When hot runner molds are offline for weeks or months due to order gaps, improper storage of built-in thermocouples will cause hidden dampness, sheath oxidation and wire fatigue damage, and direct reuse without inspection will trigger mass production temperature faults. This article divides the workflow into offline mold pre-storage treatment, long-term storage protection, re-inspection before re-production and standardized reuse judgment criteria.
Step 1 Pre-storage cleaning and sealing treatment before mold offline
1. Cool the hot runner completely to room temperature, disassemble all thermocouples one by one (prohibit long-term storage attached to the mold).
2. Thoroughly remove carbon deposits, oil mist and plastic residue on sensing heads, sheaths and plug pins with neutral cleaning agent and low-pressure nitrogen blowing; fully dry for 2 hours at 120℃ to eliminate internal sheath moisture.
3. Coat a thin anti-rust conductive grease on plug pins, apply a thin layer of nano anti-stick thermal paste on sensing contact surfaces, and seal the wire outlet with supplementary high-temperature silicone glue if the original seal is aging.
4. Classify each thermocouple with a label marked with mold number, installation zone, disassembly date and cumulative working hours, then put into independent sealed moisture-proof plastic bags with desiccant packets.
Step 2 Long-term warehouse storage environmental specifications
1. Storage warehouse constant temperature 18~26℃, relative humidity 40%~65RH, equipped with dehumidifiers and ventilation fans, away from mold cleaning chemicals, oil storage areas and mold preheating furnaces.
2. Store thermocouples in sponge-lined plastic storage boxes, coiled into large-diameter loops (radius ≥10cm), no tight small winding that creates permanent wire stress; separate ultra-thin 0.8mm probes in independent partition slots to avoid extrusion bending deformation.
3. Classify storage by type: medical E-type, high-temperature N-type and ordinary K-type stored in separate boxes to prevent cross-contamination of residual corrosive plastic vapor on sensor surfaces.
4. Quarterly inventory inspection: Replace failed desiccant bags, wipe off pin rust, screen out sensors with cracked outer sleeves and oxidized sheaths for scrapping.
Step 3 Full re-inspection items before reinstallation on molds
Thermocouples stored for more than 3 months must complete four inspection items before reuse:
1. Appearance inspection: Check sheath pitting, wire sleeve embrittlement, plug pin corrosion and sensing head deformation.
2. Electrical performance test: Measure loop resistance and 500V insulation resistance; eliminate units with resistance exceeding standard +15% or insulation resistance below 500MΩ.
3. Rapid temperature comparison calibration: Use a heat gun constant temperature block to test 25℃ and 300℃ points; drift deviation over ±1℃ cannot be directly reused and needs formal furnace calibration.
4. Polarity verification: Heat the sensing bead and measure millivolt output to avoid reversed polarity caused by messy wire sorting during storage.
Step 4 Differentiated reuse limit rules
1. Storage period ≤3 months, all inspection items qualified: Directly install on the original matched mold for production, shorten the first monthly calibration cycle by half.
2. Storage period 3~6 months, slight drift within ±1℃ after calibration: Only allowed for household appliance and packaging low-precision molds, prohibited for medical and automotive core parts molds.
3. Storage period over 6 months: Even if inspection passes, replace for high-precision molds; can only be used for short-run trial molds with a maximum service limit of 1 month.
4. Thermocouples disassembled from corrosive PVC/flame-retardant plastic molds: Regardless of storage time, must pass full three-point furnace calibration and insulation test before reuse, with biweekly maintenance inspection after installation.
Forbidden reuse scenarios
Thermocouples with micro-perforated sheaths, cracked wire outlet sealing layers, fatigue-bent armored sections and spring loss of elasticity during storage are prohibited from reinstallation and must be classified as scrapped metal waste for centralized recycling.
