I. Visual and Odor Monitoring
Nozzle Overflow Observation: During heating, periodically observe the small amount of molten material overflowing from the hot runner nozzles. If the molten material rapidly turns yellow and develops small, dark brown spots, this is the most direct sign of impending degradation.
Abnormal Odor Identification: Detect gas odors around the hot runner. PVC degradation produces a pungent, acidic smell, while POM degradation produces a strong, formaldehyde-like odor. The presence of these abnormal odors indicates that the material has begun to decompose.
Fume Overflow Monitoring: Continuous light-colored fumes overflowing from the nozzles or runner plate gaps indicate that the melt has undergone thermal decomposition, a clear sign of impending degradation.
II. Temperature Control System Data Monitoring
Abnormal Temperature Fluctuation Monitoring: Monitor the temperature data of each channel in the temperature control box in real time. If the actual temperature of a heating zone suddenly and significantly exceeds the set value, triggering a continuous over-temperature alarm, the melt in that area has most likely begun to degrade.
Heating Power Anomaly Monitoring: If the output power of a heating zone suddenly spikes abnormally, far exceeding the normal power value under the same operating conditions, it indicates that local melt decomposition and heat absorption have triggered continuous reheating of the heating system, a precursor to latent degradation.
Temperature Rise Curve Anomaly Monitoring: Compare with the standard temperature rise curve of the same material. If, during the heating process, there is an unexplained prolonged temperature stagnation above 100℃, indicating abnormal absorption of a large amount of heat, it indicates that the internal melt has begun to vaporize and decompose.
III. Indirect Monitoring of Melt Characteristics
Breakthrough Viscosity Change Judgment: Use a clean metal rod to collect a small amount of melt overflowing from the nozzle and observe its stringing state. If the melt is easily broken when drawn into strings and its fluidity suddenly becomes abnormally thinner, it indicates that the molecular chains have broken, a precursor to degradation.
Predictive Pressure Anomalies: If, during subsequent test injections, the injection pressure of the injection molding machine suddenly drops significantly, and a large number of bubbles are present in the melt, it indicates that the material in the hot runner has degraded, decomposing and producing a large amount of low-molecular-weight gas.
IV. Specific Monitoring Points for Different Easily Degradable Materials
PVC Material: Focus on monitoring the duration of temperature stays above 180℃. Immediately stop heating if a sour odor is detected and quickly replace the melt in the runner.
POM Material: After heating to 220℃, check the nozzle status every 10 minutes. If fumes overflow, immediately lower the temperature to avoid a sudden increase in decomposition pressure and the risk of material spraying.
PET Material: Before heating, confirm the material moisture content is ≤50ppm. After heating to 280℃, focus on monitoring melt transparency. The appearance of fogging or silver streaks indicates an impending hydrolytic degradation.
V. Monitoring Frequency and Emergency Trigger Rules
Complete a full-channel temperature inspection and appearance/odor check every 10 minutes throughout the heating process. After reaching the material processing temperature, conduct an inspection every 5 minutes.
If any signs of degradation appear, immediately lower the hot runner temperature to a safe range, quickly replace any residual melt in the runner with a dedicated cleaning agent, identify any overheating points, and then restart heating.
