Lubricants and Lubrication Part 13 pot

67716.8 Grease Performance 16.8.1 Test Methods Many test methods are used today; all are meant to judge the single or combined and more or less complex properties of greases. The last summary containing detailed descriptions of ASTM and DIN methods was written by Schultze in 1962 [16.196]; another emphasizing on Russian GOST and former East German TGL methods was published in 1984 [16.197]. The most important ASTM and DIN methods are described in Tables 16.10 and 16.11. Complete collections are pub- lished regularly [16.198, 16.199], the same is true for the French AFNOR, the Eng lish IP, the Japanese JIS, and some other national collections. The develop- ment of international standards (EN and ISO) is slowly proceeding. Tab. 16.10 Important ASTM test methods for lubricating greases. ASTM D 0128-95 Analysis ASTM D 1092-93 Apparent viscosity ASTM D 1263-94 Leakage tendencies of automotive wheel bearing greases ASTM D 1264-96 Water washout characteristics ASTM D 1478-91 Low-temperature torque of ball bearing greases ASTM D 1742-88 Oil separation during storage (air pressure method) ASTM D 1743-94 Corrosion preventive properties ASTM D 1831-88 Roll stability ASTM D 2509-93 Load carrying capacity, Timken method ASTM D 3337-94 Life and torque in small bearings ASTM D 3527-95 Life performance of automotive wheel bearing greases ASTM D 4049-86 Resistance to water spray Tab. 16.11 Important DIN (ASTM) test methods for lubricating greases. DIN 51350-4 (ASTM D 2596-97) Testing in the Shell four-ball tester, determination of the welding load of consistent lubricants DIN 51350-5 (ASTM D 2266-91) Testing in the Shell four-ball tester, determination of the wear parameters of consistent lubricants DIN 51801-2 (ASTM D 566-97), replaced by DIN ISO 2176 Determination of dropping point of greases DIN 51802 Testing of rolling bearing greases with regard to their corrosion-inhibiting properties, SKF-Emcor method DIN 51804-1 (ASTM D 217-97), replaced by DIN ISO 2137 Determination of cone penetration of greases with hollow cone and solid cone DIN 51804-2 (ASTM D 1403-97), replaced by DIN ISO 2137 Determination of cone penetration of greases with one-quarter cone DIN 51805 Determination of yield pressure of lubricating greases, Kesternich-method DIN 51807-1 Test for the behaviour of greases in the presence of water, static test 678 16 Lubricating Greases DIN 51808 (ASTM D 942-90) Determination of oxidation stability of greases, oxygen method DIN 51810 Determination of flow behaviour of greases in the rotary viscometer DIN 51811 (ASTM D 4048-86) Testing of corrosive effects of greases on copper, copper strip test DIN 51817 Determination of oil separation from greases under static conditions DIN 51821-2 Test using the FAG roller bearing grease testing apparatus FE 9 Because of the large number of publications about the different test methods, their improvement, and their comparison, only some surveys concerned with EP [16.200], wear [16.201] and with standard tests [16.202, 16.203, 16.384] or perfor- mance tests using real components [16.204–16.208] are cited. One remark about the last group – the FAG FE 8 test, which has become an increasingly important repla- cement for the SKF R2F and Timken tests in Europe, has found its way to the USA where it is used for the development of greases for all kinds of heavy-duty applica- tion [16.385]. The methods themselves are described in Chapters 18 and 19. One point in dealing with standards and test methods according to Jünemann [16.212] cannot be taken serious enough –critical analysis. 16.8.2 Analytical Methods The time of chemical separation procedures as described by ASTM D 128 has nearly gone, elemental analysis of greases is nowadays performed by spectro- scopic methods, e.g. X-ray fluorescence spectrometry (XRF), inductively coupled plasma atomic emission (ICP), or atomic absorption spectrometry (AAS) [16.213], with attention being directed mostly to methods of p reparation [16.214, 16.215]. Infrared spectroscopy was introduced as a means of identifying greases and their com- ponents ca 45 years ago [16.216–16.218]. Its use has steadily grown since and been extended to questions of structure, development, and manufacture also [16.219]. Nuclear magnetic resonance spectroscopy (NMR) has also been used to investigate structural questions [16.220] and electron microscopy has enabled not only the scrutiny of soap fibers [16.221] but also studyof thermal changes in greases [16.222]. The use of thermogravimetry (TG) is usually limited to investigations of base oils [16.223], but the other thermoanalytical method, differential scanning calorimetry (DSC) [16.224, 16.225, 16.386, 16.387], or a combination of both, is expected to become a valuable tool in the analysis of grease and antioxidant analysis. Chromatographic methods, e.g. gas (GC) and high-pressure liquid chromatogra- phy (HPLC), are mainly used to identify the components of liquid or liquefied grease [16.226, 16.227]. The automation of analytical methods has led to a demand for tools that not only facil- itate the documentation of data but also aid their interpretation. This can be achieved 67916.9 Applications of Greases with suitable laboratory information systems (LIMS) [16.228, 16.229]. The use of such a system must be accompanied by intensified concern with the efficiency of tests [16.230] and critical analysis of possible errors in the resulting data [16.231, 16.232]. Suitable databases [16.233]or internet resources [16.234] can be also used. 16.9 Applications of Greases Increased knowledge of base oils and thickener systems enables the selection and naming of greases on the basis of these chemical and physical insights. The selection of a grease is always a compromise between the demands of a customer and the circumstances the grease must face during i ts operational life –tempera- ture, speed, load including centrifugal forces and vibrations, re-lubrication inter- vals b ased on a knowledge of the lubrication points, for appl ications which can be roller bearings, plain bearings, chassis, joints, 5th wheels, door locks, switches and seals of diffe rent design [16.235–16.237]. It has already been mentioned that the desired 24 grease properties described by 12 characteristics sometimes con- tradict each other. 16.9.1 Rolling Bearings The rolling bearing industry, one of the key industries for greases, supports all kinds of manufacturer not only with bearings, which can be standard or tailor-made prod- ucts, but also with consulting and service concerning the design of new equipment and the maintenance of that already in existence. The lifetime of rolling bearings is connected with that of the grease used, especially under extreme conditions [16.238]. Sophisticated test equipment has been developed, mainly to ensure better lifetime predictability for the selected bearing together with the selected grease [16.239, 16.240]. The test rigs SKF R2F and later FAG FE 9 have found great accept- ance in Germany [16.241, 16.242]. Clean production and low-noise greases are meeting reliability and lifetime requirements of rolling bearings. The stringent requirements of high-precision bearings, for small bearings in video and audio applications, and bearings for mili- tary use have been established for years [16.243, 16.244]. On the basis that ca 80 % of all bearings are grease-lubricated, in 1992 the American Society of Tribologists and Lubrication Engineers published a book about the life factors of rolling bearings [16.245]; the German Society for Tribol- ogy published another in 1994 [16.246]. These handbooks describe calculation of the lifet ime of bearings, taking into consideration the effects o f the tribological system. The latter book focuses on the so-called a 23 value, which describe the influence of a grease taking into account bearing size, speed, viscosity, and tem- perature. Current knowle dge of the factors affecting calculation of the lifetime of these bearings has bee n released in the new handbook of the German Society for 680 16 Lubricating Greases Tribology, the second edition of which has been published in September 2006 [16.392]. In Ref. [16.393] it is shown that the lifetime can be prolonged substan- tially by changing specific influencin g factors which do not reduce the lifetime but, on the contrary, increase it. Design of a grease reservoir for the bearings containing a greater volume of grease will also increas e the lifetime of rolling bearings [16.394]. In general greases used in rolling bearings such as ball-, deep groove ball-, thrust ball-, spherical-, taper-, cylindrical- or needle roller bearings must have good working stability. This can be checked by the prolonged penetration test and the Shell-Roller test (ASTM D 1831) [16.247]. Conventional lithium greases in the NLGI class 2 are recommended for most types of bearing at working temperatures up to 120 C. Greases of the NLGI class 1 are preferred for needle bearings. For bearings exposed to temperatures above 120 C complex soap or polyurea thickened greases are prefer- able. For bearings that must operate under high load and/or low speed the base oil viscosity must be 200 mm 2 s –1 minimum at 40 C. Greases for cold climates or for aerospace or military use have to ensure performance down to below –70C. Low- temperature performance can be checked with the low-temperature torque (ASTM D 1263), the low-temperature penetration (AFNOR NF T 60-171) and the flow pres- sure (DIN 51805) tests [16.248–16.250]. Greases of that kind need base oils with suf- ficiently low pour points. In many military applications long-life properties are also required; these can be fulfilled by use of synthetic base oils only [16.251] Because plain bearings are often exposed to moisture or water, calcium soap- thickened greases are recommended. When open housings are used in a dusty atmosphere frequent re-lubrication makes it possible to wash out the contaminated grease. The n  d m value (speed multiplied by the average of inner and outer diameter of a bearing) as a means of selecting the right base oil viscosity for a grease can be accepted only as a rule of thumb; its dependence on base oil viscosity has not yet been established and a commonly accepted test method is not yet available [16.252]. 16.9.1.1 Re-lubrication Intervals The lubrication interval t f is based on the F 10 value of a standard grease as agreed in DIN 51 825 [16.253] under normal environmental conditions with temperatures up to 70 C and a mean bearing load of P/C < 0.1. Figure 16.8 and Table 16.12 take into consideration the type of bearing and the speed. For each 15 K temperature increase the re-lubrication interval is said to be reduced by 50 %. Severe working conditions reduce the lubrication interval t f to a reduced lubrication interval t fq . t fq = f 1  f 2  f 3  f 4  f 5  t f (16.1) 68116.9 Applications of Greases 100000 50000 30000 20000 10000 5000 3000 2000 1000 500 300 200 20 30 50 70 100 150 200 300 500 700 1000 1500 2000 k ·n·d [10 mm/min] fm 3 Lubrication interv alt [h] f Fig. 16.8 Re-lubrication intervals. Tab. 16.12 Relationship between bearing type and correction factors for re-lubrication intervals (GFT Worksheet 3). Bearing type k f Deep grove ball bearings Single row 0.9–1.1 Double row 1.5 Angular contact ball bearings Single row 1.6 Double row 2 Spindle bearings a = 15  0.75 a = 25  0.9 Four point bearings 1.6 Self-aligning ball bearings 1.3–1.6 Thrust ball bearings 5–6 Angular contact thrust ball bearings Double row 1.4 Cylinder roller bearings Single row 3–3.5 a) Double row 3.5 Full complement 25 Cylindrical roller thrust bearings 90 Needle roller bearings 3.5 Tapered roller bearings 4 Barrel roller bearings 10 Spherical roller bearings without lips (E-design) 7–9 Spherical roller bearings with center lip 9–12 a) k f = 2 for radial load or increasing thrust load and k f = 3 for constant thrust load. 682 16 Lubricating Greases The reduction factors are shown in Table 16.13. Tab. 16.13 Reduction factors for re-lubrication cycles. Reduction factors f 1 to f 5 for poor operating and environmental conditions (GfT Worksheet 3). Effect of dust and moisture on the bearing contact surfaces Moderate f 1 = 0.7–0,9 Strong f 1 = 0.4–0.7 Very strong f 1 = 0.1–0.4 Effect of shock loads and vibrations Moderate f 2 = 0.7–0.9 Strong f 2 = 0.4–0.7 Very strong f 2 = 0.1–0.4 Effect of high bearing temperature Moderate (up to 75 C) f 3 = 0.7–0.9 Strong (75–85 C) f 3 = 0.4–0.7 Very strong (85–120C) f 3 = 0.1–0.4 Effect of high loads P/C = 0.1–0.15 f 4 = 0.7–1.0 P/C = 0.15–0.25 f 4 = 0.4–0.7 P/C = 0.25–0.35 f 4 = 0.1–0.4 Effect of air current passing through the bearing Light current f 5 = 0.5–0.7 Strong current f 5 = 0.1–0.5 In re-lubrication it is usually impossible to remove the used grease. Consequently the re-lubrication interval t fq has to be reduced by 30 to 50 %. General advice on the amount of grease necessary for re-lubrication is given in Table 16.14. Tab. 16.14 Amount of grease necessary for re-lubrication. Amounts of grease lubrication (GfT Work sheet 3). Re-lubrication quantity m 1 for weekly to yearly re-lubrication m 1 = D  B  x [g] Re-lubrication x Weekly 0.002 Monthly 0.003 Yearly 0.004 Re-lubrication quantity m 2 for extremely short re-lubrication interval m 2 = (0.5–20)  V [kg h –1 ] 68316.9 Applications of Greases Re-lubrication quantity m 3 before restarting after several year of standstill m 3 = D  B  0.01 [g] V = free space in the bearing (p/4)  B (D 2 – d 2 )10 –9 –(G/7800) [m 3 ]or (p/4)  B (D 2 – d 2 )10 –9 –([G¢  0.4536]/7800) [m 3 ] d = bearing bore diameter [mm] D = bearing outside diameter [mm] B = bearing width [mm] G = bearing weight [kg] G¢ = bearing weight [lb] 16.9.2 Cars, Trucks, Construction Vehicles Most modern cars do not need re-lubrication, with the exception of door hinges, lock mechanisms, and battery poles. But among the approximately 30 hidden greases (Fig. 16.9 and Table 16.15) in a modern car [16.254, 16.255] only the con- stant-velocity (CV) joint greases are required in substantial quantities. Although improved conventional lithium greases containing molybdenum disulfide are still in use [16.256], lithium complex or polyurea greases are already preferred in some modern cars and this usage will increase in the future [16.257]. Most of the greases used in cars, for example the greases for CV joints, hub units, starters, alternators, seat adjustments, clutches release bearings, belt–pulley bearings, window levers and windshield wiper gears, are specified and approved by the large motor companies and developed in close cooperation with the grease manufacturers. For the same application, however, different motor companies have different grease specifications Fig. 16.9 Greases hidden in a modern car. 684 16 Lubricating Greases Tab. 16.15 Thirty hidden greases–a partial list of grease applications. Powertrain Brake system Belt–pulley bearing ABS follower/motor bearings Clutch bearing/spline Caliper pin Cruise control module CV joint Electrical Fan clutch bearing Fuel pump bearing Alternator bearing Turbo/supercharger Electrical contacts Horn contact Body hardware Heating/cooling Door check arms/hinges Door locks/latches Cable actuators Electric antenna gear/clutch Temperature sensor Remote control mirror assembly Visco fan bearing Seat adjustment gears Water pump bearing Sunroof rails Window levers Other Windshield wiper gear Wheel bearing U-Joint and approvals; for example, most European and US motor companies prefer lithium complex greases in the front wheel bearings, whereas Japanese manufacturers pre- fer polyurea greases. ASTM D 4950 (Tables 16.16 and 16.17) describe the minimum requirements of current greases in automotive service–fill applications for passenger cars, trucks, and other vehicles operating under various service conditions [16.258]. Grease packs fulfilling these minimum requirements can have the NLGI certification marks as shown in Fig. 16.10, these labels are provided by the NLGI on request. Tab. 16.16 ASTM D 4950 Specifications LA and LB. Chassis grease classifications–intended use of chassis (L) classified greases: LA Classification Chassis components and universal joints under mild duty – Frequent re-lubrication – Non-critical applications LB Classification Chassis components and universal joints under mild to severe duty – Prolonged re-lubrication intervals – High loads – Severe vibration – Exposure to water or other contaminants 68516.9 Applications of Greases Tab. 16.17 ASTM D 4950 Specifications GA, GB and GC. Intended use of wheel bearing (G) classified greases: GA Classification Service typical of wheel bearings operating under mild duty – Frequent re-lubrication – Non-critical applications GB Classification Service typical of wheel bearings operating under mild duty/moderate duty – Normal urban, highway and off-highway service GC Classification Service typical of wheel bearings operating under mild duty/severe duty – High bearing temperatures – Frequent stop and go service (buses, taxis, police) – Severe braking service (trailer towing, heavy towing, mountain driving) Lithium-based multipurpose greases have replaced several other greases for the re- lubrication of trucks and construction equipment. Conventional lithium soap based greases that require frequent re-lubrication are still in use for the wheel bearings of trucks and trailers.Modern trucks and trailers with prolonged oil-drain intervals require lithium complex greases with semi-synthetic or fully synthetic base oils. Lithium greases containing black solid lubricants are recommended for 5th-wheel applications, for chassis points, and for plain bearings of construction equipment. Many trucks and buses and much construction equipment uses centralized lubricating systems, de- signed for semi-fluid greases of NLGI class 00 or 000, for onboard re-lubrication. Other systemsrequire greasesofNLGI class 2. Lithiumgreases optimized forlow temperature applications, good pumpability, and low oil separation are recommended. 16.9.3 Steel Mills In Europe calcium complex and sometimes polyurea greases based on mineral oil are used for lubricating continuous casting equipment. The US market prefers alu- Fig. 16.10 NLGI certification marks. 686 16 Lubricating Greases minum complex and polyurea greases and Japanese equipment manufacturers mainly recommend polyurea greases. Calcium sulfonate complex greases are achieving increasing commercial acceptance in Europe and the USA, because of their high EP values and excellent corrosion-protection properties. Some rolling bearing manufacturers equip continuous castings with double- or triple-sealed bear- ings that are greased for life, preferably with synthetic polyurea greases. When the sealing of the bearings is not perfect re-lubrication has a cleaning function. Con- taminated grease that could result in limited lifetime is squeezed out. Conventional EP lithium greases, calcium complex greases, calcium sulfonate complex greases, lithium complex greases, and aluminum complex greases, all based on mineral oils are used in hot rolling equipment. In India a successful trial has been conducted with a locally produced titanium complex grease [16.259]. Most customers require a minimum base oil viscosity of 200 mm 2 s –1 at 40 C [16.260]. The rotating shift system is typically used for hot-rolling lubrication. In general the bearings are not re-greased during operation, only during maintenance. Many different greases, e.g. conventional EP lithium greases, lithium complex greases, calcium complex greases, and calcium sulfonate complex greases, all based on mineral oil, are used in cold rolling equipment. Modern greases use a lithium– calcium mixed soap for improved water resistance. Some calcium complex greases have helped to prolong the lifetime of bearings in the pickling section significantly. 16.9.4 Mining Open pit mines which use hydraulic excavators and dumper trucks and/or wheel bucket excavators and belt systems to ship the spoil and coal are especially large grease consumers. Lithium, lithium–calcium mixed-soap-based or lithium complex greases with base oil viscosities > 350 mm 2 s –1 at 40 C and an effective EP and AW additive package are used. Black solid lubricants are also recommended. Because the equipment is exposed to dust or water and mud, the sealing efficiency of the bearings determines their lifetime and must be supported by a grease. Kilometers of wire rope are used on the excavators or drag lines and in the under- ground mines. During production of the wire ropes lubricants are applied to ensure corrosion protection and to minimize friction of the single wires when the rope stretches under load. The amount of lubricant in the core should be ca 25 % w/w of the core. Lay-up lubricants based on wax-resin are applied during manufacture to ensure lubrication of the individual wires and stands. After production the wires must have corrosion protection; this can be achieved by painting or by applying a bitumen- based lubricant with a solvent. During operation in some countries the wire ropes are maintained by cleaning the surface and re-lubrication. In many countries bitumen-based products are still in use, but are being replaced by bitumen-free greases or even biodegradable lubri- cants. It is essential to apply the lubricant on top of the sheave-wheel or shortly after [...]... materials and coatings could be judged to behave as solid lubricants on the basis of this definition Various systems are used to classify the different types of solid lubricant An arbitrary, but useful, classification is into structural lubricants, mechanical lubricants, soaps, and chemically active lubricants (Sections 17.1.1 to 17.1.4, respectively) Lubricants and Lubrication 2nd Ed Edited by Th Mang and. .. material, and serious wear The maximum wear depth exceeds 13 lm 250 µm of black solid lubricants such as graphite and MoS2 also have a beneficial effect on running-in processes and the capacity to withstand wear and tear in boundary and mixed friction areas Where oscillating movements or vibration is involved, white solid lubricants have the advantage These effects are illustrated in Figs 17.1 and 17.2... as a function of surface roughness 100 Sand blasted and phosphated Relative useable life [h] 80 60 40 Sand blasted 20 Ground 0 0 2 4 6 8 10 12 14 16 Surface roughness [mm] 18 20 (iii) environmental (local) conditions, in particular the demands, and types of demand, placed on the lubricant (e.g load, Figs 17.5 and 17.8), the type and speed of movement (Figs 17.6 and 17.7), the temperature (Fig 17.9),... dispersions and suspensions in water MoS2 plays a dominant role as an additive to lubricating gears and for general use in oil lubricating systems 17.3.3 Greases and Grease Pastes Addition of solid lubricants to greases is primarily intended to have a positive effect on their capacity to absorb pressure, and the ability to withstand wear and tear, and friction The specific advantages of solid lubricants. .. The life of lubricated machine parts depends on the functional and tribological design and optimization of lubricants as calculable functional elements To make a systematic choice of a suitable lubricant it is absolutely necessary to understand the relationship between friction, wear, and lubrication and the interaction between the elements of the tribological system and the specific properties of... this particular application area are usually made up of combinations of solid lubricants and special metal powders More recent developments show that the use of formulations which do not contain metal, and are based on white solid lubricants, perform well when used at high temperatures 17.3.5 Dry-Film Lubricants Lubricating varnishes or dry-film lubricants are suspensions of solid lubricants and other... powders Dispersions and suspensions of solid lubricants in water are usually used to coat mass elements for cold and hot forming The most commonly used substances here are salts, special white solid lubricants, and graphite Dispersions and suspensions in oils also act as aids in forming techniques, and they are also used as additions in gear- and oil-lubricating systems The solid lubricants used here... prevents metal–metal contact and thus reduces surface friction and wear The three main types of phosphating solutions contain zinc, iron, and manganese phosphates, and of these the zinc phosphate is probably the most widely used Metal Powders In contrast with structural lubricants and self-lubricating mechanical lubricants, the lubricating properties of the other mechanical lubricants are mainly based... inorganic silicates and phosphates Hydrocarbons or water are used as solvents Dry-film lubricants can be used in a variety of ways; these depend primarily on the number, shape, and/ or particular requirements with regard to partial coating They are applied by dipping centrifuges and drums and by various types of spraying procedure The hardening process depends on the type of binding system and happens at... ready-to-build-in axle boxes and the increasing speed of modern trains have led to improvement of the high-temperature performance and lifetime of greases Switch lubrication, wheel flange lubrication (mainly used in Europe), and rail track-side lubrication in curves, used mainly in the USA and Canada, cause environmental problems Biodegradable greases based on esters have better wear-protection and consumption . mechanical lubricants, soaps, and chemically active lubricants (Sections 17.1.1 to 17.1.4, respectively). 17 Solid Lubrication Christian Busch Lubricants and Lubrication. 2nd Ed. Edited by Th. Mang and. high-temperature performance and lifetime of greases. Switch lubrication, wheel flange lubrication (mainly used in Europe), and rail track-side lubrication in curves, used mainly in the USA and Canada, cause. up to 70 C and a mean bearing load of P/C < 0.1. Figure 16.8 and Table 16.12 take into consideration the type of bearing and the speed. For each 15 K temperature increase the re-lubrication