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Hot Melt Glossary


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

Angel Hair

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.


Ball Check Valve

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.

Bead Thickness

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.

Cartridge Heater

See Heater Cartridge.

Cast-in Resistive Heating Element

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


Charring in Tank

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

Circuit Breaker

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.

Close-on rise Thermostat

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

Crossover Tube

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

Crop-out Time

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

Dual-acting Piston Pump

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

Enclosure Rating

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.

Extrusion Gun / Applicator

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.

Filter Bung

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.

Flow Rate

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.

Four-way Air Valve

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.

Ground Wire

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".

Heater Cartridge

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

Heating Bong

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.

Hot Melt Material

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

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.

Level Indicator

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

Light Emitting Diode

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

Low Level Indicator

See Level Indicator.


The device that distributes fluid and/or air.

Maximum Operating GunSpeed

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

Maximum Pumping Rate

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.

Melt Rate

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.

Open Time

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.

Operating Air Pressure

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

Operating Temperature Range

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

Overtemperature Protection

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

Parent Machine Interlock (PMI)

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

Pattern Control

A device that controls the dispensing of material.

Pressure-sensitive Adhesive

An adhesive that remains tacky after curing or setting.

Pull-in Time

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

Pulses per Minute

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

Pumping Rate

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

Rebuilt Exchange Program (RBX)

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.

Relief Valve

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

Resistance Temperature Detector (RTD)

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.

Service Block

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

Setting Time

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

Shifter Assembly

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


A common shape of adhesive.

Slot Nozzle

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

Solenoid Valve

An air control valve actuated by an electromagnetic coil.

Solid-state Circuitry

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.

Solid-state Device

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.

Tank Capacity

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.

Tank Strainer

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

Tank Volume

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

Temperature Sensor

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

Temperature Setback

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

Thermoplastic Material

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

Timing Device

See Pattern Control.

Touch Pad

Operator interface.

Unlubricated Air

Air free of oil.


A physical measurement of resistance to flow.

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