Surface Roughness Defects in Casting Process and Solutions
Casting process is widely used in manufacturing industry for producing metal parts, which contributes to over 40% of the turning manufactured metal. Casting process is characterized by forming shapes by pouring melted metal in a mold. The metal is hardened by cooling and the mold is removed from the casting product when it is solidified. Besides, casting process can be tailored to create complex shapes. As the process occurs at extremely high temperatures, imperfections can occur on the surface of the casting product. Such surface roughness defects can reduce the strength or performance of the metal parts. The common surface roughness defects in the casting process and the solutions to mitigate such defects are discussed in this article.
The most common surface roughness defect in the casting process is shrinkage. Shrinkage occurs when the metal filled in the mold cools down and begins to shrink as the metal solidifies. This shrinkage may occur in certain areas of the metal due to uneven cooling and solidification rate, resulting in the formation of small pockets or cavities in the finished product. In addition, shrinkage can also occur when the molten metal is overfilled into the mold and then solidifies. To address the shrinkage issue, the mold design should be optimized for efficient cooling and heat transfer. In addition, the control of pouring temperatures should be maintained to promote uniform contraction during the solidification process.
Another common surface roughness defect in the casting process is porosity. Porosity is caused when air enters the mold during the pouring process and forms small air bubbles. The air bubbles will form cavities in the casting product once the metal is solidified. To reduce this, it is important to use defects-free molds and ensure that molds are properly closed before pouring the molten metal. Another solution is to use a vacuum or a protective atmosphere to remove all the air from the mold.
Gas porosity is another common type of porosity which is usually caused by the presence of gases inside the mold and results in the formation of pores and voids in the finished product. Common gases associated with gas porosity are hydrogen and oxygen, which are introduced when melting the metal or when non-filtered water is used as a quenching agent. To reduce gas porosity, it is important to use high purity metal, use filters when melting the metal, and use clean water for cooling the metal.
In addition to the mentioned surface roughness defects, other defects such as hot tears and veining are also common in the casting process. Hot tears refer to the fissures on the metal surface due to metal contraction during the cooling process, while veining refers to the formation of veins or lines which are formed when the metal flows unevenly during pouring. To reduce the risk of these defects, it is important to use higher quality metal and regulate pouring speed during the pouring process.
To conclude, casting process is widely used in the metal manufacturing industry and it is well-known that defects may occur on the casting surface. Shrinkage, porosity, gas porosity, hot tears, and veining are the common surface roughness defects that may limit the performance of the casting products. To reduce the risk of such defects, it is important to optimize the mold design, maintain pouring temperatures, ensure defect-free molds, use filters when melting the metal and use clean water for cooling the metal.
