Mold manufacturers purchase thermocouples in batches as standard supporting spare parts for new hot runner molds. Complete standardized batch incoming inspection can screen unqualified products with alloy impurity, poor welding, insufficient insulation resistance and excessive resistance before entering warehouse storage, avoiding assembly of defective sensors on finished molds and delaying mold trial delivery progress. This article forms a complete batch inspection process covering appearance, electrical performance, precision and mechanical performance.
First link: Appearance sampling inspection according to batch quantity. For each delivery batch of thermocouples, extract 10% of the total quantity for full appearance inspection, with a minimum sampling quantity of no less than 5 pieces regardless of small batch size. Inspection items include: smooth and seamless laser welded sheath without pinholes, dents and welding cracks; mirror-polished measuring base without burrs and rust; uniform tight braided shielding wire mesh without wire shedding; clear standard color-coded wires without mixed-color confusion; intact connector shells without deformation and oxidation of terminal sheets; complete product specification labels marked with alloy type, sheath diameter, wire length and precision grade. Any single unqualified appearance item in sampled products triggers full 100% appearance re-inspection of the whole batch.
Second link: Electrical performance full batch testing (100% inspection for all delivered thermocouples). Item one: continuity test with digital multimeter, eliminate probes with broken internal alloy wires. Item two: 500V megohmmeter insulation resistance test, qualified standard insulation resistance ≥100MΩ, reject all probes with resistance below the threshold due to damp sheath or micro-cracks. Item three: loop resistance measurement, record the total wire resistance of each thermocouple, compare with the theoretical resistance value of customized wire core diameter and length, screen out ultra-thin wire core products with excessive resistance that cause false TC OPEN alarms. Item four: polarity identification test, confirm positive and negative wires comply with international color standards, mark reversed polarity defective products separately for return to the supplier.
Third link: Precision sampling calibration test. Extract 5% of each batch as calibration samples, use metal block constant temperature calibrator for three-point temperature testing at 150℃, 280℃ and 380℃. Judgment standard: Class 1 thermocouple error ≤±0.5℃, Class 2 error ≤±1.0℃. If more than one sample exceeds the tolerance range, carry out full batch precision re-calibration; if the unqualified rate exceeds 10%, return the whole batch of products to the supplier for rework. Record all calibration error data of sampled products and file the test report together with the delivery order for mold quality traceability.
Fourth link: Mechanical performance spot check for structural durability. Randomly select 2–3 samples per batch for bending fatigue test: bend the sheath at the minimum allowable radius 10 times repeatedly, then re-test insulation resistance and continuity; probes with resistance drop or wire breakage after bending are judged as unqualified, indicating unqualified internal alloy wire fatigue resistance. For spring ring integrated thermocouples, carry out elastic compression cycle test; after 5,000 compression cycles, the spring cannot lose obvious elasticity, otherwise the batch spring accessories have unqualified heat treatment process.
Fifth link: Batch classification and qualified warehousing management. After passing all inspection links, paste qualified inspection labels on each bundle of thermocouples, classify and store them by alloy type, sheath material, wire length and thread specification in independent drying storage boxes with desiccant. Unqualified products are divided into appearance defective, electrical performance defective and precision drift defective three categories, issue a unified unqualified notice and contact the supplier for replacement or rework within the agreed delivery cycle. Establish a batch inspection archive system, recording delivery batch number, sampling quantity, unqualified quantity and inspection personnel signature, forming complete incoming quality control records for subsequent mold after-sales quality tracing.
