Hot runner thermocouples are not universal industrial temperature measuring sensors; they are customized and classified according to hot runner structural characteristics such as nozzles, manifolds, valve gates and miniature multi-cavity molds. Different types of thermocouple products differ in sheath size, sensing head structure, wire length and installation mode, with clear applicable scenarios in hot runner matching. Systematic classification of mainstream hot runner thermocouple products can help mold designers quickly select matching sensors in the mold design stage and reduce later mold modification work caused by inappropriate thermocouple selection.
Contact flat-head thermocouples are the standard matched products for hot runner manifolds. The sensing end is processed into a flat circular metal surface, which closely fits the reserved temperature measuring plane on the manifold surface through spring compression structure. The flat contact surface increases heat transfer area, accurately capturing the overall temperature of the flow distribution plate to avoid local cold material in the main flow channel. This product series is mostly K-type with sheath diameters of 1.0mm and 1.5mm, equipped with built-in compression springs at the installation end to eliminate contact gaps generated by thermal expansion and contraction of the manifold during heating. For large multi-cavity manifolds with long flow channels, long-line flat-head thermocouples with 3m to 5m outgoing wires are configured to adapt to the layout of mold external temperature control boxes. High-temperature modified N-type flat-head thermocouples are separately developed for manifolds used for LCP and PPS molding, with Inconel alloy sheath to resist high-temperature volatile gas corrosion.
Deep probe inserted thermocouples are dedicated to single hot runner nozzles. The slender cylindrical sensing head can be inserted into the reserved deep temperature measuring hole of the nozzle body, directly contacting the metal matrix near the nozzle flow channel to obtain the most accurate plastic melting temperature. This product is divided into two specifications: short probe for small open nozzle and long probe for large valve gate nozzle. The probe length can be customized according to nozzle wall thickness, ranging from 5mm to 25mm. The outer sheath adopts thin-diameter seamless stainless steel tube, which can be bent appropriately during mold assembly without breaking internal alloy wires. Miniature 0.8mm ultra-thin probe thermocouples belong to a special subdivision product, mainly supporting micro needle nozzles for electronic connector molds with narrow installation space, which will not interfere with the assembly of valve needle driving components around the nozzle.
Valve gate integrated thermocouples are customized products for needle valve hot runners. Traditional separate thermocouples need to reserve independent installation holes on the valve nozzle, increasing mold processing difficulty; integrated products integrate the temperature sensing wire and valve needle positioning sleeve into one component, completing temperature measurement and valve needle limiting at the same time. The sensing head is attached to the heating sleeve of the valve nozzle, real-time monitoring the temperature near the gate to prevent plastic curing and wire drawing at the gate position. This series mostly uses E-type high-sensitivity thermocouple wires, which can capture tiny temperature changes at the gate and feed back signals to the temperature control box to adjust local heating power, effectively solving the burr and wire drawing defects of transparent plastic products. The wire outgoing end adopts high-flexibility anti-fatigue wires to adapt to the frequent up and down movement of the valve needle without wire breakage.
Spring compression button thermocouples belong to general universal products for small hot runner nozzles. Without deep drilling on the nozzle body, the spring top button structure is directly pressed on the outer surface of the nozzle heating sleeve, with simple installation and low mold processing cost. This product is widely used in small household appliance plastic molds with low precision requirements, such as bottle caps, daily plastic shell parts. The disadvantage is that the temperature measurement accuracy is slightly lower than inserted probe thermocouples, affected by the heat loss of the nozzle surface air layer. Manufacturers launch enhanced button thermocouples with high thermal conductivity gaskets to reduce temperature measurement deviation, balancing cost and basic temperature control demand.
High-temperature flexible armored thermocouples are special products for ultra-high temperature hot runner systems processing special engineering plastics. The overall wire body can be bent arbitrarily, suitable for hot runners with complex internal pipeline layout and narrow installation gaps. The alloy wire adopts N-type high-temperature resistant formula, continuous working temperature up to 450℃, and the outer armored tube is made of anti-oxidation alloy material, which can resist long-term high-temperature baking without aging. The wire outer layer is covered with thick fiberglass protective sleeve to avoid scalding damage during mold disassembly and maintenance.
In addition to the above mainstream classification products, there are also split quick-plug thermocouples, multi-point combined thermocouples and miniature patch thermocouples for special hot runner molds. Each product category has fixed matching hot runner structure scenes. Mold engineers need to confirm the nozzle type, manifold structure and plastic processing temperature range in advance to select the most suitable thermocouple product model, ensuring the temperature control stability of the hot runner system from the hardware matching link.
