Excessive contact force (>15N) at the bottom of a hot runner sensor aperture will directly accelerate sensor aging and failure, and may also cause abnormal temperature measurement and structural damage. Specific consequences are as follows:
1. Significantly shortened sensor lifespan: When the contact force is excessive, the sensor probe housing and internal sensing elements (coupled wire/platinum wire, insulation layer) will be subjected to additional compressive stress for a long time. Under the thermal expansion and contraction caused by repeated hot and cold cycles in the hot runner:
The internal coupled wire/platinum wire is more prone to deformation and breakage, shortening the sensor's lifespan by 30%~50%. A sensor that could have lasted 3 years may fail in 1~1.5 years;
The insulation layer will be damaged by compression, causing internal short circuits, signal jumps, and resulting in irregular fluctuations in the temperature curve.
2. Causes Abnormal Temperature Measurement Accuracy
Excessive compression alters the physical properties of the sensing element:
For thermocouples, deformation of the thermocouple wire under stress changes its thermoelectric properties, leading to a fixed deviation in temperature measurement that cannot be stably maintained even after calibration.
For resistance temperature detectors (RTDs), compression of the platinum wire changes its resistance, resulting in a consistently high temperature reading that fails to reflect the true temperature of the melt.
3. Directly Causes Mechanical Structure Damage
For set screw-mounted installations, excessive contact force can easily crush the stainless steel housing of the sensor, or even break the probe, causing the sensor to completely fail.
In extreme cases, overtightening can strip the threads of the mounting hole, damaging the installation structure of the mold itself, requiring re-tapping and repair, and delaying production.
4. Increases the Risk of Subsequent Production Failures
Damage caused by excessive contact force is often gradual. Initially, small deviations are difficult to detect, but they slowly lead to an increase in the product defect rate, potentially resulting in batch quality scrap and additional production losses.
