Wear behavior of polymeric compositions in dry reciprocating sliding

The development of Stirling engines as high efficiency motors for automobiles is critically dependent on the ability of sliding seals to operate for long periods (up to 3500 h) without excessive leakage or wear. Piston rings must run completely dry while sealing against hydrogen leakage under a pressure drop of 5–20 MPa. Main seals, cooled by oil, must seal against similar pressures without admitting any oil which could contaminate the high temperature sections of the engine.The results of an initial search for materials with lower wear rates than the polytetrafluoroethylene (PTFE) polymer compositions currently used in test engines are described in this paper. On the basis of a literature review, the results of engine development tests and experience with solid lubricants, several commercially available formulations were selected for a screening test program. In addition, some custom formulations were prepared by commercial vendors.A reciprocating screening tester, operating at 1200 cycles min^?1 with a stroke of 40 mm, was used to determine material wear rates at a PV factor below the first PV limit of the reference PTFE material. Materials with wear rates in the range of 0.13 × 10^?6–0.16 × 10^?6 mm³ N^?1 m^?1 (the reference material wear rate was 0.40 × 10^?6 mm³ N^?1 were found.Friction coefficients were also measured since friction power loss in the seals represents a significant portion of the total mechanical engine losses. Compositions which significantly reduced the friction coefficient while retaining a low wear rate were found.     

High-temperature tribology of future diesel engines

Future diesel engines will be operated at higher cycle temperatures. These higher cycle temperatures will invariably pose tribological problems of the top ring, piston, valve seats, and valve guides. Current lubricating oil with a thermal oxidative stability up to 204°C will be inadequate: polyol ester-base formulated synthetic oil, such as Stauffer Chemical SDL-1 or US TACOM MRI-1, with 310°C thermal oxidative stability could possibly be the next generation of lubricating oil. However, as we get nearer to the time when diesel engines will be constructed in advanced structural ceramics or composites for ‘adiabatic’operation, the thermal stability of the lubricating oil will have to approach 445°C. To withstand a top ring reversal temperature beyond 310°C, polyphenyl ether base oil and other high-temperature liquid lubricants are sought, but the highly aromatic polyphenyl ether type oil has thus far shown little promise for this application. The hybrid piston with solid lubricated top ring has potential. Densified Cr₂O₃ on Cr₂O₃ has demonstrated the possibility of operating at 380°C top ring reversal temperature, with acceptable wear and life. NASA PS212 with Stellite 6B has also been tested without a liquid lubricant. The tribological needs of the next generation of high-output, high-temperature diesel engines can therefore be met with the synthetic polyol ester base, cost-effective, formulated lubricant. The adiabatic ceramic engine will require much higher temperature capability. To this end, tribologists will have to direct their efforts to other higher temperature liquid lubricants and to solid lubricants. A laboratory coefficient of friction of < 0.06 must be achieved in order to maintain acceptable brake-specific fuel consumption. This target is based on cast iron on cast iron with lubricating oil, and it must be achieved with acceptable wear and cost.     

Physical properties and testing of organosilicon esters for their applicability as synthetic lubricants

The constantly growing needs of the operational parameters of machines and engines, especially for aeronautical use, have brought about greater demands on lubricating oils. Various synthetic materials have been used since the Second World War,¹ in increasing quantity, as substitutes for mineral based oil: esters from organic alcohols and mono- or dicarboxyl acids are among the most widespread. Quite a different type of synthetic oil is organosilicon compounds, known as ‘silicones’. This paper reports experimental data for a group of silicon compounds examined in comparison with other materials normally used as bases for synthetic lubricants.     

气液两相条件下迷宫密封泄漏分析与试验研究

为解决大型船用柴油机曲轴箱轴端漏油问题,通过仿真和试验对气液两相条件下迷宫密封的泄漏行为开展研究。基于FLUENT软件进行迷宫密封流场仿真,利用离散相模型开展油滴逃逸行为分析,揭示迷宫密封在气液两相环境中的密封机理和泄漏规律。在试验器上模拟了曲轴箱密封的实际结构和工况条件,测量了不同转速条件下的漏油速率,研究了密封装置中的不同结构特征的功能作用,最终提出了两种改进措施并验证了措施的有效性。研究结果表明：交错迷宫结构与直通型迷宫结构相比可以更显著地减少空气泄漏,增加交错迷宫结构可大幅减少空气对液相介质的向外输运,此外,合理利用迷宫结构进行回油亦能显著减少滑油泄漏。     

液压往复密封的摩擦特性分析

基于往复式密封的弹性流体动力润滑的数学模型,对影响密封性能的因素进行了综合分析。综合考虑了形变理论、接触力学理论以及流体-固体耦合理论,采用MATLAB数值分析法,通过数学迭代计算完成最终求解。深入研究了润滑油黏度、界面摩擦系数以及密封圈的表面粗糙度对密封性能的综合影响。结果表明:随着耦合界面摩擦系数的增加,接触摩擦力都呈现出增大的趋势;总摩擦力随着粗糙度的增加呈现出抛物线式变化趋势;润滑油的黏度存在一个临界值,当润滑油黏度小于此临界值时,随着润滑油黏度的增加,总摩擦力先增加后降低;当润滑油黏度超过此临界值时,接触摩擦力呈现出单调增加的趋势;润滑油黏度和界面粗糙度的增加会导致流体泄漏的增大。     

Oil Degradation in a Diesel Engine with Dual-Loop Lubricating System

A common lubricating oil sump is used in most modern internal combustion engines for cooling, wear protection, and friction reduction. This requires compromises during base oil and additive selection as a result of differing needs for lubricant performance in engine subsystems. The use of a dual lubricating loop, providing separate oil sumps for the power cylinder and valve train subsystems, was investigated experimentally to determine the effect of system segregation on oil degradation. A small diesel engine was modified, installed in a commercial generator unit, and operated for one oil drain cycle. Oil sampling was tailored to assess base and acid numbers, oxidation, soot concentration, water content, and viscosity changes. The experiment complemented an earlier study that investigated the fuel economy benefits of such a lubricating configuration. These include longer drain intervals for the cylinder head and power cylinder subsystems, improved wear performance for the valve train, and opportunities for alternative material selection during engine design. The experiment demonstrated protection of the valve train subsystem from soot contaminants in the power cylinder. Lower total acid number and oxidation tendency was also observed in the valve train.     

大型水泵导轴承梳齿迷宫密封研究

推导了大型水泵油润滑导轴承梳齿迷宫密封泄漏量计算公式。通过实例计算了梳齿迷宫密封的泄漏量及各密封段的压降,分析了各段对密封效果的影响。比较了梳齿迷宫密封与端面密封的密封效果,分析了油润滑导轴承浸水的可能原因,指出了梳齿迷宫密封的适用性。结果表明:在水泵导轴承梳齿迷宫密封中O形密封圈的磨损量对泄漏量影响很大,O形密封圈必须选用耐磨性能好的材料,并控制泵轴摆度以减小O形密封圈的磨损量;在正常运行情况下梳齿迷宫密封的泄漏量远大于端面密封,因此要保证足够的排漏水能力,以免因排漏水不畅造成导轴承浸水。     

Experimental Investigations and Field Applications of Oil-Film-Lubricated Mechanical Face Seals with Spiral Grooves

The oil-film-lubricated mechanical face seal described here is a hydrodynamically lubricated, noncontacting, mechanical face seal with zero leakage. On the basis of systematic theoretical analyses, research on design methods, and experimental investigations, many field applications have been made. The experimental investigations include test rig development; long-time high-speed running tests; frequent start-up and shut-down tests; measurements of the seal leakage, face temperature, and characteristics of the self-circulating screw pump; observation, measurement, and solution of interface wear, and so on. Until now, this new seal design has been successfully applied in more than 40 high-speed turbocompressors in the oil refinery and petrochemical industries, achieving zero leakage and long operation. These seals are all designed with different face spiral-groove patterns, structure arrangements, and supporting systems.     

Transient EHL analysis of an elastomeric hydraulic seal

Recent steady-state numerical analyses of reciprocating hydraulic rod seals have revealed many important details about the operation of such seals, including the fact that they generally operate with mixed lubrication in the sealing interface. However, these seals frequently operate under transient conditions, with the rod speed and sealed pressure undergoing cyclic variations with time. In the present study, a transient numerical model has been developed to take account of the varying rod speed. The model consists of a fluid mechanics analysis of the lubricating film of hydraulic fluid, a contact mechanics analysis of the contacting asperities on the seal lip and a structural analysis of the seal deformations. The fluid mechanics analysis consists of a finite volume solution of the Reynolds equation using a mass-conserving algorithm, which accounts for possible cavitation. The contact mechanics analysis utilizes the Greenwood–Williamson model. The structural analysis consists of a finite element analysis. Typical results are presented for an injection molding application. Of greatest importance is the net leakage per cycle. Also presented are the cyclic histories of such performance characteristics as the lubricating film thickness, contact pressure and fluid pressure distributions, the friction force on the rod and the instantaneous flow rate.     

Bio-Fuel-Contaminated Lubricant and Hardening Effects on the Friction and Wear of AISI 1045 Steel

A study has been made on the wear and friction of hardened AISI 1045 steel using a tri-pin-on-disc type of friction and wear apparatus. During the investigation the linear pin wear, coefficient of friction and rise in pin specimen temperature were monitored and wear and friction curves plotted. Wear surfaces and mechanisms were investigated by means of optical microscopy. Analysis of used lubricating oil was performed using FTIR spectroscopy.

It was shown that the wear rate, type of wear and friction coefficient were influenced by contaminating the lubricant with bio-fuel as well as the surface hardening treatment. Corrosive wear and pits on the specimen surface were found when plain bio-fuel was used as lubricating oil. The results also confirmed that better wear resistance was obtained from the surface-hardened steel specimen with 4 % bio-fuel-contaminated lubricant.

Results from this study will be useful in material selection for tribological components in diesel engines running on vegetable fuel.     

蜂窝密封及其应用的研究

实验研究了蜂窝密封的泄漏特性,发现蜂窝深度对漏气量的影响并不呈线性的规律。蜂窝深度接近蜂窝宽度时,对应较小的漏气量。将蜂窝密封应用在汽轮机的轴端汽封和级间汽封,为多家电厂的3~650MW汽轮机设计、安装了蜂窝汽封。使用蜂窝汽封后显著减少了漏气,提高了真空度,解决了润滑油含水问题。     

The Effect of Lubricating Oil Additives on the Properties of Fluorohydrocarbon Elastomers

Fluorohydrocarbon elastomers are well known for their resistance to heat and fluids. However, certain additive packages in lubricating oils have been found to have a deleterious effect on the properties of these rubbers. Consequently, a study was undertaken to determine the effect of oil additive on the properties of fluorohydrocarbon rubbers under total immersion conditions. Most of the tests were conducted at 163°C to accelerate the effects that might be observed under normal automotive operating temperatures. Performance was based on the change in elongation, degree of crazing and volume increase.

Of the several classes of additives tested, only the strong nitrogenous organic bases or compounds which decompose to form strong bases had a deleterious effect on the elongation. Additives have been identified which perform functionally similar to these strong bases but without exerting harmful effects. Properly compounded, high fluorine-containing fluoropolymer rubbers have been demonstrated to provide excellent resistance to attack by strong bases present in many commercial lubricants.

The different performances of rubbers in lubricants are usually, but not exclusively, due to the chemical composition of the additive packages. Future consideration by the lubricating oil industry for the formulation of additive packages, based on the rubber materials to be used, would greatly increase the reliability and serviceability of seals and other elastomeric components.     

The influence of lubricating oil on deposits formation in a diesel engine under the operation condition of high power density

The requirements of higher power density and stricter regulations on emissions of internal combustion engines lead to lubricating oil's role shifting from simply lubricating to adapting higher power density and to achieving lower emissions. An important factor influencing an engine's power and emissions is the deposits in the engine. Lubricating oil is a chief contributor to deposits formation. The objective of this paper is to investigate the influence of lubricating oil on deposits formation when the engine is operated under high power density. Metal elements content in lubricating oil and changes to power and emissions were measured to verify deposits changes. Different power densities can be achieved by adjusting the fuel supply system in the engine. Three kinds of synthesised lubricating oils were used in the investigation. The temperature of the oil pan and cooling water was strictly controlled. The experimental results demonstrated well the influence of the quality of different kinds of oil on deposits formation. Copyright © 2013 John Wiley & Sons, Ltd.     

Bulk Modulus of Lubricating Oils as Predominant Factor Affecting Tractional Behavior in High-Pressure Elastohydrodynamic Contacts

The phase diagrams corresponding to transition from liquid to viscoelastic solid and that from viscoelastic solid to elastic-plastic solid of Santotrac100 (SN100), mineral oil, synthetic naphthenic oil, polybutene, and tetradecane were first made up by high-pressure density measurements and others. The bulk modulus of lubricating oils under a quasi-static condition was evaluated using a phase diagram. The results indicated that the bulk modulus of lubricating oils is closely related to the oil molecular packing parameter T _VE ?T (where T _VE is the viscoelastic solid transition temperature at pressure p, and T is the oil temperature). The constant values of the bulk modulus in the elastic-plastic range are different depending on the molecular structures of the oils. It has also been shown that SN100, mineral oil, synthetic naphthenic oil, and polybutene converted to amorphous solids at high pressures and tetradecane converted to molecular crystal. Next, the elastohydrodynamic lubrication tractions were measured by a ball-on-disk machine. The results indicated that the maximum traction coefficient is closely related to T _VE ?T. As a result, the importance of the bulk modulus as a predominant factor for traction characteristics of lubricating oil was pointed out.     

Prevention of oxidative degradation of ZnDTP by microcapsulation and verification of its antiwear performance

Prevention of oxidative degradation of zinc dialkyldithiophosphate (ZnDTP) is very important to prolong the antiwear performance of the engine oil. The microcapsulation of ZnDTP was attempted so as to isolate ZnDTP from peroxides in bulk lubricating oil during use. Microcapsulation allows for the isolation and protection of ZnDTP in bulk lubricating oil, and the ability to release control of ZnDTP at the contact surfaces. The protection of ZnDTP from oxidative degradation was evaluated by adding cumenhydroperoxide to the microcapsule-containing sample oil or by blowing NO_x gas into the sample, followed by analysis with ³¹P NMR. The antiwear performance of the microcapsule-containing sample oil was studied using a 4-ball tribometer. It was confirmed that the microcapsulation of ZnDTP significantly reduced the oxidative degradation of ZnDTP additive, and antiwear performance was effectively maintained.     

浅议气门油封的密封

对发动机在气门杆处泄漏造成的烧机油问题,采用气门油封密封的方案,分析气门油封结构参数、材料选取及发动机工况的影响,讲述了气门油封的基本结构与密封原理,通过使用气门油封,达到降低发动机的机油消耗,提高经济性,改善尾气排放的目的。     

压缩机径向泄漏通道润滑油量的实验研究

在压缩机运行过程中,通过径向泄漏通道从压缩腔泄漏到吸气腔的气体泄漏量与堆积在该处的润滑油量有极大的关系,为了准确描述径向间隙处的润滑油量,以滚动活塞压缩机本体为基础设计一套试验装置,采用高速摄影技术对径向间隙处的润滑油进行观察和图像采集,将采集的图像导入MatLab进行图像处理,得到滚动活塞压缩机在运行过程中的径向间隙处的润滑油量。以润滑油密封角为衡量润滑油量大小的指标,分析润滑油密封角与偏心轴转速、供油量、润滑油黏度的关系。结果表明:以汽缸中心点和活塞与汽缸的理论接触点的连线作为分界线,润滑油并不以该分界线作为对称中心均匀地分布在吸气腔和压缩腔两侧,而是整体偏向压缩腔侧,并且该分布规律与润滑油黏度、偏心轴转速和供油量都无关;润滑油密封角随着转速的提高而增大,随着供油量的增大而增大,随润滑油黏度的增加而减小。     

An investigation on tribological properties of graphite nanosheets as oil additive

Graphite nanosheets with average diameter of 500 nm and thickness about 15 nm were prepared by stirring ball milling. The tribological behavior of the graphite nanosheets as additive in paraffin oil were investigated with a four-ball and a pin-on-disk friction and wear tester. The wear surfaces of the steel ball lubricated with the additive-containing paraffin oil were analyzed by means of scanning electron microscopy (SEM). It has been found that the graphite nanosheets as additive in oil at proper concentration show better tribological properties than pure paraffin oil. The load-carrying capacity and antiwear ability of the lubricating oil were improved. Moreover, the friction coefficient of the lubricating oil was decreased by the addition of the graphite nanosheets. The optimal concentration of the additive in paraffin oil is about 1.0 × 10⁻² wt.%.     

CFM56系列发动机篦齿结构多目标参数优化分析

为解决CFM56系列发动机在低转速情况下滑油腔内润滑油的渗漏问题,运用VOF两相流理论对其篦齿封严进行数值模拟,分析篦齿的齿数、齿距、篦齿间隙、篦齿齿高、齿顶宽以及齿形角等结构参数对润滑油渗漏量的影响。结果表明:润滑油的渗漏量随齿顶间隙的增加而明显增大,当齿顶间隙在0.3～0.4 mm时,渗漏量增加趋势较为明显;齿距对渗漏量的影响较小,随齿距增大渗漏量小幅增大;渗漏量随齿形角的增大而明显降低,尤其在齿形角小于90°时;随齿顶宽度的增大渗漏量先增大后减小;随齿数的增大渗漏量降低,齿数为2～4时渗漏量降低明显,齿数高于4后变化趋于缓和。以篦齿渗漏量最小为目标,采用响应曲面法进行多目标参数优化,优化后润滑油渗漏下降了87.5%。     

Tribological properties of fluorine-containing additives of silicone oil

An oil soluble fluorine-containing octadecylamine salt of decapentylfluorooctanoic acid was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), ¹H-nuclear magnetic resonance (¹H NMR) and ¹⁹F NMR. The thermal stability of octadecylamine salt of decapentylfluorooctanoic acid was measured by a thermogravimetric (TG) analysis. The anti-wear and friction-reducing properties of the amine salt as a silicone-based lubricating oil additive were evaluated using a four-ball tribotester. The results indicated that both the wear resistance and the load-carrying capacity of a silicone-based lubricating oil 4609 shock absorption liquid were improved and the friction coefficient was decreased by the additive. The wear scar, after being cleaned using an ultrasonic bath in petroleum ether, was characterized with scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS). It was found that the boundary film on the worn surface was composed of fluorine-containing organic film and iron fluoride such as FeF₂, which provided the oil with improved anti-wear and friction-reducing properties.