Replacing the heating elements in the hot runner is a critical operation to ensure stable injection molding. It must be performed only after the mold has completely cooled, the system power is off, and the safety lockout (LOTO) is engaged. Improper operation may result in equipment damage or personal injury.
I. Preparations Before Replacement
Safety Measures
Turn off the power to the hot runner controller and hang a "Do Not Power On" sign on the distribution box.
Wait for the mold temperature to drop below 60°C to prevent burns and thermal damage to the elements.
Tools and Spare Parts Preparation
Hex wrench, torque wrench, insulated screwdriver
Digital multimeter (for measuring resistance)
Megohmmeter (500V, for testing insulation)
New heating element (confirm model, power, and size are consistent with the original)
High-temperature sealing grease, heat shrink tubing, labels
Information Verification
Refer to mold drawings or system manual to confirm heating element specifications (voltage, power, resistance)
Record the fault area number and original component parameters to avoid misinstallation
II. Removing the Old Heating Element
Disconnect Electrical Connections
Gently unplug the heating wire; do not pull on the wires.
Use labels to mark each wire's corresponding channel to prevent incorrect connection.
Disassemble the Fixing Structure
Depending on the mold type, use an Allen wrench to remove the heated half-mold or nozzle assembly.
Remove the retaining ring, heat shield, and other accessories, and carefully remove the old heating probe or distributor tube.
Inspect the Flow Channel Condition
Clean the flow channel of carbon deposits and residual plastic, ensuring the mounting holes are not blocked or deformed.
Check the sealing surface for flatness; replace the sealing ring if necessary.
III. Install the New Heating Element
Verification and Pre-inspection
Use a multimeter to measure the cold resistance of the new element to verify it meets the nominal value (e.g., 200W/24.2Ω).
Check for any external damage and ensure the lead wire insulation is intact.
Correct Installation
Slowly insert the heating element into the designated position, ensuring a tight fit with the flow channel plate.
If it is an internal heating probe, ensure it is centered in the flow channel to avoid localized overheating due to eccentricity.
Use a torque wrench to tighten the screws to the manufacturer's specified torque, preventing overtightening and deformation.
Sealing and Protection
Apply a small amount of high-temperature sealing grease to the sealing surface to improve heat transfer efficiency and prevent leakage.
Wrap all terminals with heat shrink tubing to prevent short circuits.
IV. Wiring and Testing
|
Steps |
Operating Requirements |
|
Wiring |
Connect according to the label, ensuring correct polarity and secure terminal crimping. |
|
Insulation Test |
Use a megohmmeter to test the insulation resistance of the heating element to ground; it should be ≥ 5MΩ. |
|
Resistance Retest |
Measure the total resistance again to confirm there are no short circuits or open circuits. |
|
Shielding |
Run the power line through a flexible metal conduit, away from signal lines, to reduce interference. |
V. Power-On Verification and Operational Testing
No-Load Heating Test
After powering on, observe whether the controller displays any abnormal alarms (such as "Short" or "Over Temp").
Monitor the heating curves of each temperature zone to ensure they are smooth and without drastic fluctuations.
Infrared Thermometry Comparison
Use an infrared thermometer to measure the nozzle surface temperature; the deviation from the controller display value should be ≤ ±3℃.
Trial Molding Verification
Perform 5–10 injection cycles and observe whether the melt flow is uniform.
Check the product for temperature-related defects such as underfill, scorch marks, and flash.
Key Note: After replacement, it is recommended to perform a temperature control system calibration to ensure that the PID parameters match the characteristics of the new component.
Prohibited Actions:
Forcibly disassembling or reassembling the device while it is not cooled down.
Using non-original or incompatible replacement parts.
Ignoring insulation testing and directly powering on the device.
