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3. Basic measurement principles
3.1 – Measurement of fusion strength index
The fusion strength index of expanded polystyrene (EPS) parts and other low density
expanded thermoplastics represents a localized percent of cells (or pearls) that
effectively fused to the adjacent cells. This index is function of several expansion process
variables, as well part geometry. Local cellular anisotropy also contributes to small
variation of this index. The fusion strength index can be used as an indirect measurement
of
manufacture
dependence/Independence and correlation to specific quality control criteria.
As an objective criteria, the fusion strength index allow technical EPS parts to be
quickly categorized based on customer quality criteria. Prototype parts are usually
subjected to mechanical stiffness tests, compression capabilities, among other
laboratorial tests, and local fusion strength indexes are defined for later use on
approval/reproval of manufactured batches.
The M20-EPS measurement column uses an air to electronic principle to detect and
evaluate the fusion strength index of low density expanded thermoplastics. State of the
art signal conditioning and processing results in high measurement, stability, repeatability
and accuracy.
The measurement column uses two reference points (free air scape and total air
blockage) for calibration and measurement. During the measurement process the
measurement needle is inserted into the part body and a small air flux constriction is
detected. This change in the air flow is due the material cellular structure and represents
a value from 0% (minimal/null restriction) and 100% (maximum/blockage restriction).
Technical EPS parts usually show local fusion strength index over 60%.
18
process
parameters,
allowing
better
comprehension
M20-EPS User Guide
of
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