Mold junction boxes serve as fixed installation positions for thermocouple cold junction plugs, converting hot-end temperature signals into identifiable data through the temperature controller's cold junction compensation algorithm. Many hot runner molds arrange junction boxes excessively close to manifolds and nozzle heating plates, resulting in long-term high-temperature radiant heat acting on plug terminals, pushing cold junction temperature far above the controller's standard 25°C calibration reference point and generating fixed cold junction drift deviation ranging from 4°C to 10°C that cannot be eliminated merely by adjusting process parameters. Systematic transformation covering mold design, junction box structure, thermal insulation protection and wiring specifications can completely cut off radiant heat interference and stabilize cold junction temperature within a constant narrow range.
The most fundamental solution lies in optimizing junction box installation positions during the early mold drawing design phase. When drafting hot runner mold blueprints, the junction box mounting plate must be arranged on cold mold base plates at least 80mm away from manifold heating zones, avoiding side plates directly attached to manifold thermal insulation layers. For compact small electronic molds with limited overall dimensions, separated extension wiring transition plates are designed to lead all thermocouple cables out of high-temperature zones first, then install junction boxes on outer cold plates of transition plates, isolating boxes from manifold radiant heat from spatial layout. Embedding junction boxes inside mold thermal insulation layers or within 50mm of nozzle heating sleeves is strictly prohibited; such layout will push cold junction ambient temperature above 40°C after heating and trigger severe compensation drift. For stacked multi-layer hot runner molds with overlapping manifolds, each layer's wiring transition plate independently extends to outer cold mold plates, with unified junction box installation on the outermost mold side to avoid superposition radiant heat from upper and lower manifolds.
Second, multi-layer thermal insulation protection structure is added to junction box shells for existing molds with immovable box positions due to finished steel structures. Wrap outer walls of metal junction boxes with 10–15mm thick high-temperature silica thermal insulation cotton, covered externally by aluminum foil reflective film to block radiant heat transfer from manifolds. Fill gaps between junction boxes and mold mounting plates with high-temperature thermal insulation gaskets to cut off heat conduction via solid metal contact. A 20mm gap is reserved between plug terminals and box inner walls inside junction boxes, with small thermal insulation partitions placed between multi-channel plug groups to prevent internal heat accumulation. Micro ventilation holes are reserved on box covers to discharge tiny accumulated heat inside boxes and avoid continuous internal temperature rise after long-term heating.
Third, wiring channel optimization reduces heat conduction transmitted by thermocouple cables. Wire grooves between manifolds and junction boxes must be wrapped with integrated thermal insulation sleeves, separated from heating sleeve metal surfaces by thermal insulation strips to prevent cables from absorbing heat and transferring high temperature to cold junction plugs. Attaching cables directly to manifold thermal insulation cotton surfaces is forbidden, as residual heat on insulation layers continuously heats cables and elevates cold junction temperature. A 1–2 meter loose cable transition section is reserved outside high-temperature mold plates before entering junction boxes, allowing cables to fully dissipate heat under normal workshop ambient temperature and ensuring temperature transmitted to plug terminals matches surrounding environment, eliminating wire-induced heat conduction drift.
Fourth, standardized internal plug layout and auxiliary constant temperature cold junction measures. Dense stacking of thermocouple plugs inside junction boxes is avoided; compact plug groups accumulate heat generated by tiny contact resistance to further raise internal box temperature. Plastic thermal insulation partitions separate each channel plug to disperse heat accumulation. For molds suffering extremely strong radiant heat that cannot be fully isolated by thermal insulation cotton, miniature constant temperature cold junction modules are installed inside junction boxes. These modules independently collect real-time temperature of each plug terminal and feed accurate cold junction temperature back to controllers for compensation, completely offsetting drift caused by high-temperature box radiation. Such constant temperature modules become mandatory transformation components for high-temperature PEEK hot runner molds with long-term junction box ambient temperature exceeding 38°C.
Fifth, daily inspection and seasonal auxiliary adjustment specifications. Before each shift's production startup, open junction box covers for 10 minutes to dissipate residual heat accumulated after last shutdown, then close covers and power on heating to avoid initial cold junction high temperature triggering early-stage temperature reading deviation. In hot summer workshops, low-speed small external fans blow air toward junction boxes for auxiliary heat dissipation, with thicker thermal insulation cotton wrapped on molds placed near workshop heating furnaces. The controller's cold junction compensation module is calibrated every six months before summer and winter seasonal temperature transitions to correct algorithm deviation caused by long-term circuit board high-temperature operation.
After implementing layered thermal insulation and position optimization measures, junction box cold junction temperature fluctuation range can be controlled within ±3°C of the standard 25°C reference value, reducing cold junction drift deviation below ±0.8°C and fundamentally eliminating hidden quality losses induced by inaccurate temperature feedback from manifold radiant heat.
