Many injection molding workshops are in high humidity environment all year round due to cooling water circulation, seasonal climate and production process demands. Long-term damp working atmosphere will produce continuous adverse effects on hot runner thermocouples and their matching wiring circuits, accelerate accessory aging speed, induce electrical faults and temperature measurement abnormities, and many unexplained temperature control failures are closely related to excessive environmental humidity.
High humidity air is easy to form condensed water droplets on the surface of hot runner wiring terminals, plug connectors and thermocouple outer sheaths under the influence of temperature difference. These tiny water droplets will adhere to the gap of wiring contacts, causing poor contact, increased contact resistance and unstable signal transmission. In serious cases, moisture will penetrate into the internal core wire along the gap of high-temperature wire skin, resulting in damp corrosion of temperature measuring alloy wire, gradual change of thermoelectric conversion performance, and continuous deviation of temperature measurement data. Especially for the thermocouples installed near the mold cooling water pipeline, the damp corrosion speed is far faster than that in dry environment.
In the closed installation space inside the mold, excessive humidity will also cause mild oxidation and rust on the metal sheath of thermocouples. The rust layer formed on the probe surface will isolate the close contact between the sensing end and the heating hole wall, hinder the normal heat conduction efficiency, make the temperature measured by the thermocouple obviously lower than the actual flow channel temperature, resulting in long-term excessive heating of the hot runner system, and then cause plastic melt carbonization and product yellowing defects. In addition, damp environment will accelerate the aging and hardening speed of high-temperature flame-retardant insulating wires, make the wire skin easy to crack and leak electricity, bringing potential safety hazards to workshop electricity use.
When the workshop humidity is too high, the temperature controller internal circuit board is also easy to absorb moisture, which interferes with the normal signal recognition of thermocouple signals, resulting in frequent data floating, random temperature jumping and false fault alarm of sensor open circuit. Such intermittent abnormal faults are difficult to troubleshoot in daily inspection, which seriously disturbs the normal production rhythm and increases the difficulty of process debugging.
In order to reduce the damage of humid environment to hot runner thermocouples, enterprises need to take targeted protective measures. Keep the workshop ventilation and dry as much as possible, do a good job in sealing and leakage prevention of mold cooling water pipes, and avoid cooling water splashing around the hot runner installation area. Select fully sealed waterproof and high-temperature resistant thermocouple models for humid workshop use, and regularly apply high-temperature anti-rust grease to the probe installation position to isolate moisture erosion. Regularly disassemble and dry the wiring plugs and terminal blocks, clean the condensed water and dust inside, and do a good job in daily moisture-proof protection. Effectively controlling environmental humidity and doing a good job in damp-proof maintenance can greatly extend the service life of hot runner thermocouples and maintain the long-term stable operation of temperature control system.
