Selecting the Right Melter for your Packaging Application

Matching the Right Hot Melt Adhesive System
to Your Case/Carton Sealing and
Tray Forming Operations
Published by: Nordson Corporation
Hot Melt Adhesive Dispensing
Systems for Packaging
The deposition of thermoplastic (hot melt) adhesives is the preferred
method for carton sealing, case sealing, tray forming and a host of
other packaging applications.
All hot melt adhesive systems employ a melting device to transform
solid adhesive in pellet, pastille, pillow, block, slat or other form, to a
liquid state required for dispensing. They also contain a pump, which
pressurizes the molten adhesive. While sometimes called a tank, unit,
system or applicator, the most globally recognized term is adhesive
melter.
A heated transfer hose carries the molten adhesive, at application
temperature, preventing it from returning to its solid form, moving
it from the melter to an application device.
The application device, sometimes referred to as a valve, gun,
manifold or dispenser, more correctly called the adhesive applicator,
deposits molten adhesive onto the package or container flap(s).
When a second flap is brought into contact with the first, the molten
adhesive cools and creates a bond between the surfaces.
Adhesive Melter Types
There are three primary melter types. While all three melt and pump
adhesives, some are more flexible and considered better suited for
packaging operations.
1. Grid and reservoir melters with tank capacities from 12 to
100 liters offer robust, higher-watt heaters and can be used
in applications that require higher adhesive melt rates and
throughput.
2. Bulk melters that use heated platens to melt and pump adhesive
directly from 5-gallon/20-liter pails up to 55-gallon/200liter drums typically have melt/throughput rates and energy
requirements that preclude their efficient use in packaging
operations.
3. Tank-style melters with capacities from 4 to 10 liters are most
common but, sizes up to 100 liters are also available. Melt rates
from 4.3 to 11 kg/hr (9.5 to 24 lbs) and throughput rates of 6 to
12 kg/hr (15 to 27 lbs) are readily available.
A distance- or time-based adhesive pattern control activates the
adhesive applicator and manages the precise placement of adhesive
beads, dots or short/modulated beads using a pre-determined
program.
Beyond basic functionality, production environment and application
requirements greatly impact melter selection. Fortunately, a wide
variety of melters with a choice of system controls, melt technologies,
tank capacities, pump types and output connections are readily
available to today’s packagers.
Tank-style melters for packaging applications
Packaging-grade hot melt adhesives are available in formulations that
permit melting and application at temperatures ranging from as low
as 200º F (93º C) to over 375º F (190º C).
Heat generated in the bottom of the tank is conducted up the tank’s
side walls, and is transferred from the heated surfaces to the adhesive.
Metal fins inside the tank are often used to attain more heatconducting surface area and better heat transfer to the adhesive.
1
Electronic temperature controls within the melter compare the
temperature of the adhesive in different areas or zones to the
temperature setting and activate tank heaters as needed, before the
adhesive cools. To help assure the bonding characteristics of your
adhesive and the quality of your packages, melters with temperature
control stability of +/- 1 º F (0.5 º C) are highly recommended.
Determine the amount of adhesive per product, per production hour
and per day by calculating:
• Number of adhesive beads per product
• Length of each bead
• Bead diameter(s)
• Number of packages you want to seal per day hour
Compared to grid and reservoir melters and bulk melters, tank
melters are typically more compact in size. A smaller footprint
provides easier installation and operation in parent packaging
machinery.
An automatic, on-line adhesive calculator can help you do this with
ease:
Tank-style melters easily accommodate a wide variety of adhesive
shapes and sizes allowing packagers to change adhesive types to meet
different package needs over time.
The best melter tank designs for packaging:
• Minimize sharp corners where adhesive can become trapped and
degrade. This reduces adhesive char, nozzle clogging, debris on
packages, maintenance and downtime
• Use non-stick surfaces for easier cleaning
• Provide easy tank access from three sides
Pump Types
Choosing the correct melter for your packaging application will
include determining whether an electric-motor-driven pump or a
pneumatic-driven pump best suits your needs.
Consider these factors when deciding between electric or pneumatic
melters:
• Adhesive type
• Adhesive viscosity ranges
• Environment and availability of factory air
• Level of adhesive output precision required
• Need for continuous or intermittent adhesive output
• Line speed
• User preferences
Calculating Adhesive Demand
The amount of adhesive you need to dispense is a key factor in
selecting the right adhesive melter for your operation. Amount
of adhesive per package, packaging line speed and the number of
packages per hour will determine your melt rate and throughput
needs.
To get started calculating your adhesive requirements, you will need
to know what it takes to securely seal your package.
Pneumatic Piston Pumps
Piston pumps use compressed air to activate an air piston which
moves a hydraulic plunger. The simple design requires no gear
reducers or electric drive mechanisms and provides long, dependable
service life.
The piston creates a continuous, even hydraulic pressure which pushes
(transports) the molten adhesive on demand.
Adhesive output can be increased or decreased by simply increasing or
decreasing the air pressure to the piston pump. Increasing air pressure
increases the hydraulic pressure which moves the adhesive through the
hose to the applicator, allowing more adhesive to be dispensed at any
given time. Similarly, decreasing air pressure results in less adhesive
being dispensed.
Piston pumps stroke only when adhesive is being used and are at rest
when adhesive is not needed, resulting in long service life.
In single-action piston pumps (also called shot pumps), adhesive is
pumped as the piston strokes in one direction only. A pause in the
pumping action occurs as the piston returns to its original position
before beginning the next stroke. Single-action pumps are used when
larger amounts of adhesive are dispensed and there is time between
products for the pump to reset. While less costly, single-action pumps
do not meet the line-speed requirements of most packaging operations.
Double-action pumps pressurize adhesive during both directions of
the pump stroke(s). The instantaneous and virtually unnoticeable
pause that occurs as the piston changes direction at the end of each
stroke usually has no effect on adhesive output.
If a piston pump melter best meets your needs, be sure to insist on
a melter with an automatic pressure discharge. Piston pumps create
hydraulic pressure typically ranging from 250 to 800 psi (17.2 to 55.2
bar). An automatic pressure discharge safely releases residual pressure
back into the melter tank in seconds.
2
Electric Gerotor Pumps
A gerotor (short for generated-rotor) pump operates using a larger
outer gear ring and a smaller inner gear that has one less tooth than
the outer gear. The inner and outer gears both rotate in a clockwise
direction but, on different, fixed centerlines. As the gears rotate, the
spaces between the teeth change, creating pockets or chambers.
The rotating gears create a partial vacuum as the gear teeth come
apart/un-mesh, drawing adhesive into the inlet side of the pump,
between the gears and the housing.
The adhesive is carried in the spaces between the gear teeth, around
the housing to the outlet port. When the gear teeth mesh again, an
increase in pressure occurs, pushing the adhesive that was between
the teeth out a pump port.
A constant amount of adhesive is output with each complete
revolution of the gears.
Spur gear pumps accommodate a wide range of material viscosities
and are well-suited for applications like beverage packaging which
require high-volume and high-speed, high-precision adhesive output.
During the gears’ rotation cycle, the size of the chambers changes
continuously. Total available chamber volume increases, creating a
vacuum and adhesive intake.
Spur gear pumps are commonly coupled with variable-speed drives
to provide flexibility and synchronization of adhesive output to
production line speeds.
Adhesive enters the inlet port, filling a chamber between the two
gears. As the gears rotate, additional chambers between the gears fill
with adhesive as they pass the inlet port.
Additionally, pump sizes can be specified for various outputs. In
some instances, multiple pumps are utilized to meet high output
requirements or provide a variety of output rates from a single melter.
As total available chamber volume decreases, compression occurs and
the inner gear forces adhesive from individual chambers through the
pump outlet producing positive-displacement, continuous adhesive
flow at constant speed.
Melter Controls
Controls have advanced dramatically since the introduction of
hot melt dispensing systems in the mid-1960’s. Today’s melters are
available with control packages ranging from simple on/off switches
to programmable systems that monitor and control multiple
temperature zones, production speeds and communication interfaces.
Their gear-and-chamber design and operation allows gerotor pumps
to process a broad range of adhesives with widely ranging viscosities.
Because they do not require factory air, gerotor pumps are suitable
for many remote, on-site and agricultural packaging operations
where only electricity is available.
While seemingly more economical than piston pumps or spur-gear
pumps, gerotor pumps deliver less precision and line speed flexibility,
limiting their use to lower-volume, less demanding and manual
dispensing applications.
Electric Spur-Gear Pumps
Spur gear pumps are positive displacement pumps that employ
meshing, counter-rotating gears in a housing.
A drive gear, attached to a power source is turned in a counterclockwise direction. The gear it is driving (the idle gear) turns
clockwise.
Complementing these technological advances, packagers can benefit
from selecting melters that feature:
• Intuitive controls that allow operation at virtually any skill or
language ability level
• At-a-glance graphic interfaces for operators to monitor, ready, fault,
service and temperature for the melter tank, hose and gun
• Graphical service indicators for filter replacement and low adhesive
level
• Serial and network communications capabilities that provide easy
integration into parent packaging machinery and system controls
• Parent machine interlocks that prevent parent machinery from
operating until the adhesive melter is ready
• Sequential start up of melter heating zones to prevent adhesive
melting and expansion from creating damaging pressure in the
melter, hose and applicator
• Remote monitoring ranging from one operator controlling a single
melter – to Fieldbus connectivity (EtherNet/IP, PROFIBUS-DP,
DeviceNet) where programming and monitoring of several melters
on multiple production lines in different geographic locations is
done from a single location
• Seven-day-clocks that provide significant energy savings through
automatic start up and automatic shut down when the melter is
not in use
• Temperature setback that delivers adhesive cost, maintenance
and energy savings by lowering the melter temperature when the
packaging line is stopped, maximizing adhesive life and reducing
adhesive charring
Automatic Adhesive Filling/Refilling
Traditionally, hot melt adhesives were manually fed into the tank or
hopper of the adhesive melter. In recent years, this practice has been
replaced with automatic filling/refilling systems that improve worker
safety, increase efficiency and minimize waste.
Flexibility for the Future
While any adhesive melter will melt and pump adhesive, it is
important to select one that not only meets current needs, but also
has the features and flexibility to meet multiple, future packaging
application requirements.
Features to look for include:
• Hose and applicator flexibility
- Plug-in hose/gun modules – allow the addition or subtraction
of the number of hoses and applicators from as few as 1 to as
many as 6 on a single melter
- Expansion base capabilities are also available for some melters
permitting up to 8 hose/applicator connections
• Quick-disconnect input/output plugs – with programmable input
and outputs
• Quick-release base – permits a melter to be easily disconnected and
moved
• Transformer option, for a 240 volt melter that accept inputs of 400
and 480 volts AC, eliminates the need for a secondary transformer
installation on the parent machine and expands global capabilities
• Piston pump flexibility – for lower volume applications that can use
a 6:1 pump rather than the standard 15:1 pump
Common Adhesive Melter Choices by Application
and Adhesive Use (For example only. Your specific operation and
needs will determine your choice.)
Operation
In principle, automatic filling is a simple concept. A sensing device
continuously monitors adhesive volume in the melter tank and
sends a signal when a pre-determined low level is reached. The signal
triggers the filling system to automatically add adhesive typically, 8 to
16 ounces (0.25 to 0.50 liters) to the melter tank. This occurs every
few minutes without operator intervention, keeping the adhesive level
within the tank relatively constant.
The economic benefits and rapid return on investment make
automatic adhesive filling systems an attractive option for virtually all
but very low-volume or manual packaging operations.
• Minimal potential for human error – including overfilling, adhesive
spilling/waste or low/dry adhesive tanks that result poor bonding
and reject packages
• Labor savings – as operators are freed from manual monitoring and
filling, they become available for other production activities and tasks
• Correct, constant adhesive temperature and viscosity –
accomplished by adding small amounts of adhesive at needed
intervals, prolongs adhesive, melter, hose and applicator life while
increasing package bonding consistency
•A
dhesive and maintenance savings – result from the elimination of
open melter tank lids that can allow debris and contaminants into
the adhesive tank and system
• Improved safety – by eliminating frequent bending and lifting of
adhesive containers, and limiting operator interaction with molten
adhesive
• Provide a return on investment – by minimizing adhesive, labor
and waste to decrease total operational and production costs while
improving package bonding integrity and quality
Adhesive
Applicator
Pump Type
Melter
Case sealing
Pneumatic
bead
Piston
10-liter
pneumatic
Carton sealing
Pneumatic
bead
Piston
4-liter
pneumatic
Tray forming
Pneumatic
bead
Piston
10-liter
pneumatic
Bliss box
forming
Pneumatic
bead
Piston
7-liter
pneumatic
Sift-proof
carton sealing
Electric
multi-bead
Piston or
Spur gear
30-liter
pneumatic
Beverage case
sealing
Pneumatic
bead
Spur gear
50-liter
pneumatic
Agricultural
case sealing
Pneumatic
bead
Piston
(single acting)
15-liter
pneumatic
Specialty
packaging
Electric dots
Piston
4-liter
Your equipment supplier will be able to assist you in refining your
exact needs, specifications and the melter that will meet and exceed
your productivity and total cost of operation goals.
Nordson Corporation
11475 Lakefield Drive
Duluth, GA 30097
(800) 683-2314
www.nordson.com/hotmelt
© 2012 Nordson Corporation
All Rights Reserved
PKL-12-5738
Printed in U.S.A.