How Humidity and Dust Affect Long-term Service Life of Hot Runner Thermocouples

Injection molding molds and hot runner installation locations have intricate and dynamic interior working environments. In addition to year-round high temperatures and mechanical vibrations, the workshop's high air humidity, collected plastic dust, metal fine powder, and oil smoke dirt will cause ongoing, gradual erosion and damage to hot runner special thermocouples. The majority of thermocouple sensor early failure, performance drift, and service life reduction are due to the long-term effects of these two significant environmental conditions rather than issues with product quality. To maximize the service cycle of temperature measurement elements, specific protection measures can only be implemented after a thorough study of the damage mechanism.

First, internal circuit corrosion and external structural rust are two ways that hot runner thermocouples are negatively impacted by a high humidity environment. During long-term production, a lot of cooling water pipelines are set up inside injection molds, and water vapor will constantly evaporate and disseminate around the hot runner. The temperature differential between the high-temperature hot runner and the low-temperature ambient air will cause a significant amount of condensed water to form on the surface of thermocouple metal probes, wiring terminals, and high-temperature wire skins, particularly in southern humid regions and workshop production seasons with high air humidity. Condensed water will eventually seep into the gap in the sealed structure of regular thermocouples, come into contact with the internal temperature-measuring alloy wires, cause electrochemical corrosion and oxidation discoloration of the core wires, ruin the stable thermoelectric conversion performance, and cause the measured temperature data to drift continuously.

Moisture intrusion into the thermocouple wiring terminal and external junction box can also result in intermittent temperature signal disconnection, poor contact between wiring contacts, and increased contact resistance. In severe situations, moisture will result in signal line short-circuit faults, cause the temperature controller to frequently sound false open-circuit warnings, and need the manufacturing line to halt for maintenance and inspection. The moisture attached to the hole wall of the thermocouple probes embedded in the hot runner heating hole will eventually form a rust layer, isolating the close fit between the probe and the heating matrix, decreasing the efficiency of heat conduction, causing the measured temperature to consistently be lower than the actual internal temperature, and seriously interfering with the system's normal temperature regulation logic.

Second, it is impossible to overlook the damage that fine impurities and workshop drifting dust cause to thermocouples. Large amounts of micro plastic powder, filler fine powder, mold release agent oil mist, and metal grinding dust will be produced in the mold interior chamber and hot runner installation area during the plastic melting, injection, mold opening, and ejection processes. These microscopic contaminants will persistently stick to the exterior of external wiring harnesses and thermocouple probes. When they build up to a certain point, they will obstruct the probe's heat induction surface, slow down the temperature response time, and prevent the sensor from recording the hot runner flow channel's instantaneous temperature change in real time, which will cause severe temperature regulation hysteresis.

In addition to accelerating the aging and hardening of thermocouple high-temperature wires' outer protective skin, the mixed buildup of dust and oil dirt will also cause the insulating layer to become brittle and cracked, lose its original high-temperature insulation and anti-wear performance, and introduce possible safety risks from electric leakage. Additionally, during mold vibration and thermal expansion and contraction, these hard, fine dust particles will continuously cause friction and abrasion on the surface of thermocouple probes. They will also gradually erode the probe's outer protective alloy layer, shorten its overall structural strength, and easily cause deformation and damage to the probe in later stages of use.

Businesses must develop thorough environmental protection and daily maintenance requirements in order to successfully withstand the twin erosion of dust and humidity and prolong the service life of hot runner thermocouples. First, enhance the workshop's overall ventilation and dehumidification efforts, check mold cooling water pipes for leaks on a regular basis, prevent cooling water splashing near the hot runner area, and maintain a dry and clean atmosphere for mold installation. Second, while purchasing equipment and replacing spare parts, give top priority to choosing fully sealed integrated waterproof and dustproof hot runner thermocouples. The entire closed structure can prevent dust and moisture from entering the interior and sustain steady internal operation for an extended period of time.

Apply a thin layer of high-temperature anti-rust and heat-conducting grease to the probe installation part on a regular basis to create a protective isolation film, and wipe and clean the dust and oil dirt from thermocouple probes, wiring plugs, and junction boxes. To prevent external dust and damp air from entering and inflicting hidden harm, use specific sealing attachments to block the hot runner nozzle outlet and all temperature measuring holes when the mold is shut down for standby for an extended period of time. In order to lower the floating concentration of plastic dust in the manufacturing operation area, plan the workshop dust removal arrangement sensibly at the same time.

The detrimental effects of the harsh, humid, and dusty environment on hot runner thermocouples can be significantly mitigated by a number of efficient isolation protection and daily cleaning maintenance techniques. Additionally, the stable temperature measurement accuracy of sensors can be preserved for an extended period of time, the frequency of replacing susceptible components can be decreased, and the stable and economical operation of the entire hot runner temperature control system can be achieved.