Direct Visual Examination:
Abnormal Solder Ball Shape: Excessive welding current, inadequate argon gas protection, and obviously improper parameter selection are indicated by the solder ball's obvious oxidation and blackening, numerous pores and fissures on the surface, and sharp burrs on the edges.
Abnormal Wire Condition: Excessive welding heat input and an overly high current setting are indicated by the thermocouple wires' obvious overheating, thinning, embrittlement, and deformation close to the solder junction.
Unusual Solder Joint Dimensions: A significant mismatch in welding energy is indicated by a solder ball volume significantly greater than three times the diameter of the thermocouple wire, partial fusing of the two wires, or a loose solder connection shape.
Verification of Electrical Performance:* High Thermoelectric Potential Deviation: Using a multimeter set to DC millivolt mode, determine the thermoelectric potential of the thermocouple output. Under standard temperature circumstances, compare the measured value with the value from the theoretical calibration table. A discrepancy greater than ±5°C suggests that the parameter settings were wrong and the alloy composition of the thermocouple wire was burnt off during welding. Abnormal Loop Resistance: When the thermocouple's total loop resistance is measured, it is more than 20% greater than that of a qualified thermocouple with the same specification. This indicates excessive contact resistance brought on by inadequate welding current setting and improper soldering.
Failure of Insulation Resistance: A measurement of the insulation resistance between the thermocouple poles and the outside shielding layer reveals a value less than 1MΩ, which indicates that the outer insulation layer has been burnt by the high temperature during welding, leading to uncontrollable thermal input parameters.
Verification of Real Operating Conditions:
Temperature Signal variations: Frequent temperature variations and unstable values throughout the heating process after connecting to the hot runner temperature management system are indicative of poor contact caused by inadequate welding energy and poor soldering.
Continuous Temperature Drift: Incomplete fusion faults within the solder ball and improper welding parameter matching are indicated by continuous unidirectional temperature departure during extended constant temperature operation of the hot runner.
Premature Solder Joint Failure: Under hot runner conditions, solder joints fracture and fail in less than 100 hours of regular operation, indicating embrittlement of the heat-affected zone and high current setting.
It is possible to validate 100% that the welding settings have been chosen appropriately by going through the aforementioned three processes. This will stop unqualified thermocouples from entering the hot runner production line and resulting in temperature control failures.
