The core quantitative standard for the contact force at the bottom of the sensor hole in hot runner systems is: the contact force should be controlled between 5 and 15 N, corresponding to an assembly preload of generally 0.1 to 0.3 mm. Specific quantitative requirements may vary slightly depending on the mounting structure. The industry-standard guidelines are as follows:
1. Basis for the Core Quantitative Standard
The core reason for setting this range is to balance heat conduction efficiency and sensor lifespan:
Contact force < 5 N: The sensor probe does not make tight contact with the hole bottom, increasing thermal resistance and causing a temperature lag of 5 to 10°C, making it impossible to accurately follow changes in melt temperature.
Contact force > 15 N: The probe shell and internal coupling wires are subjected to excessive compression. Long-term thermal expansion and contraction can easily lead to coupling wire deformation and insulation layer damage, accelerating sensor aging and failure.
5~15 N range: Thermal resistance is stable within an acceptable range, while not causing additional mechanical stress to the sensor, ensuring long-term accuracy.
2. Quantitative Adjustment for Different Mounting Structures
|
Mounting Structure |
Contact Force Quantitative Range |
Corresponding Preload Control |
Explanation |
|
Threaded Clamping Type |
8~12 N |
0.15~0.25mm |
The most common structure, this range balances ease of assembly and contact stability. |
|
Set screw type |
5~10N |
0.1~0.2mm. |
The set screw has a small force-bearing area; excessive force can easily damage the sensor housing, so the standard should be appropriately lowered. |
|
Large mold high-pressure forming |
10~15N |
0.2~0.3mm. |
High melt pressure requires greater contact force to prevent the probe from loosening or shifting. |
3. On-site quantitative control methods:
When no force measuring instrument is available, quick control can be achieved through assembly operations:
Threaded clamping type: After tightening to the designated position with a small wrench, tighten an additional 1/12 to 1/6 turn (corresponding to a preload of 0.1 to 0.3 mm) to achieve a contact force of 5 to 15 N.
Set screw fixing type: After tightening to the designated position with a screwdriver, tighten another 1/8 to 1/4 turn to meet the quantitative requirements.
For precise control, a torque wrench can be used: M3 threads correspond to a torque of 0.3 to 0.6 N·m, and M4 threads correspond to a torque of 0.5 to 1.0 N·m. The torque and contact force correspond to the 5 to 15 N range.
4. Effects of unqualified contact force:
Too low contact force: Temperature measurement lag and large fluctuations; deviation amplification speed is faster after aging.
Too high contact force: Sensor lifespan is shortened by 30% to 50%, and problems such as probe cracking and coupler wire breakage are likely to occur.
