Why Do Multi-layer Hot Runner Structures Put Forward Higher Requirements on Thermocouples

Multi-layer stacked and combined hot runner structures are widely used in multi-material composite parts, double-color integrated products, and thick-wall composite plastic parts because to the ongoing advancements in composite molding technology. Compared to standard single-layer hot runner systems, these sophisticated structural hot runners have more tougher comprehensive performance requirements on matched thermocouples due to their more intricate internal temperature variations and layered heat distribution.

Due to overlapping layout and interval heat conduction, multi-layer hot runners create clear temperature gradient variations between inner and outer layers as well as between higher and lower layers in terms of temperature sensing accuracy. Typical single-standard thermocouples are unable to provide layered temperature differential data in real time; they can only detect local single-point temperature. To provide layered independent temperature monitoring, high-precision thermocouples with minute temperature error must be used in order to prevent uneven melting degrees of various layers, product delamination, and poor bonding issues.

The internal area of the multi-layer hot runner is crisscrossed and tight, with many hidden corners and small reserved installation spots, making it structurally adaptable. Customized bent, ultra-short, and special-angle thermocouples are needed to accommodate complex hole location layouts since traditional straight long thermocouples are challenging to insert at fixed points. Thermocouples must have greater anti-extrusion, anti-bending, and anti-vibration mechanical qualities because multilayer structure molds are prone to producing small position deviations during closing and opening movements.

Within multi-layer hot runners, the heat superposition effect is evident in terms of working environment resistance, resulting in prolonged high-temperature continuous acting times and greater local comprehensive temperatures. To withstand a prolonged superimposed thermal load, thermocouples must have outstanding high-temperature stability and low drift performance. Furthermore, separate layers may circulate different kinds of plastic raw materials, and mixed volatile gasses are more complex and corrosive, raising the bar for thermocouple probes' resistance to oxidation and corrosion.

To ensure the stable molding quality of complex multi-layer injection products, a layered zoning temperature measurement scheme must be developed in advance based on the structural characteristics of multi-layer hot runners, select high-precision special-shaped thermocouples in a targeted manner, and collaborate with multi-group independent temperature controllers to realize layered precise temperature regulation.