Four-ball Extreme Pressure Research Articles

Experimental Evaluation of the Tribotechnical Properties of Engine Oils for Combine Harvesters

A four-ball extreme pressure test has been performed to study and evaluate the tribotechnical properties of motor oils. The studies have shown that the tribotechnical properties of the engine oil stored in the crankcase during the winter period exhibit a significant change. The average ball wear level has shown a 40% increase compared with that observed in the case of new oil. The average ball wear diameter for the oil samples taken from the combine engines in autumn amounted to 0.5 mm, whereas the average ball wear diameter for the oil samples taken from combine engines in spring amounted to 0.7 mm. When testing new semisynthetic engine oil, the average ball wear diameter varied within 0.48 ± 0.04 mm. It is assumed that the boundary layer formed by the oil is weaker, which causes an increase in the risk of its breaking and sealing the friction pores.

A Friction–Wear Correlation for Four-Ball Extreme Pressure Lubrication

AbstractA first-ever friction–wear model for four-ball extreme pressure (EP) lubrication is developed in this work based on 12 oil samples comprising minerals, esters, and other formulated lubricants. The model considers the rate of entropy generation and dissipation within the lubricated tribosystem to describe the interaction between the friction and the wear behaviors at extreme pressure conditions. The model can be used to calculate the probability to pass or fail at a specific load to estimate the weld point of a lubricant. The calculated probability exhibited a similar trend as a load-wear index from the ASTM D2783 EP test method. Besides, the model is able to estimate the EP performance of an unknown lubricant based on the model parameter, namely the dissipative coefficient. This parameter describes the proportionality between the friction and the wear phenomena from the perspective of thermodynamic analysis. This work provides useful tools to better understand the fundamentals of EP lubrication and to characterize the lubricants without overly relying on tribotest machines.

The effect of particle size on the dispersion and wear protection ability of MoS2 particles in polyalphaolefin and trimethylolpropane ester

The effect of particle size and surfactant on dispersion stability and wear protection ability was experimentally evaluated for polyalphaolefin (PAO 10) and bio-based base oil (palm trimethylolpropane ester) added with molybdenum disulfide (MoS2) particles. Nanolubricants were developed by adding 1 wt% of MoS2 particles that varied in size. In addition to the variation in particle size, an anionic surfactant was also used to analyze its interaction with both types of nanoparticles for stable suspensions and for the related effects on the antiwear characteristics. The wear protection characteristics of the formulations were evaluated by four-ball extreme pressure tests and piston ring on cylinder sliding wear tests. The wear surfaces were analyzed by scanning electron microscopy along with an energy-dispersive X-ray and an atomic force microscopy. The MoS2 nanoparticles with a nominal size of 20 nm exhibited a better load-carrying capacity, while better sliding wear protection was provided by nanoparticles with a nominal size of 50 nm.

Antiwear Behavior of CuO Nanoparticles as Additive in Bio-Based Lubricant

This work presents and discusses the anitwear characteristics of surface modified CuO nanoparticle suspensions in bio-based lubricant. 1.0 wt% unmodified as well as surface modified CuO nanoparticles (nominal size of 50 nm), were dispersed in base oil using an ultrasonic probe. Wear protection was evaluated by using Four-Ball Extreme Pressure (EP) testing and sliding wear tests. The scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analysis of the worn surface shows that: surface modification helped to improve the dispersion stability of CuO nanoparticles and related suspension show high EP characteristics in terms of load wear index and low cylinder liner wear due to surface mending effect of nanoparticles.

Dispersion Stability and Tribological Characteristics of TiO2/SiO2 Nanocomposite-Enriched Biobased Lubricant

ABSTRACTThe stable dispersion of nano-additives is highly desirable for the effective lubrication performance of nanolubricants. The compatibility of base oil with selected nano-additives is required for uniform and stable dispersion. This research evaluated the dispersion stability and tribological characteristics of nano-TiO2/SiO2 (average particle size 50 nm) as an additive in a biobased lubricant. The wear protection and friction reducing characteristics of the formulations were evaluated by four-ball extreme pressure tests and piston ring–cylinder liner sliding tests. Surface analysis tools, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy, were used to characterize the worn surfaces. Results showed that the nanolubricants demonstrated appreciable dispersion capability in the absence of a surfactant and an improvement in load-carrying capacity, antiwear behavior, and friction reduction capability.

EVALUATION OF LUBRICATION EFFICIENCY BASED ON WEAR DURING VARIABLE LOADS AND SLIDING VELOCITIES

The results of the tribological studies on the lubrication efficiency of greases evaluated based on tribological tests performed at varying pressure p and rubbing speed v are presented. For the efficiency criterion, the volume of wear VF(d) obtained from the regression equations of wear was adopted (wear F (d) = f (F, v)). Six different lubricants were tested; two of them were commercial greases, and four of them were compositions based on them, including conventional solid greases (PTFE, tin, copper, and boron nitride). The experiment was carried out on a four-ball extreme pressure tester according to a rotatable design on five levels. For each of the selected lubricants, a regression function was developed that defined wear as a function of rubbing speed and load. The volume of the obtained wear VF(d) was calculated and relevant conclusions were drawn.

Effects of the Nano-Diamond Additives on the Tribological Performance Improvement of Lubricating Grease

Ball screw is a very important element in precision machine industry. It has a lot of superior characteristics such as low friction coefficient, long life, high positioning accuracy and as well as converting rotational motion to linear motion. Therefore, the lubricant used in the ball screw should be low friction and wear in order to meet the aims of the above mentioned properties. The ultra-dispersed nanodiamond (UDD) is dispersed in the dispersant. The UDD is served as an extreme pressure additive in the test grease that is applied to the ball screw. Four-ball extreme pressure tests and bearing life tests were conducted in this study to evaluate the extreme pressure performance and durability enhancement of the test grease. The four-ball test results showed that the optimum selection of the dispersant category, UDD mean particle diameter and concentration added to the test grease provided by the cooperated ball screw manufacturer in this study are OLA, 200 nm and 100 ppm, respectively.

THE AFTERMARKET ADDITIVES USED IN LUBRICATING OILS

The paper presents literature review concerning the aftermarket additives used in lubricating oils. Classification, principle of operation and scientific research of aftermarket additive operational effectiveness was presented. In majority of cases lubricating oils modified by aftermarket, additives are tested by means of a four-ball extreme pressure tester T-02 or friction machine T-05. Tester T-02 is used to determine lubricating oil parameters like weld load Pz, maximum non-seizure load Pn, seizure load Pt, load wear index Ih and load limit of wear Goz according to Polish Norm (PN-76/C-04147). Investigation of the tribological properties (friction force, wear of the matching elements) is executed by means of friction machine T-05. Until now, scientific research does not result in unequivocal assessment of the aftermarket additives. It come from big variety of aftermarket additives (chemical interaction aftermarket additives, additives that contain molecules of solid lubricants, additives that are able to form conditions for selective transfer lubrication) and their various principles of operation. Now the chemical interaction aftermarket additives have the widest application. These additives join permanently with lubricating oil, so they do not precipitate on the filters and do not create heat-insulating layers unlike the additives which contain molecules of solid lubricants (for example PTFE). Chemical interaction aftermarket additives improve antiwear (AW) and antiseizue (EP) properties of lube oils, decrease temperature in friction area and consequently minimize wear of the machines metal elements. Their functioning efficiency is usually the highest in hard working conditions (high loads, polluted environment, deteriorating technical condition of friction node elements) and in case of oils worse equipped with AW and EP additives (machine and hydraulic oils). In case of polymers, the influence of aftermarket additives is ambiguous.

Effects of Chlorinated Paraffin and ZDDP Concentrations on Boundary Lubrication Properties of Mineral and Soybean Oils

Concentration effects of chlorinated paraffin and zinc di-ethylhexyl dithio phosphate on boundary lubrication properties were tested in vegetable and mineral base stocks. Solvent refined low sulfur paraffinic mineral oil (150 N oil) and conventional food grade soybean oil (soy oil) with EP additive concentration of 0–20% (w/w) were used in ASTM D2783 four-ball extreme pressure (4-ball EP) and Twist Compression Tribotests (TCT). Weld points in 4-ball EP and times to failure in TCT at 200 MPa showed that 150 N oil needed more than double treat levels of EP additives to achieve similar boundary lubrication performance as their 5% blends in soy oil. Also, incorporation of 20% soy oil into 150 N oil-based EP additive blends improved the performance to nearly the same level as soy oil only blends of corresponding additives. Boundary lubricity of some soy oil samples was similar to that of a commercial straight oil chlorinated metal forming lubricant. Several suggestions are provided to explain such pronounced influence of the base stock type on EP additive response. The findings suggest that soy oil and other farm-based oils may provide strategies for formulating cost effective industrial fluids and other lubricants.

The effect of ball hardness on four-ball wear test results

The hardness of mating surfaces is an important component of the so-called friction parameters vector and has a significant influence on the magnitude of the friction and on the wear of the surfaces. Investigations aimed at determining the influence of hardness on the wear of machine parts working in mixed lubrication range were carried out using a four-ball extreme pressure tester. The test balls were made of 100Cr6 steel with a hardness of 24–62 HRC. A mixed lubrication model (an objective function) correlating the hardness of the steel sliding surfaces, the magnitude of the friction and the wear of the surfaces in a defined area of excitations (pressure p H and sliding velocity v ) for lubrication with oil Transol 150 has been developed. Hardness has been found to have a significant influence on wear. Thanks to the correlation of hardness with the excitations it has been observed that the objective function d = f( p H, v , H) is not a monotone function, but it has an extremum. The model allows one to match steel materials for sliding nodes working under concentrated contact (e.g. in gears) without the need to carry out experimental tests.

A study of the tribological behaviour of perfluoro-polyethers

The tribological behaviour of perfluoropolyethers (PFPEs) was investigated by performing four-ball extreme-pressure (EP), Falex, four-ball wear, Reichert, SRV (both point-plane and plane-plane contacts), Amsler and TE 77 determinations on four commercially available Fomblin Y fluids, which cover the entire viscosity range. For comparison a petroleum-based hydraulic oil was subjected to the same tests. In load-carrying capacity measurements (four-ball EP and Falex tests) the PFPEs also surpassed the hydraulic oil as an EP gear lubricant. The performances of the PFPEs in determinations of their wearpreventing characteristics were variable. They were better than the hydraulic oil in Reichert tests but behaved in a roughly identical way in four-ball wear determinations and were inferior to it in the SRV (point-plane contact) method. The irregular behaviour is due to the different severity of operating conditions. The harsh strains exerted in four-ball EP, Falex and Reichert tests led to elevated contact temperatures, thus causing the decomposition of fluorinated macromolecules. The subsequent reactions of decomposition products originated the fluoride films to which the relevant performances of PFPEs are ultimately due. As the stresses to be endured in the SRV (point-plane contacts) tests had not been so extreme, the temperature at which the thermal decomposition of PFPEs would have begun was not attained. The more fluid the grade, the better was its performance in four-ball wear tests, since a lower viscosity led to a more abundant supply of lubricant at the rubbing spots and thus to a smaller wear rate. Lubrication was hydrodynamic in SRV (plane-plane contact), Amsler and TE 77 tests, and hence no damage took place in them. Friction coefficients, which depended on both testing machine and test conditions, were slightly higher for PFPEs than for the hydraulic oil.

Effect of wear debris on wear in rolling-sliding motion

The effect of wear particles on wear was investigated using a four-ball extreme pressure lubricant test apparatus. The wear particles present in both filtered and unfiltered oil samples were examined using a duplex Ferrograph analyser and a bichromatic microscope. The wear track widths were measured for various wear modes and were found to increase if the wear debris was recirculated. The size of the wear particles increased with test duration.

The mechanism of lubrication by molybdenum disulphide dispersed in oil and the effect of a zinc dialkyldithiophosphate additive

The effectiveness of the lubrication of hard smooth steel surfaces by molybdenum disulphide (MoS 2) dispersed in a mineral oil, both with and without a zinc dialkyldithiophosphate (ZDDP) additive, has been investigated using a four-ball extreme pressure lubricant test machine. Each oil, additive-oil or MoS 2 dispersion, exhibited a wear scar diameter-load curve with an abrupt transition from mild to severe wear at a characteristic load. When ZDDP was present in the oil, MoS 2 was effective at pre-transition but not post-transition loads, whereas in the absence of ZDDP the converse applied, with MoS 2 only beneficial above the transition load. These results are explained in terms of the adherence (or not) of MoS 2 particles to the films physically adsorbed on the steel surfaces at pre-transition loads. At the transition load the surface temperature reaches the desorption (or decomposition) temperature of the particular oil or additive film and MoS 2 then adheres to exposed metal, unless the latter chemically reacts with oil constituents to form a chemisorbed film.

Investigations of the activity of cutting oil additives II. organochlorine containing compounds

A wide variety of organochlorine compounds has been tested in a tapping torque cutting test at 15 mg atoms chlorine per 100 g blend in liquid paraffin. The relative effectiveness of the blends was compared with that given by the same fluids in the four-ball extreme pressure test. A representative number of the fluids was tested in another cutting test, the drill life test. In general, good correlation between these tests was found. The tightness of the curl of the swarf obtained from the tapping test was seen to be characteristic of the activity of the test fluid. Examination of the outer surface of the swarf using the scanning electron microscope showed scoring marks when pure carbon tetrachloride was used as the cutting fluid. These marks were not observed when cutting with any of the liquid paraffin blends. A five-fold increase in concentration of the additive gave a rank order of the blends in the tapping test similar to that found at the lower concentration. The chemical reactivity towards steel of certain of the blends was found and the bond dissociation energies of those organochlorine compounds where data were available were calculated. The reactivity and the carbon-chlorine bond strength correlated well with the cutting efficiency and EP activity of the fluids. The cutting results can be explained in terms of the ability of the blends to form a low shear chloride film on the rake face-chip interface. This function appeared to be controlled by the carbon-chlorine bond strength in the additive, which in increasing order was found to be benzyl chloride < tertiary chloride < secondary chloride < primary chloride < aryl chloride.