The sand casting process of metal casting is used for over 70% of all metal castings. There are many reasons why the sand casting process is the most commonly used: most notably for its cost, freedom of design capabilities, and lead times.
Within the sand casting process, there are two different methods. The first is the Green Sand casting process, and the other is the Air Set casting process.
Green Sand casting does not mean that the sand used is green, but rather it is a wet sand mixture. Once the sand is compacted on the pattern, it is able to hold its shape due to its unique mixture. At this point, the casting is almost ready for pouring as soon as the cores are in place.
The Air Set casting process uses dry sand, rather than wet sand, and is bonded with materials other than clay. This method also uses an adhesive that is fast curing.
Each method’s accuracy depends on the type of sand and the molding process. An easy way to identify coarse green sand is that it causes a rough surface texture.
Castings made from fine green sand can shine as cast, but the depth to width ratio of pockets in the pattern can cause limitations.
If a smoother surface is needed than coarse green sand, air-set molds can produce castings that are smoother. Air-set castings can typically be identified by the burnt color on the surface, and are primarily chosen when deep narrow pockets in the pattern are necessary.