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The mould plate containing all supply lines as well as the valve technology for active closing of the valve pins is installed behind the clamping plate. |
When using multi-cavity hotrunner systems in complex multi-component or insert-moulding applications cavity failures such as broken cores and faulty ejectors or cooling can cause unexpected production downtimes. For moulds equipped with a pneumatic valve gate system EWIKON now offers a new technology which allows the active shut-off of single cavities. Thus, regardless of broken cavities the production can be continued for example until a certain order quantity has been moulded.
The new technology was developed for use with valve gate drive units which are integrated in the clamping plate. The cavity shut-off is realised by permanently closing the respective valve pin and decreasing the nozzle temperature at the same time. To enable this the air supply is different compared to conventional systems. Normally the clamping plate contains a layout of bores that supplies several drives simultaneously with compressed air. The EWIKON technology features a separate, balanced air supply for each drive which is integrated in an additional compact mould plate placed behind the clamping plate. The compressed air is fed "horizontally" into the drive supply bores. In addition to all supply lines the plate contains a newly developed valve technology.
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View onto a valve operating unit. The permanent closing of valve pins can take place while the mould is mounted on the machine. |
For each drive unit the supply lines for valve pin opening and closing have special valves integrated. To shut off a cavity the supply line for valve pin opening is closed with the first valve and thus made pressureless. In the next step the second valve disconnects the line for valve pin closing from the air supply but due to its special construction at the same time couples it with an additional supply line which is permanently pressurised. By doing this the valve pin is actively kept in closed position. Combined with the decreased temperature in the nozzle a further protruding of plastic material into the cavity is prevented. The operating units for the valves are positioned sideways in the mould plate and are easily accessible while the mould is mounted on the machine. Of course it would also be possible to shut off a cavity by uninstalling the valve pin and decreasing the nozzle temperature. This is easily possible for all EWIKON single drive units but would require to take the mold off the machine. Furthermore, when processing materials with a tendency to drool such as TPE a decrease of the nozzle temperature alone is not sufficient to prevent plastic material from leaking out of the gate. Here the new technology with active closing of the gate offers enhanced reliability.
Up to now the new technology has been integrated into five 24+24-drop two-component moulds for a customer from the cosmetics industry who processes TPE as soft component.
