False brinelling: a form of fretting corrosion, caused by vibration, that occurs in rolling element bearings while sitting idle and subject to friction oxidation.

Fat: raw material used in the manufacture of most greases, composed of various fatty acids and glycerol (glycerine) that form triglyceride esters. Fats are found in nature but may also be made synthetically.

Fatigue: the phenomenon leading to fracture under repeated or fluctuating stresses whose maximum value is less than the tensile strength of the material.

Fatty acids: components of all animal and vegetable oils, with the general chemical formula of CnH(2n+1)CO2H; palmitic, stearic and oleic are the most prominent.

Fatty oil: an oil of animal, vegetable or marine origin that is liquid at normal temperature, whose composition resembles that of solid fat, except for differing types and percentages of fatty acids. Owing to “polarity”, these oils have a physical affinity for metal; they increase load-carrying ability by enhancing “oiliness”.

FDA: Food and Drug Administration, an agency of the United States Department of Health and Human Services; reviews the toxicology of fluids and additives, among other things.

Feedback: the practice of using a measure of output to modify input; in hydraulics, the controlled output, such as position, velocity or pressure, would be measured and compared with the input valve to modify the input.
Ferrography (direct read and analytical): method that examines ferrous wear particles in used fluid; used in preventive and predictive maintenance programs.

Fibrous grease: describes a specific type of grease that exhibits a distinctive fibrous structure when portions of the grease are pulled apart. The gelling agents for many greases have unique fibrous structures, depending on the type of soap or thickener employed, that are easily distinguished under an electron microscope. Some greases are smooth and buttery to the feel, even though they are microscopic fibrous structures. It is customary to use the term “fibrous grease” for grease that resists being pulled apart.

Fillers: an extensive variety of solid substances, primarily inorganic powders or flakes such as mica, talc, graphite, molybdenum disulfide and others that are added to grease to increase bulk or incorporated into non-metallic bearing materials to improve lubrication under high loads, low speeds and/or high temperatures.

Fillet curve (gears): the concave portion of the tooth profile where it joins the bottom of the tooth space at the root circle.

Filter: a porous substance or device that cleans fluids by removing suspended matter.

Filter element: removable portion of a filter that houses the filtering medium.

Film strength: general term indicating the capacity of an oil to maintain an unbroken film on a lubricated surface under operating conditions; used without reference to the type of film. “Load- carrying capacity” is another general term used in calculations. Film strength additives are usually considered anti-wear additives, not EP additives.

Fingerprint neutralizer: a polar compound used in rust preventives for steel surfaces that prevents corrosion attacks from perspiration during handling.

Fire point (Cleveland Open Cup, or COC; ASTM D-92): the temperature to which a combustible liquid must be heated so that the vapor released will burn continuously when ignited under specific conditions.

Fire-resistant (FR) fluids: hydraulic fluids that exhibit fire-resistant properties; they include the water-in-oil emulsions known as invert emulsions, water-glycol fluids, non-aqueous synthetic fluids like phosphate esters, silicones and halogenated hydrocarbons and high water-based fluids (95% water) and microemulsions.

Fitted bearings: partial journal bearings in which the radius of the bearing surface is the same as the radius of the journal surface.

Fixed oils: obsolete term, generally applied to fatty oils, indicating fluids that tend to decompose during distillation instead of remaining intact during the process; such oils are also known as non-volatile oils.

Fixed pad bearing: an axial or radial load type of bearing equipped with fixed pads (or lands), the surfaces of which are contoured to promote the establishment of a hydrodynamic film.

Flammable fluids: describes fluids with COC flash points under 100°F, as determined by the National Fire Protective Association (NFPA) (see combustible fluids).

Flash point (ASTM D-92, D-93, D-56): the temperature to which a combustible liquid must be heated to give off sufficient vapor to form a flammable mixture with air; this mixture should burn momentarily without sustaining combustion when a small flame is applied under specific conditions. Because it indicates the temperature at which a flammable vapor is produced, flash point is generally the most useful single index of fire hazard potential.

Flexible coupling: a device that connects two rotating shafts, designed to accept limited varying amounts of misalignment between shafts; a common coupling for mill spindles is a spade and yoke design with mill slippers.

Fluid drive (hydraulics): drive in which hydraulic fluid transmits power from one part of the system to another, without a mechanical connection between them.

Fluid friction: friction resulting from fluid molecules sliding past each other during flow through a duct (pipe, tube, hose). Its value depends on the duct diameter, flow rate, fluid density and viscosity. Where all other factors remain constant, the higher the viscosity, the greater the fluid friction.

Fluid power: energy transmitted and controlled by a pressured fluid.

Fluid power system (hydraulics): a system that transmits and controls power by moving pressurized fluid through fluid conductors to actuators, for accomplishment of work.

Flushing oil: oil used to flush dirt out of a newly constructed or rebuilt circulating or hydraulic system, generally after chemical cleaning.

Foam test: (usually ASTM D-892) measures the ability of a lubricant to resist foaming caused by excessive agitation, contamination or air ingression in suction lines.

Follower plate: a plate fitted to the surface of lubricating grease in a container, designed to employ atmospheric pressure to assist gravitational forces in delivering grease to the inlet of the dispensing system.

Foot valve: a check valve installed at the entrance to the suction line.

Force-feed lubrication: describes a kind of self-contained lubricator, designed to pump small quantities of oil sequentially from its small reservoir into individual tubes leading to the various points to be lubricated. Lubricators are usually belt driven, to ensure delivery of oil during operation. These lubricators find service in once-through applications, with each feed line independently adjusted, metered to deliver feeds in drops per min.

Forging compound: a general term signaling a product used at the die: cold forging requires anti-friction and EP properties to prevent metal pickup and extend die life; compounds used in hot forging employ solid lubricants with thermal stability that resist burn-off and the formation of deposits on the die.

Form oil: an oil used to lubricate wooden or metal concrete forms to keep cement from sticking to them.

Four-way slide valve (lube systems): device that alternates pressure between the two main supply lines.

Frequency response: how well a servo or proportional valve output follows the electrical input. The concept is critical in system design because of system stiffness.

Fretting corrosion (ferrous corrosion): a combination of corrosive and abrasive wear that results from fretting of ferrous metals where the wear particles oxidize to a reddish, abrasive iron oxide (Fe2O3).

Friction bearing: obsolete term for plain bearing or sliding bearing (see plain bearing).

Front cone (gears): the inner ends of the teeth in a bevel gear with elements perpendicular to those of the pitch cone. Though the surface of the gear blank at the inner ends of the teeth is customarily formed to such a front cone, occasionally it takes the form of a plane on a pinion or a cylinder in a nearly flat gear.

Full flow filtration: a system of filtration in which the total flow of a circulating fluid system passes through a filter.

Fungicide: a substance that kills, prevents or retards the growth of fungi. Fungicides and biocides are most often used with fluids like soluble oils that contain water.

FZG: acronym for German gear test rig, also known as the four-square gear oil tester. The test uses small gears driven under increasing loads in a heated oil bath until failure, at which point a 10-mg weight loss has occurred. Results are expressed as load stage at the time of failure.