| GLOSSARY
Of Terms Used In Sealing |
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- A -
Abrasion
Resistance: The ability of
a rubber compound to resist surface
wearing by mechanical action.
Accelerator:
A chemical compound that speeds up
the vulcanization of natural or synthetic
rubbers.
Aeration:
Aor (or gas) bubbles entrained or
accumulated in a liquid.
Aliphatic: A major
group of organic compounds characterized
by the presence of straight chain
arrangements of carbon atoms. The
three subgroups that comprise aliphatic
hydrocarbons are: paraffins (alkanes),
olefins (alkenes), and acetylenes
(alkynes).
Ageing:
Change in characteristics of rubbers
with time specifically influenced
by environmental factors (eg. light,
heat etc).
Air Checks
/ Traps: Surface markings
or depressions resulting from the
trapping of air between the rubber
surfaces being cured and the mold
or press surface.
Air
Side: THe side of a seal
which faces outwards or towards atmosphere,
as opposed to the fluid being sealed.
Ambient Temperature:
The temperature of the environment
surrounding a particular object.
Aniline Point:
General indication of the aromatic
content of an oil fluid determined
as the lowest temperature at which
the oil is miscible with an equal
volume of aniline.
Anti-Extrusion
Ring (Device): A washer-like
device of a relatively hard, tough
material installed in the gland on
the downstream side of the seal to
prevent seal extrusion into the diametrical
gap while under pressure. In short,
A ring or similar device assembled
with a seal to prevent the seal extruding
into the clearance space. (alternative
description for Back-up Ring or or
Back-up washer).
Antioxidents:
Additive in a rubber mix to resist
oxidation.
Antiozonant:
Addotove om a rubber to resist degradation
caused by ozone.
Automatic
Seal: General term applied
to describe seal designs that are
pressure energised. More specifically
it is used to classify certain types
of flexible lip seals.
Axial
Clearance: Clearance between
a sealing slement and the inside face
of the cover.
Axial
Interfrence: Clearance or
dimensional difference between the
ID or OD of a seal and the assembled
rod (or shaft) or housing diameter
respectively.
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- B -
Back (of
seal): The side of a seal
facing outwards or opposite to that
facing the fluid being sealed.
Back-up Ring:
A washer-like device of a relatively
hard, tough material installed in
the gland on the downstream side of
the seal to prevent seal extrusion
into the diametrical gap while under
pressure. In short, A ring or similar
device assembled with a seal to prevent
the seal extruding into the clearance
space. (Alternative name for Anti-Extrusion
ring or Back-up washer)
Back-up
washer: A washer-like device
of a relatively hard, tough material
installed in the gland on the downstream
side of the seal to prevent seal extrusion
into the diametrical gap while under
pressure. In short, A ring or similar
device assembled with a seal to prevent
the seal extruding into the clearance
space. (Alternative name for Anti-Extrusion
ring or Back-up Ring)
Bellows:
Pseudo-static 'boot' type exclusion
seal, also known as a garter.
Bench Test:
A laboratory test approximating product
service conditions.
Bending
Modulus: The measure of applied
force required to bend a material
a given distance around a specified
radius. A measure of material elasticity
(stiffness).
Bleeding:
A film or beads formed by such compound
components as plasticizers that have
migrated to the surface of rubber
products because of incompatibility
with the base elastomer and/or the
compound ingredients.
Blemish:
A surface mark or deformity.
Blisters: A raised
spot on the seal’s surface created
by an internal void, or air-filled
pocket.
Bloom:
A milky surface discoloration caused
by the migration of certain compound
components (such as antiozonants)
to the rubber’s surface after
molding or storage. The waxy film
serves as a protective coating shielding
the part from oxidation. This discoloration
DOES NOT adversely affect material
performance.
Braid:
Hollow or solid sructure of round,
square or polygonal section constructed
from interlocking filaments or yarn
strand laid obliqquely to the axis
of the braid.
Braid-over-Braid:
A braid produced by more than one
pass through a multiple-carrier braiding
machine.
Break-out
Friction: Frictional force
to be overcome to initiate movement.
Specifically static friction
Brittler Point: Temperature
at which an elastomer becomes brittle.
Bulls Ring:
A type of pistom ring. A rigid or
semi-rigid ring employed at one end
or both ends of a acking to exclude
extrusion of the packing into the
clearance space.
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- C -
Case:
Metal component of a seal to which
the sealing element is bounded, clamped
or otherwise contained.
Centring
Ring (Centering Ring): Am
extemsion of a gasket designed to
locate the gasket centrally on a flange.
Checking: Cracking
or crazing of the surface of an elastomer
due to the action of sunlight.
Chevron Seal:
Seal ring (or ring set) of V-shaped
cross-section.
Chrysotile:
Fibrous mannesium silicate, or 'white'
asbestos mineral.
Clearance:
Dimensional difference between sealing
element and related component.
Co-axial Seal:
A composit seal in the form of two
(or more) Co-axial ring members.
Collar: Characteristic
type of flexible lip rod sea, also
known as a hat seal or hat ring.
Coefficient of Thermal
Expansion: Value used to
determine the amount of linear dimensional
change for a particular elastomer,
which is temperature dependent.
Cold Flexibility:
Flexibility following elastomer exposure
to a specified low temperature for
a specified period of time.
Cold Flow: A term
describing the tendency of certain
materials to continue to deform or
“creep” under constant
sealing pressure (compressive load).
Cold Resistant:
Capable of low temperature operation
without loss of serviceability.
Composite Seal:
Combines the sealing performance of
elastomers with the physical properties
of the bonded material (i.e. metal,
plastic, etc.).
Compound:
An elastomeric material resulting
from the combination of a number of
individual chemical ingredients into
a batch mix. Further processing of
the thoroughly mixed ingredients,
to induce cross linking of polymer
chains (vulcanization), results in
the creation of a useful rubber-like
product.
Compression
Modulus: The ratio of applied
compressive force (stress) to the
resulting deformation of the test
material (strain). Compressive strain
is expressed as a fraction of the
original height or thickness of the
test specimen in the direction of
the applied force. In short, Its the
ratio of compression stress to resulting
compression strain expressed as percentage
of the original dimension.
Compression Seal:
Seal working on the principle of being
compressed to fill the clearance space.
Compression Set:
Permenant deformation of rubber after
subscription to compression for a
period of time. Specifically determined
as the ratio of dimensional change
to compression strain. OR The amount
by which an elastomeric material fails
to return to its original size after
release from a constant compressive
load.
Conductivity:
Elastomers are considered conductive
when they posses a direct current
resistivity of less than 10,00,000
ohm/cm.
Contact Force
(Contact Load): Total interface
pressure between a seal and the adjacent
surface.
Controlled
Gap Seal: A seal designed
to maintain constant clearance with
shaft.
Copolymer:
A polymeric material compromising
molecules of two or more different
kinds.
Cover:
Member or casing protecting or strengthening
a seal element.
Creep:
Movement or deformation of a substance
under the effect of prolonged load
stress.
Crocidolite:
Fibrous iron silicate, or 'blue' asbestos.
Crown Height:
The height of a (gasket) sealing element
above the surface of the retainer.
Cup: Specific
type of piston seal defined by its
geomerty (ie cup-shaped); but also
utilized as a description of a (seal)
case.
Cure:
Vulcanization process applied to rubbers.
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- D -
Deflash:
A process of removing unwanted, excess
material (flash) from a finished product.
Degassing: Intentional,
controlled outgassing of the volatile
(evaporative) components of elastomeric
materials.
Diametrical
Clearance: The gap between
the two mating metal surfaces forming
a gland’s internal cavity. Through
slight oversizing and accompanying
“squeeze,” the O-Ring
seals this gap to prevent system leakage.
In short, difference between ID of
a seal and the shaft or rod diameter;
or the ID of a seal and its housing.
Dielectric Strength:
The voltage required to puncture a
sample of known thickness and is expressed
as volts per mm of thickness.
Die Formed Ring:
A packing ring mechanically compacted
into an (apparently) homogeneous form.
Double Acting Seal:
Seal for reciprocating movements capable
of sealing with both directions of
movement.
Dry Running:
Rubbing contact without any liquid
being present at the interface.
Dynamic Friction:
Friction generated when relative movement
takes place between two contacting
surfaces.
Durometer:
Durometer Hardness: Arbitrary measurement
of hardness of a rubber compound related
to the resistance to penetration of
an indentor point on a durometer.
In a Shore A scale, the resultant
numerical rating of hardness runs
from lower numbered (30 or 40) softer
materials to higher numbered (80 to
90) harder materials. Usually designated
with a +/-5 tolerance.
Dynamic
Seal: A seal capable of working
with relative movement (either reciprocating
or rotary) between components being
sealed.
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- E -
Elasticity:
Property inherent in elastomeric materials
of readily returning to its original
form when released from a deforming
load.
Elastomer:
A general term used to describe both
natural and synthetic polymers possessing
the resilience required to return
to approximate original shape after
major or minor distortion.
Elongation: Generally
referred to in terms of tensile (pull
apart) testing, elongation is the
increase in length of a test specimen,
expressed as a percentage of its original
(unstretched) length...relative to
a given load at the breakpoint. Ultimate
elongation is the elongation at the
moment rupture.
Extrusion:
The forced extension of part of the
seal into the diametrical clearance
gap of the gland, caused by excessive
system pressure.
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- F -
Face:
Front surface of a seal (where appropriate).
Face Seal:
Squeezed, like a gasket, on both the
top and bottom surfaces of the seal’s
cross section. An axial seal. Seal
embodying two faces in rubbing contact
in a plane at right angles to the
axis of the seal.
FDA:
Food and Drug Administration is a
U.S. government agency that regulates
the ingredients in rubber compounds
that are intended for use in food
and medical applications.
Filler: A finely
divided material used to reinforce
or modify elastomer physical properties,
impart certain processing properties,
or reduce cost. Typical examples are
carbon black, clays, calcium carbonates
and silicas.
Filler
Ring: Elastic ring assembled
with a U-ring or V-ring to consolidate
the section.
Finger
Ring: A spring form with
flexible fingers.
Flash:
Excess rubber around a molded part
due to cavity overflow and/or parting
line of molded surfaces.
Flash Line: Exaggerated
degree of flash due to clearance or
gap between mould parts.
Flex Cracking: Surface
cracks resulting from repeated flexual
cycling.
Flex Fatigue
Resistance: The ability to
withstand fatigue resulting from repeated
distortion by bending, extension or
compression
Flexual
Modulus: Stress at a certain
stran - not a ratio and not a constant,
but merely the co-ordinate of a point
on the stress-strain curve.
Flinger (Ring): Washer-form
ring mounted next to a gland or gland
follower for directing any leakage
away from the shaft.
Flinger
Ring: Secondary seal element
in the form of a ring generating ‘windback’
action.
Flow Crack:
Imperfection in a moulding due to
imperfect flow of material during
moulding.
Flow Lines:
Molded article surface imperfections
caused by failure of the rubber stock
to blend with itself during the molding
operation.
Flow Mark:
Imperfection in a moulding due to
imcomplete flow of material in the
mould.
Fluid:
A liquid or gas.
Follower:
See Gland Follower.
Friction
(Break-Out): Friction developed
in dynamic seal situations during
machine start-up. When machine operation
is irregular, O-rings tend to conform
(adhere) to the microfine grooves
of surrounding glandular surfaces,
requiring extra initial force to break
them out of these microfine grooves.
Friction (Running):
A force which resists objects already
in motion.
Front:
The side of a seal facing the fluid
to be sealed. Specifically applied
to rotary shaft in seal descriptions.
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- G -
Garter:
Pseudo-static exclusion seal, usually
in the form of elastomeric bellows.
Garter Spring:
Helical wire spring of circular geometry
fitted to a lip seal (specifically
an oil seal) to enhance lip contact
pressure.
Gasket:
Static seal made from deformable sheet
material sandwiched and compressed
between two mating plane surfaces.
Used to retain fluids under pressure
or to seal out foreign matter.
Gland: Complete
cavity into which the seal is installed.
Includes a machined groove and mating
metal surfaces. General description
of housing or cavity for accommodating
compression packings or sealing rings.
Gland Cover:
Fixed gland member fitted on the non-pressure
side of a gland to retain the seal
against the action of pressure.
Gland Follower:
Adjustable gland member, which can
be tightened to compress and expand
radially the packing in a gland.
Groove: The
machined glandular recess into which
the seal is fitted.
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- H -
Hardness:
Resistance of rubber to forced distortion
as measured by the indentor point
of a durometer gauge. Resistance to
indentation of a rubber, normally
measured and specified in IRHD (International
Rubber Hardness Degrees).
Hardness, Shore A:
Durometer reading in degrees of rubber
hardness as measured on a Shore A
gauge. Scale is 0-100, with higher
numbers indicating greater hardness.
Hard Face: A
facing of high hardness applied to
softer materials.
Hat
Ring: Alternative name for
a collar seal.
Head:
Portion of a seal carrying the sealing
edge.
Header:
Ring of hard material used in conjunction
with seal ring(s) to locate the seal(s)
and eliminate axial movement.
Heart Seal:
Solid elastomeric ring seal with a
heart shaped cross-section.
Heat Build-up: The
temperature rise in a rubber body
resulting from hysteresis.
Heel: The part of
the seal cross-section adjacent to
the clearance gap on the non-pressurized
side; or adjacent to the shaft on
the back of an oil seal.
Hermetic Seal: An
airtight seal.
Housing:
Annular recess into which a shaft
or rod seal is assembled.
H-Ring: Solid elastomeric
seal ring of H-shaped cross-section.
Hydraulic Packing:
A packing specifically designed for
the sealing of hydraulic fluids in
cylinders etc.
Hysteresis:
The precent energy lost per cycle
of deformation, or 100% minus the
resilience percentage. Results
from internal friction and is manifest
by the conversion of mechanical energy
into heat.
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- I -
I.D.:
The inside or hole diameter of an
O-ring.
Interference:
Negative dimensional difference between
a seal ID or OD and the final seal
assembly diameter.
ISO:
International Organization for Standardization
model for quality assurance in design,
development, production, installation
and servicing.
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- J -
Junk Ring:
Alternative name for an anti-extrusion
ring.
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- L -
Lantern
Ring: Ring with radial ports
located at an intermediate position
in a gland to allow coolant or lubricant
to be introduced.
Lead-in
(Chamfer): Chamber introduced
in component(s) to facilitate assembly
of seal on to a rod or shaft, or into
a cylinder or housing.
Leakage
Rate: The rate at which a
fluid (either gas or liquid) passes
a barrier.
Life Test:
A laboratory test of the amount and
duration of product resistance to
a set of destructive forces or conditions.
Used to compare the relative performance
capabilities of various product designs.
LIM: “Liquid
Injection Molding” is a closed
manufacturing process using LSR in
an injection molding machine.
Lip: The part
or edge of a seal which forms the
sealing surface.
Lip
Opening Pressure: Air pressure
required to lift a lip seal off its
shaft and allow air leakage at the
rate of 10 l/mm.
Lip
Seal: A seal where the sealing
surface is in the form of a flexible
lip.
Load:
Actual pressure at sealing face of
a seal, normally the sum of the interference
load and fluid pressure acting on
the seal.
Low Temperature
Flexibility: The ability
of an elastomeric product to be flexed
or bent at low temperatures without
cracking.
LSR:
“Liquid Silicone Rubber”
is composed of a two-component, low
viscosity, heat-curable rubber system.
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- M -
Memory:
Ability of an elastomeric material
to return to its original size and
shape after deformation.
Migration: Degradation
products removed from an elastomeric
sealing element and escaping to other
parts of the system.
MIL:
Abbreviation for Military.
MIL STD: Military
Standard.
Mismatch:
Unequal O-ring cross-sectional radii
caused by dimensional differences
in the mold cavity.
Mix:
General description of a rubber compound
formulation.
Modulus:
The tensile stress force in p.s.i.
required to produce a specified increase
in material length (usually 100% elongation).
Specifically the shape of the stress/strain
curve for a material at a given elongation.
Modulus of Elasticity:
One of several measurements of stiffness
or resistance to deformation. The
ratio of stress to the strain produced
by that stress when stress is proportional
to strain. But in rubber, modulus
measurements are made in comparison
or shear, rather than in tension,
and they are only valid for strains
up to about 15%.
Mold:
Typically made from steel. Product
is formed within machined cavity.
Mold Cavity:
Hollow space of the mold within which
the uncured rubber compound is shaped
and cured to the desired finished
product form.
Mold
Finish: The surface finish
of the mold which imparts the desired
surface quality to the finished molded
product.
Mold Marks:
Slight irregularities in the surface
of molded articles caused by mold
machining marks,or damage to the mold
itself.
Mold Release:
A lubricant used to assist in the
removal of rubber products from the
mold.
Moulding Shrinkage:
Loss of dimension of a moulded product
after removal from the mould and subsequent
cooling.
MS:
Abbreviation for Military Standard.
Multiple Seal:
A seal set comprising two or more
seal rings of sealing elements.
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- N -
Neck Bush:
Throttle bush fitted at the bottom
of a stuffing box or gland.
Nominal Dimension:
The mean dimension of a molded article,
from which small dimensional (plus
and minus) deviations are allowed
as manufacturing tolerances.
Non-Fill: A molding
condition where the rubber fails to
completely fill the mold cavity, resulting
in an incomplete part.
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- O -
Occlusion:
The mechanical entrapment of gases,
liquids or solids within the folds
of a substance.
O.D.:
The outside diameter of an O-ring.
A dimensional reference.
Off Register: Eccentric
O-ring cross-sectional radii caused
by lateral shift of one mold cavity
relative to the other.
Offset:
Step or break in the surface or a
moulded product due to faulty register
of the mould.
Oil
Resistant: Ability of vulcanized
rubber to resist swelling and other
detrimental effects of exposure to
various oils.
Oil-side:
The side of a seal facing the fluid
being sealed (specifically applied
in the case of an oil seal).
O-Ring: Solid elastomer
ring seal of circular cross-section.
A doughnut-shaped object, or torus,
that functions as a seal, blocking
the passage of liquids or gases, by
being compressed between the two mating
surfaces comprising the walls of the
cavity (gland) into which the ring
is installed.
Oscillating
Seal: Most commonly used
in faucet valves, in this application
the inner or outer member of the gland
moves in an arc around the axis of
a shaft. Movement is limited to a
few turns in one direction and a few
turns in the return direction (i.e.
faucet on, faucet off).
Outgassing:
Primarily occurring in vacuum situations,
the volatile (evaporative) components
of some rubber compounds may become
vaporized in the vacuum and released
(outgassed) by the compound into the
surrounding environment.
Oxidation: The reaction
of oxygen with a rubber compound,
typically resulting in surface cracking
of the rubber material. As oxidation
involves the transfer of electrons,
reduction in the physical strength
of elastomers may also occur from
exposure to the oxidizing agent.
Ozone Cracking:
Surface cracking of rubber due to
the degrading effect of ozone.
Ozone Resistance:
The ability of vulcanized rubber to
withstand cracking and physical deterioration
from exposure to ozone, a more active
oxidizing agent than oxygen itself.
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- P -
Packing:
General name for a compression type
dynamic seal housed in a gland. Also
applicable to the materials used in
this type of seal.
Panting:
Movement between sealed surfaces of
a static seal due to pressure fluctuations
and insufficient clamping or tightening.
Pedestal Ring:
Support for a U-ring seal.
Permanent Set: The
deformation remaining in a rubber
specimen following both stress and
relaxation over a period of time.
; The amount of residual displacement
in a rubber part after a distorting
load has been removed.
Permeability:
The rate of gas flow through a particular
rubber material. ; A measure of the
ease with which a liquid or gas can
pass through a rubber film.
Pitting: Surface
voids produced by mechanical erosion
(wear) or chemical action.
Plasticizer:
A chemical agent added to the rubber
compound batch mix to soften the elastomer
for processing, as well as to improve
physical properties of the compound
product (i.e., increase elongation,
reduce hardness, improve tack). ;
Constituent of a rubber mix controlling
the hardness and plasticity of the
final product.
Polymer:
A long molecular chain material formed
by the chemical combination of many
similarly structured, small molecular
units. Eg. natural rubber and synthetic
rubbers.
Post Cure:
A second step in the vulcanization
of certain elastomers, used to drive
off residual decomposition products
resulting from initial vulcanization.
Pseudo-static Seal:
An exclusion seal (eg bellows or garter)
for excluding dust, dirt etc, but
also capable of accommodating relative
movement between the components to
which it is attached.
Pusher-Type
Seal: A mechanical seal in
which the secondary seal is automatically
pushed along the shaft or sleeve to
compensate for wear.
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- Q -
QS 9000:
Quality System model, used in conjunction
with the ISO 9000 standard, for the
automotive industry.
Quad
Ring: Solid elastomeric ring
seal of modified circular cross-section
giving four sealing ridges.
Quench: A neutral
fluid introduced into a seal cavity
to dilute fluid which may have leaked
past the seal.
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- R -
Radial Clearance:
Clearance between the shaft and internal
dismeter of an oil seal cover.
Radial Interference:
Negative dimensional difference between
the radial dimension of a seal and
its housing or space into which it
is fitted.
Radial
Load: Total load carried
by the lip of a rotary shaft seal
or rod seal.
Radial
Seal: Compression is applied
perpendicular to the seal centerline.
Reciprocating Seal:
Seals used in moving piston and rod
situations.
Reinforcing
Agent: Fillers, such as Carbon
Black, added to the elastomeric batch
mix to improve such physical properties
as tensile strength.
Relaxation:
Decrease in stress occurring with
time under constant load or deformation.
Rectangular Seal:
Solid elastomeric ring seal of rectangular
cross-section.
Resilience:
Energy recovery property of an elastomer
under deformation cycles. Specifically
the ratio of energy returned to energy
input, per cycle of rapid deformation.
; The capability of returning to original
size and shape after deformation.
Rider Ring:
Wear or load-carrying ring associated
with some form of ring seal (usually
a metallic ring or piston ring).
Ring: Any circular
seal or seal element.
Ring
Gasket: A flange gasket which
lies wholly within the ring of bolts.
RMA: Rubber
Manufacturer’s Association.
RMS: Root Mean
Square. A measure of surface roughness
typically applied to the machining
of metal gland and shaft surfaces.
RMS stands for the square root of
the sum of the squares of micro-inch
deviation from true flat.
Rotary Seal: Seals
for rotating shafts, with the turning
shaft protruding through the I.D.
(hole) of the O-ring. ; Seal type
specifically suitable for sealing
rotating shafts of rotary motions.
Rotary Seal Ring:
Driven or rotating face of a mechanical
seal.
Rubber:
A common name for both naturally occurring
and synthetically made elastomers.
; Elastomeric substance, either natural
or synthetic.
Rubber
Face: Rubber coating applied
to a seal case to provide a sealing
surface against the seal housing.
Rubber, Natural:
A natural product of the juices of
certain tropical plants (latex), improved
through heat treating with sulfur
(vulcanization).
Rubber,
Synthetic: Man-made elastomers
such as Nitrile, Fluorocarbon, Silicone,
etc.
Running Friction:
A force which resists objects already
in motion. ; Friction generated by
a seal under dynamic operating conditions.
Run-in: Period
of initial operation and wear during
which a seal becomes properly bedded
down.
Runout (Shaft):
Same as gyration. When expressed in
inches along, or accompanied by abbreviation
“TIR” (total indicator
reading), it refers to twice the radical
distance between shaft axis and axis
of rotation.
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- S -
SAE:
Society of Automotive Engineers.
Scorching: Premature
curing of compounded rubber stock
during processing (Eg. Excess heating)
or storage, with the potential for
adversely affecting material flow
and plasticity during subsequent shaping
and curing processes.
Scorch:
Premature curing of vulcanized rubber
due to excessive heat.
Scraper
(ScraperRing): Heavyduty
wiperseal to exclude grit and heavier
contaminants with reciprocating rod
movements.
Scuffing:
Surface roughness produced by mechanical
wear.
Seal:
Any device used to prevent the passage
of a fluid (gas or liquid) or fine
particles.
Sealing
edge: The extreme section
of an oil seal which provides the
actual seal.
Sealing
Element: Portion of the seal
section or seal element covering the
sealing edge.
Sealing
Land: Flat portion of sealing
edge of an oil seal after prolonged
contact with shaft.
Seal
Plate: Alternative description
for a gland cover.
Seal
Width: The overall axial
dimensions of a seal.
Secondary
Seal: O-Ring, bellows or
similar device which accommodates
leakage from the primary seal of a
mechanical face seal.
Separator:
An intermediate ring of thin, stiff
material which allows individual rings
in a seal assembly to slide over one
another.
Shaft Run-out:
A dimension equivalent to twice the
displacement of the axis of a shaft
from normal at any particular point
on the shaft under running conditions.
Shelf-Aging:
The potential degradation of seal
performance capabilities due to exposure
of seal elastomers to stressful environmental
factors during storage. Proper packaging
and storage conditions help to avoid
this problem.
Shell:
Case of an oil seal.
Shore
A Hardness: Durometer reading
in degrees of rubber hardness as measured
on a Shore A gauge. Scale is 0-100,
with higher numbers indicating greater
hardness.
Shrinkage:
(1) All rubber materials shrink to
some extent during molding. This is
normal and should be taken into consideration
(by individual polymer shrink rates)
when designing rubber parts. (2) Decreased
seal volume due to exposure to adverse
environmental factors. Can be an indication
of plasticizer extraction from system
chemicals.
Single
Acting Seal: Dynamic seal
capable of sealing in one direction
of movement only.
Size,
Actual: Actual dimensions
of a molded article (including manufacturing
tolerances).
Slinger
Ring: Alternative name for
a flinger.
Slipper
Seal: Co-axial seal comprising
an O-ring and a hard low-friction
PTFE bearing ring (slipper ring).
Soft Packing:
Gland packing of soft resilient material.
Spew: Excess
material forced from a mould during
moulding process.
Split-ring
Seal: Split rigid section
ring (usually metallic) similar in
form and principle to a piston ring.
Split Seal:
Elastomeric seal ring split to facilitate
assembly.
Squeeze:
Deformation of a seal produced when
assembled with an interference fit.
Static Friction:
Instantaneous or 'holding' friction
of a seal under static conditions.
Stationary Seal Ring:
Static face of a mechanical seal.
Stick-Slip:
Jerky or irregular motion when a seal
is operating under varying static-dynamic
friction.
Stiction:
Initial friction or break-out friction
when motion is started.
Strain
Relaxation or Creep: Is that
characteristic of all elastomers to
show gradual increase in deformation
under constant load with passage of
time. It is usually expressed as percent
relative creep, which equals total
deformation minus intial deformation
divided by initial deformation times
100.
Stress relaxation:
The loss in stress when an clastomer
is held at a constant strain over
a period of time.
Stuffing
Box: Alternative name for
a gland for containing packings or
seal rings.
Swell:
Increase in volume of a seal or elastomeric
material when in contact with a fluid.
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- T -
Tear Resistance:
Resistance to the growth of a cut
in the seal when tension is applied.
; The force per unit of thickness
required to propagate a nick or cut
in a direction normal to the direction
of the applied force, or to initiate
tearing in a direction normal to the
direction of the stress.
Temperature Range:
The working range marked by the limits
of minimum and maximum operating temperatures
for effective seal performance.
Tensile Strength:
Pull-apart strength. A measure of
the compound’s strength when
stretched to the breaking point. ;
The force per unit of the original
cross-sectional area which is applied
at the time of the rupture of a specimen.
Tensile Stress:
More commonly called "modulus",
is the stress required to produce
a certain elongation.
Tension
Set: Increase in normal (unstressed)
length of an elastomeric specimen
after initial stretching and release.
Terpolymer:
A polymer resulting from the chemical
combination of three monomers.
Thermal Expansion:
Linear or volumetric expansion caused
by temperature increases.
Thermoplastics: Polymeric
materials that soften and can be re-formed
when heated, returning to original
properties when cooled.
Thermoset:
Elastomers that undergo a permanent
chemical crosslinking of molecules
when processed, heated and molded,
and therefore cannot be reprocessed.
Thread Stretch:
Loosening of bolted assemblies or
unions due to bedding down of threads.
Throttle Bush:
Restructive bush fitted at the bottom
of a stuffing box or gland; also descriptive
of a bushing seal.
TIR
(Total Indicator Reading):
A measurement of roundness with relationship
to a centerline and expressed in total
diametric deviation.
Torque:
A turning or twisting force, generally
associated with the rotation of a
shaft.
Toroidal Seal:
Alternative name for an O-Ring.
Torsional Strength:
Ability of a seal to withstand damage
due to twisting.
TPE:
“Thermoplastic Elastomer”
combines the rubber-like performance
of elastomers with the processing
advantages of plastic. Scrap material
can be recycled without significant
loss in physical properties, unlike
thermoset materials.
Track:
Mark made on a shaft by a rotary seal.
Trapped O-Ring:
Static seal using an O-ring in a special
groove.
Trim:
Removal of excess material (flash)
from a molded rubber article.
Trim Cut: Damage
to the molded article by trimming
too close.
Trim Diameter:
Of an oil seal, without spring.
Trim face: Front
surface of a rotary oil seal trimmed
to an angle to firm the sealing edge.
Triumming Angle:
Angle between the trimmed face of
a seal lip and the seal axis.
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- U -
Ultimate
Elongation: The % of specimen
stretching at the point of breaking.
Generally referred to in tensile testing.
Under-Cure:
A condition where rubber has not been
cured enough, exhibiting poor physical
properties and/or tackiness.
Unidirectional Seal:
A seal which provides fluid sealing
from one side only.
Unirotational
Seal: A rotary shaft seal
designed for application with one
direction of shaft rotation only.
Unit Seal: A
seal ring consisting of a single ring,
and not normally subject to axial
compression.
U-Ring:
Flexible lip seal of U-shaped cross-section.
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- V -
Viscosity:
Resistance to flow.
Voids:
Empty pockets where not intended.
Volume Change:
Increase or decrease in the size of
a specimen expressed as a percentage
of original volume. Generally associated
with immersion of elastomer samples
in various chemical agents.
Volume Swell: A term
generally used to describe the increase
in physical size of a specimen immersed
in a particular chemical agent.
V-Ring: Flexible
lip seal of V-shaped cross-section:
also known as a chevron seal.
Vulcanization:
The heat induced cross linking (curing)
of polymer chains, converting basic
visco-elastic liquids into three-dimensional
networks of flexible, elastomeric
chains (the molded rubber product).
; Heat process treatment for rubber
to stabilize and harden it.
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- W -
Wear Bond:
Mark made by a rotary seal on a shaft.
Wear Ring: A
ring of hard material associated with
a seal or seal assembly and intended
to take rubber wear.
Weathering:
The tendency of some O-ring seals
to surface crack upon exposure to
atmospheres containing ozone and other
pollutants.
Weeping:
Small amount of leakage from a seal,
arbitrarily defined as leakage rate
of less than one drop per minute.
Width: 1. The
cross-sectional diameter of an O-ring.
2. One half the difference between
the I.D. and O.D. of the ring.
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