On which parts should the temperature sensor of the injection molding machine be installed?

In the injection molding machine, the installation position of the temperature sensor must accurately correspond to the key temperature control components to ensure effective control of the melt plasticization, mold temperature and hot runner system. The following are the components that need to be installed and the specific requirements:
I. The core installation position of the barrel (plasticization system)
1. The middle of the metal wall of each heating section
Components/position: The middle of the outer surface of the feeding section (rear section), compression section (middle section), and metering section (front section) of the barrel (≥50mm from the joint of the heating ring, avoiding the shearing area).
Installation requirements:
The sensor probe must be embedded in the barrel wall to a depth of 1/3~1/2 of the barrel radius (such as Φ80mm barrel, the probe is inserted 25~40mm), ensuring that it contacts the metal body rather than the heating ring.
The distance between sensors in adjacent heating sections is ≥100mm to avoid cross-section temperature interference (for example, when processing ABS, the middle section sensor should be located 30mm after the starting point of the compression section thread).
Function: Directly monitor the temperature of the inner wall of the barrel, reflect the conductive heat during the plasticization of the melt, and avoid the influence of screw shear heat (dynamic interference) and uneven heat of the heating ring joint.
2. Nozzle (front end of the barrel)
Parts/location: middle of the nozzle body (15~20mm from the tip, avoiding the heat insulation area in contact with the mold).
Installation requirements: Use a threaded sensor, parallel to the nozzle axis, and keep the probe end 2~3mm away from the inner wall of the nozzle (do not directly contact the melt to prevent material adhesion and damage).
Function: Control the transition temperature of the melt from the barrel to the mold to avoid condensation at the nozzle (for example, when PC is injected, the nozzle temperature needs to be 5~10℃ higher than the front section).
2. Key monitoring points of the mold (molding system)
1. 5~10mm below the cavity surface
Parts/location: The metal body of the mold cavity side wall or core (5~10mm vertical distance from the cavity surface, avoiding cooling water holes ≥30mm).
Installation requirements:
Use embedded sensors, the probe is parallel to the cavity surface, and the hole wall is coated with thermal conductive silicone to fill the gap (thermal resistance ≤ 0.5℃・cm²/W).
Multi-cavity molds need to be installed at symmetrical positions in each cavity (such as next to the end cavity of the runner of a three-plate mold).
Function: Real-time monitoring of the mold surface temperature during melt filling, control of crystallinity and cooling rate (such as PBT mold temperature needs to be stable at 80±2℃).
2. Nozzle and manifold of hot runner system
Components/location:
Inside the tip of the hot runner nozzle (within 5mm from the gate, directly in contact with the melt flow channel);
Midpoint of the manifold heating zone (avoid the flow channel joints and thermal insulation pads, such as ≥20mm from the edge of the manifold).
Installation requirements: Use a needle sensor, coaxial with the flow channel axis, and the probe end extends into the flow channel metal wall 1/2 thickness (to avoid melt pressure shock).
Function: Ensure uniform melt temperature in the hot runner (e.g. PET hot runner needs to be controlled at 285±3℃) to prevent gate solidification or material decomposition.
III. Sensor arrangement of auxiliary temperature control components
1. Hopper seat (front end of feed section)
Component/location: Outside of the hopper seat where the hopper and barrel are connected (≥80mm from the feed port, avoiding the direct impact area of ​​cold material particles).
Function: Monitor the initial temperature of the feed section to prevent screw feeding from slipping due to low-temperature particles (e.g. PA66 feed section temperature needs to be ≥80℃).
2. Hydraulic oil/oil temperature cooler
Component/location: Hydraulic oil tank outlet pipe (≥100mm from the cooler inlet, avoiding the direct impact area of ​​the cooler fins).
Function: Indirectly control the temperature of the hydraulic system (e.g. the oil temperature needs to be stable at 45~55℃ to avoid excessively high temperature causing aging of the seal).
4. General installation principles and precautions
Contact principle
The sensor probe must fit tightly with the metal surface of the measured component (barrel, mold, hot runner) to avoid air gaps (use copper gaskets or thermal conductive glue to enhance thermal conductivity).
Counterexample: If there is a 0.5mm gap between the sensor and the barrel wall, the temperature measurement delay can reach 10~15 seconds, resulting in temperature control lag (such as the risk of decomposition during PVC processing).
Representative principle
Installation in the stable temperature field area: the barrel sensor must be located in the center of the heating section (not the seam of the heating ring), and the mold sensor must be away from the cooling water channel and inserts (such as ≥3 times the aperture of the water hole).
Case: When processing PMMA, if the mold cavity sensor is close to the cooling water hole, the measured temperature may be 12℃ lower than the actual temperature, resulting in a decrease in surface gloss.
Signal shielding principle
The sensor signal line must use a twisted shielded pair cable and stay away from the servo motor cable (spacing ≥200mm) to avoid temperature jumps caused by electromagnetic interference (such as sudden fluctuations in the displayed value of ±5℃).
Summary: List of core installation locations
Component category Specific installation location Typical depth/distance Applicable sensor type Control target
Barrel segmentation The outer surface of the middle of each heating section (avoid seams) Inserted into the barrel wall 1/3~1/2 radius Threaded thermocouple/PT100 Plasticizing section temperature (such as PP barrel front section 220±5℃)
Nozzle The middle of the nozzle body (15~20mm from the tip) Probe 2~3mm from the inner wall Needle thermocouple Melt transition temperature (to prevent nozzle condensation)
Mold cavity 5~10mm below the cavity surface (avoid cooling water holes ≥30mm) Vertically embedded in the mold steel Embedded PT100 Filling temperature (such as PC mold 80±3℃)
Hot runner nozzle Inside the metal wall of the nozzle flow channel (5mm from the gate) Coaxially inserted into the flow channel wall 1/2 thickness Micro armored thermocouple Melt temperature (such as POM Hot runner 205±2℃)
Hydraulic system Oil tank outlet pipe (100mm from cooler) Pipe outer wall clamping installation Surface temperature sensor Oil temperature control (45~55℃)
By accurately installing sensors on the above components, the full process control of the injection molding machine temperature can be achieved: from barrel plasticization, nozzle transition, hot runner allocation to mold molding, the temperature data of each link can truly reflect the material state, avoiding problems such as uneven plasticization, product defects (such as shrinkage, welding marks) or material decomposition caused by improper installation position. Especially in precision injection molding (such as optical lenses) or heat-sensitive materials (such as PVC, PC) processing, the correct installation position is the prerequisite for process stability.