SAND CASTING EQUIPMENT.

Inclusions in castings mainly affect the fatigue strength, processing performance, and microstructure properties of castings, and are also one of the reasons for casting cracks.
A certain number of microscopic inclusions inevitably exist in castings, and the general number is within the range of 10 to the 7th power and 10 to the 7th power. Too many inclusions affect the quality of castings and cause casting defects, but controlling them within a certain range is conducive to solidification, crystallization and nucleation of the castings. What our casting workers should do is to control their number within the range we need to make Just enrich our production.
During the casting process, the sources of inclusions are mainly endogenous and exogenous sources. The endogenous inclusions come from:
1. Degassing and desulfurization products, especially some high-density deoxidation products, were not removed in time.
2. As the alloy temperature decreases, the solubility of elements such as sulfur, oxygen, and nitrogen decreases correspondingly, and reaches supersaturation. These supersaturated precipitated components remain in the casting in the form of low-melting eutectic or compound. The type and composition of endogenous inclusions depend on the smelting process and alloy composition of the alloy.
1. Degassing and desulfurization products, especially some high-density deoxidation products, were not removed in time.
2. As the temperature of the alloy decreases, the solubility of elements such as sulfur, oxygen, and nitrogen decreases correspondingly and reaches supersaturation. These supersaturated precipitated components remain in the casting in the form of low-melting eutectic or compound. The type and composition of endogenous inclusions depend on the smelting process and alloy composition of the alloy.
The exogenous inclusions come from:
1. Sticky sand, rust, slag on the surface of alloy liquid and metal material, as well as non-metallic inclusions generated by the interaction with furnace lining, cladding lining, etc.
2. The alloy liquid is oxidized by the atmosphere to produce oxides. The foreign inclusions are mostly oxides with complex composition, their size is large, the shape is mostly polygonal, and the distribution is irregular.
The impact of non-metallic inclusions on the quality of castings: First, it affects mechanical properties such as impact absorption and fatigue limit. Oxidized inclusions in inclusions have a great influence on the impact absorption energy of steel castings. Inclusions will reduce the fatigue strength limit of the material. The larger the inclusions, the lower the fatigue limit of the material. Inclusions are often the source of cracks in part fracture. Sharp-angled inclusions cause stress concentration and accelerate the destruction of parts. The second is to affect the casting performance. When the alloy contains solid inclusions, its fluidity decreases. The low melting point inclusions distributed on the grain boundaries are one of the reasons for the cracks in the castings. Low melting point inclusions can also promote microscopic shrinkage and porosity in castings.

The beneficial effect of inclusions on castings: In some cases, non-metallic formamides have a good effect on the quality of castings. For example, the oxides and sulfides in steel and the phosphorus eutectic in cast iron can increase the hardness of the material and increase the wear resistance. Some refractory non-metallic inclusions can become the core of non-spontaneous crystallization and refine the structure of the casting.

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