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 eects 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-eectiveness – but what does this term mean? ere was a time when the cost-eectiveness 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-eciency. 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 identied 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 dierent 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 dierent types of cutting uids available they can be classied according to widely varying criteria, although some unied system of terminology exists in various countries guidelines and Standards. is commonality of ‘language’ reects both the chemical and technical requirements of the users. On the basis of the various countries publicised cutting uid literature, the following classication 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 ‘emulsiable’ 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 briey 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-rened ‘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 dierent chemical structures. Such widely varying characteristics make it impossible to supply mineral oil to closely dened specications, 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 dierent 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 olen 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 signicant 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 eect 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: emulsier-to-oil in the formulation, either by reducing the oil content, or by increasing the level of emulsiers, the product takes on dierent characteristics from those of min - eral-soluble oils. Due to this increased ‘ratio’ , the oil particles formed, are signicantly 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 emulsiers in the product leaves some ‘spare capacity’ , which enables the ‘micro-emulsion’ to emulsify any oil-leakage from the machine. is emulsication 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 denition of Semi-synthetic cutting uids 9 can cause some diculty, 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 oen 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 emulsiers to ensure that ne micro-emulsion of oil particles are formed in water. As previously mentioned, these ‘spare’ emulsiers enable the micro-emulsion to absorb tramp oil. Hence, as these ‘spare’ emulsiers 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 reected and results in the visual ‘clouding eect’ 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 ‘Emulsication of tramp-oil’ when using Semi-synthetic oils, will only occur, until all of the ‘spare’ emulsiers are used up! erefore, aer 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 denition is this: ‘A semi- synthetic cutting uid forms a translucent emulsion and con- tains mineral oil’. 10 ‘Lubricity’ , or ‘Oiliness’ as it is oen known, is dicult to de- ne with any precision. One reasonable denition is that Lu- bricity is: ‘[e signicant] dierences in friction greater than can be accounted for on the basis of viscosity, when comparing dierent 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 oer 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 signicance is suciently 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 oen known. Such corresponding cutting uids are of two types: ‘emulsive’ , or ‘emulsiable’ – 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 ‘emulsiable’ 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: ‘emulsiers’; 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 ‘emulsiers’ are necessary to help form a stable emulsion and as such, are very important for the tech - nical characteristics of the cutting uid. ‘Emulsiers’ 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. ‘Emulsiers’ reduce the surface tension and form a lubricating lm at the boundary surface. ese ‘emulsier’ 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 dierent 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 dierence 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 dierence 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 dierence 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 eectively prevent the electro-chemi - cal process of corrosion, such as passivation by means of nitride, but the latter type is now being eectively 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 oen 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 aerward it may prove dicult 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 oen arise around the pipe unions, or at pipe-connectors to either the valves and pumps in the coolant delivery system. Microbiocides Microbiocides are oen 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; oen 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 dierent orders of magni - tude. So, depending on its composition, water can aect the aqueous-based cutting uid in many ways and since the composition varies throughout the year, these seasonal variations will have an eect on its use. By far the greatest eect 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 eect on the uid’s corrosion protection. Equally, so water can be a problem, but for a dierent 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 aects 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, aects the growth of microbes (i.e. see Fig. 203b) and the degree of corrosion protection aorded 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 aer one month’s use its hardness will have increased to between 12–14 grains and, aer 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 signicantly reducing water of its hardness minerals, is to run it through a water soener, which removes the calcium and magnesium ions, replacing them with sodium ions, although residue build-up will be signicantly reduced, corrosion may now be a problem, so for this reason soened water is not recommended when using water-miscible coolants. Other- wise, boil the water – ensuring that no soener, 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 eectiveness 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 classications, 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, – Oer 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 dierences 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 diering 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 eect, 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, eciently 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 . 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. 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 oer 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 . 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