Tribologie F

FLASH POINT
This is the lowest temperature at which a fluid to be tested develops vapours in an open or closed flash cup under specified conditions so that a vapour-air mixture develops to burst into flame in the flash cup as a result of external ignition. It then flares briefly and extinguishes again. DIN 51 755 P2, DIN ISO 2592, DIN pr EN 57 – also see burning point.
 

FLOCCULATION POINT
Is the temperature in °C for refrigerating equipment oils, at which the first deposits can be seen in transmitted light in the form of milky turbidity or flocks, when cooling down in a homogenous mixture of refrigerating equipment oil and refrigerant at a ratio of 10 to 90 (parts by volume): DIN 51 351.
 

FLOW PROPERTIES
The viscosity properties of individual substances can be shown in flow curves (rheograms      showing the relationship between speed gradients and shearing stress) or viscosity curves (shows viscosity h to shearing stress). The form of flow properties depends on the type of substance, e.g. mineral oils, synthetic fluids, lubricating greases, etc.
 

FLUIDITY
Properties of lubricating oils (fluidity) at temperatures below 0°C. Determination of fluidity (procedure using U-tube). DIN 51 568.
 

Foam suppressor
Polysilicone (silicone polymers), polyethylene glycol, etc. reduce the tendency to foam during vigorous movement, better foam release; promote the formation of larger air bubbles that dissipate rapidly. The formation of foam has a substantial detrimental effect on the lubricating properties (oxidation, pressure behaviour, etc.) of a lubricant. For this reason, foam formation must be specifically suppressed.
 

Foaming tendency of mineral oils
The quantity (ml) of oil foam produced under specified conditions (blowing through air) indicates the tendency of an oil to foam. To determine the air release characteristics: DIN 51 381. Determination of foaming behaviour: DIN E 51 566.
 

Formwork oils
Emulsifiable or non-emulsfiable oil for concrete formwork. Requirements vary greatly depending on the formwork material, the porosity of the concrete, concrete type, etc.
 

Four-ball apparatus
Oil tester for checking lubricants with active ingredients (EP lubricants). There are four balls arranged in the shape of a pyramid. The ball on top turns and loading can be increased until the balls fuse together (fusing. load); the loading in N is used as the wear index. DIN 51 350 P 1 / P 2 / P 3
 

FRACTIONS
Hydrocarbon mixtures with different boiling ranges for atmospheric and vacuum distillation. See distillation.
 

Friction
If the mating surfaces of materials move against each other, a distinction is made between the following friction situations:
a) Dry friction – Boundary friction (starting friction, solid friction, surface layer friction).
b) Semi-fluid friction – mixed friction (from boundary friction to viscous friction).
c) Fluid friction – viscous friction (hydrodynamic friction).
Friction modifier
(FM)
Fatty acids, fatty acid derivatives, organic amines, amine phosphates, mild EP additives, etc. are called friction modifiers. Their role is to reduce frictional losses or create defined friction behaviour of various lubricants.
 

FRICTION-MODIFIER (FM)
See friction modifier.
 

Fuels
All gaseous and liquid flammable substances that are suitable for the operation of internal combustion engines: refinery gas, coal gas, sewage gas, natural gas, compressed gas, propellant gas, generator gas, petrol, tractor fuel, diesel fuel and aviation fuel, etc.
 

Full lubrication
For instance, elastohydrodynamic lubrication in the case of matching gears or hydrodynamic lubrication for plain bearings where the surfaces that slide on each other are completely separated by the lubricant.
 

FURFUROL PROCESS
Selective extraction of fluids, in particular mineral oils, using furfurol. Also see duo-sol process.