Tribological analysis of hydrocarbon refrigerants applied to the hermetic compressor

This paper describes the tribological impacts of hydrocarbon refrigerants deployed in the domestic refrigerator hermetic compressor. In-use durability is examined from a tribological viewpoint. Experimental tribological information is presented from physical test procedures involving sliding tests to establish wear mechanisms and friction coefficients within critical components. Hydrocarbon refrigerant R600a is compared with hydroflourocarbon R134a using aluminium on steel samples within a novel pressurised micro-friction test rig. The refrigerant R600a is tested for its influence upon the tribological performance of mineral oil (MO) and poly-ol-ester (POE) lubricant, whilst an R134a/POE charge combination is used as a benchmark. Although wear rates were significantly greater for samples utilising POE lubricants than for MO, the friction coefficients were much lower.     

A study on the tribological characteristics of graphite nano lubricants

Many researchers have tried to improve the tribological characteristics of lubricants to decrease friction coefficients and wear rates. One approach is simply the use of additives in the base lubricant to change its properties. Recently, nanoparticles have emerged as a new kind of additive because of their size, shape and other properties. A nano lubricant is a new kind of engineering lubricant made of nanoparticles, dispersant, and base lubricant. In this study, graphite nanoparticles were used to fabricate nano lubricants with enhanced tribological properties and lubrication characteristics. The base lubricant used was industrial gear oil, which has a kinematic viscosity of 220 cSt at 40°C. To investigate the physical and tribological properties of nano lubricants, friction coefficients and temperatures were measured by a disk-on-disk tribotester. The surfaces of the fixed plates were observed by a scanning electron microscope and an atomic force microscope to analyze the characteristics of the friction surfaces. The results show that when comparing fixed plates coated with raw and nano lubricants, the plate coated with a nano lubricant containing graphite nanoparticles had a lower friction coefficient and less wear. These results indicate that graphite nanoparticle additives improve the lubrication properties of regular lubricants.     

Tribological Properties of Muscovite/La2O3 Composite Powders as Lubricant Additives

Muscovite/La₂O₃ composite powders were prepared by ball-milling solid-state chemical reaction at room temperature. The phase composition and micromorphology of the composite powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The tribological properties of different samples were tested and compared using four-ball wear testing on an MMW-1A multifunctional friction and wear testing machine. The SEM micrography and energy spectrum of the composite powders illustrated that La₂O₃ particles were coated on the surface of muscovite particles. The results of the friction tests indicated that lubrication oil with muscovite/La₂O₃ composite powders presents better friction reducing and antiwear properties than that of the base oil, and the friction coefficients and diameters of wear scars decreased by 47.6 and 11.2% using 500SN base oil with 0.6g/L of muscovite/La₂O₃ composite powders as additives, respectively. The composite powders with 5 wt% La₂O₃ present the best comprehensive tribological properties. The micromorphology and chemical composition of the worn surface were analyzed by SEM and EDX, which confirm that the composite powders directly participate in the complicated physicochemical process of reactions on the worn surfaces, therefore improving the tribological properties of the base oil.     

稀土化合物改性复合材料在油润滑下的摩擦学性能

以竹纤维为增强相,通过稀土化合物改性制备一种树脂基复合材料;采用环块式摩擦磨损实验,研究稀土化合物改性复合材料在油润滑状态下载荷、转速对试样摩擦学性能的影响,以及稀土化合物改性对复合材料试样摩擦学性能的影响;比较干摩擦状态和油润滑状态下复合材料的摩擦学性能,观察和分析试样磨损表面形貌,探讨其磨损机制。实验结果表明:油润滑条件下,稀土化合物改性复合材料的摩擦因数和磨损率都随着载荷的增大而增加;较高载荷下摩擦因数随着转速的增大先增加后减小,而磨损率则呈现逐步增加的趋势;稀土化合物的改性使竹纤维和基体界面结合更为紧密,提高摩擦因数的同时降低了磨损率;在油润滑作用下,试样磨损由干摩擦时的磨粒磨损和疲劳磨损转变成为轻微的疲劳磨损;在油润滑状态下,复合材料处于边界润滑状态,故摩擦因数和磨损率均低于干摩擦。     

废润滑油/再生润滑油的摩擦学性能

使用可见分光光度计初步评价实验室自主研发工艺处理得到再生润滑油的质量,采用四球摩擦磨损试验机考察再生润滑油的摩擦学性能并与废润滑油、新润滑油进行对比研究,借助扫描电子显微镜对磨斑表面形貌进行观察分析,对再生润滑油的抗磨减摩与润滑机制进行探讨。结果表明,废润滑油摩擦学性能严重下降,较新润滑油摩擦因数升高26%以上,磨斑直径增大58%以上;再生润滑油表现出了优良的减摩抗磨性能,较废润滑油摩擦因数能够降低25%,磨斑直径可减小50%左右,基本达到了新润滑油的水平。     

Synthesis and tribology of aluminium hexoxylborate as an antiwear additive in lubricating oil

An oil-soluble compound containing aluminium and boron has been synthesized. The tribological properties of the compound in SN500 oil were evaluated on a four-ball and block-on-ring test apparatus. The results showed that the wear resistance and load-carrying capacity of the oil were improved, and the friction coefficient was decreased. Evidence of deposition was found in the wear scar by SEM. It is concluded that this deposition provided the oil with its good wear resistance properties.     

N-酰基谷氨酸在矿物油中的摩擦学性能研究

分别在油酸和月桂酸分子中引入氮,合成了2种新型的含氮润滑油添加剂——N-油酰基谷氨酸和N-月桂酰基谷氨酸。利用四球摩擦磨损试验机考察了2种添加剂作为HVI350矿物基础油极压抗磨添加剂时的摩擦学性能,通过测定不同条件下的最大无卡咬负荷和磨斑直径及摩擦因数,分析和研究了载荷、摩擦时间、添加剂含量对矿物油最大无卡咬负荷和磨斑直径及摩擦因数的影响。试验结果表明:2种添加剂均可以明显提高基础油的承载能力和抗磨减摩性能,添加剂N-油酰基谷氨酸在矿物油中的承载能力明显优于N-月桂酰基谷氨酸,而N-月桂酰基谷氨酸对提高矿物基础油抗磨减摩性能的效果好于添加剂N-油酰基谷氨酸。试验还表明添加剂的含量并非越高越好,否则磨斑直径将增大。     

Assessment of lubricity of compositions of fuel oil with biocomponents derived from rape-seed

This paper presents an assessment of tribological properties of compositions of fuel oil containing fatty acid methyl esters derived from rape-seed oil. An HFRR (high-frequency reciprocating rig – ball-on-flat) apparatus was used in this investigation. The studies were carried out for a steel–steel pair in the concentrated contact.The tribological properties were determined by motion resistances, wear and lubricant film concentration. The surfaces were analysed after tribological tests. The aim of the investigation was an attempt to obtain a correlation between wear quantities being measured and percentage content of bioadditives in fuel oil. It was found that at as little as 5% of the additive the coefficient of friction decreases by about 20% while wear decreases twofold relative to fuel oil, which may result from an increase in the stability of the lubricant film.     

Effects of Resin Type and Fiber Length on the Mechanical and Tribological Properties of Brake Friction Materials

In this study, the effects of resin type and fiber length on mechanical properties and friction characteristics of automotive brake materials were studied. Three types of resin, viz. straight phenolic resin (SR), cashew nut shell liquid modified resin (CR), and melamine resin (MR) were used as matrix material. Lapinus with different lengths was used as inorganic fiber. Three series of friction composites composed of nine composites in the form of brake materials were manufactured. Physical, mechanical, and tribological properties of all composites were investigated. The friction tests were performed using a Chase type friction tester. The results showed that both resin type and fiber length played an important role on the mechanical and tribological properties of the friction materials. The highest and the lowest friction coefficient for resin types were recorded for SR and MR composites, respectively, while MR and CR composites showed the highest and the lowest wear resistance, respectively. For the fiber length considered, increasing the fiber length increased the wear resistance of the composites. The coefficient of friction, in general, showed a good correlation with the wear resistance of the composites. But, there was no clear correlation with the mechanical and tribological properties of the composites. The morphological features of worn surfaces and wear debris of the composites were analyzed in order to understand the friction and wear mechanisms of this tribosystem.     

Microstructural Characterization of Wear Particles Formed During Tribological Stressing of TiC and Ti(C,N) Coatings

An attempt was undertaken to obtain a better understanding of the tribological properties of two wear-resistant coatings on tool steel by structural and microchemical analysis of wear particles using a transmission electron microscope. Coatings were deposited by physical vapor deposition and plasma-assisted chemical vapor deposition techniques and tribological properties were derived from reciprocating sliding tests of the coatings against alumina balls. Three types of wear particles were identified by electron diffraction and energy dispersive X-ray spectroscopy: nanocrystalline rutile (TiO₂), nanocrystalline graphite and microcrystalline graphite. Low coefficients of friction, of the order of 0.2, were attributed to the formation of solid lubricant films of sub-stoichiometric TiO_2-x Magnéli phases and/or graphite.     

Tribological behaviour of modified polyacetal against MC nylon without lubrication

Compared with other polymers, polyacetal or polyoxymethylene (POM) which is widely used as bearing, guide, gear and other sliding parts, has high strength and stiffness, excellent chemical resistance and superior antifriction and wear resistance. To improve the toughness and self‐lubrication capacity of POM due to its higher crystallizability, other components, which include toughening phase and solid lubricants, are often added to the POM matrix. This paper deals with the friction and wear behaviours of POM which was modified by the toughening phase polyurethane (PU) and filled with polytetrafluoroethylene (PTFE) and silicone oil, during rubbing against MC nylon without liquid lubrication. Friction and wear tests show the tribological performance of the modified POM (M‐POM) with 10 wt% PU is better than those of pure POM and POM blended with PTFE under dry friction. The frictional coefficient of the M‐POM decreases with increasing nominal load. The sliding velocity has a more obvious effect on the tribological properties of the M‐POM than the nominal load. The higher sliding velocity leads to thermal degradation and melting of the experimental polymers because of the frictional heat. This revised version was published online in June 2006 with corrections to the Cover Date.     

Tribological behaviour and wear mechanism of MoS2–Cr coatings sliding against various counterbody

MoS₂–Cr coatings with different Cr contents have been deposited on high speed steel substrates by closed field unbalanced magnetron (CFUBM) sputtering. The tribological properties of the coatings have been tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The coating microstructures, mechanical properties and wear resistance vary according to the Cr metal-content. MoS₂ tribological properties are improved with a Cr metal dopant in the MoS₂ matrix. The optimum Cr content varies with different counterbodies. Showing especially good tribological properties were MoS₂–Cr8% coating sliding against either AISI 1045 steel or AA 6061 aluminum alloy, and MoS₂–Cr5% coating sliding against bronze. Enhanced tribological behavior included low wear depth on coating, low wear width on counterbody, low friction coefficients and long durability.     

Grey theory applied to evaluate the tribological performances of the a-C:H(N) coating films prepared by differing the nitrogen content and the film thickness

The purpose of this paper is to study the tribology performances of the aC:H(N) films by using a nanotester under different scratch loads and velocities. From the measurements of the friction coefficient and wear volume, the tribological performances including wear resistance and friction coefficients were evaluated for the hydrogenated amorphous carbon films prepared by differing film thickness and nitrogen volume friction in the gas mixture of (C₂H₂+N₂). Taguchi experimental design and the grey relational analysis were used to investigate the influence of specimen parameters (film’s thickness, nitrogen content in the film), and operating conditions in tribological tests (scratch load and scratch velocity) on the friction coefficients and the wear volume arising in the specimens with different coating films. It is found that the wear volume of thin film is increased by increasing either the nitrogen volume fraction or film thickness. Moreover, the optimal combination of the testing parameters was also determined in the use of the present model.     

Tribological properties of AlCoCrFeNiCu high-entropy alloy in hydrogen peroxide solution and in oil lubricant

Pin-on-disc tests to investigate the tribological behavior of AlCoCrFeNiCu high-entropy alloy under lubrication conditions with 90% hydrogen peroxide solution and lubricant oil, respectively, were performed. The study demonstrates that the AlCoCrFeNiCu high-entropy alloy lubricated correspondingly with lubricant of 90% hydrogen peroxide solution (hereafter termed hydrogen peroxide lubricant) and lubricant oil significantly improves its friction and wear-resistance properties. Results showed that the friction coefficient, after a grinding stage, of the rubbing pair was lower than that with normal lubricant oil. The AlCoCrFeNiCu alloy in the lubricant with 90% hydrogen peroxide solution and lubricant oil exhibits a high resistance to wear. Analysis of the worn surface revealed that the AlCoCrFeNiCu high-entropy alloy lubricated with the hydrogen peroxide lubricant exhibited signs of inhomogeneous polishing oxidation and abrasive wear, with the wear mechanism changing with sliding distance, while the rubbing pair in normal lubricant oil is mainly dominated by abrasive wear.     

Tribological properties of carbon nanotube-doped carbon/carbon composites

Carbon nanotube (CNT)-doped carbon/carbon (C/C) composites were fabricated by the chemical vapor infiltration (CVI) method to investigate the effect of CNTs on tribological properties of C/C composites. CNTs, which had been synthesized by catalytic pyrolysis of hydrocarbons, were added to carbon fiber formed preforms before CVI process. Ring-on-block-type wear tests were performed to evaluate the frictional properties of CNT-doped C/C composites. Results show that CNTs can not only increase wear resistance of C/C composites but also maintain stable friction coefficients under different loads. Polarized light microscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy analyses demonstrate that favorable effects of CNTs on tribological properties of C/C composites have been achieved indirectly by altering microstructure of pyrocarbons and directly by serving as high-strength lubricative frictional media at the same time. Electron dispersive spectroscopy (EDS) analyses verify the existence of adhesive wear mechanism in both pure C/C composites and CNT-doped C/C composites albeit the two-body abrasive mechanism dominates in pure C/C composites.     

Influence of friction on the surface characteristics of EPDM elastomers with different carbon black contents

Tribological properties and surface characteristics of ethylene-propylene-diene elastomers were studied as a function of carbon black (CB) content. The surface analysis was performed inside and outside the wear track by X-ray photoelectron spectroscopy (XPS) in order to evaluate possible compositional changes produced by rubbing. Carbon black content had only a small influence on the surface chemistry of the unworn surfaces. However, on the surfaces subjected to friction, the oxygen concentration decreased with increasing CB content. Neither the surface analysis by XPS nor the wettability tests revealed important thermal degradation of the polymer in these friction tests.     

镍基Si3N4复合镀层的摩擦磨损特性

通过复合电镀法制备了N i-Si3N4和N i-P-Si3N4两种复合镀层,分别与热处理45#钢组成摩擦副,进行环-环摩擦磨损试验,测试了摩擦因数和磨损量,并观察了磨损表面形貌,探讨了摩擦副的摩擦磨损机理。结果表明,N i-P-Si3N4/45#钢摩擦副的摩擦因数较小,磨损量低,具有良好的减摩耐磨性能。镀层基体的性能明显影响复合镀层的摩擦磨损性能。磨料磨损是N i-Si3N4/45#钢摩擦副的主要磨损形式,导致45#钢的磨损量增大;N i-P-Si3N4镀层对Si3N4颗粒具有良好的把持力,避免了磨料磨损的产生,摩擦副处于稳定的边界润滑摩擦状态。     

Wear Characteristics of Traditional Manganese Phosphate and Composite hBN Coatings

In this study, the tribological properties of traditional manganese phosphate coatings and composite hBN coatings

composed of nano-hexagonal boron nitride (hBN) in layered manganese phosphate crystals on AISI 1040 steel were investigated. Wear tests were carried out under controlled temperature and humidity using ball-on-disc tribometers for samples that were either submerged in oil or retaining oil on their surfaces at a sliding speed of 2.5 cm/s with loads of 1, 3, 5, and 10 N and sliding distances of 40, 80, 100, and 120 m. The surface profiles before and after the tests were used to characterize the wear. The surfaces of the coated samples were examined using scanning electron microscopy (SEM). The coefficients of friction and wear rates of the coated samples were also measured. The average wear rates of the composite hBN-coated samples were significantly lower than those of the traditional manganese phosphate–coated samples for each of the loading conditions for the oil submersion and retained oil tests. The coefficient of friction (COF) values for the traditional manganese phosphate–coated samples did not change significantly with increasing load. The COF values for the composite hBN coated–samples decreased with increasing load in the oil submersion test.     

不同润湿组合配流副的摩擦磨损试验研究

为调控配流副表面润湿性以提高摩擦学性能，采用低面能修饰法制备具有不同润湿性的上试样超级双相不锈钢SAF2507和下试样碳纤维增强聚醚醚酮(CFRPEEK)组成配流副，利用MMD-5A标准摩擦磨损试验机测试并分析其在蒸馏水、海水、L-HM46抗磨液压油3种润滑条件下的摩擦磨损特性。结果表明：低面能修饰使配流副上试样与下试样由亲水表面转变为疏水表面，上下试样表面虽仍保持亲油性但其油接触角明显增大；同种配流副在油、海水、水介质中摩擦因数依次减小；在水、海水、油介质下双疏水表面配流副较双亲水表面配流副摩擦因数分别减小8.2%、38.2%、24.4%；同种配流副在水、海水、油介质中磨痕深度依次减小。配流副的摩擦主要以犁沟效应和黏着磨损为主，双低表面能组合配流副能有效减小摩擦过程中的黏着磨损，从而表现出较好的摩擦学性能。     

不同含量盐水介质中丁腈橡胶水润滑轴承材料摩擦学特性分析

以水润滑轴承用丁腈橡胶(NBR)材料为研究对象,在CBZ-1摩擦磨损试验机上开展其在清水及不同盐分含量水介质中以及不同速度及载荷下的摩擦学试验,对比分析其摩擦因数、磨损量以及磨损表面形貌等摩擦学特性的变化规律。结果表明:盐水质量分数、速度和载荷对丁腈橡胶的摩擦学性能影响显著,其摩擦学特性的变化是盐水质量分数、载荷、速度以及丁腈橡胶的黏弹性等因素共同作用的结果;丁腈橡胶材料与锡青铜配副的摩擦因数随转速的升高而降低,随载荷的增加而降低;随着盐水质量分数的增加,摩擦副的摩擦因数和磨损量先增大而后均有所减小,这是因为盐水质量分数通过影响润滑介质的黏度来改变水润滑的效果,通过对铜盘的腐蚀作用来改变摩擦副的摩擦情况,从而在整体上影响摩擦因数和磨损量的变化。