What is the frictional heat error under high shear flow in hot runners?

The primary cause of the frictional heat error in hot runners under high shear flow is the excess heat produced by the melt flow being mistakenly perceived as a change in heater temperature, which raises readings in the temperature control system and reduces the precision of temperature control.

 

1. How frictional heat errors are generated

High shear rate causes internal friction: When the plastic melt passes through narrow runners in high-speed injection molding or micro-part molding, it encounters incredibly high shear rates, which cause severe intermolecular friction and additional frictional heat (up to 10~30°C);

Temperature sensor response hysteresis: The heat is transferred to the thermocouple and mistakenly interpreted as "heater overheating" because the sensor's installation location is unable to detect the shear heat at the runner's center;

Misadjustment of the control system: When the temperature controller lowers the heating output, the actual melt temperature is insufficient, leading to uneven fills or short shots.

Practical example: When a medical catheter mold was being filled quickly, the surface temperature reading was 300°C, but the actual melt temperature was only 278°C. This 22°C difference was verified as frictional heat interference.

 

2. Frictional Heat Error's Effect

A factor

Range of Errors

An explanation

Shear Rate > 10^s⁻¹ + 10^30°C

Common in microfluidic systems and thin-walled components

Materials that are viscous, such as PC and ABS

Greater deviation

Stronger internal friction and longer molecular chains

Diameter of Channel < 2 mm

Heat builds up and is challenging to release.

especially noticeable in micro-parts

Response Time of the Sensor > 1s

More pronounced hysteresis

Incapable of monitoring brief temperature variations

Risk Warning: This error is caused by a mismatch between the process and temperature measurement, which is readily misinterpreted as an inaccurate temperature control. It is not the result of equipment failure.

 

3. Steps to Cut Down on Frictional Heat Error

Optimize the location of the sensor:

To minimize flow thermal interference, pick the central region of the main flow channel or the hot half-mold connection area instead of high-shear places (such as nozzle tips or flow dividers).

Use Fast-Response Sensors: For more precise temperature fluctuations, choose exposed K-type probes or thin-film thermocouples with a response time of less than 0.5 seconds.

Combined Melt Temperature Measurement Verification: To accurately determine the material temperature and adjust the hot runner display value, install a melt temperature sensor at the mold output.

Process Parameter Compensation: To counteract the temperature drop brought on by frictional heat, appropriately raise the high-speed section's fixed temperature by 5–10°C.

Safety Principle: Frictional heat mistakes cannot be effectively suppressed unless "position optimization + fast sensing + melt verification" are combined.