Industrial Maintenance & Reliability · SOP

Glue Pot Temperature Calibration & Purge Procedure: PUR & EVA

Comprehensive calibration and purge procedure for Nordson/Meltex-style glue pots and applicators. Ensures thermal accuracy, prevents adhesive degradation, and reduces nozzle plugging.

Estimated Time

45 min

Difficulty

Advanced

Regulation

ISO 9001:2024 / CSA Z432

Version

1.0

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Purpose

The purpose of this SOP is to establish a standardized methodology for calibrating the integrated resistance temperature detectors (RTDs) and thermocouples on PUR and EVA glue pots, and for executing a complete hot melt system purge. Accurate thermal control is critical to prevent charring (EVA) or cross-linking (PUR) which leads to costly nozzle and hose replacement.

Scope

This procedure applies to all PUR and EVA adhesive application equipment within the finishing department, including hand-held applicators and fully automated slot-die coating stations. It covers temperature verification against a NIST-traceable reference, PID controller offset adjustment, and the complete purge cycle using manufacturer-recommended flushing fluids.

Safety Precautions

BURNHOT SURFACE HAZARD: Glue pot and applicator hoses operate at 175–210°C. Allow system to cool to < 50°C before performing physical maintenance or purge fluid handling. Use high-temperature rated gloves (ASTM D120).
FUMETOXIC FUME EXPOSURE: PUR adhesive reacts with moisture and produces isocyanate vapors when heated. Ensure local exhaust ventilation (LEV) is operational and reading >0.5 m/s capture velocity at the source before beginning.
LOTOLOCKOUT/TAGOUT: Disconnect main electrical supply to the glue pot controller and pneumatically isolate the applicator before accessing thermocouple junctions or heater bands.

Required Tools & Materials

NIST-traceable surface/immersion thermometer (range: 0–300°C, resolution: 0.1°C)
PUR-grade purge fluid (e.g., DOP oil or manufacturer-specified glycol-ester blend)
EVA-compatible flushing compound (e.g., paraffin wax-based cleaner)
Torque wrench (for heater band bolts, spec: 8–12 N·m)
Isopropyl alcohol (99.9%) and lint-free wipes
High-temperature silicone grease (for thermocouple reinstallation)
ServiceGrid CMMS mobile device (to log calibration results and asset history)

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Procedure: Step-by-Step

1 PREPARE SYSTEM: Ensure the glue pot has been idle for at least 30 minutes. Set temperature controller to standby (130°C for EVA, 110°C for PUR). Verify main adhesive supply is closed and applicator air pressure is bled down to 0 psi.

2 ACCESS THERMOCOUPLE SENSOR: Remove the protective cover plate on the glue pot manifold. Loosen the compression fitting securing the RTD or thermocouple. Carefully withdraw the sensor without bending the probe tip.

3 REFERENCE MEASUREMENT: Immerse the NIST-traceable probe into the adhesive bath (or a prepared glycerin bath of known temperature). Allow 5 minutes for thermal stabilization. Record the reference value (T_ref).

4 CONTROLLER VERIFICATION: Using the HMI, navigate to the 'Temperature Calibration' menu. Compare the controller reading (T_c) to T_ref. Calculate the offset: Offset = T_ref - T_c. If |Offset| > 3°C, proceed to Step 5. If < 3°C, note in ServiceGrid and skip to Step 6.

5 OFFSET ADJUSTMENT: Input the calculated offset into the controller calibration parameter. Perform a second verification cycle. Lock the calibration parameter with the supervisor passcode. Generate a calibration label and affix it to the controller face.

6 PURGE CYCLE INITIATION: Refill the glue pot with the appropriate purge fluid (PUR-grade DOP oil or EVA wax-based cleaner). Set temperature to 150°C. Activate the applicator in manual bleed mode. Cycle the purge fluid through the hoses and gun for 15 minutes or until the discharged fluid is clear.

7 FINAL PURGE & RESIDUAL REMOVAL: Reduce temperature to 100°C. Wipe down the glue pot surface and nozzle tips with isopropyl alcohol and lint-free wipes. Reinstall the thermocouple with a small dab of high-temperature silicone grease. Tighten compression fitting to 8 N·m.

8 RESTORE & DOCUMENT: Close all inspection panels. Restore pneumatic and electrical power. Load fresh adhesive and perform a test bead. Document the calibration offset, purge fluid lot number, and technician ID in the ServiceGrid asset log. Mark the PM work order as complete.

Glue Pot Temperature Calibration & Purge Procedure: PUR & EVA

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