Page 309 - The Tribology Handbook

Mineral oils 62

Thermal properties

Table 25 Typical physical properties of highly refined mineral oils (courtesy: institution
of Mechanical Engineers)

Naphthenic oils Parajinic oils
Light Heavy Light Heauy
machine machine machine machine cy1inde'
Density (kg/m3) at 25°C 862 880 897 862 875 89 1
Viscositv (rnNs/mZ) at 30°C 18.6 45.0 171 42.0 153 810
60°C 6.3 12.0 31 13.5 34 135
100°C 2.4 3.9 7.5 4.3 9.1 27
Dynamic viscosity index 92 68 38 109 96 96
Kinematic viscositv index 45 45 43 98 95 95
Pour point, "G - 43 -40 - 29 -9 -9 -9
Pressure-viscosity coefficient (,mZ/N x lo8) at 30°C 2.1 2.6 2.8 2.2 2.4 3.4
60°C 1.6 2.0 2.3 I .9 2.1 2.8
100°C 1.3 1.6 1 .a 1.4 1.6 2.2
Isentropic secant bulk modulus at 35 MN/mz and 30°C - - - 198 206 -
60°C - - - 172 177 -
100°C - - - 141 149 -
Thermal capacity (J/kg "C) at 30°C 1880 1860 1850 I960 1910 1880
60°C 1990 1960 1910 2020 2010 1990
100°C 2120 2100 2080 2170 2150 2120
Thermal conductivity (Wm/m2 "C) at 30°C 0.132 0.130 0.128 0.133 0.131 0.128
60°C 0.131 0.128 0.126 0.131 0.129 0.126
100°C 0.127 0.125 0.123 0.127 0.126 0.123
Temperature ("C) for vapour pressure of 0.001 mmHg 35 60 95 95 110 125
Flash point, open, "C 163 175 210 227 257 300
D ETE R IO RATIO N Factors influencing oxidation
Lubricating oils can become unfit for further service by: Temperature Rate doubles for every 8-10°C temperature
oxidation, thermal decomposition, and contamination. rise.
Oxygen access Degree of agitation of the oil with air.
Oxidation Cutalysb Particularly iron and copper in finely
divided or soluble form.
Mineral oils are very stable relative to fatty oils and pure
hydrocarbons. This stability is ascribed to the combination TOP-@ rate Replenishment of inhibition (natural or
of saturated and unsaturated hydrocarbons and to certain added).
of the hydrocarbon derivatives, Le. compounds containing Oil ope Proportions and type of aromatics and
oxygen, nitrogen and sulphur atoms-the so-called 'natural especially on the compounds containing
inhibitors'. nitrogen, oxygen, sulphur.
Table 2.6 Effects of oxidation and methods of test

Type5 of product produced oxidation Factors involved Methods gtest
Organic acids,which are liable to corrode The relative proportions of the various Total acid number or neutralisation value,
cadmium, lead and zinc and thereby to types of products depend on the condi- which assesses the Concentration of
-
uromoee the formation of emulsions tions of oxidation and the type of oil organic acids, and is therefore an in-
..
Lightly polymerised materials which in- The degree of oxidation which can be dication of the concentration of the
is
crease the viscosity of the oil tolerated depends on the lubrication usually materials, more the deleterious convenient polymerised and
Moderately polymerised materials which System: more can be tolerated in simple precise test to carry out. Limits vary
become insoluble in the oil, especially easily cleaned bath systems without between 0.2 mg KOH/g and 4.0 or
-
when cold. When dispersed these also sensitive metals, less in complex circu- __--_
mnre
promote emulsification and increase of lation systems
viscosity. When settled out they clog With many additive oils proof of the con-
filter screens and block oil-ways tinued effective presence of the neces-
Highly polymerised coke-like materials sary additives, e.g. anti-oxidant, is
formed locally on very hot surfaces more important
where they may remain
C2.5