Chapters are placed between mould and core surfaces in order to :

Gating ratio of $$1:2:4$$ is used to design the gating system for magnesium alloy casting. This gating ratio refers to the cross section areas of the various gating elements as given below

$$1.$$ $$Down$$ $$sprue$$ $$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,$$ $$2.$$ $$runner$$ $$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,$$ $$3.$$ $$Ingates$$
The sequence of the above elements in the ratio $$1:2:4$$ is

A casting of size $$100\,\,mm \times 100\,\,mm \times 50\,\,mm$$ is required. Assume volume shrinkage of casting $$2.6\% $$. If the height of the riser is $$80$$ $$mm$$ and riser volume desired is $$4$$ times the shrinkage in casting, what is the appropriate riser diameter in $$mm?$$