Probe insertion depth is a core customized parameter for bayonet and embedded thermocouple supporting Husky, Synventive and domestic mainstream hot runner brands; excessively long or undersized probe dimension breaks original pre-designed thermal contact structure and causes persistent measurement deviation and abnormal hot runner heating faults, which is a common easily ignored mistake during spare part ordering and field installation. When probe length exceeds mounting hole depth obviously, redundant front tip tightly compresses hole bottom metal surface and pushes built-in bayonet spring to ultimate compression limit for permanent plastic deformation. After repeated hot runner thermal expansion and cold contraction cycles from daily startup and shutdown, deformed spring can no longer provide stable preload pressure, forming intermittent separation gap between sensing tip and measured surface and irregular temperature jump on controller. In extreme cases overlong probe stretches into internal flow channel, protruding into melt flowing space to cause flow mark and local plastic carbon accumulation around protruding position.
On the contrary, too-short probe cannot reach deep effective measuring area inside mounting hole and leaves thick air gap between probe end and hot runner metal base; air is poor heat conductor forming natural thermal insulation barrier blocking effective heat transfer, making displayed temperature permanently lower than real hot runner working value. Receiving false low-temperature feedback signal, controller continuously increases heating output power and induces local nozzle or manifold overheating, plastic pyrolysis, gate drooling and surface gas mark defects on finished parts. Such measuring error brings more serious loss on narrow-window high-temperature PPS and PEEK engineering plastic hot runner, a small range of temperature out-of-control easily leads to full-batch product scrapping.
Standard maintenance specification requires measuring original hole depth from disassembled old thermocouple before ordering replacement parts, reserving 1~2mm reasonable spring compression allowance to avoid length mismatch risk. Many small maintenance teams directly purchase fixed-size standard thermocouple for urgent rush repair without on-site dimensional measurement, resulting in secondary mold disassembly and repeated spare part waste. Spare part incoming inspection adds probe length sampling test item to block nonstandard dimension products from entering production line, fundamentally eliminating hidden trouble induced by improper probe size and stabilizing long-term hot runner temperature precision.
