EuroWire May 2017

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Technical article
May 2017 48
characterised as contamination and
automatically separated. The technology
allows for the detection of impurities
down to a size of 50μm.
X-ray technology
The basic detection principle of the X-ray
technology uses the different attenuation
of the material. XLPE mainly comprises
carbon.
The carbon atom has six protons in its
core. A typical contamination would
be steel particles from the extruder or
granulator, which is mainly iron (FE). Iron
has 26 protons in its core.
These 26 protons have a much higher
X-ray attenuation than the six protons
from the carbon and this results in
a perfect contrast between the two
materials in the X-ray image.
Optical technology
Regarding the optical inspection, the
illumination plays an essential role. In
order to allow precise recordings of
material flows at industrial speed, modern
camera technologies (optical, infrared and
colour cameras) are used.
Powerful image processing software
similar to the one used for the
X-ray inspection is used to detect
contamination with the optical system.
Therefore, by setting a certain threshold,
all contaminated pellets which are
above the threshold in the mathematical
algorithm are sorted out.
Typical contamination
detected by X-ray and
optical technology
The combination of both X-ray and optical
technologies enables the detection of
contamination in the pellet itself and on its
surface (Figure 4).
The X-ray system inspects transparent
and coloured (eg black) pellets as well
as semi-conductive XLPE material for
impurities.
Typical impurities detected with X-ray are
metallic as well as organic contamination
and inhomogeneities (TiO2) inside the
pellet. In addition, the optical system
detects, for example, black specks on
the pellet, foreign objects and foreign
pellets as well as other organic or metallic
contamination.
Integration of
the system in the
production line
The system is typically installed between
the hopper that is fed from the XLPE and
HPTE supply (octabin, bag or silo) and
the hopper of the extruder, whereas the
compound is fed by gravity.
On- and offline
inspection and analysis
of pellets, flakes and
tapes/films
In addition to online inspection and
sorting devices there are modular
designed systems available for on- and
offline inspection and analysis of pellets,
flakes and tapes/films. These are used for
smaller throughputs as well as production
lines where sample testing is sufficient, or
for the control of incoming goods.
Depending on application, the systems
are equipped with X-ray technology (X),
infrared technology (IR) or optical sensors
(V) to be used during the production or for
sample testing and detect contamination
from 50μm.
For example, a laboratory inspection and
analysis device with X-ray technology
(Figure 5 ) inspects up to 3,000 pellets
(200ml) that are placed on a tray.
Within seconds, these pellets are
inspected for contamination. Sub-
sequently, contaminated pellets are
optically highlighted, which makes the
extraction of the individual contamination
significantly easier.
▼ ▼ Figure 4: By means of X-ray technology and an optical inspection the system detects contamination inside the plastic pellet and on its surface. The system detects metal
contamination, black specks, yellow discolourations and colour variations in transparent and non-transparent material