Valve gate is an on-off valve, which is often used in hot runner systems to control melt flow front and pressure holding process. Valve gate is also often used to eliminate weld lines. At this time, we can call it a sequential gate. Open the first gate at beginning, close second gate, and open it when melt flows to second gate to avoid formation of weld lines.

 

Valve gate in hot runner is actually a one-way needle valve. In order to control flow in cavity, valve gate can be programmed to open and close, during filling and pressure holding stage, valve gate can be opened and closed as many times as necessary.

 

Valve gates are required for various reasons, including:

When part is too large, single gate cannot fill cavity, and surface of product is not allowed to have weld lines. At this time, valve gates are required. At the beginning, the first gate on the side of part is opened first, and when melt flows to second gate, second gate is opened until all gates are opened and cavity is filled.

Sometimes reason for using valve gates is because valve gates have very small residues on parts, just like traces left by an ejector pin, which are much smaller than gate residues left by latent gate and end traces of other types of branch hot runners.

 

Since valve gate has a closing function, valve gate can be closed at a certain time to control final pressure holding process.

For "complete product molds", valve gates can be used to solve flow balance problem. If a valve gate is installed in each cavity, a balanced flow state can be obtained by switching valve gate.
Modeling of gate
1. Modeling of annular branch hot runner
In order to simulate ring-shaped branch hot runner, properties of column unit must be set. First, column unit is set to "hot runner". In most cases, shape of ring-shaped branch hot runner is not tapered, outer diameter is diameter of hole. Inner diameter is diameter of needle valve.

 

First confirm that gate is a hot gate, and turn last unit of gate into a valve gate controller. Do not set other gate units to valve gate types. For flexibility of use, each gate should have a different controller. Initial state of center gate is open, and two outer gates will be in the flow front state. Nature of valve gate is determined by "valve gate controller". Therefore, to generate a valve gate, first open valve gate controller and change default name of controller to a special name to distinguish it from other valve gate controllers, then set initial state of valve gate and timer settings.

 

Initial state of timer related to valve gate may be one of following three situations:
Open means that valve gate is initially open, and the first timing record will be that valve gate is closed.
Closed means that valve gate is initially closed, and the first timing record will be that valve gate is open.

 

Melt front active: Select this option, valve gate is closed at the beginning, and once melt reaches valve gate, it will automatically open. Resulting output file on screen will give real gate opening time, which can also be used as a benchmark for our further analysis. Timing of valve gate is mainly used to set time for state of valve gate to change. Valve gate can be opened and closed many times during filling and pressure holding process. When all valve gates are in closed state, it means that end time of holding pressure has been reached.

 

It is best to define a different valve gate controller for each valve gate, although this is not entirely necessary, but doing so will provide greater flexibility in gate planning. In addition, at least one valve gate must be opened at initial moment, the other valve gates can be closed and activated by melt front.

Note: Injection time cannot be set to automatic, and an injection time must be given.
Following figure shows comparative analysis result of whether valve gate is used or not.