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Dictionary of Lubricant Terms

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RAFFINATE - in solvent extraction, that portion of the oil which remains undissolved and is not removed by the selective solvent.

R&O - rust-and-oxidation inhibited. A term applied to highly refined industrial lubricating oils formulated for long service in circulating systems, compressors, hydraulic systems, bearing housings, gear cases, etc. The finest R&O oils are often referred to as turbine oils.

RATE OF SHEAR - see shear rate.

REACTION DILUENT - a material (usually a light saturated hydrocarbon; e.g., pentane, hexane) that is used as a carrier for the polymerization catalyst in the manufacture of polyolefins (see polymer). The material must be very pure, since impurities “poison” the catalyst or hinder the polymerization by reacting with the olefins.

RECLAIMING - process of restoring used lubricating oils by filtration, clay absorption, and/or chemical treatment to a condition similar to virgin stocks. This is not to be confused with re-refining operations in which the used oil is vacuum distilled and chemically treated to return it to a state similar to its virgin condition.

REDWOOD VISCOSITY - method for determining the viscosity of petroleum products; it is widely used in Europe, but has limited use in the U.S. The method is similar to Saybolt Universal viscosity; viscosity values are reported as “Redwood seconds.”

REFINING - series of processes for converting crude oil and its fractions to finished petroleum products. Following distillation, a petroleum fraction may undergo one or more additional steps to purify or modify it. These refining steps include: thermal cracking, catalytic cracking, hydroforming, hydrogenation, hydrogen treating, hydrofinishing, solvent extraction, dewaxing, de-oiling, acid treating, clay filtration, and de-asphalting. Refined lube oils may be blended with other lube stocks, and additives may be incorporated, to impart special properties; refined naphthas may be blended with alkylates, cracked stock or reformates to improve octane number and other properties of gasolines.

REFORMING - thermal or catalytic refining process in which the hydrocarbon molecules of a naphtha are rearranged to improve its octane number; the resulting product is used in blending high-octane gasoline.

RE-REFINING - a process of reclaiming used lube oils and restoring them to a condition similar to virgin stocks by filtration, clay absorption or more elaborate methods.

RESEARCH OCTANE NUMBER (RON) - see octane number.

RESINS - solid or semi-solid materials, light yellow to dark brown, composed of carbon, hydrogen, and oxygen. Resins occur naturally in plants, and are common in pines and firs, often appearing as globules on the bark. Synthetic resins, such as polystyrene, polyesters, and acrylics, are derived primarily from petroleum. Resins are widely used in the manufacture of lacquers, varnishes, plastics, adhesives, and rubber.

RHEOLOGY - study of the deformation and flow of matter in terms of stress, strain, temperature, and time. The rheological properties of a grease are commonly measured by penetration and apparent viscosity.

RING FEATHERING - metal drag from the face of a ring beyond the ring side to form burred edge.

RING (FREE) - one that falls of its own weight from side to side in its own groove.

RING (COLD STUCK) - one that is firmly bound in its groove but is assumed to be free at operating temperatures. See engine deposits.

RING (HOT STUCK) - one that is firmly bound in its groove and exhibits vertical blow-by tracks or carbon build-up on its face surface. It is assumed to remain bound at operating temperatures. See engine deposits.

RING (TIGHT OR SLUGGISH) - one that offers resistance to movement in its groove, but which can be pressed into or out of the groove under finger pressure without springing back. See engine deposits.

ROAD OCTANE NUMBER - see octane number.

RUST - the chemical combination of oxygen with ferrous engine parts, including other iron complexes not removable by organic solvents.

RUST INHIBITOR - type of corrosion inhibitor used in lubricants to protect the lubricated surfaces against rusting. See R&O.

RUST PREVENTIVE - compound for coating metal surfaces with a film that protects against rust; commonly used for the preservation of equipment in storage. The base material of a rust preventive may be a petroleum oil, solvent, wax, or asphalt, to which a rust inhibitor is added. A formulation consisting largely of a solvent and additives is commonly called a thin-film rust preventive because of the thin coating that remains after evaporation of the solvent. Rust preventives are formulated for a variety of conditions of exposure; e.g., short-time “in-process” protection, indoor storage, exposed outdoor storage, etc.

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