Insufficient CMRR in a hot runner system can lead to inaccurate temperature control, frequent product defects, and decreased equipment stability. Specifically, this manifests as temperature fluctuations, short shots, flash, and damage to heating elements.
1. Inaccurate Temperature Control (Core Issue)
Temperature display jumps or drifts: Common-mode noise is misinterpreted as a temperature signal, causing drastic fluctuations in the temperature controller reading (e.g., ±10℃ or more);
PID control malfunction: Frequent controller malfunctions cause inconsistent heating output, resulting in overheating or cold material;
Multi-cavity imbalance: In multi-nozzle systems, different channels experience varying degrees of interference, leading to uneven filling, flash, or short shots.
Practical Case: A medical plastic parts factory experienced hot runner temperature fluctuations of ±15℃ due to insufficient CMRR (only 50dB), resulting in out-of-tolerance product dimensions and batch scrap.
2. Product Quality Defects
|
Defect Type |
Cause |
|
Short Shot |
Noise causes temperature control to misjudge "overheating," automatically cooling down when the actual temperature is insufficient. |
|
Flash (Burs) |
Misjudged as "low temperature," leading to continued heating, causing material carbonization and overflow. |
|
Increased Internal Stress |
Temperature fluctuations cause uneven melt flow, resulting in uneven stress distribution after cooling. |
|
Color Difference or Surface Defects |
Localized overheating leads to material degradation, affecting appearance quality. |
Risk Warning: In demanding industries such as automotive and medical, these defects directly lead to customer returns or production line shutdowns and claims.
3. Impact on Equipment and Production Efficiency
Shortened Heating Element Lifespan: Frequent start-ups and overload heating accelerate heating element aging.
System Alarm Shutdown: Temperature control malfunctions trigger protection mechanisms, causing unplanned shutdowns.
Increased Maintenance Costs: Requires repeated troubleshooting of "suspected sensor malfunctions," increasing labor and spare parts expenses.
Correct understanding: "Insufficient CMRR ≠ equipment failure", but its impact is equivalent to chronic system collapse and is difficult to eradicate.
