First, accurately assess the nature of damage. Use a multimeter to run three tests: continuity resistance, millivolt signal, and insulation resistance. Determine whether the damage is a partial break in the electrode wire, partial damage to the insulation layer, or total burning and breaking of the sensor end.
Rule out extrinsic defects like terminal oxidation or compensating wire damage. Confirm that the damaged area is on the thermocouple itself.
Repairable Scenarios and Practical Solutions.
Partial Break/Poor Contact Repair: Locate the break point, remove the oxide layer from the damaged thermocouple wire, and repair it accurately with argon arc welding. After welding, grind the weld junction to ensure that it does not exceed 1.2 times the diameter of the original electrode wire. Re-insulate the thermocouple.
Partial Insulation Damage Repair: Remove any remaining impurities from the damaged region, rewrap with high-temperature resistant magnesium oxide insulation tape, and insert a high-temperature resistant insulation sleeve that meets the relevant standard. After repair, check the insulation resistance, which should be ≥100MΩ.
To repair damaged compensatory lead segments, trim the damaged segment and connect it with a compensating lead of the same index number. After welding, provide sufficient shielding and insulation to achieve a loop resistance deviation of ≤5Ω.
Handling Unrepairable Scenarios: If the thermocouple sensing end is completely burnt, the armoured protective tube is heavily corroded and penetrated, or there are multiple breaks in the internal electrode wires, simply replace it with a brand new thermocouple of the same model and index number. Forced repair is not recommended to avoid repeated temperature drift failures in future use.
Post-Repair Closed-Loop Verification: After repair, verify the loop resistance, insulation resistance, and heating millivolt signal output; if all are normal, reinstall the thermocouple in the hot runner and repeat the calibration operation. Check for temperature deviation of ≤±1℃ and no temperature drift after 2 hours of continuous operation. The fix is then completed.
This tiered repair method reduces spare part replacement costs while maintaining temperature measurement accuracy, adjusting to the field maintenance requirements of Husky hot runner systems.
