Lubrication Fundamentals 2011 Part 4 pps

Figure 5.8 Glycols. Ethylene glycol is the simplest glycol; when polymerized, the oxygen bond is formed and it becomes a polyglycol ether. for the bulk of the materials used in lubricants. Small quantities of simple glycols, such as ethylene and polyethylene glycol, are also used as hydraulic brake fluids. Typical structures for the two types are shown in Figure 5.8. Polyglycols are polymers made from ethylene oxide (EO), propylene oxide (PO), or their derivatives. The primary raw materials are ethylene or propylene, oxidized to form cyclic ethers (alkylene oxides). Combining ethers derived from ethylene oxide (EO) to propylene oxide (PO) has a profound effect on the solubility of the product in other fluids: EO:PO ؄ 4Ϻ1 Water-soluble, not soluble in hydrocarbons EO:PO ؄ 1Ϻ1 Soluble in cold water, soluble in alcohol and glycol ethers, not soluble in hydrocarbons EO:PO ؄ 0Ϻ1 Not soluble in water, conditionally soluble in hydrocarbons These comparisons help explain the differences between the various types of, and uses for, polyglycol: automotive antifreeze, brake fluid, water-based hydraulic fluids, hy- drocarbon gas compressors, and high temperature bearing lubricants. In addition to ethyl- ene and propylene oxides, butylene oxide is used to provide some polyglycols with specific properties and is oil soluble. Polyglycols made with butylene oxide are more expensive and do not exhibit traction coefficients equal to combinations of EO and PO. One of the major advantages of polyglycols is that they decompose completely to volatile compounds under high temperature oxidizing conditions. This results in low sludge buildup under moderate to high operating temperatures, or complete decomposition with- out leaving deposits in certain extremely hot applications. Polyglycols have good viscos- ity–temperature characteristics, although at low temperatures they tend to become some- what more viscous than some of the other synthesized bases. Pour points are relatively low. High temperature stability ranges from fair to good and may be improved with additives. Thermal conductivity is high. Not generally compatible with mineral oils or additives developed for use in mineral oils, polyglycols may have considerable effect on paints and finishes. They have low solubility for hydrocarbon gases and some refrigerants. Seal swelling is low, but with the water-soluble types some care must be exercised in seal selection to be sure that the seals are compatible with water. Even if the glycol fluid does not initially contain any water, it has a tendency to absorb moisture from the atmosphere. The applications for the polyglycols are divided into those for the water-soluble types and those for the water-insoluble types. The largest volume application of water-soluble polyglycols is in hydraulic brake fluids. Other major applications are in metalworking lubricants, where they can be removed by water flushing or being burned off, and in fire-resistant hydraulic fluids. In the latter application, the polyglycol is mixed with water, which provides the fire resistance. Water- Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. soluble polyglycols are also used in the preparation of water-diluted lubricants for rubber bearings and joints. Water-insoluble polyglycols are used as heat transfer fluids and as the base fluid in industrial hydraulic fluids of certain types, as well as high temperature gear and bearing oils. They are also finding application as lubricants for screw-type refrigeration compres- sors operating on R12 and hydrocarbon gases, and compressors handling hydrocarbon gases. (The use of R12, a potential ozone layer depleting substance, is being phased out; see Chapter 17 for additional information on refrigeration compressors and refrigerants.) In these latter applications, the low solubility of the gases in the polyglycol minimizes the dilution effect, contributing to better high temperature lubrication. IV. PHOSPHATE ESTERS Phosphate esters are one of the other commonly used classes of synthetic base fluids. A typical phosphate ester structure is shown in Figure 5.9. One of the major features of the phosphate esters is their fire resistance, which is superior to mineral oils. Their lubricating properties are also generally good. The high temperature stability of phosphate esters is only fair, and the decomposition products can be corrosive. Generally, they have poor viscosity–temperature characteristics (low VI), although pour points are reasonably low and volatility is quite low. Phosphate esters have considerable effect on paints and finishes, and they may cause swelling of many seal materials. Their compatibility with mineral oils ranges from poor to good, depending on the ester. Their hydrolytic stability is only fair. They have specific gravities greater than 1, which means that water contamination tends to float rather than settle to the bottom, and pumping losses are higher than is the case with products lower in specific gravity. Their costs are generally high, and they are limited in viscosity. The major application of phosphate esters is in fire-resistant fluids of various types. Hydraulic fluids for commercial aircraft are phosphate ester based, as are many industrial fire-resistant hydraulic fluids. These latter fluids are used in applications such as the electrohydraulic control systems of steam turbines and industrial hydraulic systems, where hydraulic fluid leakage might contact a source of ignition. In some cases they may also be used in the turbine bearing lubrication system. Phosphate esters are also used as lubricants for compressors where discharge temper- atures are high, to prevent receiver fires and explosions that might occur with conventional lubricants. Some quantities of phosphate esters are also used in greases and mineral oil blends as wear and friction reducing additives. Figure 5.9 Phosphate ester. The R group can be either an aryl or an alkyl type. If, for example, the methyl group (CH 3 )isused, the ester is tricresyl phosphate. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. V. OTHER SYNTHETIC LUBRICATING FLUIDS Brief descriptions and principal applications of some of the other synthetic base fluids are given in Sections V.A–V.D. A. Silicones Silicones are among the older types of synthetic fluid. As shown in Figure 5.10, their structure is a polymer type with the carbons in the backbone replaced by silicon. Silicones have high viscosity indexes, some on the order of 300 or more. Their pour points are low and their low temperature fluidity is good. They are chemically inert, nontoxic, fire resistant, and water repellent, and they have low volatility. Seal swelling is low. Compressibility is considerably higher than for mineral oils. Thermal and oxidation stability of silicones are good up to quite high temperatures. If oxidation does occur, oxidation products include silicon oxides, which can be abrasive. A major disadvantage of the common silicones is that their low surface tension permits extensive spreading on metal surfaces, especially steel. As a result, effective adherent lubricating films are not formed. Unfortunately, the silicones that exhibit this characteristic also show poor response to additives aimed at reducing wear and friction. Some newer silicones show promise of overcoming these deficiencies. Silicones are used as the base fluid in both wide temperature range and high tempera- ture greases. They are also used in specialty greases designed to lubricate elastomeric materials that would be adversely affected by lubricants of other types. Silicones are also used in specialty hydraulic fluids for such applications as liquid springs and torsion dam- pers, where their high compressibility and minimal change in viscosity with temperature are beneficial. They are also being used as hydraulic brake fluids and as antifoam agents in lubricants. Some newer silicones are also offered as compressor lubricants. B. Silicate Esters Silicate esters have excellent thermal stability and, with proper inhibitors, show good oxidation stability (see Figure 5.11 for their chemical structure). They have excellent viscosity–temperature characteristics, and their pour points are low. Their volatility is low, and they have fair lubricating properties. A major factor for their limited use is their poor resistance to hydrolysis. Small quantities of silicate esters are used as heat transfer fluids and dielectric coolants. Some specialty hydraulic fluids are formulated with silicate esters. C. Polyphenyl Ethers Polyphenyl esters are organic materials that have excellent high temperature properties and outstanding radiation resistance. They are thermally stable to above 800ЊF (450ЊC) Figure 5.10 Dimethyl polysiloxane, one of the more widely used silicone polymer fluids. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. 6 Environmental Lubricants With concerns for protecting and preserving the environment in all aspects of our daily lives, it is only natural that as lubricant technology has advanced, so has the development of oils and greases that would be less detrimental to the environment if inadvertently spilled or leaked. Accelerating research and development in this area has also been driven by public demand, industry concerns, and governmental agencies to find better ways to protect the biological balance in nature, or at least to reduce the negative impact of spills or leakage of lubricants that do occur. Many names are used for the class of lubricants to address these concerns: environmentally friendly, environmentally acceptable, biodegrad- able, nontoxic, and others. For purposes of discussions in this chapter, we shall refer to this class of lubricants as environmentally aware (EA). Of primary interest in selection and use of this class of EA lubricants is defining and measuring the product attributes that could affect the environment. In addition, the lubricants must provide performance in key areas such as oxidation stability, viscos- ity–temperature properties, wear protection, friction reduction, rust and corrosion protec- tion, and hydrolytic stability where water or moisture may be present. In other words, the EA products must perform at levels equivalent to those achieved by conventional mineral- or synthetic-based lubricants in the equipment, while providing characteristics that reduce the negative impact in the event of inadvertent introduction into the environment. I. ENVIRONMENTAL CONSIDERATIONS Environmental acceptability of lubricants is not well defined and can encompass a broad range of potential environmental benefits: use of renewable resources, resource conserva- tion, pollutant source reduction, recycling, reclamation, disposability, degradability, and so on. Therefore, any claim of environmental acceptability must be supported by appropriate technical documentation. Most petroleum-based lubricants can be considered to be envi- ronmentally acceptable by various standards. For example, long-life synthetics (discussed in Chapter 5) and other lubricants that provide extended oil drain capability might be Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. classed as EA materials because they conserve resources and aid in potential pollutant source reduction (since quantities for disposal will be lower). Many oils can be reclaimed, recycled, or burned for their heat energy value, again resulting in conservation of resources. All these efforts to help reduce the environmental impact of lubricants have positive effects and should be an integral part of the planning to establish an environmental program. The remainder of this chapter is devoted to discussions of a class of lubricants exhibiting specific characteristics such as biodegradability and low toxicity. II. DEFINITIONS AND TEST PROCEDURES The two environmental characteristics most desirable in EA lubricants are speed at which the products will biodegrade if introduced into nature and toxicity characteristics that might affect bacteria or aquatic life. Most lubricants are inherently biodegradable, which means that given enough time, they will biodegrade by natural processes. They will not persist in nature. In certain applications, however, much faster rates of biodegradation are desired. These are referred to as readily biodegradable products. All lubricants range in toxicity from low (sometimes called nontoxic) to relatively high. Toxicity has a direct effect on naturally occurring bacteria and aquatic life and therefore needs to be an important part of the development of EA lubricants. Unlike traditional lubricant development, where the predominant focus is on product performance in equipment, a major part of developing EA lubricants involves understand- ing and defining environmental test criteria and developing ways to assess the effects of new and used lubricants in actual applications where environmental sensitivity is an issue. Since both base fluids and additive systems impact the environmental characteristics, these tests must evaluate the ecotoxicity of base fluids, additives, and finished lubricants. A. Toxicity The impact of lubricants on the aquatic environment is evaluated by conducting acute aquatic toxicity studies with rainbow trout (a freshwater fish that is sensitive to environ- mental changes) or other aquatic life-forms that are sensitive to changes in their environ- ment. Since oil is insoluble in water, the aquatic specimens are exposed under oil–water dispersion (mechanical dispersion) conditions to increasing concentrations of test materials up to a maximum concentration of 5000 ppm. This oil–water dispersion technique follows a modification of the procedure used by the British Ministry of Agriculture, Fisheries and Food (MAFF). In the oil–water dispersion procedure, the test materials are added to aquaria equipped with a central cylinder-housed propeller system that provides mechanical agitation to continuously disperse the test material as fine droplets in the water column. The propeller is rotated to produce flow in the cylinder by drawing small quantities of water and test material from the surface into the top of the cylinder and expelling a suspension of oil droplets in water through apertures near the bottom of the cylinder. This procedure, which simulates physical dispersion by wave and current action, is used to evaluate the relative toxicity of lighter-than-water materials. The aquatic specimens are exposed to five concentrations of test material and a control (without test material) during each study. Toxicity is expressed as the concentration of test material in parts per million (wt/vol) required to kill 50% of the aquatic specimens after 96 hours of exposure (LC 50 ). Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. B. Biodegradability Two tests are most commonly used to assess the biodegradability of lubricants. The shake flask test* is used to determine ultimate biodegradability (conversion to CO 2 )ofthe test material. The second, the CEC (Coordinating European Council) test, is not as discriminat- ing but is widely used in Europe for assessing the biodegradability of lubricants and was, in fact, specifically designed to evaluate the aerobic aquatic biodegradation potential of two-stroke-cycle engine oils. Both tests use a mineral salts mix for the growth medium, with the carbon substrate being supplied only by the test material. Both the shake flask and CEC tests use unacclimated sewage inoculum, which is typically obtained from a municipal wastewater treatment plant that has no industrial inputs. The shake flask test, in addition, utilizes a soil inoculum. The shake test flasks, closed with neoprene stoppers from which are suspended alkali traps, are placed on a rotary shaker and heavily shaken at 25ЊC. Periodically, over a 28- day period, the flasks are removed and titrated to quantify the trapped CO 2 . The medium is then sparged with air to maintain aerobic conditions, and the fresh traps are placed back in the flasks. Blank controls, which are run alongside the flasks containing the test material, have all components present in the test flasks except the test material. At each time point, the quantity of CO 2 evolved from the blanks is subtracted from CO 2 values in the test material flasks. A positive control containing a readily biodegradable material is also run to ensure inoculum viability. ASTM has issued a test for biodegradability to standardize testing for biodegradabil- ity of environmental type products. This test (ASTM D 5846) is a modified Sturm test and very similar to the shake flask test just described. It also measures CO 2 evolution as the bacteria metabolizes the test material. The CEC test utilizes cotton-stoppered flasks and, as with the shake flask test, the flasks are placed on a rotary shaker table and heavily shaken at 25ЊC. At 0, 7, and 21 days, flasks are extracted with Freon 113 and the quantity of test material in each of the extracts is determined by infrared (IR) analysis at 2930 cm ؊1 (C—H stretch). The percent of material biodegraded after 7 and 21 days is determined by comparing the intensity of the IR absorbance in the test flask extracts, after each period of time, against zero time values and against values in the abiotic controls (HgCl 2 -poisoned). C. Environmental Criteria At the present time, there are no generally accepted worldwide regulations to define criteria for lubricants used in environmentally sensitive areas. There are products with limited applications such as those receiving the German Blue Angel Label for lubricants. A lubri- cant can carry a Blue Angel label if all major components meet OECD ready biodegradabil- ity criteria and all minor components are inherently biodegradable. Secondary criteria include a ban on specific hazardous materials, and lubricants must meet aquatic toxicity limits. Based on an evaluation of current legislation for new product registration by the European Inventory of Existing Commercial Chemical Substances (EINECS) and on ma- rine transport requirements by Marpol, the International Maritime Organization (IMO), as well as a review of proposed labeling schemes, there is some consensus in industry for * ‘‘Shake flask test’’ refers to either the U.S. Environmental Protection Agency test described in EPA 560/6- 82-003 or the Organization for Economic Development and Co-operation tests described in OECD 301. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. biodegradation and aquatic toxicity criteria for lubricants that will be used in environmen- tally sensitive areas. A product may be considered acceptable if it meets the following criteria: Aquatic toxicity Ͼ1000 ppm (50% min survival of rainbow trout) Ready biodegradability Ͼ 60% conversion of test material carbon to CO 2 in 28 days, using unacclimated inoculum in the shake flask or ASTM D 5846 test Aquatic toxicity and ready biodegradation studies were conducted on products formulated with mineral oils and non–mineral oil base stocks (Table 6.1). In general, the base stocks that comprise the major component of most lubricant formulations are nontoxic. The aquatic toxicity observed following exposure to the formulated products in Figure 6.1 is caused by one or more of the additives. Vegetable oils, such as Mobil EAL 224H, and a number of synthetic esters easily met the ready biodegradation criterion (Ͼ 60% conversion to CO 2 in 28 days) and always had CEC test results exceeding 90% conversion after 21 days. None of the formulations tested containing mineral oil base stocks were able to meet the ready biodegradation criterion, although 42–49% of these materials were converted to CO 2 in 28 days (Figure 6.1). This does not appear to be a significant difference from the 60% criterion, but in actual field conditions, it is a major difference. The polyglycol-based materials, although soluble in water, failed to meet the ready biodegradability criterion, with only 6–38% of the test material converted to CO 2 in 28 days. The biodegradation of polyglycols is determined by the ratio of propylene oxide to ethylene oxide, with polyethylene glycols being more biodegradable. The average molecu- lar weight of the material is also critical, with material under a molecular weight of 1000 being rapidly biodegraded. The rate and extent of biodegradation diminishes with increasing molecular weight. Some additional studies of the polyglycol materials is needed to further quantify biodegradation rates of these materials. Evaluations of the impact of base stocks used to formulate hydraulic oils, formulated conventional hydraulic oils and EA hydraulic fluids have been conducted to determine the various levels of aquatic toxicity that these materials may exhibit. The toxicity testing was done using the EPA 560/7-82-002 (for all intents and purposes, this is the same test as the OECD 203Ϻ1–12). The results of this study of base stocks and fully formulated hydraulic fluids, given in Figure 6.2, indicate that the toxicity of most lubricants is due to one or more of the additives in the formulation. Table 6.1 Ecotoxicology Data for Select Hydraulic Fluids Biodegradability (%) Product base stock Trout LC 50 (ppm) Shake flask CEC test Mineral oil 389 to Ͼ5000 42–48 (Not tested) Vegetable oil 633 to Ͼ5000 72–80 Ͼ90 Synthetic ester Ͼ5000 55–84 Ͼ90 Polyglycol 80 to Ͼ5000 6–38 (Not tested) Sources: Shake Flask Test Measures Carbon Dioxide Evolution, EPA Method 560/6-82-003; CEC Method- CEC-L-33-T-82. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. III. BASE MATERIALS One of the primary choices of base oils for EA lubricants today is vegetable oils. This is due to their good natural biodegradability and very low toxicity in combination with very good lubricity characteristics. These renewable resources also provide a cost advantage over other EA base materials such as synthetic base stocks. But, there are some performance limitations of the vegetable-based lubricants that have been and continue to be addressed. These characteristics are mainly high temperature oxidation stability, low temperature performance, viscosity limitations, and cost. Although less expensive than synthetic alter- natives, vegetable-based products can cost several times as much as conventional mineral- based lubricants. Genetic engineering will provide improved performance in the future in areas of oxidation stability and low temperature performance by increasing the high oleic acid content as well as other by means of genetic alterations (branching). In most applica- tions, the vegetable-based EA lubricants can be formulated to perform in all but the most severe equipment. It is important to note that not all vegetable-based EA lubricants will provide the same levels of performance. Vegetable-based oils derived from rapeseed plants, cotton seeds, soybean oil, sunflower seed oil, corn oil, palm oil, and peanut oils are frequently used materials, with rapeseed being the most common. Synthetic-based materials such as polyglycols (discussed earlier), polyol esters, pen- taerithritol esters, and certain PAOs (see Chapter 5) are used to formulate the synthetic EA lubricants. Their advantages over vegetable-based EA lubricants are wider temperature range application, longer drain capability (oxidation stability), and excellent performance in systems with close-tolerance servo valves. Some of the more general performance characteristics of the various base materials can be discussed in the following categories. 1. Vegetable oils. The choices of correct processes to refine, bleach, and deodorize vegetable-based oils can yield very satisfactory base materials for the formulation of fin- ished lubricants. This renewable resource provides excellent natural lubricity, low volatil- ity, and good environmental characteristics. Weaknesses are in low temperature perfor- mance, hydrolytic stability, and oxidation stability in high temperature applications. These products are also currently limited to low viscosity (ISO 32–68) materials. Properly manu- factured and formulated vegetable-based lubricants can equal conventional mineral oil based lubricants in performance in all but the most severe applications. 2. Polyalphaolefins (PAOs). As discussed in Chapter 5, PAOs provide a good option for formulating environmental lubricants. Their ready biodegradability in the lower viscosity range is good. They also provide excellent low and high temperature (oxidation stability) performance, good hydrolytic stability, and low volatility. Their disadvantages are in costs and lower rates of biodegradability rates as viscosities increase. To achieve the good characteristics of the PAOs in finished products, they are often blended with biodegradable synthetic esters to get both the performance and environmental characteris- tics desired. 3. Synthetic esters. Several materials based on synthetic esters exhibit good biode- gradability as well as high levels of oxidation stability, low and high temperature perfor- mance, and good hydrolytic stability and seal swell performance. The synthetic esters will allow formulation of higher viscosity lubricants typically used in circulating systems and some gear oils. Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. Table 6.2 Comparison of Fully Formulated EA Lubricants with Various Bases a Properties Mineral Vegetable PAOs Diesters Polyol esters PAGs Viscosity temperature Fair Good Good Fair VG VG characteristics Low temperature properties Poor Poor VG Good Good Good Oxidation stability Fair Poor VG Good Good Good Compatibility with mineral oils Exc Exc Exc Good Fair Poor Low volatility Fair Good Exc Exc Exc Good Varnish and paint compatibility Exc VG Exc Poor Poor Poor Seal swell (NBR) Exc Exc VG Fair Fair Good Lubricating properties Good VG Good VG VG Good Hydrolytic stability Exc Poor Exc Fair Fair VG Thermal stability Fair Fair Fair Good Good Good Additive solubility Exc Exc Fair VG VG Fair a These ratings are generalizations. Specific manufacturers of products should be consulted for current data. Exc, excellent; VG, very good. Table 6.2 shows a general comparison, against mineral oils, of some of the more common performance characteristics of fully formulated EA lubricants using the various base materials. Actual finished product performance could vary from these ratings as a result of technological advancements in such areas as additive technology, use of blends of base materials, and manufacturing processes. As a result of the higher costs, EA lubricants will typically be used in areas where environmental sensitivity is an issue. In many instances of spillage or leakage that are reportable to governmental agencies such as the U.S. National Response Center, the added costs of EA lubricants may be offset by the potential for lower fines and remediation costs. EA lubricants are not meant for use in all applications but only when their use can be economically justified or the environmental sensitivity issues are of prime importance. In many cases, economic justification of the EA lubricants based solely on equipment performance is not sufficient to merit their use. The economics must be derived from reducing costs of remediation in the event of spills or leakage. Also, in some localities, limited legislation or regulations promote or require the use of such products. Environmen- tal sensitivity issues prevail in the following specific areas. Dredging operations for waterways Operation of equipment for dams and locks Offshore drilling Marine equipment Recreation and parks Construction sites on or near water or groundwater systems Agricultural operations Forestry and logging Mining Automotive service lifts Hydraulic elevators Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. A. Product Availability and Performance Because of the large volumes of hydraulic fluids used around the world and the tendency of these products to leak under conditions of relatively high pressures and severity of some applications, the first category of EA fluids to be developed and widely marketed were hydraulic oils. Once readily biodegradable base oils and low toxicity additive systems had been identified, the next hurdle was to provide fully formulated oils that exhibited required equipment performance as established by the builders of equipment as well as the users. Equipment builders have received many requests to approve the use of EA lubricants by their customers and need to be assured that the EA products will perform satisfactorily in their equipment and meet the service life requirements of the customers. Certain EA lubricants are formulated not only to meet the environmental criteria but also to provide performance equal to that of conventional mineral based lubricants. Much of the performance in hydraulic systems is determined by industry standard pump tests. We list three common tests. 1. Vickers V-104C Pump Test (ASTM D 2882). A rapeseed-based EA antiwear hydraulic fluid provided little or no pump wear in the ASTM D 2882 pump test. In addition to the standard 100 h dry test, a more severe 200 h test was undertaken in which 1% water was added at 0 and 100 hs. Because water contamination affects some EA fluids with poor hydrolytic stability, this 200 h test simulates wet systems and evaluates the oil as it degrades at accelerated rates or loses pump wear protection in the presence of water. Test results (Table 6.3) indicate low cumulative wear as well as good viscosity control and low total acid number (TAN) increase. Fluid characteristics did not change appreciably and wear protection was excellent, even in the presence of high moisture levels. 2. Vickers 35VQ pump test. This severe industry-accepted antiwear vane pump test is based on the Vickers 35VQ25 vane pump run at 3000 psi and 200ЊF. Standard procedures require that the same fluid be subjected to three successive 50 h test runs, and total ring and vane wear be less than 90 mg for each run. The tests (Table 6.4) showed low wear and good pump component appearance at the end of five successive 50 h pump test inspections. While fluid color darkened rapidly, increases in viscosity and TAN were small. Table 6.3 Extended ‘‘Wet’’ Vickers 104C Vane Pump Test Results with Mobil EAL 224H Vegetable-Based Oil Test hours Properties New oil 100 200 Viscosity, cSt at 40ЊC (ASTM D 445-3) 35.4 35.1 35.6 Total acid number (ASTM D 664) 0.92 0.97 1.14 Water addition 1% 1% Cumulative wear (vanes and ring) — 16 mg 25 mg Test conditions Duration: 200; 1% water added at 0 and 100 test h; wear measured at 100 and 200 h Temperature: 150ЊF Pressure: 2000 psi Copyright 2001 by Exxon Mobil Corporation. All Rights Reserved. [...]... important part of hydraulic systems Hydraulic presses have been used for forging operations since about 1860, and an adjustable-speed hydraulic transmission was effectively used in 1906 Some consider this last date as the beginning of modern hydraulics, but larger scale manufacture of hydraulically actuated machines did not occur until the 1920s The elementary press circuit shown in Figure 7.3 has several parts... or ram) Accumulators are also used in current systems to reduce shock and dampen flow pulsations resulting in smoother operation, particularly for systems that are subject to large flow changes under high pressure Other features of hydraulic circuits are shown in Figure 7 .4, which is a simple system that could be used to reciprocate a work table of a machine tool such as a surface grinder or milling... pressures Valves are essential components of all hydraulic systems They range from a simple check valve, which permits flow only in one direction (Figure 7. 14) to complex electrohydraulic control valves (Figure 7.15), which may be required to Figure 7. 14 A check valve permits free flow in one direction but prevents flow in the other This check valve is one of several types used in hydraulic circuits such... directional control valves was briefly discussed in connection with Figure 7 .4 Directional control valves such as the four-way spool valve shown in Figure 7.17 can be operated in several ways They can be operated by hand levers such as those found on most home-use hydraulic log splitters; by mechanical linkage, cams, or stops on moving parts such as a ram or workpiece; or by means of air or oil pressure supplied... time If the application involves low temperatures, data on low temperature performance should be obtained from the supplier 3 Hydrolytic Stability It is almost impossible to keep moisture out of most lubrication systems, and water can be detrimental to lubricant performance regardless of the base material used to formulate the lubricant Vegetable oils, as well as all natural and synthetic esters, have... for environmental acceptability, but at present there are no universal industry/regulatory agency agreements on definitions and test procedures This should not be a deterrent to the use of EA products, particularly in areas that are sensitive to spills or leakage of conventional lubricants Where such spills have inadvertently occurred, EA lubricants have clearly demonstrated much less negative impact... for operational problems after start-up due to loosened debris getting into the close clearances Where high detergent oils (engine oils) have been in service, more attention to flushing is recommended, particularly if vegetablebased EA lubricants will be used This is due to potential reactions between the highly additized oils with the additive packages used to formulate the EA oils As a general rule... hydraulic jack to lift our vehicles to hydrostatics that operate recreational amusement park rides to very complex and very precise machines such as robotics capable of producing extremely close tolerance parts to exploration of space, the principles of hydraulics are applied because of the versatility and dependability of such systems to meet the requirements of many applications As a result, hydraulics... home and shut it off completely in one swift motion This often results in a ‘‘bang’’ (shock wave) in the system due to hydrodynamic forces Although the water pressure in your supply system may only be 40 –50 psi, the instantaneous pressure rise generated by the sudden stoppage of motion can be very high In hydraulic systems, the pressures are considerably higher, and sudden stoppage of flow at higher... III.F B Fundamental Hydraulic Circuits Although water hydraulic circuits have been used for many centuries, the basic concepts were first put into practice in hydraulic presses that came into use in last part of the eighteenth century—after Pascal’s time Water was used as the hydraulic medium in these early presses Instead of having a small piston move through a relatively great distance, as in Figure . Vickers 104C Vane Pump Test Results with Mobil EAL 224H Vegetable-Based Oil Test hours Properties New oil 100 200 Viscosity, cSt at 40 ЊC (ASTM D 44 5-3) 35 .4 35.1 35.6 Total acid number (ASTM D 6 64) . LC 50 (ppm) Shake flask CEC test Mineral oil 389 to Ͼ5000 42 48 (Not tested) Vegetable oil 633 to Ͼ5000 72–80 Ͼ90 Synthetic ester Ͼ5000 55– 84 Ͼ90 Polyglycol 80 to Ͼ5000 6–38 (Not tested) Sources:. be an important part of the development of EA lubricants. Unlike traditional lubricant development, where the predominant focus is on product performance in equipment, a major part of developing