A function of tear strength, friction co-efficient, resilience, heat dissipation and other properties. Generally, copolymer elastomers are superior to flexible materials such as vinyl and some rigid plastics.
A procedure to determine the influence of elevated temperature on the physical properties of various polymers.
Having no real or apparent crystalline form.
Characterized as a high aniline point, moderate viscosity immersion/extraction fluid used for rubber applications. Extracting oil in ECO and NBR. Swelling oil in CR, SBR, EPDM.
Characterized as a medium aniline point, moderate viscosity immersion/extraction fluid used for rubber applications. Represents service fluids – engine oil, power steering fluid, etc. and has slight swelling effect. Usually used to test seal compounds.
Characterized as a low aniline point, high viscosity immersion/extraction fluid used for rubber applications. Extracts plasticizer from compound. Will be absorbed by compound.
100% Isooctane. Generally an extracting fuel in NBR.
70% Isooctane, 30% Toluene. Represents high octane leaded fuels.
50% Isooctane, 50% Toluene. Represents high octane unleaded fuels.
The name of the inventory of an internal mixer for rubber. See Internal Mixer.
A liquid or solid material that has migrated to the surface of the elastomer and changes its appearance.
Temperature at which five specimens fist “pass”.
A polymer formed from two types of monomers.
An arrangement of polymer segments of repeating patterns into geometric symmetry.
An instrument for measuring the indentation hardness of rubber.
The extension of a uniform section of a specimen expressed as percent of the original length.
(final length – original length)
Elongation % = ——————————————X 100
Machine designed to force a rubber or rubber mix through an orifice, which is often shaped to the geometry of the desired product.
BARWELL EXTRUDER: A short barrel ram extruder used to convert stripped form elastomers into what is referred to as “shots” for molding.
COLD FEED: This extruder is generally fed rubber compound at room temperature in the form of strips or pellets. The screw must transmit sufficient mechanical energy to plasticizer the compound to near minimum viscosity as well as to overcome the head restriction.
HOT FEED: An extruder which is fed rubber compound at a temperature above ambient. A hot feed extruder receives rubber compound at near minimum viscosity and must overcome the head restriction with a minimum temperature rise and hold time.
HEAT TRANSFER FLUID (SALT BATH): The bath must be totally inert to the elastomeric composite over the entire operating range of temperatures of the process. It is used in continuous vulcanization processes, more commonly, but not exclusively. It is non-pressurized and provides reasonably rapid temperature rise and moderate vulcanization speeds.
HOT AIR OVEN: Ovens can be used to vulcanize thin articles which have been preshaped. The system is not too efficient due to the poor heat transfer of hot air and this requires longer cure times at lower temperatures.
LEAD PRESS: This process uses molten lead to cover soft, large extruded sections with a protective cover for vulcanization in steam. The process is used for garden and other hose.
RADIATION: Systems using either gamma radiation from cobalt 60 or electron beams have been used for vulcanization. The electron beam method has been used to cure both polyethylene and silicone rubber. This is generally accomplished by passing the materials through the beam on a conveyor.
UHF (ULTRA HIGH FREQUENCY): UHF fields are developed by alternating electromagnetic circuits to warm up or vulcanize articles with large or uneven cross sections. The process requires polar rubber or additives within the mixture to absorb electromagnetic energy and vibrates rapidly thereby producing a very localized temperature rise.
A delayed phase separation of incompatible material. Also called bleeding, spewing or sweating. See Bloom.
A procedure to compare the ability of rubber and rubber like compositions to withstand the effect of liquids.
T2, T5, T10, T100 – Temperature for which the relative modulus is 2, 5, 10, 100. The relative modulus at any temperature is the ratio of the modulus at that temperature to the modulus at 23°C.
The resistance to deformation of a rubber stock in the uncured state.
The resistance to indentation as measured under specified conditions.
A machine with a closed cavity in which a specially shaped rotor (or rotors) masticates the rubber to incorporate and disperse compounding materials into the rubber.
Molten phase that is used as a heating medium for the continuous vulcanization of a rubber mix, usually following extrusion. A commonly used material is a mixture of sodium nitrite and potassium nitrate.
The minimum torque reported when doing Rheometer testing is ML. MH is the highest torque obtained during a specified period of time. Both are measure in dN*M (lbf*in) – dynes per meter or pounds force per inch.
(or Tensile Stress at a given Elongation)
The stress required to stretch the uniform cross section of a test specimen to a given elongation. Represents functional strength of compound. Plasticizers reduce modulus.
COMPRESSION: A molding process in which the material is placed directly in a mold cavity and compressed to shape by closure of the mold.
INJECTION: The process of forming a material by forcing it from an external heated chamber through a runner system and gate into cavity of a closed mold by means of a pressure gradient that is independent of the mold clamping force.
TRANSFER: The process of forming a material by forcing it from an auxiliary heated chamber through a sprew and gate into the cavity of a closed mold by means of a pressure gradient that is dependent upon the mold clamping force.
A low molecular weight substance consisting of molecules capable of reacting with like or unlike molecules to form a polymer.
Minimum Viscosity – The minimum value during the test interval
t5: The time required for an increase above the
t35: The time required for a 35 unit increase
above the minimum viscosity.
A measure of the viscosity of a rubber or rubber compound determined in a Mooney shearing disc viscometer.
An internal mixer that does not imploy ram pressure and used primarily for low viscosity polymers such as silicone rubber compounds and adhesives. See Internal Mixer.
A substance consisting of molecules characterized by the repetition of one or more types of monomeric units.
Some products because of the elastomer characteristics, the article size or its shape may require a post cure. That is additional heat and energy must be applied after the press cure. The post cure might occur in a hot air oven or in a liquid heat bath.
The rate at which crosslinking and the development of the stiffness of the compound occur after the scorch point.
A phenomenon whereby a vulcanized product is exposed to conditions that result in devulcanization. Natural Rubber reverts if over cured.
ML: Minimum torque
MH: Highest torque attained during specified time.
For C. P. Hall this specified time is at the
central point of one lbf.in rise with 5 min.
ts2: Time to 2 lbf.in rise above ML
t’c(90): Time to 90% of torque increase
Cure Rate Index: 100/ (tc (90) – t52)
An elastomer with no unsaturation, thus not susceptible to ozone attach. Some elastomers have saturated backbones with pendant unsaturated cure sites.
Premature (and usually unwanted) vulcanization of a rubber compound.
A terms used to indicate the development of a property of the rubber as cure progresses. Frequently good state of cure is thought of as being representative of good compression set.
See Mooney Values.
The maximum force required to tear a specified specimen, the force acting substantially parallel to the major axis of the test specimen.
The maximum tensile stress applied during stretching a specimen to rupture or ultimate tensile.
Plasticizers reduce tensile strength.
The maximum tensile stress applied during stretching a specimen to rupture. Also known as tensile strength.
See Rheometer Value
Compounds with the ability to united directly with certain other substances such as iodine, bromine, hydro-bromic acid and ozone to form saturated addition products. Sulfur cure systems require unsaturated elastomers (double bonds) to achieve crosslinking. The ability to add iodine or bromine and the amount added is nearly always used as the test and measure of unsaturation.
An irreversible process during which a rubber compound through a change in its chemical structure (i.e. 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.