The core principle for safely drying a hot runner system after it has been exposed to moisture is as follows: provided that the insulation resistance is confirmed to be no less than 100 kΩ, a low-temperature, phased approach should be adopted to heat the system and drive out the moisture. Priority should be given to utilizing the system's own heating capabilities or external hot-air equipment; under no circumstances is it permissible to directly power up and operate the system at full power.
1. Safety Prerequisites Before Drying
Power Disconnection and Testing Required: Use a 500V DC megohmmeter to measure the insulation resistance between the heating elements, cable harnesses, and connectors, and ground.
Initial Resistance Requirement: Drying may proceed only if the measured value is ≥ 100 kΩ; if the value is < 100 kΩ, a severe short-circuit risk exists, and powering up the system is strictly prohibited.
Clean the Work Area: Disconnect the connectors and wipe the terminals with anhydrous alcohol to remove any water films, oil stains, or carbonized residues; subsequently, blow them clean using dry compressed air.
2. Safe Drying Methods and Operating Procedures
Method 1: Low-Temperature Heat Soaking (Recommended)
Suitable for situations where the insulation resistance falls between 100 kΩ and 1 MΩ, and there is no visible accumulation of standing water.
Temperature Setting: Set the temperature controller to 80–100°C-a temperature lower than the material's molding temperature-to prevent thermal shock.
Operation Duration: Maintain continuous heating for 1–2 hours, allowing the hot runner's own heat to slowly evaporate the internal moisture.
Monitoring Frequency: Every 30 minutes, power down the system and use a megohmmeter to re-measure the insulation resistance, observing whether the value shows a steady upward trend.
Advantages: Provides uniform heating, does not damage the insulation materials, and is effective for drying the micro-channels located within the mold.
Method 2: External Hot-Air Drying
Suitable for drying specific localized areas that have been exposed to moisture, such as connectors, junction boxes, and cable entry points.
Tool Selection: Use a heat gun or an industrial hot-air blower, maintaining the air temperature at ≤ 80°C to prevent high heat from carbonizing the insulation layer.
Key Operational Points:
Maintain a distance of 15–20 cm between the air outlet and the surface being heated;
Move the airflow evenly to prevent localized overheating;
Focus drying efforts on areas prone to moisture accumulation, such as sealing rings, terminal boxes, plugs, and sockets.
Complementary Measures: The terminal box cover may be opened simultaneously to enhance air circulation and improve drying efficiency.
Method 3: Natural Drying During Downtime (Auxiliary Method)
Suitable for cases involving minor moisture ingress where there is no immediate urgency to resume production.
Relocate the mold to a dry, well-ventilated environment and allow it to sit for 24–48 hours;
Desiccant packets may be placed inside the terminal box, or a small dehumidifier may be used to assist the process;
This serves solely as a preventive measure and cannot substitute for active heat drying.
3.Critical Precautions During the Drying Process
Strictly Prohibited: Direct Full-Power Startup: Attempting to set the temperature directly above 200°C while the unit is still damp carries a high risk of localized conductivity, potentially leading to arcing, short circuits, or even the burnout of heating elements.
Avoid Rapid Thermal Shock: The heating rate should ideally be controlled within 10–20°C/min to prevent thermal expansion and contraction from causing further failure of sealing structures.
Monitor Insulation Levels Continuously:After drying, the system must be allowed to cool to room temperature before re-measuring insulation resistance; ensure that all channels exceed 1 MΩbefore resuming operation.
Strictly Prohibited: Testing Under Load: Upon initial resumption of operation, run the system under a "no-load" condition for 30 minutes; proceed to mold trials only after confirming that the temperature has stabilized and there are no abnormal noises.
Note: Drying serves merely as "first aid"; a thorough inspection and component replacement must be scheduled within 72 hours. If insulation values fail to recover after multiple drying attempts, it should be assumed that carbonization or permanent damage has occurred, necessitating the replacement of the heating elements.
