Designing Balanced Multi Cavity Runner Systems for Polymer Injection Tooling
Balanced multi cavity runners match flow length, shear history, and pressure drop across all branches to achieve simultaneous mold cavity filling.
Submarine Gate Depth
Meaning
Vertical placement of the orifice in an edge-gated system determines the point at which the polymer enters the cavity relative to the parting line. Submarine gate depth refers to the distance between the parting line and the center of the gate opening in an injection mould. This type of gate, also known as a tunnel gate, is designed to shear off automatically when the part is ejected.
The depth must be calculated precisely to ensure that the gate vestige is minimized and that the part fills completely without excessive pressure.
Material Shear
Flow through the tunnel experiences intense friction that temporarily lowers its viscosity as it enters the cavity. The submarine gate depth influences the angle of this entry and the resulting shear rate. If the depth is too shallow, the gate may break prematurely or leave a large mark on the part.
Conversely, a gate that is too deep might not shear off cleanly during ejection.
Proper Depth
Calculation ensures that the flow front enters the cavity at the optimal location to avoid jetting or air entrapment. In multi-cavity moulds, the submarine gate depth must be identical across all cavities to maintain a balanced fill. Even a small variation in this dimension can cause one cavity to fill faster than another, leading to weight inconsistencies.
Tapered Designs
Modification facilitates the clean separation of the gate from the part.