ALL YOU NEED TO KNOW ABOUT OIL AND SEALS.

Nomenclature and functions of seal 

(1) Nomenclature of components

Oil seals work to prevent leakage of sealed objects
such as lubricants from inside and also to prevent the
entry of dust and contaminants from outside.
1.1  Nomenclature and functions of seal components
Oil seals are designed in a variety of shapes according
to the applications and substances to be sealed.

(2) Component Functions

Main lip
The main lip is the most critical component of seals.
Its sealing edge contacts around the shaft surface in
order to provide excellent sealing performance.
During service, seals are placed under various
stresses, such as machine vibration, shaft runout, and
changes in the temperature and pressure of substances
to be sealed.
The main lip is designed so as to generate force (radial
lip load) and to keep the sealing edge consistently in
contact with the shaft under such stresses.
For such stresses, seal rubber material is made from
synthetic rubber, which is highly elastic and abrasion-resistant.
Minor lip
The minor lip prevents the entry of dust and
contaminants from outside.  As a lubricant, grease can
be retained in the space between main lip and minor lip.
Sealing edge
Section of the sealing edge is wedge-shaped to be
pressed against the shaft surface and linearly contacts
with the shaft to ensure sufficient sealing performance
and suitability for operation at high peripheral speed.
Spring
The spring supplements the tension at the sealing edge
to ensure tight contact between the shaft and the sealing
edge and enhanced sealing performance.  The spring also
prevents the deterioration of main lip sealing performance
caused by high heat or others. 
Because this spring is a closely wound type coil, the
initial tension can be obtained high level, and then
changes in load characteristics can be gradual with
respect to spring elongation.  Tension at the sealing edge
can thus be kept stable at an appropriate level.
Metal case
The metal case provides rigidity on seal, helping it settle
on the housing securely.  It also ensures easy seal
handling and mounting.
O.D surface
Seals are fitted tightly into the housing bore generally. 
O.D surface prevents the oil leakage through fitting area,
while excluding contaminants.  This surface may be made
of either metal or rubber and selected depending on the
application.
Fluid side face
The front end face of the seal is called the nose.  Seals
are usually mounted for the nose to face the substances
to be sealed.  The nose is made of rubber and forms a
gasket seal when compressed on housing shoulder.
Air side face
The oil seal surface vertical to the center line of the shaft
on the side that does not come in contact with substances
to be sealed is generally called the back face. Either metal
or rubber peripheral surface is available, depending on the
application.