Hot Melt Glossary

Any material that can be used to adhere or "stick" one surface to another.

Fine threads of adhesive caused by incomplete transfer of the adhesive mass from applicator to substrate, followed by elongation of the connecting bridges. May be caused by improper nozzle shutoff with a high viscosity adhesive.

The device that dispenses a material (adhesive) onto a substrate or product. Sometimes called "guns".


An automatically actuated valve which is opened by fluid flow in one direction and closed by flow in the opposite direction.

The width of an adhesive bead which has been deposited on a substrate. The measurement is taken before the bead has been flattened by adhering it to another surface.

See Heater Cartridge.

A non–replaceable heating element specifically shaped to provide a uniform thermal profile in the heated object.

The degradation of a fluid that occurs as a result of time and exposure to atmospheric air and/or heat.

An electronic device that acts to shut down a powered AC circuit when current draw (amps) exceeds some preselected value or when certain fault conditions exist.

A temperature control device that closes, completing an electronic circuit upon reaching a specific temperature.

The tube that connects the outlet port of a pump to the distribution manifold of a hot melt applicator.

The time between when the gun is signaled to stop and when the adhesive flow actually does stop.

A pump that delivers material on both the upstroke and the downstroke.

A manufacturer’s statement of the maximum level of some external condition, such as water or dust level, that the enclosure is capable of withstanding.

A speed–sensing device which outputs a frequency of pulses proportional to the measured line speed.

A spring–loaded triggering device for dispensing or depositing material. There are two basic types of guns, the manual gun which is actuated by hand and the automatic gun which is actuated by process controls.

That part of a filter assembly external to the unit to which the filtering element is attached, or contained within the unit. It is also used for access or cleaning.

The amount of material flowing through the system per unit of time. The amount may be expressed in gravimetric (weight) or volumetric terms. Examples: grams/minute, ml/min, lb/hour, gallons/hour.

A valve typically used to pressurize one side of a double acting cylinder while opening a exhaust path for the opposite side.

See Key–to–line.

A cross–linked, insoluble material which can form in a hot melt applicator under extended thermal stress.

A wire that connects all AC powered devices to earth ground.

The device that dispenses a material (adhesive) onto a substrate or product. Sometimes called "applicators".

A replaceable resistive heating element, tubular in
shape, designed to fit in a machined hole in the object to be heated.

The volume that is heated and thermally controlled by a single control device.

A container allowing non–melted adhesive to be supplied on a continuous basis to a melt zone.

The adhesive or thermoplastic material dispensed by the hot melt system.

The melter, hose(s), gun(s)/applicator(s) and timing mechanism.

A system that regulates flow rate in proportion to the substrate (line) speed.

A device that shows the level of material in a tank, reservoir or hopper.

A device that converts applied voltage to light. LEDs appear as colored lights that indicate operating conditions.

See Level Indicator.

The device that distributes fluid and/or air.

The highest cycle rate of the gun that produces a repeatable pattern.

The maximum adhesive flow rate achievable without exceeding any operating limits. The maximum pumping rate is measured at the manifold outlet. The rate is based on an adhesive with a given viscosity.

The rate at which a material can be melted continuously on a long–term basis while maintaining the output fluid temperature within a desired temperature band. Commonly expressed in units of grams/minute, grams/hour, lb/min or lb/hr.

That part of the hot melt system that is used to heat adhesive to its required application temperature and pump it to the hose(s) and gun(s). It consists of a tank or reservoir, pump, filter, distribution manifold and temperature controlled heating system.

The extrusion tip, the point at which the adhesive exits the gun. The nozzle controls the adhesive stream’s volume, shape and direction. Nozzles may have single or multiple orifices.

The time after adhesive is applied during which a serviceable bond can be made. Many factors affect open time, including temperature, substrate, the adhesive used and the amount of adhesive applied.

The pressure at which the pump and/or guns are operated. See product specifications.

The range of temperatures in which the specific material or adhesive in use functions satisfactorily in a particular application.

A product feature that shuts down the unit or produces an alarm when temperatures are outside a specified band.

A product feature that prevents the parent machine from
operating before the hot melt system is ready.

A device that controls the dispensing of material.

An adhesive that remains tacky after curing or setting.

The time between when the gun is signaled to start and when the adhesive flow actually begins.

Output signal frequency, often from an encoder, tach generator or similar device.

The amount of material a pump can deliver per unit of time.

A Nordson program which offers factory rebuilt equipment at a reduced cost in exchange for the customer’s old equipment.

An adjustable device for maintaining pressure at the preset valve.

A safety device designed to release pressure if it exceeds a preset level.

A temperature–sensing device that changes resistance at a predetermined rate in response to changes in temperature.

A special case of Key–to–line or Gear–to–line, often applied to air control for piston pumps.

Part of an automatic extrusion gun, the service block supplies the needed air, adhesive and heat to make the gun operate.

The time required for a material to reach a set state after being applied in a fluid state.

A mechanical or electrical device used to switch a 4–way air valve.

A common shape of adhesive.

A nozzle that applies a film of adhesive instead of a bead.

An air control valve actuated by an electromagnetic coil.

An electronic circuit whose operation depends upon any combination of optical, electrical or magnetic phenomena within a solid. Specifically excluded are circuits that depend upon physical movement, as well as those requiring either contact with or avoidance of other solids, liquids, gases or plasmas.

A device whose electrical functions are performed by semiconductors or otherwise completely static components such as resistors and capacitors. The device may contain components that do not depend on electronic conduction in a vacuum or gas.

In the Nordson context, a material used to dissolve hot melt adhesive to facilitate system cleaning.

A defect in adhesive application characterized by hair–like fibers of adhesive emanating from the trailing edge of the bead. Stringing may produce continuous fibers attached to the nozzle. It is most often caused by the gun temperature being too cold.

The material or product on which the adhesive is applied.

The amount of material that the tank can hold with the fluid level 25 mm (1 inch) from the top of the hopper or tank.

A product feature that helps keep large pieces of foreign material out of the pump.

The volume that the tank can hold when it is filled. The displacement of the pump is taken into account in this measurement.

That part of a temperature control system that detects the temperature and feeds this information to the control device.

A product feature by which the system temperature may be automatically reduced to a preset number of degrees.

A synthetic material which is solid at room temperature, becomes soft when heated, and returns to solid form upon cooling.

See Pattern Control.

Operator interface.

Air free of oil.

A physical measurement of resistance to flow.