Page 305 - The Tribology Handbook

c2 Mineral oils

Structural group analyses
This is a useful way of accurately characterising mineral atoms in aromatic groups (%eA), in naphthenic groups
in
oils and of obtaining a general picture of their structure (% CN), paraffinic groups (% Cp), and the total number
which is particularly relevant to physical properties, e.g. (RT) of naphthenic and aromatic rings (RN and RA)
increase of viscosity with pressure. From certain other joined together. Table 2.3 presents examples on a number
physical properties the statistical distribution of carbon of typical oils.
Table 2.3 Typical structural group analyses (courtesy: Institution of Mechanical Engineers)
Spec@
grauip Viscosip Mean % % %
Oil pppc at 15~6°C Ns/m2 molecular cA cN cP RA RN RT
at 100°C weighf
LVI spindle oil 0.926 0.0027 280 22 32 46 0.8 1.4 2.2
~~~~ ~ ~~
LVI heavy machine oil 0.943 0.0074 370 23 26 51 1.1 1.6 2.7
MVI light machine oil 0.882 0.0039 385 4 37 59 0.2 2.1 2.3
MVI heavy machine oil 0.910 0.0075 440 8 37 54 0.4 2.7 3.1
HVI light machine oil 0.871 0.0043 405 6 26 68 0.3 1.4 1.7
HVI heavy machine oil 0.883 0.0091 520 7 23 70 0.4 1.8 2.2
~~
HVI cylinder oil 0.899 0.0268 685
Medicinal white oil 0.890 0.0065 445 0 42 58 0 2.8 2.8

R EFl Nl NG
Distillation Refining processes
Lubricants are produced from crude petroleum by dis-
tillation according to the outline scheme given in Figure 2.1. Table 2.4 Refining processes (courtesy:
Institution of Mechanical Engineers)

Proccss Purpose
De-waxing Removes waxy materials from paraf-
finic and mixed-base oils to prevent
DISTILLATE {GASOLINE] early solidification when the oil is
-(KEROSINE I cooled to low temperatures, i.e. to
reduce pour point
De-asphal ting Removes asphaltic matter, particu-
lady from mixed-base short residues,
I OR LONG RESIDUE
which would separate out at hig5
and low temperatures and block
oil-ways
Solvent extraction Removes more highly aromatic mat-
erials, chiefly the polyaromatics,
in order to improve oxidation
stability
BASE OILS)
Figure 2.1 (courtesy: Institution of Mechanical Hydrotreating Reduces sulphur content, and accord-
Engineers) ing to severity, reduces aromatic
content by conversion to naphthenes
The second distillation is carried out under vacuum
to avoid subjecting the oil to temperatures over about Acid treatment Now mainly used as additional to
370°C, which would rapidly crack the oil. other treatments to produce special
The vacuum residues of naphthenic crudes are bitu- qualities such as transformer oils,
mens. These are not usually classified as lubricants but white oils and medicinal oils
are used as such on some plain bearings subject to high Earth treatment Mainly to obtain rapid separation of
temperatures and as blending components in oils and oil from water, i.e. good demulsi-
greases to form very viscous lubricants for open gears, bility
etc.
c2.2