Reasonable matching of thermocouple lead length is an important detail easily ignored in hot runner configuration and maintenance. Too short lead will be pulled tightly during mold opening and closing, causing internal wire breakage and terminal falling off; too long lead will be tangled and squeezed in the mold wiring groove, easy to be worn, high-temperature scorched and interfere with mold closing. Scientific selection of lead length according to mold size, runner layout and wiring path can effectively avoid mechanical damage and extend the service life of thermocouples.
For small single-cavity hot runner molds with compact structure, the wiring path is short and the mold opening stroke is small. It is suitable to configure standard short leads to avoid redundant wire winding and occupation of mold gap space. For medium-sized multi-cavity molds with middle layout manifolds, it is necessary to reserve enough margin according to the maximum mold opening distance, ensuring that the lead is naturally stretched without tension when the mold is fully opened, and smoothly folded without extrusion when the mold is closed.
Large automotive molds and stacked hot runner molds have large mold opening stroke and complex multi-layer wiring paths. The thermocouple lead needs to be lengthened in sections, and reserved bending loops are set at the corner of the wiring groove to buffer the displacement generated by mold movement. It is forbidden to arrange the lead in a straight tension state, otherwise the long-term tensile force will cause fatigue fracture of the internal alloy wire and insulation layer cracking.
In addition, the layout of temperature control cabinet distance should also be considered. If the mold is far away from the electrical cabinet, excessively short leads cannot reach the terminal row, and forced docking will cause poor contact and signal attenuation. Too long leads will increase the sensing signal transmission distance, easily coupled with external electromagnetic interference, resulting in temperature jumping. Professional hot runner manufacturers will reserve standard length specifications according to mold tonnage and structural type, and customize non-standard length for special molds, ensuring the lead length is perfectly matched with the mold structure, wiring path and cabinet layout, eliminating hidden dangers from the source.
