ALTANA BYK-Gardner Permeability Cup - Manual (Page 6)

5
Operation
Remove the cover and retaining ring from the
cup. Use the ring as a template, placing it on the
surface of the sample to be tested. Cut out with a
razor blade a circular disc of exactly the same dia-
meter as the ring. The disc of sample can now be
weighed, then mounted between the rubber gas-
ket and the ring covered with the plastic gasket
and placed on top of the fl anged cup which holds
a few grains of desiccant, or 10 ml of aqueous salt
solution. The assembly is now slipped over the
pins. During tightening of the ring cover, the retai-
ning ring prevents any shear forces from operating
on the fi lm sample. The threaded cover is then
put on and tightened with hand pressure. This is
suffi cient to give a gas-tight seal.
Now weight the loaded cup on an analytical
balance and place in a desiccator containing the
desired adsorbent or solution and reweigh it at in-
tervals of 1 to 24 hours, depending on how rapidly
the cup gains or loses weight.
Paper, plastic or cloth to be tested in an uncoated
condition can be cut without any preliminary treat-
ment. The thickness of this sample disc that is cut
out can be measured with a sensitive micrometer
or calculated as outlined below.
CALCULATION OF SAMPLE THICKNESS:
The ratio of exposed fi lm area to be tested
(10.0 cm2) to the total area of the sample disc
(26.4 cm2) is a constant equal to 0.380.
The weight ratio of the exposed fi lm to the total
fi lm is in the same proportion.
In the case of supported fi lms, a disc of the
uncoated support shall be cut in the manner
Operation