Lubricant and additive effects on spur gear fatigue life

Spur gear endurance tests were conducted with six lubricants using a single batch of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricant was divided further into four batches, each of which had a different additive content. Lubricants tested with a phosphorus-type load carrying additive showed a statistically significant improvement in life over lubricants without this type of additive. The presence of sulphur-type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwear additives. Gears tested with a 0.1 wt % sulphur and 0.1 wt % phosphorus EP additives in the lubricant had reactive films that were 200 to 400 Å (0.8 to 1.6 μin) thick.     

Effect of the type and concentration of lubricating additives on the antiwear and extreme pressure properties and rolling fatigue life of a four‐ball tribosystem

Tests were performed on two different four‐ball testers. The first was used to determine antiwear (AW) and extreme pressure (EP) properties at sliding friction. The second was used to assess the surface fatigue (pitting) life at rolling movement. Lubricating oils of various chemical compositions were tested. A base mineral oil was blended with two different commercial packages of lubricating additives of AW and EP types. The AW additives contained ZDDP and were blended with the base oil at 0.2 and 3wt %. The EP additives were organic compounds of sulphur and phosphorus, blended with the base oil at 1 and 10wt %. It is shown that AW additives not only improve AW and EP properties but also — at 0.2% — are beneficial for the fatigue life. An increase in the concentration of AW additives leads to an improvement of AW and EP properties but — for one of the packages — reduces the fatigue life. EP additives — at 1% concentration — significantly improve EP properties, and to a lesser extent AW properties. Such a concentration of EP additives has no influence on the fatigue life. An increase in the concentration of EP additives leads to a further improvement of EP and AW properties. However, this is accompanied by a considerable decrease in the fatigue life. By using a scanning electron microscope and energy dispersive spectrometer for analysis of the worn surface, mechanisms of action of various lubricating additives under different friction conditions were identified. Copyright © 2006 John Wiley & Sons, Ltd.     

纳米Al/Sn金属颗粒对润滑油抗磨极压性能的影响

利用四球试验机分别对添加有纳米铅粉、锡粉以及Al Sn金属粉的润滑油进行极压和抗磨性能实验。采用SEM(扫描电子显微镜)对摩擦表面进行观察，采用EDS(能量色散谱仪)对表面进行元素测定。测试结果表明．纳米Al Sn金属粉可在较宽的载荷范围内明显改善润滑油的极压抗磨性能。其作用机理是锡粉在低载荷阶段沉积到摩擦表面起到抗磨剂作用，铝粉在高载荷阶段沉积到摩擦表面起到极压剂作用．从而实现了在低载荷到高载荷范围内对润滑油抗磨极压性能的提高．     

EP/AW performance evaluation of some zinc alkyl/dialkyl/alkylaryl‐dithiocarbamates in four‐ball tests

Tribochemistry, the chemistry of interacting surfaces under the influence of a lubricant, helps in the appropriate selection of suitable lubricant additives for specific uses. Modern lubricants are usually formulated from a range of petroleum base oils or synthetic fluids incorporating a variety of chemical additives for performance enhancement. Extreme‐pressure (EP) and anti‐wear (AW) additives are used extensively in lubricants for hypoid gears and metal cutting and forming operations to reduce wear, modify friction, and prevent scuffing of moving metallic parts. The present paper includes the synthesis and the evaluation of the tribological properties of 0.5% (w/v) solutions of some zinc bis‐(alkyl/dialkyl/alkylaryldithiocarbamates) in paraffin oil using 12.7 mm diameter steel bearing ball specimens in four‐ball tests. All the synthesised zinc dithiocarbamate additives in general, and zinc bis‐(morpholinodithio‐carbamate) (A₄) in particular, exhibited good AW, EP, and friction‐reducing properties. Additive A₄ especially gave low values of wear‐scar diameter and coefficient of friction at higher loads and higher values of load wear index and flash temperature parameter during EP tests (ASTM D 2783) and afforded lower values of wear‐scar diameter in a one‐hour wear test (ASTM D 2266–67). The surface topography of the wear‐scar matrix of the used ball specimens was investigated by scanning electron microscopy.     

Enhancing AW/EP property of lubricant oil by adding nano Al/Sn particles

This paper presents results of experiments to enhance antiwear/extreme pressure (AW/EP) properties of a lubricant oil by adding metal nano particles. In this experiment, Al, Sn and Al + Sn nano-particles were selected as trial additives. The AW and EP properties were evaluated on Four-Ball test machine, while the feature and composition of the wear scar surface were investigated by scan electron microscope (SEM) and energy dispersion spectrum (EDS). The test results show that the AW and EP performance can be improved within a wide load range by adding Al + Sn nanoparticles. Analysis of the enhancement mechanism has also been conducted in this experiment and presented in this paper. It is found that nano-Sn particles can be deposited on the friction surface when the pressure was moderate and act as AW additive. It is also found that the nano-Al particles can be deposited under the condition of high load pressure and act as EP additive. Thus, the AW and EP properties of tested lubricant oil have been improved at the same time due to adding both Al and Sn.     

Effects of extreme pressure additive chemistry on rolling element bearing surface durability

Lubricant additives have been known to affect rolling element bearing surface durability for many years. Tapered roller bearings were used in fatigue testing of lubricants formulated with gear oil type additive systems. These systems have sulfur- and phosphorus-containing compounds used for gear protection as well as bearing lubrication. Several variations of a commercially available base additive formulation were tested having modified sulfur components. The variations represent a range of “active” extreme pressure (EP) chemistries. The bearing fatigue test results were compared with respect to EP formulation and test conditions. Inner ring near-surface material in selected test bearings was evaluated on two scales: the micrometer scale using optical metallography and the nanometer scale using transmission electron microscopy (TEM). Focused-ion beam (FIB) techniques were used for TEM specimen preparation. Imaging and chemical analysis of the bearing samples revealed near-surface material and tribofilm characteristics. These results are discussed with respect to the relative fatigue lives.     

The lubricant-coating interaction in rolling and sliding contacts

The research presented in this paper was aimed at elaboration of a new technology for heavy-loaded machine elements, lubricated with ecological oils.The tribological experiments were performed using four-ball tester (scuffing resistance), cone-three balls pitting tester (fatigue life), as well as gear test rig (resistance of lubricated gears to scuffing). The tribosystems were lubricated with various base oil and vegetable-based eco-oil.The tested components were coated with standard single coatings (TiN, CrN) and low-friction coatings (a-C:H:W, MoS₂/Ti). The results obtained confirm that low-friction a-C:H:W coating has a great potential for application in heavy-loaded machine components. Under extreme-pressure conditions this coating can take over the functions of anti-wear/extreme-pressure (AW/EP) additives and through this it is possible to minimise the application of toxic lubricating additives and achieve “ecological lubrication”.     

硫代磷酸酯胺盐抗磨剂的性能及应用

硫代磷酸酯胺盐具有好的热氧化安定性,极压抗磨性,水解安全性,是一种性能较全面的抗磨添加剂。该剂与其他功能添加剂复配,可调制７５Ｗ／９０,８０Ｗ／９０,８５Ｗ／９０重负载车辆齿轮油,多种粘度级别的重负荷工业齿轮油和７０ＴＢＮ船用气缸油。     

An ESCA study of the effectiveness of antiwear and extreme‐pressure additives based on substituted phosphorodithioate derivatives,and a comparison with ZDDP

Ashless substituted dithiophosphoric acid derivatives (ADPs) are a new generation of multifunctional additives with promising antiwear (AW) and extreme‐pressure (EP) characteristics. Three such additives synthesised in the authors' laboratory have been evaluated for their AW and EP properties by standard four‐ball friction and wear tests. The friction‐reducing properties of these additives were compared with those of a commercial zinc dialkyldithiophosphate (ZDDP). It was found that the phosphorodithioate compounds studied here possessed excellent AW/EP properties. Their AW characteristics were found to be comparable to those of ZDDP at low loads. However, at higher loads they show inferior AW characteristics in comparison to ZDDP. Nevertheless, ADP derived from cashew nut shell oil had a higher load‐carrying capacity than ZDDP. The mechanism of the AW and EP behaviour exhibited by the different additives was investigated using X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) of the worn surfaces formed during friction. XPS and AES analyses of the worn surfaces reveal that the tribochemical film formed on the ADP‐tested surfaces consisted mainly of metal phosphates and only a small amount of metal sulphides, even though the ADPs contained twice the number of sulphur atoms than phosphorus atoms. The ZDDP‐tested surface showed a mixture of metal sulphides and metal phosphates. Alkylamino substitution appeared to have no significant effect on the AW/EP properties of the additive. XPS and AES analyses also revealed that the tribochemical film formed on an ADP‐tested surface was thicker than that present on the ZDDP‐tested surface at low loads, whereas at higher loads the reverse was true. The higher weld load obtained for the blend containing cashew nut shell oil‐derived ADP is attributed to the thicker adsorbed reaction film formed on the surface due to the long alkyl groups present in the original additive structure. Short‐chain alkyl groups, however, form only a thin adsorbed layer, which may get rubbed off during the friction at high load. The low sulphide formation on ADP‐tested surfaces was attributed to the absence of any metal atom in the additive, which would help in the formation of metal sulphides during tribofragmentation and further tribochemical reactions.     

油品组成对蜗杆副传动效率的影响

通过对15种不同添加剂配方的试验蜗轮蜗杆油进行传动效率台架评定试验,以考察不同类型、不同含量的极压抗磨剂、油性剂等对蜗杆副传动效率的影响结果.     

Load‐carrying capacity of WC/C‐coated gears lubricated with a low‐viscosity oil

The application of low‐friction coatings on the surfaces of gear teeth is primarily motivated by the increasing demands for load‐carrying capacity or the rolling‐contact fatigue life. Despite the costs of manufacturing being higher, better performance is an important consideration for many demanding applications. In the present study, we have investigated the load‐carrying capacity of WC/C‐coated gears that were lubricated with an oil blend that was formulated in‐house. A significantly higher load‐carrying capacity was found for the WC/C‐coated gears lubricated with a tailored, low‐viscosity oil in comparison with the case‐carburised gears lubricated with a conventional gear oil of a similar viscosity. The carburised gears failed due to scuffing on the pinion tip, while coating thinning on the pinion face and coating fracture in the wheel‐root area are the dominant failure mechanisms for WC/C‐coated gears. An approximately 40% lower roughness was found on the coated gear flanks. Copyright © 2015 John Wiley & Sons, Ltd.     

Additive—additive interaction: A study of the ep and AW performance of sulphurised jojoba oil and sulphurised xanthate in the presence of mocontaining friction modifiers

The extreme-pressure (EP) and antiwear (AW) performance of three soluble molybdenum compounds (commercial molybdenum dialkyldithiophosphate, commercial molybdenum dialkyl dithiocarbamate, and synthesised molybdenum dialkyl dithiocarbamate), and two sulphur-containing EP compounds (sulphurised jojoba oil and sulphurised O-stearyl-S-oleyl xanthate) have been studied alone and in combination, using a four-ball tester. The behaviour of the additives in combination has been found to be selective, and dependent on the chemistry and ratio of the additive components. In general, the addition of Mo-type friction modifiers (FM) to sulphurised EP compounds has shown a synergism, of varying order, in their EP and AW properties.     

Micropitting performance of nitrided steel gears lubricated with mineral and ester oils

This study compares the gear micropitting performance of high pressure nitriding (HPN) steel gears, lubricated with three different gear oils: a standard mineral lubricant, containing a special micropitting additive package, and two biodegradable esters with low toxicity additivation. The physical, chemical and wear properties of the three lubricants were determined, as well as their biodegradability and toxicity characteristics. The gear material and the corresponding heat treatment are presented.Gear simulation tests were performed in a Falex machine, using a roller-disc geometry, in order to evaluate the lubricant temperature and friction coefficient corresponding to each gear oil.Gear micropitting tests were performed on the FZG machine, using type C gears, and lubricant samples were collected during the tests for wear particle analysis. Post-test analysis included the mass loss measurement of the gear (pinion and wheel), the ferrometric analysis of the lubricant samples and the teeth flank roughness measurement below and above the pitch line. The teeth flanks were inspected using scanning electron microscopy (SEM) and surface topography measurements to assess the number and depth of micropits. Metallurgical cuts were done to observe the size and depth of micropits as well as contact fatigue crack initiation and propagation.The ester lubricants show better micropitting performance than the mineral oil, confirming the potential of environmental friendly fluids as high-performance gear oils.     

Antiwear Action of Mineral Lubricants Modified by Conventional and Uncoventional Additives

The authors of this paper investigated the influence of esters of rapeseed oil fatty acids on the lubricating properties of mineral lubricants containing chosen AW/EP additives. Methyl esters, ethylene glycol esters, and glycerol esters as well as some commercial AW/EP packages based on zinc dialkyldithiophosphate, S–P organic compounds, and sulphurized esters of fatty acids were tested. The tribological tests were carried out with the use of a four-ball machine. Antiwear (AW) properties of tested compositions were determined using their limiting load of wear (G_oz(40)). It appears that the AW action of esters of rapeseed oil fatty acids depends on their structure. The best AW action is shown by compositions of mineral oil lubricants containing AW/EP additives and methyl esters of rapeseed oil fatty acids. The SEM/EDS analysis of the scar surface layer indicated that the presence of these esters in lubricants causes a change in the interaction between AW/EP additives and the metal surface. These observations were confirmed by the XPS surface analysis.     

Influence of Oil Viscosity,Chemical Oil Structure,and Chemical Additives on Friction Loss of Spur Gears (Concerning the Influence of Synthetic Oil and Mineral Oil)

The friction loss of gears and its quantitative estimation are important problems because of their relevance to energy conservation and load-carrying capacity. Recent research results do not provide satisfactory estimates of friction loss of spur gears. Therefore, the authors carried out experiments to study the influences of lubricating oil viscosity and additives, as well as base oil type and load and rotational speed on friction loss of spur gears. Base oil types used were paraffin mineral, poly-α-olefin, and polyglycol with several oil viscosities. An EP and a mild EP additive were studied in these oils. Finally, the temperature rise of teeth of gears as a function of friction power loss was investigated, and an empirical formula for calculating the temperature rise of the spur gear teeth was derived.     

油品组成对蜗杆副承载能力的影响

通过对15种不同添加剂配方的试验蜗轮蜗杆油进行胶合承载能力台架评定试验，以考查不同类型、不同含量的极压抗磨剂、油性剂等对蜗轮蜗杆承载能力影响的结果。     

Effect of Running-In (Load and Speed) on Surface Characteristics of Honed Gears

The initial running-in cycles alter the surface integrity characteristics and influence gear performance. This article shows how the surface characteristics of honed spur gears evolved due to the combined effect of running-in load (0.9 or 1.7?GPa) and speed (0.5 or 8.3 m/s) in Forschungsstelle fur Zahnräder und Getriebebau tests. Running-in affected the surface layers to a depth of 5 µm. High running-in load promoted plastic deformation of asperities, created microstructural changes associated with surface cracks, and relaxed residual stresses. It also enhanced the amount of phosphorous from extreme pressure (EP) additives at the surface. The surface contact fatigue failure—that is, micropitting—was promoted by running-in speed rather than load.     

Influence of lubricants on the pitting fatigue of gears

Using the FZG gear tester with heat-treated and case-hardened gears the effect of lubricants and additives on the incidence of pitting fatigue was investigated. The influence of base oil type and additives requires further investigation before general conclusions can be derived. From the results now available extreme pressure additives which increase the scuffing load carrying capacity of case-hardened gears allow increased load testing without surface pitting failure. Additives have a direct beneficial influence on retarding the pitting of heat-treated gears. Of the additives tested, the most effective in reducing pitting fatigue failure was MoS₂, but with a high concentration of about 1.5%.     

Tribological Behavior of Some Long-Chain Dimercaptothiadiazole Derivatives as Multifunctional Lubricant Additives in Vegetable Oil and Investigation of their Tribochemistry Using XANES

A series of novel long-chain dimercaptothiadiazole derivatives are prepared and used as antiwear (AW) and extreme pressure (EP) additives in vegetable oil, and their tribological performance is tested by using a four-ball tester. In order to understand the friction process further, X-ray absorption near edge structure spectroscopy is adopted to analyze the chemistry of tribofilms under AW/EP regime, and meanwhile thermal films are also considered for comparison. These derivatives are capable in improving the tribological characteristic of the base stock, and disubstituted derivatives are more effective than other derivatives. Though disubstituted derivatives and disubstituted polysulfur derivatives all fail in improving tribological performance at 0.1 wt%, they are still helpful at other additive concentrations. All these long-chain thiadiazole derivatives, in particular the disubstituted polysulfur ones, are good at improving the EP characteristic of the base colza oil. Thermal films generated from these derivatives are composed of ferrous sulfate and a small amount of adsorbed organic sulfide. During the heating process, these long-chain derivatives easily undergo thermal oxidation to generate high-valent sulfate on the metal surface. Ferrous sulfide is the main component of tribofilms generated by these derivatives, while ferrous sulfate in these films almost vanishes at 1.0 wt%. These long-chain derivatives tend to react with metal surface to generate low-valent sulfide under rubbing conditions. On the other hand, ferrous sulfide is also the main component of EP films generated by monosubstituted derivatives and disubstituted polysulfur derivatives at 1.0 wt%. But the EP films formed by disubstituted derivatives are composed of ferrous sulfide and ferrous sulfate.     

Tribochemistry and the development of AW and EP oil additives — a review

The antiwear (AW) and extreme pressure (EP) properties of chlorine, sulphur, phosphorus-containing organic compounds and zinc dialkyldithiophosphate (ZDDP) oil additives are affected greatly by their reactive ability to the metal surface, as well as by the chemical composition, chemical state, physical and mechanical properties of the protective films formed. Over four decades, research has taken place on boundary lubrication, and a much better understanding of the AW and EP action mechanism of one additive by itself in base oil has been obtained, and much more knowledge on the relationship between wear and decomposition of additives, adsorption and reaction of the additive or its decomposed products with metal, has been gained. A series of analytical methods and a great number of modern surface analytical tools have been set up and used for research in this area. The problems and some suggestions for the future study on boundary lubrication of oil additive are proposed.