Published by admin on 16 Dec 2008
Hot Melt Hose Operation
Heated hoses are used to convey hot melt (thermoplastic) adhesives in the typical adhesive application system from the melt tank to the dispensing valves. The hoses are temperature controlled by means of a sensor, located on the outside of the hose core, usually between the hose heater and the hose outer wall. Remote temperature controls are capable of holding temperatures fairly close to the setpoints today, as compared to years ago.
There is still a problem with contamination over time within the hose itself, despite manufacturer’s efforts to minimize this tendency. Some adhesives can virtually eliminate charring within the hose, but most of the standard hot melt adhesives today have some limit in terms of ‘pot life’. This is the length of time that a material can be held at a given temperature before signs of degradation begin to occur. This period of time can range from several hours to almost indefinitely, depending on the adhesive and its formulations. The average hot melt has a pot life of 50-100 hours at application temperature, often 350F.
The issues begin to occur within hoses that are not kept in continuous production first, but can eventually affect all hoses over time. When the material is not flowing within the hose, the hot melt that is in contact with the hose wall is the hottest material in the hose. The adhesive, over time, if exposed to high heat will eventually begin to break down, often leading to an increase in viscosity, gelling, and ultimately charring which forms over time on the hose interior walls. The use of ‘cleaning fluids’ to try and dislodge this ‘char’ often is not fully effective, rather loosening and removing some, but leaving the rest to become dislodged after the hose is put back in service.
Users can minimize problems with hoses over the long term by using the newer ‘standby’ feature on hot melt tanks which lower the hose temperatures when not in use. Other options are to manually lower hose and gun temperatures or simply turn off the entire system to minimize periods where they are kept hot but material is not being dispensed. It is recommended to replace hot melt hoses every 3 or so years, depending on system usage and materials being used, to ensure clean system operation and minimized downtime due to clogged nozzles and filter maintenance.
Hot Melt Hose Operation by John Neu at Glue Machinery Corporation
