The key to preventing overheating in hot runner systems is to strictly control the heating temperature, optimize the heating regime, and monitor the furnace atmosphere to prevent grain boundary oxidation or localized melting of the material at high temperatures.
1. Precisely Control Heating Temperature
Set a safety upper limit: Ensure the heating temperature does not exceed the overheating temperature of the mold steel (e.g., H13 steel generally does not exceed 1150°C). The operating temperature should typically be controlled within the range of 200–600°C.
Zoned temperature control: Implement independent temperature control for different areas of the hot runner, such as nozzles and manifolds, to avoid localized overheating.
Use a high-precision temperature controller: Employ a temperature controller with PID control function to provide real-time feedback and correct temperature deviations.
Practical suggestion: Set the maximum heating value based on the material's heat treatment curve, leaving a safety margin of at least 50°C.
2. Optimize Heating and Standby Systems
Strictly adhere to heating specifications: Set the heating rate and holding time according to process requirements to avoid prolonged exposure to high temperatures;
Cool down during non-production periods: When stopping the machine or changing molds, lower the temperature to 100–150°C and hold to reduce ineffective high-temperature exposure;
Avoid frequent start-ups and shutdowns: Continuous production is superior to repeated heating and cooling, reducing the risk of thermal shock and overheating.
References indicate that prolonged residence time of billets in high-temperature zones is one of the main causes of overheating.
3. Control Environmental and System Status
Adjust furnace gas composition: Maintain a neutral or weakly reducing atmosphere in the heating environment to avoid strong oxidizing atmospheres that exacerbate grain boundary oxidation;
Prevent direct flame injection: If using gas heating, ensure the flame does not directly contact the metal surface to prevent localized overheating;
Regularly maintain the temperature measurement system: Calibrate thermocouples and the temperature control box to prevent uncontrolled actual temperature due to sensor malfunction.
Special reminder: Once overheating occurs, and voids or remelting have appeared at the grain boundaries, it cannot be repaired by any heat treatment and must be scrapped and replaced.
