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A true grease consists of an oil or other fluid lubricant that is mixed with a thickener, typically a soap, to form a solid or semisolid. [1] Greases are usually shear-thinning or pseudo-plastic fluids, which means that the viscosity of the fluid is reduced under shear stress.
where an additional function (), often a polynomial fit to experimental data, has been added to the Walther formula. The Seeton model is based on curve fitting the viscosity dependence of many liquids (refrigerants, hydrocarbons and lubricants) versus temperature and applies over a large temperature and viscosity range:
Critical viscosity and critical thermodynamic properties of n-alkanes therefore show a trend, or functional behaviour, when plotted against molecular mass or number of carbon atoms in the molecule (i.e. carbon number). Parameters in equations for properties like viscosity usually also show such trend behaviour. This means that
Both gas and liquid lubricants can transfer heat. However, liquid lubricants are much more effective on account of their high specific heat capacity. Typically the liquid lubricant is constantly circulated to and from a cooler part of the system, although lubricants may be used to warm as well as to cool when a regulated temperature is required.
Motor oil may be composed of only a lubricant base stock in the case of mostly obsolete non-detergent oil, or a lubricant base stock plus additives to improve the oil's detergency, extreme pressure performance, and ability to inhibit corrosion of engine parts.
The lubricity of a substance is not a material property, and cannot be measured directly. Tests are performed to quantify a lubricant's performance for a specific system. This is often done by determining how much wear is caused to a surface by a given wear-inducing object in a given amount of time. Other factors such as surface size ...
A common type of degradation is the formation of tramp oil, also known as sump oil, which is unwanted oil that has mixed with cutting fluid. [17] It originates as lubrication oil that seeps out from the slideways and washes into the coolant mixture, as the protective film with which a steel supplier coats bar stock to prevent rusting, or as ...
The most common one is a type of paraffinic crude oil, although there are also naphthenic crude oils that create products with better solubility and very good properties at low temperatures. By using hydrogenation technology, in which sulfur and aromatics are removed using hydrogen under high pressure, extremely pure base oils can be obtained ...