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Rise Pressure Measurement of Sealing Foams and Microcellular Foams
ERLAND E. HOFMANN
Format Messtechnik GmbH
D-76187 Karlsruhe
Germany
D. JEFFREY GROSS
Eurotech Distributors, Inc.
Northfield, Ohio 44067
USA
Sealing foams and microcellular foams are traditionally
tested in small cups measuring their rise profile. Format
Messtechnik GmbH, Karlsruhe, Germany has introduced
the new Foam Pressure Measurement Device FPM 70
(Fig. 1), making a new approach for testing the rise
pressure and the viscosity of high density foams. The FPM
70 test container consists of a cardboard cylinder and a
heatable pressure plate inside an aluminum tube (Fig. 5).
The foam can expand along the cylinder while the pressure
is being measured as stress over the pressure plate. The
rise profile is measured by the proven ultrasonic fan-sensor
PFT mounted on a stand.
The pressure plate is protected by a PE cling film in order
to avoid any foam contamination. The compound of foam
and the cardboard cylinder produce stress over the bottom
of the cylinder. The pressure plate is connected to a load
cell which transmits a signal to the controller unit of the
FOAMAT® system. The pressure data is simultaneously
recorded with the foam rise height (Fig. 3). The software
FOAM processes all data and enables the user to display
the rise profile and the rise pressure superimposed in one
graph. After the test, the foam sample can easily be
removed from the FPM 70 device by just loosening the
clamp ring. The cardboard cylinder containing the foam
sample is pulled off the lower part of the FPM 70. The foam
sample can then be used for further tests.
FPM 70 has been specially designed for small foam
samples of high density. Compared to other measurement
containers like the Advanced Test Container (ATC) the
foam volume has been reduced down to 15% (Fig. 4).
Pressure as low as 40 Pa can be measured with high
accuracy. From the pressure data, the gel time, the
maximum pressure, the pressure decay and the remaining
stress, can be evaluated. The remaining elastic stress is of
main interest regarding sealing foams. It should be high to
seal a gap properly.
Another advantage of the FPM 70 design is that the
viscosity model of Hagen-Poisseuille can be applied.
Having measured the rise height and the rise pressure, the
viscosity of the expanding foam can be calculated by using
simple physical principles (Fig. 2).
patent 19730891
cardboard
cylinder
pressure
plate with
PE foil
clamp ring
- Measurement of
rise pressure, rise
height and
temperature
- Determination of
gel point, max.
pressure and
elastic stress
- Heatable pressure
plate
Fig. 5: Cross section of the
new FPM 70, designed for
the pressure measurement
of high density foams.
- Replaceable
cardboard
cylinders
www.format-messtechnik.com
η [Pa s] P[Pa]
high density sealing foam
H[mm]
20000 2000
150
100
rise height
16000 1600
12000 1200
90
rise pressure
8000
60
800
viscosity
30
4000 400
gel point
0 0
0
0
40
120
80
160
200
time [s]
Fig. 1: The new Foam Pressure Measurement Device FPM 70
®
on the stand of the Foam Qualification System FOAMAT . Rise
height, rise pressure and reaction temperature are measured
simultaneously.
Fig. 2: Rise height, rise pressure and viscosity of a low
density sealing foam measured with the FPM 70. The
viscosity data is calculated by using the physical model of
Hagen-Poisseuille.
rise height
rise height
max. pressure
rise height
80
viscosity / rise pressure
120
P[Pa]
200000
H master
160000
60
120000
40
rise pressure
20
80000
P master
mixing ratio
100 : 80
100 : 100
0
0
300
900
600
1200
rise pressure
low density sealing foam
H[mm]
40000
0
1500
time [s]
Fig. 3: Two rise height and rise pressure profiles of a high
density sealing foam. The mixing ratio was changed from
100:80 to 100:100. The master curves can be adapted to
acceptable QC margins.
Fig. 4: The new Foam Pressure Measurement Device FPM
70 compared to the Advanced Test Container ATC. The test
volume is reduced down to 15%.
