The calculation of flow velocity at specific position of gating system is based on Torricelli formula of ideal free falling object
Where V is the velocity of the object after free falling from the height h, and G is the acceleration of gravity. In practice, when the object falls freely, there will be a certain loss of velocity, so it needs to be corrected by the loss factor M.
The value of M is from 0 to 1, which describes the overall effect of metal velocity reduction in gating system. The main factors affecting the loss factor are the change of metal flow energy and metal flow rate. When the shape of runner or casting is very complex, the metal flow energy decreases, and the value of M decreases.
The metal static height h is defined as the height from the upper surface of the metal surface in the gate cup to the pressurized section, which is related to the position of the gate in the cavity. Generally, the three main gate locations are top gate, bottom gate and side gate . Figure 1 shows the calculation method of internal metal pressure corresponding to three different gate positions. The average metal static pressure height of the top gate is the vertical distance from the metal surface in the gate cup to the gate. The average metal static pressure height of the bottom gate under pressure is slightly more complicated. At the beginning of pouring, the metal static pressure height at the inner gate is a, and at the end of pouring, the metal static pressure height of the casting is C Therefore, in the whole pouring process, the average static pressure height of the gating system is between these two values. For convenience, the average static pressure height of this type of gate is calculated as the distance between the metal level of the gate cup and the gate minus half of the casting height
From the beginning of pouring to the metal level in the cavity to the height of the gate, the static pressure of the inner gate is 0 a. In this stage, the top pouring method is actually adopted. When the metal level in the cavity is higher than that of the inner gate, the remaining pouring process can be regarded as the bottom pouring mode. At the end of pouring, the static pressure height of the inner gate is a – b. For convenience, the average metal static pressure height of the gate in such side gating system is the distance between the metal level of the gate cup and the inner gate minus half of the distance between the inner gate and the upper end of the casting