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[ B ]
BACKRINDING
A "breaking up" of the rubber normally observed around tool
split lines. It results from the rubber shrinking during
cure and tearing away at points where the molding is held.
BANBURY MIXER
An
internal mixer commonly used in the rubber industry. It
consists of two shaped rotors which turn inside a sealed
chamber.
BLEEDING
The exudation of droplets of excess plasticizer onto the
surface of the rubber. This happens when rubbers contain
unsuitable levels of plasticizers which are not fully
compatible.
BLOOM
A white or light colored crystalline deposit on the surface
of the rubber. Many chemicals added to rubber have a limited
solubility. If they are present in a cured rubber at levels
higher than their solubility, they crystallize out onto the
surface.
BUILDING TACK
Term
used to describe the ability of a rubber to stick to itself
in the uncured state, so allowing pre-building of the
material before curing.
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[ C ]
CALENDERING
Producing rubber in continuous sheets by processing it
through a series of rollers.
CLAY
Commonly used as an "extender" in rubber. Treated clays
reinforce the rubber and are termed "hard" clays. Those
which do not provide reinforcement are called "soft" clays.
COMPOUND
A general word used to describe a particular formulation or
"recipe", or as a descriptive term for unvulcanized rubber
in general. It is used in such applications as "Compounding
ingredients", "Compound no. xyz", etc.
COMPRESSION SET
The
degree to which a rubber does not recover fully to its
original state after it has been compressed for a long
period of time. (See also "Measurement of Rubber
Properties").
CRYSTALLISATION
Rubber materials tend to crystallise on standing, resulting
in an increase in hardness. This increase is usually small,
but can be more significant in the case of some
Neoprenes (polychloroprenes).
CURATIVES
The chemicals involved in curing the rubber, e.g.
accelerators, vulcanising agents, activators etc.
CURING
Also known as vulcanisation, this is the permanent change
which the rubber undergoes during moulding. When mixed,
rubber compounds are thermoplastic and will melt and deform
easily. After curing, the rubber is heat stable.
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[ D ]
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[ E ]
ELASTOMER
General
term used to describe all natural and synthetic polymeric
materials which have rubbery or "elastic" properties.
ELECTRIC
STRENGTH
Describes the ability of a rubber to withstand high
voltages. It is usually quoted in KV per mm of rubber
thickness. (Link to Electric Strength properties
EXTRUSION
Producing continuous lengths of rubber with a constant
profile by forcing it through a die under pressure and
vulcanising it.
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[ F ]
FILLERS
General
term describing the bulk materials which are added to the
rubber (usually as powders).
FLASH
Excess
rubber found on moldings as a result of the molding process,
but which does not form a part of the molding itself. This
does not usually include feed gates but refers particularly
to thin films of rubber formed at tool split lines etc.
FLEX
CRACKING
The
tendency of some materials to crack as a result of repeated
bending or stressing at the same point.
FORMULATION
The term
used to describe a rubber "recipe".
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[ G ]
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[ H ]
HEAT
(see "Lift")
HEAT AGEING
Also
known as "accelerated ageing". Rubber materials are often
tested for shorter times at higher temperatures to predict
what will happen over longer times and at lower
temperatures.
HYSTERESIS
The difference between the amount of energy absorbed when a
rubber is stretched and the amount of energy released when
the rubber is relaxed. High hysteresis indicates a high loss
of energy (and so is good for energy absorbing
applications). Low hysteresis rubbers are more resilient.
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[ I ]
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[ J ]
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[ K ]
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[ L ]
LIFT
The set of rubbers resulting from a single mould cycle or
pressing. Also called a "heat".
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[ M ]
MODULUS
The relationship between stress (force) and strain (extended
length). Modulus is usually given as the stress (or force)
required to extend a rubber (e.g. 100%, 200% extended).
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[ N ]
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[ O ]
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[ P ]
PLASTICIZERS
Liquids
which are incorporated into rubber, generally described as
plasticizers because of their softening effect.
POLYMER
General
term used to describe all rubbers and plastics. In fact, it
is the chemical term used to describe all organic materials
which are formed from chains of repeated chemical units.
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[ Q ]
[ R ]
RESILIENCE
The
technical term used to describe "bounce" or "snap".
Increasing resilience means an increasing "bounciness".
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[ S ]
SCORCH
The
onset of cure, when chemical reactions begin to take place
in the rubber as it is being heated. A "scorched" rubber is
no longer processable.
SET
The
degree to which a rubber does not fully recover to its
original shape after it has been deformed for a long period
of time. Also called "permanent set".
STRAIN
The
change in length of a rubber under tension or compression. A
rubber stretched to double its original length would be at
100% strain.
STRESS
An
applied force or load. A load of 1kg applied to a test piece
would be a stress of 1kgf.
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[ T ]
THERMOPLASTIC
Any
material which melts on heating and resets on cooling. This
melting and refreezing can be repeated indefinitely.
THERMOSET
Any
material which melts on heating but then undergoes a
permanent chemical change after which it is heat stable
(i.e. it will degrade on further heating rather than
"melt").
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[ U ]
UNDERCURE
Removing
rubber from the mould before the vulcanization process has
been completed. Often results in porosity in the rubber or
unusually poor compression set.
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[ V ]
VULCANIZATION
The
permanent chemical change that a rubber undergoes on heating
together with chemicals. The chemicals which accomplish this
change are called "vulcanizing agents".
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[ W ]
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[ X ]
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[ Y ]
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[ Z ]
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