Disappearance Defects and Prevention of Cold Shut and Inadequate Pouring
Introduction
Defects related to the cold-shut and inadequate molds pouring process account for a major of casting component defects. High quality castings require precision and maintenance free from any defects. For that purpose, it is important to understand and prevent these defects before they occur.
Disappearance Defect
A disappearance defect results from the leakage of the hot molten metal in the mold causing it to solidify before the mold is completely filled. This defect causes the metal to be incompletely filled leaving a void in the casting and can cause problems like a decrease in mechanical strength and an increased chance of failure. This defect is primarily caused in either component fabrication or component design phase and can be classified in to two main categories:
1. Cold shut: Cold shut occurs when there is a sudden decrease in the flow amount of molten metal and subsequent solidification of the same. This usually occurs when the flow of molten metal stops at the same location and from the same direction multiple times.
2. Inadequate pouring: This occurs when the molten metal does not completely fill the mold or does not reach certain points in the mold or component. This may cause shrinkage or pitting on those areas.
Prevention of Cold Shut and Inadequate Pouring
1. Adjustments in gating and risering designs: Adjustment in gating and risering designs can help to maintain a consistent flow of molten metal in to the mold and help to prevent cold shuts. Increasing the liquid melt pressure can also help maintain a steady flow and fill the mold completely.
2. Sufficient time for solidifying: During the filling process, it is important to provide enough time for the combination of solidifying and cooling of the metal in the mold. This will ensure that the metal doesnt solidify before the mold is completely filled.
3. Proper rising: During metal casting process, the molten metal tends to be channeled via the risers which act as holding tanks to maintain metal pressure and flow. If a proper risering design is not implemented, inadequate metal supply and leakages in the mold can lead to formation of cold shuts and inadequate pouring.
4. Timely pouring: It is important to ensure timely pouring of the molten metal in to the mold and ensure that the metal is adequately filled before it begins to solidify.
5. Fluxing: Fluxing is a process used to remove impurities from molten metal and reduce the surface tension of the fluid stream. This helps in avoiding surface irregularities and channeling of molten metal at the time of pouring to ensure smooth flow.
Conclusion
Defects caused due to cold-shut and inadequate pouring process are a major problem in the field of metal casting process. It is important to understand the various aspects of preventing these defects and designing the components or the molds accordingly for avoiding the defects. By following proper gating and risering design along with timely pouring and fluxing, it is possible to prevent cold shut and inadequate pouring defects to a great extent.
