Thermocouple short-circuit is one of the most dangerous sudden faults in hot runner production, which will cause disordered temperature signals, uncontrolled heater full-power output, severe plastic carbonization and even manifold overheating deformation if not dealt with timely. Mastering rapid judgment steps, temporary emergency treatment and thorough permanent repair methods minimizes mass scrap loss during continuous molding shifts.
On-site rapid fault judgment features: Controller displays temperature value fixed at ultra-low or negative reading without fluctuation; corresponding heating zone temperature rises rapidly out of control regardless of parameter adjustment; adjacent channel temperature data interferes synchronously. Immediately cut off the heating power supply of the fault zone first to avoid overheating damage to hot runner manifold and nozzles.
Three common root causes of short-circuit faults: First, damp insulation powder inside the sheath, water vapor reduces insulation resistance leading to internal alloy wire short circuit; second, outer wire sheath abrasion fracture, positive and negative alloy wires contact each other or touch mold steel plate to form short circuit; third, excessive high-temperature carbon deposit accumulation on thermocouple measuring base, conductive carbon layer connects the measuring junction with manifold metal to trigger sheath short-circuit.
Emergency temporary treatment during non-stop production shifts for delayed maintenance: If the short-circuit point is at the external wiring harness part far away from the mold, cut off the damaged wire section, re-strip and re-weld the alloy wire terminals, wrap with double-layer high-temperature insulation tape to restore insulation, which can support continuous production until planned shutdown maintenance. If the short-circuit occurs inside the mold near high-temperature manifolds, no temporary repair is allowed; replace the spare pre-calibrated thermocouple directly to avoid recurrent short-circuit causing material burning.
Thorough permanent repair and prevention measures after mold shutdown: For damp internal sheath short-circuit, disassemble the thermocouple and bake it at 200℃ constant temperature for 3 hours to remove internal moisture; if insulation resistance cannot recover after dehumidification, scrap the probe directly. For wire abrasion short-circuit, rearrange the wire routing path, add thickened PTFE insulation sleeves at friction and extrusion positions, fix harnesses with cable ties to avoid contact with sharp mold steel edges. For carbon deposit conductive short-circuit, polish the measuring base mirror surface completely to remove all carbonized residue, reapply thin high-temperature thermal conductive paste during reinstallation, and shorten the quarterly cleaning cycle of contact surfaces.
Post-fault inspection specification: After repairing or replacing the thermocouple, conduct 500V megohmmeter insulation resistance test before restarting heating, confirm insulation resistance above 100MΩ and no short-circuit hidden dangers, then power on and heat up gradually to observe temperature reading stability, preventing repeated short-circuit faults in the next production batch.
