Your focus on hot runner internal heating systems is very professional. While these systems are highly efficient, their maintenance requires exceptional precision. Proper maintenance not only extends equipment lifespan but also prevents material degradation and production interruptions caused by localized overheating or blockages. The following is a systematic maintenance guide for the heating system within the hot runner:
I. Preventative Maintenance During Daily Operation
Temperature Monitoring and Recording
Check the deviation between the actual temperature and the set value of each temperature control zone every shift. The allowable range is ±3℃.
Record temperature fluctuation trends and promptly investigate any persistent drift or jumps.
Clean Nozzle Surface
After shutdown, use a copper brush or wooden chip to remove carbon deposits from the nozzle end face. Do not use steel tools to scrape.
Wipe the runner outlet with a lint-free cloth dampened with a special cleaning agent (such as DCE) to prevent residue from solidifying.
Inspect Heating and Sensing Circuits
Visually inspect cables for damage, aging, overheating, or discoloration.
Use a multimeter to measure the resistance of the heating element to determine if there is an open circuit or short circuit (normal values refer to the manufacturer's specifications).
Measure the resistance of the sensing wire (PT100 should be 109.6Ω at 25℃) to ensure accurate temperature measurement.
II. Regular Deep Maintenance (Recommended every 6 months)
1. Disassembly and Cleaning
Completely cool the mold to below 60°C, disconnect power and lock (LOTO).
Remove the hot nozzle assembly, take out the heating probe and distributor tube.
Use a dedicated carbon removal tool or compressed air to remove carbon deposits and stagnant material from the flow channels.
For stubborn carbides, a combination of low-temperature baking and mechanical cleaning can be used to avoid high-temperature ablation damage to the metal.
2. Key Component Inspection
|
Component |
Inspection Points |
|
Heating Probe |
No cracks or bulges on the surface, stable resistance value. |
|
Distributor Tube |
Smooth inner wall without carbon deposits, no deformation of the positioning hole. |
|
Sealing Ring |
No aging or flattening, replacement cycle recommended ≤2 years. |
|
Thermocouple Sheath |
No blockage, good contact of the sensing head. |
3. Reassembly and Sealing
During installation, ensure uniform clearance between the heating element and the flow channel plate.
Use a torque wrench to tighten screws to the manufacturer's specified torque to prevent overtightening and deformation.
Apply high-temperature sealing grease to all sealing surfaces to improve sealing and heat transfer efficiency.
III. Common Fault Prevention and Handling
Flow Channel Blockage
Causes: Material degradation, incomplete material replacement, lack of cleaning during prolonged shutdown.
Solutions:
Use high-flowability cleaning material (such as PP or special cleaning material) when changing materials.
Empty and cool the system before prolonged shutdown.
Perform "hot soaking" cleaning regularly: Raise the temperature to the material's upper limit +20°C, maintain for 30 minutes, then push out with new material.
Local Overheating or Burnt Material
Causes: Heater power imbalance, temperature control misalignment, poor thermocouple contact
Solutions:
Calibrate the temperature control system to ensure PID parameters match for each channel.
Check that the thermocouple is inserted correctly, with the sensing point ≤10mm from the flow channel wall.
Replace aging heating elements to prevent power decay leading to compensatory overheating.
Increased Pressure Loss
Causes: Thickened outer ring solidified layer, dead angles in flow channel design
Solutions:
Optimize temperature settings, appropriately increase flow channel temperature to thin the solidified layer.
Ensure the melt flow direction at bends is a smooth transition to eliminate flow dead angles.
IV. Post-Maintenance Verification Steps
Insulation and Continuity Test
Use a megohmmeter to test the insulation resistance of the heating rod to ground. ≥ 5MΩ
Check if the temperature sensing wire shield is grounded at a single point to prevent interference.
No-load heating test
After powering on, observe whether the temperature rise of each zone is synchronized and whether there are any alarm codes (such as E1, Over Temp).
Use an infrared thermometer to compare the nozzle surface temperature with the controller display value; the deviation should be ≤ ±3℃.
Trial production verification
Conduct 5–10 trial production cycles.
Observe whether the melt flow is uniform and whether there are any jetting marks, scorch marks, or insufficient filling.
✅ Best practice: Establish a "maintenance file" to record the time of each disassembly, cleaning status, replaced parts, and test data for easy traceability and prediction of the next maintenance cycle.
