Meaning
Flow control mechanism in hot runner systems uses pneumatically, hydraulically, or electrically driven pins to open and close individual gates in a multi-cavity or large part mould. Implementing valve gate actuation allows the moulder to run a sequential fill process, which controls the location of weld lines and improves the packing of the part. By keeping the gate closed until the polymer melt has reached the gate area, the system prevents cold slugs and cosmetic blemishes on the part’s surface.
This mechanism is common in high-volume packaging and large automotive moulding, providing a cosmetic finish.
Actuation Type
Selection of the drive method depends on the precision required and the cleanroom standards of the moulding environment. Pneumatic systems are common and cost-effective, while hydraulic systems provide higher seating forces for larger gates. Electric systems offer the highest precision and are preferred for medical moulding because they eliminate the risk of oil or air contamination.
Process Control
Sequential opening of the gates allows the moulder to direct the flow front of the polymer through the cavity. In large parts like car bumpers, this sequential fill prevents the formation of weak weld lines where flow fronts would otherwise meet. This control ensures that the finished part has uniform mechanical properties and a flawless surface appearance.
Tool Maintenance
Mechanical complexity of the valve gate actuation requires regular maintenance to prevent pin sticking or leakage of the polymer melt. The sliding action of the pins can cause wear on both the pin and the gate insert, especially when moulding glass-filled resins. Moulders must monitor this wear to prevent flash or gate defects from appearing on the moulded parts.
