Analysis of Causes and Solutions of Thermocouple Open Circuit Fault in Hot Runner System

One of the most frequent abrupt failures of hot runner thermocouples is an open circuit fault, which causes the controller screen to show no temperature, the heating function to be forced to stop, and injection molding production to immediately stop. When this problem arises, manufacturing must be halted for maintenance, which results in immediate financial losses like decreased output and delayed deliveries. Gaining a thorough understanding of defect sources and quick troubleshooting techniques is crucial.

Internal thermoelectric wire core fracture is the primary reason. The internal alloy wire core continues to undergo thermal expansion and contraction deformation in a long-term, alternating cold and hot working environment, and thermal fatigue builds up daily. Furthermore, the fine wire core inside the probe and wiring section is readily broken by frequent mold opening and shutting vibration, artificial bending, and tugging during maintenance, which completely disconnects the signal transmission loop. This type of fracture, which is classified as irreversible structural damage, typically happens at the transition connection portion of the wire body and the welding position of the measurement head.

Welding joint failure and sliding off is the second reason. The thermocouple's weakest point is the welding place at the temperature measuring head. Under prolonged high-temperature baking, inferior products with a rough welding process are vulnerable to oxidation and loosening. The welding gap will be continuously eroded by corrosive gas, which will cause the two sets of alloy wires to gradually separate, eventually generating an open circuit state and losing all ability to sense temperature.

Virtual disconnection and terminal wiring breaking off are the third cause. The vibration produced by the machinery will progressively loosen the temperature control box terminals' fixing screws throughout the regular production process, causing the wire core and the metal connecting terminal to separate. Additionally, when the wire skin ages and hardens, the interior wire core will retract, creating an undetectable separation inside the wiring port that prevents regular temperature signal transmission.

Insulation deterioration and external force shearing constitute the fourth inducement. Long-term friction and extrusion wear down and shatter the outside protective sleeve and insulating layer, while sharp metal components inside the mold sever the interior wire core. In the meantime, an excessively high temperature will melt the high-temperature insulating filler, resulting in the thermocouple's internal wire core separation and structural collapse.

Hierarchical inspection and removal is the most effective technique given the aforementioned open circuit problems. First, determine whether the external wiring is broken, loose, or fallen off. Then, promptly repair and replace any damaged compensation wires. Second, to determine whether the internal wire core is damaged, perform on-off detection on the entire thermocouple loop using a multimeter. There is no maintenance value and a new matched thermocouple needs to be installed right away if the measuring head is damaged or the internal circuit is totally disconnected. Standardize the wiring mode after replacement, give the wire body adequate bending allowance, securely fasten the wiring to prevent pulling and extrusion, and successfully stop open circuit problems from occurring again.333