Wet Sand Casting Defects
Wet sand casting is a casting process that involves using a very wet sand mold to cast metal parts. This method of casting is used to produce a variety of objects in different shapes, sizes, and materials. It is one of the oldest known forming processes and is still in use today for many applications.
The wet sand casting process involves filling a sand mold with a liquid metal. This liquid metal is heated until it becomes a liquid and is poured into the sand mold. The liquid metal cools and solidifies in the mold and the mold is then broken away and the casting is removed. The casting is then machined, finished and assembled as necessary. The casting is then ready for its specific application.
The wet sand castings produced by this process can be of exceptional quality, but there are certain problems that can arise. These problems, or defects, can occur due to variables that involve both the process used in production and the materials used.
The most common defect seen in wet sand castings is porosity. Porosity occurs when trapped air or gases within the casting become trapped in the solidified metal during cooling. These gases expand upon cooling and create bubbles and pockets within the metal. The larger these bubbles and pockets are, the more likely the casting can fail or break under load or stress.
Another common defect associated with wet sand casting is gas porosity. Gas porosity is a defect that occurs when gas bubbles or pockets form within the casting. These gas bubbles and pockets can significantly weaken the castings because they reduce the strength of the metal in that area. This can be caused by air or gases coming from the process of casting itself. Other causes include air or gases coming from the mold material itself, or from other materials used in the process.
Mold distress can also be a problem in wet sand castings. This occurs when the sand mold is not properly constructed or is over packed. This will cause the mold to deform leading to thin walls, sharp edges and will cause a poor surface finish in the finished cast product. It can also cause part of the piece to separate from the main body causing more defects and an uneven surface.
In wet sand castings, shrinkage defects can also occur. Shrinkage can occur when there is not enough liquid metal to fill the entire mold. As the metal cools and solidifies, a void is left in the shape of the parts that was not filled by the liquid metal. This defect can be avoided by making sure there is enough liquid metal in the mold to fill it completely.
Wet sand castings can have a variety of other defects as well. These may include but are not limited to; sand inclusions, oxide inclusions, non-fill areas, misruns, cold shuts, and many more. Each of these defects can have different causes and solutions depending on the material used and the process employed.
Remedies and prevention methods are available to reduce or eliminate defects in wet sand casting processes. Quality control procedures should be in place to inspect both incoming raw material and the finished parts. Having a good understanding of the material and process being used is essential in predicting and avoiding defects before they occur. Process variables such as pouring temperature, sand grain size and compaction pressure need to be monitored and adjusted accordingly to ensure good casting results. In addition, to prevent corrosion and other damages of the castings, coatings and proper storage conditions should be employed.
In conclusion, sand casting is very versatile and cost effective method of forming materials into the desired shapes and sizes. With careful and consistent quality control of both the process parameters and the raw materials, high quality castings can be consistently achieved.
