Industrial seal self study guide - SKF.com

Glossary of Seal Terms (cont...)
MPM – Meters per minute. Calculate as shaft
diameter (mm) x RPM x .001 x 3.142
Nick – A void created in the seal material after
molding.
Nitrile – A general term for the co-polymer of
butadiene and acrylonitrile. ASTM class NBR.
Non-Spring loaded – Seal without a spring.
Applies radial force only through elasticity of the
rubber lip and interference.
Non-Synthetic – Before synthetic materials were
developed, naturally occurring materials were used.
Leather was the sealing element commonly found
in earlier seals. Felt was also extensively used for
grease and dust seals.
Oil Resistance – The measure of an elastomer’s
ability to withstand the deteriorating effect of
lubricant on the mechanical properties.
O-Ring – A toroidal shaped seal, commonly round.
Variations are square, lobed or rectangular.
Out-Of-Round, Shaft – The deviation of the shaft
cross section from a true circle.
O.D. – See Seal, Outside Diameter.
Paper Polishing – Finishing the surface of a shaft
with abrasive paper.
Parabolic – Like a parabola; a plane curve formed
by the locus of points equidistant from a fixed line
and a fixed point not on the line.
Plunge Ground – The surface texture of shaft or
wear sleeve produced by presenting the grinding
wheel perpendicular to the rotating shaft without
axial motion.
Polyacrylate - A type of elastomer characterized
by an unsaturated chain and being a copolymer
of alkyl acrylate and some other monomer such
as chloroethyl vinyl ether or vinyl chloroacetate.
ASTM class ACM.
Press Fit – Retention force achieved by installing
an element whose contact diameter is greater (or
less) than its mating surface.
Primary Lip – The flexible elastomeric component
of a seal lip which contacts the rotating surface,
performing the main sealing function.
psi – Pounds per square inch. Measure of
pressure for fluids and gases.
PTFE – Polytetrafluoroethylene. A thermoplastic
polymer developed by Dupont with outstanding
heat and chemical resistance.
Radial Seal – A seal which exerts radial sealing
pressure in order to retain fluids and/or exclude
foreign matter.
Radius – A line segment that joins the center
of a circle with any point on its circumference.
Retention – To retain lubricants or pressure
within the bearing cavity.
Retention Seals – These seals are often springloaded
to retain lubricants or confine pressure in
the bearing cavity.
Roller Burnishing – A method of shaft surface
finishing in which the surface peaks caused by
lathe cutting appear to flatten. The original lead
grooves are compressed and not removed.
Roto preening – A method of shaft surface
finishing in which the shaft surface dimples and
kerfs at one side of the depression.
Run-In – The period of initial operation during
which the seal-lip wear rate in greatest and the
contact surface is developed. Synonym:
bedding-in.
Run-Out – That run-out to which the seal lip is
subjected due to the outside diameter of the shaft
not rotating in a true circle. Usually expressed as
TIR (Total Indicator Reading).
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