Surface topography and tribology of cast iron in boundary lubrication

This work aims to study and understand the influence of the surface topography on wear of grey cast iron used for heavy duty diesel engine cylinder liners. A micro-alloyed grey cast iron was tested with different surface topographies. These were polished surfaces, honed surfaces (with two different honing parameters) and three model surfaces with well defined grooves on a polished specimen.Reciprocating friction tests using a steel ball rubbing against a flat or a cylindrical sample (extracted from a cylinder liner) were carried out on a Cameron Plint test rig. A commercial synthetic oil for diesel engine was used as the lubricant. The friction coefficient and the electrical contact resistance were measured during the tests. The wear volume of the cylinder liner part was also measured at the end of the test.The influence of the surface topography on the tribochemical film formation and on the wear behaviour of cast iron was established. Surfaces exhibiting lots of surface asperities had the highest wear, mainly due to delayed formation of protective tribochemical film. In our test conditions, the spacing between the grooves on model specimens had no influence on the wear behaviour of the cast iron specimens.     

A method of measuring ‘zero-wear’ of the cylinder liner

In this paper, new methods of linear wear estimation of the cylinder liner are proposed. They can be used if the deepest honed valleys remain unaltered during the wear process. In the first part of the paper, the possibility of using various amplitude parameters as measures of wear is studied. The second part presents a new procedure for cylinder liner wear analysis based on the ‘fax-film’ method that allows us to estimate the wear of the cylinder liner without disassembly of the cylinder-piston-piston ring group.     

Effect of Initial Cylinder Liner Honing Surface Roughness on Aircraft Piston Engine Performances

Reciprocating piston engines are the major propulsion devices for light aircrafts, helicopters, and essentially all automotive vehicles. They are expected to fulfil both present-day and future demands for engine performance, durability, fuel economy, and exhaust emissions legislation. One of the key factors related to these demands is the need to the limit thermomechanical internal losses, wear, and lubricating oil consumption, which are in turn conditioned by the tribological behavior of the piston–cylinder assembly. Consequently, this latter system requires a multi-directional approach in terms of manufacturing. Apart from various modifying techniques (e.g. laser texturing), a conventional plateau-honing operation is still the standard technology for shaping cylinder liner surface microstructure. This paper describes the distinctions between variations in the performance of the engines in relation to cylinder liner roughness parameters due to different honing settings. Five air-cooled reciprocating aircraft engines (FRANKLIN 4A-235-B31) served as the objects of research. The engines passed durability tests on the dynamometer bed, including operation under artificially intensified wear conditions. The results show a significant impact of the brand-new honed cylinder liner surface microstructure on the engine output parameters. Detailed study proves that some of the cylinder liner roughness parameters, specifically, the slope of the root mean square line (RMS) for valley roughness Rvq and the linear triangle area for valleys A2, are strongly correlated with the engine operational properties. Higher values of Rvq and A2 are associated with an improvement in engine performance but result in a deterioration in the exhaust harmful emission.     

激光微造型表面摩擦磨损性能研究

采用声光调Q二级管泵浦固体光源（DPSS）Nd：YAG激光器对缸套试件表面进行了,微造型州纹加工。在往复式活塞环-缸套摩擦磨损模拟试验机上进行了激光造型缸套试件与未造型光滑缸套试件的摩擦磨损性能对比试验研究。试验结果表明,在重载高速条件下,激光网纹试件与未造型试件相比,摩擦因数降低23％,磨损量降低66％。说明激光网纹沟槽具有贮油、积屑和动压润滑作用,同时激光加工的网纹淬火效应也有利于提高支承表面的耐磨抗擦伤性能。     

Improving tribological behaviour of piston ring–cylinder liner frictional pair by liner surface texturing

Experiments were carried out on a reciprocating tester. The lubricant was supplied into the inlet side of the contact zone. The construction of tribological tester allows to measure the friction force between specimen and counter-specimen. Tribological behaviours of cylinder liners with and without oil pockets were compared. Specimens were cut from plateau honed cylinder liners made of grey cast iron. Counter-specimens were cut from grey cast iron piston rings. A special tool acted as a hammer to form additional dimples on the liner surfaces. The area density of oil pockets was about 13%. Specimen surfaces had dimples with average depths about 5 μm and diameters in the range 0.15–0.2 mm. Two batches of tribological tests were carried out, in regimes of full and starved lubrication. Friction tests were conducted at three mean sliding speeds: 0.44, 0.66 and 0.88 m/s. Experiments were performed with normal load in the range 50–300 N, starting from the lowest load. Normal load increased in a stepwise manner after 2 min at each load, until the maximum load was reached. Areal surface topographies of specimens and counter-specimens were measured before and after two batches of tests by white light interferometer.     

Fractal surface synthesis based on two dimensional discrete Fourier transform

The discrete Fourier transform（DFT） is used for fractional Brownian motion（FBM） surface synthesis in tribology（i.e., contact, sliding, and sealing, etc）. However, the relationship between fractal parameters（fractal dimension and scale factor） and traditional parameters, the influence of fractal parameters on surface appearance, have not been deeply discussed yet. These lead to some kind of difficulty to ensure the synthesized surfaces with ideal fractal characteristic, required traditional parameters and geometric appearance. A quantitative relationship between fractal parameters and the root mean square deviation of surface （Sq） is derived based on the energy conservation property between the space and frequency domain of DFT. Under the stability assumption, the power spectrum of a FBM surface is composed of concentric circles strictly, a series of FBM surfaces with prescribed Sq could be synthesized with given fractal dimension, scale factor, and sampling numbers, but the ten-point height（Sz）, the skewness（Ssk） and the kurtosis（Sku） are still in random, where the probability distributions of Sz and Ssk are approximately normal distribution. Furthermore, by iterative searching, a surface with desired Abbott-Firestone curve could be obtained among those surfaces. An intuitive explanation for the influence of fractal dimension and scale factor on surface appearance is obtained by discussing the effects on the ratio of energy between high and low frequency components. Based on the relationship between Sq and surface energy, a filtering method of surface with controllable Sq is proposed. The proposed research ensures the synthesized surfaces possess ideal FBM properties with prescribed Sq, offers a method for selecting desired Abbott-Firestone curve of synthesized fractal surfaces, and makes it possible to control the Sq of surfaces after filtering.     

A Study of Torn and Folded Metal (TFM) on Honed Cylinder Bore Surfaces

Torn and folded metal (TFM) on honed cylinder bore surfaces has been observed and studied for decades. However, there is no objective and quantitative method for ranking the severity of TFM. Studies on its effect on the scuffing resistance of a cylinder bore and piston skirt/piston ring are also very limited. Machined surfaces are currently evaluated and ranked qualitatively based on fax film images. The results may vary greatly depending upon the individual's experience and also the image quality. In this study, an attempt has been made to develop a method that can be used to evaluate cylinder bore surfaces objectively. A “surface index” has been developed for classifying honed bore surfaces. To further examine the effect of TFM on a cylinder bore performance, bench tests have been conducted to evaluate cylinder bore scuffing resistance and its correlation with the bore surface quality in terms of the value of the surface index.     

润滑油中加入纳米氧化铝对缸套-活塞环摩擦副摩擦磨损特性的影响

在普通CD40润滑油中加入纳米氧化铝,研究了在不同载荷条件下对缸套活塞环摩擦副摩擦磨损特性的影响;用铁谱仪对试验油样进行了磨粒分析;用原子力显微镜对缸套试样表面的微观形貌进行了测试;用LAS-3000型表面分析系统对磨损表面进行了成分分析。结果表明：缸套活塞环摩擦副在含纳米氧化铝的润滑油作用下,表现出优越的抗摩减磨性能,其效果随栽荷的增大而增强;在高载荷作用下缸套试样表面形貌有了明显的改观,减小了摩擦阻力,降低了摩擦因数。     

Functional properties of microstructured cylinder liner surfaces for internal combustion engines

Internal combustion engines are still of major importance as propulsion systems. To fulfil future market and legislative demands it is necessary to improve engine performance, reduce fuel consumption, and limit exhaust emissions. Mechanical and thermodynamic losses, wear, and the emissions caused by lubricating oil combustion are principally influenced by the tribological behaviour of the piston assembly. The trend towards compact engines with high power densities and increased thermomechanical loads increases the importance of this tribological system and requires new approaches. One promising possibility is the utilisation of liner surfaces with specially machined microstructures. This paper describes a comparison between a conventional liner surface and a laser‐structured liner as regards their tribological behaviour. Measurements of wear as well as of oil film thickness and friction force in operation have been carried out. The results show better tribological behaviour for the laser‐structured liner surface than for the conventional plateau‐honed surface. This leads to lower fuel consumption and less wear.     

The break-in stage of cylinder-ring wear: A correlation between fired engines and a laboratory simulator

The wear of the piston ring-cylinder wall contact area in fired engines has not been satisfactorily simulated in bench testers so far. This paper reports the development of a successful test device in which the same progression of surface change occurs as in fired engines. These changes were observed by microscopy, by hardness indentations and by the use of the stylus roughness tracer. The test device uses ring and cylinder segments and it oscillates at 350 cycles min^-1 over a stroke of 19 mm. It is apparently not necessary to duplicate the temperature, atmosphere, fluid film thickness and other obvious conditions in an engine to achieve simulation. At least, the materials in the engine were not affected by the conditions in the engine that were not duplicated in the laboratory tester.The purpose in developing the tester was to study the role of the honed roughness pattern found on most cylinder walls. Several engine manufacturers attempt to achieve “fplateau honing”. No manufacturer polishes new cylinder walls. The reason for the honed roughness is to allow a high wear rate, without catastrophic scuffing, in locations of high stress between poorly conforming parts.     

金属陶瓷添加剂对船舶主机汽缸套-活塞环摩擦学行为的影响

将普通CD40润滑油作为基础润滑油，在3种不同的载荷作用下，对含有金属陶瓷添加剂润滑油对汽缸套-活塞环摩擦磨损特性的影响进行了模拟试验研究，并与实际使用的普通CD40润滑油的试验结果进行了比较。研究结果表明，汽缸套-活塞环摩擦副在这种添加剂作用下，其磨损失重及摩擦因数都大幅度降低。摩擦副表面扫描电镜分析结果也表明，这种添加剂使摩擦表面更光滑，其本身具有表面自修复作用。     

3D Surface Characterizations of Wear Particles Generated from Lubricated Regular Concave Cylinder Liners

Wear particle analysis can be developed as an effective method for assessment of the running conditions of concaved cylinder liners. The aim of this study was to numerically characterize the topographical features of wear particles generated from different surface textured cylinder liners and to investigate their changes with alternations in both rotational speeds and surface textures. To achieve this goal, cylinder liners with three different surface textures were prepared and tested in four different speeds. In addition to an untreated surface, concave cylinder liner surfaces with two different diameters (1 and 2 mm) and two different depths (200 and 300 μm) were investigated. Wear particles were extracted from the lubrication oil; three-dimensional images of the wear debris were acquired using laser confocal microscopy; and their topographical features were analyzed quantitatively. This study has revealed that running-in conditions and stable state can be detected using wear debris analysis techniques at a micrometer scale. It has also been discovered that concave B cylinder liner with a depth–diameter ratio of 0.1 always generated wear particles different to those from the other two cylinder liners on each rotational speed. It is believed that the quantitative surface topography characterization results obtained in this study provide a practical base for developing a new, non-intrusive tool for monitoring the operation conditions of cylinder liner–piston rings in diesel engines.     

Topographic features of cylinder liners — an application of three-dimensional characterization techniques

Studies of wear patterns on engine cylinder liners show that radial wear is greatest on the anti-thrust side, and close to top dead centre. As a result of this wear, surface topography features at different positions exhibit different characteristics. Quantitative representation of the features is helpful for functional analysis and functional control of cylinder liner manufacture. In this paper three-dimensional characterization techniques are applied to produce a comprehensive characterization of cylinder liner wear at different longitudinal positions. The areal autocorrelation function and the areal power spectrum reveal the changes in topographic features. The different topographic features of newly created, after running-in, severely worn and bore polished surfaces of cylinder liners are identified by quantitative functional indices. The characterization techniques and parameters used in the paper constitute an effective approach to the characterization of surface topography of cylinder liners and other tribological surfaces.     

New cylinder liner surfaces for low oil consumption

Anticipated emission legislation and reduced fuel consumption are the main driving forces when developing new engines. Optimization of the active surfaces in the piston system is one possible way to meet the above demands. In this study the effects of surface topography and texture direction of the ring/liner contact on oil film thickness and friction were simulated and experimentally tested. “Low wear” results from the experimental wear tests with “glide honed” smooth liner surfaces supported the “low friction” simulation results. In addition a new wear volume sensitive surface roughness parameter, R_ktot, based on the Abbot–Firestone bearing area curve was introduced.     

Running-in wear of a compression ignition engine: Factors influencing the conformance between cylinder liner and piston rings

The conformance between the liner and rings of an internal combustion engine depends mainly on their linear wear (dimensional loss) during running-in. Running-in wear studies, using the factorial design of experiments, on a compression ignition engine show that at certain dead centre locations of piston rings the linear wear of the cylinder liner increases with increase in the initial surface roughness of the liner. Rough surfaces wear rapidly without seizure during running-in to promote quick conformance, so an initial surface finish of the liner of 0.8 μm c.l.a. is recommended. The linear wear of the cast iron liner and rings decreases with increasing load but the mass wear increases with increasing load. This discrepancy is due to phase changes in the cast iron accompanied by dimensional growth at higher thermal loads. During running-in the growth of cast iron should be minimised by running the engine at an initial load for which the exhaust gas temperature is approximately 180 °C.     

Effect of Bio-Lubricant and Biodiesel-Contaminated Lubricant on Tribological Behavior of Cylinder Liner–Piston Ring Combination

This article addresses the issue of friction and wear characteristics of diesel engine cylinder liner–piston ring combinations under different lubricating conditions using a pin-on-disc wear tribometer. The discs were made out of actual engine cylinder liner material using a casting process. Pins were made out of top compression ring material. The tests were conducted on a pin-on-disc tribometer for wear and friction characteristics of the cylinder liner and piston ring combination with diesel-contaminated rapeseed oil–based bio-lubricant, diesel-contaminated commercial synthetic lubrication oil (SAE 20W40), biodiesel-contaminated commercial synthetic lubrication oil (SAE 20W40), and used (150 h) commercial synthetic lubrication oil (SAE 20W40). Experimental results demonstrated that the rapeseed oil–based bio-lubricant and biodiesel-contaminated synthetic lubricant exhibited better performance in terms of wear, friction, and frictional force under similar operating conditions. Thus, usage of newly formulated bio-lubricant and biodiesel in the long run may have a positive impact on engine life.     

Roughness variations in cylinder liners induced by honing tools’ wear

The manufacturing and finishing (honing) of cylinder liners for the automotive industry is a constant challenge in order to reduce friction losses and oil consumption. A better knowledge of surfaces generated during plateau honing is then required for optimization of the process. Despite a well-known and controlled honing process, variations in surface roughness appear due to honing tool wear and need to be mapped and analyzed. The following paper proposes to map the variations in roughness by using confocal 3D measuring equipment able to inspect any area of a cylinder liner. Six motor blocks, each with five cylinder liners, were evaluated with 20 topography measurements per liner (giving six hundred 3D measurements in total). In addition to standard 3D roughness parameters, tailor made parameters extracting honing texture information are computed. The results show that only a few parameters (Spk, Ssc and Sk) do correlate with the honing tool wear specific to each cylinder. Tailor made parameters indicate similar results. Indeed, as the honing tool wears down, the cylinder liner surface gets rougher plateau or peaks and sharper asperities indicating that ploughing occurs instead of cutting. In future, experimental models could be built in order to perform production and functional optimizations.     

Experimental investigation of oil pockets effect on abrasive wear resistance

The experiments were carried out using a block-on-ring tester. The stationary blocks were modified by a burnishing technique in order to obtain surfaces with oil pockets of spherical shape. The area density of oil pockets varied in order to explore their effect on wear resistance and wear intensity. Specimen surfaces had dimples with depths 45-60 μm and diameters 1-1.2 mm. The area density of oil pockets S_p was in the range 4-20%. The block samples were made from bronze B101 (CuSn10P) of 138 HB hardness. The rotated rings were made from 42CrMo4 steel, hardness of 40 HRC obtained after heat treatment. The tested assembly was lubricated by mineral oil L-AN 46. The experiment was carried out under artificially increased dustiness conditions. The dust added to oil consists mainly of SiO₂ (74%) and Al₂O₃ (15%) particles. During the test friction force and temperature of block sample were registered. The tendencies of block surface topography changes during wear were analysed. It was found that sliding pairs with textured specimens were not superior to a system with a turned block with regard to abrasive wear resistance.     

柴油机缸套磨损故障的机体振动监测研究

研究了柴油机缸套磨损故障的机体振动监测,包括缸套破坏性磨损故障时的机体振动。首先分析了活塞对气缸套的冲击,建立了活塞撞击气缸套侧推力的数学模型,探讨侧推力的大小及作用时间。分析表明,柴油机活塞撞击是机体表面振动的主要激励源。通过模拟试验得知,缸套磨损状态有4种,当缸套间隙正常或中等磨损时,机体振动的增长速度较慢;严重磨损时,振动特征参数值明显增大;如果缸套处于破坏性磨损程度时还继续工作,机体振动则呈指数式增长。这说明机体表面振动特征值的改变可以反映缸套间隙的变化,因此,基于柴油机机体振动对缸套的磨损进行监测是可行的、有效的。     

The use of surface metrology instrumentation to measure rates of wear of internal combustion engine components

A study was made of the effects of operating conditions on internal combustion engine service life. It was found after extensive investigation of major engine components (piston, piston rings, bearings and cylinder liner) that engine service life appears to be more a function of the acceptable wear of the cylinder liner than of any other engine parts.A method was developed to determine the amount of cylinder liner wear; this involved measuring the depth of scratch marks (using Talysurf model 3 or Surtronic 3 instruments). We describe the method employed and the results; these are at least as reliable as and give more details than conventional methods.