Pre-welding Source Control: To guarantee that the metal surface is fully clean and free of any barrier layer that prevents solder wetting, thoroughly wipe the oxide layer and oil stains within 25–30 mm of the thermocouple measurement end with alcohol or a specialised cleaning solution before welding.
Make use of a highly active flux that is precisely matched to the material of the thermocouple. Throughout the procedure, give top priority to DC TIG welding with high-purity argon gas protection to avoid oxidation and carburisation of the solder joints, guaranteeing full penetration and removing porosity within the solder ball.
Process Consolidation During Welding: Adhere strictly to standardised welding conditions, matching the welding time and current to the diameter of the thermocouple wire. This prohibits both excessive heat input from generating wire embrittlement and insufficient heat input from causing incomplete fusion.
Clean the solder junctions' surface right away after welding to get rid of any leftover flux and slag. This stops residual contaminants from corroding the contacts over time, which could eventually result in poor contact.
A 100% check of the solder joint appearance is carried out to make sure that the thermocouple wires are secure and that the solder balls are smooth and full, free of fractures and dark grey oxide rings. Unqualified solder joints are promptly rectified and re-welded.
Installation and Operating Condition Adaptation Protection: When installing thermocouples, try not to bend or pull the solder joints excessively. To lessen the mechanical stress impact on the solder connections brought on by the hot runner channel's prolonged vibration, make sure the thermocouple is put into the hot runner channel to the necessary depth.
To avoid solder connection fusion interface cracking from repetitive thermal expansion and contraction of the thermocouple wires under high-temperature cycling settings, choose armoured thermocouples appropriate for the hot runner channel's high-temperature working conditions.
To prevent signal anomalies brought on by intense electromagnetic interference in the field, properly insulate the signal lines electromagnetically. To avoid false cold solder connections brought on by terminal oxidation and loosening, check the terminals' tightness on a regular basis.
Establish a routine thermocouple inspection system for long-term operation and maintenance management. Every three months, check the thermocouple circuit resistance at random to look for early indicators of cold solder connections and unusually high contact resistance.
To prevent signal anomalies brought on by ageing and insulation deterioration, replace ageing thermocouple wires on a regular basis in accordance with hot runner maintenance guidelines. This will lower the likelihood of recurrent cold solder joints throughout the course of the product's lifetime.
This all-inclusive preventive solution is entirely adaptive to the challenging working conditions of hot runners under prolonged high temperatures and vibrations, and it may reduce the recurrence rate of cold solder joints in hot runner thermocouples by over 90%.
