Enveloped Gaskets
PTFE flange gaskets are being more and more frequently
used for flanged joints which are subjected to extreme
chemical attacks. PTFE composites and PTFE-enveloped
gaskets with increased pressure stability are chiefly used
because of the cold-flow tendency of filler-free PTFE.
PTFE-enveloped gaskets have proved themselves because
of high resistance to chemicals as well as on account
of their excellent sealing properties at changing pressures
and temperatures of between -195°C up to +250°C. Glass
tubes, metal-sheathed glass tubes and glass apparatuses
in laboratory systems or pilot plants can be just as easily
connected to each other as enamelled, coated or lined
tubes and apparatuses in large-scale plants.
PTFE-enveloped gaskets are particularly used in the chemical
industry because of their high resistance to aggressive
chemicals. Since PTFE is generally recognised as physiologically
safe, it is also used in the food and pharmaceuticals
field.
In addition to its high chemical resistance, PTFE stands out
for its extremely anti-adhesive behaviour. This anti-adhesive
effect causes no material to adhere to the surface of
PTFE. PTFE-enveloped gaskets consist of a stable gaskets
insert and a PTFE envelope. Various inserts such as
corrugated steel plate with cord or soft material layers,
rubber, RivaTherm-Super and FA* are covered with a
PTFE envelope. Only high-grade, non-porous PTFE is
used for the envelope so that the insert is protected against
chemical attack. Depending on requirements, the PTFE
envelopes are open at the outer or inner diameter or fully
envelop the insert. The thickness of the envelope is 0.5 mm
and that is the reason for its high stability. Turned envelopes
can have a increased thickness from 2 up to 4 mm at
the inner diameter so that a greater imperviousness to
diffusion is given.
Profile TF2: The insert usually consists of RivaTherm-
Super, rubber, reinforced rubber-steel or FA*. This gasket
with an insert of RivaTherm-Super or rubber is also suited
for a plastic flange or a glass-fibre-reinforced flange because
of its great adaptability and softness. With the
surface pressure required for PTFE rubber without a
reinforcing insert can more or less be strongly pressed out
of the envelope.
