435 Technical Terms in Rubber Industry

435 Technical Terms
You Need To Know
in Rubber Industry
A Compilation by Rubber & Tyre Machinery World

435 Technical Terms You Need To Know in Rubber Industry
http://rubbermachineryworld.com
A Rubber & Tyre Machinery World Compilation – Aug 2016. Page 2 of 20
A
1. Abrasion :
The wearing away of a surface in service by
mechanical action, such as rubbing, scraping or
erosion.
2. Abrasion Resistance :
The ability of a rubber compound to resist
mechanical wear.
3. Abrasion Resistance Index :
A measure of the abrasion resistance of a rubber
relative to that of a standard rubber under the
same specified conditions, expressed as a
percentage.
4. Absorption :
The physical mechanism by which one substance
takes up another substance (liquid, gas or vapor)
into its interior.
5. Accelerated Life Test :
Any set of test conditions designed to reproduce,
in a short time, the deteriorating effect obtained
under normal service conditions.
6. Accelerated Service Test :
A service or bench test in which some service
condition, such as speed, temperature or
continuity of operation, is exaggerated in order
to obtain a result in shorter time.
7. Accelerator :
A compounding material used in small amounts,
with a vulcanizing agent, to increase the speed of
vulcanization..
8. Acid Resistance :
The ability to resist the action of identified acids
within specified limits of concentration and
temperature.
9. Acrylic :
A polymer for which resistance to air and hot oil
at temperatures above 30 degrees Fahrenheit are
required.
10. Adhere :
To cling or stick together.
11. Adhesion :
Tendency of rubber to bond or cling to a contact
surface.
12. After Cure :
Continuation of vulcanization after the desired
cure is effected and the heat source removed
(also referred to as Post-Cure).
13. Ageing :
To undergo changes in physical properties with
age or lapse of time.
14. Ageing, Accelerated :
Tests run on various rubbers to find out, in as
short a period as possible, the destructive
influence of light, oxygen, heat and ozone.
15. Ageing, Oxygen Bomb :
A means of accelerating the change in the
physical properties of rubber compounds by
exposing them to action of oxygen at an elevated
temperature and pressure.
16. Ageing , Air Bomb :
Similar to an oxygen bomb, but used with air.
17. Ageing, Shelf :
Ageing during storage.
18. Agglomerate, Compounding material :
A cluster of particles of one or more
compounding materials loosely held together.
Most commonly used to describe carbon black.
19. Air Checks :
Surface markings or depressions due to trapping
air between the material being cured and the
mold surface.
20. Air Curing :
Vulcanization of a rubber product in air, as
distinguished from in a press or steam
vulcanizer.
21. Alpha Particles :
Positively charged particles composed of two
protons and neutrons (often referred to simply as
helium atom molecule); characterized by limited
penetration.
22. Ambient Temperature :
The surrounding temperature relative to the
given point of application.
23. Aniline Point :
The lowest temperature at which equal volume
of pure, fresh aniline and oil will completely
dissolve in one another is the aniline point of the
oil.
24. Antidioxidant :
An organic substance which inhibits or retards
oxidation.
25. Antiozonant :
A substance that retards or prevents the
appearance of cracks from action of ozone when
the elastomer is exposed under tension, either
statically or dynamically, to air containing ozone.

26. Antirad :
A material which inhibits radiation change.
27. Aromatic oil:
A hydrocarbon process oil containing at least
35%, by mass, of aromatic hydrocarbons.
28. Atmospheric Aging Resistance :
Loss of physical properties due to the normal
action of its surroundings (weather).
29. Atmospheric Cracking :
Cracks produced in the surface of rubber articles
by exposure to atmospheric conditions.
30. Autoclave :
A vessel used for vulcanizing rubber products by
means of steam under pressure.
31. Axial Seal :
A term usually applied to an O-Ring where the
squeeze is applied on the top and bottom
surfaces. Another term for face seal.
B
32. Backrind :
A molding defect in which the rubber adjacent to
the parting line shrinks below the surface of the
molded product, with the parting line often being
ragged and torn.
33. Back-Up-Ring :
(Anti extrusion device) A ring of relatively hard
and tough material, placed in the gland between
the O-Ring and groove side walls, to prevent
extrusion of the O-Ring.
34. Bake Out :
A process whereby a vacuum system is heated
for a given time at some predetermined
temperature to degas all the components, i.e.
gauges, fittings, valves, seals.
35. Banbury Mixer :
A specific type of internal mixer used to blend
fillers and other ingredients with an elastomer.
36. Bank:
The reservoir of material at the opening between
rolls of a mill or calendar.
37. Batch :
The product of one mixing operation.
38. Bench Marks :
Two marks of known separation, applied to a
specimen to measure the strain of the specimen
during extension.
39. Bench Test :
A modified service test in which the service
conditions are approximated, but the equipment
is conventional laboratory equipment and not
necessarily identical with that in which the
product will be employed.
40. Blank :
A portion of a rubber compound of suitable
volume to fill the cavity of a mold.
41. Beta Particles :
Negatively charged particles or electrons,
characterized by limited penetration.
42. Bleeding :
Migration to the surface of plasticizers, waxes or
similar materials, to form a film or bead.
43. Blemish :
A mark, deformity or injury which impairs
appearance.
44. Blister :
A raised spot in the surface, or a separation
between layers, usually forming void or air-filled
space in the vulcanized article.
45. Bloom :
A dusty or milky looking deposit that sometimes
appears on the surface of an molded product
after molding and storage, caused by migration
of a liquid or solid to the surface. Not to be
confused with dust from external sources.
46. Blow :
The volume expansion that occurs during the
production of cellular or sponge rubber.
47. Blowing Agent :
A compounding material used to produce gas by
chemical or physical action, or both, in the
manufacture of hollow or cellular articles.
48. Bond :
The term commonly used to denote the
attachment of a given elastomer to some other
member. Bonds may be classified by types, as
follows:
a. Mechanical - purely physical
attachment accomplished by such
means as "through" holes,
interlocking fingers, envelope design,
riveting, etc.;
b. Cold - adhesion of previously
vulcanized elastomer to another
member through use of suitable
contact cements;
c. Vulcanized - adhesion of an elastomer
to a previously primed surface using

heat and pressure, thus vulcanizing
the elastomer at the same time.
49. Break :
A separation or discontinuity in any part of an
article.
50. Break-Out :
Force to inaugurate sliding. Expressed in same
terms as friction. An excessive break-out value is
taken as an indication of the development of
adhesion.
51. Brittleness :
Tendency to crack when deformed.
52. Brittle Point:
The highest temperature at which a rubber
specimen will fracture under sudden impact.
53. Buna -N :
See Nitrile.
54. Buna-S :
A general term for the copolymers of butadiene
and styrene. Also known as SBR and GRS.
55. Butaprene :
See Nitrile.
56. Buffing :
The grinding of a vulcanizate, producing a
roughened or velvety texture.
57. Bumping, Moulding Process :
The application, release, and reapplication of
pressure prior to the start of vulcanization to
vent entrapped gases, thereby facilitating
complete filling of the mould cavities.
58. Butt Joint :
Joining two ends of a seal whereby the junction is
perpendicular to the mold parting line.
59. Butyl :
A copolymer of iso-butylene and isoprene.
C
60. Calender :
A machine with two or more parallel, counter-
rotating rolls, with controllable roll-to-roll
spacing, rotating at selected surface speeds and
controlled temperatures.
61. Carbon Black :
A material consisting essentially of elemental
carbon in the form of near-spherical colloidal
particles and particle aggregates. It is produced
by partial combustion or thermal decomposition
of hydrocarbons. Primarily used as a reinforcing
agent, but also affects many other dynamic
properties of a rubber compound.
62. Catalyst :
A chemical that, in small quantities, accelerates a
chemical reaction without itself necessarily
becoming part of the final product.
63. Cell :
A single small cavity surrounded partially or
completely by walls.
64. Cell, Closed :
A cell totally enclosed by its walls, hence not
interconnected with other cells.
65. Cell, Open :
A cell not totally enclosed by its walls and hence
interconnected with other cells.
66. Cellular Rubber :
A generic term for materials containing many
cells (either open, closed, or both) dispersed
throughout the mass of rubber.
67. Cellular Material, Collapse :
An undesirable densification of a cellular
material resulting from the breakdown of its
cellular structure.
68. Cement, Rubber :
An adhesive that is either a liquid dispersion or
solution of raw or compounded rubber, or both.
69. Chalking :
The formation of a powdery residue on the
surface of a rubber, commonly resulting from
surface degradation.
70. Checking :
The short, shallow cracks on the surface of a
rubber product, usually resulting from damaging
action by environmental elements.
71. Chemical Bonding :
A method of bonding rubber to inserts by
applying special adhesives to the insert prior to
molding.
72. Chemigum :
(TM, R.T. Vanderbilt Co.) See Nitrile.
73. Closure Dimension :
Dimensions of a molded rubber product that are
affected by flash thickness (mold closure)
variation.

74. Coagent:
A compounding ingredient used in small
amounts to increase the crosslinking efficiency of
certain non-sulfur vulcanizing systems
(especially organic peroxides), or to modify the
properties given by such systems.
75. Coating :
A uniform layer of chemical primers or
adhesives to produce a chemical bond between
the rubber and substrate. May also refer to
special surface treatments that can be applied to
rubber to achieve special properties.
76. Coated Fabric :
A flexible product composed of a textile fabric
and an adherent polymeric material applied to
one or both surfaces.
77. Coefficient of Thermal Expansion :
Average expansion per degree over a stated
temperature range, expressed as a fraction of
initial dimension. May be linear or volumetric.
78. Cold Checks :
A defect on calendered sheeting consisting of
surface roughness.
79. Cold Flexibility :
Flexibility following exposure to a
predetermined low temperature for a
predetermined time.
80. Cold Flow :
Slow deformation, under gravitational force, at
or below room temperature. Sometimes referred
to as “creep”.
81. Cold Resistance :
Able to withstand the effects of cold or low
temperatures without loss of serviceability.
82. Commercially Smooth :
Degree of smoothness of a surface of an article
which is acceptable for use.
83. Compound :
A term applied to a mixture of polymers and
other ingredients to produce a usable rubber
material.
84. Compound, Standard:
A control or reference compound prepared
according to a prescribed formula and mixing
procedure.
85. Compression Molding :
Molding process in which the material is placed
directly in the mold cavity and compressed to
shape by closure of the mold, under heat and
pressure.
86. Compression Modulus :
The ratio of the compression stress to the
resulting compression strain (the latter
expressed in the direction of force). Compression
Modulus may be either static or dynamic.
87. Compression Set :
The permanent deformation experienced by a
rubber material when compressed for a period of
time. The term is commonly used in reference to
a test conducted under specific conditions
wherein the permanent deformation, expressed
as a percentage, is measured after a prescribed
period of time. A low compression set is desirable
in molded rubber parts such as seals and gaskets,
which must retain their dimensions to maintain
an effective seal.
88. Conditioning (Environmental) :
The storage of a rubber, under specified
conditions (time, temperature, humidity) prior to
testing.
89. Conditioning (Mechanical):
The prescribed program of deformation of a
specimen prior to testing.
90. Conductive Rubber :
A rubber capable of conducting electricity. Most
generally applied to rubber products used to
conduct static electricity.
91. Copolymer :
A polymer consisting of two different monomers
chemically combined.
92. Corona Resistance :
The ability of a rubber acting as insulator to
withstand the effects of high voltage discharge.
Indications of failure appear as surface cracks.
93. Corrosion (Packing) :
Corrosion of rigid member (usually metal) where
it contacts packing. The actual corroding agent is
fluid medium trapped in the interface.
94. Corrosive (Packing) :
A property of packing whereby it is assumed
(often incorrectly) to promote corrosion of a rigid
member of a trapped fluid.
95. Cracker :
A heavy-duty mill having two deeply corrugated
or pyramid-cut rolls for breaking down a rubber
or a mix, or for cutting rubber or a mix into
pieces.
96. Crack :
A fissure originating in the surface of a rubber
vulcanizate or product as a result of natural
weathering.

97. Crack, Flex :
A fissure originating in the surface of a rubber
vulcanizate, resulting from cyclic deformation
(usually bending).
98. Crack, Ozone :
Fissures originating in the surface of a rubber
vulcanizate, caused by exposure to an ozone-
containing environment; these fissures are
perpendicular to the direction of strain, and
usually occur in rubbers having main chain
unsaturation.
99. Cracking :
The sharp break or fissure in the surface.
Generally due to excessive strain.
100. Crazing :
Formation of a random pattern of shallow cracks
on a rubber surface usually due to ageing by
light. Unlike ozone cracking, crazing does not
depend on the presence of a tensile strain in the
rubber.
101. Creep :
The progressive relaxation of a given rubber
material while it is under stress. This relaxation
eventually results in permanent deformation, or
"set".
102. Crosslink :
The chemical bond bridging one polymer chain
to another.
103. Crosslinking :
Formation of chemical bonds between polymer
chains to give a network structure.
104. Cross-Linking Agents :
A chemical, or chemicals, that bonds the polymer
chains together to form a thermoset rubber
product.
105. Cross-Section :
A seal as viewed if cut at right angles to the
molding line, showing internal structure.
106. Crystallinity :
Orientation of the disordered long chain
molecules of a polymer into repeating patterns.
The degree of crystallinity effects stiffness,
hardness, low temperature flexibility, and heat
resistance.
107. Cure :
The thermo process that causes a chemical
change in the raw stock, turning it into the
finished rubber part . Also see Vulcanization.
108. Cure Date :
The date a rubber product was molded. Normally
expressed, for example, as 1Q04, meaning the
first quarter of the year 2004.
109. Cure Meter :
A testing device that measures the progress of
vulcanization.
110. Curing Temperature :
The temperature at which the rubber product is
vulcanized.
111. Cure Time :
The preset time needed to complete the curing
process
112. Cylinder :
Chamber in which piston, plunger, ram, rod or
shaft is driven by, or against, the system fluid.
D
113. Damping :
The quality of an elastomer to absorb forced
vibrational energy. That property of a material
or system that causes it to convert mechanical
energy to heat when subjected to deflection; in
rubber the property is caused by hysteresis.
114. Deflashing :
Any of various processes used to remove the
waste edge from a molded rubber part.
115. Degassing :
The intentional, but controlled, outgassing of a
rubber substance or other material.
116. Density :
The mass per unit volume of a material. Also
referred to as specific gravity.
117. Desiccant :
A compounding material used to irreversibly
absorb moisture, particularly for the purpose of
minimizing risk of porosity during vulcanization.
118. Die Swell :
The difference between the dimensions of the
cross section of an extrudate, and the
corresponding dimensions of the die orifice from
which the extrudate was formed. It is usually
expressed as the percent increase in the cross-
sectional area.
119. Diene Polymer :
A polymer formed from one or more monomer
species, at least one of which is a diolefin.

120. Dielectric Properties :
The ability of a material to resist puncture due to
electric stress. The property is expressed in terms
of "volts per MIL thickness".
121. Dielectric Strength:
The measure of a vulcanizate’s ability to resist
passage of a disruptive discharge produced by an
electric stress.
122. Diffusion :
The mixing of two or more substances (solids,
liquids, gasses, or combinations thereof) due to
the intermingling motion of their individual
molecules. Gasses diffuse more readily than
solids.
123. Dispersion :
The application of shearing forces to distribute
one or more compounding materials uniformly
throughout the mass of a rubber compound.
124. Dumbbell Specimen :
A flat specimen of rubber having a narrow
straight central portion of essentially uniform
cross section with enlarged ends. Used for testing
purposes.
125. Durometer :
An instrument for measuring the hardness of a
rubber; measures the resistance to the
penetration of an indentor point into the surface
of the rubber.
126. Dusting :
The application of a powder to a rubber surface,
generally to prevent adhesion to another surface.
127. Dynamic :
An application in which the seal is subject to
movement, or moving parts contact the seal.
128. Dynamic Packing :
A package employed in a joint whose members
are in relative motion.
129. Dynamic Properties :
Mechanical properties exhibited under repeated
cyclic deformation.
130. Dynamic Seal :
A seal required to prevent leakage past parts
which are in relative motion. Also means a seal
which is subjected to reciprocating, rotational, or
oscillating motion.
E
131. Ejector Pins :
Pins or blades that, when activated internally to
the mold, eject the part from the mold cavity.
Sometimes referred to as “knock outs”.
132. Elasticity :
The property of an article which tends to return
to its original shape after deformation. A
rubber's ability to return to its original size and
shape after removal of the stress causing
deformation such as stretching, compression, or
torsion. It is the opposite of plasticity. The term
elasticity is often loosely employed to signify the
“stretchiness” of rubber
133. Elastomer :
Any natural or synthetic material with resilience
or memory sufficient to return to its original
shape after major or minor distortion.
134. Electron Volt :
Unit of energy in atom calculations equal to 1.602
X 1012 ergs.
135. Elongation :
Extension produced by a tensile stress.
136. Elongation, Percent :
The extension of a uniform section of a specimen
expressed as percent of the original length.
137. Elongation, Ultimate :
The elongation at the time of rupture.
138. EPDM :
Terpolymer of Ethylene-Propylene-Diene (noted
for excellent ozone resistance).
139. Erg :
Unit of energy (C.G.S.) equal to one dyne
centimeter, or approximately equal to the work
done by force of One (1) milligram, causing a
movement of one (1) centimeter.
140. Evaporation :
The direct conversion from liquid to vapor state
of a given fluid.
141. Explosive Decompression :
The rupture of a rubber article caused by the
rapid reversal of pressure, causing dissolved
gases in the rubber to escape quickly to the
surface of the vulcanizate.
142. Extender :
A material (usually organic) used to augment the
polymer in a compound.
143. Extensometer :
A device for determining elongation of a
specimen as it is strained.

144. Extrudate:
The material that issues from an extruder.
145. Extruder :
A machine designed to force rubber through an
orifice, which is shaped to the geometry of the
desired end product.
146. Extrusion :
The continuous shaping of a material during
passage through a die.
147. Extrusion (seal) :
Distortion, under pressure, of a portion of a seal
into the clearance between mating metal parts.
F
148. Face Seal :
A seal between two flat surfaces. In an O-Ring,
this means it seals on the top and bottom, not the
ID and OD. Also referred to as an axial seal.
149. Fatigue Breakdown :
The deterioration of an elastomeric product
during repeated deformation.
150. Fatigue Life :
The number of deformations required to produce
a specified state of fatigue breakdown in a test
specimen or product that is deformed under a
prescribed set of conditions.
151. Feather Edge :
The sharp, thin edge on parts, such as wiper seals
and cups. (Also called "Knife Edge").
152. Filler :
A solid compounding material, usually in finely
divided form, which may be added in relatively
large proportions to a polymer for technical or
economic reasons. The most commonly used
filler is carbon black. Most fillers also function as
reinforcing agents.
153. Filler, Inert :
A filler having no reinforcing effect.
154. Fixed Dimension :
Dimensions on a rubber product that are not
affected by flash thickness or mold closure
variation.
155. Flame Resistance :
The resistance to burning of material that will
not withstand combustion under ordinary
conditions.
156. Flash :
Excess rubber left around a rubber part after
molding, due to space between mating mold
surfaces; removed by trimming.
157. Flex Cracking :
A surface cracking induced by repeated bending
or flexing.
158. Flex Life :
The number of cycles required to produce a
specified state of failure in a specimen that is
flexed in a prescribed method.
159. Flexometer :
A machine that subjects a test specimen to
repeated deformation by compression, tension,
shear, bending, torsion or any combination
thereof.
160. Flex Resistance :
The relative ability of a rubber article to
withstand dynamic bending stress.
161. Flexural Strength :
The ability of a material to flex without
permanent distortion or breaking.
162. Flock :
Fibrous filler sometimes used in rubber
compounding.
163. Flow :
Ability of heated plastic, or uncured rubber, to
travel in the mold and runner system during the
molding process.
164. Flow Cracks :
Surface imperfections due to improper flow and
failure of stock to knit or blend with itself during
the molding operation.
165. Flow Marks :
Marks or line on a molded product, caused by
imperfect flow of the raw compound during
forming.
166. Fluid :
A liquid or a gas.
167. Fluorocarbon :
A polymer designed to meet the most rigid
requirements in oils, solvents, synthetic
lubricants and corrosive chemicals, at elevated
temperatures.
168. Friction :
Resistance to motion due to contact of surfaces.
169. Friction (Break Out) :
Friction developed during initial or starting
motion.

170. Friction (Running) :
Constant friction developed during operation of a
dynamic O-Ring.
171. Frosting :
T he formation of a matte, whitish appearance on
a rubber surface exposed to air, resulting from
the action of ozone. Often confused with bloom.
172. Fuel (Aromatic) :
Fuel which contains benzene or aromatic
hydrocarbons; causes little swell of rubber.
173. Fuel (Non-Aromatic) :
Fuel which is composed of straight chain
hydrocarbons; causes little swell of rubber.
174. Furnace Carbon Black :
A type of carbon black produced by the
decomposition reaction of hydrocarbons, when
injected into a high velocity stream of
combustion gases under controlled conditions.
G
175. Gamma Radiation :
Electromagnetic disturbance (photons)
emanating from an atomic nucleus. This type of
radiation travels in wave form, much like X-Rays
or light, but has a shorter wave length (approx. 1
Ado or 107 mm). It is very penetrating.
176. Gasket :
A deformable material clamped between
essentially stationary faces to prevent the
passage of matter through an opening or joint. A
static mechanical seal.
177. Gas Permeability :
The degree to which a substance resists
permeation of gas under pressure.
178. Gates :
The openings in an injection or transfer mold
that ensure the even flow of material into the
cavity.
179. Gate Mark :
A raised spot or small depression on the surface
of an injection or transfer molded part, where
the gates interface the cavity. (Also called "Sprue
Mark")
180. Gland :
The cavity into which an O-Ring is installed.
Includes the groove and mating surface of the
second part, which together confine the O-Ring.
181. Glass Transition Temperature :
The approximate mid-point of the temperature
range over which a reversible change in a
polymer occurs from (or to) a viscous or rubbery
condition to (or from) a hard and relatively
brittle one.
182. Grain :
The unidirectional orientation of rubber or filler
particles in a rubber compound.green strength:
the resistance to deformation of rubber stock in
the uncured state.
183. Groove :
The machined recess into which a seal is
fitted.ground vulcanized rubber: vulcanized
rubber in particulate form; used as an extender
or filler.
184. Guayule Rubber:
A form of natural rubber, cis polyisoprene,
obtained from the shrub, Parthenium
Argentatum.
185. Gum Compound :
A rubber compound containing only those
ingredients necessary for vulcanization and
small amounts of other ingredients for
processing, coloring, and for improving the
resistance to ageing.
H
186. Hardness :
Resistance to a disturbing force. Measured by the
relative resistance of a material to an intender
point of any one of a number of standard
hardness testing instruments. (Also see
Durometer).
187. Heat Aging :
A test for degradation of physical properties as a
result of exposure to high temperature
conditions.
188. Heat Build-up :
The accumulation of thermal energy generated
within a material as a result of hysteresis,
evidenced by an increase in temperature.
189. Heat Deflection Temperature :
The temperature at which a standard plastic test
bar deflects 0.010 in. under a stated load of either
66 psi or 264 psi.
190. Heat History :
The accumulated amount of heat a rubber stock
has been subjected to during processing
operations. Incipient cure or scorch can take
place if heat history is excessive.

191. Hermetic Seal :
An airtight seal having no evidence of detectable
leakage.
192. Homogeneous :
A material of uniform composition throughout.
193. Homopolymer :
A polymer formed from a single monomer
species.
194. Hydrocarbon Solvents - Aromatic :
Solvents having basic benzene structure, usually
coat tar types such as benzene, toluene orxylene.
195. Hysteresis Loss :
The loss of mechanical energy due to hysteresis.
196. Hysteresis :
The conversion of mechanical energy to heat in
rubber undergoing strain.
I
197. Identification :
Colored dots or stripes on seals for identification
purposes; seldom used.
198. Immediate Set :
The deformation found by measurement
immediately after removal of the load causing
the deformation.
199. Immersion :
Placing an article into fluid, generally so it is
completely covered.
200. Impact :
The single, instantaneous stroke or contact of a
moving body with another, either moving or at
rest, such as a large lump of material dropping
on a conveyor belt.
201. Impact Resistance:
Resistance to fracture under shock force.
202. Impact Strength :
A measure of the toughness of the material, as
the energy required break a specimen with a
single blow.
203. Inhibitor :
A material used to suppress a chemical
reaction.insert: typically, a metal or plastic
component to which rubber is chemically and/or
physically bonded during the molding process.
204. IRHD (International Rubber Hardness
Degrees) :
International Rubber Hardness Degrees. An
alternate method of measuring rubber hardness.
IRHD units are approximately equivalent to
Shore A durometer units, although a different
apparatus is used.
205. Injection Molding :
Molding in which the rubber or plastic stock is
heated and, while in the flowable state, is forced
or injected into the mold cavity.
206. Insert :
Typically, a metal or plastic component to which
rubber or plastic is chemically and/or physically
bonded during the molding process.
207. Isoprene-acrylonitrite Rubber :
A low-plasticity copolymer with around 34 per
cent ACN.
K
208. Knit Line :
An internal or external defect in a vulcanizate,
where raw stock did not unite into a
homogeneous mass during vulcanization.
209. Knuckles :
Small tough rubber pieces scattered throughout a
bale of raw rubber that do not disperse easily or
accept carbon black and other compounding
materials during mixing.
L
210. Leakage Rate :
The rate at which a fluid (either gas or liquid)
passes a barrier. Total Leakage Rate includes the
amounts that diffuse or permeate the material of
the barrier as well as the amount that escapes
around it.
211. Life Test :
A laboratory procedure used to determine the
amount and duration of resistance of an article
to specific sets of destructive forces or conditions.
212. Linear Expansion :
Expansion in any one linear dimension, or the
average of all linear dimensions.
213. Liquid Curing Medium (LCM) :
A molten phase, generally a mixture of sodium
nitrate, that is used as a heating medium for the
continuous vulcanization of a rubber mix,
usually following extrusion.
214. Logy :
Sluggish, low snap or recovery of a material.

215. Low Temperature Flexibility :
The ability of a rubber product to be flexed, bent
or bowed at low temperature without cracking.
M
216. mm Hg :
Millimeters of Mercury. In vacuum work, a
measure of absolute pressure, being the height of
a column of Mercury that the air or other gas will
support. Standard atmospheric pressure will
support a Mercury column 760 millimeters high.
Any value less than that represents some degree
of vacuum.
217. Mandrel :
A bar, serving as a core, around which rubber is
extruded, forming a center hole.
218. Masterbatch :
A homogeneous mixture of rubber and one or
more materials in known proportions for use as
a raw material in the preparation of the final
compounds. Masterbatches are used to facilitate
processing or enhance the properties of the final
product, or both.
219. Mastication :
The breakdown or softening of raw rubber by
the combined action of mechanical work (shear),
and atmospheric oxygen, sometimes accelerated
by the use of a peptizer, and frequently at
elevated temperatures.
220. Mechanical Bond :
A method of physically bonding rubber to inserts
through the use of holes, depressions or
projections in the insert.
221. Memory :
The tendency of a material to return to original
shape after deformation.
222. Microhardness :
An electronic measurement of rubber hardness
for specimens below .25 inch in thickness.
Microhardness, like Shore A durometer, is also a
measure of indentation.
223. Mill :
A machine used for rubber mastication, mixing,
or sheeting, having two counter-rotating rolls
with adjustable longitudinal axis separation that
usually rotate at different speeds.
224. Mirror Finish :
A bright, polished surface.
225. Mismatch :
A mold defect which produces an asymmetrical
part, caused by dissimilar cavities in mating
mold plates.
226. Mixer :
A machine that incorporates and disperses
compounding ingredients into rubber to form a
mix or a compound through the action of
mechanical work (shear).
227. Mixer, Internal :
A machine with a closed chamber in which
specially shaped rotors masticate the rubber or
incorporate and disperse compounding
materials, or both, into the rubber.
228. Modulus :
The ratio of stress to strain; that property of a
material, which, together with the geometry of a
specimen, determines the stiffness of the
specimen. In the physical testing of rubber, the
force necessary to produce a stated percentage of
elongation.
229. Modulus of Elasticity :
One of several measurements of stiffness or
resistance to deformation, but often incorrectly
used to indicate specifically static tension
modulus.
230. Mold Cavity :
Hollow space, or cavity, in the mold, which is
used to impart the desired form to the product
being molded.
231. Mold Finish :
The uninterrupted surface produced by intimate
contact of rubber with mold surface at
vulcanization.
232. Molding, Compression :
The process of forming a material to a desired
shape by flow induced by a force applied after
material is placed in the mold cavity.
233. Molding, Injection:
The process of forming a finished product by
forcing material from an external heated
chamber through a sprue (runner, gate) into the
cavity of a closed mold. This is accomplished by
means of a pressure gradient that is independent
of the mold clamping force
234. Mold Lubricant :
A material usually sprayed onto the mold cavity
surface prior to the introduction of the uncured
rubber, to facilitate the easy removal of the
molded part.
235. Mold Marks :

Indentations or ridges embossed into the skin of
the molded product by irregularities in the mold
cavity.
236. Mold Register :
Accuracy of alignment/fit of mold sections.
237. Molding Solutions :
In the field of custom molded rubber or plastic,
the solution to your problems.
238. Mooney Scorch :
The measurement of the rate at which a rubber
compound will cure or set up by means of the
Mooney Viscometer test instrument.
239. Molding Shrinkage :
The difference in dimensions between a molded
product and the mold cavity in which it was
molded, both the mold and product being at
normal room temperature when measured.
240. Molding, Transfer :
The process of forming a material by forcing it
from an auxiliary heated chamber through a
sprue hole (runner, gate) into the cavity of a
closed mold by means of a pressure gradient that
is dependent on the mold clamping force.
241. Monomer :
A low molecular weight substance consisting of
molecules capable of reacting with like or unlike
molecules to form a polymer.
242. Mold Marks :
A surface imperfection transferred to a molded
product from corresponding marks on a mold.
243. Mooney Viscosity :
Measurement of the plasticity or viscosity of an
uncompounded, or compounded vulcanized,
elastomer seal material by means of the Mooney
Shearing Disk Viscometer.
N
244. Naphthenic Oil :
A hydrocarbon process oil containing more than
30 %, by mass, of naphthenic hydrocarbons.
245. Necking :
The localized reduction in cross section that may
occur in a material under tensile stress.
246. Nerve :
The elastic resistance of unvulcanized rubber or
rubber mixes to permanent deformation.
247. Nip :
The radial clearance between rolls of a mill or
calendar on a line of centers.
248. Neoprene (GR-M) :
A DuPont Dow Elastomers polymer of
chloroprene which is prepared from coal, salt
and limestone.
249. Nitrile : (see also Buna-N)
The most commonly used elastomer for O-Rings
because of its resistance to petroleum fluids, its
good physical properties, and its useful
temperature range.
250. Nominal Dimension :
Nearest fractional equivalent to actual decimal
dimension.
251. Non-aromatic :
Straight chain organic structures, such as
petroleum type solvents.
252. Non-blooming :
The absence of "bloom".
253. Non-fill :
A defect resulting from the failure of the rubber
material to fill out all of a mold cavity.
254. Non-Sulfur Vulcanizing System :
A vulcanizing system not requiring free or
donated sulfur.
O
255. Occlusion :
(A) The mechanical process by which vapors,
gases, liquids or solids are entrapped within folds
of a given substance during working or
solidification; (B) the materials so trapped.
256. Off-register :
Misalignment of mold halves causing
asymmetrical parts, i.e. top and bottom mold
plates don’t line up properly..
257. Oil Resistant :
Ability to vulcanize rubber to resist the swelling
and deteriorating effects of various types of oils.
258. Oil Swell :
The change in volume of a rubber article due to
absorption of oil or other fluid.
259. O-Ring :
A product of precise dimensions, molded in one
piece, to the configuration of a torus (doughnut)
with a circular cross section, suitable for use in a
machined groove for static or dynamic sealing.

260. O-Ring Seal :
The combination of a gland and O-Ring providing
a fluid tight closure. (Some designs permit
minimum leakage.)
261. O-Ring Seal / Moving (Dynamic) :
O-Ring seal in which there is relative motion
between some gland parts and the O-Ring;
oscillating, reciprocating or rotary motion.
262. O-Ring Seal / Non-moving (Static) :
O-Ring seal in which there is no relative motion
between any part of the gland and the O-Ring.
(Distortion from fluid pressure or swell from
fluid immersion is excluded.)
263. Optimum Cure :
State of vulcanization at which the most
desirable combination of properties is attained.
264. Outgassing :
A vacuum phenomenon wherein a substance
spontaneously releases volatile constituents in
the form of vapors or gases. In rubber
compounds, these constituents may include
water vapor, plasticizers, air, inhibitors, etc.
265. Over-Cure :
A degree of cure greater than the optimum,
causing some desirable properties to be
degraded. Usually results in a loss of elongation
and an increase in hardness.
266. Overflow Groove :
A groove around the mold cavity used to accept
excess material from the cavity and to create a
better "pack" for the part.
267. Oxidation :
The reaction of oxygen on a compound, usually
detected by a change in the appearance or feel of
the surface, or by a change in the physical
properties, or both.
268. Oxygen Bomb :
A chamber capable of holding oxygen at an
elevated pressure which can be heated to an
elevated temperature. Used for an accelerated
aging test.
269. Ozone Resistance :
Ability to withstand the deteriorating effect of
ozone (which generally causes cracking.)
P
270. Packing :
A flexible device used to retain fluid under
pressure, or seal out foreign matter. Normally
refers to a dynamic seal.
271. Paraffinic Oil :
A hydrocarbon process oil, most or all of which is
composed of alkanes
272. Parting Line :
The line on the surface of a molded part where
the mold plates meet.
273. Peptizer :
A compounding material used in small
proportions to accelerate, by chemical action, the
softening of rubber under the influence of
mechanical action, or heat, or both.
274. Permanent Set :
The deformation remaining after a specimen has
been stressed in tension for a definite period, and
released for a definite period.
275. Permeability :
The rate at which liquid or gas, under pressure,
passes through a solid material by diffusion and
solution. In rubber terminology : the rate of gas
flow, expressed in atmospheric cubic centimeters
per second, through an elastomeric material, one
centimeter square and one centimeter thick.
276. Permeation :
The diffusion of a media (generally a gas)
through a rubber or plastic component.
277. PH :
Determines the concentration of either an acid or
a base.
278. PHR :
Abbreviation for parts per hundred of rubber,
used for indicating the proportions of ingredients
in a rubber compound.
279. Pigment :
An insoluble compounding material used to
impart color to rubber.
280. Pit (or Pock) Mark :
A circular depression, usually small.
281. Plasticity :
When subject to sufficient shearing stress, any
given body will be deformed. After stress is
removed, if there is no recovery, the body is
completely plastic. If recovery is complete and
instantaneous, the body is completely elastic. A
balance between the two is required.
282. Plasticizer :

A substance, usually a heavy liquid, added to an
elastomer to decrease stiffness, improve low
temperature properties, and improve processing.
283. Plastometer :
An instrument for measuring the plasticity of a
raw or unvulcanized compounded rubber.
284. Polymer :
A material formed by joining together many
(poly) individual units (mer) of one or more
monomers; synonymous with elastomer.
285. Polymerization :
Chemical reaction whereby simple materials,
either one or more, are converted to complex
material which possesses properties entirely
different from the original materials used to start
the reaction.
286. Polyurethane :
An organic material noted for its high abrasion,
ozone, corona and radiation characteristics.
287. Porosity :
Quality or state of being porous - the presence of
numerous small cavities.
288. Post Cure :
The second step in the vulcanization process for
some specialized elastomers. Provides
stabilization of parts and drives off
decomposition products resulting from the
vulcanization process.
289. Pot :
The chamber, in the transfer or injection mold,
where raw material is placed before it is
transferred into the cavity.
290. Pot Life :
The period of time during which a reacting
thermosetting composition remains suitable for
its intended use, after mixing with a reaction-
initiating agent.
291. Prevulcanization Inhibitor (PVI) :
A compounding material that increases the time
to incipient vulcanization of a rubber mix. Unlike
a retarder, a PVI does not significantly affect the
vulcanization rate.
292. Primary Accelerator :
The principal highest concentration accelerator
used in a vulcanizing system.
293. Processability :
The relative ease with which raw or compounded
rubber can be handled in rubber machinery.
294. Processing Aid :
A compounding material that improves
processability of a polymeric compound by
reducing nerve, providing better dispersion of
dry material, increasing the extension rate,
reducing power consumption during mixing,
producing smoother surfaces on calendered and
extruded products, improving knitting, etc.
295. Process Oil:
A hydrocarbon oil derived from petroleum or
other sources, used as an extender or process aid.
296. Pure Gum State :
A non pigmented, translucent basic polymer.
R
297. Radiation :
An emission, of varying content, from a
disturbed atom undergoing internal change.
There are two broad classifications : (A)
Corpuscular, comprising streams of particles,
either neutral or charged, e.g. protons, neutrons,
electrons; and (B) Electromagnetic, comprising
wave-like emissions as gamma, ultraviolet, etc.
298. Radiation Damage :
A measure of the loss in certain physical
properties of organic substance, such as
elastomers, due principally to ionization of the
long chain of molecules; believed to result in
redundant cross-linking and possible scission of
the molecules. The effect is cumulative.
299. Radiation Dosage :
The total amount of radiation energy absorbed
by a substance. This value is usually expressed in
"ergs per gram", and is denoted by the following
units : (a) Roentgen - a quantity of gamma or X-
Ray radiation equal to approximately 83 ergs of
absorbed energy per gram of air; (b) REP
(Roentgen Equivalent - Physical) - a quantity of
ionization that causes an energy absorption of
approximately 83 to 93 ergs per gram of tissue;
(c) REM (Roentgen Equivalent - Man) - similar to
REP, except used to denote biological effects; and;
(d) RAD - the unit of dosage related to elastomers,
independent of type of radiation specimen, and
denoting energy absorption level of 100 ergs per
gram of elastomer :
approximately equal to 1.2 Roentgens.
300. Rebound :
A measure of the resilience, usually as a
percentage of vertical return of a body which has
fallen and bounced.
301. Rebound Test :
The method of determining the resilient
properties of vulcanized rubber by measuring

the rebound of a steel ball or pendulum from a
defined height onto a rubber sample.
302. Recipe :
A formula, mixing procedure, and any other
instructions needed for the preparation of a
rubber compound.
303. Reclaimed Rubber :
Vulcanized rubber that has been thermally,
mechanically, and/or chemically plasticized for
use as a rubber diluent, extender, or processing
aid.
304. Reciprocating Seal :
Seal used in linear motion application.
305. Register :
The accurate matching of the plates in a mold.
306. Reinforcement:
The act of increasing the mechanical
performance capability of a rubber by the
incorporation of materials that do not participate
significantly in the vulcanization process.
307. Reinforcement Agent :
Material dispersed in an elastomer to improve
compression, shear or other stress properties.
308. Relative Humidity :
The ratio of the quantity of water vapor actually
present in the atmosphere, to the greatest
amount possible at a given temperature.
309. Release Agent (Mold) :
A substance applied to the inside surface of a
mold or added to a material to be molded, to
facilitate removal of the product from the mold.
310. Resilience :
Ability of an elastomer to return to original size
and shape after deforming forces are removed;
generally expressed in per cent of the ratio of
energy removed, to the energy used in
compressing. (Resilient : having that capability.)
311. Resin :
An organic material of indefinite and relatively
high molecular mass that may be used as a
softener, processing aid, vulcanizing agent, or
reinforcing agent.
312. Retarder :
A material used to reduce the tendency of a
rubber compound to vulcanize prematurely.
313. Reversion :
Deterioration of vulcanizate properties that may
occur when vulcanization time is extended
beyond the optimum.
314. RMS:
Root mean square. A measure of surface
roughness, calculated as the square root of the
sum of the squares of micro-inch deviation from
true flat.
315. Rotary Seal :
A seal, such as an O-Ring or a Quad-Ring seal,
exposed on either the ID or OD sealing surface to
a rotating component, e.g. shaft seals.
316. Rough Trim :
Removal of superfluous material by pulling or
picking; usually the removal of a small portion of
the flash or sprue which remains attached to the
product.
317. Rubber :
A material that is capable of recovering from
large deformations quickly and forcibly, and can
be, or already is, modified to a state in which it is
essentially insoluble. Also see Elastomer.
318. Rubber, Bound :
The portion of the rubber in a mix that is so
closely associated with the filler as to be
unextractable by the usual rubber solvents.
319. Rubber, Cellular, Closed cell:
A cellular material in which practically all the
individual cells are non-connecting.
320. Rubber, Expanded:
Cellular rubber having closed cells made from a
solid rubber compound.
321. Rubber, Gel:
The portion of rubber insoluble in a chosen
solvent.
322. Rubber Hardness Degree,
International:
A measure of hardness, the magnitude of which
is derived from the depth of penetration of a
specified indenter into a specimen. Commonly
referred to as IRHD.
323. Rubber, Natural:
cis-1,4-polyisoprene that is obtained from a
botanical source, usually Hevea Brasiliensis.
324. Rubber, Oil-extended :
A grade of raw rubber containing a relatively
high proportion of processing oil.
325. Rubber, Raw :
Natural or synthetic elastomer, usually in bales
or packages, that is the starting material for the
manufacture of rubber articles.

326. Rubber, Sponge:
Cellular rubber consisting predominantly of open
cells and made from a dry rubber compound.
327. Rubber, Synthetic:
Rubber produced by polymerizing one or more
monomers with or without post-polymerization
chemical modification.
328. Rubber, Vulcanized Compound:
A crosslinked elastic material compounded from
an elastomer, susceptible to large deformations
by a small force and capable of rapid, forceful
recovery to approximately its original
dimensions and shape upon removal of the
deforming force.
329. Runner (Injection or Transfer mold) :
The secondary feed channel for transferring
material under pressure from the inner end of
the sprue to the cavity gate.
330. Runner :
The system for leading rubber and plastic
materials into the gate of an injection mold.
331. Runout (Shaft) :
Expressed in inches and/or TIR (Total Indicator
Reading); refers to twice the radial distance
between shaft axis and axis of rotation.
S
332. Salt Bath :
A heat transfer apparatus, utilizing molten salts
as the heating medium, generally used for
vulcanization. Commonly used in extrusion
systems.
333. SBR :
Copolymer of Butadiene and Styrene; an all
purpose type synthetic, similar to natural rubber.
(Butadiene is a gaseous material of petroleum;
Styrene, a reaction product of ethylene and
benzene.)
334. Scorch :
Premature curing or setting up of a raw
compound during processing.
335. Seal :
Any device used to prevent the passage of a fluid,
gas or liquid.
336. Seal-Off :
A minimum .032 inch (.813 mm) step on an insert
that minimizes flash on the OD, and prevents
flash from forming across the insert.
337. Secondary Accelerator :
An accelerator used in smaller concentrations
compared to the primary accelerator, to achieve
a faster rate of vulcanization.
338. Service :
Operating conditions to be met.
339. Set :
The strain remaining after complete release of
the force producing the deformation.
340. Shaft :
Reciprocating or rotating member, usually within
a cylinder; not in contact with the walls.
341. Shelf Aging :
The change in a material's properties which
occur in storage with time.
342. Sheeting :
The process of converting a rubber, rubber mix,
rubber dough, or latex into a sheet.
343. Shelf Life :
The period of time after production during which
a material or product, that is stored under
specified conditions, retains its intended
performance capabilities.
344. Shock Load:
The sudden application of an external force.
345. Shore A :
See Durometer.
346. Shore M :
A Durometer hardness instrument, using a
micro-indentor designed for the purpose of
measuring O-Ring hardness.
347. Shrinkage :
1) The ratio between a mold cavity size and the
size of a product molded in that cavity, 2)
Decreased volume of a seal, usually caused by
extraction of soluble constituents by fluids
followed by air drying.
348. Silicone Rubber :
Elastomer that retains good properties through
extra wide temperature ranges.
349. Size, Actual :
Actual dimension of the product, including
tolerance units.
350. Size, Number :
Number assigned to indicate inside and cross
section diameters of an O-Ring; established in the
SAE standard AS 568, adopted by the military and
industry.

351. Skin :
A relatively dense layer at the surface of a
cellular polymeric material.
352. Sliding Core :
A pin on a mold that automatically retracts when
the mold opens.
353. Softener :
A compounding material used to produce a mix
of reduced viscosity, which facilitates
incorporation of rubber additives.
354. Sorption :
A term used to denote the combination of
adsorption and absorption processes in the same
substance.
355. Specific Gravity :
Ratio of the weight of a given substance, to the
weight of an equal volume of water, at any
specific temperature.
356. Specimen, Test :
A piece of material appropriately shaped and
prepared so that it is ready to use for a test.
357. Spew :
Surplus material forced from a mold on closure
under pressure. Synonym for flash.
358. Spiral Failure :
Seal failure in reciprocating applications that
result from a twisting
359. Spiral Twist :
A type of seal failure in reciprocating application
that results from the twisting action that strains
or ruptures the rubber.
360. Splice :
The uniting of two parts of a vulcanized rubber
product to form a continuous length.
361. Sprue :
The primary feed channel that runs from the
outer face of an injection or transfer mold, to the
mold gate in a single cavity mold, or to the
runners in a multiple cavity mold.
362. Sprue Hole :
The passageway through which a rubber is
forced into a mold.
363. Sprue Marks :
Marks left on the surface of a rubber part,
generally elevated, after removal of the sprue or
cured compound in the gate, through which the
compound is injected or transfer molded.
364. Squeeze :
Cross section diametrical compression of O-Ring
between surface of the groove bottom and
surface of the other mating metal part in the
gland assembly.
365. Stabilizer :
A substance present in or added to raw rubber to
maintain properties at or near their initial values
during its production, processing, and storage.
366. Static Seal :
Part designed to seal between parts having
relative motion. (See Gasket)
367. Statistical Process Control (SPC) :
The use of statistical techniques on processes and
their output, to establish process stability and
increase capabilities.
368. Stiffener :
A compounding material used to increase the
viscosity of an unvulcanized rubber mix.
369. Stiffness :
That property of a specimen that determines the
force with which it resists deflection.
370. Stiffness, Bending :
The force required to produce a bent
configuration under specified conditions.
371. Strain :
Deflection due to force.
372. Strainer :
A machine designed to force a rubber or rubber
mix through a sieve to remove extraneous
material.
373. Stress :
Force per unit of original cross section area.
374. Stress Relaxation :
Decreasing stress with constant strain over a
given time interval. (Viscoelastic response.)
375. Stock :
Unvulcanized, mixed rubber compound of a
definite composition.
376. Sublimation :
The direct conversion of a substance from solid
state to vapor state, passing through a transitory
liquid state. The vapor, upon recondensing,
reforms into the solid state with no intervening
liquid phase.
377. Surface Finish :
A numerically averaged value of surface
roughness, generally in units of microinches or
micrometers.

378. Sulfur Donor Vulcanizing System:
A vulcanizing system in which there is no
elemental sulfur present, and all of the sulfur
available for the crosslinking is provided by the
partial decomposition of sulfur-containing
materials.
379. Sulfur, Free :
The uncombined sulfur in a rubber mix or
vulcanizate.
380. Sulfur, Total :
All the sulfur present in a material irrespective of
its chemical form or origin.
381. Sun Checking :
Surface cracks, checks or grazing caused by
exposure to direct or indirect sunlight.
382. Swell :
Increased volume of a specimen, caused by
immersion in a fluid (usually liquid).
T
383. Tack :
The property that causes contacting surfaces of
unvulcanized rubber to adhere to each other.
384. Tackifier :
A compounding material that enhances the
ability of vulcanized rubber to adhere to itself or
another material.
385. Tear :
Mechanical rupture initiated and propagated at a
site of high stress concentration caused by a cut,
defect, or localized deformation.
386. Tear Strength :
The force required to rupture a sample of stated
geometry. The maximum force required to tear a
specified test specimen, the force acting
substantially parallel to the major axis of the
specimen.
387. Tear Resistance :
Resistance to growth of a cut or nick when
tension is applied to the cut specimen. Commonly
expressed as pounds per square inch thickness.
388. Temperature Range :
Maximum and minimum temperature limits in
which a seal compound will function in a given
application.
389. Tensile Strength :
Force, in pounds per square inch, required to
cause the rupture of a specimen of rubber
material.
390. Tensile Stress :
A stress applied to stretch a test specimen.
391. Tension Fatigue:
A fracture, through crack growth, of a
component or test specimen subjected to a
repeated tensile deformation.
392. Tension Set:
The extension remaining after a rubber
specimen has been stretched and allowed to
retract.
393. Tension Modulus :
Resistance to being stressed; defined as the force,
in pounds, necessary to stretch a piece of rubber,
one square inch in cross section, a specified
amount. Normally expressed as a percentage of
original length, and the stress as pounds per
square inch at the fixed elongation.
394. Terpolymer :
A polymer consisting of three different
monomers, chemically combined.
395. Thermal Carbon Black :
A soft carbon black formed by the thermal
decomposition of natural gas.
396. Thermal Degradation :
Irreversible and undesirable change in the
properties of a material due to exposure to heat.
397. Thermal Expansion :
Expansion caused by increase in temperature;
may be linear or volumetric.
398. Thermoplastic :
A plastic capable of being repeatedly softened by
increase of temperature, and hardened by
decrease of temperature.
399. Thermoplastic Elastomer (TPE) :
A diverse family of rubber-like materials that,
unlike conventional vulcanized rubbers, can be
processed and recycled like thermoplastic
materials. Often referred to as TPR
(thermoplastic rubber).
400. Thermoplastic Vulcanizate (TPV) :
A thermoplastic elastomer with a chemically
cross-linked rubbery phase, produced by
dynamic vulcanization.
401. Thermoset Rubber :

An elastomer or plastic cured under application
of heat or chemical means, to make a product
substantially infusible or insoluble.
402. Thiokol :
An organic polysufide.
403. Threshold :
The maximum tolerance of an elastomer to
radiation dosage, expressed as a total number of
ergs per gram (or rads) beyond which physical
properties are significantly degraded. This is
generally an arbitrary value, depending on
function and environment.
404. Torque :
The turning force of a shaft.
405. Torr :
The unit of pressure used in vacuum
measurement; equal to 1/760 of a standard
atmosphere, and for practical purposes, is
equivalent to one millimeter of Mercury (mmHg).
406. Torsion Strength :
Ability of rubber to withstand twisting.
407. Total Indication Reading (TIR) :
System that measures the roundness of a part in
relationship to a center line.
408. TR-10 :
A measure of the low temperature capability of
an elastomer. It is the temperature at which a
stretched and frozen specimen has retracted 10%
of the stretched amount. TR stands for
“temperature retraction”.
409. Transfer Molding :
A method of molding in which material is placed
in a pot, located between the top plate and
plunger, and squeezed from the pot through
gates (or sprues) into the mold cavity.
410. Trapped Air :
Air which is trapped in a product or a mold
during cure. Usually causing a loose ply or cover,
or a surface mark, depression or void.
411. Trim :
The process involving removal of mold flash.
412. Trim Out :
Damage to mold skin or finish by close trimming.
U
413. Under Cure :
Degree of cure less the optimum; may be
evidenced by tackiness, loginess or inferior
physical properties.
414. Ultimate Elongation :
A measure of how far a material will stretch
before breaking; expressed as a percentage of its
original length.
415. Undercut :
A groove on either the outside or the inside of a
molded part.
416. UV Absorber :
A compounding material that, through its ability
to absorb ultraviolet radiation and render it
harmless, retards the deterioration caused by
sunlight and other UV light sources.
V
417. Vacuum :
The term denoting a given space that is occupied
by a gas at less then atmospheric pressure. For
degrees of vacuum, see Vacuum Level.
418. Vacuum Level :
The term used to denote the degree of vacuum
evidenced by its pressure in torr (or mmHg) :
(a) Rough vacuum = 760 torr to 1 torr, (b)
Medium vacuum = 1 torr to 10-3 torr, (c) High
vacuum = 10-3 torr to 10-6 torr, (d) Very High
vacuum = 10-6 torr to 10-9 torr, (e) Ultra High
vacuum = below 10-9 torr.
419. Vapor :
The gaseous state of a fluid that normally exists
as a liquid under atmospheric conditions, i.e. a
gas whose temperature is below its critical
temperature.
420. Vapor Pressure :
The maximum pressure exerted by a liquid or a
solid, heated to a given temperature in a closed
container.
421. Vibration Dampening :
The ability of an elastomer to absorb vibrational
or shock energy.
422. Viscoelasticity :
A combination of viscous and elastic properties
in a material, with the relative contribution of
each being dependent on time, temperature,
stress, and strain rate.
423. Viscosity :
The property of fluids and plastic solids by which
they resist an instantaneous change of shape, i.e.
resistance to flow.

424. Void :
The absence of material, or an area devoid of
materials where not intended.
425. Volatilization :
The transition of either a liquid or a solid directly
into vapor state. In the case of a liquid, this
transition is called evaporation, whereas in the
case of a solid, it is termed sublimation.
426. Volume Change :
A change in the volume of a seal as result of
immersion in a fluid; expressed as a percentage
of the original volume.
427. Volume Swell :
An increase in the physical size caused by the
swelling action of a liquid.
428. Vulcanization :
An irreversible process during which a rubber
compound, through a change in its chemical
structure (for example, crosslinking), becomes
less plastic and more resistant to swelling by
organic liquids, while elastic properties are
conferred, improved, or extended over a greater
range of temperature.
429. Vulcanizing Agent :
A material which produces vulcanization of an
elastomer.
430. Vulcanizing System :
The combination of vulcanizing agent and, as
required, accelerators, activators, and retarders
used to produce the desired vulcanizate
characteristics.
W
431. Water Absorption :
The amount of water absorbed by a material
under specified test conditions.
432. Weather Resistance :
The ability to withstand weathering factors, such
as : oxygen, ozone, atmospheric pollutants,
erosion, temperature cycling and ultraviolet
radiation.
433. Weathering :
The detrimental effect upon an elastomer or
plastic after outdoor exposure.
434. Width :
Seal cross-section or thickness.
435. Wiper Ring :
A ring employed to remove excess fluid, mud,
etc., from a reciprocating member before it
reaches the packings.

435 Technical Terms in Rubber Industry

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435 Technical Terms in Rubber Industry