Tallow: animal fat prepared from beef and mutton, sometimes a combination of solid and fluid fats; acidless tallow is used in the formulation of compounded cylinder oils to increase wettability properties in the presence of steam. Ordinary tallow contains 25% fatty acids; acidless tallow contains less than 0.5%.

Total acid number: (TAN): see neutralization number, strong acid/strong base numbers.

Tapered pad/land bearing: a fixed pad (land) bearing in which the surfaces of the pads are tapered to promote the establishment of a hydrodynamic film.

Tapping and plugging: refers to the use of a non-tapered tap, known as a bottoming or plug tap, after starting threads with two previous tapered taps.

TBN: see neutralization number, strong acid/strong base numbers.

Tricresyl phosphate/TCP: a colorless liquid used as a lubricant additive and plasticizer.

Teflon: polymer of tetrafluoroethene, also known as PRFE; material trademarked by DuPont.

Temper oil/martempering oil: heavy mineral oil kept at relatively high temperatures for long periods of time, suitable for tempering operations. Hot metal is placed in a bath of oil, at a temperature of 400-600°F, after which the metal and oil are permitted to cool slowly; in the alternative, the hot bath may be used to heat the metal slowly and uniformly without oxidizing the surface.

Texture (grease): the property of a grease that is observed when a small portion is compressed, then slowly drawn apart, described in the following terms: brittle, tends to rupture or crumble when compressed; buttery, separates in short peaks with no visible fibers; long fibers, tends to stretch or string out into a single bundle of fibers; resilient, capable of withstanding moderate compression without permanent deformation or rupture; short fiber, shows short break-off with evidence of fibers; stringy, tends to stretch or string out into long threads with no visible evidence of fibrous structure (see bulk appearance).

Thermal Gravimetric Analysis/TGA: a measure of weight loss under specific conditions; normally, temperature is maintained (isothermal) or increased in an atmosphere of nitrogen or oxygen; used to study oil volatility and oil residues, for example, contaminated roll oils.
Thermal conductivity – a measure of a material’s ability to conduct heat Thermal cracking: a process utilizing heat to break high molecular weight substances into smaller units; facilitated in a controlled manner during refining by the presence of a catalyst.

Thief (sample) Bomb: device for obtaining samples of liquid from different depths in a tank.

Thin film/mixed film lubrication: a condition of lubrication in which the lubricant film is so thin that the friction between the surfaces is determined by the properties of the surfaces as well as the viscosity of the lubricant (see boundary lubrication); also known as mixed film lubrication.

Thixotropy: the property of a material like lubricating grease that is manifested by a softening in consistency as the result of shearing, followed by a hardening in consistency that begins immediately after the shearing stops. With thixotropic cleansers, shearing may occur with shaking, mixing, vibrating, pumping or stirring.

Thread cutting oil: Petroleum based product formulated to cool and lubricate the threading tools that produce external threads on metal rods or pipes. Single- point tools can be used, but the majority of threading is performed by feeding special threading dies into the workpiece until the desired length of thread is reached.

Thrust bearing: an axial-load bearing.

Thrust collar: see collar thrust bearing.

Timken OK load: measure of the EP properties of a lubricant. The Timken testing machine uses a lever arm that can be loaded to bring a stationary block to bear against the rotating outer race of a bearing until scoring occurs. The maximum load prior to scoring is called the OK load.

Tolerance: term describing deviation from the prescribed dimensional specifications for bore, O.D. and ring widths of standard bearings; the slighter the deviation, the smaller the tolerance and the closer the bearing comes to precision. The Annular Bearing Engineering Committee has standardized the tolerances for ball bearings, and the Roller Bearing Engineering Committee has developed similar tolerances for roller bearings; higher numbers mean greater precision.

Tooth depth (gears): sum of the addendum, dedendum and a small clearance space.

Total acid/total base numbers: total acid number (TAN) and acid number are synonymous, indicating the strong acid number values. Total base number (TBN) reflects all basic constituents, including the strong base component (see strong acid/base numbers).

TQIT: bearing manufacturers’ nomenclature describing tapered roll-neck, interference-fit bearings used in high-speed, heavy-duty rolling mills where close gauge and shape tolerances are required.

TQO: nomenclature used by tapered roller bearing manufacturers to denote the straight-neck, loose-fit roller bearings used on heavy-duty, low-to-medium speed rolling mills.

Traction fluids: fluids displaying high traction coefficients; under high stresses they develop a glass-like structure, simultaneously transmitting shear forces and protecting the contacting surfaces from wear. Cycloaliphatics are superior traction fluids.

Tramp oil: describes undesired oil scum in a system, e.g., lubricants or hydraulic fluids that mix with rolling oil systems in cold mill areas.

Transducer: an electrical device that converts a signal from one form of energy to another.

Transformer oil: oil suitable for use in a transformer, to dissipate heat, keep the insulation on the wire pliable and retard the oxidizing effect of the air. Since it circulates between coils of wires that carry high-voltage currents, it must resist the flow of current through it from one coil to another; otherwise, the transformer short-circuits. Such resistance is termed dielectric strength; oil that is extremely dry, clean and acid-free has high dielectric strength.

Transverse plane (gears): in helical gears, a cross-section (perpendicular) to the line of action.

Tribology: the science and technology of interacting surfaces in relative motion and associated subjects and practices. This term, first used in 1966, effectively coordinates many technical disciplines such as chemistry, metallurgy, machine design, lubrication engineering, etc., for solving friction and wear problems.

Trunnion: either of two opposite pivots or cylindrical projections from the sides of an assembly, supported by bearings, that offer a means of swiveling or turning an assembly or part of an assembly. Trunnion bearings are used with basic oxygen furnaces.

Tung oil/chinawood oil: a drying oil from the seeds of tung trees that dries to a soft, opaque white film.

Turbulent flow: characterizes flow in eddies and currents through a pipe, in contrast to streamline, or laminar, flow; turbulent flow causes fluid friction loss. Flow quality depends on a combination of factors; pipe diameter, fluid density, viscosity and velocity.