Hot melt gun modules are high pressure fluid valves. These are typically attached to heated hot melt gun manifolds for quick and easy removal to minimize line downtime when they do not shut off completely. Incomplete shut off results in extended patterns, leaking, dripping or the “stringing” of the hot melt adhesive.
In these modules a needle valve lifts off the internal seat with compressed air or electric coil. It closes with compressed air or a spring. This action stops the hot melt flow between the needle tip and the needle seat which then flows into and through a nozzle tip onto the
substrate. When the needle is forced down against the seat with compressed air or compressed spring the flow of adhesive is, or should be, stopped completely. Adhesive in the typical hot melt system can be pressurized to over 1000 psi making the intimate seating of the needle
and seat critical.
Needle valves in the modules come in all shapes and sizes with each offering certain features and benefits but they should all accomplish the same goal of shutting off pressurized hot melt. This needle valve seating process can be dramatically affected by adhesive viscosity, the compressed air or spring used to force the needle into the “Off” position and debris or char in the adhesive.
When a hot melt is very thick or does not machine well, the air solenoid or compressed spring do not force the needle valve “off” position or debris gets between the needle and seat the module will not operate properly.
Please note that other factors such as internal module seals and the nozzle tip attached to the module can affect pattern performance as well.
For more information call or email Pierce Covert,
Glue Machinery Corporation