Control system for regulating cavity packing during injection moulding - to minimise shot wt. variations via feedback to the screw ram pressure system

摘要

The hydraulic systems of an injection machine for holding the mould closed and for applying the injection and dwell pressure are complemented by a control circuit which receives signals from one or more displacement transducers which monitor the closing or parting of the mould tools and constantly stores and compares the mould tool motion with the theoretical positions of the mould tool relative to a further signal indicating the start of the mould cycle. Any differential between the signals for the actual and theoretical position of the mould, e.g. due to premature parting by excessive injection pressure, is used via a regulator to modify hydraulic conditions in the injection circuits as appropriate while the mould locking force is maintained constant. Used in screw injection moulding machines to ensure, that correct cavity packing pressures are reproduced and avoid excessive flash, to reduce associated variations in the physical properties of the mouldings, as indicated by e.g. reducing the variation in wt. of mouldings of nominally 300g from a range of 11g to a range of 0.77g.