How to Use Thermocouple Calibration Furnaces for On-Site Mold Workshop Testing?

The necessity of regular thermocouple calibration to avoid concealed drift fault in large injection molding workplaces with several hot runner molds makes the portable temperature calibration furnace become necessary testing equipment. The mastering of the standard calibration furnace operating stages, temperature point setting and data recording standards, can assure reliable test results, and avoid the occurrence of erroneous calibration data that cannot reflect the real measurement error of the thermocouple.

Preparation for calibration include equipment check, probe pretreatment. Before starting the calibration furnace, verify the temperature homogeneity of the heating tank. Clean the metal heating blocks to remove leftover carbon and oil stains, which impede heat conduction. Remove all thermocouples to be calibrated from the mold and allow to cool to room temperature. Clean sensing tips with an alcohol wipe to remove carbon deposits. Probes with deeply scratched or perforated sheaths are rejected immediately without calibration. Damaged hardware will not return to accuracy even after recalibration. Use a standard reference thermocouple with a valid national calibration certificate as the benchmark comparison object. Group the probes into K-type and J-type categories so as to avoid mixed testing.

Three important temperature calibration points are determined according to the actual production temperature range of hot runner, including the low, medium and high working sections, to comprehensively evaluate the drift performance. First point is 200°C which is the low temperature PP/PE packaging molding temperature. Second point is 450°C which is the conventional ABS, PC, PA66 engineering plastic production temperature. Third point is 600°C which is the high temperature glass fiber reinforced plastic and PPS molding working condition. For PEEK ultrahigh temperature hot runner thermocouples, add one more 700°C calibration point to verify high temperature anti-drift performance.

The formal calibration operation flow is as follows: Insert standard reference thermocouple and test probes at the same depth in the heating block of the calibration furnace to make sure they are close to the heat source. Seal the cap of the furnace tank so that temperature consistency is not affected by heat losses. Set the target temperature of the furnace, wait for the consistent temperature holding for 15 minutes, and then record data. Unstable changing temperature of the furnace will bring error test values. Record the reading of the standard probe and each test thermocouple correspondingly, then calculate the deviation value between the test probe and standard benchmark for each temperature point.

Calibration result judgment standards are according to IEC Class 1 & Class 2 precision regulations. For the deviation of K-type probes at all three temperature points, less than ±1.5°C is Class 1 qualification, suitable for automotive, medical precision molds; deviation between ±1.5°C and ±2.5°C is Class 2 qualification, suitable for ordinary packaging and household appliance molds; deviation over ±2.5°C are classified as severely drifted, and must be scrapped directly without reinstallation. J-type thermocouples are allowed a maximum deviation of ±3°C below 450°C; any high-temperature point beyond 700°C with a considerable deviation is deleted, as J-type wires cannot remain stable at high heat.

Post calibration data archival and probe marking required. Fill out the unified calibration record form, containing the serial number, type, calibration date, three-point deviation data and judgment result of the probe, and archive paper and electronic copies for quality traceability. Mark probes with waterproof tags showing calibration expiry date. Severely drifted probes are kept separately as waste parts to minimize accidental reuse by maintenance staff.

Portable calibration furnaces provide routine on-site verification without shipping the probes to third-party testing institutions, decreasing calibration cycle time and outsourcing expenses. Standardized furnace operation ensures reliable correction data, hence in principle eliminating batch faulty products generated by uncalibrated drifting thermocouples.333