The flow rate W is defined as the metal weight passing through the cross-sectional area of the gating system within a certain time T. for the mold cavity, it can be calculated by dividing the casting weight g by the total metal filling time t, that is:
The flow rate w can also be described as the velocity of the molten metal passing through the gate, multiplied by the cross-sectional area F of the gate, and then multiplied by the density of the metal
By combining the above two formulas, we can get the following results:
Replace the previous velocity formula with,
Thus, the calculation formula of runner section f is derived, in which the weight g is the weight of all metal flowing through the calculated section f in the whole pouring process.
The pouring time t should be less than the molding cycle time, otherwise the production line efficiency will be affected. The molding cycle time includes mold rest time and mold conveying time, the latter is 1-2s, so it is difficult to pour during mold movement. T only represents the pouring time into the casting cavity, and the maximum allowable pouring time formula is as follows:
B depends on the thickness of the thinnest arm of the casting and the corresponding modulus. By substituting the density of molten iron ρ and gravity acceleration g into the above formula, the calculation formula of cross-sectional area f is obtained as follows:
Similar to other fluids, the flow state of molten metal in runner can be divided into three situations, as shown in Fig. 3.5. Laminar flow is the stratified flow of fluid particles, no material flows in the direction perpendicular to the layer; turbulence is the random flow of fluid particles in each layer; non turbulence is the flow mode of fluid particles between laminar flow and turbulence. A good gating system should avoid the metal liquid flowing in the form of turbulence, because the turbulence will destroy the metal shell of the contact surface between the metal and the mold, increase the slag / oxide content, gas content, sand content and metal penetration
In order to determine which way molten metal flows in the runner, Reynolds number Re is introduced
V is the actual velocity of metal in the gating system, D is the hydraulic diameter of the channel, ρ is the density of the metal, μ is the dynamic viscosity of the metal. R is dimensionless, so the formula can also be written as:
