Expansion Measurement of One Component Foam - 20130 pages

Polyurethanes 2013 Technical Conference
Sept. 22 –24, 2013
Phoenix, Arizona

Expansion Measurement of One Component Foam
ERLAND E. HOFMANN
Format Messtechnik GmbH
D-76187 Karlsruhe
Germany

FRANK BERTUZZI
Eurotech Distributors Inc.
Northfield, Ohio 44067
USA

The main expansion reaction of One Component Foams (OCF) is based on the water
isocyanate reaction. In typical application of OCF, e.g. back foaming and fixation, the water is
extracted from the moisture of the ambient air. This is a long term process lasting for hours or even
days. In laboratory test cycles the foaming process needs to be speeded up by adding a significant
amount of water directly into the OCF froth. This is usually done by water films sprayed between
each layer of OCF froth extruded from aerosol cans. Alternatively two parallel vertical walls at a low
distance are impregnated with water and the OCF froth is filled in layers to a certain height. Due to
different amounts of water between the foam layers and an undefined amount of froth being
injected, the surface of the foam is very uneven. Therefore the rise measurement depends on the
measurement position over the uneven surface. Beyond that a crust may form on the surface of
the foam. This can be destroyed later by high pressure within the foam bulk resulting in foam
geysers spoiling the rise measurement.
Based on this, Format Messtechnik GmbH has introduced the new One Component Foam
Measurement device OCFM (fig. 1) for measuring the rise profile, the rise pressure and the
reaction temperature of OCF. The OCFM comprises a narrow cylindrical expansion container
made of cardboard and a special holder for aligning the cylinder under an ultrasonic distance
sensor. The test volume of the expansion container is confined by the walls of the narrow
cardboard cylinder, the circular pressure plate of the Foam Pressure Measurement device FPM 50
at the bottom and a movable plug on top of the foam. In order to avoid contamination of the
pressure plate, it is protected by a thin PE foil (cling film). During the foam expansion the movable
plug is lifted towards the ultrasonic distance sensor giving precise rise readings. The cylinder
holder contains a photo switch detecting the cardboard cylinder in its final measurement position.
The reaction temperature of the foam is measured with a thin glass fiber insulated thermocouple
having a low heat capacity. A cross section of the OCFM is shown in figure 4.
When using the OCFM, the cardboard walls are impregnated with a defined amount of water
thus giving reproducible measurements independent of the ambient air humidity. The moistened
cardboard cylinder is placed over the Perfect Preparation Aid (PPA) and the movable plug is put
into the cylinder at a pre-aligned vertical position. A defined mass of OCF froth is injected into the
cylinder, the quantity being checked with a balance. After turning the cylinder upside down, it is
placed onto the FPM 50 and is fixed with a clamp ring. The FPM 50 / cardboard cylinder unit is
aligned then with the cylinder holder of the OCFM, initiating data acquisition via the photo switch.
During the foam rise the thermocouple is inserted through the cylinder wall into the foam.
Measurement results of the OCFM are shown in figure 2. Different rise reactions due to
different water contents in the cardboard cylinders can be seen in figure 3. The foam sample can
easily be lifted from the FPM 50 by just loosening the clamp ring and pulling off the cardboard
cylinder containing the foam sample and the plug. The sample is available for further physical
investigation (fig. 5). The new measurement technology of the OCFM can be used in R&D and
quality control applications.

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