processes: cold core box core making and coated sand hot core box core making. Water-based paint is applied to the sand mold as a whole. After drying in the drying tunnel, the intermediate frequency electric furnace smelts. Casting defects in this process are mainly pores, which will cause product defects, form waste products, and affect the production efficiency and yield rate of the product. The sources of pores are:

1. The sand core has a large amount of gas
The inner cavities of the castings are all formed by sand cores. Due to the thin wall and complex shape, high-strength coated sand is used, which produces a particularly large amount of gas.

2. sand type has a large amount of gas
The casting cavity has a deep depth. After the drying process of the drying tunnel, the bottom of the cavity cannot be completely dried, and a large amount of gas is easily generated during pouring. Also, resin sand inevitably generates a large amount of gas.

3. sand mold exhaust is not smooth
The exhaust area of the sand mold is small. If the exhaust cross-sectional area of the flange ring is excessively enlarged, it is easy to cause a lack of meat in the casting.

Improved process measures are taken:

1. Reduce the air volume of the sand core of the cold box
By adjusting the ratio of the resin components of the cold box sand core to ensure that the tensile strength of the sand core is ≥1MPa, the component ratio is adjusted to reduce the amount of gas generation.

2, reduce the amount of gas generated by sand
Because the upper cylindrical core and the inner cavity oil passage core use coated sand. Under the premise of ensuring the basic strength to meet the requirements of sand core circulation and use, the development of coated sand with low air volume, the air volume is about 12g/ml.

3. Change the method of sanding
The sand-type paint brushing method is changed from the overall spraying water-based paint to the whole spraying water-based paint and the partial manual brushing alcohol-based paint. When painting by hand, apply alcohol-based paint and ignite it with fire in time after the paint is applied to ensure the drying of the two deep holes, reduce the amount of air generated by the sand mold, and reduce the occurrence of pore defects.