Ali kheirabi - MSC student of Engineering and High-Tech., Iran University of Industries and Mines (IUIM), Tehran, Iran
Morteza Tamizi far - Faculty of Engineering and High-Tech., Iran University of Industries and Mines (IUIM), Tehran
Amir Baghani - MSC, Razi Metallurgical Research Center (RMRC), Tehran
Ahmad Bahmani - MSC, Razi Metallurgical Research Center (RMRC), Tehran, Iran

During the mold filling process, surface turbulence cause the entrainment of oxide films into the bulk liquid which are detrimental to the cast integrity. For avoiding these defects, non-pressurized and bottomgating systems are strongly recommended for reducing the surface velocity of the liquid metal entering into the mold cavity at the early stages of mold filling. In spite of using mentioned gating system in casting process, exceeding surface velocity from the critical value has been observed at the mold entrance.In this study numerical simulation was used to analyze mold filling and distribution of velocity in differentportions of gating system thoroughly, in order to evaluate why surface turbulence was observed even innon-pressurized and bottom-gating systems. It has been concluded that by formation of dead zones and vortex flows in runner's tail, the new entered liquid will push to the ingate and then cavity with a higher velocity. Therefore, it was proved that runner's tail play an important role in making a chaotic regime andunexpected flow pattern in the ingate. This means that, design based on conventional gating system ratio is not valid enough to avoid surface turbulence

gravity casting, surface turbulence, gating system, numerical simulation, velocity distribution, vortex flow