Combining cavity sensors with hot runner valve gate control

Related Vendors

HASCO Hasenclever GmbH + Co KG

Ramada Acos

Synventive Molding Solutions GmbH

Cavity sensors also can be used for statistical process control to determine the rejection of a given shot or cavity. Instead of relying on feedback from the injection moulding machine to determine if a cycle was successful, the moulder can look to the data related to cavity fill provided by the sensors, which is a more accurate indicator of a successful shot. Depending on the application, this can reduce or eliminate part inspection while still ensuring that parts meet specifications.

A final application for sensor data is as a trigger for other equipment. For example, information from the cavity sensors can be used to transfer the injection moulding machine from the injection phase to the holding phase.

Traditional valve gate hot runners

Traditional valve gate hot runners control the flow of melted plastic into the mould cavity by simply opening and closing the valve pin on the nozzle. With these systems, the user initiates a pin move based on either time, screw position or a signal from a cavity sensor. Once a pin move is initiated, the moulder has no control over the speed or distance of the pin movement. Recent technological advances now enable that control over the speed and stroke of the valve pin. Valve gate hot runners control more than the flow as explained in the following paragraphs.

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Controlling the valve pin movement. In producing large, sequentially filled parts, pressure builds up behind the delayed valve pins. The abrupt opening of these delayed pins can cause sudden accelerations in melt-front velocity near the gates and stagnation away from the gates, often resulting in cosmetic defects on the parts. Slowing the initial opening speed of the valve pins on the delayed gates can reduce the variations in melt-front velocity and eliminate cosmetic defects.

Varying valve pin opening speeds and strokes. To balance mould families without resorting to different opening and closing times, the moulder should vary the valve pin opening speeds and strokes.

Manipulating valve pin movement. Manipulating the movement of the valve pins in direct-gated cosmetic applications is beneficial as well. Controlling the valve pin opening speed, closing speed and stroke yields improved gate-area cosmetics.

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