About Valve Gates

Valve gates open and close to control the filling and packing of injection-molded parts for simulations with hot runner systems. Since valve gate systems can add considerable cost and complexity to the mold design, simulation can be a valuable resource to help you choose the valve locations and mechanisms.

The following topics are discussed:

This page discusses:

See Also
Defining Valve Gates

Usage

Valve gate systems control the filling and packing of an injection-molded part using gates that open and close with pneumatic or hydraulic controls. The opening and closing of the valve gates can be sequential, independent, or time based, which provides greater flexibility in hot runner systems than with thermal gates.

Most hot runner systems use thermal gates rather than valve gates to control the introduction of injectable material into the mold. Thermal gates work by freezing at the end of the packing phase and remelting at the beginning of the subsequent filling cycle.

Although thermal gates are preferred in hot runner systems, valve gates offer the following advantages:

  • Improved physical appearance
  • Reduced molded-in stresses
  • Elimination of weld-lines
  • Cycle time reduction
  • Balancing flow in family molds
  • Facilitation of very rapid filling in thin-wall molding

Assignment

You can assign valve gates to the coincident face of a hot runner and part body, or a hot runner and cold runner. You can also add valve gates automatically for all locations where hot runners meet the cavity, or you can add individual valve gates manually in specific locations. Manual definition provides greater control over the gate behavior; with this method, you can define valve gates that open and close based on the following criteria:

  • Automatic, which opens the control valve automatically when the polymer melt's front passes the valve location and keeps it open for the rest of the simulation.
  • Volume ratio, which controls the opening and closing of the control valves based on the percentage of the cavity volume that is filled.
  • Time ratio, which controls the opening and closing of the control valves based on the elapsed time since the start of Filling.

Automatically created valve gates always use the automatic valve control behavior.