Most
people may not be familiar with the scientific name
polytetrafluoroethylene or PTFE even though they probably encounter
this substance on an almost everyday basis. PTFE is more popularly
known by its common name, Teflon, most notably in the form of
cookware and other household goods. However, PTFE has other uses
aside from non-stick cooking pots and frying pans.
For
instance, various industries today make use of PTFE rotary shaft
seals made from a combination of fluorine and carbon. These
components boast exceptional heat- and water-resistant properties,
making them ideal for automobiles and hydraulic equipment that are
constantly exposed to extreme environments. PTFE rotary shaft seals
also serve as barriers that keep other machine components from
rubbing against each other, thereby reducing damage from friction as
well as wear and tear.
Not
all manufacturers use rotary shaft seals made of PTFE, however, as
some opt to use rubber rotary shaft seals for various reasons. Yet
these materials often don’t resist damage quite as well as PTFE
variants when exposed to extreme heat or cold. As such, it is
important to correctly identify one’s exact requirements and
thereby choose the type of rotary shaft seal that best suits specific
industrial applications.
A substance that's
“chemically inert” means it won't react to anything. You can
leave a chemically inert plastic out in the sun, douse it with water,
or pour acid on it. You won't get a nudge out of it.
Being inert is important for
essential
substances such as polytetrafluoroethylene (PTFE), known to the
world simply as Teflon. Generally, it means PTFE can be used in a
wide array of situations sans risk of a chemical reaction that may
pose a health or safety threat. The bond of carbon and fluorine atoms
is strong enough to shrug off anything that comes their way.
On an atomic point of view,
the secret for inert of substances lies in the outer shells. Case in
point: noble gases; their outer shells have the right amount of
electrons, which is 8 (save for helium, with 2). As these gases have
the right amount of electrons, there's no more reason for them to
gain or lose some. In addition, inert substances themselves don't
participate in any chemical reaction.
This is good news for
industries that will be using inert substances. Handling chemicals
has always been an edgy job requiring nerves of steel to make sure
you don't drop that vial of volatile compounds. Substances like PTFE
were chosen to assume various duties that commonly come in contact
with a variety of compounds and other substances.
Sealing,
as any respectable engineer knows, involves wedging a gasket between two parts
to create a pressurized seal. There are as many seals as there are junctions
that need sealing; and each seal is exclusively meant to close off the joint
between two specific parts. Shafts, tubes, and other radial parts are usually
linked via an o-ring or another similar gasket, but o-rings aren't always the
go-to seals for radial applications.
Enter
the rotary shaft seal. A hybrid between a PTFE (polytetrafluoroethylene) sealing
lip and a mechanical body usually energized by a spring, this seal can secure
radial parts together with a firm and solid grip. Movement and imperfections in
the parts' shapes don't faze rotary shaft seals in the slightest; thanks to the
spring inside these seals, they're able to conform to whatever shape the parts
take while maintaining their tight leak-proof interface.
Even
heat can't dampen the performance of these specialized seals. PTFE is
chemically-resistant, and can endure very high heat. Simply put, there couldn't
be a more appropriate and durable material to serve as a sealing lip. Although they
can count on the seals being sturdy, operators might still want to inspect their
machines once in a while to ensure these seals hold up and deny fluid passage.
Source:
http://www.engineerlive.com/content/21015
