Every iron casting starts long before the metal hits the mold. The gating system, the network of channels that carries molten iron from the ladle into the cavity, decides whether you get a sound part or scrap full of slag, sand, and gas. Anatomy of a gating system: - Pouring basin: absorbs the ladle stream’s turbulence and keeps the sprue full - Sprue: the vertical channel, tapered narrower toward the bottom - Sprue well: a cushion at the base that reduces splash and erosion - Runner: the horizontal channel that distributes metal and traps slag - Ingates: the final openings into the casting cavity - Risers: reservoirs that feed shrinkage as the metal solidifies Why the sprue tapers: Falling metal accelerates, roughly v = sqrt(2gh). By continuity (A1v1 = A2v2), a faster stream needs a smaller cross section. A straight sprue lets the stream pull away from the walls, which creates low pressure that pulls air and sand into the metal. The taper keeps the channel full. Pressurized vs unpr...