LUBRICANTS Flashcards
1
Q
Lubricants
A
Substances which are used to reduce the friction and deformities between two moving/sliding surfaces.
2
Q
Function of a lubricant
A
1) Reduce friction
2)As a coolant
3)Reduce wear and tear
4)As a sealing material
5)Prevent corrosion
6)Transmit fluid power
7)Improve efficiency of a machine
3
Q
Types of Liquid lubricants
A
Animal Oil
Vegetable Oil
Mineral Oil
Blended Oil
4
Q
Animal Oil
A
Extracted from animal bodies.
Ex: bone oil, cod-liver oil, lard oil
5
Q
Vegetable oil
A
Extracted from plants
Ex: Coconut, sunflower, mustard oil
6
Q
Mineral Oil
A
Extracted from earth
Ex: Petrol, diesel, crude oil
7
Q
Blended Oil
A
Mixed according to requirements
8
Q
Types of Blended Oil
A
1) Lubricant protective additives (LPA)
2)Surface Protective Additives (SPA)
3)Performance Additives
9
Q
Types of LPA
A
Antioxidants
Metal deactivator
Anti-foamants
10
Q
Antioxidants
A
Retards oxidative decomposition
Ex: Aromatic Amines, Hindered Phenol
11
Q
Metal Deactivators
A
Decreases catalytic activity on Oxidation rate
Ex: Amines, Sulphide, Phosphides
12
Q
Anti-foamants
A
Prevent persistent foam formation
Ex: Silicon Polymers
13
Q
Types of SPA
A
Rust and corrosion inhibitors
Anti-wear agents
Friction modifiers
Detergents
Dispersants
14
Q
Rust and corrosion inhibitors
A
Prevents rusting and corrosion of metal parts in contact with the lubricant
Ex: Metal Phenol, Fatty acid, Amines
15
Q
Friction modifier
A
It changes the coefficient of friction
Ex: Organic fatty acids, Amines, Phosphoric acids, ester, etc..
16
Q
Anti wear agent
A
Reduces wear and tear
Ex: zinc dithiophosphate, organic phosphates
17
Q
Detergents
A
Keep surface deposit free
Ex: magnesium phenolates, phosphates , etc.
18
Q
Dispersants
A
Keep the lubricant’s insoluble contaminants dispersed in the liquid
Ex: thiophosphates, alkylsuccinimides
19
Q
Types of performance additives
A
Viscosity modifier
Pour point depressants
20
Q
Viscosity modifier
A
Reduces the rate of viscosity change in temperatures
Ex: Polymers and copolymers of oletins, alkylated styrenes, etc
21
Q
Pour point depressant
A
Enables lubricants to flow at low temperatures
Ex: polymethacrylates, phenolic polymers
22
Q
Semi solid Lubricants
A
AKA grease
made from petroleum products
23
Q
Types of Grease
A
Cap grease
Soda based grease
Lithium based grease
Axle based grease
24
Q
Cap grease
A
Petroleum product + Calcium soap of fatty acid + water
25
Conditions of Cap grease
under 80 degree Celsius
26
Calcium soap of fatty acid
Oleic acid or stearic acid
27
Soda based grease
petroleum product + sodium soap of fatty acid+ water
28
Conditions of Soda grease
under 175 degree celsius
29
Lithium based grease
petroleum product+ lithium soap of fatty acid + water
30
Conditions of lithium grease
under 15 degree Celsius
31
problem with Lithium grease
Costly
32
Axle based grease
Petroleum product + slaked lime + water + rosin oil
33
Conditions of Axle grease
under 160 degree celsius
34
Solid lubricant
Graphite, molybdenum disulphite
35
Emultion Lubricant
emulsion is a mixture of at least 1 immiscible liquid dispersed in another liquid in form of droplets whose diameter exceeds 0.1 µm.
Used in metal working and cutting
36
Synthetic Lubricants
Manufactured in chemical plants or refineries to produce tailor made products that can lubricate like conventional lubricants but at severe conditions
37
Characteristics of a good lubricant
High BP
Low FP
Adequate viscosity
High resistance to heat and corrosion
non-corrosive properties
stability to decomposition
38
problem with vegetable oil and animal oil
Costly
less resistant to oxidation
thicken in air
hydrolyze easily
39
How to increase oiliness of mineral oil
Adding oleic acid and stearic acid
40
Dewaxing
removal of wax from an oil otherwise wax raises the pour point and makes lubricant unfit at low temperatures
41
Additives
Material that imparts new or desired properties to the lubricating oil
42
Application of Grease
1)In rail axle boxes
2)in bearing and gears that work at high temperatures
3)in machines where dripping of oil is undesirable
4)in situations where bearing needs to be sealed against entry of dust, grit or moisture.
43
Flash point
Temperature of lubricant oil at which vapours of any lubricant catch fire
44
Fire Point
If vapours of lubricant brun for more than 5 sec at a certain temperature then that temperature is called fire point.
45
Lubrication
process or technique applied to reduce friction and wear between 2 relatively sliding or moving surfaces by interposing a lubricant between the surfaces to carry or to help carry the load
46
Tribology
Science of friction,lubrication and wear
47
Mechanisms of Lubrication
Hydrodynamic or fluid film lubrication
Boundary lubrication or thin film lubrication
extreme pressure lubrication
48
difference btw mechanisms of lubrication
Book pg no 111
49
Acid refining of mineral oils
Treatment with conc.H2SO4 so that asphaltic and naphthenic impurities and other undesirable constituents can be eliminated from dewaxed oil
50
Chemically active additives
those which chemically react with the metals and with polar oxidation and degradation products.
51
Chemically inert additives
those which improve the physical properties that are critical to the effective performance of the lubricant
52
Non newtonian lubricant
grease
53
Grease with water
fiber structure of thickener is adversely affected by water and the grease undergoes degradation
54
Consistency value or yield value
distance in tenths of a millimeter that a standard cone penetrates vertically into the sample of grease under the standard conditions of load(150gm), temperature (25C) and time (5s)
55
Factors affecting consistency of grease
1) structure and interactions of the gelling elements in it
2)viscosity of oil used in preparation of the grease
56
Determination of consistency of grease
penetrometer
57
Drop point
temperature at which grease passes from semi-solid state to liquid state
58
significance of drop point
it determines the upper limit of temperature upto which the grease can function with a satisfactory lubricant
59
Properties of graphite
low coefficient of friction
non-inflammable
not oxidized in air
60
aquadag
graphite dispersed in water
61
oildag
graphite dispersed in oil
62
graphite acts as lubricant on moon
cause temperature ranges from 110C in day to -150C in night
absence of air
63
Characteristics of synthetic lubricants
1) thermal stability at high temp
2)chemical stability in corrosive environment
3) high viscosity index
4)low freezing point
5) non-inflammability and high flash point
64
advantages of mineral oil and synthetic oil
easily dissipate heat
easy to refill and drain
greater range of operating speeds and temperatures
65
limitations of mineral oil and synthetic oil
poor sealing abilities
more maintenance
leak proof design required
66
advantages of grease
better sealing abilities
easily retained as it is non-newtonian
no need for leak proof design
less maintenance
67
limitation of grease
More energy demanding due to higher coefficients of friction
ineffective dissipation of heat
on storage grease seperates into soap and oil
68
advantages of soild lubricants
lubrication for lifetime
reduce fretting caused by vibration
they solve lubrication problem caused by abrasive contamination
69
limitations of solid lubricants
do not dissipate heat
wear life is less than oil lubricant
70
viscosity
property of a fluid that determines its resistance to flow
71
temperature and viscosity
inversely proportional to temperature
72
pressure and viscosity
proportional to pressure
73
significance of viscosity
in lubrication that lubricant is selected which should have a sufficient high viscosity to adhere to the bearing and resist being squeezed out due to high pressure and get fluid enough to resist excessive friction due to the shearing of oil itself
74
Redwood viscometer
book pg 127
75
Viscosity index
rate at which viscosity of an oil changes with temperature is measured by an empirical number known as viscosity index. a relatively small change in viscosity with temperature is denoted by a high viscosity index
76
pennsylvanian oil
it consists mainly of paraffins and are assigned a VI of 100 due to relatively small change in their viscosity with temperature
77
gulf oil
it consists mainly of alicyclics and are assigned a VI of 0 due to a large change in their viscosity with temperature
78
Formula for viscosity
V.I.=[ (L-U) / (L-H) ] * 100
79
VI and molecular structure of oil
a high VI is exhibited by those oils which have a linear or rod like shaped molecules of higher molecular weights
80
VI in terms of Viscosity temperature curve
numerical expression of average slope of viscosity temperature curve of a lubricating oil between 100 F and 210 F.
81
significance of flash and fire point
used to indicate fire hazards and evaporation losses under high temperature operations
82
factors affecting flash and fire point
moisture
low molecular weight
contamination with organic compounds
experimental factors
83
Cloud and pour points
temperature at which solidified compounds like paraffin wax present in the oil begin to crystallize or seperate from solution when the oil is cooled under specified conditions
84
significance of cloud and pour point
it indicates the suitability of lubricants in cold conditions. lubricants used in a machine working at low temperature should possess low pour-point otherwise solidification of lubricant will cause jamming of the machine
85
aniline point
minimum equilibrium solution temperature for equal volume of aniline and oil sample
86
significance of aniline point
lower aniline point means higher percentage of aromatic hydrocarbons which means more chances of deterioration of an oil when it comes in contact with rubber sealings etc
87
emulsification
property by virtue of which an oil gets mixed with water to form on emulsion
88
demulsibility
ability of lubricating oil to seperate from water
89
steam emulsion number (SEN) or demulsification number
time in second in which oil and water emulsion separate out in distinct layers . faster they seperate lower the SEN
90
importance of SEN
to avoid corrosion of polished steel surfaces like roll necks and to ensure proper lubrication
91
Saponification number
the number of milligrams of potassium hydroxide required to saponify the fatty material present in one gram of the oil
92
significance of saponification number
helps in calculating
1)avg molecular weight of oil or fat
2)avg length of carbon chain of fatty acid components
3)estimate of non-fatty impurities in oil
4)amount of alkali required for conversion of triglyceride to stop
93
carbon residue
lubricating oils contain high percentage of carbon in combined form. On being subjected to high temperature they decompose and form a carbonaceous deposit
94
Total acid number (TAN)
the number of milligrams of potassium hydroxide needed to neutralize any acid in one gram of oil
95
Total base number (TBN)
number of milligram of hydrochloric acid needed to neutralize any base in one gram of oil
96
significance of TAN and TBN
it shows relative changes in an oil due to oxidation. comparing TAN or TBN values of a new oil will indicate the development of harmful products or the affect of additive depletion.
