Open circuit fault is one of the most common sudden failures of hot runner thermocouples, which directly leads to no temperature display on the controller screen, forced stop of heating function and immediate interruption of injection molding production. Once this fault occurs, production must be suspended for maintenance, causing direct economic losses such as delayed delivery and reduced output. It is essential to fully master the fault causes and rapid troubleshooting methods.
The first main cause is internal fracture of thermoelectric wire core. Under long-term alternating cold and hot working environment, the internal alloy wire core continues to produce thermal expansion and contraction deformation, and thermal fatigue accumulates day by day. In addition, frequent mold opening and closing vibration, artificial bending and pulling during maintenance will easily break the fine wire core inside the probe and wiring section, resulting in complete disconnection of the signal transmission loop. This kind of fracture mostly occurs at the welding position of the measuring head and the transition connection part of the wire body, which belongs to irreversible structural damage.
The second cause is welding joint falling off and failure. The welding spot at the temperature measuring head is the weakest part of the whole thermocouple. Inferior products with rough welding process are prone to oxidation and loosening under long-term high-temperature baking. Corrosive gas will continuously erode the welding gap, resulting in gradual separation of the two groups of alloy wires, eventually forming an open circuit state and completely losing temperature sensing capacity.
The third reason is terminal wiring falling off and virtual disconnection. In the daily production process, the vibration generated by the equipment will gradually loosen the fixing screws of the temperature control box terminals, leading to the separation between the wire core and the metal connecting terminal. In addition, aging and hardening of the wire skin will cause the internal wire core to retract, resulting in invisible disconnection inside the wiring port, making it impossible to transmit temperature signals normally.
The fourth inducement is insulation damage and external force shearing. The outer protective sleeve and insulating layer are worn and cracked by long-term friction and extrusion, and the internal wire core is cut off by sharp metal parts inside the mold. Meanwhile, excessive high temperature will melt the high-temperature insulating filler, causing structural collapse and wire core separation inside the thermocouple.
In view of the above open circuit faults, the most efficient solution is hierarchical inspection and elimination. Firstly, check whether the external wiring is fallen off, loose or broken, and re-fix and replace the damaged compensation wires in time. Secondly, use a multimeter to conduct on-off detection on the whole thermocouple loop to judge whether the internal wire core is broken. If the measuring head is broken or the internal circuit is completely disconnected, there is no maintenance value and a new matched thermocouple must be replaced directly. After replacement, standardize the wiring mode, reserve enough bending allowance for the wire body, fix the wiring firmly to avoid pulling and extrusion, and effectively prevent the recurrence of open circuit faults from the source.
