Negative Impacts of Frequent Temperature Switching on Thermocouple Service Life

Hot runner thermocouples will experience severe cold and hot alternating impacts in injection molding production due to frequent start-stop heating, repeated temperature adjustments, and intermittent production downtime. This unstable operating condition may shorten the steady service cycle of temperature sensor elements, inflict irreparable damage to internal components, and significantly speed up aging.

The internal alloy wire core and external protective sleeve of the thermocouple will repeatedly undergo thermal expansion and cold contraction deformation whenever the temperature rises quickly from room temperature to molding temperature and then falls back to low temperature. The metal material will progressively develop microscopic, imperceptible cracks at welding locations and wire core transition positions as a result of long-term, repeated deformation that continuously builds up thermal fatigue stress. Early on, it simply causes mild temperature drift and sensitivity loss; later on, it can easily result in abrupt fracture and open circuit failure, necessitating production to halt for an emergency replacement.

The internal high-temperature insulating filler will also be harmed by frequent temperature changes. The infill materials' compactness will be diminished by the expansion and contraction gap created by the alternating cold and heat, leading to a loose internal fixed structure. High temperatures clearly reduce insulating ability, which makes it easier to cause internal partial short circuits, signal disorders, and other problems. Frequent temperature changes will also hasten the exterior compensating wire insulating layer's aging and hardening, raising the possibility of wire skin cracking and core wire exposure.

Furthermore, the probe surface's oxidation corrosion speed will increase with repeated cold and hot alternation. The workshop moisture easily condenses on the probe's metal surface when the temperature lowers, creating oxidation rust patches. The initial smooth sensor surface is continuously worn down, the anti-oxidation protective coating is destroyed, and the temperature measurement precision rapidly decreases when the rust layer quickly peels off under high temperatures during reheating.

Scientific operating techniques must be used for production lines that must perform intermittent production in order to minimize losses. Reduce the temperature differential between cold and hot alternation during temporary shutdown by maintaining the hot runner in a low temperature heat preservation state rather than completely cooling down. When production resumes, use segmented slow heating mode rather than a single, quick temperature increase to gradually relieve the thermocouples' internal structural stress. To reduce the overall loss brought on by frequent temperature switching, increase the frequency of daily inspections of such frequently switched temperature zone thermocouples, promptly screen out items with fatigue damage, and plan ahead for replacement.