Just as there are a number of adhesives to suit different substrates
and circumstances, so there are a variety of methods of applying the
adhesive to accommodate specific design, production or maintenance needs.
But what are the options when choosing adhesive application equipment?
Steve Ginger has some answers
In some cases, it is sufficient to squeeze a tube or unscrew a bottle in
order to apply the appropriate amount of adhesive or sealant on the
surfaces to be joined. For many jobs, however, there are significant
benefits to be gained by using application equipment. Utilising
dispensing equipment ensures that no more than the required amount of
product is used for each application. Automatic equipment allows the
product to be applied accurately at rates that are beyond even the
speediest of human operators, and it will also apply the adhesive or
sealant in the required volume, in a defined position, at a given time
and with consistently repeatable accuracy.
So, with these not inconsiderable benefits in mind, what should you look
for when choosing application equipment for adhesives or sealants?
Basically, there are three important considerations in selecting
dispensing equipment - viscosity, dispense pattern and adhesive type.
Viscosity will largely determine the power of equipment you will need,
while the dispensing pattern may vary from single to multiple spots,
linear beads to circular coating. Adhesive type will also influence
choice. For instance, a UV-curing adhesive will need to be dispensed from
a container and through tubing that restricts natural light, in order to
avoid premature curing, while an anaerobic adhesive must not come in
contact with metal surfaces or reside in a container that allows some air
to be present.
Before a decision on the equipment can be made, the supplier will ask a
number of pertinent questions: What is the size and shape of the parts to
be bonded and/or sealed? How are the parts moved along the assembly line?
At what stage of the production process does the adhesive or sealant need
to be applied? What is the production rate? How much time elapses before
the parts must be handled or tested? What type of adhesive is to be used?
Can the adhesive be supplied in packaging suitable for automatic
dispensing? Once these questions have been answered, then equipment can
be selected to match user needs.
Handgun dispensers can accommodate anaerobics, acrylics and silicones,
but are unsuitable for cyanoacrylate ('instant') adhesives. Some models
dispense a continuous bead, while others are capable of applying single
precise drops in quantities as small as 0.005ml. Cartridge packed
adhesives can also be dispensed by hand, using skeleton guns or
pneumatically operated cartridge guns. Next in the range are the
semi-automatic systems, which dispense adhesive in measured doses while
allowing the operator to control (via a footswitch or pushbutton) when
and where the bead will be applied. Such systems would commonly be seen
in production environments where medium to high volume repetitive work is
required. Where fully automatic adhesive application is required, most
equipment manufacturers will design and build dispensing systems to meet
specific requirements. These can either be integrated into existing
production equipment or be completely self-contained assembly systems,
featuring monitoring facilities, low level tank warning signals and
equipment failure alert.
Many users express concern about the possibility of the adhesive clogging
up the nozzle of their system. This depends on the type of adhesive being
used. An anaerobic will only cure when it comes into contact with a metal
and when air is excluded from the joint, whereas cyanoacrylates cure when
they come into contact with airborne moisture. If the adhesive does
solidify at the dispensing end of the equipment, then the answer is to
c