Introduction
In metal casting, a kind of common hidden defect is air pores. If air pores are not eliminated or properly treated in the casting process, they will cause quality problems such as casting cracks, air leakage, surface defects and reduced strength of castings.
Types Of Air Pore
Air pores can be divided into three categories: surface air pores, intergranular air pores and internal air pores. Surface air pores form due to the defoaming of the molding sand, and are the most easily detected by visual inspection. Internal air pores are formed when air enters the solidifying castings, and are the most difficult to identify. Intergranular air pores form between the particles of the material and often penetrate the material.
Causes Of Air Pore
1) Process causes: the molten iron has too shallow pouring system, the pouring temperature is too low, the cooling time can not be guaranteed, the molding sand is too wet and porous, the draw of the core has too small injection distance and the height is too high.
2) Material causes: the fluidity of the molten iron is insufficient, the carbon content is too high, the element content is not balanced; the preparation of the molding sand is not standardized, the atmosphere is too moist, and the molding sand is uneven.
3) Craftsmanship caused by the personnel: inadequate cleaning of the molten iron, improper pouring speed and pouring temperature, non-standard core installation and sand compaction.
Prevention Of Air Pore
1) Process control: Scientific formulas are formulated for the molten iron, pouring system optimization design by CFD calculation is used to set the pouring temperature, pouring speed and cooling time, and the molding sand is properly compacted.
2) Optimization of materials: Optimization of material mixture ratio, appropriate increase of pouring temperature, moderate decrease of carbon content, timely adjustment of element content balance, standardization of molding sand preparation, anti-humidity and anti-moisture measures of sand, uniform distribution of particle size, etc.
3) Strengthen process management: Training the personnel and comprehensive knowledge of the quality requirements of the casting products, timely maintenance of the equipment, precise closure of the pouring molds, regular inspection of the sand compactness, etc.
Conclusion
To ensure the quality of the castings, attention should be paid to the prevention of air pores and the elimination of other defects in the casting process. Through the improvement of the formulation, process, materials and craftsmanship, the quality of the castings can be improved.
