Meaning
Division of a single liquid stream into separate channels during transport allows for the distribution of materials to multiple delivery points. This fluid bifurcation is a common feature in injection moulding feed systems, where molten polymer travels from the main sprue into runner branches. The geometry of the split determines the uniformity of the material behavior downstream.
Flow Dynamics
Friction against the channel walls creates a non-uniform shear distribution across the flowing melt. When fluid bifurcation occurs, the hot, low-viscosity material close to the walls splits unevenly if the runner layout is asymmetric. This separation leads to differences in temperature and viscosity between the various mold cavities.
Mould Design
Balanced runner networks use symmetrical splits to ensure that every cavity receives polymer under the same conditions. During the engineering phase, fluid bifurcation must be modeled to prevent one cavity from filling faster than another. Poor design results in uneven part weights and dimension variations across a multi-cavity tool.
Process Optimization
Controlling the shear distribution at the branches improves the consistency of the moulded parts. Rheological inserts or flow flippers can be installed at the point of fluid bifurcation to mix the high and low shear regions. This adjustment eliminates the thermal differences, leading to uniform shrinkage and a wider processing window.
By ensuring that every cavity behaves identically, the operator can set a single, stable packing pressure without risking flash or short shots on any individual part.
