This week let us understand what a core is in the casting process. A core is defined as a metal or sand insert that is used to shape any casting part that cannot be shaped by the main pattern which is removable. A pattern once sand-pressed and then extracted, the impression it leaves should be concave. Cores allow for more complexity in the design. With perfect cores, the foundry can produce chambers or holes in the casting. Automotive moulds may contain up to five cores in them to make the chambers required for the combustion engine to work.
Cores can also help produce angles that ideally would not be possible using a pattern. Any overhang above an empty space would make it quite difficult to withdraw the pattern without disrupting the overhang. In such cases, a core may be used. Castings that are utilizing cores generally contain some opening in the moulding’s outer shell to take out the core after the process of casting, although this opening may be mechanically plugged during finishing.
Cores produced of sand are constructed to break down; internal cores are generally shaken out of the casting at the completion of the process. The placement of the core is facilitated by the “shakeout” opening. The place or point that the core comes into contact with the mould is where molten metal cease to flow; therefore, to obtain a metal’s consistent thickness a core should “bridge” the space that required to be filled without getting into contact with the sides.
For the foundry to achieve this, the casting usually is no longer than the core and fixed in place through divots in the sand outside of the casting pattern.