How to Prevent Overheating in Hot Runner Systems

In an effort to prevent the overheating of hot runner systems, rigorous control of the heating temperature, optimisation of the heating regime and monitoring of the furnace atmosphere are necessary in an effort to prevent the grain boundary oxidation or local melting of the material at high temperatures.

1. Accurate Temperature Control for Heating

Define a safety upper limit: Make sure that the heating temperature does not exceed the overheating temperature of the mould steel (e.g. H13 steel normally does not exceed 1150°C). The working temperature is usually maintained in the region of 200-600°C.

Zoned temperature control : Apply independent temperature control to distinct sections of the hot runner (such as nozzles and manifolds) to minimise localised overheating.

Use high precision temperature controller: Use temperature controller with PID control capability to provide real time feedback and correct temperature deviation .

Practical suggestion: Define the maximum heating value according to the heat treatment curve of the material, with a safety margin of at least 50°C.

2. Upgrade Heating and Standby Systems

Strictly control the heating specifications: Adjust the heating rate and holding time according to the process requirements, and do not expose the material to high temperature for a long time;

Cooling down during non-production: Reduce the temperature to 100-150°C and hold when halting the machine or changing moulds, to reduce inefficient high-temperature exposure;

Limit start-ups and shut-downs: Continuous operation is preferable than repeatedly heating and cooling which might cause thermal shock and overheat.

According to references, one of the most important reasons for overheating is protracted residency time of billets in high temperature zones.

3. Control Environment and System Status

• Adjust furnace gas composition • Maintain a neutral or mildly decreasing heating atmosphere • Avoid strong oxidising atmospheres which worsen grain boundary oxidation;

Prevent direct flame impingement: When utilising gas heating, make sure the flame does not impinge directly on the metal surface to prevent localised overheating;

Regular maintenance of the temperature measuring system: Calibrate thermocouples and temperature control box to avoid the real temperature out of control due to sensor malfunction.

Special reminder: Once the overheating has happened and voids or remelting have developed at the grain boundaries, it can not be restored by any heat treatment and must be scrapped and replaced.