Purpose-built system delivered to laboratory at Washington State University for research and development wood composites with improved resistance to moisture and biological decay
Celsum Technologies has delivered and commissioned a
purpose-built instrument system, Cest (combined extrudate swell
and temperature) to the wood materials and engineering laboratory
at Washington State University for research and development of
highly filled wood composites with improved resistance to
moisture and biological decay.
The Cest system comprises an
optical micrometer capable of measuring to 0.2 micron, an
infrared pyrometer which monitors a target of diameter only
0.8mm, an instrumentation pack and a computer system with
Richard Carter, Celsum's marketing
manager, said, "Cest is a synthesis of two of Celsum's
measuring instruments, the Cads optical micrometer for die swell
and the Cirp close-focus, small-target IR pyrometer".
optical micrometer uses a low-power blue-green LED light fan
(which is more stable and safer than a laser light source) to
illuminate the target (ie the extruding material), projecting it
onto a precision CCD array via a sealed lens system.
instrumentation pack includes 'glass logic' in order to
compensate for spurious signals caused by light transmission
through transparent or translucent specimens.
The field of view
is 30mm, and the maximum rate of scan is 2.4kHz.
transmitter and receiver are mounted 300mm apart on an
especially-designed flat bracket made from hard-anodised
aluminium tool plate, with a mount for a photographic tripod
The distance between transmitter and receiver was
chosen so that the electronics and optics would fit snugly on
either side of the barrel of an Acer capillary extrusion
rheometer (which was co-designed by one of Celsum
Technologies's directors), to enable the diameter of the
extruding material to be measured as soon as possible after exit
from the extrusion die.
The use of a photographic tripod allows
the use maximum flexibility in order allow the equipment to be
used on a pilot extrusion line as well as in the laboratory.
measuring head of the Cirp infra-red pyrometer is fitted with an
aluminium cone to exclude extraneous radiation, and measures
surface temperature of suitable materials from sub-ambient up to
The unit takes readings at approximately 4Hz, and is
equipped with built-in functions to allow for surface emissivity
and to operate in peak or trough mode.
The instruments are used
to measure some aspects of the viscoelastic properties of the
materials during processing.
Long-chain molecules such as
polymers need time when their shape is changed for the molecules
to align themselves to their new geometry.
If the force which is
creating the change of shape relaxes before the molecules are
newly aligned and before, for example, a molten material cools,
the molecules will tend to snap back to their original shape.
the case of extrusion, this produces and effect known as die
swell, extrudate swell, or the Barus effect, where the material
expands after exiting the extrusion die.
Of course, this can have
dire repercussions on product quality.
The Cads optical
micrometer in the Cest system will measure the die swell for
different compositions over a range of extrusion conditions, and
will provide information to allow the die geometry for the
manufacturing plant to be designed in order to produce the
required product dimensions.
Similarly, when materials,
especially high filled ones, are extruded under pressure through
an extrusion die, friction both with the die wall and internal
between particles can cause significant increases in temperature,
particularly near the surface of the profile.
increase can cause premature curing or scorch of thermosetting
materials such as rubbers and phenolic resins, can cause surface
degradation and discolouration, and can lead to in-built stresses
in the product which can have deleterious long-term effects, and,
in some processes with certain materials, can lead to health and
safety problems such as starting fires and generating toxic
The Cirp IR pyrometer within the Cest package will measure
the temperature of a small target spot on the moving extrudate
for different formulation combinations under a range of test and
processing conditions, and will provide information to allow the
processing geometry and conditions to be optimised.