Quick-freeze low-temperature mold trial is commonly used to verify product molding shrinkage of precision thin-wall plastic parts; sudden sharp temperature drop from hot runner working temperature down to below zero brings severe thermal shock to installed thermocouple for domestic and YUDO precision hot runner, improper protection during freeze test easily causes irreversible internal insulation damage and measuring drift. Rapid temperature plummet makes outer stainless steel sheath shrink sharply while internal core alloy wire and magnesia filler have different linear shrinkage coefficient; inconsistent contraction generates internal tiny gap between filler and sheath after repeated freeze-thaw circulation, air penetrating into gap destroys original compact insulation structure and reduces heat conduction efficiency permanently. Ordinary unprotected thermocouple after several rounds of quick-freeze test gradually appears slow measuring offset and cannot recover original precision via simple calibration.
Moisture inside workshop air quickly condenses into frost and liquid water on thermocouple sheath and terminal surface under ultra-low test temperature; condensed water permeates along micro cracks into internal insulation layer after temperature rebound and evaporates into high-pressure steam during subsequent hot runner heating, further expanding inner gap and accelerating core wire corrosion. Standard pre-test protection specification wraps probe and outer wiring with heat-insulation anti-freeze sleeve before mold quick-freeze operation; removable bayonet thermocouple is detached and stored in constant-temperature dry cabinet preferentially to avoid low-temperature thermal shock damage directly.
After finishing freeze test and mold full natural recovery to ambient temperature, maintenance workers implement insulation resistance test and precision calibration for recovered thermocouple, eliminating hidden early failure risk induced by drastic cold-hot alternation.
