Hot Runner
Cascade injection is a filling technique that opens and closes the valve-gate nozzles of a hot runner in sequence, based on time or screw position. The melt front first advances from the first gate; when the front reaches the second gate, that valve opens. In this way no weld line forms, or it is moved to a non-visible area; long and large parts fill at lower pressure and with less warpage.
The valve gate controller sets the opening time (0.1 s) or opening position (screw stroke, 0.1 mm) of each valve. Correct timing means opening the valve at the point where the melt front passes: if it opens early a weld line forms, if it opens late a hesitation mark remains.
It is standard for automotive bumpers, door panels and parts for large household appliances. Feedback of the valve position (end position monitoring) catches faulty parts early in the event of a malfunction.
Valve-gate hot runner nozzles, pneumatic or hydraulic actuators driving the valves, and a valve gate controller working on a time or position basis. A temperature controller is also required.