Lubricants and Lubrication Part 10 pptx

49714.8 Metalworking Fluid Circulation System Petroleum Ether-extractable Components The presence of petroleum hydrocarbons are most often determined by extraction with petroleum ether. However, it should be remembered that other products may also be extracted. Exact determination of hydrocarbon content requires another ana- lytical step (e.g. chromatography). Petroleum ether extractables have been divided up into saponifiable and non-saponifiable components. Thresholds and Legislation There are no national guidelines on the quality of separated-water in Germany and in Britain which can assist the operator of cutting fluid separation plants. Thresh- olds are set by local water authorities which can also reflect the local situation regarding waste water treatment plants and the condition of rivers and streams. This leads to greatly differing evaluations between areas. Apart from BOD 5 and COD and petroleum ether extractables, pH value, insoluble solids, a series of metals and ions such as sulfate, cyanide and nitrite have thresholds. As regards the latter, the importance is either their toxicity or, as in the case of sulfate, the damage it causes to concrete pipes and drains. In Germany, national legislation only applies indirectly to water separated-out of emulsions. Among other things, the German Law on Water regulates the disposal of wastes into public sewers and rivers, the notification obligation if petroleum prod- ucts are stored or the location of protected water zones. German Waste Disposal Law deals with the treatment of sludges which remain after emulsion separation processes. This includes incineration, land-fill and special land-fill sites for hazardous wastes. The German Law on Emissions is focussed on keeping the air clean. As regards disposal of cutting fluids, this is limited to incineration of separated oils and used emulsions. Extreme Pressure (EP) agents with high levels of sulfur and chlorine can be problematic. Waste Oil Provisions, whose focal point up to now was protecting the ground, water and air, have gained economic significance with the increase in recycling. The German Waste Water Levy affected all who disposed of waste water into rivers and streams. The level of the payments depend on the contaminants in the water. Such contaminants are determined by the amount of insoluble solids, Chemical Oxygen Demand and fish toxicity. Even though this levy does not directly affect the operator of emulsion separation facilities, but mainly the operator of waste water treatment plants, it does influence emulsion separation technologies and the possi- ble initial formulation of emulsion concentrates. Those disposing of waste water into rivers etc. try to use the causer pays’ principle to transfer the costs to the user of the cutting fluids [14.108–14.110, 14.155]. 14.8.7.3 Electrolyte Separation Salt Splitting Splitting water-miscible cutting fluids with salts is still widely practiced for conven- tional emulsions. The addition of salts such as sodium chloride, magnesium chlo- 498 14 Metalworking Fluids ride or calcium chloride affects the efficiency of the emulsifiers. This breaks down the emulsion and the lighter oil phase floats to the top. This floating oil can be col- lected by an overflow pipe or by pumping the water phase out from below. Large separation plants use centrifuges to accelerate the process. Overall, the capital investment costs of salt separation are comparatively low. Figure 14.43 illustrates the simple principle of salt splitting. The splitting process can also be accelerated by heating the emulsion up to 90 C. The emulsion and the splitting salts should be stirred vigorously to assist the pro- cess. Price is a major factor in the selection of the salt. Sodium chloride is the cheapest but also the slowest. Ferrous and aluminum salts have good separation properties but require subsequent hydroxide precipitation with adsorption. Separated water normally contains more than 150 mg l –1 petroleum ether extrac- table components. As most thresholds range from 10 to 20 mg l –1 , this means that subsequent treatment is necessary. The considerable salt contamination in separat- ed water which can be over 1500 mg l –1 , is a further limitation to the use of salt splitting because such salt concentrations are unacceptable for waster water treat- ment plants and, of course, rivers. The best salt splitting results are obtained with conventional emulsions using high levels of anionic emulsifiers. As the general trend is towards greater electrolytic stability of emulsions, electrolytic splitting pro- cesses are gradually disappearing due to their less satisfactory results with more modern coolants. Acid Splitting Similarly to salt splitting, emulsions can be split with the acids which many plants have used for etching processes (sulfuric and hydrochloric acid). Separating emul- sions with acids is faster than with salts and, in the case of stable emulsions, also more effective. Particularly effective acid separation processes are often combined with physical or physico-chemical splitting methods. Successful processes are those which employ splitting temperatures of over 90 C and a downstream separation column filled with inorganic solids to accelerate the splitting process. Such acid splitting combina- Stirrer Salt solution feed Split oil overflow Treated waste water Heating Process tank Floating oil Contaminated emulsion feed Fig. 14.43 Emulsions undergoing salt splitting. 49914.8 Metalworking Fluid Circulation System tions can generate petroleum ether extractable values of under 20 mg l –1 . Neutrali- zation of the separated water is necessary. The electrolyte content in the separated water, as in salt splitting, is also a problem. 14.8.7.4 Emulsion Separation by Flotation In this procedure, fluid droplets are dispersed by air bubbles. Emulsion oil droplets and solid impurities are carried to the surface by the air. However, as only hydropho- bic oil droplets float, hydrophilic oil droplets must be treated by breaking-down the emulsion. The air bubbles necessary for flotation can be created in a number of ways [14.111]: . in release flotation, the air bubbles are formed as water which is saturated with air is de-pressurized. . in stirring flotation, air is distributed throughout the fluid by rapid agitation. Electro-flotation has become an accepted form of emulsion separation. The elec- trolytic breakdown of water releases hydrogen and oxygen. If total-loss electrodes are used, the metal ions (iron, magnesium and aluminum) which end-up in solution split the emulsion. The precipitating hydroxide floc absorb the oil and then float back to the surface through a layer of oily sludge. This method is a combination of salt splitting, adsorption splitting and flotation. A major hazard of electro-flotation is the formation of mixed oxygen and hydrogen gases. 14.8.7.5 Splitting of Emulsions with Adsorbents Adsorption with Amorphous Silica Adsorption with hygroscopic, fine-grain (ca 10 lm) amorphous silica has been gain- ing popularity. The process involves the powdery adsorption medium being placed in the emulsion. The oily and watery sludges formed can be de-watered with belt- type filters or filter presses. To keep the cost of the expensive adsorption medium under control, adsorption sep- aration is often preceded by salt splitting because the adsorbent consumption depends on the amount of oil in the emulsion. A rough guide to the consumption of adsorbent is 30 % weight of the oil in the emulsion. It must be remembered that non-ionic emulsifiers which are often unaffected by electrolyte splitting are easily adsorbed by amorphous silica. On the other hand, anionic emulsifiers are poorly adsorbed [14.112]. Hydrophilic amorphous silica, which is of major importance to adsorptive emulsion separation, is most effective on anionic-active emulsifiers. Adsorption with Metal Hydroxides In the case of salt splitting with ferrous or aluminum salts, subsequent alkalization can precipitate the metals as hydroxides. The hydroxide flakes thus formed readily adsorb oil droplets and emulsifiers. Anionic emulsifiers are much easier to process than non-ionic products. 500 14 Metalworking Fluids In general, such combinations of salt and adsorption separation processes using aluminum and ferrous salts can provide good splitting results with low oil and salt levels in the separated water. However, the disposal of oily hydroxide sludges is a big problem. The problem is somewhat eased if filter presses are used to de-water the sludge. Figure 14.44 shows a schematic diagram of the emulsion splitting process with the two stages: salt splitting and adsorptive hydroxide precipitation. 14.8.7.6 Separating Water-miscible Cutting Fluids by Thermal Methods Thermal separation processes use heat to evaporate the water in cutting fluid emul- sions which is then re-condensed. Such processes require the implementation of some sort of energy recovery. Although disadvantages include expensive technical equipment and high energy costs, the most important advantage is its suitability for almost all types of water-miscible cutting fluids. Contrary to the previously-men- tioned methods, thermal processes do not require a dispersed organic phase but can also separate real organic solutions, popularly known as fully synthetic cutting fluids. Immersion Heaters Immersion heater separation involves a gas- or oil-fired immersion heater being lowered into the emulsion. The water which evaporates and then re-condenses must normally be treated because organic compounds can be released during the evapora- tion process. This method has never found great acceptance because the exhaust gas problems can only be eliminated at great expense. Thin-film Evaporator This method has a promising future. The method involves the water in the emul- sion being evaporated on indirectly-heated evaporation plates. The quality of the evaporated water normally requires some subsequent treatment but generally less than in the immersion heater method. Active charcoal filters have proved successful for treating the water. Incineration The incineration or thermal treatment of water-miscible cutting fluids works with some highly-concentrated cutting fluids. Burning cutting fluids in heating systems requires the cutting fluid to be clean and also some modification to the nozzles. In the case of conventional emulsions, heat output is reduced if the emulsion concen- tration is less than 6 %. The incineration of cutting fluids containing chlorine com- pounds can cause damage to the furnaces. And finally, cutting fluids with large pro- portions of EP additives can cause exhaust gas emission problems. 14.8.7.7 Ultrafiltration This method of separating water-miscible cutting fluids has gained the most accept- ance over the past few years. Ultrafiltration involves the cutting fluid being passed through a semi-permeable membrane under pressure. Water and low-molecular- 50114.8 Metalworking Fluid Circulation System Stirrer Coagulating agent feed Treated waste water Process tank Contaminated emulsion feed Sludge de- hydration filter Sludge Water from sludge dehydration Stirrer Acid/ acid salt feed Split oil overflow Acid water Acid splitting process tank Contaminated emulsion feed Alkaline feed Filter press Hydroxide precipi- tation tank Hydroxide precipi- tation waste water Treated water Oily hydroxide sludge Dehydrated hydroxide sludge outlet Fig. 14.44 Splitting of emulsions with adsorbents and schematic diagram of the emulsion splitting process with the two stages; salt splitting and adsorptive hydroxide precipitation. 502 14 Metalworking Fluids weight substances can pass through the membrane and form the permeate while oil droplets and large-molecular-weight substances are retained. The actual filter, which is the heart of ultrafiltration equipment, is often a stacked module in which organic materials such as polyamides, cellulose acetates or inorganic materials are used. If modules of organic materials are used, make sure that the fluid to be separated is free of solvents which can destroy the membranes. Figure 14.45 illustrates the ultra- filtration principle. As separation performance falls with increasing concentration in the retained material, 30–50 % has proved to be an acceptable figure. The enriched, retained material could be treated by evaporators to produce material with less than 10 % water content. Ultrafiltration plants consume little energy and they can mostly be run continu- ously and automatically. The capacity can be varied to meet needs by selecting the number of modules in the circuit. There are ultrafiltration plants with capacities ranging from a few hundred liters per day through to 1000 l h –1 . The retained filtrate has a low hydrocarbon content but often a relatively high COD. This could become an important factor if ultrafiltration is evaluated according to the German waste water levy system. In some circumstances, ultrafiltered fluids can be reused similarly to the recycling of degreasing baths. With the necessary technical complexity through to reverse osmosis which can generate drinking water quality, this type of cutting fluid separation offers a wealth of further development opportunities. 14.8.7.8 Evaluation of Disposal Methods The selection of the disposal method must take into consideration the applicable thresholds, the cutting fluid volumes, the disposal of filter residues, investment costs, operating costs and personnel costs. If a metalworking factory only generates small quantities of used cutting fluid emulsions (e.g. less than 3 m 3 per week), in- house splitting is not recommended and it is cheaper to hire a disposal company. The most reliable method of meeting all waste water thresholds for all types of cut- Module Treated water Tank Concentrated oil Pressure feed to membrane module Feed of cutting fluid free of solid contaminants Floating oil outlet Fig. 14.45 The continuous separation of water-miscible cutting fluids by ultrafiltration. 50314.9 Coolant Costs ting fluids including fully synthetic solutions are the thermal processes. However, these normally require high capital expenditures. For lower investment costs, good waste water values, low personnel requirements and very low operating costs, ultra- filtration is a good alternative. Salt and acid splitting methods require the least investment but high operating costs, high personnel requirements and above all, residue disposal problems limit their practicability. For special applications, electro- flotation and thermal acid splitting in columns are possible solutions. Optimized combination of evaporation with ultrafiltration as methods of treat- ment could eliminate production of waste water in workshops. This complete water- recycling concept has been realized in some European manufacturing plants. 14.9 Coolant Costs This issue has had a considerable influence on the development of coolants in the nineties. This was not so much a matter of the costs of the volume of coolants bought by the consumer but rather the costs for the use of the coolants which are considerable, at approx. 12 % of production costs (serial production, central circula- tion systems). In this case the actual coolant costs themselves are only about 1 %. Pioneer work in system cost analysis has been done especially by Fuchs Petrolub AG [14.113], Daimler Chrysler [14.114], K. Weinert [14.115]. 14.9.1 Coolant Application Costs Coolant application costs include the costs for the operation of all equipment, the investment costs as well as the coolant costs, costs for their preparation and dispo- sal, energy costs, costs for coolant care as well as the costs for all auxiliaries. However, to assess coolant systems the influence on the entire production sequence also has to be considered, for example, on tool costs, setting up times for tool changing, degree of machine utilization, workplace safety, workpiece quality. 14.9.1.1 Investment Costs (Depreciation, Financing Costs, Maintenance Costs) This is the most significant proportion of the costs and is some 60 % of the coolant application costs in serial production with central systems. This includes the costs of the plant tanks, pumps, pipelines, filter equipment, delivery of the coolant to the machine tool, de-oiling the chips, tramp oil separators and extraction systems. It is also possible to consider depreciation and maintenance for coolant splitting and dis- posal systems. Since preparation and disposal are frequently carried out by third parties it is more expedient to total these costs in a cost analysis (for example, as costs m –3 ). 504 14 Metalworking Fluids 14.9.1.2 Energy Costs These include all the energy costs to operate the above-mentioned equipment in- cluding lighting. 14.9.1.3 Coolant and Coolant Additives Summarized under this are the costs for buying the coolant, chemical additives as well as the mix water. 14.9.1.4 Coolant Monitoring These are the costs for the analysis and labor costs for coolant care and monitoring. 14.9.1.5 Other Auxiliaries These are filter materials for coolant filtration and extraction. 14.9.1.6 Coolant Separation and Disposal Summarized here are the costs for the splitting of water-miscible products and the disposal of the oil and water phase. 14.9.2 Coolant Application Costs with Constant System Shown in the following is an analysis for the use of water-miscible coolants with a standard continuous system. It is assumed that the coolant circulation system is pre- determined and cost minimization can only be achieved by selecting the right water- miscible coolants [14.113]. 14.9.2.1 Specific Coolant Costs To make the following optimization considerations more understandable it is first necessary to define some terms. Circulation Factor, f This shows how many times the total volume of a coolant system –whether it is an individually filled machine or a central system – is circulated by pumping in 1 h. For example, the same number of machines can be supplied with a small volume in a central system and higher circulation number as with a high volume and a small circulation number. Here it is also obvious that the coolant in the system with a high circulation number is more stressed and the specific drag out losses –related to the volume–are greater. The coolant requirement for machine tools is normally given in l min –1 . If the circulation factor, f, is only defined for the volume flow which runs through the machine tools and possible hydraulic chip transport by special coolant nozzles is ignored, then the following is valid: 50514.9 Coolant Costs f = 0.06B/V (h –1 ) where V is the coolant system volume and B coolant machine tool requirement in l min –1 . Drag-out Coefficient, a This is understood to be the number of times the volume of a plant is changed per month. A drag-out coefficient a = 1 means that the total volume is taken out of the system and has to be replaced every month; a drag-out coefficient a = 4 means change every week and a = 0.25 change of the volume after 4 months. Figure 14.46 shows the most important working area of coolant circulation sys- tems concerning the drag-out coefficient and circulation factor. The coolant losses take place on the one hand by chips, especially in the serial production sector with close interlinking of different working processes and through drag-out losses through geometrically complex parts such as, for example, engine crank or transmission housings. High costs are incurred for the coolant itself and for the disposal of the coolant from systems with high drag-out coefficient a. In the case of a lower drag-out coefficient, these costs are low by comparison; however, the maintenance costs are higher through the rapid increase in the concen- 0 5 10 15 Circulation factor [1/h] 0 0.25 0.50 0.75 1.00 1.50 2.00 2.50 3.00 3.50 4.00 Drag-out coefficient [1/month] Fig. 14.46 Most important working area for central circulation systems in respect of drag-out coefficient and circulation factor. 506 14 Metalworking Fluids tration of harmful substances. Since, in systems with high drag-out, fresh coolant has to be filled over and over again, the concentration of harmful substances remains at a lower level. In this case the most significant harmful substances are tramp oils from leakage, other dragged-in coolants, corrosion protection agents from machined parts, dragged-in cleaners, heat treatment salts, non-filterable con- tamination from outside, water salt enrichment, decomposition products of coolant and microorganisms. The following consequences arise due to over-concentration of harmful substances due to drag-out: either high care costs are obtained when using coolants with low drag- out coefficients, or more stable and thus also more expensive products must be used. Figure 14.47 shows how the maintenance costs per kilo of water-miscible coolant used can depend on the drag-out coefficient; the curve shows the average values given in serial production over many years in studies. The easiest way is to consider costs for coolant systems when both the different types of costs and the full costs are related to 1 m 3 volume of the system; 1 year is selected as the calculation period. The various costs can then be expressed as costs units (KE) per m 3 and year. The following breakdown has been split into three cost groups for the specific total costs K: k 1 = Costs for coolant change k 2 = Costs for drag-out losses k 3 = Costs for coolant maintenance This is then applicable: K = k 1 + k 2 + k 3 0,25 1 1,5 20,5 0,50 1,00 1,50 Drag-out coefficient a [1/month] Maintenance costs [KE/kg] Fig. 14.47 Maintenance costs. [...]... concentration and particle size 14 .10. 2.3 Coolants for Minimum Quantity Lubrication Today greases and oils as well as esters and fatty alcohols are in use, apart from conventional mineral oils and water-miscible coolants Since minimum quantity lubrication is a matter of pure total loss lubrication and the coolant is frequently completely dispersed in the working area in the form of vapors and mist, particular... low-emission metalworking with minimum quantity lubrication, correct selection of the lubricant is of decisive importance To minimize emissions, the lubricants used should be toxicologically and dermatologically safe, with favorable lubrication properties and high thermal stress capacity 14 .10 New Trends in Coolant Technology Synthetic ester oils and fatty alcohols, in particular, which have low evaporation... the anisotropy and finally, the formability of the material As friction and wear take place at the surface, the material’s micro structure near the surface and any coatings have a fundamental effect on any operations on the material Finally, the lubricant is described by its chemical additives and physical properties such as viscosity Lubricants and Lubrication 2nd Ed Edited by Th Mang and W Dresel Copyright... The “Unifluid” with 10 mm2s–1 at 40 C shows excellent results in a german automotive engine plant for machining and lubricating a complete transfer line (including the hydraulic system) 14 .10. 1.4 14 .10. 2 Minimum Quantity Lubrication The ever-changing legislation and an ever increasing awareness of the environment have led to a change in the production processes used up to now and especially in the... iron, steel and aluminum Fatty alcohols offer the advantage that the machined parts are dry as a result of the rapid evaporation However this evaporation must be considered critically because of the threshold values for oil mist and oil vapor in the workplace (10 mg m–3) Ester oils are used with preference for all machining operations in which the lubrication effect between tool and workpiece and the passing... achieved in the fields of emission and of optimization of a coolant medium for minimum quantity lubrication areas 14 .10. 2.4 Oil Mist Tests with Minimum Quantity Lubrication When metalworking with minimum quantity lubrication systems, aerosols are generated which need to be delivered to the machining point, and high concentrations of the aerosol gets into the working atmosphere, particularly when using external... eliminated because undesirable mixtures are avoided as a result of compatible lubricants Chips and solid contaminants are removed from the cutting fluid by ultra-fine filtration Apart from the high investment costs of washing lines, detergent, energy, water and monitoring costs are also eliminated 14 .10. 1.2 14 .10. 1.3 De-oiling of Chips and Machined Components The harmonized additives in all process oils allows... coatings along with evolving workplace health and safety concerns There are so many processes in sheet metal working that these cannot all be covered here Besides deep- and stress-drawing stamping and fineblanking will be covered in this chapter Process combinations are frequently used and secondary demands placed on lubricants in forming operations including stamping and fineblanking are often similar 15.1.2... However, it has been shown that, particularly in the case of processes with a geometrically non-defined cutting edge, both cooling as well as lubrication are necessary to increase the service life of a tool In the case of grinding and honing the cooling and rinsing effect of the lubricant is particularly important to the process The coolant system plays an important part in the functionality of a machine... result in lower overall costs than the low priced, less stable products On the other hand it is also revealed that the lowest total costs are given in medium size and large central systems with particularly high carry-off of low priced products 509 510 14 Metalworking Fluids 14 .10 New Trends in Coolant Technology 14 .10. 1 Oil Instead of Emulsion Back in the early nineties, the discussion about replacing . concentration and particle size. 14 .10. 2.3 Coolants for Minimum Quantity Lubrication Today greases and oils as well as esters and fatty alcohols are in use, apart from con- ventional mineral oils and water-miscible. hand it is also revealed that the lowest total costs are given in medium size and large central systems with particularly high carry-off of low priced products. 510 14 Metalworking Fluids 14 .10 New. different lubricants are used in every machine tool. Apart form the leakage problem and the incompatibility of some lubricants, costs are also generated by the stocking of all necessary lubricants.