Abstract
The inclusion is one of the common casting defects in metal casting process, the most typical form is nodule. The presence of the shrinkage cavity in the industrial casting production process, which lead to inclusion defects. This article will discuss the common sources of nodule caused by shrinkage, and various prevention methods used in the industrial process in order to reduce the number of inclusions, or even eliminate the possibility of their appearance.
Introduction
Nodule is a casting defect which has been encountered in industrial casting production. It is a lump or truncated cone shape and it may have rough surface with various sizes. It is caused by the presence of the shrinkage cavity when the molten metal solidify during the process and the gas and ash that are not completely discharged. The inclusion of nodule affects the quality of the casting and can potentially reduce the strength of the casting; moreover, if it caused by a certain degree of mechanical strength fracture, it’s also dangerous to the life and health of the personnel and maishance. Therefore, the control and prevention of nodule is of great significance for the production and use of casting.
The Common Sources of Nodule
1. Operating Environment: According to the industrial production, the more the environment contaminants, the higher the possibility of generating shrinkage cavity and nodule.When welding on the casting surface, burning and welding spatter can cause shrinkage cavity and nodule. Gas oil, diesel and other pollution sources, plastic bag or PVC in the air, near the casting, etc., also may cause shrinkage cavity and nodule.
2. Poor Pourability: Good pourability is essential for the good quality of the castings. Poor pourability may impede the escape of gas and ash, resulting in shrinkage cavity and nodule.
3. Casting Mold Temperature: Insufficient casting mold temperature may also lead to shrinkage cavity and nodule.
4. Sand System: The quality of sand, sand additives and sand properties will directly affect the air permeability of the sand mold and its own structure, improper sand or improper casting system, insufficient tightness or air permeability of the sand mold, with the chill or secondary cooling shrinkage cavity and nodule.
5. Metal Alloy Composition: If the content of inclusions in the metal is higher, due to the low melting point of the inclusions, it tends to form shrinkage cavity and nodule when the molten metal solidifies in the casting process.
Various prevention methods used in the industrial process
1. Operating Environment: Strictly implement environmental treatment requirements, to control the welding, burning, welding and other production processes. Prevent the polluted air and other objects from reaching the mold.
2. Casting Mold Temperature: Improve the baking process of the cope and drag, accelerate the speed of warm up and casting and improve the casting mold temperature.
3. Sanding System: Optimize sanding system measures, improve compaction densities of sand,reduce the size of sand particles, improve the tightness and air permeability of the sand mold, reduce the air escape channel and form a good core frame.
4. Metal Alloy Composition: Adjust the content of alloying elements and inclusions in molten metal to meet the requirements for casting at can reduce the risk of shrinkage cavity and nodule.
Conclusion
In conclusion, various sources of nodule caused by shrinkage and various prevention methods used in industrial process in order to reduce the number of inclusions, or even eliminate the possibility of their appearance must be taken into serious consideration. Adopting these preventive measures would enable the industry to produce better quality castings, free of nodules and accompanied with improved mechanical properties.
