A well-designed gating system is a perquisite for achieving perfect casting. The key objective of a gating system is to ensure smooth and complete flow of molten metal from ladle to the casting cavity.
Elements of gating system
The main components include pouring basin, sprue, well, runner and ingate. Gating systems can be classified based on the position of the parting plane and also on the basis of ingate position as follows, i) Horizontal systems- Suitable for flat castings filled under gravity and commonly used in sand casting of ferrous metals and gravity die casting of non-ferrous metals. ii) Vertical systems- Suitable for tall castings and used in high pressure sand and shell mold and die casting processes. iii) Top gating systems- wherein the molten metal enters at the top of the casting promoting directional solidification from bottom to top of the casting. iv) Bottom gating systems- wherein the molten metal enters from the bottom and fills the mold slowly with minimal v) Middle gating systems- these combine the features of top and bottom systems.disturbances.
The number and position of ingate(s) is very important in designing the gating systems. The diagram given below describes the different considerations in the channel layout in horizontal gating system with side ingates.
Heuristics for ingate location
i) Side feeders- - When side feeders are used their efficiency can be improved by filling the first stream of hot molten metal through ingates, thereby reducing the fettling effort and subsequent marks on the casting.
ii) Thick sections - This allows molten metal to flow to other sections with minimal cooling reducing breakage during fettling of ingates.
ii) Tiii) Clear path - In case of sand casting it is essential to allow the metal to flow with minimal obstructions or direction changes to curb turbulence. In such systems ingates should never be placed opposite to a core.
iv) Low free fall - here the...