The primary reasons for a decline in the insulation resistance of hot runner systems include: moisture ingress, high-temperature aging, mechanical damage, contaminant accumulation, partial discharge, and material degradation. Among these factors, moisture ingress and high temperatures are the two most common and critical triggers.
1. Moisture Ingress (The Most Common Cause)
Condensation Formation: When a mold is shut down after operating at high temperatures, if the ambient humidity is high, water vapor in the air will condense on the cooling metal surfaces, seeping into junction boxes, connectors, or cable sheaths.
Cooling Water Leakage: Poor sealing in the mold's cooling channels or ruptured piping allows water to infiltrate the electrical components.
Storage in High-Humidity Environments: Molds that have been out of service for extended periods-particularly those stored in damp workshops or outdoors-are susceptible to moisture slowly penetrating their insulation layers.
Typical Symptoms: The insulation resistance value drops significantly after shutdown; tests conducted prior to restarting the system often yield readings below 1 MΩ, though the value may temporarily recover after drying.
2. Aging of Insulation Materials Due to High Temperatures
Prolonged Operation at Excessive Temperatures: When heating elements operate continuously above their designed temperature limits, the thermal degradation of insulation materials-such as silicone rubber or mica-is accelerated.
Thermal Cycling Fatigue: Frequent system startups and shutdowns induce thermal expansion and contraction, leading to cracking or delamination of the insulation layers and a subsequent reduction in dielectric strength.
Localized Overheating: Uneven heating or inadequate heat dissipation creates "hot spots," causing localized carbonization of the insulation material and the formation of conductive pathways.
Typical Symptoms: The insulation resistance value exhibits a gradual, downward trend over time; even after drying, it fails to recover to its original baseline level.
3. Mechanical Damage
Damage During Installation or Handling: During mold hoisting or the mold-closing process, cables may be pinched or pulled, resulting in damaged cable sheaths or deformation of the internal conductors.
Vibration Fatigue: Prolonged equipment operation involving constant vibration can cause terminal connections to loosen or internal wires to fracture, potentially triggering short circuits or ground faults.
Accidental Damage During Machining/Repair: Internal wiring may be inadvertently damaged during mold maintenance, such as during drilling or machining operations.
Typical Symptoms: The insulation resistance value drops suddenly and drastically, often accompanied by a complete electrical breakdown in a specific circuit. 4. Contaminant Accumulation
Excessive Mold Release Spray: Oil-based mold release agents adhere to terminal blocks, forming a conductive film.
Oil and Carbon Residue: Leaking hydraulic oil or carbon particles resulting from plastic decomposition deposit on connector surfaces, thereby reducing surface resistance.
Dust Accumulation: Workshop dust enters the junction box; upon absorbing moisture, it creates conductive leakage paths.
Typical Symptoms: Insulation resistance values recover significantly after cleaning, particularly in the connector areas.
5. Partial Discharge and Ionization Degradation
Voltage Concentration: Electric fields concentrate at sharp metal edges or air gaps, generating minute electrical arcs (partial discharge).
Continuous Ionization: Ozone and nitrogen oxides generated by the discharge corrode insulation materials, gradually forming carbonized conductive paths.
Harmonic Effects: High-order harmonics within the power grid increase voltage stress, thereby exacerbating discharge phenomena.
Typical Symptoms: Fluctuations in insulation resistance values, accompanied by a "hissing" sound or a burnt odor; frequently observed in low-quality or aging components.
6. Material Degradation or Manufacturing Defects
Substandard Heating Elements: Use of inferior mica sheets or silicone materials results in poor heat resistance and moisture-proofing capabilities, making them prone to delamination and moisture absorption.
Inadequate Sealing Structure: The connector's IP protection rating is insufficient (e.g., below IP65), rendering it unable to effectively block moisture ingress.
End of Service Life: The insulation material has reached the end of its expected service life (typically 5–8 years), resulting in natural performance degradation.
Typical Symptoms: Simultaneous degradation across multiple channels; the issue is resolved after replacing the components with high-quality alternatives.
