Quantitative Standards for Sensor Hole Bottom Contact Force in Hot Runner Systems

In hot runner systems, the contact force at the bottom of the sensor hole should be adjusted between 5 and 15 N, which corresponds to an assembly preload of typically 0.1 to 0.3 mm. This is the fundamental quantitative norm. Depending on the mounting structure, certain quantitative requirements could differ slightly. The following are the industry-standard guidelines:

 

1. The Core Quantitative Standard's foundation

This range was chosen primarily to balance sensor longevity and heat conduction efficiency:

Contact force < 5 N: It is unable to precisely track changes in melt temperature because the sensor probe does not establish tight contact with the hole bottom, increasing thermal resistance and creating a temperature lag of 5 to 10°C.

Contact force > 15 N: Excessive compression is applied to the internal coupling wires and probe shell. Sensor aging and failure can be accelerated by long-term thermal expansion and contraction, which can readily cause coupling wire deformation and insulation layer degradation.

5–15 N range: Long-term accuracy is ensured by thermal resistance, which is steady within an appropriate range without adding to the sensor's mechanical stress.

 

2. Quantitative Modification for Various Mounting Structures

Structure for Mounting

Quantitative Range of Contact Force

Preload Control Corresponding

Justification

Type of Threaded Clamping

8–12 N

0.15–0.25 mm

This series, which is the most popular structure, strikes a balance between contact stability and ease of assembly.

Choose the type of screw

5–10N

0.1–0.2 mm.

The standard should be adequately decreased because the set screw has a small force-bearing surface and excessive force can easily destroy the sensor housing.

High-pressure large-mold formation

10–15N

0.2–0.3 mm.

More contact force is needed at high melt pressure to keep the probe from shifting or loosening.

 

3. Quantitative control techniques used on-site:

Assembly procedures can provide rapid control in the absence of a force measuring device:

Threaded clamping type: To obtain a contact force of 5 to 15 N, tighten an extra 1/12 to 1/6 turn (equivalent to a preload of 0.1 to 0.3 mm) after tightening to the specified position with a tiny wrench.

Set screw fastening type: To satisfy the quantitative criteria, tighten an additional 1/8 to 1/4 turn after using a screwdriver to tighten to the specified position.

A torque wrench can be used for accurate control; M3 and M4 threads correspond to torques of 0.3 and 0.6 N·m and 0.5 and 1.0 N·m, respectively. The range of 5 to 15 N is represented by the torque and contact force.

 

4. Unqualified contact force effects:

Too little contact force causes substantial fluctuations and a lag in temperature measurements; during aging, the pace of deviation amplification increases.

Excessive contact force reduces the lifespan of the sensor by 30% to 50% and increases the risk of issues such coupler wire breakage and probe cracking.