Typical signs of hot runner aging and drift include: persistently low end nozzle temperature, inconsistent filling rhythm across multiple cavities, progressively longer filling times, frequent cold sprue heads or stringing at the gate, and continuously increasing temperature controller compensation range. These phenomena, seemingly independent, are actually external manifestations of systemic degradation, often indicating the onset of heating element attenuation, thermocouple drift, or carbon buildup in the runner.
1. Abnormal Temperature Control
Increased deviation between set temperature and measured temperature: Even if the temperature controller displays normally, measurements using a handheld thermometer show that the actual nozzle temperature is more than 5°C lower than the set value, and the temperature difference shows a trend of increasing month by month.
Slower heating response in each section: The mold preheating time is significantly prolonged, and a certain section consistently fails to reach the set temperature, requiring manual increases in the set value to maintain production.
Tip: This is usually an early signal of heating coil power attenuation or thermocouple signal drift.
2. Unstable Filling Process
Filling time fluctuations exceeding ±0.5 seconds: Under the same process parameters, the filling time per mold cycle gradually increases, especially after several hours of continuous production.
Increased weight variation in multi-cavity products: Within the same mold cycle, the weight deviation of preforms or plastic parts in each cavity increases from ±1% to over ±3%, affecting assembly consistency.
Tip: This reflects decreased melt flowability, possibly related to low end temperature or localized blockage in the runner.
3. Increased Appearance and Structural Defects
Frequent occurrences of cold sprue, flow marks, and haze: Incompletely melted sprue or uneven surface gloss frequently appear in the gate area, especially prominent in low-temperature seasons.
Alternating flash and short shots: Overflow and short shots occur intermittently at different locations within the same mold, indicating a severe imbalance in temperature and pressure distribution.
Tip: The system is no longer able to maintain an ideal thermal equilibrium.
4. Temperature Control System Alarm or Compensation Limit
Delta 5 and other intelligent temperature controllers frequently issue "out-of-tolerance" warnings: The system indicates that the heating power in a certain section has been adjusted to over 95% but the set temperature still cannot be reached.
PID self-tuning failure or sluggish response: The temperature control curve fluctuates violently, the adjustment process oscillates, and it cannot quickly return to stability.
Note: Hardware aging has exceeded the software compensation capability; immediate testing is required.
