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BRITTLENESS
Tendency to crack when subjected to deformation.
BUNA N
A general term for the copolymers of butadiene and acrylonitrile.
Typical commercial polymers are Hycar and Paracril.
BUNA S
A general term for the copolymers of butadiene and styrene.
BUTT JOINT
Joining two ends of material whereby the junction is
perpendicular to the ID of an O-Ring.
BUTYL
A synthetic rubber of the polybutene type exhibiting very low
permeability to gases.
COEFFICIENT OFTHERMAL EXPANSION
Average expansion per degree over a stated temperature range,
expressed in a fraction of initial dimension. May be linear or
volumetric.
COLD FLEXIBILITY
Flexibility following exposure to a predetermined low
temperature for a predetermined time.
COLD FLOW
Continued deformation under stress.
COLD RESISTANT
Withstands the effect of cold or low temperatures without loss of
serviceability.
COMMERCIALLY SMOOTH
Degree of smoothness of the surface of an article which is
acceptable for use.
COMPOUND
A term applied to either vulcanized or unvulcanized mixtures of
elastomers and other ingredients necessary to make a useful
rubber-like material.
COMPRESSION MODULUS
The ratio of the compressive stress to the resulting compressive
strain (the latter expressed as a fraction of the original height or
thickness in the direction of the force). Compression Modulus
may be either static or dynamic.
COMPRESSION SET
The decrease in thickness of a rubber specimen which has been
deformed under specific conditions of load, time and
temperature.
CONDUCTIVE
A rubber having qualities of conducting or transmitting heat or
electricity. Most generally applied to rubber products used to
conduct static electricity.
CONDUCTIVITY
Quality or power of conducting or transmitting heat or electricity.
COPOLYMER
A polymer consisting of two different monomers chemically
combined.
CORROSION (PACKING)
Corrosion of rigid member (usually metal) where it contacts
packing. The actual corroding agent is fluid medium trapped in
the interface.
CORROSIVE (PACKING)
A property of packing whereby it is assumed, often incorrectly, to
promote corrosion of the rigid member by the trapped fluid.
CRACKING
A sharp break or fissure in the surface. Generally due to
excessive strain.
CROSS-SECTION
An O-Ring as viewed if cut at right angles to the axis showing
internal structure.
CURING DATE
O-Ring molding date.
CURINGTEMPERATURE
The temperature at which the rubber product is vulcanized.
CYLINDER
Chamber in which piston, plunger, ram, rod, or shaft is driven by
or against the pressure medium.
DUROMETER
An instrument for measuring the hardness of rubber. Measures
the resistance to the penetration of an indentor point into the
surface of rubber.
DYNAMIC
O-Ring application in which the O-Ring is subject to movement
or moving parts.
DYNAMIC PACKING
A packing employed in a joint whose members are in relative
motion.
DYNAMIC SEAL
A seal required to prevent leakage past parts which are in
relative motion.
ELASTICITY
The property of an article which tends to return to its original
shape after deformation.
ELASTIC LIMIT
The greatest stress which a material is capable of developing
without a permanent deformation remaining upon complete
release of the stress. In rubber, the elastic limit as above defined
is very low and sometimes practically non-existent. Usually this
term is replaced by various load limits for specific cases in which
the resulting permanent deformations are not zero but are
negligible.
ELASTOMER
A general term for elastic, rubber-like substances.
ELONGATION
Increase in length expressed numerically as a fraction or
percentage of initial length.