Meaning
Pneumatic or hydraulic control systems regulate the opening and closing of individual gates within a hot runner system during the injection cycle. An advanced valve gate control allows for the sequential filling of large or complex moulds to eliminate weld lines and reduce packing pressures. This system utilizes a physical pin inside each gate that retracts to allow melt flow and advances to seal the gate before the mould opens.
Precise timing of these movements is critical to producing high quality parts with clean gate vestiges.
Actuation Timing
Machine controllers trigger the movement of each pin based on screw position or cavity pressure. By opening the gates in a specific sequence, the melt front can be directed smoothly through the cavity without colliding. This sequencing is particularly useful for moulding long automotive panels where aesthetic weld lines are forbidden.
Flow Sequencing
Opening gates only when the melt front has passed them prevents the formation of flow marks and pressure drops. This controlled flow path ensures that the polymer fills the cavity evenly, which reduces internal stresses and subsequent part warpage. It also allows for smaller clamp forces by distributing the fill pressure more efficiently.
Defect Prevention
Mechanical seals at the gate prevent drool and stringing when the part is ejected. This clean cutoff eliminates the need for manual gate trimming and improves the cosmetic finish of the gate area.
