Leak detector for an injection moulding machine

A plastics injection moulding machine including an injection nozzle and a sprue bush, and having a leak detector for leaks of molten plastics comprising

• a conduit for supplying intermittent pulses of fluid to a conduit outlet located adjacent to the nozzle and the sprue bush,
• a source of fluid in communication with the conduit outlet,
• means capable of sensing changes in fluid back pressure inside the conduit caused by the presence of leaked material blocking the conduit outlet and of producing an electronic output signal, and
• electronic indicating means responsive to the electronic output signal and capable of instantaneously indicating a leak condition.

A plastics injection moulding machine including an injection nozzle and a sprue bush, and having a leak detector for leaks of molten plastics comprising

• a conduit for applying a vacuum to a conduit outlet located adjacent to the nozzle and the sprue bush,
• a source of air in communication with the conduit outlet,
• means capable of sensing changes in less than atmospheric air pressure inside the conduit caused by the presence of leaked material blocking the conduit outlet and of producing an electronic output signal, and
• electronic indicating means responsive to the electronic output signal and capable of instantaneously indicating a leak condition.

A plastics injection moulding machine including an injection nozzle and a sprue bush, and having a leak detector for leaks of molten plastics comprising

• a conduit for applying a pulsed vacuum to a conduit outlet located adjacent to the nozzle and the sprue bush,
• a source of air in communication with the conduit outlet,
• means capable of sensing changes in less than atmospheric air pressure inside the conduit caused by the presence of leaked material blocking the conduit outlet and of producing an electronic output signal, and
• electronic indicating means responsive to the electronic output signal and capable of instantaneously indicating a leak condition.

A system for detecting leaks of molten plastics at a plurality of potential leak sites in a plastics injection moulding machine which machine comprises a multi-gate hot runner arrangement comprising a manifold defining channels communicating with gates through which molten plastics is injected via a main injection nozzle and sprue bush into a two-part mould defining a mould cavity, the manifold also defining heater wiring ducts, in which the leak detection system comprises

• at least one conduit for supplying a flow of fluid to an outlet thereof located adjacent to a respective potential leak site in the system,
• a source of fluid in communication with each respective conduit outlet,
• means capable of sensing changes in fluid pressure inside each of the conduits caused by the presence of leaked molten plastics material blocking the respective conduit outlet and capable of producing an identifiable electronic output signal, and
• control circuit means for simultaneously monitoring said identifiable output signals so as to detect a leak at the different potential leak sites, and for indicating the location of any leak condition.