A method for testing lubricants under conditions of scuffing. Part I. Presentation of the method

A method for the tribological assessment of lubricants under conditions of scuffing is presented. The method uses a four‐ball tester, and allows one to assess the effect of lubricant on scuffing intensity through an analysis of changes in the friction torque and wear of the stationary balls, at continuously increasing load. The behaviour of a lubricant under scuffing conditions can be characterised using the so‐called limiting pressure of seizure p_oz, which depends on the load at which the balls seize and the average value of the wear area calculated from the wear‐scar diameters measured on the stationary balls. A comparison is made ‐ from the point of view of the resolution, time consumption, and cost ‐ of the new method with the existing, standard tests, using a four‐ball tester and a gear test rig (FZG). It is concluded that the proposed method, unlike standard FZG and certain four‐ball tests, enables one to differentiate between gear oils, in agreement with their API GL performance level. The very short run‐time of the new method enables one to perform more tests and obtain a low standard deviation. The new method is much cheaper than the standard four‐ball and FZG methods.     

Evaluation of ball and disc wear scar data in the HFRR lubricity test

The high‐frequency reciprocating rig (HFRR) lubricity tester has become a widespread method for determining the lubricity of diesel fuels. The test is a ball‐on‐disc method, in which a steel ball scrapes over a steel disc immersed in the liquid to be tested. According to standards, the wear scar generated on the ball, in the form of the average of the x‐ and y‐axes, is used for evaluating the lubricity of the sample. Generally, the smaller the wear scar, the greater the lubricity of the sample. However, a wear scar is also generated on the disc. The size of the wear scar on the disc also depends on the lubricity of the sample. In this work, the wear scar data of the balls and discs of 230 samples related to the testing of biodiesel and related compounds with petrodiesel were evaluated. Data comparisons for all wear scar combinations correlated well by linear regression. Although correlations are slightly better when using only ball wear scar data (r² > 0.99), other wear scar data, including those generated on the disc, appear just as useable (r² ≈ 0.97–0.99) for evaluating lubricity by the HFRR test. The wear scars on the disc have the advantage of being more easily measurable and recognisable under the microscope, especially if the wear scars are small. Limits for all wear scar values corresponding to current limits for average ball wear scar data in standards are presented. Published in 2007 by John Wiley & Sons, Ltd.     

The effect of nitrogen and sulphur compounds on extreme pressure lubrication

This paper reports the synthesis of hydroxyheptadecyl-substituted-1,3,4-thiadiazoles and mercapto-1,2,4-triazoles and the evaluation of extreme pressure activity of their admixtures (0.5% and 1% w/ v) with a paraffinic oil in a four-ball test. Alloy steel bearing balls of 12.7 mm diameter were used as test specimens. All the additives exhibited good activity in reducing wear and increasing the values of mean Hertz load (MHL) and flash temperature parameter (FTP) as compared to the base fluid. The presence of p-methoxy- and p-chloro- groups in the thiadiazole and mercapto triazole rings has been found to enhance the activity of these additives. Scanning Auger Electron Spectroscopy surface studies were conducted to analyse the additive-metal interaction.     

Tribological studies of 1-alkyl-2,5-dithiohydrazodicarbonamides and their Mo–S complexes as EP and multifunctional additives

This communication reports a comparative study of the anti-wear, extreme pressure and friction reducing properties of 0.5% (w/v) admixtures of paraffin oil with 1-alkyl-2,5- dithiohydrazodicarbonamide ligands and their Mo–S complexes, i.e. μ-hydroxo-μ-(1-alkyl-2,5-dithiohydrazodicarbonamido)-bis-[dioxohydroxo molybdenum VI] using 12.7 mm diameter steel bearing balls in a four-ball test. In particular, the additive μ-hydroxo-μ-(1-n-butyl-2,5-dithiohydrazodicarbonamido)-bis-[dioxohydroxo molybdenum VI] exhibits an increase in the load carrying capacity of the lubricant and a decrease in the values of wear and coefficient of friction. The surface analysis of the wear-scar matrix of the used ball specimen has been investigated by SEM and AES techniques.     

EP-efficient 1,2,4-dithiazolines and their tribological effect on steel bearing balls of different composition

This paper deals primarily with the potential extreme-pressure (EP) activity of certain cyclic disulphide additives in paraffin oil. The antiwear and antifriction properties of 1,2,4-dithiazo-line additives have been evaluated on a four-ball machine by using 12.7 mm diameter steel ball bearing specimen-I. The paper also includes a discussion on the effectiveness of 3-p-Cl-phe-nylimino-5-(N-methylphenyl)amino-1,2,4-dithiazoline on steel bearing balls of different compositions. The topography and the surface chemistry of the bearing ball wear scar were studied by Scanning Electron Microscopy (SEM) and Auger Electron Spec-troscopy (AES).     

Study of the tribological performance of a rare earth naphthenate as a lubricant additive

The tribological behaviour of a rare earth naphthenate (REN) as a lubricant oil additive in VG26 white oil and the complexes of REN and organo‐sulphur or organo‐phosphate compounds have been evaluated with a four‐ball friction and wear tester. The chemical features and elemental composition of the boundary lubricating film were examined by means of Auger electron spectroscopy (AES) and X‐ray photoelectron spectrometry (XPS). The results show that REN exhibits good antiwear, load‐carrying, and friction‐reducing properties in the base stock. When 2.0% REN is added, the wear‐scar diameter value reduces to 54.7% of that for the base stock alone and the maximum non‐seizure load increases 2.95 times. A synergistic effect is found for the load‐carrying capability of the complex of REN and organo‐sulphur while poor compatibility is exhibited for the complex of REN and organo‐phosphate. The analytical results of AES and XPS indicate that the good performance of REN is attributable to the formation of a boundary lubricating film mainly composed of naphthenic acid, rare earth oxide, and complexes of rare earth metals, which is formed on a rubbed surface when lubricated by oil containing the REN additive.     

Lubricant oils additivated with polymers in EHD contacts: Part 2. Tests using a four‐ball machine

A mineral oil of low viscosity was additivated with different concentrations of low‐density polyethylene. The wear behaviour of the additivated samples and the base oil was evaluated using a four‐ball wear tester at constant speed and variable load. Steel and ceramic (silicon nitride) were chosen for the balls. The scuffing resistance of the ceramic balls was higher than that of the steel balls. No scuffing appeared in the case of an upper steel ball in contact with lower ceramic balls. As far as the minimum wear‐scar diameter on the lower balls was concerned, an optimum concentration of polymer added to the base oil was found from the experimental data, for both types of ball. For the systems investigated, the optimum concentration was about 1.0% polyethylene.     

Tribological properties of 2 novel Mo/B–based lubricant additives in polyalphaolefin

Two kinds of Mo/B oleic diethanolamide derivatives (coded as YXM and YXB) were synthesised, and their tribological properties were evaluated using a 4‐ball machine. Results indicate that the 2 novel additives show excellent antiwear and extreme pressure properties. When 2.5 wt% YXM was added into the base oil, the wear scar diameter was reduced by 42.2%, and the P _B value was increased by 170.4%; when 2.5 wt% YXB was added into the base oil, the wear scar diameter was reduced by 23.1%, and the P _B value was increased by 167.1%. The worn surfaces of the lubricated GCr15 steel were analysed by using scanning electron microscopy and X‐ray photoelectron spectroscopy. It is indicated that the variation of tribofilm species produced by a chemical reaction between the additives and the steel surface plays an important role in inhibiting wear and friction. A model was used to analyse the action mechanism. According to the analysis, the tribofilm is composed of an adsorption layer and a reaction layer, and it could effectively protect the steel surfaces from direct contact.     

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.     

Low sulfur,phosphorus and metal free antiwear additives: Synergistic action of salicylaldehyde N(4)-phenylthiosemicarbazones and its different derivatives with Vanlube 289 additive

With a view to develop metal free, low SAPs antiwear additives, the antiwear properties of salicylaldehyde N(4)-phenylthiosemicarbazone and its p-methylphenyl, p-methoxyphenyl and p-chlorophenyl derivatives(1%w/v) and their synergistic/antagonistic behavior with Vanlube 289(1%w/v) additive were tested in base oil using four-ball lubricant tester and ZDDP as a reference additive. Antiwear testing of additives(1%w/v) was done by varying load and time. The performance of antiwear additives has been compared on the basis of tribological parameters. An appreciable synergistic activity is observed between 1% concentrations of the thiosemicarbazones and Vanlube289. The efficiencies of the synergistic formulations are far better than that of ZDDP. The topography and composition of the wear scar were analyzed by AFM and SEM with EDX. The synergistic formulations cause enormous reduction in surface roughness. The EDX analysis of the wear scar in the case of base oil with additive exhibits presence of sulfur and nitrogen.     

The tribochemical performance of nano/micrometre borate modified by an N‐containing compound as an oil additive

An N‐modified nano / micrometre borate (MNMB) as an oil additive was synthesised by an ultrasonic dispersion and emulsion reaction in the microemulsion phase. The particles of the MNMB additive were between 20 and 500 nm in diameter. The tribological properties of the MNMB as an oil additive were investigated using a four‐ball tester. The results reveal that the MNMB possesses good tribological properties. When the boron concentration is 0. 05 wt. %, the wear‐scar diameter is smallest and the seizure load is highest. The antiwear and extreme‐pressure properties of the MNMB were best at a viscosity of 65. 3 mms2. Small‐area X‐ray photoelectron spectroscopy (XPS) and electron probe microanalysis (EPMA) indicate that the MNMB additive can form a tribological mixed reaction film containing C, O, B, N, and Na on a rubbing surface. The elemental boron exists in four different chemical states, but is mainly present in the form of BN on the rubbing surface.     

Tribological evaluation and tribochemistry of some dialkyldithiomalonamides and their Mo‐S complexes as EP additives

The reported use of molybdenum dithiocarbamates and molybdenum dithiophosphates as antiwear and EP additives has led to attempts by the authors to synthesise certain novel Mo‐S complexes, and evaluate their effectiveness. In the present paper, the synthesis of certain 1,5‐dialkyl‐2,4‐dithiomalonamides and their Mo‐S complexes, namely, bis(1,5‐dialkyl‐2,4‐dithiomalonamido)‐dioxo‐molybdenum (VI), and the tribological evaluation of their 0.5% w/v admixtures in paraffin oil by a four‐ball test are reported, and the results compared with a dioxo‐bis(N,N‐diethyldithiocarbamato)‐molybdenum(VI) reference additive. The additive, bis(1,5‐diethylhexyl‐2,4‐dithiomalonamido)‐dioxo‐molybdenum(VI), has been found to reduce significantly both coefficient of friction and wear‐scar values, and to give higher load wear index values and flash temperatures, and has been found to be equally effective with alloy steel balls of three different compositions. However, all the Mo‐S complexes afforded smaller wear‐scar diameters in a one‐hour wear test. The wear spots on the used steel ball specimens were subjected to SEM and AES surface analysis for understanding the additive‐metal interaction tribochemistry.     

烷基咪唑-螯合硼酸离子液体摩擦学性能

以1,3-二癸基咪唑为阳离子,双水杨酸螯合硼酸为阴离子开发一类新型的环境友好螯合硼酸酯-烷基咪唑离子液体n-DICB/i-DICB,采用四球试验机考察2种添加剂在三羟甲基丙烷三油酸酯(PETO)基础中的摩擦学性能,采用SEM、EDX和XANES分析磨损表面的形态和摩擦中形成的摩擦膜的化学成分。结果表明：n-DICB/i-DICB具有优异的综合摩擦学性能,可显著提高可生物降解基础油的减摩、抗磨和极压性能;i-DICB的减摩性能和极压性能优于n-DICB,质量分数2.5%的i-DICB可使PETO的摩擦因数和磨斑直径分别降低33.0%和22.1%,最大无卡咬负荷提高66.6%。摩擦过程中,n-DICB/i-DICB形成了由B₂O₃、Na₂B₄O₇、NaBO₃和BN等混合物组成的致密摩擦膜,这是离子液体具有优异的摩擦性能根本原因。     

Antiseizure properties of aqueous solutions of compounds forming liquid crystalline structures

Amphiphilic compounds composed of a hydrophilic part and a hydrophobic alkyl chain were investigated. The compounds—sodium lauryl sulfate (SLS) and ethoxylated sodium lauryl sulfate (ESLS)—exhibit strong affinity for solid surfaces and form liquid crystalline structures in water. It is expected that they may become effective additives that could significantly modify antiseizure properties of water. They may extend the possibilities for applying water as an ecological base for lubricating substances. Rheological and structural X-ray studies as well as measurements of conductance and wetting angle were carried out. Their aim was to verify and validate the structures being formed in aqueous solutions of the compounds studied. Tribological studies were conducted to measure friction torque as a function of linearly increasing load by means of a four-ball apparatus. The tests were followed by measurement of the wear scar diameter on the balls. Based on the results obtained, antiwear properties were characterized by seizure and scuffing loads as well as by limiting pressure of seizure. The test results are highly surprising. The systems in which simple one-component aqueous solutions were the lubricating substance did not undergo seizure up to the maximum load of 8 kN designed for the tribological tester used. A number of typical antiwear additives in suitable oil bases do not exhibit such good characteristics. Also, the quantities characterizing seizure show relatively high values. Local maxima for the two compounds tested are formed in the area of low concentrations in the dependences of antiseizure properties as a function of concentration. It can be assumed that this is due to ordered structures being formed in the surface phase. The hexagonal phase of high viscosity of the order of several thousand Pa·s which forms in the bulk phase for ESLS and SLS solutions has no visible effect on antiseizure properties, whereas the existence of the lamellar phase for a 70% solution of ESLS affects an increase in the values being measured.     

Wear of water lubricated silicon nitride in ball on disc test

Abstract

The ball on disc test configuration is preferred to the flat ended pin on disc because the ball is self-aligned and measurement of wear on the ball is of higher accuracy, compared to the pin. Silicon nitride, sliding on itself in water, was tested with the ball on disc tribometer. Misalignment of the test ball from its proper position behind the disc axis of rotation leads to friction measurement errors, which were analysed. The disc wears non-uniformly, the wear track depth and width vary in longitudinal direction by a factor of 2–3. The uneven wear of the disc is explained by the combined effects of sliding surface anisotropy and disc material non-homogeneity on the one hand and by the friction force and the normal load periodic variation on the other hand. During the running-in process at particular sliding velocity amplitude modulated friction force was observed and an explanation by the mechanical vibration 'beating' phenomenon was suggested. Predictive model of the running-in process is presented, which describes the evolution of the ball wear scar area, the contact pressure and the wear rate. The model predictions are consistent with the experimental data.     

A study of the tribological behaviour of an organotin compound

Oil‐soluble stannous oleate (SO) has been synthesised using oleic acid and SnO and its molecular structure confirmed. The tribological performances of SO and of complexes of SO with organosulphur or organophosphate compounds as lubricant additives in a VG26 white oil have been evaluated using a fourball friction and wear tester. The results show that SO exhibits good antiwear, load‐carrying, and friction‐reducing properties in the base stock, which are better than those of ZDDP. When 2.0% SO is added, the wear‐scar diameter reduced to 70% of that for the base stock alone, and the maximum non‐seizure load increased by 2.4 times. The friction coefficient was clearly reduced when SO was added. Synergistic effects were observed between SO and tricresol phosphate as regards the antiwear and load‐carrying properties, while a synergistic effect occurred only in terms of the antiwear properties for SO and a sulphurbased olefin. The elemental composition of the boundary lubricating film was examined by means of Auger electron spectroscopy (AES). The analytical results of AES indicate that the good performance of SO is attributable to the formation of a boundary lubricating film containing Sn on the rubbed surface.     

Antiwear,Antifriction, and Extreme Pressure Properties of Motor Bike Engine Oil Dispersed with Molybdenum Disulfide Nanoparticles

This work presents studies on the antiwear, antifriction, and extreme pressure properties of motor oil dispersed with MoS₂ nanoparticles. Commercial oil (SAE 20W-40 grade) is dispersed with stabilized MoS₂ nanoparticles in 0.25, 0.5, 0.75, and 1 wt%. The test oils are tested for antiwear, antifriction, and extreme pressure properties on a four-ball wear tester. The wear and friction offered by nanolubricants has decreased remarkably compared to the commercial base oil. The weld load and load wear index of oils dispersed with nanoparticles were improved substantially compared to the commercial base oil. Metallographic studies conducted on the wear balls from the extreme pressure test show that nanoparticles are deposited on the worn area along with additives in the oil, thereby preventing welding of the surfaces. An optimum weight fraction is arrived at for best performance. A synergy between the additives in the oil and dispersed nanoparticles has been observed, resulting in less dispersion for best results. It is found that beyond an optimum weight percentage of nanoparticles, the trends tend to reverse, resulting in greater wear and friction.     

The effect of ethoxylated esters on the lubricating properties of their aqueous solutions

In many applications strict ecological criteria are crucial. Water is often used in these cases as a lubricant base. Its disadvantageous properties, in particular lubricity, can be modified by introduction of additives. Ethoxylated methyl esters of fatty acids from rapeseed oil were chosen for that purpose. In order to verify tribological properties of aqueous solutions of these compounds, anti-seizure properties under linearly increasing load, friction and wear under 2 kN (four-ball machine) were assessed. Not only radical change of tribological properties as compared to water was observed, but also the results are comparable to the ones obtained for mineral oils, which contained typical, commercial additives. Significant changes in scuffing load (P _t), seizure load (P _oz), limiting pressure of seizure (p _oz) were recorded even at 0.1% wt concentration of the additive. At optimal concentration P _t, P _oz, p _oz, increased even almost 6-, 2- and 3-fold (respectively). The quantities measured increased with ethoxylation degree. Also at constant load, friction (6-fold) and wear (almost 2-fold) were reduced. In this case, however, no influence of concentration and ethoxylation degree on the quantities measured, was observed.The tribological properties can be discussed in terms of results of physical–chemical tests. Ethoxylates are surface active compounds. Within the range of concentrations analyzed, they form micelles in a bulk phase and liquid-crystalline structures in a surface phase. High surface activity of these additives and creation of specific structures in solutions were proved by measuring surface tension, wetting angle and mesophases observation in polarized light. On the basis of the results of the physical–chemical and tribological tests one can conjecture that profitable tribological properties of the lubricating compositions are the result of strong affinity to the surface and their ability to form ordered structures. One can expect that over the cooperating surfaces a deposit is formed. Presence of the deposit increases real contact area and prevents seizure. This hypothesis gives a simple explanation of the unexpected improvement of anti-seizure properties, which accompanies the increase of ethoxylation degree. Ethoxylates with higher number of ethylene oxide attached, reveal smaller surface activity and better solubility in water. On the other hand, they can be characterized by higher dehydratation temperature. This means that at higher temperatures they reveal surface activity. That is why, during seizure tests, at high temperature, under high loads the esters of higher ethoxylation degree protect friction couples against seizure much more efficiently.     

EP activity evaluation of some 2-phenyl-3-phenylimino-5-arylimino-1,2,4-thiadiazolidines

A four-ball test was conducted to evaluate the EP activity of 2-phenyl-3-phenylimino-5-arylimino-1,2,4-thiadiazolidines (0.5% w/v) in paraffin base oil using a 12.7-mm diameter steel ball specimen. 2-phenyl-3-phenylimino-5-p-chlorophenylimino-1,2,4-thiadiazolidine exhibited good activity in reducing wear scar diameter and friction coefficient values at higher loads and increasing the values of flash temperature parameter (FTP), mean Hertz load (MHL) and pressure wear index (PWI) as compared with commercially available sulphur-phosphorous reference additives. The wear surface tribochemistry and topography were investigated using scanning Auger electron spectroscopy and scanning electron microscopy techniques.     

Synthetic aluminium complex grease: A tribological evaluation using a four‐ball test

This paper describes the preparation and performance evaluation of a synthetic aluminium complex grease. The aluminium complex grease was prepared in situ by reacting stearic acid and benzoic acid in the presence of a synthetic base oil, polyalphaolefin. The preparation of the soap (aluminium benzoate stearate hydroxide) was monitored using Fourier transform infrared. Two different extreme‐pressure additives blended with the prepared aluminium complex grease were evaluated for their extreme‐pressure activity in four‐ball and Timken tests. These greases exhibited higher Timken OK loads (60 lb), lower values of wear‐scar diameter at higher loads, and higher values of weld load in the four‐ball test than the aluminium complex grease without additive. The blended greases were also found to pass rust and corrosion, oxidation‐stability, and shear‐stability tests. The topography of the specimens after four‐ball testing was studied with scanning electron microscopy.