How to clean hot melt coating machine
Regular cleaning of a hot melt coating machine is essential to prevent adhesive charring, nozzle clogging, coating defects such as streaks, and premature wear of pumps and seals. Unlike water-based adhesives, hot melt solidifies at room temperature and requires heat or specialized solvents for removal. The cleaning frequency depends on the adhesive type (EVA chars faster than polyolefin), operating temperature (higher temperatures accelerate degradation), and production hours. For high-volume lines, a partial clean every shift and a full clean weekly is typical. This guide covers safe cleaning procedures for the melt tank, hoses, pump, slot die, roll coaters, and spray nozzles. Always wear heat-resistant gloves, safety glasses, and follow the machine manufacturer's lockout/tagout procedures.
General safety and preparation: Before cleaning, turn off the heaters and allow the machine to cool to a safe handling temperature (typically 80-120°C – hot enough to keep adhesive molten but not burning). Do not let the machine cool completely to room temperature because solidified adhesive is extremely difficult to remove. Set the temperature controller to a "purge" or "cleaning" setpoint (e.g., 120°C for EVA). Place heat-resistant containers under the die or hose ends to catch purge material. Have brass scrapers, copper brushes (steel brushes may scratch), lint-free cotton rags, and approved cleaning solvents (e.g., hot melt cleaner or mild petroleum distillate) ready. Some machines have a "reverse flush" capability. For PUR adhesives, use special PUR cleaning agents because moisture-cured PUR cannot be melted again.
Hot Melt Coating Machine - Hot Melt Adhesive Coating Machine
Cleaning the melt tank: 1) Drain the tank by pumping out as much adhesive as possible. 2) Add a commercial hot melt tank cleaner or low-viscosity polyolefin flush material. 3) Heat to 150-180°C and circulate for 15-30 minutes. 4) Drain again. 5) Wipe the interior walls with a brass scraper and rags. Avoid scratching the tank surface. 6) For stubborn char, use a soft wire brush on a drill (low speed). 7) Remove and clean the filter screen (replace if damaged). Never use water or water-based cleaners because water trapped in the tank will flash to steam and can cause explosive spattering when reheated.
Cleaning hoses and pumps: The pump can be flushed by running the cleaning material through it. For gear pumps, run at low speed while flushing. After draining, some operators run a small amount of clean adhesive through to "prime" the pump. Hoses should be flushed individually if possible. If a hose is severely blocked, it may need replacement. For maintenance, keep a set of "cleaning hoses" that can be swapped in. Do not use sharp objects to clear a hose; instead, apply heat and pump high-viscosity cleaner through under pressure. Never exceed the hose's rated pressure.
Cleaning slot die: The die is the most critical component. First, raise the die from the substrate. Purge the die by running the pump while the die is over a waste tray. Then, reduce temperature to 100-120°C. Remove the die from the machine (follow manufacturer's procedure). Disassemble the die by removing bolts and separating the two halves. Carefully remove the shim (note its orientation). Use a brass scraper and copper brush to remove adhesive from the manifold, lip, and outer surfaces. For fine cleaning of the lip, use a wooden or plastic stick – never metal that could nick the lip. Soak parts in a heated hot melt cleaner bath if available. For ultrasonic cleaning, use a mild solvent. After cleaning, inspect the lip edge for nicks under magnification. Reassemble with new gaskets, applying even torque to bolts.
Cleaning roll coaters and spray guns: For roll coaters, heat the rolls to 100-120°C and use a brass doctor blade to scrape off adhesive while the roll rotates slowly. Then wipe with rags. For spray guns, disassemble the nozzle and air cap. Soak in solvent or heat them in an oven at 150°C to soften adhesive, then wipe. Use compressed air to blow out small passages. Never poke wires into orifices. For all components, after cleaning, apply a thin layer of release agent (e.g., silicone spray) to surfaces that contact adhesive, but avoid getting it into the melt stream. Document all cleaning activities in a logbook. A well-maintained hot melt coating machine will produce consistent quality and last for decades.
