Cutting Fluids Everything flows and nothing pdf

8

Cutting Fluids
‘Everything ows and nothing abides.’

(540 – 480 BC)
[An early Metaphysician from Ephesus (Asia Minor), in: On Nature]
8.1 Historical Development
of Cutting Fluids
General speaking, metalworking mass production
techniques can be traced back to the 16
th
century, but
it was really not until the late 18
th
century that engi-
neers in the industrialised countries paid close atten
-
tion to increasing production, due to the vast rise in
their populations and signicant industrial growth. In
Europe at that time, two countries where important
areas of applied machining and uid research were
being pursued was: in France, where the machining
of metals was being investigated and developed into
a science – specically in terms of the eects of tool
feeding and lubrication and its aect on surface nish;
also in the mid-19
th
century in England, where the ef-
fects of water as a coolant to enhance tool performance
was also studied. us, as these research activities pro

-
gressed, complementary advances were taking place
into the study of tool materials their heat treatment
and in particular, tool hardening techniques. As has
happened on many occasions in the past, considerable
advances took place as a result of the enormous de
-
mands for armament manufacturers and their produc
-
tion needs during times of war, signicantly adding
advancements and renements to the: machine tools;
tooling; as well as for lubricants. As these research
programmes developed, it soon became clear that for
cutting uids, while water may have had the optimum
specic heat capacity of all available uids, it brought
real problems due to corrosion of the machined com
-
ponents and to the exposed surfaces of machine tools.
Frequently, such related losses far outweighed the ben
-
ets of increased production throughput and the im
-
provement in tool life that it imparted to the overall
manufacturing process. A simple solution was at hand
in the form of corrosion inhibition, via the use of:
animal oils; fatty acids; soda; which when combined
with water to form a ‘soap’ , oered an improvement
in product protection against rusting, while eectively
retaining the overall cooling properties of water.
In particular in the North of England during the

mid-19
th
century, notably around Manchester and the
Hudderseld areas – where the world’s major cotton
and woollen industries were now in full production.
ese areas, had for centuries used the benets of
‘so-water’ , which unfortunately had a tendency for
the coolant solutions to generate large quantities of
foam, hence the term ‘suds’ which is sometimes used
to the present day, although this name is hardly rele
-
vant to modern-day cutting uids. Almost by accident
and as an incidental benet of these ‘soap solutions’ ,
they were found to impart improved lubricating prop
-
erties between the tool and the component, through a
‘machining mechanics’ and ‘chemical relationship’ that
was at the time, not fully comprehended.
In the meantime, mineral oil: which had advanced
from being simply thought of and used as just an ali
-
phatic additive to vegetable oil, to that of becoming
recognised as a useful lubricant, which was at the time
currently and widely available. is mineral oil was de
-
monstrably shown at the time, to oer improvements
to both the machined surface nish quality and en
-
hancing the tool’s lubrication. At the beginning of the
20

th
century, experimental studies into topics such as
the initial studies into: boundary lubrication; lubricity;
plus its relative viscosity; for the newly-developing en
-
gines in the automotive industries were being rapidly
developed. Moreover, when general manufacturing
industries started the mass production of consumer
goods, the resultant quality was of prime importance
and basic water lubrication was now no longer su
-
cient. By the mid-20
th
century, the preliminary forays
into the basic development of today’s modern-day cut
-
ting uids occurred. At this juncture, it soon became
evident that it was essential to combine the properties
of several dissimilar uids to produce an early, but
‘workable’ form of cutting uid, these ‘ingredients’
were:
•
Oil – to act as a lubricant between the chip, tool
and machined workpiece,
•
Water – for cooling, to extract the heat from the
cutting process,
•
Detergent – to break down the ‘surface tension’
1

be-
tween the oil and water,
1 ‘Surface tension’ , this is oen generally dened as the: ‘Inter-
facial tension between two phases, one being a liquid, while the
other is a gas’. More specically, surface tension is a physical
force in the surface of the liquid that arises as a result of the
liquid’s atoms pulling their neighbours in all directions. While
atoms deep in the liquid have no net force applied to them,
conversely, surface atoms have no neighbours above them, as
a result they experience a net inward force from the bulk of
atoms below them. Hence, this net inward force is known as
its surface tension, with the greater the radius of curvature, the
higher the surface tension (i.e see Fig. 208a). Hence, a ‘droplet
of water’ sitting on a at surface – termed a ‘spherical cap’ has
 Chapter 
•
Sulphur – to act as an ‘extreme pressure’ (EP) ad-
ditive to reduce frictional eects at the various cut
-
ting interfaces.
NB Sulphur was soon to prove unpopular as a sat-
isfactory EP additive, as it had a tendency to stain,
or erode certain decorative machined nishes for
specic metals and alloys.
8.2 Primary Functions
of a Cutting Fluid
In the previous section, it was recognised that two of
the primary functions of a cutting uid was to cool and
lubricate both the workpiece and cutting tool’s edge. In
addition, one could add the improvement of machined

surface quality and an increase in tool life (i.e. see Fig.
193b). Further, it has been shown that a reduction in
spindle power is an added bonus to many machining
processes, which oers considerable savings when this
reduction in electrical demand is accrued per annum.
If a problem occurs where work-hardened swarf dis
-
posal from the cutting vicinity presents an obstacle
to ecient cutting, then ushing this zone with
ood
coolant, may eliminate this diculty. Eective chip re-
moval by the application of ood coolant (Fig. 194a:
showing a twist drilling operation, 194b: milling with
the periphery using a ‘porcupine cutter’), can mini
-
mise an otherwise serious problem on machining cen
-
tres where large volumes of densely-packed swarf can
impede the cutting process. Even on continuous cut
-
ting operations such as when undertaking external/in
-
a high contact angle (i.e. the angle of tangency that the spheri-
cal cap, or a bubble makes with the surface). When this angle
is considered on a ‘wetability scale’ it has a high contact angle
and as such, is not considered as ‘wet’!, due to its high curva-
ture (Fig. 208a), as indeed does a typical lubrication oil. Con-
versely, a liquid detergent does not have particularly a high
contact angle and as such, will chemically react with both the
oil and water and breaks-down this surface tension between

the concentrations of an unmixed oil and water. is loss of
surface tension between these two ‘products’ thereby produces
a basic mixture, or suspension and it then becomes somewhat
‘milky’ in appearance, thus it is oen termed a (basic) ‘emul-
sion’.
ternal turning processes, an insert’s chip-breaker will
break the swarf into convenient shapes and sizes, but
these chips may still necessitate ushing-away – being
deposited into a swarf conveyor and then onward into
an adjacent skip. Swarf removal has become of sig
-
nicant importance as material removal rates have in
-
creased with latest tooling advances and high-produc
-
tion machine tools, where they may be continually fed
wrought material allowing them to operate untended
for 24 hours per day. Possibly the most stringent test
for any cutting uid is in deep-hole drilling applica
-
tions (Fig. 58), where coolant is delivered under high-
pressure through suitable coolant holes and is forced
up to the cutting edge to not only cool the drill, but
provide lubrication and ush any swarf back and away
from the cutting vicinity. In fact, with extremely high-
pressure coolant delivery systems having pressures
>300 MPa, such as when using a through-the-nose
indexable insert short-hole drill as illustrated in Fig.
195, the advantages are: increased speeds; penetration
rates; more holes per insert edges are achievable – see

the following section for more details on this high-
pressure coolant delivery topic, with particular refer
-
ence to turning operations.
8.3 High-Pressure Jet-
Assisted Coolant Delivery
Probably the most important criteria in many metal
cutting operations is an acceptable chip control, with
respect to its: chip form; chip-ow; plus its chip-break
-
ing ability. It has been mentioned earlier in Chapter 2:
Section 2.5, that good chip control will have an aect
on: tool life, machined surface texture; cutting forces;
reliability; etc. Productivity is strongly inuenced by
poor chip control, as the machine tool must be fre
-
quently stopped to manually remove the vast quanti
-
ties of swarf present in the working area. is problem
becomes especially acute when turning smaller inter
-
nal diameters on products, since limited space soon
becomes lled and compacted with work-hardened
chips, that can damage the recently machined surfaces.
Reasonable chip control can oen be achieved by in
-
dexable inserts with an appropriate cutting geometry
that is having chip-formers, these being developed to
meet the requirements for specic machining opera
-

tions.
Cutting Fluids 
Figure 193. Heat dissipation during machining can be lessened by utilising appropriate cutting uids.
 Chapter 
Figure 194. ‘Standard-pressure’ (i.e. <40 bar) coolant supply for drilling and milling operations.
Cutting Fluids 
Trends of late, have been toward either ‘dry-’ , or
‘near-dry’ machining strategies – more will be men-
tioned on these machining applications later in the
chapter, however many modern materials cannot be
machined dry, even with the latest coated cutting in
-
serts, because of the high temperatures generated in
the cutting vicinity. Typically, alloys such as: austenitic
stainless steel; high-temperature alloys; titanium, etc.;
demand the application of appropriate cutting uids.
In industrial machining applications, the availability
of
‘high-pressure cooling’ (HPC) of cutting tools has
proven to be very eective when machining the met
-
als just mentioned, while at the same time increasing
production throughput. By utilising a high-pressure
uid jet, it is possible to signicantly decrease cut
-
ting zone temperatures, while extending tool life – in
certain instances by >200%, operating with lower cut
-
ting forces because of the improved frictional condi
-

tions between tool/chip interface, with an attendant
reduction in machining-induced vibration levels. All
of these advantages will improve the machined surface
texture and oer better and more consistent dimen
-
sional accuracy, by a reduction in component process
variability.
Figure 195. High-pressure coolant supply for high penetration rate drilling. [Courtesy of Sumitomo Electric Hardmetal Ltd.].
 Chapter 
When utilising high-pressure jet-assisted machining
at cutting uid pressures of >110 MPa with a velocity
of >122 ms
–1
, some precautions need to be considered,
prior to applying this cutting uid strategy. Caution
should be made, when using certain types of cutting
tool geometries and grades, as they may not have been
designed for this increased level of coolant delivery,
which could if
inappropriately applied, actually lower
productivity. e above mentioned eects do not only
depend on eective heat dissipation, but require the
contact length between the chip and the rake face to be
reduced. Since the application of a coolant by a high-
pressure jet, partially penetrates between the tool/chip
interface, via a ‘hydro-wedge’
2
which here is created
and, then provides hydrodynamic lubrication at this
position in the ‘friction zone’. Hence, the shorter the

contact length the lower the friction, causing a larger
shear angle, which in turn lowers the chip compres
-
sion factor (Fig. 196). is
‘hydraulic wedge’ – as a re-
sult of HPC, inuences the chip formation in several
ways, it aects both the ‘up- and side-curl’ , thus break
-
ing them into manageable pieces as well as vectoring
the chips. By aiming the HPC cutting uid jet to either
the main, or secondary cutting edges this will inu
-
ence and aect chip-curling behaviour. is chip-curl
-
ing action in turn, aects the resultant tool life, as it is
thought that a reason for this dierence in respective
tool life is due to the temperature distribution on the
rake’s face – as a result of the vectoring angle of the jet-
assisted coolant application.
8.4 Types of Cutting Fluid
Introduction
Modern cutting uids can be sub-divided into two
major classications:
‘Oil-’ , or ‘Aqueous-based’ , with
further sub-division into
‘Semi-synthetic’ , or ‘Synthetic’
uids (i.e. see Fig. 197, for a ‘family-tree’ and break-
2 ‘Hydrodynamic wedge’ , as its name implies, cannot actually
penetrate into the chip/tool interface, as the separation pres-
sures here – at the interface – are simply far too high. How-

ever, this hydrodynamic wedge acts as a sort of ‘lever’ (Fig.
196) on the emerging formation of the curling chip, changing
its contact length, which in turn, modies the shearing zone
and as a result, inuences the chip compression factor.
down of these cutting uid groupings). In most tech-
nological countries, relevant Standards for both the
chemical and technical requirements are published
concerning their: storage, usage and disposal, along
with their pertinent operator health needs. e ‘Aque
-
ous-based’ cutting uids can be divided into either:
‘emulsiable’; or ‘water-soluble’ types (Fig. 197). e
former
‘Oil-based’ cutting uids are supplied as ready-
to-use products, while the
‘Aqueous-based’ products
are normally oered in the form of a concentrate,
which must be admixed with water to the desired con
-
centration, prior to use. Once these latter products
have been mixed with water, the
‘emulsiable’ versions
form an ‘emulsion’
3
, whereas the ‘soluble’ type forms a
‘solution’
4
. In both cases, the resulting cutting uid is
termed
‘water-mixed’.

The ‘Ideal’ Cutting Fluid
Having accepted the fact that a cutting uid is a re-
quirement for the machining of many of today’s en
-
gineering materials, be they either metallic, non-me
-
tallic in composition and are necessary for various
production processes. en one must ensure that the
selected ‘uid’ achieves its intended purpose, more
-
over, that it does not create additional problems. ese
conditions imply that there are many and varied spe
-
cic characteristics that an ‘ideal’ cutting uid should
possess, such as:
•
Optimum cooling and lubrication – clearly, the
‘ideal’ cutting uid would have the most favourable
cooling and lubricating properties, to ensure para
-
mount cutting performance as measured by: pro
-
duction rate; tool life; surface texture,
3 ‘Emulsions’ , are a disperse system (consisting of several
phases), which arises through mixing of two liquids which are
not soluble in each other. Hence, one liquid forms the inner,
or disperse phase, distributed in droplet form in the carrier
liquid (the outer, or continuous phase).
NB e emulsiable metalworking uids are what is known as
‘oil-in-water’ emulsions, that is the oil forms the inner phase,

conversely, its counterpart is formed by emulsifying metal-
working uids, which are ‘water-in-oil’ emulsions. (Source:
Cincinnati Milacron/Cimcool, 1991)
4 ‘Solutions’ , are a metalworking uid solution, these are water-
soluble uids mixed with water. (Source: Cincinnati Milacron/
Cimcool, 1991)
Cutting Fluids 
Figure 196. The eect of rake angle on chip thickness – with and without coolant supply .
 Chapter 
Figure 197. The main types of cutting uids for machining operations.
Cutting Fluids 
•
Acceptability to the operator (i.e. when machine
tool is manned) – as all operators have some de
-
gree of exposure/contact with the cutting uid. Op
-
erators will consider the lubricant’s overall perfor
-
mance, but even when the uid is ‘perfect’ in every
other respect, complaints are likely if, for example,
the smell was unpleasant. e following features are
likely to be of particular interest to the operator:
–
Smell – ideally, the cutting uid should have
no perceivable odour, but if present, it certainly
should not be objectionable,
–
Colour and clarity – most operators prefer prod-
ucts which are perceived to be ‘clean and fresh’

throughout their life and, some operators prefer
dye-coloured translucent products for this rea
-
son,
–
Misting – high-speed cutting operations tend to
generate a mist. Occasionally these mists may
be associated with operator health problems:
dry-throats; stinging eyes; etc.; leading to com
-
plaints. Although misting is largely dependent
on the: machine tool; its operation; atmospheric
ventilation; etc.; dierent uids have diverse
misting characteristics and, ‘ideally’ the uid
should be non-misting – more will be said on
the operator’s health issues later in the chapter,
–
Irritation to the skin and eyes – these operator
issues have been associated with physical con
-
tact from cutting uids, such as: skin and eye
irritation; itching; rashes, swellings; stinging;
etc. Once again, uid formulations that are ‘kind
and gentle’ are preferred. As mentioned above,
more will be mentioned on these health issues
shortly,
•
Long ‘sump-life’- with all machining uids having
a
nite life, at some point, the machine’s cutting-

uid system must be completely emptied, cleaned,
ushed through and relled with new uid. ere
are numerous reasons why the cutting uid might
be regarded as ‘dead’ – these points will be raised
when investigating the ‘problems’ with cutting
uids later in the chapter. e uid’s life is an im
-
portant economic consideration in terms of: uid
usage; labour costs; down-time; etc. Some leading-
manufacturer’s cutting uid formulations are capa
-
ble of achieving signicantly better overall perfor
-
mance and have an extended ‘sump-life’ over their
cheaper contemporaries. e increased ‘sump-life’
will enable better use of a company’s maintenance
department’s manpower resources, thereby en
-
abling it to be more ecient in their anticipated
‘planned maintenance scheduling’
5
over prescribed
shut-down periods, or ‘maintenance windows’ ,
•
Corrosion protection – all cutting uids are for-
mulated to provide corrosion protection to the
machine tool and the workpiece during and, for a
short time aer the cutting operation. In the main,
these uids should preserve their corrosive-protec
-

tion properties throughout their useful life, to avoid
the potentially expensive problems of rusting of the
machine and machined components alike, the lat
-
ter being rejected by the customer. More informa
-
tion will be given on corrosion protection later in
the chapter,
•
Low foaming properties – on some of today’s ma-
chine tools, they incorporate uid systems that
agitate the cutting uid to such an extent that foam
spills out of the coolant tank and onto the oor.
e ‘ideal’ uid will withstand: swarf-washing jets;
high-pressure uid delivery; centrifuges; etc.; even
when prepared with the soest quality water sup
-
ply. e subject of foaming will be addressed spe
-
cically later in the chapter,
•
Machine tool compatibility – no self-respecting
engineer wants to see their newly purchased, or
well-maintained older machine being attacked by
its cutting uid. e optimum uid should create
no detrimental eects on the machine tool’s: paint
nishes; seal materials; screens and guarding; etc.,
•
Workpiece compatibility – means that the widest
possible range of workpiece materials should be

machined with a particular, but versatile grade of
5 ‘Planned maintenance scheduling’ , many companies adopt
either a ‘Total Productive Maintenance’ (TPM), or ‘Reliabil-
ity-centred Maintenance’ (RCM) philosophical and practical
approach to their overall maintenance organisational needs.
NB TPM is dened as: ‘A system of maintenance which cov-
ered the entire life of every piece of equipment in every division
including planning, manufacturing and maintenance. (Source:
Japan Institute of Plant Maintenance – JIPM, 1971). RCM is
dened as: ‘A process used to determine the maintenance re-
quirements of any physical asset* in its operating context’.
(Source: Moubray, 1996) Oen, companies run both a TPM
and RCM strategy together, to achieve an overall high level of
maintenance planning discrimination, coupled to plant secu-
rity – in association with individual asset reliability.
* A physical asset is any piece of operating plant, or equip-
ment that requires a maintenance function to be undertaken
upon it at some prescribed time period, or requiring various
modications to it for its operating context.
 Chapter 
cutting uid, although certain non-ferrous metals
may have a susceptibility to staining, so here, it is
prudent to discuss the problem with the cutting
uid manufacturer,
•
Water-supply compatibility – a water-soluble cut-
ting uid should ‘ideally’ be capable of being diluted
with
any water supply. Geographical locations can

create variations in water supply and its condition,
this latter factor is especially true for water hardness
(i.e see Fig. 199b), where its hardness can vary quite
considerably. us, the ‘ideal’ cutting uid would
not cause the typical problems of:
foaming in so
waters; or forming
insoluble soaps in hard waters,
•
Freedom from tacky, or gummy deposits – as water
soluble uids dry out on a machine, or component’s
surface, the water content evaporates to leave a resi
-
due which is basically the product concentrate. is
residue should ideally be light and wet, allowing
it to be easily wiped-o. However, any gummy, or
tacky deposits collect swarf and debris, necessitat
-
ing increased machine and component cleaning,
•
‘Tramp oil’ tolerance – is a lubricating, or hydraulic
oil which leaks from the machine tool and contam
-
inates the cutting uid. Most modern machines are
equipped with ‘total-loss’
6
slideway lubricating sys-
tems which can contaminate the cutting uid with
up to a litre of oil per day – on a large machine tool.
e ‘ideal’ cutting uid would be capable of toler

-
ating this contamination without any detrimental
eects on its operating performance. Some cutting
uids are formulated to emulsify the ‘tramp-oil’ ,
while other uid formulations reject it, allowing
6 ‘Total-loss’ uid systems, are as their name implies in that they
purposely leak oil to the machine’s bearing surface, requiring
periodic tank replenishment. When this oil leaks-out of the
machine tool it is termed: ‘tramp-oil’ , therefore the oil will
eventually end up in the machine tool’s coolant tank, where it
is either tolerated by the coolant product, or is separated-out,
requiring periodic ‘tramp-oil skimming’.
NB ‘Tramp-oil’ losses are invariably not accounted for in
many production shops, which invariably means their ‘eco-
nomic model’ for such losses are habitually not considered,
or not even thought about by the company. It has been re-
ported that on a quite ‘large-sized’ horizontal machining cen-
tre, it can lose up to 365 litres of ‘tramp-oil’ per annum, which
is an on-going cost that needs to be addressed. Multiply this
individual machine tool loss by the number of machines in
the manufacturing facility and this will represent considerable
unaccounted for expenditure!
the residual ‘tramp-oil’ to oat to the surface for re-
moval by physical ‘skimming’ ,
•
Cost-eectiveness – but what does this term mean?
ere was a time when the cost-eectiveness was
simply judged in terms of the price per litre of the
product concentrate. Fortunately, there are only
few engineering companies who still take this view,

with most recognising that there are many inter
-
related factors that contribute to cost-eciency.
Some of these factors might be the: dilution ratio;
sump-life; material versatility; tool life; machined
component quality; health and safety aspects; plus
many others.
Having identied the ‘ideal’ cutting uid features, one
must unfortunately face reality, as there is
no such
product that encompasses
all of these desirable charac-
teristics – at the
optimum level in just one cutting uid
product. However,
all cutting uids are not equal and
even apparently similar products may well perform in
quite dierent ways! erefore, it is for the machine-
shop supervisors/managers – in conjunction with
other interested parties: purchasing; health and safety;
unions; etc., to select a reputable supplier who is pre
-
pared to undertake the necessary survey and ‘trouble-
shooting’ exercise to recommend the best uid(s) for a
particular manufacturing environment.
Today, there are many dierent types of cutting
uids available they can be classied according to
widely varying criteria, although some unied system
of terminology exists in various countries guidelines
and Standards. is commonality of ‘language’ reects

both the chemical and technical requirements of the
users. On the basis of the various countries publicised
cutting uid literature, the following classication
is perhaps the most useful – from the user’s point of
view. Broadly speaking, it was previously shown in Fig.
197, that cutting uid groups are of two main types,
either
‘oil-’ , or ‘aqueous-based’. e ‘aqueous’ cutting
uids can be divided into
‘emulsiable’ and ‘water-sol-
uble’ types. As has already been mentioned, the former
‘oil-based’ cutting uids are supplied as ready-for-use
products, while ‘aqueous’ types are normally found in
the form of a concentrate, which must be mixed with
water, prior to use. Once mixed with water, the
‘emulsi-
able’ cutting uids form an emulsion, conversely, the
‘soluble’ variety forms a solution. In both of these cases,
the resultant cutting uid product is termed:
‘water-
mixed’. In the following section, the various types of
cutting uids currently available will be briey men
-
tioned.
Cutting Fluids 
.. Mineral Oil, Synthetic,
or Semi-Synthetic Lubricant?
Mineral Oil
In order to manufacture cutting uids the raw materi-
als are naturally occurring oils, such as: mineral oils;

animal and vegetable oils; or fats. Of these oils, the for
-
mer mineral oils are probably most commonly utilised
by the manufacturing industry. ese mineral oils, in
a similar fashion to naturally occurring oils, tend to
be complex mixtures of widely varying compounds.
Such
compounds consist of carbon and hydrogen and as
such, are usually referred to a
‘hydrocarbons’. In addi-
tion, they will contain: sulphur; nitrogen; plus various
trace elements.
So that the
mineral oil can be separated out to form
a
‘stock oil’ – with natural lubricating properties, ther-
mal processes are employed by the uid manufacturer.
ese partly-rened ‘stock-oils’ are still chemically
complex mixtures of hydrocarbons, with widely vary
-
ing characteristics. By way of an example of the di
-
verse nature of ‘crude oil’ , it is a mixture of more than
one thousand hydrocarbons, with dierent chemical
structures. Such widely varying characteristics make
it impossible to supply mineral oil to closely dened
specications, which limits its uses and performance
as a cutting uid. e complex structure of a cutting
uid made up entirely from naturally occurring oils, is
schematically illustrated in Fig. 198a.

Synthetic Lubricants
e use of Synthetic lubricants cannot be compared
with those lubricants that are extracted from natu
-
rally occurring oils, since the properties of the latter
are always an aggregate of the properties of their many
dierent components, as such, cannot be exactly pre
-
dicted. While the former synthetic lubricants are made
from two types of raw material:
1. Mineral oil – normally from: polyalpha olen and
alkali aromatics,
2. Polybutenes.
At present (i.e. from around the late 1980’s, until
now), synthetic hydrocarbons predominate, as they
are not derived from mineral oils, they have become
of increased importance. In particular, they include
derivatives from
‘fractioning’
7
of plant oils. e most
signicant classes of
compounds are the esters and
polyglycols. ese synthetic lubricants being a solution
of chemicals, which usually contain: corrosion inhibi
-
tors; biocides; dyes; in water. Moreover, they may con
-
tain such additions as synthetic lubricity additives and
wetting agents.

Synthetic lubricants form transparent
solutions and as a result, provide good visibility of the
cutting operation.
In use, synthetic uids require special attention in
their application, because they contain no mineral oil,
they tend not to leave a corrosion-protective oily lm
on machine surfaces. As a result, it is essential to lubri
-
cate exposed machine tool surfaces carefully. In addi
-
tion to this lack of protection, there may be some eect
on certain paint nishes and even degradation of the
machine’s seals, as a result of this synthetic uid enter
-
ing the machine tool’s lubrication system. Normally,
these problems of practical usage, limit these synthetic
lubricants in the main, to grinding operations.
Semi-Synthetic Lubricants
Today, the use of Semi-synthetic lubricants, or ‘Micro-
emulsions’ – as they are sometimes known, has become
much more widespread, because of certain advantages
they have over mineral-soluble oils.
By increasing the ratio of: emulsier-to-oil in the
formulation, either by reducing the oil content, or
by increasing the level of emulsiers, the product
takes on dierent characteristics from those of min
-
eral-soluble oils. Due to this increased ‘ratio’ , the oil
particles formed, are signicantly smaller than those
found with the mineral-soluble oil types (i.e. see Fig.

201a). Hence, these
‘micro-emulsions’ , visually appear
to be
translucent, or even transparent, owing to the fact
that the
oil particles are smaller than the wavelength of
light (i.e. <0.5 µm). is translucency is an obvious ad-
vantage where workpiece visibility is important to the
machine setter/operator. In addition, the high level of
emulsiers in the product leaves some ‘spare capacity’ ,
which enables the ‘micro-emulsion’ to emulsify any
oil-leakage from the machine. is emulsication of
7 ‘Fractionation’ , is the breakdown of crude oil into its constit-
uents (i.e. fractions), by distillation.
 Chapter 
Figure 198. The basic structure of an oil-based cutting uid and an ‘oil-in-water’ emulsifying molecule. [Courtesy of
Cimcool]
.
Cutting Fluids 
Figure 199. The principle of polar and passivating corrosion protection and the minimum requirements for water
quality. [Courtesy of Cimcool]
.
 Chapter 
the oil
8
, keeps the machine tool cleaner and will delay
the formation of a layer of ‘tramp-oil’ on the surface –
which might otherwise encourage unwanted bacterial
growth. e
denition of Semi-synthetic cutting uids

9

can cause some diculty, but generally the oil content
is
much lower than with the mineral-soluble oils, rang-
ing from approximately 10 to 40%.
Additives for: corrosion inhibition; bacterial con
-
trol; lubricity
10
; EP; are employed in the same manner
as for mineral-soluble oils, also, there is oen an addi
-
tion of a blue, or pink dye, as these translucent micro-
emulsions can appear to look somewhat ‘watery’ oth
-
erwise. Although translucent micro-emulsions are
initially formed,
Semi-synthetics do not go cloudy in
use. ey contain excess emulsiers to ensure that ne
micro-emulsion of oil particles are formed in water. As
previously mentioned, these ‘spare’ emulsiers enable
the micro-emulsion to absorb tramp oil. Hence, as
these ‘spare’ emulsiers are consumed by suspending
the ‘tramp-oil’ , both the amount of oil in the emulsion
and the oil particle size increases. is
increase in oil
particle size causes more incident light to be reected
and results in the visual
‘clouding eect’ within the lu-

bricant. In particular, this ‘cloudiness’ of the lubricant
is not necessarily an indication that there is anything
wrong with the uid, it is merely an suggestion of the
oil absorbed by the cutting uid.
All cutting uids, whether ‘aqueous-’ , or ‘oil-based’ ,
may contain some: mineral oils; synthetic products; or
a combination of both. e choice of raw material and
composition depends on certain parameters and their
actual composition (i.e its formulation) will depend
8 ‘Emulsication of tramp-oil’ when using Semi-synthetic oils,
will only occur, until all of the ‘spare’ emulsiers are used up!
erefore, aer this time, the excess ‘tramp-oil’ will oat on
the cutting uid’s surface.
NB Some Semi-synthetic formulations will emulsify only
small quantities of ‘tramp-oil’ , while others can emulsify
much larger concentrations.
9 Perhaps the easiest and best uid denition is this: ‘A semi-
synthetic cutting uid forms a translucent emulsion and con-
tains mineral oil’.
10
‘Lubricity’ , or ‘Oiliness’ as it is oen known, is dicult to de-
ne with any precision. One reasonable denition is that Lu-
bricity is: ‘[e signicant] dierences in friction greater than
can be accounted for on the basis of viscosity, when comparing
dierent lubricants under identical test conditions.’ [Source:
American Society of Automotive Engineers]
upon many factors, which is closely-guarded secret by
any lubricant manufacturer.
.. Aqueous-Based Cutting Fluids
A large proportion of cutting uids used for machin-

ing operations are still of the aqueous-based types (Fig.
197), as they combine the excellent heat-absorbing ca
-
pacity of water, with the lubricating power of chemical
substances. Such cutting uids oer excellent cooling,
lubricating and wetting properties. Machine tools re
-
quire protection from the lubricant ingress and should
be compatible with lubricating and hydraulic systems
on the machine, making it possible to apply water-
mixed cutting uids to the manufacturing environ-
ment. e aqueous-based lubricants can be utilised
across quite a diverse range of workpiece materials,
ranging from steels, to non-ferrous metals.
An aqueous cutting uid can consist of naturally
occurring oils such as: mineral oil; synthetic mater-
ial; or a combination of both, but generally they are
present in the form of an emulsion, or solution – as
previously discussed. Other forms of cutting uids,
such as: suspensions; gels; pastes; are rarely used in
the production process. Hence, the commonest form
in which aqueous cutting uids are used is as an emul
-
sion. Much of this cutting uid terminology has al
-
ready been discussed, but is worth restating, to ensure
that its signicance is suciently comprehended. An
emulsion is a disperse system formed by mixing two
uids which are not soluble in each other. In the emul
-

sion, one of the uids forms the internal phase, which
is dispersed in the form of droplets suspended in the
external phase, or ‘medium’ – as its is oen known.
Such corresponding cutting uids are of two types:
‘emulsive’ , or ‘emulsiable’ – of which the former type
is normally the most commonly used. e ‘emulsive’
cutting uid consists of an oil-in-water emulsion, in
which the oil forms the internal phase. While its coun
-
terpart, the ‘emulsive’ type is the ‘emulsiable’ solu
-
tion, consisting of a water-in-oil emulsion, but here,
the water is the internal phase – lately this cutting uid
has become less important.
An aqueous ‘emulsive’ cutting uid always contains
a stock oil, usually having a: mineral oil; synthetic
hydrocarbon; synthetic ester; or fatty oil, etc.; together
with certain additives to the formulation. e most
important additives tend to be: ‘emulsiers’; corro
-
sion inhibitors; stabilisers and solubilisers; anti-foam
Cutting Fluids 
agents; micro biocides; as well as complex formers (i.e.
see Fig. 197). Consideration will now be given to each
of these ‘additives’ in turn:
‘Emulsifiers’
e ‘emulsiers’ are necessary to help form a stable
emulsion and as such, are very important for the tech
-
nical characteristics of the cutting uid. ‘Emulsiers’

make it possible for the oil droplets to form and re
-
main suspended in water, preventing them from merg
-
ing and oating upwards to form a surface layer in the
uid’s tank.
‘Emulsiers’ reduce the surface tension and
form a lubricating
lm at the boundary surface. ese
‘emulsier’ molecules are bipolar in characteristic and
as a result ‘line-up’ like the bristles on a brush, with
one end toward the oil and the other end facing the
water, as shown in Fig. 198b. In this way, the ‘emulsi
-
er’ forms a lm which is one molecule thick at the
boundary surface.
Corrosion Inhibitors
e main task of a corrosion inhibitor in any aqueous
cutting uid is to prevent the water in the uid from
corroding the exposed portions of the machine tool,
such as its: slideways; spindle nose; ballscrews; etc. e
mechanism by which dierent corrosion inhibitors
operate, will vary widely and one commonly used ver
-
sion of ‘inhibitor’ , consists of an additive which forms
a protective lm on the exposed metal’s surface
11
.
11 ‘Galvanic corrosion’ , for two metals in contact in the ‘electro-
chemical series’ the further apart they are in this ‘series’ , the

greater their electro-potential and the faster the rate of corro-
sion. For example, in this ‘series’ gold (i.e. being a ‘noble metal’)
is at one extreme, thus having a potential dierence of +1.70
v – being cathodic, while at the other end of the galvanic table,
calcium (i.e. being a ‘base metal’) has a potential dierence
of –2.87 v – being anodic. Hence, the anodic metal will cor-
rode, while the cathode remains unchanged, hence in gold’s
case, the term ‘noble’ metal is used.us, water-miscible u-
ids can penetrate between bolt threads, setscrews and xtures
and as water is an electrolyte – a liquid that can conduct an
electrical current, the presence of water produces a galvanic
electrical current ow between these mating parts. So, say on
a lightweight workpiece xture – perhaps made from alumin-
ium (–1.67 v) with this being located onto a machine tool’s
table – normally produced from cast iron (–0.44 v). us, the
potential dierence here being 1.23 v, which is not too acute,
as both these metals are in fact, relatively close-together in the
‘electro-chemical series’.
ese corrosion inhibitors consist of long, narrow
molecules which are negatively-charged and as such,
are attached to the metal in contact (Fig. 199a – top
schematic diagram, shows:
rust protection by polari-
sation, whereas the lower schematic diagram depicts;
rust protection by a passifying lm). ese ‘lms’ that
are subsequently formed, are no thicker than just a
few molecules and as such, are invisible. Nevertheless,
such ‘lms’ can eectively prevent the electro-chemi
-
cal process of corrosion, such as passivation by means

of nitride, but the latter type is now being eectively
phased-out.
Stabilisers and Solubilisers
Stabilisers considerably extend the life of the concen-
trate, while solubilisers act to increase the oil’s solubil-
ity. Various alcohols and glycols can be used as stabi-
lisers, or solubilisers.
Anti-Foaming Agents
Anti-foaming agents are oen known by the alter-
native names of: ‘anti-froth-’; or ‘defrothing-agents’;
being utilised to prevent the formation of foam. Sili
-
cones, while being subject to certain restrictions have
proved in the past to be very popular anti-foaming
agents. A typical restriction to that of using silicones
additives in machining operations, might be because
aerward it may prove dicult to either: paint; coat;
or adhesively-bond to the machined parts. In the
past when both the coolant pressures and ow rates
were low, foaming did not present too great a prob
-
lem, but nowadays, the pressures and ow rates are
much greater and severe coolant agigtation can re
-
sult, creating potential foaming conditions. Foaming
is at its most prevalent when a newly-charged clean
and fresh cutting uid is employed and as this coolant
is contaminated with: ‘tramp-oil’; metal nes; abra
-
sive grains; from the subsequent machining process,

these contaminants will tend to suppress foaming
tendencies.
NB Galvanic corrosion occurs between contact of dissimilar
metals – in the presence of an electrolyte. is electrolytic con-
tact might at the least cause either: surface staining; mild corro-
sion; or pitting, with its severity depending upon how long the
two metallic surfaces are in contact in the presence of water.
 Chapter 
Today, anti-foaming agents tend to be ‘branch-
chained’ higher alcohols – being insoluble in wa
-
ter, or as mentioned above, silicones. Both alcohols
and silicones evidently disrupt the foam-producing
surface lm with that of an alternative gas-perme
-
able surface lm, causing the surface-active liquid
surrounding each bubble to drain away, causing the
foam layer to collapse. If severe foaming occurs, anti-
foaming agents are not the answer, as eventually these
‘anti-foams’ get carried away, or ltered-out of the
coolant on the resultant machined: chips and swarf;
workpieces; or on coolant lters. e problem to
foaming may
not be due to the lack of ‘anti-foams’ ,
but may be the result of air leaks that are sucking air
into the coolant stream. ese air leaks oen arise
around the pipe unions, or at pipe-connectors to
either the valves and pumps in the coolant delivery
system.
Microbiocides

Microbiocides are oen added to the aqueous-based
cutting uid as they help prevent the dramatic and un
-
controlled growth of microbes in the coolant. Micro-
biocides uses are normally limited, owing to the po
-
tential skin-care consideration – more will be said
concerning this very important topic later in the chap
-
ter, when ‘health-issues’ will be discussed.
.. Water Quality
e main constituent of any aqueous-based cutting
uid is obviously water and by nature, it is impure. e
impurity depends on the source: rain-; river-; spring-;
ground-water; etc. e water may also contain: dust
particles; oxygen; nitrogen; calcium and magnesium
salts; oen with smaller quantities of: ammonia; bo
-
ron; ourine; iron; nitrate; strontium; aluminium;
arsenic; barium; phosphate; copper and zinc. Addi
-
tionally, the water has in its presence micro-organ
-
isms, such as: algae; bacteria; fungi and viruses (i.e.
see Fig. 203); although in dierent orders of magni
-
tude. So, depending on its composition, water can
aect the aqueous-based cutting uid in many ways
and since the composition varies throughout the
year, these seasonal variations will have an eect on

its use. By far the greatest eect on the properties of
the cutting uid is caused by the hardness of the water.
Water’s hardness depends on the concentration of ele
-
ments
12
such as: calcium, magnesium and other heavy
metals like iron and manganese. Hard water may cause
a soapy deposit, which will eventually block lters, or
destabilise the emulsion and may have a detrimental
eect on the uid’s corrosion protection. Equally, so
water can be a problem, but for a dierent reason, in
this case it can promote foaming under ‘abusive’ ma
-
chining conditions.
e degree of alkalinity of the water can be ex
-
pressed as a
pH-value (i.e. see the pH-scale shown in
Fig. 202b) and this is an important measurement, as
it aects its usage and can react to human skin
13
caus-
ing ‘serious complaints’ – more will be said concerning
these health issues later in the chapter. Alkalinity in
the main, aects the growth of microbes (i.e. see Fig.
203b) and the degree of corrosion protection aorded
12 ‘Water hardness levels’ , are calculated based upon the quantity
of ‘grains’ of hardness minerals the water contains. By way
of example, one grain of calcium carbonate, constitutes 17.1

parts million
–1
(ppm) per 3.785 litres (i.e. equivalent to a U.S.
gallon). ‘Salts’ such as sodium chloride and sodium sulphate
are found in hard water, where they contribute to corrosion, or
rust – if not ‘inhibited’. Moreover, the greater the cutting uid’s
solution salt content, the more coolant concentrate is required
to prevent subsequent corrosion. Further, coolant degradation
occurs with time and usage. For example, a new charge of
relatively so water admixed with coolant concentrate, will
initially have say, a 3-grain hardness, but aer one month’s use
its hardness will have increased to between 12–14 grains and,
aer two months this hardness will have increased still further,
to between 24–27 grains. is problem is exacerbated if the
water content evaporates, needing periodic cutting uid analy-
sis to maintain optimum coolant performance.One method of
signicantly reducing water of its hardness minerals, is to run
it through a water soener, which removes the calcium and
magnesium ions, replacing them with sodium ions, although
residue build-up will be signicantly reduced, corrosion may
now be a problem, so for this reason soened water is not
recommended when using water-miscible coolants. Other-
wise, boil the water – ensuring that no soener, or anti-cor-
rosion agents were present prior to using the condensed water
product (i.e from the boiling process). Deionized water is the
best source of pure water, as a deionizer removes all dissolved
minerals, creating distilled water.
13 ‘Human skin’ , varies from one body-region to another, but
generally, it has a pH-level slightly biased toward the acidic
region of the scale, at approximately 6.8 pH (e.g. a value of 7.0

pH is considered as ‘neutral’).
NB Skin also has a protective layer of natural oils, that act
to retard moisture evaporation, acting as a form of ‘defensive
shield’ against some forms of biological attack.
Cutting Fluids 
by the emulsion. If alkaline levels increase this results
in improved protection, particularly when machining
ferrous workpieces. In view of the importance of water
composition for the eectiveness of a water-mixed
cutting uid, it is essential to know the quality of the
water source available and to take account of this fac
-
tor when selecting a concentrate. Cutting uid manu
-
facturers undertake water analysis, as do local water
companies. In Fig. 199b, the minimum requirements
for water quality for aqueous-based cutting uids is
shown.
8.5 Cutting Fluid
Classification – According
to Composition
Generally speaking, cutting uids are purchased under
the following classications, according to their com
-
position:
•
Synthetic uids – are those cutting uids which
contain very little, or no natural oil. e various
components such as the actual cutting uid are
nely distributed in water, as such, they form a

watery transparent solution – shown in a schematic
representation in Fig. 200a. e applications of
synthetic cutting uids range from light-to-heavy
cutting, together with usage in grinding applica
-
tions. In order to ensure the necessary lubricating
power desirable for heavy cutting operations, some
of these products contain synthetic lubricants (Fig.
200b). e major properties of synthetic cutting
uids can be summarised as follows:
–
A very clean and transparent uid,
–
Excellent corrosion protection,
–
A long life cutting uid,
–
Outstanding cooling capabilities,
–
Easy to mix,
–
Does not burn, or smoke.
•
Semi-synthetic uids – can contain up to 41% oil
and when mixed with water they have a translucent
property (Fig. 200c). Extreme pressure (EP) addi
-
tives and synthetic lubricant can be added, in order
to widen the range of potential workpiece materials
and applications. e properties of semi-synthetic

cutting uids can be summarised in the following
manner:
–
Very clean in appearance,
–
Excellent corrosion protection,
–
Long life of cutting uid,
–
Outstanding cooling capabilities,
–
Good wetting properties,
–
Easy to mix,
–
Does not burn, or smoke.
•
Emulsion uids – contain a high proportion of oil
and when the concentrate is mixed with water it
has a ‘milky appearance’ (Fig. 201a). Cutting uid
products intended for very heavy cutting operations
additionally contain EP additives (Fig. 201b). e
properties of an emulsion cutting uid, are sum
-
marised below:
–
Clean,
–
Oer good corrosion resistance,
–

Long life of emulsion,
–
Outstanding cooling capabilities,
–
Easy to mix,
–
Do not burn, or smoke.
Finally, for all of these various cutting uid types and
compositions, the dierences in the range of applica
-
tion of: synthetic; semi-synthetic; emulsion uids; de
-
pends upon the respective machining requirements. In
general, the
heavier the cutting operation, the higher the
cutting forces produced and the greater the oil content
required. is observation, means that
synthetics are
normally used for
lighter cutting operations, whereas,
emulsions are usually utilised for heavy-cutting appli-
cations, while the
semi-synthetics tend to be employed
as a
general-purpose (i.e. alternative) cutting uid.
8.6 Computer-Aided
Product Development
e latest cutting uids are very complex products and
a considerable amount of research and development (R
and D) is required to perfect them. e quantity of raw

materials that have diering characteristics and the
number of interactions between them, means that the
possible combinations are potentially enormous. Even
when most of the possible combinations are obviously
unnecessary and hence could be disregarded, this still
leaves the possibility of many thousands of coolant ad
-
ditive permutations and their respective interactions
to investigate, which would be a ‘Herculean task’ to
 Chapter 
Figure 200. Schematic representation of synthetic variaties of cutting uids. [Courtesy of Cimcool].
Cutting Fluids 
decipher and then to optimise! To press the point still
further, this situation of determining the optimum
combination is analogous to that of: ‘looking for a
needle in a haystack’ , where the conventional empiri
-
cal methods become no better that in eect, searching
at random! Luckily a solution is at hand, by the evalu
-
ation using computer technology, when utilised with
specially-developed programs. Computer-aided prod
-
uct development will as a result, eciently provide a
solution backed-up by statistical techniques, enabling
many thousands of combinations to be assessed, re
-
ducing the nal choices to just a few cutting uid com
-
binations. In this way it is possible to rapidly and ac

-
curately optimise the solution, as depicted in Fig. 204,
where a Computer-aided Design (CAD) application is
used to select – in this case – a corrosion inhibitor for
a potentially-new cutting uid. Such computer-based
techniques have brought about a means of develop
-
ing cutting uid products, using the CAD to not only
‘screen-out’ formulations which do not t the present
machining requirements, but can also uncover previ
-
ously unsuspected properties – resulting form syner
-
Figure 201. Schematic representation of emulsion varieties of cutting uids. [Courtesy of Cimcool].
 Chapter 
Figure 202. A cutting uid emulsion’s diametral size (0.2 to 1.5 µm) in comparison with micro-organisms and ‘tramp oil’, together
with the ‘pH scale’. [Courtesy of Kuwait Petroleum International Lubricants]
.
Cutting Fluids 
Figure 203. Bacterial contamination: aqueous cutting uid.
 Chapter 
Figure 204. Computer-Aided Design (CAD), utilised to select a corrosion inhibitor for an aqueous-based
cutting uid. [Courtesy of Cimcool]
.
Cutting Fluids 
gies
14
. As an example of this phenomenon, anionic
emulsiers normally have corrosion inhibiting charac
-

teristics, but these properties are usually so slight that
any side-eects are usually disregarded. However, by
using CAD, it is possible to nd emulsiers – normally
several are needed, whose side-eects add up syner
-
getically.
When the correct emulsiers are selected and in the
right proportions, not only is the desired emulsifying
action obtained, but at least some of the required cor
-
rosion protection also occurs. In Fig. 204, an example
of the ‘construction’ of a corrosion inhibitor system
using a variety of inhibitors – either singly, or in com
-
bination – can be comprehended. Here, the ‘zero-line’
on the vertical axis of the graph represents: ‘no eect’ ,
while values greater, or less than zero represent a: posi
-
tive; or negative eects; respectively.
Such CAD for chemical compounds makes it pos
-
sible to develop ‘atomised’ cutting uids far faster
than by previous techniques and oers the prospect of
discovering entirely new cutting uid combinations.
Computer analysis, oers a way to develop, analyse
and test new cutting uids, enabling very rapid modi
-
cations to be incorporated in order to meet new tech
-
nical and commercial requirements. Further, these

CAD-based techniques guarantee a chemically-stable
product with the optimum properties, reducing the
risk of selecting the wrong type of cutting uid both
by the manufacturer and user. CAD product develop
-
ment still necessitates practical product testing, during
its development phase utilising standardised proce
-
dures of: ‘calibration and laboratory test methods’ – to
model the computerised-uid data in a real-time cut
-
ting environment.
.. Cutting Fluid – Quality Control
For practical reasons industrial cutting uid manufac-
turers have to use mass produced raw materials and
chemicals, which may be less pure than those used in
their formulations in the laboratory (Fig. 205). Not
only are there variations in quality, owing to variance
in the production process, but dierences can also oc
-
14 ‘Synergy’ , refers to the outcome when substances are com-
bined and produce ‘side-eects’ , which add to, or even amplify
each other, giving rise to a much stronger resultant eect.
cur depending on the raw material source and the sea-
sons of the year. In order to ensure constant quality
of the nished product despite these variations and
the factors which determine the quality of the raw
materials, they must be checked prior to entering the
cutting uid production processing stage. e labo
-

ratory-based technique of computer-aided statistical
process control that ensures: ‘preventative quality con
-
trol’ , will enable the researcher to set the upper and
lower quality levels for a particular raw material – un
-
der test. us, on the basis of these user-dened sta
-
tistically-acceptable levels, the correlation between the
analysis and the practical results can be determined.
Raw materials analysis using computer-aided design
in conjunction with sophisticated analysis equipment,
plays a vital role in any new cutting uid development
process.
An important criterion for the quality of the 
-
nal cutting uid formulation is its stability. By com
-
parison, synthetic cutting uids produce fewer prob
-
lems than semi-synthetic and emulsion cutting uids,
in their development. In the case of the semi-syn
-
thetic and emulsion cutting uids, not only must cool
-
ing water and lubricating oil be brought together –
two naturally incompatible substances, they must also
‘persuaded’ to remain mixed together under widely
varying and extreme cutting and environmental con
-

ditions. When dierent degrees of water hardness,
varying mix ratios and a diverse range of impurities
occur, they will strongly inuence the overall water-oil
system. e conventional way of stabilising such a sys
-
tem is to add plenty of emulsiers. is action can lead
to excessive foaming, especially if the water is so,
which in itself necessitates adding anti-foam agents.
Anti–foam agents are an expensive alternative – par
-
ticularly in a large central-based ‘Niagara’ reservoir-
type system feeding several machine tools in say, an
FMC/S (Fig. 203a), which here, by ‘anti-foaming dop
-
ing’ in any event, will only work for a limited period
of time.
More important for cutting uid stability, is the
size and distribution of the oil droplets in the water
phase (i.e. see Fig 206-inset photomicrograph). It is
the even distribution of the many oil droplets which
ensures that the oil-water system is stable. e growth
of micro-organisms (Fig. 203b) aects the droplet size
and as a result, as these droplets spherically-increase in
size, the number and distribution of droplets decreases.
us, an oil-water system with many evenly-spaced
and small droplets, will be more stable than systems
 Chapter 
Figure 205. Laboratory-based testing procedures on cutting uid coolant products.
Cutting Fluids 