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.
Valve Gate Actuation Timing
Meaning
Coordinated opening and closing of mechanical shut-off pins in a hot runner system manages the flow of melt into different areas of a mould. Valve gate actuation timing refers to the programmed schedule that controls when each valve pin retracts or advances during the injection cycle. This precision is used to eliminate weld lines in large parts or to balance the filling of parts with varying wall thicknesses.
By delaying the opening of certain gates, a processor can ensure that the melt front from an earlier gate has passed the secondary gate location.
Controlling Pressure
Action at the melt front prevents the formation of hesitation marks or visible knit lines where two flow fronts meet. Valve gate actuation timing is often adjusted in millisecond increments to fine-tune the appearance of the finished surface. A well-timed sequence creates a seamless part with uniform structural properties.
Closing Gates
Movements before the end of the holding phase prevent the over-packing of material near the entry point. This action reduces internal stresses and helps to prevent part warpage. In family moulds where parts of different sizes are made simultaneously, the timing is used to stop the flow to smaller cavities once they are full.
This prevents the smaller parts from flashing while the larger parts continue to pack.
Delays
Intervals between gate openings prevent air pockets.