Your continued focus and in-depth questioning of the hot runner system truly demonstrates a high level of professional expertise! Determining whether a heating system within a hot runner has failed cannot be based on a single symptom; rather, a systematic diagnosis should be conducted from four dimensions: temperature performance, physical state, electrical performance, and process results.
I. Temperature and Control System Abnormalities (Primary Signals)
Temperature fails to reach set value
A certain zone heats slowly or consistently below the set temperature (e.g., set to 250℃, actually only 220℃)
Possible causes: Heating element power attenuation, open circuit, or temperature control parameter mismatch
Severe temperature fluctuations or loss of control
Controller displays temperature jumps (e.g., ±10℃ or more), unable to stabilize
Possible causes: Poor thermocouple contact, electromagnetic interference, or PID parameter misalignment
Continuous alarm codes appear
Displaying "Over Temp," "E1" (sensor open circuit), or "Short" (short circuit) Further investigation using a multimeter and calibrator is needed to determine if the fault lies with the sensor, heating element, or controller.
Excessive temperature difference across multiple zones
Temperature difference between nozzles on the same manifold > ±5℃, outside the normal equilibrium range.
Possible causes: Flow channel blockage, uneven heating, or thermocouple inaccurate response.
II. Physical and Structural Condition Inspection (On-site Confirmation)
Severe carbonization of the nozzle end face.
Significant blackening, carbon buildup, or dripping occurs, recurring shortly after cleaning.
Indicates localized overheating or melt stagnation, possibly due to heater eccentricity or flow channel design defects.
Deformation or bulging of the heating probe.
After disassembly, bulging, cracks, or oxidation discoloration are found on the probe surface.
Indicates long-term overheating or material mismatch, resulting in metal fatigue.
Blocking or wear of the distributor tube.
Narrowing of the melt flow channel, with obvious scratches or deposits on the inner wall.
Increased pressure loss and difficulty in filling.
Aging and failure of seals.
Flattened, cracked, or leaking seals, affecting heat transfer efficiency and system sealing.
III. Electrical Performance Testing (Precise Criteria)
|
Test Item |
Normal Standard |
Failure Manifestation |
|
Heating rod resistance |
Meets manufacturer's stated value (e.g., approximately 24.2Ω for 200W) |
Infinite resistance (open circuit) or close to 0Ω (short circuit) |
|
Insulation resistance to ground |
≥ 5MΩ (megohmmeter test at 500V) |
< 1MΩ, leakage risk exists |
|
Temperature sensing wire resistance |
PT100 is 109.6Ω±1Ω at 25℃ |
Resistance fluctuation, open circuit, or short circuit. |
|
Shielding layer grounding |
Single-point grounding, no multi-point loop |
Multi-point grounding causes signal interference. |
Testing recommendation: Use a digital multimeter and megohmmeter for power-off testing to ensure safety.
IV. Injection Molding Process Abnormalities (Final Verification)
|
Process Defect |
Possible Related System Failures |
|
Insufficient Filling or Cold Sprue |
Runner temperature too low, insufficient heating or inaccurate temperature sensing |
|
Flash or Overflow |
Localized overheating leading to viscosity decrease and uncontrolled flow |
|
Scorch Marks, Silver Stains, or Bubbles |
Excessive melt residence time, resulting in thermal degradation |
|
Unstable Product Dimensions |
Large temperature fluctuations, inconsistent shrinkage rates |
|
Uneven Filling of Multiple Cavities |
Runner imbalance or heating failure in a certain area |
Note: If the problem persists after changing materials or adjusting process parameters, the hot runner system itself should be the primary focus of investigation.
V. Comprehensive Judgment Process (Rapid Diagnosis)
Step 1: Check Alarms → Are there codes such as E1 or Over Temp?
Step 2: Measure Resistance → Are the heating element and temperature sensing wire normal?
Step 3: Check Insulation → Is there leakage or interference?
Step 4: Observe the Manufacturing Process → Are product defects related to temperature?
Step 5: Disassemble and Inspect → Confirm internal carbonization, blockage, or component damage.
Best Practice: Establish a "temperature record + regular inspection + maintenance file" mechanism to achieve a shift from passive maintenance to proactive early warning.
