Gaskets embody a host of different technologies. There are the myriad natural and synthetic materials they can be made out of, the cutting and finishing processes used to tailor them to specific applications and conditions, and the measurements and test engineers rely on to evaluate them. Hereâs a long list of words and terms used in one these aspects of gasket design, manufacturing, and application, from abrasion to zinc oxide.
Magnesia: (a) Heavy calcined: Magnesium oxide by calcination of magnetite (natural magnesium carbonate), and then ground for use as a compounding ingredient for molded goods and hard rubber. (b) Light calcined: Magnesium oxide by calcinations of purified magnesium carbonate and/or magnesium hydroxide. It has a fine particle size and a bulk factor of 10 to 30 pds. per cubic ft. Used chiefly in neoprene stocks. (c) Extra light calcined: Prepared similarly by calcinations of magnesium carbonate, but with a bulk factor of 4 to 6 pds. per cubic ft. Used chiefly in neoprene stocks.
Maintainability: The probability that a failed system can be made operable in a specified interval or downtime.
Masterbatch: A preliminary mixture of rubber and one or more compound ingredients for such purposes as more thorough dispersion or better processing, and which will later become part of the final compound in a subsequent mixing operation.
Matte Finish: A more uniform surface finish imparted to the sheet surface by temper rolling with shot-blasted rolls.
Mechanical Properties: The properties of a material that reveal its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications.
MerKamm: This is a basic Camprofile with no outer ring. It is used in confined spaces or recessed flanges such as tongue-and-groove or male/female flanges.
MerKamm IG Gasket: This is designed with an integral outer guide ring for aligning accuracy. This is primarily used in standard ANSI B 16.5 flanges, raised face or flat face flanges.
MerKamm LG Gasket: This is designed with a loose-fitting outer guide ring. It is usedÂ for flanges where thermal expansion mayÂ be encountered.
Micrometer: A caliper for making precise measurements that has a spindle moved by a finely threaded screw.
Mill: A machine consisting of two adjacent, heavy, chilled iron rolls set horizontally which revolve in opposite directions used for mechanically working of rubber. For masticating and mixing compounds, the rolls are smooth and revolve at different speeds. For creeping and washing rubber, mills have scored or fluted rolls and differential speeds and may be equipped to spray the rubber with water. Mills with even-speed rolls are occasionally used for different purposes. Mills can be hollow and equipped for internal heating with steam or cooling with water.
Mixing: The process of adding ingredients or a rubber compound into rubber, usually done on a mixing mill or in an internal mixer. The mixing process consists ofÂ (1) breaking down the rubber, (2) gradual incorporation or compounding ingredients, (3) final working of the rubber after all ingredients are in, and (4) removing the mixed compound from the mill in sheets.
Modulus: The ratio of stress to strain. In the physical testing of rubber, the load necessary to produce stated percentage of elongation, compression, or shear.
Modulus: In the physical testing of rubber, the ratio of stress to strainâi.e., the load in pounds per square inch or kilos. Per square cm. of initial cross-sectional area necessary to produce a stated percentage-elongation. It is a measure of toughness. ItÂ is influenced by pigmentation, state of cure, quality or rubber and other factors.
Mooney Scorch: A measure of the incipient curing characteristics of a rubber compound using the Mooney viscometer.
Mooney Viscometer: A laboratory testing machine for measuring the plasticity of raw rubber or unvulcanized rubber compounds. A knurled steel rotor disc winch is centrally embedded in a heated rubber specimen firmly held in a cavity under pressure. The specimen is rotated at a low speed (2 rpm). The resistance offered by the plastic rubber mass to the rotation of the rotor disc is the measure of the rubberâs plasticity. The machine is also used to determine the scorch characteristics of rubber mixes.
Mooney Viscositr: A measure of the viscosity of a rubber or rubber compound determined in a Mooney shearing disc viscometer.
Mounts: A rubber molded part used as a motor mount or to mount device against a frame without allowing vibration to pass through the mounting.
Natural Rubber: Natural Polyisoprene-NR. Excellent properties, outstanding performance in many mechanical applications. 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 synthetics.
Neoprene: Synthetic rubber made by polymerizing 2-chlor-1, 3-butadiene. Neoprene compounds are rioted for their resistance to oil, sunlight,Â and ozone. There are various types, most of which are vulcanizable without the use or sulfur.
Nerve: The elastic resistance of unvulcanized rubber or rubber compounds to permanent deformation during processing.
Nitrile Rubber: A generic term comprising the various copolymers of butadiene and acrylonitrile. The copolymers vary essentially in their butadiene-to-acrylonitrile ratios, Mooney values, and staining properties. They are resistant to solvents, oils, and greases, as well asÂ bending and abrasion. Some trade names are Chemigum, Krynac, Nipol, Hycar, and Paracril. German engineers first produced nitrile rubbers, namingÂ them Buna N and Perbunan.
Oil Resistance (a): Ability to withstand swelling by a specified oily liquid for specified time and temperature, expressed as percentage swelling or volume increase of specimen.
Oil Resistance (b): Ability of vulcanized elastomer compositions to resistance to change in size and shape, and to losing physical (mechanical) properties due to contacts with or immersion in an oil.
Oil Resistant: The ability of a vulcanized rubber to resist the swelling and deteriorating effects of various types of oils.
Oil Seals: Also called grease seals, rotary seals,Â or shaft seals. They are made of rubber and seal grease in housing with a rotating shaft.
Open Cells: A porous material with cells or cavities not totally enclosed by walls, and hence interconnecting with other cells.
Open Steam Cure: A vulcanization process that takes place under direct steam pressure in an autoclave. It is used where direct pressure molding is not possible. In the case of vulcanization of sheeting or coated fabrics, rolls of product are wound onto steel drums (with suitable a interleaf) and placed in the autoclave for cure. Some tubing and shaped products can be placed on pans for extra curing.
Optimum Cure (b): The physical properties of a rubber compound vulcanized at a given temperature for increasing periods of time undergo continuous change. For example, tensile strength may rise to a maximum, continue on a plateau, and then decline,Â whereas breaking elongation may continuously decrease. Therefore it is impossible to choose any one time of cure at which every property will be at its optimum. Hence, optimum cure is a compromise and may be considered as that time required to obtain the combination of properties most desirable for the article under consideration.
O-rings: O-ring seals are circular rings of various cross-sectional configurations installed in a gland to close off a passageway and prevent escape or loss of a fluid or gas. An O-ring is specified by three of its features: its dimensions, material, and hardness. Material and hardness specify the elastomeric compound and Shore A (durometer) hardness of the compound used to manufacture the O-ring. An O-ringâs dimensions are described by stating its inside diameter (I.D.) and its cross-section. Designing for O-rings depends on three major and interrelated variables: the operating conditions and the environment the seal will experience, and the gland geometry into which the seal will be installed. The three variables account for the fact that there are so many different types of seals and applications.
Overcure: A state of excessive vulcanization resulting from overstepping the optimum cureâe.g.., vulcanizing longer than necessary to attain full development of physical strength. It is manifested by softness or brittleness, as well as anÂ impaired ability to resistÂ age resisting.
Oxidation: Active oxygen degrading organic materials. Rate of degradation increases with rising temperatures.
Ozone: An allotropic from oxygenÂ (03)Â produced by electrical discharges in air. It is a gas with a characteristic odor and is a powerful oxidizing agent. Rubber compounds in a stretched condition are susceptible to the deteriorating action of ozone in the atmosphere, which results in a surface cracking.
Ozone cracking: The surface cracks, checks, or crazing caused by exposure to an atmosphere containing ozone.
Packaging: A unit that provides protection and containment of items plus ease of handling by manual or mechanical means.
Packing: An adjustable sealing device on a ram, valve stem, or pump shaft. If packing leaks, it is simply tightened slightly to "control"Â the leakage. For pumps and valves, packings can be rope-like, braided into continuous lengths, and then cut to size to fit a shaft. For hydraulic applications, V-shaped fabric reinforced rubber rings are used. Early hydraulic packings were made from leather.
Parachute Packings: Also called V-Packing, Vee packing, Chevron Packing, or V-set packing. A complete vee packing set contains multiple V-shaped sealing rings stacked and nested together with a male adapter on one end and a female adapter on the other end.
Parbacks: A back-up ring with a concave shape on one side, used as an anti-extrusion ring for an O-ring.
Permanent Set: The amount by which an elastic material fails to return to its original form after deformation. In the case of elongation, the difference between the length after retraction and the original length, expressed as a percentage of the original length. Permanent set depends on quality and type of rubber, degree and type of filler loading, state of vulcanization, and amount of deformation.
Piston Bearing Rings: Also called guide rings, wear rings, piston guide rings. Rings usually made from nylon or POM and are used on the piston of a hydraulic or pneumatic cylinder.
Piston Seals andÂ Packings: Any seal or packing ring used on the piston of a hydraulic or pneumatic cylinder.
Piston T-Seals: A T-shaped rubber seal, with back-up rings of a harder material on each side, used as a piston seal.
Plasticity: A measure of the resistance to shear of an unvulcanized elastomer,Â or the tendency of a material to remain deformed after reducing the deforming stress to or below its yield stress.
Pneumatic Seals: Any seal or packing ring, usually flexible rubber, used to seal against compressed air instead of hydraulic fluid or other liquid.
Points of Tangency: The points at which the straight portions of the shell walls intersect the beginning of the radius corners.
Poissonâs Ratio: The ratio of lateral concentration per unit of diameter to longitudinal extension per unit of length in a bar of material longitudinally stressed. For a body which does not change its volume on deformation, it is 0.5. For metals, the ratio is usually considerably less than 0.5. In the case of vulcanized rubber or pure gum, which have practically no volume change on extension,Â it shows a ratio of approximately 0.5 for small deformations; compounded rubber may increase in volume on extension, consequently the ratio drops below 0.5. For rubber the ratio is constant only for small extensions.
Polyester: A durable substrate that is resilient to moisture, solvents, oils, and chemicals. It is available as clear or white material and with a moralized finish.
Polymer: A material formed by the joining together of many individual units or monomers. A polymer is a long chain of monomer units prepared by means of an addition and/or a condensation polymerization. The units may be the same or different. There are copolymers, dipolymers, tri- or terpolymers, quadripolymers, and high polymers.
Post cure: Heat or radiation treatment, or both, for a cured or partially cured thermosetting plastic or rubber composition that improves one or more properties.
Preliminary Bill of Material: An initial bill of material completed prior to design and print release.
Preliminary Process Flow Chart: An early depiction of the anticipated manufacturing process for a product.
Press-in Wipers: A wiper or scraper ring for a hydraulic cylinder which has a metal outside diameter so it can be press-fitted into a housing.
Pressure Sensitive: Describes an adhesive that can be applied to a substrate by using light pressures.
Process Failure Mode and Effects Analysis (PFMEA): An analytical technique used by manufacturing engineers to ensure potential failure modes and their associated causes/mechanisms have been considered and addressed.
Processing Aids: Materials including waxes, low-molecular-weight polyethylene, metal soaps, and petroleum oils, which dissolve or lubricate rubbers, softening them and act as processing aids.
Product Assurance Plan: A part of the Product Quality Plan. It is a prevention-oriented management tool that addresses product design, process design, and, when applicable, software design.
Production Trial Run: Product made using all production tools, processes, equipment, environments, facilities,Â and cycle times.
Protectors: A rubber or plastic cap or cup-shaped ring used to protect threads or fragile items during shipping or assembly.
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Prototypes: A finished product made during the design process to determine the feasibility or suitability of a project.
Pusher Rings: A ring that fits against another sealing device to push it and activate or energize it in the absence of pressure or in low-pressure applications.
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