Page 304 - The Tribology Handbook

Mineral oils c2

CLASS1 FI CAT10 N Traditional use
Mineral oils are basically hydrocarbons, but all contain Dating from before viscosity could be measured accur-
thousands of different types of varying structure, molecular ately, mineral oils were roughly classified into viscosity
weight and volatility, as well as minor but important grades by their typical uses as follows:
amounts of hydrocarbon derivatives containing one or Spindle oils Low viscosity oils (e.g. below about 0.01
more of the elements nitrogen, oxygen and sulphur. They Ns/m2 at 60DC,) suitable for thelubrica-
are classified in various ways as follows. tion of high-speed bearings such as
textile spindles.
Light machine oils Medium viscosity oils (e.g. 0.01-0.02
'Types of crude petroleum Ns/mZ) at 60°C, suitable for machinery
running at moderate speeds.
Parafinic Contains significant amounts of waxy hydro- Heavy rnachine oils Higher viscosity oils (e.g. 0.02-0.10
carbons and has 'wax' pour point (see below)
but little or no asphaltic matter. Their naph- Ns/mZ) at 60DC, suitable for slow-moving
thenes have long side-chains. machinery.
Cylinder oils Suitable for the lubrication of steam
Naphthenic Contains asphaltic matter in least volatile engine cylinder; viscosities from 0.12 to
fractions, but little or no wax. Their naph- 0.3 Ns/m2 at 60°C
thenes have short side-chains. Has 'viscosity'
pour point.
Mixed base Clontains both waxy and asphaltic materials.
Their naphthenes have moderate to long side-
chains. Has 'wax' pour point.
Hydrocarbon types
The various hydrocarbon types are classified as follows:

Viscosity index (a) Chemically saturated (i.e. no doubie valence
bonds) straight and branched chain. (Paraffins
Lubricating oils are also commonly classified by their or alkanes.)
change in kinematic viscosity with temperature, i.e. by (b) Saturated 5- and 6-membered rings with attached
their kinematic viscosity index or KVI. Formerly, KVIs side-chains of various lengths up to 20 carbon
ranged between 0 and 100 only, the higher figures repre- atoms long. (Naphthenes.)
senting lower degrees of viscosity change with temperature, (E) As (b) but also containing 1,2 or more 6-membered
but nowadays oils may be obtained with KVIs outside unsaturated ring groups, i.e. containing double
these limits. They are generally grouped into high, medium valence bonds, e.g. mono-aromatics, di-aromatics,
and low, as in Table 2.1. polynuclear aromatics, respectively.
A typical paraffinic lubricating oil may have these
hydrocarbon types in the proportions given in Table 2.2.
Table 2,9 Classification by viscosity index

Kinematic uiscosity
Group index
Low viscosity index (LVI) Below 35 Table 2.1 Hydrocarbon types in Venezuelan 95
VI solvent extracted and dewaxed distillate
Medium viscosity index (MVI) 35-80
Hydrocarbon types yo Volume
High viscosity index (HVI) 80-1 10
~ Saturates Paraffins 15
Very high viscosity index (VHVI) Over 110 (KVI = 105) Naphthenes 60
Mono-aromatics 18
It should be noted, however, that in Table 2.5 viscosity Aromatics Di-aromatics 6
index has been determined from dynamic viscosities by Poly-aromatics 1
the method of Roelands, Blok and Vlugter,' since this is
a more fundamental system and allows truer comparison
between mineral oils. Except for low viscosity oils, when The VI of the saturates has a predominant influence
DVIs are higher than KVIs, there is little difference on the VI of the oil. In paraffinic oils the VI of the saturates
between KVI and DVI for mineral oils. may be 105-120 and 60-80 in naphthenic oils.

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