Liantuo Expanded PTFE in terms of test-to-test and thickness variations

Sealing and mechanical behaviors of expanded PTFE gasket sheets characterized
by PVRC room temperature tightness tests. This paper presents sealing and
mechanical properties of isotropically liantuo
Expanded PTFE Gasket, characterized by the room
temperature tightness test (ROTT), developed by the Pressure Vessel Research
Council (PVRC). The expanded PTFE sheets are highly fibrillated and porous.
Three types of sheets were tested, including two regular 1/16 and 1/8-in. thick
sheets of density 0.85 g cm?3, and one 1/8-in. thick rigid type gasket sheet of
density 1.2 g cm?3.

Helium mass leak rates and gasket deflection values were measured. The
regular 1/16 in. sheet leaks less than the 1/8 in. sheet by 2–4 times, and the
regular and rigid 1/8 in. sheets show comparable leakage. All the tests reveal a
drastic improvement in sealability between gasket stress of 1025 and 5390 psi;
above that, the leakage still steadily decreases, although improvement occurs at
a lower rate. The deflection results, when adjusted with initial thickness, are
similar between the regular 1/16 and 1/8 in. sheets, but lower in value for the
rigid sheet due to its higher density, and hence lower compressibility.

Both leakage and gasket deflection results indicate very similar sealing and
mechanical behaviors for all types of expanded PTFE products. The results of
expanded PTFE sheets are further compared with those of a skived, virgin PTFE
sheet and a filled PTFE sheet. The deflection results confirm the high
compressibility, low recovery and excellent creep resistance for the expanded

These property differences are attributed to the differences in
micro-structures of the materials. The comparison shows that the expanded PTFE
sheet seals the tightest and creeps the least up to 6500 psis. Tightness
hardening effect has greatly limited the sealing performance of the skived and
filled PTFE at such high gasket stresses. In addition, the sealing and
mechanical behaviors of virgin and filled PTFE are less consistent than expanded
PTFE in terms of test-to-test and thickness variations. Gasket selection
criteria based on the ROTT test data are discussed. Further, the tightness
concept, tightness data, and PVRC gasket constants associated with the test
results are presented. PTFE Rod:

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