cpp – Process technology for the chemical industry 01.2019

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PLANTS, APPARATUS, COMPONENTS
acetic acid was chosen to represent the acid
class at a temperature of 98 °C. Pure methyl
ethyl ketone (MEK) represented the solvent
class at a temperature of 80 °C, while pure
toluene at 40 °C represented the alkylbenzenes.
Demanding, challenging conditions
were deliberately created for the materials,
with storage temperatures very close to
boiling point in the first two cases. The test
samples were exposed to acetic acid and
MEK for three days and immersed in toluene
for an entire week.
Picture: Freudenberg Sealing Technologies
Fig. 3: Results relating to volume changes in acetic acid, methyl ethyl keton (MEK), and toluene
Results of the lab tests
Changes in volume such as swelling or
shrinkage give an indication whether a material
absorbs media or gives off components.
Swelling was the sole relevant criterion
for the Chem XP lab tests. If swelling
is not limited to a certain degree, seals can
lose their functionality and leaks could
occur. For the purposes of the tests, a maximum
permissible volume change of +10 %
was set. A standard FKM, the proven
75 Simriz 495 and four special, highly
fluorinated varieties of FKM from competitors
were used for reference.
As Figure 3 shows, the standard FKM material
is not suited for these demanding test
conditions. Especially in acetic acid and
MEK, the swelling was far too great; the
seals would deteriorate in the foreseeable
future. The tested elastomer mixtures from
manufacturers 1 and 2 exhibited clear
weaknesses during the acetic acid test. The
same was true of the mixtures from manufacturers
2 and 3 in MEK. Only the material
from manufacturer 4 could be used with
certain limitations in the test conditions. In
acetic acid and toluene, the Chem XP 1 variant
delivered results that were comparable
to the very low volume change for
75 Simriz 495, the FFKM material par -
ticipating in the test. At temperatures below
+80 °C, the material also showed outstanding
stability in MEK. The Chem XP 2 variant
which was tested in parallel likewise demonstrated
good resistance to acetic acid and
toluene, but is only limitedly suited for use
in MEK at +80 °C.
Standard FKM also proved to be unsuitable
during the strength tests (see Figure 4). In
addition to a high degree of swelling, the
more than 30 % reduction in strength indicates
chemical breakdown of cross-linkages
and polymer chains in the elastomer matrix.
The materials from manufacturers 1 to 4
showed an impermissible deterioration in
Picture: Freudenberg Sealing Technologies
Fig. 4: Results relating to strength changes in acetic acid and methyl ethyl ketone (MEK) and toluene
strength in MEK, similar to the picture for
manufacturers 3 and 4 in toluene. This puts
the moderate swelling values of manufacturer
1 in MEK (Figure 3) into perspective:
with an up to 60 % loss of strength, it was
discarded as a potential candidate. In all
cases, the strength values for Chem XP 1
were within the tolerance limits and
comparable to the very good values of
75 Simriz 495. The excellent volume stability
of Chem XP 2 in acetic acid and toluene
was confirmed by the only slightly reduced
strength in both cases.
In summary, it can be said that the newly
developed Chem XP materials rank directly
below FFKM in terms of media resistance
and in the future can serve as standard materials
for the chemical processing industry.
Lab tests confirmed that they provide a very
good balance between performance and
cost.
The first seals made from Chem XP are expected
to be ready for serial production in
early 2019. O-rings and formed parts are
among the possible varieties of seals suited
for this material. The exact material types
and applications will be determined in joint
tests with customers. Freudenberg’s development
engineers are simultaneously working
on other variations of the new material
family.
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AUTHOR:
DR. ROBERT ROTZOLL
Business Development
Manager Process Industry,
Freudenberg Sealing
Technologies
58 cpp 01-2019