I. Pre-Heating Prevention Measures
Confirm Hot Runner Dryness: Ensure the hot runner is thoroughly dried and cooled, with a stable insulation resistance ≥20MΩ. Avoid residual moisture that could accelerate material hydrolysis and degradation.
Clean Residual Material from the Runner: Before heating, completely replace any residual material from the previous production runner with a dedicated cleaning agent for the corresponding material. This prevents prolonged overheating and decomposition of the old material.
Check Temperature Control System Accuracy: Calibrate all hot runner sensors in advance to ensure a temperature measurement deviation ≤±1℃. This prevents underestimation of the actual temperature, which could lead to overheating and degradation.
II. Staged Gradient Heating Control
Low Temperature Preheating Stage: Increase the temperature from room temperature to 30℃ below the material's heat distortion temperature, controlling the heating rate at 2℃/minute. Hold for 30 minutes to prevent localized rapid overheating.
Medium Temperature Transition Stage: Increase the temperature to the lower limit of the material's recommended processing temperature and hold for 20 minutes. This ensures uniform temperature throughout the hot runner and eliminates localized hot spots.
Production Temperature Stage: Gradually increase the temperature to the midpoint of the recommended processing temperature range for the material. Do not set the temperature directly to the upper limit. Hold the temperature for 15 minutes before starting material feeding.
III. Melt Residence Time Control
Shorten Idle Heating Waiting Time: After the hot runner reaches the production temperature, material feeding and injection molding must be completed within 30 minutes. Prolonged idle holding that allows the melt to remain in the runner is prohibited.
Optimize Runner Structure: Ensure the hot runner has no dead corners or sharp bends to prevent prolonged melt residence in localized areas, which could lead to thermal degradation.
Quick Handling of Temporary Shutdowns: If equipment malfunctions during heating and material feeding cannot be completed in time, immediately lower the hot runner temperature to below the material's glass transition temperature to reduce the risk of thermal degradation.
IV. Specialized Adaptation for Different Easily Degradable Materials
PVC Material: Maintain a small amount of inert nitrogen gas throughout the heating process. Strictly control the processing temperature between 160~180℃. Do not exceed 200℃ to prevent rapid decomposition and release of hydrogen chloride.
POM Material: Feeding must be completed within 15 minutes of reaching the production temperature. The processing temperature should not exceed 220℃ to avoid decomposition and formaldehyde gas release.
PET Material: Before heating, ensure the chips are fully dry with a moisture content ≤50ppm. The processing temperature should be controlled between 260~280℃ to avoid hydrolytic degradation at high temperatures.
V. Process Monitoring and Emergency Response
Continuous Temperature Data Monitoring: Monitor temperature fluctuations in all heating areas in real time through the temperature control system, confirming a temperature deviation ≤±2℃ and no localized overheating points.
Rapid Handling of Pre-Degradation Signs: If fumes are observed overflowing from the nozzle or yellow spots appear in the material flow, immediately stop heating. Quickly replace the melt in the flow channel with a low-temperature cleaning agent to identify overheating points.
