Produced by copolymerizing isobutylene with small amounts of isoprene. These rubbers have excellent impermeability to gases, outstanding dielectric properties, good resistance to tearing, good aging properties at elevated temperatures and good chemical stability.
A gasket material's degradation resistance to the fluid or fluids being sealed.
CI:
The abbreviation for cloth-inserted. indicating a sheet of rubber containing one or more plies of fabric covered with rubber.
Cloth-both-sides sheet:
See CBS.
Compressed asbestos sheet:
A sheet prepared from a rubber compound containing a high percentage of asbestos fiber and vola solvent by the use of a special calender (sheeter) in such a manner that the solvent is volatilized and the compound is caused to build as an oriented sheet on one roll of the sheeter.
Compressibility:
The property of exhibiting compression under stress In the case of sheet material, the percent of loss of thickness when subjected to a given load applied by a disc of a given diameter for a specified short time and at a specified temperature as defined according to ASTM F-36 test procedures
Compression molding:
A method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, while heat and pressure are maintained until the molding material has cured. The process employs thermosetting resins in a partially cured stage, either in the form of granules, putty-like masses, or preforms. Compression molding is a high-volume, high-pressure method suitable for molding complex, high-strength fiberglass reinforcements. Advanced composite thermoplastics can also be compression molded with unidirectional tapes, woven fabrics, randomly oriented fiber mat or chopped strand. The advantage of compression molding is its ability to mold large, fairly intricate parts.
Compression set:
The deformation which remains in rubber after has been subjected to and released from a specific compress stress for a definite period of time at a prescribed temperature. Cc Compression set measurements are used to evaluate the creep and stress relaxation properties of rubber.
Cork-composition sheet:
Sheet made from cork granules treated with a binder.
Creep relaxation:
In a flange gasket, loss of stress accompanied constantly decreasing compressed thickness. This type of relaxation is encountered in bolted flange joints.
Cure time:
The time required to produce vulcanization at a given temperature.
Curing:
A term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation, electron beam or heat. In rubber, the curing process is also called vulcanization.
A diaphragm seal is a flexible membrane that seals and isolates an enclosure. The flexible nature of this seal allows pressure effects to cross the barrier but not the material being contained. Common uses for diaphragm seals are to protect pressure sensors from the fluid whose pressure is being measured.
Diaphragm sheet:
Generally of fabric reinforced rubber, from which flat diaphragms may be cut.
Die cut:
Shaped by punching from a sheet of rubber with a die.
Durometer:
An instrument for measuring the hardness of vulcanized rubber and plastic.
Durometer hardness:
An arbitrary numerical value which measures the resistance to indentation of the blunt Indentor point of a durometer. Value may be taken immediately or after a very short specified time.
A polymer which uses a sulfur cure system. It is recognized for its resistance to weathering and high temperatures. EPDM rubbers are use extensively in outdoor applications. They will withstand the abuse of all types of weather including sunlight, ozone and oxidants, and they exhibit excellent resistance to animal and vegetable oils, water, steam, oxygenated solvents.
Elastomer:
A macromolecular material which, in the vulcanized state, at room temperature can be stretched repeatedly to at least twice its original length and which, upon release of the stress, will immediately return to approximately its original length.
Elongation:
An increase in length expressed numerically as a fraction or percentage of the initial length.
Extrusion:
The act or process of shaping sealing compounds by forcing them through a die.
A pattern in a rubber surface formed by contact with fabric during vulcanization.
Full-face gasket:
A gasket covering the entire flange surface and drilled with bolt holes.
Flange gasket:
A flange gasket is a type of gasket made to fit between two sections of pipe that are flared to provide higher surface area. Flange gaskets come an a variety of sizes and are categorized by their inside diameter and their outside diameter.
Flash or flashing:
Flash or flashing is excess material attached to a molded, forged, or cast product, which must usually be removed. This is typically caused by leakage of the material between the two surfaces of a mold. (This leak begins along what is called a parting line in mold design) Molding flash is seen when the optimized parameter on cull height is not calibrated. Proper design of mold parting surfaces can reduce or eliminate flash.
Any of a wide variety of seals or packings used between matched machine parts or around pipe joints to prevent the escape of a gas or fluid. It is a mechanical seal that fills the space between two mating surfaces, generally to prevent leakage from or into the joined objects while under compression. Gaskets allow "less-than-perfect" mating surfaces on machine parts where they can fill irregularities. Gaskets are commonly produced by cutting from sheet materials, such as gasket paper, rubber, silicone, metal, cork, felt, neoprene, nitrile rubber, fiberglass, or a plastic polymer. It is usually desirable that the gasket be made from a material that is to some degree yielding such that it is able to deform and tightly fills the space it is designed for, including any slight irregularities.
Gasket extrusion:
Refers to the tendency of a gasket to flow from between flanges, particularly around bolt holes where stresses are concentrated.
A chemical element with chemical symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to aluminum. Indium was discovered in 1863 and named for the indigo blue line in its spectrum that was the first indication of its existence in zinc ores, as a new and unknown element. The metal was first isolated in the following year. Zinc ores continue to be the primary source of indium, where it is found in compound form. Very rarely the element can be found as grains of native (free) metal, but these are not of commercial importance.
Injection molding:
A manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the mold cavity. After a product is designed, usually by an industrial designer or an engineer, molds are made by a moldmaker (or toolmaker) from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part.
Similar to transfer molding but the silicone rubber material is supplied through an injection nozzle and is injected into the mold cavity. Under heat and pressure, the silicone rubber cures. The part is then ejected from the cavity and the LIM molding cycle restarts.
A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage (e.g., in a plumbing system), containing pressure, or excluding contamination. A seal may also be referred to as "packing".
Natural polyisoprene offers an excellent balance of properties, resulting in outstanding performance in many demanding mechanical applications. The major advantages of natural rubber are high resilience, high tensile and tear properties and excellent resistance to cold flow. When exposed to petroleum derivatives, ozone, sunlight and oxygen, natural rubber and its heat aging properties are inferior to many of today's synthetics.
A polymer chloroprene rubber known for its resistance to oil, gasoline, sunlight, ozone and oxidation. It's ability to combine all of these properties make it an excellent general purpose polymer for most applications.
Nitrile(chemical identification: butadiene acrylonirile, Buna N, - NBR):
A copolymer of Butadiene and Acrylonitrile. Most nitrile compounds have a relatively high acrylo content, making them exceptionally resistant to petroleum-base oils and hydrocarbon fuels over a temperature range of -40F to +250F.
Functions as a seal through the mechanical deformation of the elastomeric compound by mating metal surfaces. This creates a condition of zero clearance which blocks the liquid or gas being sealed. The pressure which causes the O-Ring to move is supplied by mechanical pressure or squeeze generated by proper gland design, material selection, and by the system pressure transmitted by the fluid itself.
A parting line in mold making is the place where two or more parts of the mold meet. At times, either because the mold halves do not meet with enough precision or because injection pressure is high, material will creep into the space between the molds. This material is generally called molding flash or simply flashing.
Permeability:
The quality or condition of allowing passage of liquids or gases through a layer.
Polyurethane:
Any of various synthetic rubber polymers produced by polymerization of hydroxyl (OH) radical and NCO group from two different compounds. Used in cushions, insulation, molded products.
A strong, waterproof, elastic substance made from the juice of a tropical tree or produced chemically.
Rubber bushing:
A rubber bushing is a type of vibration isolator. It provides an interface between two parts, damping the energy transmitted through the bushing. A common application is in vehicle suspension systems, where a bushing made of rubber (or, more often, synthetic rubber or polyurethane) separates the faces of two metal objects while allowing a certain amount of movement. This movement allows the suspension parts to move freely, for example, when traveling over a large bump, while minimizing transmission of noise and small vibrations through to the chassis of the vehicle. A rubber bushing may also be described as a flexible mounting or anti-vibration mounting.
Rubber-to-metal-bonding
In rubber-to-metal bonding, the metal gives the required stiffness and opportunities to mount the product, while rubber gives it elasticity and damping properties. Only a few specific rubber types serve best for bonding to metal. The metals giving the best results are steel and aluminum. For alloys like brass and bronze, the result depends very much on the composition of the alloy. When manufacturing, it is important that the metal is smooth and free from rust and other impurities. The metal is prepared by degreasing and sandblasting. Finally, before molding, a bonding agent is sprayed onto the metal and, after drying the metal, the rubber is placed into the mould for forming and curing.
The abbreviation for the Society of Automotive Engineers.
SBR rubber(chemical identification: styrene butadiene, Buna S, GRS):
A synthetic copolymer composed of styrene and butadiene used more often than any of the other synthetics produced today. SBR has similar resistance to solvents and chemicals as natural rubber, and it can successfully bonded to a wide range of materials.
Seal:
Any material or device which prevents or controls the passage of matter across the separable members of a mechanical assembly.
Silicone:
Offers a broad temperature use range of -80F to +400F, and excellent dry heat resistance. Our silicone compounds are inert and guarantee complete compliance to ASTM, military, and FDA specifications required by food, medical, electrical, and filter manufacturers. They are not used in dynamic seals because of relatively poor tensile, tear, and abrasion resistance
Suction cups:
Sometimes known as a "sucker", is an object that uses negative fluid pressure of air or water to adhere to nonporous surfaces. The working face of the suction cup has a curved surface. When the center of the suction cup is pressed against a flat, non-porous surface, the volume of the space between the suction cup and the flat surface is reduced, which causes the fluid between the cup and the surface to be expelled past the rim of the circular cup. When the user ceases to apply physical pressure to the centre of the outside of the cup, the elastic substance of which the cup is made tends to resume its original, curved shape. Because all of the fluid has already been forced out of the inside of the cup, the cavity which tends to develop between the cup and the flat surface has little to no air or water in it, and therefore lacks pressure. The pressure difference between the atmosphere on the outside of the cup, and the low-pressure cavity on the inside of the cup, is what keeps the cup adhered to the surface.
Synthetic rubber:
Any type of artificial elastomer, invariably a polymer. An elastomer is a material with the mechanical (or material) property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation. Synthetic rubber serves as a substitute for natural rubber in many cases, especially when improved material properties are required.
A gasket material's ability to withstand elevated temperatures.
Tensile strength:
The maximum tensile stress applied while stretching a specimen to rupture.
Transfer molding:
Like compression molding, is a process where the amount of molding material (usually a thermoset plastic) is measured and inserted before the molding takes place. The molding material is preheated and loaded into a chamber known as the pot. A plunger is then used to force the material from the pot through channels known as a sprue and runner system into the mold cavities. The mold remains closed as the material is inserted and is opened to release the part from the sprue and runner. The mold walls are heated to a temperature above the melting point of the mold material; this allows a faster flow of material through the cavities.
Transfer molding is an automated operation that combines compression-, molding, and transfer-molding processes. This combination has the good surface finish, dimensional stability, and mechanical properties obtained in compression molding and the high-automation capability and low cost of injection molding and transfer molding. Transfer Molding is having a "piston and cylinder" like device built into the mold so that the rubber is squirted into the cavity through small holes. A piece of uncured rubber is placed into a portion of the transfer mold called the "pot." The mold is closed and under hydraulic pressure the rubber or plastic is forced through a small hole (the "gate") into the cavity. The mold is held closed while the plastic or rubber cures. The plunger is raised up and the "transfer pad" material may be removed and thrown away. The transfer mold is opened and the part can be removed. The flash and the gate may need to be trimmed. Another key point is that a premeasured amount of thermosetting plastic in powder, preform, and even granular form can be placed into the heating chamber.
Trapped air
Air which is enclosed in a product or between a product and a mold surface during cure. (Usually causes a loose ply or cover or a surface mark, depression,or void.)
The reaction products of polyethers and polyesters diisocyanates. These rubbers are complex and varied, offering a wide range of pyisical properties. Urethanes come in three basic forms: liquid cast, millable gums, and thermoplastic. Urethanes have outstanding tensile strength and abrasion resistance, and have oil and fuel resistance comparable to nitriles.
The process of isolating an object, such as a piece of equipment, from the source of vibrations.
Viton:
DuPont Dow Elastomer's trade name for fluorocarbon elastomers. This fluoroelastomer is well known for its excellent (400¡F/200¡C) heat resistance. Viton offers excellent resistance to aggressive fuels and chemicals and has worldwide ISO 9000 registration.
Vulcanization:
A chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks (bridges) between individual polymer chains. Vulcanized material is less sticky and has superior mechanical properties.
