With the continuous upgrading of composite molding technology, multi-layer stacked and combined hot runner structures are widely applied in multi-material composite parts, double-color integrated products and thick-wall composite plastic parts. Such complex structural hot runners have more layered heat distribution and more complicated internal temperature changes, which put forward far stricter comprehensive performance requirements on matched thermocouples than ordinary single-layer hot runner systems.
In terms of temperature detection accuracy, multi-layer hot runners form obvious temperature gradient differences between upper and lower layers and inner and outer layers due to overlapping layout and interval heat conduction. Ordinary single-standard thermocouples can only detect local single-point temperature, unable to feed back layered temperature difference data in real time. It is necessary to deploy high-precision thermocouples with tiny temperature error to realize layered separate temperature monitoring, so as to avoid unbalanced melting degree of different layers and product delamination and poor bonding problems.
In terms of structural adaptability, multi-layer hot runner internal space is crisscrossed and compact, with many hidden corners and narrow reserved installation positions. Traditional straight long thermocouples are difficult to complete fixed-point installation, so customized bent, ultra-short and special-angle thermocouples are required to adapt to complex hole position layout. Meanwhile, layered structural molds are easy to produce slight position deviation during closing and opening movements, which requires thermocouples to have stronger anti-extrusion, anti-bending and anti-vibration mechanical properties.
In terms of working environment resistance, heat superposition effect is obvious inside multi-layer hot runners, leading to higher local comprehensive temperature and longer high-temperature continuous acting time. Thermocouples need to have excellent high-temperature stability and low drift performance to resist long-term superimposed thermal load. In addition, different layers may circulate different types of plastic raw materials, and mixed volatile gases are more complex and corrosive, which puts forward higher standards for the anti-corrosion and anti-oxidation ability of thermocouple probes.
In actual matching application, layered zoning temperature measurement scheme must be formulated in advance according to the structural characteristics of multi-layer hot runners, select high-precision special-shaped thermocouples in a targeted manner, and cooperate with multi-group independent temperature controllers to realize layered precise temperature regulation, so as to ensure the stable molding quality of complex multi-layer injection products.
