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Test & Measurement
NON-CONTACT
TEMPERATURE MEASUREMENT
PLASTICS INDUSTRY
Plastics industry
Wavelength in µm
2 4 6 8 10 12 14 16
ENGINEERING / PHYSICS
Inuence from the surroundings
The illustration shows that the transmissivity of air strongly
depends on the wavelength. Strong attening alternates with
areas of high transmissivity – the so-called atmospheric windows.
The transmissivity in the long-wave atmospheric window
(8 – 14 µm) is constantly high whereas there are measurable
extinctions by the atmosphere in the shortwave area, which may
lead to false results. Typical measuring windows are
1.1 – 1.7 µm, 2 – 2.5 µm and 3 – 5 µm.
Additional inuences can arise from heat sources in the
environment of the measuring object. To prevent wrong
measuring results due to increased ambient temperatures,
the infrared thermometer compensates the inuence of ambient
temperatures beforehand (as e.g. when measuring temperatures
of plastic foils in heating areas whereby the walls are hotter than
the measuring objects). A second temperature sensing head
helps to generate accurate measuring results by automatically
compensating the ambient temperatures and a correctly adjusted
emissivity.
Radiation
from
ambient
n
T
Object
amb
ρ
n
T
n
T
amb
obj
= α
ε
τ
Sensor
α = Absorption ρ = Reflectance τ = Transmission ε = Emissivity
Compensating ambient influences
Emissivity and temperature measurement
of plastics
Emissivity is a key factor in the accurate measurement
of temperatures. It depends on various inuences and must
be adjusted according to the application.
100
75
Transmissivity in %
50
25
0
Spectral transmissivity of air (1 m, 32 °C (90 °F), 75 % r. F.)
Dust, smoke and suspended matter in the atmosphere can pollute
the optics and result in false measuring data. Here air purge
collars (which are installed in front of the optics with
compressed air) help to prevent deposition of suspended
matter in front of the optics. Accessories for air and water
cooling support the use of infrared thermometers even in
hazardous surroundings.
Emissivity theoretically depends on the material, its surface
quality, wavelength, the measuring angle and, in some cases,
even the applied measuring conguration.
Plastics with a thickness of > 0.4 mm (0.02 in) and pigmented
lms can be measured very easily in the long-wave IR spectral
range (8-14 µm) with emissivities of ≥ 0.9.
IR Transmission of polyimide foil
Transmission [%]
Wavelength [µm]
Transmission of PE foil
Transmission [%]
2
Wavelength [µm]
The CoolingJacket Advanced enables an
operation within an ambient temperature
of up to 315 °C (599 °)
innovative infrared technology
Line scan with compact infrared camera
for thick plastic lms
Plastics processors produce a wide range of products
of various dimensions, thicknesses, textures, colors
and embossed patterns. Here the manufacturing is
subject to numerous thermal processes which have
to be continually and rigorously checked at various
critical points.
In order to ensure quality, a high level of temperature
homogeneity is required and this is checked at
various stages, including during thermoforming and
in the calender zone, by means of a line scan.
In-depth inspection of preforms during bottle production.
Very thin plastic lms are, however, transparent in this spectral
range, meaning that a temperature measurement is only possible
with the aid of material-specic absorption bands in the IR
spectrum via correspondingly narrow-band sensitive IR sensors.
Polyethylene, polypropylene, nylon und polystyrene, for example,
are IR opaque at 3.43 μm; for polyester, polyurethane, Teon,
FEP and polyamide, in contrast, it is 7.9 μm.
C-H band
3.43 μm
P3 > 50 °C (122 °F)
C-F Ester band
7.95 μm
P7 > 0 °C (32 °F)
Polyethylene (PE) Yes No
Polypropylene (PP) Yes No
Cellophane Ye s No
Polystyrene (PS) Yes No
Fluoroplastic (FEP) No Yes
Polyimide No Yes
When using an infrared camera as a line scanner,
an arbitrary line is selected from the detector array.
In addition to the compact construction and the lower
price, there are two signicant benets: the line to
be scanned can be positioned anywhere using the
software and the user receives a complete IR image
quasi as additional information – these are important
advantages, especially during system setup.
The cameras can accurately measure surface temperatures of moving measurement objects using minimal
apertures. This function is of particular signicance
in the plastics industry, since homogeneity of foil
temperature has a direct impact on the quality of the
nal product. During the production process,
temperatures are measured accordingly at many
points and it is possible to intervene in the process,
when necessary, if there are deviations in setpoint
temperatures.
The optris PI 640, in combination with the 90° lens,
allows for high-resolution line scanning with up to
800 pixels and a maximum scan angle of 111° with
the use of the diagonal dimension.
Acrylic Yes Yes
Polycarbonate Yes Yes
Polyester Yes (>10 μm) Yes
F2F
–C–C–C–C–
Polyethylene
Further information in our infrared basics brochure:
www.optris.com/optris-downloads
CF
3
2
F
n m
FEP
Lines have FOV of
up to 111° for detailed
process analysis.
F
2
111 °
any number of lines
800 Pixel
Up to 125 Hz data recording
of unlimited lines which in turn
produce a thermal image of
any given resolution
3
Applications of
temperature measurement technology
PRODUCTION OF PLASTICS
The measurement of process, instrument and workpiece
temperatures is a crucial factor in production and quality
control in the plastics industry. In many areas only
non-contact temperature monitoring is possible, and this is
where infrared cameras and infrared thermometers are used.
Optris offers compact cameras in the long-wave range as well
as point sensors.
Flat lm and sheet extrusion
In at lm and sheet extrusion the molten mass is pressed through
a wide slit die and then processed further using a
calender. In this process the lm is gradually cooled. The
infrared sensors measure the temperature of the lm at various
points, thereby monitoring the process. Infrared cameras also
allow cracks and surface defects to be detected.
Injection molding
Infrared
thermometer
Infrared
camera with
line scan
mode
Extruder
Infrared
camera
Infrared
thermometer
Rotational molding
The rotational molding process is a specialist technique used
in the manufacturing of plastic parts and is primarily used for
larger objects. Here a negative mold is lled with a powdered or
liquid raw material such as PE or PP and then sealed. The mold
is then heated in an oven to a maximum of 320 °C (608 °F) and
rotated biaxially. This causes the material to stick to the mold,
layer by layer. The mold is subsequently cooled in a chamber and
the plastic part removed. Upon opening the mold, the product is
thermally tested to allow the production process to be readjusted
if necessary.
Infrared
camera
Injection molding is the most common production process in the
manufacture of moldings from thermoplastic polymers. It is used
in particular in the intermittent mass production of complex moldings where the size of the workpieces ranges from the smallest
of cogs right up to large containers. The weight of a workpiece
starts at 1 mg (0.001 g) and goes up to 100 kg (220.5 lb).
The pellets, often mixed with additives, are added to the cylinder
via the funnel. The pellets are plasticized by the mechanical
friction caused by the movement of the screw inside the cylinder
as well as the external application of heat from the heating bands.
The resulting liquid mass is pushed to the tip of the screw and
is then forced into the die in front of it through the injection unit
nozzle.
The molding compound cools in the die which then opens when
the hardening process is complete. To ensure the high quality of
the molding it requires optimum temperature management,
especially during the cooling phase in the die. The moldings,
meanwhile, are automatically checked for homogenous
temperature distribution immediately after
ejection with infrared cameras.
Further information can be found in our application note “Injection molding” at
www.optris.com/plastics
4
innovative infrared technology
Extrusion blow molding of lms
Film
tube
Infrared
thermometer
Infrared camera
Infrared
thermometer
Extruder
Similar to injection molding, the molten mass is pushed out of the
extruder – however, in this case not into a die, rather through a
die with a ring nozzle. The resulting lm tube is then pulled
vertically and blown up in the process. During this process air is
used to cool the tube both inside and out.
From the moment the molten mass emerges from the nozzle, the
temperature of the lm tube needs to be measured at various
points in order to ensure the characteristics and quality of the
product.
Thermoforming
Sheets or unrolled lm made from thermoplastic polymers are fed
into the molding machine and then, in the rst step, warmed up
on both sides until the semi-nished product is completely melted.
When a pre-dened temperature has been reached, the lm is
then sucked into a tempered mold using a vacuum. Only when
the product has cooled down again and is dimensionally stable is
it transported further to be nished.
Further information can be found in our application note “Plastics industry“ at
www.optris.com/plastics
Thermoforming
Heating zone
(Injection) stretch blow molding
For the manufacturing of PET bottles, the stretch blow
molding or injection blow molding processes are used, whereby
the preforms are heated until viscous. The heated forms are then
fully formed in a blow mold using a stretching process. Before
being transported further the bottle is
(Injection) stretch blow molding
Heating zone
Infrared
camera
Temperature control
Molding zone
cooled inside a die. Depending on the texture of the
preform and the desired end product, the preform needs
to be brought up to a process temperature of 100 °C.
Optris PI cameras are used to monitor this process.
5
Plastics industry
INFRARED CAMERAS AND INFRARED THERMOMETERS
The optris CT P3 infrared thermometer, with its
extremely narrow-band spectral range of 3.43 µm,
is particularly suited to the temperature
measurement of very thin plastic
materials such as PE, PP and PS.
optris
The temperature range extends from 50 to 400 °C (122 °F to 752 °F)
with a machine response time of 100 ms. The sensing head can
withstand temperatures of up to 75 °C (167 °F) without additional coo-
ling. The lm thermometer‘s separate electronics box is equipped with
easy-to-access programming buttons and a backlit LCD display.
The innovative optris CT P7 infrared thermometer,
with its specic spectral range of 7.9 µm, is particularly suited to the temperature measurement
of thin plastic materials such as PET,
PU, PTFE and PA.
optris
It has a temperature range of 0 to 710 °C ( 32 to 1,319 °F), while the
sensing head is resistant to temperatures of up to 85 °C (185 °F)
without additional cooling. The machine sensing time is 150ms.
The pyrometer‘s separate electronics box features easy-to-access
programming buttons and a backlit LCD display.
®
CT P3
®
CT P7
New
The optris CTlaser P7 infrared thermometer is
suited to the temperature measurement of thin
plastic materials like, for example, PET, PU,
PTFE and PA. It measures the smallest
objects with the greatest of accuracy.
optris
The IR thermometer boasts a wide temperature range of 0 to 710 °C (1,319 °F) and can be
used at temperatures of up to 85 °C (185 °F) without additional cooling. It can capture objects as
small as 1.6 mm (0.06 in) from a distance of 70 mm (2.76 in). A double laser precisely marks the
measuring spot. The pyrometer‘s separate electronics box has easy-to-access programming buttons
and a backlit LCD display. Additionally, a variety of selectable outputs ensures the reliable transfer of
measured data and easy SPS integration.
6
®
CTlaser P7
The infrared cameras in the optris PI series are xed thermography systems
that offer outstanding value for money. In the plastics industry the LT cameras
(8-14 µm) are used for molding or lm thicknesses of over 0.4 mm (0.02 in). The
thermal imaging cameras are connected to a computer via USB 2.0 or integrated
into a PLC and are ready to use immediately after connecting.
Compact infrared cameras
innovative infrared technology
At 120 Hz the optris PI 160 (160 x 120 px) is ideally
suited to fast processes.
For applications which require bi-spectral recording, the
optris PI 200 / 230 (160 x 120 px) is a good solution.
The optris PI 400 / 450 (382 x 288 px) impresses
with its high thermal sensitivity from 40 mK.
For high-resolution line scanning at high speeds
(125 Hz) or for close, detailed inspection, the
optris PI 640 (640 x 480 px) VGA camera is an
outstanding choice.
optris
®
PI Connect
Software (Merging function)
In conned spaces in a machine, when there is
not enough room to measure at the recommended
distance, it may be necessary to use two or more
infrared cameras to scan, for example, the entire
product width. With the PI Connect software the data
streams of the individual cameras can be simply
combined to form an overall IR image, meaning the
user can see the whole process or the temperature
distribution across the entire lm width in a single
software window.
7
Subject to change · Temperature measurement plastics industry-BR-US2017-11-A
Optris Infrared Sensing, LLC
200 International Drive
Suite 170
Portsmouth, NH 03801 USA
Phone: (603) 766-6062
E-mail: sales@optris-ir.com
www.optris.com
innovative infrared technology
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