How to Detect Leakage in Hot Runner Heaters

I. Safety Preparations Before Testing: Completely disconnect the 220V high-voltage power supply circuit to the hot runner heater, leaving only the low-voltage temperature measurement circuit of the sensor open to avoid the risk of electric shock during testing. Prepare a 500V range digital megohmmeter, a high-precision AC millivoltmeter, and high-temperature resistant insulating gloves. Ensure the megohmmeter is undamaged and its calibration is valid. Disconnect all terminals between the heater and the temperature controller to prevent damage to the internal circuitry of the temperature controller from the high voltage of the megohmmeter. II. Offline Static Insulation Testing: Connect the L terminal of the megohmmeter to any power input line of the heater, and the E terminal to the metal casing/hot runner body of the heater. Roll the handle at a constant speed (or press the test button on the electronic megohmmeter) for 1 minute, then read the insulation resistance value. Judgment Criteria: Insulation resistance ≥ 5MΩ is fully qualified; 0.5MΩ~5MΩ is a warning of insulation degradation; < 0.5MΩ indicates a clear leakage fault. Repeat the above steps for each heater channel in the hot runner system, marking any leakage paths with abnormal insulation resistance. III. Live Dynamic Leakage Detection Restore normal power supply to the hot runner heaters, raise the system temperature to the rated operating temperature of 320℃ and hold for 2 hours to bring the heaters into actual operating condition. Connect one end of an AC millivoltmeter to a reliable grounding point of the equipment, and then sequentially contact the heater casing, the flow channel body, and the metal shielding layer of the thermocouple probe with the other end. If an AC voltage ≥5V is detected, dynamic leakage is identified in the circuit; the higher the voltage value, the greater the leakage current. Simultaneously observe the temperature data from the temperature controller. If the sensor reading changes synchronously when the leakage voltage appears, it confirms that the leakage has caused crosstalk to the sensor. IV. Precisely Locating Leakage Points in Sections Disconnect the heater terminals and individually test the insulation resistance of the heating core body to eliminate leakage interference from external wiring and connectors. If the insulation of the heating core body is qualified, then test the insulation performance of the heating cable and aviation connectors in sections to locate leakage points where the cable insulation is damaged or the connectors are oxidized and damp. The heater suspected of leakage was disassembled and inspected to confirm whether there was a leakage path caused by moisture in the magnesium oxide insulation layer, heating wire touching the shell, or a broken ceramic lining. V. Post-Inspection Verification and Confirmation After the leakage fault was resolved, the insulation resistance was retested under high-temperature conditions to confirm that the value had recovered to ≥5MΩ and there was no dynamic leakage voltage. After continuous operation for 4 hours, it was confirmed that the sensor temperature measurement data showed no jumps, and the crosstalk caused by the leakage was completely eliminated.