Plastics News Europe - June 2019 - 15

automotive plastics

From static charge
to static control
Static on plastic automotive parts causes quality
problems that can result in high reject and rework
rates, says Eleni Fotopoulou, Product Manager,
Meech International. What's the solution?

D

ue to tight margins and a
fiercely competitive marketplace, automotive manufacturers are under constant pressure. The
essential delivery of clean, fully operational vehicles requires all levels of
the automotive supply chain to be
monitored closely and any failings or
issues to be quickly flagged and identified to help in the elimination of
poor practice.
One of the biggest challenges to
quality and production efficiency in
the sector is the generation of static
on plastic automotive parts, which
can cause machinery issues, harm to
operators, product contamination
and wastage. In fact, electrostatic attraction (ESA) causes product rejection rates of up to 10-30% in automotive parts manufacturing.
Static charges are caused when a
material or object holds a positive or
negative charge. This can be caused
through friction (when two materials
are in constant contact with one another), separation (when they are
separated), or induction (when the
surface of a material in close proximity to a high positive voltage becomes
positively charged).
The strength and duration of a
static charge depends on the plastic
material's resistance. Plastics found in
the automotive sector, such as lighting clusters, generally have very high
resistances and can maintain static
charges for long periods.

The consequences of
static charges
Various fibres, ambient dust and dirt
can be attracted to statically charged
plastic lighting clusters, which can pull
foreign bodies to its surface during assembly and trap these contaminants
inside, once fully sealed. This taints the
part and increases the chance of it being rejected during the testing phase.
Another example is a car bumper.
Following the injection moulding
phase in which the bumper is formed,
the part must then be ionised and
cleaned to ensure the paintwork can
be applied immaculately to its sur-

june 2019

face. However, up to 30% of bumpers are rejected during the car manufacturing stage as they are too heavily
contaminated for painting.
ESA can also disrupt automated
processes by causing plastic parts to
adhere to each other, or to other
equipment. This comes at a significant cost, as it forces manufacturers
to run machines at slower speeds
than usual.
Shocks are another consequence
of static charges; typically, they are
the result of an accumulated charge
or "battery effect" that occurs during
the collection of parts in a bin or assembly area. In most cases the effects
are short-lived, however a sudden reaction to a shock can cause an operator to make an involuntary reaction
and impact nearby equipment or another individual, potentially leading
to injury.

Automated nozzle and vacuum system provides
effective ionisation and cleaning

Tackling static charges
The methods typically used to clean
and ionise automotive elements before sealing or painting come in the
form of air guns or compressed air
controlled via a footswitch, but these
devices can be inefficient and inconsistent. Static cloths or "tack rags",
which are designed to remove static
charges when wiped across a surface

"

Up to 30% of
bumpers are rejected
during the car
manufacturing stage

prior to its painting, can actually increase static levels. However, recent
developments in static control and
cleaning for automotive parts have
resulted in new automated devices
that are greatly contributing to reduced rejection rates.
For speedometer casings or light
clusters, there are nozzle cleaning
systems that are designed to remove

15

Air knife system removes and prevents re-contamination

dry, un-bonded contamination via
powerful ionisation and blowing and
vacuuming airflow. These machines
can provide consistent, reliable results
by ionising and cleaning each component to exceptionally high levels.
Another example of efficient ionisation and cleaning comes in the form
of air knife technology, which breaks
the electrostatic bonds holding contaminants to the surface through a
high-velocity laminar blade of clean,
ionised air, removing and preventing
re-contamination. This can improve
paintjob quality and increase "first
time pass" rates for bumpers.
Automotive part manufacturers
should be actively looking into the recent developments static control and
parts cleaning has to offer. The latest
automated technology can greatly reduce or even eliminate component
rejection altogether and pay for itself
by significantly offsetting the cost of
spoiled, contaminated parts.
Plastics News Europe - June 2019

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