Lubricants and Lubrication Part 8 ppsx

378 13 Turbine Oils Siemens TLV 901304 (July 1999) e.g.General Electric GEK 101941 A (Nov. 1999) e.g. General Electric GEK 32568 E (May 1999) Alstom HTGD 90117 V0001U 7/2005 Alstom HTGD 90117 V0001U 7/2005 Testing according to DIN ISO Testing according to ASTM Oxidation stability by rotating bomb (modified) N2-blown RBOT 85 % (min.) of time in unmo- dified test 85 % (min.) of time in unmo- dified test –– – ASTM-D 2272 Viscosity Index (VI) 95 (min.) 95 (min.) ‡ 90 ‡ 90 – ASTM-D 2270 Atomic emission spectroscopy Zinc content < 5 ppm £ 5 ppm £ 5 ppm – ASTM-D 4951 Filtrability Stage I min 93 % Stage II min 85 % ISO 13 357-2 * Neutralization Number < 1.8 mg KOH g –1 , sludge < 0.4 % according to DP 7624 Base Oils: 1) Mineral oils or synthetic oils with additives to improve corrosion protection and aging stability (additionally EP/AW additives in the case of gearbox lubrication). 2) Petroleum lubricating oil – Synthetic Hydrocarbons with greater high temperature, oxidation stability and R&O inhibitors, EP/AW additives 3) Petroleum lubricating oil – Synthetic Hydrocarbons with greater high temperature, oxidation stability and R&O inhibitors 4) Refined mineral oils with additives mainly aging inhibitors and corrosion inhibitors (no EP/AW additives). Other important specifications (examples): Westinghouse: I.L. 1250-5312–Steam Turbines 21 T 0591–Gas Turbines Solar: ES 9-224–Gas Turbines 5) L.S. = Load Stage Tab. 13.6 Continued. 37913.6 Flushing Turbine Oil Circuits coolers to reduce the temperature of the filtered oil. It must also be possible to remove the oil from the tank with a mobile filter unit or centrifuge if water, steam or other contaminants enter the system. For this, the lowest point of the oil tank is normally fitted with a corresponding connector which can also be used to draw oil samples [13.3, 13.4]. Oil aging is also influenced by the frequency with which the oil is pumped through the circuit. If the oil is pumped too fast, excessive amounts of air are either dispersed or dissolved (problem: cavitation in bearings, premature aging etc.). Oil tank foaming can also occur but this generally collapses rapidly. Engineering design measures can positively influence air release and tank foaming. These include oil tanks with larger surface areas and larger return circuit pipe cross-sections. Simple measures such as returning the oil to the tank through an inverted U-tube can pro- duce astonishing benefits. Fitting baffles to the tank also positively influences air release. These have the effect of prolonging the time in which air, water and solid contaminants can be released from the oil [13.2–13.4]. 13.6 Flushing Turbine Oil Circuits Before commissioning, all oil circuits should be mechanically cleaned and finally flushed. Every effort should be made to remove all contaminants such as cleaners and corrosion preventives (oils and/or greases) from the system. The oil can now be added for flushing purposes. About 60–70 % of the total oil volume is required for flushing [13.4, 13.6]. The flushing pump should be operated at full power. It is recommended that the bearings are removed and temporarily replaced with blanks (to avoid the penetration of contaminants into the gap between shaft and bearing shells. The oil should be repeatedly heated to a maximum of 70 C and then cooled to about 30 C. The expansion and contraction in the pipework and fittings is de- signed to dislodge dirt in the circuit [13.4]. The shaft bearing shells should be flushed in sequence to keep the flow rate high. After at least 24 h of flushing, oil filters, oil sieves and bearing oil sieves can be fitted. Mobile filtering units, which may be used, should work with a mesh size of £ 5 lm. All parts of the oil supply chain, including reserve machinery, should be extensively flushed. Finally, the flush- ing oil should be drained from the oil tank and coolers. All system components should be thoroughly cleaned externally. The flushing oil may be re-used after very fine filtering (by pass filtration). However, a careful oil analysis should first be made and care should be taken that the oil still fulfils DIN 51 515 or the equipment-specif- ic specifications [13.4]. Flushing should be performed until no solid contaminants are found in the filter and/or no measurable increase in pressure is recorded in by- pass filters after 24 h. It is recommended that a few days of flushing and a subse- quent oil analysis follows any system modifications or repair work [13.4]. 380 13 Turbine Oils 13.7 Monitoring and Maintenance of Turbine Oils In normal circumstances, oil monitoring intervals of one year are perfectly accepta- ble. [13.2, 13.4, 13.6]. As a rule, these should be performed in the oil manufacturer’s laboratories. In addition, a weekly visual inspection of the oil should be performed to spot contamination and impurities in the oil in good time. Filtering the oil with a centrifuge in a by-pass circuit is a reliable method. The contamination of the air surrounding a turbine with gases and other particles should be considered when operating a turbine. Topping-up lost oil (refreshing of additive levels) is a method worth considering. Filters, sieves as well as oil temperature and oil level should be checked regularly. In cases of longer shut-downs (longer than two months), the oil should be circulated on a daily basis and the water content should be checked regu- larly [13.4]. The control of used . fire-resistant fluids in turbines, . used lubricants in turbines and . used turbine oils in turbines is performed by the laboratory of the oil supplier. The analysis and the warning val- ues of the different properties and their following-up are described in the VGB- Kraftwerkstechnik Merkblätter, Germany (VGB = Association of German Power Plants). 13.8 Life of (Steam) Turbine Oils Oil life of 100 000 h is not uncommon in large steam turbines [13.2, 13.3]. However, the antioxidant level in the oil can fall to about 20–40 % of the fresh oil (oxidation, aging). The life of turbineoil depends heavily on the quality of the turbine base oil, the operating conditions such as temperature and pressure, oil circulation speed, filtering and the quality of maintenance and finally, the amount of oil topped-up (this helps maintain adequate additive levels). The temperature of the oil in a turbine depends on the bearing loading, speed, bearing dimensions and the oil’s flow rate. Radiated heat can also be an important parameter. The oil circulation factor, i.e. the ratio between flow volume h –1 and tank volume should be between 8 and 12 h –1 [13.3–13.5]. Such relatively low oil circula- tion factors ensure that gaseous, fluid and solid impurities can be efficiently separat- ed while air and other gases can be released. Furthermore, low oil circulation factors reduce the thermal loads on an oil (with mineral oils, oxidation speed doubles when the temperature increases by 8–10 K). During operation, turbine oils are exposed to considerable oxygen enrichment. Turbine lubricating oils are exposed to air at a number of points around a turbine. The temperatures of bearings can be monitored with thermo-elements. High bearing temperatures can be around 100 C [13.2, 13.5] 38113.9 Gas Turbine Oils–Application and Requirements and sometimes even more in the lubrication gap. The temperature of bearings can reach up to 200 C if localized overheating takes place. Such conditions can only be countered by large oil volumes and rapid circulation. The oil draining from plain bearings can be about 70–75 C [13.3] and the oil in the tank can be about 60–65 C. Depending on the oil circulation factor. The oil remains in the tank for between 5 and 8 min [13.3, 13.4]. During this time, any trapped air can be released, solid con- taminants can settle and water can be separated. If the temperature of the oil in the tank is higher, additive components with high vapor pressures can evaporate. This evaporation problem is worsened by the installation of oil vapor extraction units. The maximum temperature of plain bearings is limited by the threshold tempera- tures of the white metal bearing shells. These are ca. 120C. The development of alternative bearing shell metals which are less heat-sensitive is currently underway [13.1, 13.3, 13.4]. 13.9 Gas Turbine Oils–Application and Requirements Gas turbine oils are used in stationary turbines. These produce either electricity or heat. The compressor fans generate pressures of up to 30 bar which vent into the combustion chambers where gas is injected [13.3]. Depending on the type involved, combustion temperatures of up to 1000 C are reached (generally 800–900 C) [13.3, 13.13]. Exhaust gas temperatures can reach about 400–500 C. Gas turbines with capacities ranging up to about 250 MW are used in urban and suburban steam heat- ing systems, in the paper industry and in the chemical industry. The advantages of gas turbines are compact size, rapid start-ups (< 10 min) as well as small oil and water requirements [13.1, 13.3, 13.4]. Common mineral oil-based steam turbine oils are used for conventional gas tur- bines. However, it should be remembered that the temperature of some bearings in gas turbines is higher than in steam turbines so that premature oil aging can be expected. Moreover, hot-spots can occur around some turbine bearings and localized temperatures can reach 200–280 C [13.3] whereby the temperature of the oil in the tank remains at about 70–90 C (hot air and hot gases can accelerate the aging pro- cess). The temperature of the oil reaching a bearing is mostly between 50–55 C and the exit temperature about 70–75 C [13.3]. As the volume of gas turbine oils is gen- erally smaller and they circulate more rapidly, their life is somewhat shorter. The volume of oil for a 40–60 MW generator (GE) is about 6000–7000 L and its life is between 20 000 and 30 000 h (in the case of a 40–60 MW Siemens, 14 000 L and 40 000–80 000 h [13.6, 13.9]. Semi-synthetic turbine oils (special hydrotreated base oils (so-called group III oils)) or fully synthetic turbine oils based on synthetic PAO’s are recommended for these applications [13.3, 13.4, 13.8]. In civil and military aviation, gas turbines are used for propulsion. Because of the high temperatures encountered, special, low-viscosity (ISO VG 10, 22) synthetic oils based on saturated esters (e.g. polyolester oils) are used in these aircraft engines or turbines [13.13]. These synthetic esters have a high viscosity index, good thermal 382 13 Turbine Oils stability, oxidation resistance as well as excellent low temperature characteristics. Some of these lubricants can contain additives and some not. The pourpoint of these oils are between –50 and < –60 C. And finally, all relevant civilian and military product specifications must be fulfilled. The lubricants used in aircraft turbines can in some cases also be used in helicopter, ship and stationary, industrial turbines. Aviation turbine oils containing special naphthenic base oils (ISO VG 15–32) with good low-temperature characteristics are also used [13.13]. 13.10 Fire-resistant, Water-free Fluids for Power Station Applications For safety reasons, fire-resistant fluids are used in control and governor circuits which are exposed to ignition and fire hazards. In power stations, this applies in particular to hydraulic systems in high temperature zones such as near to super- heated steam pipes. Fire-resistant fluids should not spontaneously ignite when they contact hot surfaces. The fire-resistant hydraulic fluids used in power stations are generally water-free, synthetic fluids based on phosphoric acid esters (type DFD-R according to DIN 51 502 or ISO 6743-0, ISO VG 32–68). These fire-resistant HFD-R fluids based on phosphoric acid esters offer the features [13.4]: Specifications of triaryl phosphate ester turbine control fluids are defined accord- ing to ISO/DIS 10 050–category ISO-L–TCD [13.17] . fire-resistance . self-ignition temperature over 500C . auto-oxidation stable at surface temperatures up to 300 C . good lubricity . good protection against corrosion and wear . good aging stability . good demulsification . low foaming . good air release and low vapor pressure Additives to improve oxidation stability (possibly foam inhibitors) as well as rust and corrosion inhibitors are sometimes used. According to the 7th Luxembourg Report, the maximum permissible temperature of HFD fluids in hydrodynamic sys- tems is 150 C. Continuous temperatures of 80 C should not be exceeded in hydrau- lic systems. These phosphoric acid ester-based synthetic fluids are generally used for control circuits, but is some special cases, also for the lubrication of plain bearings in turbines as well as other hydraulic circuits in steam and gas turbine installations. However, these systems must be designed for these fluids (HFD-compatible elasto- mers, paint finishes and coatings). (E) DIN 51 518 lists the minimum requirements which power station control circuit fluids have to fulfil. Further information can be found in guidelines and specifications relating to fire-resistant fluids, e.g. in the VDMA Sheet 24 317 and in the CETOP recommendations R 39 H and RP 97 H. 38313.11 Lubricants for Water Turbines and Hydroelectric Plants Information relating to the change of one fluid to another is contained in VDMA Sheet 24 314 and CETOP RP 86 H [13.4]. 13.11 Lubricants for Water Turbines and Hydroelectric Plants Hydroelectric power stations have to pay particular attention to the handling of water-polluting substances, i.e. lubricants. Lubricants with or without additives are used in hydroelectric power stations. The oils are used to lubricate the bearings and gearboxes of principal and ancillary machinery as well as for hydraulic functions in control and governing equipment. The specific operating conditions of the hydro- electric plant need to be considered when selecting lubricants. The lubricants must display good water and air release, low foaming, good corrosion protection, FZG Wear protection > 12 in gearboxes, good aging resistance and compatibility with standard elastomers [13.4]. As there are no established standards for water turbine oils, the existing product specifications for general turbine oils are adopted as basic requirements. The viscosity of water turbine oils depends on the type and design of the turbine as well as its operating temperature and can range from 46 to 460 mm 2 s –1 at 40C. Type TD and LTD lubricating and control oils according to DIN 51 515 are used. In most cases, the same oil can be used for bearings, gear- boxes and control equipment. In many cases, the viscosity of these turbine and bear- ing oils is between 68 and 100 mm 2 s –1 . When starting up, control and gearbox oil temperatures should not fall below 5C and bearing oil temperatures should not fall below 10 C. In the case of machinery located in cold ambient conditions, the instal- lation of oil heaters is strongly recommended. Water turbine oils are subject to little thermal stress, and as oil tank volumes tend to be high, the life of water turbine oils is very long. In hydroelectric power stations, the oil sampling and analysis intervals can be correspondingly long. Particular care should be taken when sealing the tur- bine’s lubricating oil circuit from possible water ingress. In recent years, rapidly bio- degradable water turbine oils based on saturated esters have proven successful in practice. Compared to mineral oils, these products are more rapidly biodegradable and are allocated to a lower Water Pollution Category. In addition, Type HLP 46 hydraulic oils (zinc and ash-free additives), Type HEES 46 rapidly biodegradable fluids and NLGI grade 2 and 3 greases are used in hydroelectric plants [13.4]. 384 The great flexibility and versatility of the different types of machining method are particularly significant in the metalworking industries. Although for some years now there has been a growing trend towards non-cutting (forming) methods for workpiece quality reasons and to save material and process costs, this has still not had any obvious effects on the volume share of lubricants. This is also apparent from the machine tool statistics. The dramatic change prophesied in the nineteen seventies did not take place in the nineteen eighties and nineties. Because of the particular significance of cooling for the cutting operation, this process is called cooling lubrication and the fluids used are called coolants. Apart from this term coolant’ which is commonly used in general practice, there are also numerous other terms for specific applications such as, for example, cutting oils, grinding oils, reaming oils, deep hole drilling oils and honing oils. There are no exact figures available as to how many machining operations are carried out without using coolants. However, there is no doubt that wet machining is applied very much more frequently than dry machining. Since 1996, efforts have been made to extend dry machining in particular through research projects. The advantages of cutting fluids can be summarized briefly as follows: accelerated heat dissipation with increased tool service life to make higher cutting speeds possible, lubrication between tool, chip and workpiece with reduced tool wear and improve- ment of the quality of the workpiece surface finish, lubrication of sliding points out- side the actual cutting zone between tool, workpiece and chips and improved chip removal. Frequently less attention is paid to lubrication outside the tool–chip contact zone which, nevertheless, can be very important. To be mentioned at this point are, for example, margins of twist drill and reamers as well as the support and guide rails on deep hole drills and honing tools. In daily practice, after the selection of a suitable coolant, the problem of lubrica- tion and cooling often takes a back seat for a long period. The actual daily work is determined by the correct application and care of these fluids and the numerous secondary demands put on them. As a result the handling of these secondary demands is to be given great attention in the following. Secondary demands and coolant care are also important cost factors in the coolant system, which is why they are also becoming more important when studying the system. 14 Metalworking Fluids Theo Mang, Carmen Freiler and Dietrich Hörner Lubricants and Lubrication. 2nd Ed. Edited by Th. Mang and W. Dresel Copyright  2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 978-3-527-31497-3 38514.1 Action Mechanism and Cutting Fluid Selection 14.1 Action Mechanism and Cutting Fluid Selection The simplest geometrical model for a machining operation is demonstrated by the orthogonal cut in a two dimensional view with continuous chip formation (Fig. 14.1). The cutting lip of the tool pushes into the workpiece after overcoming a crowding force and shearing occurs. The chip formed slides over the cutting face of the tool. The main forming work is carried out in the region of the shear zone, the position of which is defined by the idealized shear plane and the shear angle. One also talks about the primary shear zone. However, the friction between chip and tool has particular significance for lubrication and cooling. This causes the shearing action in the contact zone of the tool material (secondary shear zone) and influences the position of the shear plane, the size of the shear angle and the plastic deforma- tion of the material in the shear zone. The magnitude of the plastic deformation, which is also expressed in the chip crowding, becomes greater with increasing tool face friction. However, here the chip crowding is still influenced by other factors, such as the tool geometry and material properties. As far as this is concerned the direct influ- ence of friction on chip formation can be recognized, which can also cause a change in chip form. The influence of friction on the plastic deformation when machining by cutting has pushed the traditional explanation using the friction coefficient into the background in view of the latest explanations as to the effects of cutting fluids. New working models have been created and the basics of plasticity principles taken into account. The decisive result of friction is tool wear. Figure 14.2 shows typical wear phe- nomena on cutting tools [14.1]. Material particles weld onto the cutting edge of the tool, leading to so-called built-up edges. This makes materials with high formability particularly susceptible to this tool destroying phenomenon (adhesion). Also, certain structure components of steel (austenite, ferrite) and cast iron (ferrite) can promote built-up edge formation. Apart from the influence on the cutting conditions the cut- ting speed can be especially effected. Chip Workpiece Tool a b c d e f g h i Fig. 14.1 Chip formation with orthogonal cutting. a, cutting depth; b, chip depth; c, primary shearing zone; d, secondary shearing zone; e, contact zone; f, chip surface; g, front clearance; h, shearing angle; i, shear plane; b/a chip compression. 386 14 Metalworking Fluids 14.1.1 Lubrication There have been very different ideas on the action mechanism of cutting fluids over the last few years. It is mainly assumed that cooling alone reduces wear at high cut- ting speeds. However, it did not seem possible that the cutting fluid could penetrate into the contact zone between chip and tool at the cutting point in order to have a tribological effect. In general, a tribological significance of cutting fluids has only been determined in the lower cutting speed range. This opinion is still valid today for a number of cutting techniques; nevertheless the tribological effects are becom- ing more and more important as a result of new findings. For example, more favor- able results are achieved with grinding oils for high performance grinding at very high speeds than are achieved with water-miscible products. The special effect of EP additives and the less favorable cooling properties of the oils compared to water-mis- cible products reflects the overwhelming importance of lubricant properties [14.2]. When machining by cutting, a very reactive clean’ workpiece material surface is continuously generated which can tend to react adhesively on the cutting surface of the tool in the workpiece material–tool contact zone. It must be assumed that this reactive surface not only tries to saturate the free valences of the tool material but that other available substances are also involved which can be bonded by absorption, chemical absorption or chemical bonding. The oxygen in the air plays a particular role. In numerous tests under vacuum it has been possible to establish that the tool wear is considerably reduced through the saturation of the surface opened up by cutting, compared to where a gas or gas mixture has been available at different par- tial pressures. This is why it is known today that even in the case of dry cutting changes in the absorption and reaction properties of the material lead to changes in the tribology and, as a direct consequence, wear. Coolant penetration into the contact surface according to more recent knowledge [14.3] is via a network of capillaries which are linked to each other. The magnitude of the capillary diameters are said to be 10 –3 to 10 –4 mm. Questions of transport kinetics indicate a special role, especially the diffusion speed. It must be assumed that it is frequently not the coolant as a whole but rather the component parts, brought about by evaporation or decomposition (pyrolysis) which impart a tribologi- cal effect. It has been established in laboratory cutting tests on model substances with chlor- ine that lubrication is improved by the following aspects: Pitting erosion Front clearance wear Tip wear Surface wear Fig. 14.2 Significant forms of wear on cutting tools. 38714.1 Action Mechanism and Cutting Fluid Selection . high reactivity of the effective components with the surfaces; . low shear strength of the reaction layer (lower than that of the basic metal); . favorable diffusion properties of the effective components (lower molecular weight, higher vapor pressure). As far as the saturation process of the newly formed surface is concerned, the surface will never be completely covered by lubrication effective molecules; there will be a clear gradient of surface activity in the direction of the tool tip, with little reaction at the outer range of the tool. High normal pressures will also prevent lubricant transport when machining materials which are difficult to cut. The assessment of cutting tests with model substances has revealed that 30 % saturation of the contact surface between chip and tool phase lead to the friction force being reduced by 75 % [14.3]. Even today in the development of coolants this knowledge is still not taken into sufficient consideration and it is still relegated by other priorities into secondary position. 14.1.2 Cooling In view of the findings relating to cooling and lubrication, it is impossible to differ- entiate the two. The changes in material properties caused by temperature are close- ly associated with the effects of friction. Cooling gains increasing significance for tool wear when maximum cutting temperature approaches the softening point of the tool material. The example shown in Fig. 14.3 [14.1] reveals how temperature can develop on a cutting surface dependent on cutting speed and chip thickness. On one hand the cooling effect of the cutting fluid and the heat dissipated depends on its thermal properties, especially the heat capacity and the heat transfer 0 60 120 180 24 0 Cutting speed [m/min] 400 800 1200 1600 Maximum chip surface temperature [°C] c b a Fig. 14.3 Dependence of tool surface temperature on chip thickness, h, and cutting speed [14.1]. (a) h = 0.062 mm; (b) h = 0.25 mm; (c) h = 1.00 mm. [...]... between internal and Particle [%/mm] One main particle size distribution peak Several particle size distribution peaks Particle Diameter [mm] Fig 14.11 Particle size distribution for emulsions 409 410 14 Metalworking Fluids external phase and the square of the particle radius, and directly proportional to the viscosity of the external phase: 1/v = Kg/[r2g(d1 – d2)] where v is the rate of climb and descent,... code letters also given in the above standard are used as an abbreviation for the lubricants themselves and are used to mark lubricant drums, lubricating equipment and lubricating points In this case, the first letter, S, stands for metalworking fluids and the letter E stands for lubricating oils which are used mixed with water The letter M in the third position stands for a water-miscible coolant with... hardened and annealed steels (C 15, C 35, 16MnCr5) – Automatic machine steels (9S20, 9SMnPb23) – Construction steels (St37, St60) 80 Group 2 Difficult to machine steels – High alloyed hardened and annealed steels (24CrMo5, 42CrMo4) – High alloyed chromium steels (X8Cr17, X40Cr13) – High alloyed chromium nickel steels (15CrNi6, 18CrNi8) – Rust and acid resistant chromium nickel steels (X2CrNi 189 , X10CrNiMoNb 181 0)... steels (X2CrNi 189 , X10CrNiMoNb 181 0) – Cast steel (GS-Ck16, GS-37SiMn75) 50 Group 3 Most difficult to machine special materials – Nickel and nickel alloys (NiCr10, NiCr 182 0) – Manganese and silica-manganese steels (40MsCr22, 65SiMn5) – Chromium molybdenum steels (24CrMo5, X6CrMo4) – Silicon steels (38Si6, 55Si7) – Titanium and titanium alloys (TiAI6V4, TiAI7Mo4) 25 Group 4 Gray and tempered cast iron (GG-25)... type having friction-reducing and/ or extreme pressure (E.P.) properties Concentrates giving, when blended with water, transparent solutions having anticorrosion properties Concentrates of MAG type having friction-reducing and/ or extreme pressure (E.P.) properties Greases and pastes applied blended with water In this very detailed list the letter L stands for lubricants M stands for metalworking but each... development and product control Only in a few cases has a serviceable relationship been found between the values of a four ball apparatus (VKA), the Almen–Wieland Test (AWT) or the Reichert Wear Test (RVT) and the service-life values of tools in operation [14 .8] This applies also to the methods used more in the English speaking regions, such as the Falex Test [14.8c, d, e] or the Timken Test [14.8f ] 14.2.1... concentrates and water-mixed finished products and in general, the terms non-water-miscible coolants and water-miscible coolants are defined The concentrates, as they are delivered to the user by coolant manufacturers are called water-miscible cutting fluids, the finished products are diluted with water by the user and called diluted cutting fluids These terms are generally used today in literature and, unlike... % of today’s wet machining will be replaced by dry machining and minimum quantity lubrication 14.1.3.7 14.1.4 Cutting Fluid Selection for Various Cutting Methods and Cutting Conditions The categorization of the different types of cutting fluids to the various cutting processes and the different cutting conditions (especially material, feed and cutting speed) has been attempted repeatedly in many documents... although the additional letters N and W are still not included in this Apart from this German terminology, ISO 6743 has become established for use in the international field and is defined under Part 7 of the metalworking group (Table 14.4) Tab 14.4 L-MHA L-MHB L-MHC L-MHD L-MHE L-MHF L-MHG L-MHH L-MAA L-MAB L-MAC L-MAD L-MAE L-MAF L-MAG L-MAH L-MAI Classification of lubricants for metalworking (family... with very high pearlite content (> 95 %) Hard part machining is an important area of application for CBN and in 14.1.3.5 14.1 Action Mechanism and Cutting Fluid Selection the case of certain materials also dry machining or the use of reduced volume or minimum quantity lubrication 14.1.3.6 Polycrystalline Diamond (PCD) This is the hardest workpiece material and is given preference when used as a sinter . Freiler and Dietrich Hörner Lubricants and Lubrication. 2nd Ed. Edited by Th. Mang and W. Dresel Copyright  2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 9 78- 3-527-31497-3 385 14.1. VDMA Sheet 24 314 and CETOP RP 86 H [13.4]. 13.11 Lubricants for Water Turbines and Hydroelectric Plants Hydroelectric power stations have to pay particular attention to the handling of water-polluting. application and care of these fluids and the numerous secondary demands put on them. As a result the handling of these secondary demands is to be given great attention in the following. Secondary demands