Most uid mixers operate based upon the ‘venturi principle’ 21 and because of this, there will usually be a degree of uctuation of the dilution, if the water pres - sure should change during its operation – particularly if other equipment within the factory draws water when required. In view of any potential water pressure variation, it is normal practice to use a water supply that is not subject to such uctuations. Many local water authorities may well require that a header tank with an air gap is used, to prevent any possibility of contamination of the water mains. When mains water is used, many local authorities will provide the nec - essary water quality information, but if another water source is used, it will need to be analysed by the user. In Fig. 207, the graph illustrates the results of concen - tration measurements, taken from zero → 6%, obtained by dierent techniques, such as: • Refractometer assessment – more on this apparatus shortly, • Measurement of the total alkalinity of a product containing nitrate, • Boron determination by Atomic Absorption (AA) method, • Measurement of the total alkalinity of a product not containing nitrate, • Hypothetical ‘real’ concentration ‘R’ , set arbitrarily at 3%, • Determination of anionic emulsier content (b) @ water hardness of 10° GH, • Determination of anionic emulsier content (a) @ water hardness of 10° GH, • Determination of nitride content, • Determination of anionic emulsier content (a) @ water hardness of 30° GH. NB Water hardness can be easily determined with suf- cient accuracy using indicators in tablet form, while the pH value and bacteria count can be estimated as 21 ‘Venturi principle’ , is: ‘A convergent-divergent duct in which pressure energy is converted to kinetic energy at the throat.’ When utilised with its associated ‘Venturi meter’ , this being a ow meter in which the pressure drop in a Venturi is used to give an indication of ow. [Source: Carvill, 1997]Where in the case of emulsion dilution ratios, this uid mixer arrange- ment – with the apparatus situated in the top of the drum and connected to the water supply – can be employed and then subsequently adjusted in-situ, to give the desired coolant mix- ture. described in the following section. For more detailed analysis, then laboratory facilities are necessary, this assistance is oen provided by the cutting uid manu - facturer’s laboratory service department. .. Monitoring, Maintenance and Testing of Cutting Fluid – in Use While in use the cutting uid is subject to various in- uences that may aect its properties. Such inuen - tial factors include: leakages from the machine tool’s lubrication and hydraulic systems (i.e. ‘tramp-oil’); surface contamination on the work piece: prior to ma - chining; or by people: spilled drinks; food particles; environmental inuences. It is paramount that the health monitoring of a cutting uid is on-going and undertaken at periodic intervals, whilst spot-checks may also be necessary in order to detect undesirable changes in the uid’s properties, enabling corrective action to be taken, as appropriate. Hence, the moni - toring of the cutting uids are fundamental to their life, but a relevant question could be raised: ‘What characteristics do we have to monitor?’ Probably the most common cutting uid tests, include the following measurements: • Concentration, • pH (Alkalinity), • Corrosion protection, • Fluid stability, • Bacteria count. e above tests will shortly be considered in more de - tail, in the appropriate section. Prior to this, it is im - portant to ensure that the machine tool is thoroughly cleaned, before a new ‘charge’ of cutting uid is poured into either the machine’s reservoir, or to a central cool - ant distribution tank – supplying the needs of several machine tools. Machine Cleaning It is important to any cutting uid system that it is cor- rectly cleaned before fresh uid is introduced, if the optimum performance from it is to be obtained. Such machine tool cleaning procedures, should include the following stages: Cutting Fluids Figure 207. The graph illustrates the results of the concentration measurements using dier- ent methods. [Courtesy of Cimcool] . Chapter Figure 208. ‘Wetability’ related to a droplet’s spherical cap, plus an automatic (aqueous) coolant mixing device. Cutting Fluids 1. Physical removal of all deposits: swarf; debris; oil and food contamination in the uid-system – using say, coolant extraction equipment (Fig. 209a and b), 2. Treatment of the uid-system with an appropriate system-cleaner – normally added to either the old cutting uid – prior to draining, or more eectively, to clean water and pumped-around the system for the specied time-period, as recommended by the uid’s manufacturer, 3. Removal of: all guarding; swarf conveyors; etc.; as necessary to allow eective cleaning of inaccessible areas – if ‘maintenance window’ time-frames per - mit, 4. Flush the uid-system – pumping around it with clean water, 5. Rell the uid-system with fresh emulsion at the correct dilution. NB Once the fresh cutting uid is in-situ, it should be inspected and checked on a regular basis, as this proactive activity will considerably prolong its working-life. Maintenance of the Fluid During Use e following on-going maintenance procedures to the cutting uid during use, will assist in prolonging its overall eectiveness and life: • Checking of the dilution regularly using a refrac- tometer (Fig. 206), to ensure that the dilution remains relatively constant – within the recom - mended range 22 , • Never wait until the uid level falls below the pump before topping-up, while regular top-ups to the re - quired level with fresh uid assists in controlling bacterial growth, • Restrict the amount of swarf build-up, as large vol- umes of swarf can encourage both corrosion and bacterial growth, • Do not allow the cutting-uid’s sump to be used as a ‘dustbin’ for example: cigarette ends; uneaten food remnants; paper cups; general rubbish; etc., 22 ‘Dilution control’ – if the emulsion is: under-diluted, never add water, but rather pour in a weaker emulsion; Over-diluted, do not add concentrate, but rather pour in a strong emulsion. – – • Avoid excessive leakage of oil from the machine (i.e. tramp-oil’), especially during maintenance overhauls/procedures. More sophisticated condition monitoring is of course possible and may be tting where the consequences of uid failure are serious, such as in a large centralised system. Some cutting uid manufacturers oer this as a service. While at another extreme, one UK cutting uid manufacturer, actually achieves ‘on-line condi- tion monitoring’ of emulsion by continuous control of an automotive company’s engine production line from a distance of over 100 km away. e monitoring and operational procedure is typically as follows: on the production line, as the cutting uid’s character - istics change – when being continuously monitored, the uid manufacturer (i.e. from the ‘HQ’), can au - tomatically ‘dope’ the system by discharging from a centralised and strategically positioned stillage, ap - propriate chemicals, or uids – as necessary. While at this remote monitoring station (HQ), they watch and monitor on-line for say, the dilution ratio to change – and as the newly-discharged ‘doping’ takes eect in real-time, thereby keeping the emulsion at its opti - mum performance. Cutting Fluid Testing ese testing procedures are important to undertake, as they dene the current status of the cutting uid. Many aqueous-based cutting uid tests can be un - dertaken, with the following ones normally being the most oen employed: • Testing for concentration levels (e.g. using a re- fractometer 23 – Fig. 206) – this being an important 23 ‘Refractometer operation’ (Fig. 206): Place a few drops of cutting uid on the instrument’s prism, Close the lid over these droplets, Hold the instrument up to the light and view through the eyepiece. NB In the eyepiece, the light and dark interface is visually- apparent and a measurement is obtained against the engraved optical graticule – which is calibrated in % readings. Some types of refractometer’s can be simply read-o from the eye- piece numerical value – as shown in Fig. 206, while other ver- sions obtain the actual % reading when the ‘interface value’ reading is compared against a specic calibration chart – to obtain the dilution level. Such refractometers can be utilised to obtain dilutions for a range of aqueous-based cutting uids. – – – Chapter Figure 209. Typical coolant extraction/reclamation units. Cutting Fluids preventative measurement for water-mixed cutting uids. ere are a variety of techniques currently available, but in all cases, the results should be treated with a certain amount of caution. As previ - ously mentioned, Fig. 207 graphically depicts how a range of methods of assessment can give quite ap - preciably diering results. For semi-synthetic prod - ucts, the concentration measurement by means of a refractometer is very popular, although they tend to be more accurate and precise only when fresh mixtures are assessed. e more the contamination from the machine tool’s lubricating system, the less accurate and precise will be the results. A refrac - tometer being a portable hand-held instrument can be transported and used anywhere within the pro - duction plant – as necessary. It is also important to ensure that only adjustable refractometers are used, as prior to taking a reading, they must be set to zero, • Testing for pH level – this is a simple, yet important test, which should be undertaken on water mixed with cutting uids – this being a measure of the pH value. e pH value, or to be more specic, the: hydrogen ion concentration, is a measure of the acidity, or alkalinity of a solution. Aqueous-based cutting uids tend to be alkaline, with a typical pH range of between 8 to 9.5 (i.e see Fig. 202b, for these values on the pH scale). us, a change in the pH value indicates a disturbance of the hydrogen ion equilibrium. is ‘disturbance’ in turn, suggests a deterioration in the uid’s properties, due to either biological, or chemical action, or both, but more specically, indicating that heavy contamination has occurred. e simplest manner of obtaining a measure of pH, is by using ‘pH indicator strips’ which once dipped in the cutting uid, the strips will now change colour. is colour change in the ‘strip’ is then visually compared and matched against a coloured and graduated scale, to obtain a pH reading. More exact measurements can be ob - tained by means of an electronic equipment for a pH measurement reading 24 . Yet another technique used to determine the pH value, is by means of ‘ti- 24 ‘pH readings’ , are in accordance with many countries na- tional Standards, such as that found in Germany, namely: DIN51369. tration’ 25 , which is a quantitative analysis method to determine alkalinity. In contrast to the pH value, which can only can only give the degree of alkalin - ity, the ‘titration method’ also establishes the alka- linity level, but it also determines the rate of change of this alkalinity – helping to estimate the cause of the alteration. So when a rapid rise in alkalinity is detected, this points towards the presence of a con- taminant, conversely, a fall in the alkalinity level in- dicates probable bacteria growth 26 – decreasing the eectiveness of the additive, • Corrosion protection – its measurement is an im- portant preventative operation when using water- mixed cutting uids, in order to avoid unexpected corrosion of ferrous workpieces – owing to insuf - cient, or ineective corrosion inhibitors in the uid. With some products, even small variations in concentration can adversely aect corrosion pro - tection 27 , • Product stability – any deviation in emulsion sta- bility in use can be quickly determined using the ‘centrifuge testing method’. In this technique, the centrifuged sample of emulsion is compared: under specied conditions; with the current working Standard, giving an indication of the cutting uid’s anticipated stability, 25 ‘Titration’ , is a volumetric analytical determination in which a reagent solution with a known content (i.e. a ‘standard solu- tion’), is bled into the metalworking uid to be determined. e rate of change in alkalinity allows inferences to be drawn on the probable causes of this increased alkalinity. 26 ‘Bacteriological eects’ , if too high a degree of alkalinity pres- ent in the aqueous-based cutting uid: which for example, can be caused by adding excessive amounts of highly alkaline bactericides, this being just one of the main causes of skin ir- ritation, indicating the importance of regular checking of the cutting uid’s alkalinity. NB More will be said on this topic later in the chapter, in the relevant section concerning setter/operator ‘health-issues’. 27 ‘Corrosion protection’ , the degree of corrosion protection can be simply measured to many national Standards, typical of these are the German: DIN51360 and DIN51759 – known as the ‘Steel strip method’. NB ese corrosion development tests are most reliable, if the local water and authentic chips taken are from the actual machine tool used. Chapter • Bacteria count – the most accurate, but an expen- sive test method of determining the ‘bacteria lev- els’ 28 present in a cutting uid is by actual count- ing – for example, according to the German unit. A much more simple technique of achieving good estimates of bacteria levels is by utilising ‘dip-slides’. Here, the slides are dipped into the cutting uid, then the potential bacteria are incubated for a set time period and, nally compared with sample pic - tures – oering a good and reliable attribute quality control test method. 8.9 Multi-Functional Fluids Tramp-oils: hydraulic uid and slideway lubricants; will inevitably become mixed into the cutting uids during machining operations. Today, one technique to minimise the deleterious eects of their unwanted inclusion in the coolants, is via usage of the so-called: ‘multi-functional uids’. ese products will extend coolant life, because they maintain their performance even in the presence of tramp-oils. e multi-functional uid concept means that to prevent a reduction in overall coolant performance – if tramp-oils leak into the machine’s sump, all uids utilised in support of the machining operation: hy - 28 ‘Bacteria levels’ , in a cutting uid like all living organisms, need trace amounts of minerals in the ‘diet’ for optimal growth. While sulphates promote the growth of sulphate-re- ducing bacteria (i.e. more specically: desulphovibrio desul- phurican). Such bacteria ‘split’ the oxygen o sulphate ions and utilise it chemically, as their oxygen source. is process ‘liberates’ hydrogen sulphide, producing the smell which is very similar to that of rotten eggs! Specically, in soluble-oil coolants, the mineral content of hard water reduces the eec- tive concentration of emulsiers in a working solution. us, reduced emulsier concentration produces a coarse emulsion having large oil droplets, in a similar fashion to simply mixing oil with pure water. Bacteria are very much ‘size-specic’ , as a result, they attack large oil droplets more readily in a coarse emulsion, the opposite is true for smaller oil droplets in a tight emulsion. So, the easier the attack, the more readily the bacte- ria can extract nutrition and as a result, they grow. Moreover, bacteria grow best at the interface of the water droplet and the tramp-oil. Certain oils have elements that promote bacte- rial attack, being exacerbated by organic materials, such as: tobacco; fruit peelings; etc.; that nd their way into the ma- chine’s sump. draulic oils; slideway lubricants; greases; should con- tain identical additives to that of the coolant. By way of a practical illustration of this concept, in an auto - motive engine machining plant, all operations are per - formed by a multi-functional oil, having a viscosity of: 10 mm 2 s –1 at 40°C. While all the hydraulic functions of the transfer-line, use a higher viscosity multi-func - tional oil, having the same additives. is identical ad - ditive usage, ensures that tramp-oils as the leak into the metalworking uid, do not degenerate, nor desta - bilise the product, thus ensuring a longer working life at optimum performance. 8.10 Disposal of Cutting Fluids Cutting uid disposal costs have been reported to be as high as 22% of the total cutting uid-related cost. With environmental laws in Europe and in particu - lar Germany, these laws have driven up uid-disposal costs to >$1 per litre. With any coolant today, once it has reached the end of its productive and useful life, whether it is a: soluble oil; preformed emulsion; solu - tion; pure oil; etc.; it cannot be simply and indiscrim - inately poured down a drain, or disposed of at will. Waste cutting uid normally contains toxic substances, which were either present when it was new, or exist via contamination during its use. Possible contami - nants include tramp-oils: lubrication and hydraulic oils and greases from the machine tool and, occasion - ally from nitrite adhering to the heat-treated hardened workpieces that have been subjected to ‘hard-part ma- chining’ – more will be said on this machining strat- egy in the following chapter. ese contaminants now being present in the ‘old’ cutting uid, markedly-dif - fer from the original product. To emphasise the point still further, if initially pure water – not a good choice today! – was used as a cutting uid, it would absorb so much contaminant that aer a signicant amount of machining operations, it could not now simply be poured away. So, any used cutting uid should be thought of as toxic waste and must be disposed of in accordance with the appropriate authority’s regulations. Normally the local water authority governs such cutting uid waste disposal by: reprocessing; incineration; or other means; with its removal depending upon the cost and the amount of toxic waste material present. Typical toxic substances that should not be present in cutting Cutting Fluids uid waste are: nitrate; chlorine compounds; poly- chlorinated biphenyl (PCB); as reputable cutting uid manufacturers try to avoid their use, although traces have been found in certain formulations. In the past, sodium nitrate was once popular as a corrosion inhibi - tor, but nowadays, should not be utilised. While PCB should not be present in any of today’s cutting uids, but previously it was sometimes illegally-added to re- rened used oils. While, chlorine compounds – used as EP additives – are no longer acceptable for cutting uids, as are many previous used emulsion additives 29 . In order to keep uid disposal costs as low as possi - ble, it is advisable to collect and separately store dier - ent types of ‘spent’ cutting uid, for future appropriate disposal, or reprocessing. ere are various processes for reprocessing, or disposal of used cutting uids available, such as: chemical and thermal processes, while ultra-ltration is oen used today (i.e. see Fig. 210 for cutting uid ltration details). Whichever in - dividual disposal, or reprocessing route that is chosen, 29 Water-based uid additives: ‘Sodium nitrate’*, was previously employed as a corrosion inhibitor – due to its eectiveness and cheapness, but it should not be used today, owing to the potential problems with nitrosamine formation. Nitrosamine formation being strongly carcinogenic (i.e. acting irrespective of the mode of intake into the body) causing tumours, attacking primar- ily the: liver; kidneys; or respiratory organs. Modern cutting uids tend to use additives such as: amine borates; amine carboxylates; carboxylic acids; amine phosphates; as well as sulphonates, while other corrosion inhibitors have been specically designed for non-ferrous metals, such as alloys of; aluminiums, or brasses; * Previously, sodium nitride can react with diethanolamine, forming very weak carcinogen nitrosodiethanolamine. ‘Chloroparans’ , moving from ‘short-chain’ chlorparans (i.e. C10-C13) – suspected in an advanced study in USA of being a carcinogen, to that of ‘longer-chain’ chlorparans (i.e. C14-C17), mainly used as an extreme pressure (EP) ad- ditive; ‘Triazine biocides’*, reduction, or elimination of triazine biocides, due to the possibility of skin sensitisation; *New and safer biocides are now available to replace ‘Triazine- types’ of biocides. ‘Endocrine hormone’ , elimination of the endocrine hor- mone-disrupting chemicals. NB Cutting uid manufacturers are attempting to replace oil- based products with ‘greener- equivalents‘, such as: Vegetable oil-based MWF’s., such as oils extracted from either: soybean; rapeseed; canola; etc. – – – – will depend on a variety of factors, including retrieval costs and local regulations 30 . 8.11 Health and Safety Factors – Concerning Cutting Fluid Operation and Usage Introduction e ‘traditional’ petroleum-based metal-working uids (MWF’s), are complex formulated products that include sophisticated mixtures of: oils; detergents; lubricants; and other additives, that have the poten - tial to be toxic. Most uid manufacturers today, have complex additive packages coupled to newly-revised formulation strategies that are based upon renewable resources to ensure that MWF’s have: longer sump- life; are safer to both the setter/operator and the en - vironment; with the added benet of being less la - bour-intensive to use – than was previously the case. Moreover, these more recent MWF products must re - sist: tramp-oil contamination; biological and chemical stresses: these latter factors could change their ‘chem - istries’ to produce otherwise unhealthy environments for the users and detract from their overall stability. In the last few years in particular in many industri - alised countries, there has been increased pressure by interested parties: unions; companies; legislation; to look into the toxic eects cutting uids have on that of worker’s health issues and more recently, their disposal and its aect on the environment. Until relatively late, 30 An example of cutting uid disposal:In the UK: which is in the top 5 users of water-based MWF’s in Western Europe; it produces approximately 20,000 tonnes of product concentrate per annum. erefore, at the most common working-con- centration of 5% (i.e. 5 parts MWF to 95 parts water), this would simply equate to 400,000 tonnes of waste cutting uid per year – which must be adequately disposed of in an envi- ronmentally-friendly manner! Although in reality, this actual gure does not take account of uid: evaporation; nor drag- out; during the overall machining processes. [Source: Kuwait Petroleum International Lubricants] Chapter Figure 210. Air-borne contamination from cutting uids and a variety of sources, can normally be l- tered-out – producing a safer user working environment. [Courtesy of Kitagawa Europe] . Cutting Fluids the cause of worker’s decline in health was only indi- rectly-related to the exposure to MWF’s. Now, with the higher-than-expected reported incidence of: skin dis - orders (i.e. see Fig. 211); respiratory illnesses; asthma; bronchitis; stomach cancer; liver and kidney tumours and disorders; etc.; together with any associated liti - gation, this has meant that such issues are taken very seriously by all interested-parties. In fact, there is some concern with the increasing usage of synthetic cutting uids, in combination with the far higher cutting feeds and speeds used today, which jointly increase the par - ticulate count in the workshop atmosphere. Bacteria tend to be more pronounced in newly-developed u - ids, where it is exceedingly dicult to control growth of both the microbes and bacteria, although it is pos - sible to manage and control the coolant mist emanat - ing from the machine tool 31 . .. Cutting Fluid-Based Health Issues Skin Conditions It is generally acknowledged that prolonged, or re- peated contact with MWF’s can cause a variety of skin complaints: dermatitis (not shown), folliculitis, skin irritation; etc.; as illustrated in Fig. 211. us occupa - tional dermatoses is a general term used to describe any skin abnormality, or aggravation induced by the working environment. While dermatitis is a more spe - cic skin condition, causing at the early stages: skin in - ammation/irritation; leading to eventual breakdown and appearance of a skin cracking condition – when at 31 ‘Permissible exposure levels’ (PEL’s), in the USA and in par- ticular the Occupational Safety and Health Administration (OSHA) Standard, previously (i.e. prior to 1999) said that mist control in the working environment had a maximum value of 0.5 mg m –3 , however aer 1999, OSHA brought this PEL down to a tenth of the previous gure, specically to: 0.05 mg m–3 over an 8-hour period – and it can be achieved at relatively small additional plant cost. In November 2001 OSHA, released a document that recommended in its ‘Best Practices Manual’ the ‘way-forward’ in achieving this PEL. NB Today, many automotive companies in particular, operate at PEL’s well below this value – but being much closer to the lower threshold value, typically having a PEL of: ≤ 0.05 mg m –3 over an 8-hour period. an acute stage. More specically, occupational derma- titis can be characterised still further, into: • Primary irritation – resulting from an immediate skin contact with MWF’s, or shortly aerward, • Sensitisation – results from an allergic reaction (i.e. an immune-system response) to a particular uid/additive substance. Initial uid contact may not in the rst instance cause skin irritation, but could initiate an exposure sensitivity build-up over time. us, once the skin has become sensitised 32 , then even the slightest exposure to this substance results in a severe reaction, being not restricted to the contact site on the body, • Photosensitisation – is virtually identical to that of ‘sensitisation’ , except that the presence of light is necessary to activate the sensitiser. Folliculitis (Fig. 211a) is a supercial irritation of the hair follicles by oil, or foreign matter suspended in it, plus secondary microbial sceptic infection. It normally occurs on the backs of arms and forearms, when the basic requirements of correct washing and skin hy - giene are neglected. Remedial medical treatment is relatively straightforward, usually clearing up aer a few days. Eczematous-type rashes, are skin inammation arising from continued contact with soluble oil emul - sions, specically on the hands and forearms. e con - tinual and daily combination of wetting and alkalinity, allied to mineral oil contact exposure. Makes the skin macerated and can develop small, eczematous erup - tions, or dry, red patches, which may itch, but tend to be more unsightly, than serious, which with correct medication, should clear up reasonably quickly. If, the allergic reaction recurs, then this indicates continuing sensitivity, meaning this particular worker may need to be transferred to other duties – not involving con - tact with aqueous-based cutting uids. 32 ‘Allergic reactions’ , most people can be allergic to virtually anything, but only 1% of the population get allergic reactions to MWF’s. Although many other factors can inuence the acuteness of the allergic reaction, such as: racial characteristics – light complexion (e.g. redheads and blondes – due to skin pigmentation have higher sensitivity levels); age – younger people tend to get dermatitis more readily than older workers; workers general good health/diet – this can build-up a toler- ance to allergic sensitivity; perspiration – can contribute to an allergic reaction; plus many other contributory factors. Chapter . Disposal of Cutting Fluids Cutting uid disposal costs have been reported to be as high as 22% of the total cutting uid-related cost. With environmental laws in Europe and in particu - lar Germany, these laws have driven up uid-disposal costs to >$1 per litre. With any coolant today, once it has . to obtain the dilution level. Such refractometers can be utilised to obtain dilutions for a range of aqueous-based cutting uids. – – – Chapter Figure 209. Typical coolant extraction/reclamation units. Cutting Fluids preventative measurement for water-mixed cutting uids. ere . this assistance is oen provided by the cutting uid manu - facturer’s laboratory service department. .. Monitoring, Maintenance and Testing of Cutting Fluid – in Use While in use the cutting uid is subject to various in- uences