Study on dynamic friction characteristics in reciprocating friction drive system

The dynamic friction characteristics of a reciprocating friction drive system are investigated under conditions of dry contact using 0·45% carbon steel pair. Three friction modes are found during the operation, i.e. stick-slip, sticking and a transition region. The critical operating conditions in classifying these three modes are examined under various driver speeds, normal loads and spring constants. The critical values of driver speed and normal load increase with increasing spring constant. Generally, in the friction drive system the disappearance of the stick-slip results in smooth rolling. It is also found that the slope at the first period of slip on the traction force–relative slip velocity curve would have a transition from negative to positive value when the friction mode of stick-slip changes into sticking. Moreover, results show that the sticking mode gives the best positioning accuracy with the least wear on the contact surfaces. In addition, a transition from severe wear to mild wear is found when the friction mode is transferred from stick-slip to sticking only.     

A procedure for evaluating the positioning accuracy of reciprocating friction drive systems

The dynamic characteristics of stick-slip motion in reciprocating friction drive systems are investigated under dry contact using a 0.45% carbon steel pair. Based on this dynamic analysis, the stick-slip motion can be eliminated under certain experimental conditions depending upon driver speed, normal load and spring constant. The effects of normal load, driver speed, and spring constant on the positioning accuracy of the reciprocating friction drive system are examined under harmonic oscillation without stick-slip motion. Results show that at very low spring constants, the slip increases with increasing driver speed such that higher normal load has better positioning accuracy or smaller slip than does lower normal load. However, at high spring constants and high normal loads, there exhibits severe wear or peak at two limit positions on the sliding region. As a result, smaller normal loads have a better positioning accuracy than larger normal loads due to severe wear at high normal loads.     

Study on slip displacement and stick-slip characteristics in reciprocating friction drive system

The effects of follower mass, time ratio, driver speed, and normal load on the slip displacement and stick-slip characteristics are experimentally and theoretically investigated in the reciprocating friction drive system under dry contact using a 0.45% carbon steel pair. Results show that the accumulative slip displacement is linearly proportional to the rotating cycle under various operating conditions. The slope for this linear relationship is defined as the slip rate. The slip rate increases with increasing driver speed, the mass of the follower, and |δ−1|, but decreasing normal load. There are three modes of relative motion between the driver ring and the follower in the present study, namely, unstable stick-slip (USS), stable stick-slip (SSS), and sticking (ST) regimes. They are significantly influenced by the driver speed, normal load, time ratio and mass of the follower. The critical operating conditions among unstable stick-slip, stable stick-slip, and sticking regimes were also established. The critical frequency can be theoretically calculated and agrees well with experimental results.     

纳米SiC对半金属摩擦材料性能的影响

通过对比试验,研究纳米SiC对半金属摩擦材料性能的影响。试验表明,在半金属材料中,用纳米SiC代替普通的SiC粉体,摩阻材料的摩擦系数并没有明显的改善,而磨损率却大大地增加。借助扫描电镜(SEM)对混合粉体和摩擦表面的观察以及试验数据的分析,找到引起磨损增大的原因。     

铜铁合金复合摩擦材料高温摩擦行为

研究高速列车用铜铁合金复合摩擦材料的高温摩擦磨损性能。在PlintTE77高温疲劳试验机上对该材料进行高温摩擦磨损性能测试 ,并对摩擦后的磨痕进行了微观组织分析     

Tribological properties of metal-plastic multilayer composites under oil lubricated conditions

Three kinds of metal-plastic multilayer composites, which were composed of a steel backing, a middle layer of sintered porous bronze and a surface layer of polytetrafluoroethylene (PTFE) filled by Pb or Cu₂O powders, were prepared. The friction and wear properties as well as the limiting pressure times velocity (PV) values of these metal-plastic multilayer composites sliding against 45 carbon steel under both dry and oil lubricated conditions were evaluated on a MPV-1500 friction tester with a steel axis rotating on a journal bearing. The worn surfaces of these metal-plastic multilayer composites and the transfer films formed on the surface of steel axis were examined by electron probe microscopy analysis (EPMA). Experimental results show that filling of Pb to PTFE reduces the friction coefficient and wear of the composite, while filling of Cu₂O to PTFE increases the friction coefficient but decreases the wear of the composite. The friction and wear properties as well as the limiting PV values of these metal-plastic multilayer composites can be greatly improved with the oil lubrication. EPMA investigations show that Pb and Cu₂O fillers preferentially transfer onto the surfaces of steel axis, which may enhance or deteriorate the adhesion between transfer films and steel surfaces. Meanwhile the transfer of these metal-plastic multilayer composites onto the steel surface can be greatly reduced with oil lubrication, which results in the remarkable decrease of the wear of these metal-plastic multilayer composites.     

Tribological behavior of sialon ceramics sliding against steel lubricated by fluorine-containing oils

The friction and wear behavior of sialon ceramics sliding against steel and lubricated by perfluoropolyethers (PFPE), tetrakis (3-trifluoromethylphenoxy)-bis(4-fluoro-phenoxy)-cyclotriphosphazene (X-1P) and ionic liquid (1-methyl-3-octylimidazolium tetrafluoroborate, coded as L108) were investigated. It was found that the three fluorine-containing lubricants reduced friction coefficient and wear volume effectively. The effectiveness of the three lubricants in reducing wear volume could be ranked as L108>X-1P>PFPE. The antiwear films mainly consisting of organic oxyfluoride or carbonfluoride species and silicon fluoride are all observed for the three lubricants, while the degradation of PFPE during friction might account for the higher wear volume therewith. The lowest friction coefficient 0.065 was recorded for L108 under load of 0.5–400 N. This is dependent on the physically adsorbed ionic liquid on the rubbing surface and the formation of BN under the harsh conditions.     

Effect of geometrical parameters in micro-grooved crosshatch pattern under lubricated sliding friction

Tribological test was carried out using a pin-on-disc geometry with textured SKD11 pin on bearing steel disc, under sliding in paraffin oil. Micro-grooved crosshatch pattern has been fabricated with various angles and widths. The effects of geometrical parameters on friction were mainly examined in mixed and elastohydrodynamic lubrication. The results show that friction control can be achieved by fabricating the micro-grooved crosshatch pattern on a contact surface. It is observed that each geometrical parameter of texture influence on friction, especially decrease of groove aspect ratio and increases of groove sliding length show friction reduction performance. Crucial parameter G_l was proposed for micro-grooved crosshatch texture. The friction mechanism is explained by micro fluid flow with limited theoretical approach.     

An ultraprecision positioning system using a twist-roller friction drive

For ultraprecision positioning, the use of the twist-roller friction drive is proposed. To improve the positioning accuracy of conventional twist-roller friction drives, the proposed design has two features: (1) the twist angle between the driving shaft and the driven rollers is very small, and (2) the driven rollers are supported by hydrostatic bearings. The twist-roller friction drive is mechanically a kind of lead screw, and the small twist angle makes the lead of the friction drive less than 0.1 mm. The use of hydrostatic bearing is effective for improving the rotational accuracy of the driven rollers and for eliminating the influence of the fluctuation in roller rotation on positioning accuracy. It has been shown by experiments that the resolution of positioning can be less than 10 nm, and the twist-roller friction drive is suitable for an ultraprecision positioning system.     

Control system design of a linear motor feed drive system using virtual friction

This paper proposes a friction compensator and a design method for control systems to improve the response characteristics of linear motor feed drive systems. The proposed friction compensator cancels the real nonlinear friction of feed drive systems by using the nonlinear friction model proposed in this study and introduces virtual linear friction to facilitate the control system design. The proposed design method enables the determination of servo gains and friction compensator parameters that lead to desirable tracking performance and disturbance rejection without many trial-and-error tuning processes. In addition, the proposed method facilitates the design of the velocity feedforward compensator by using the inverse transfer function of the velocity control loop to correct the position tracking errors for various position commands. The effectiveness of the proposed method with the friction compensator and the velocity feedforward compensator was verified in simulations and experiments using a one-axis feed drive system consisting of a rod-type linear motor and linear roller guides. The results confirmed that the proposed method enables desirable overshoot-free responses and corrects motion trajectory errors due to nonlinear friction characteristics, and the proposed velocity feedforward compensator can correct tracking errors in both constant velocity motion and circular motion.     

Metallic sliding friction under boundary lubricated conditions: Investigation of the influence of lubricant at the start of sliding

Experiments are described in which a hard half-wedge, representing a scaled up model asperity, was indented into the horizontal surface of a relatively soft specimen with the specimen then moved in a direction parallel to its surface and normal to the wedge edge. Forces measured at the wedge-specimen interface are used to investigate the state of lubrication at the interface at all stages of the experiment, i.e. from initial indentation to final steady-state wave formation. The results are used to offer possible explanations for the nature of boundary lubrication and of stick-slip motion.     

Effect of angular speed on behavior of a V-belt drive system

For a V-belt drive system, the effect of angular speed on the three-dimensional frictional contact behaviors on the contact surfaces between the V-belt and pulley flange is studied in this work. To deal with the frictional contact phenomena for the V-belt drive system, an effective three-dimensional finite element procedure is developed herein. By this procedure, the deformation of the V-belt and the normal/tangential contact forces occurring on the contact surfaces can be estimated accurately. The friction angles of contact points along the edge of the V-belt cross section are also presented for various dynamic friction coefficients. From the computed results, it is found that smaller friction angles are obtained as dynamic friction coefficients get larger. The results achieved are very helpful for the estimation of operation efficiency of the V-belt drive system.     

大型天文望远镜高精度摩擦传动的研究

提出了一种大型天文望远镜高精度摩擦传动的光学检测机构,用来检测主、从动轮旋转轴线的扭转角.并设计了相应的调整机构.利用这套机构使得主、从动轮的扭转夹角控制在30″以内.实验结果表明,在运行过程中没有出现抖动现象.传动系统长时间平稳运行的低速可达0.2″/s,运动位置精度RMS值为0.01″左右.30min内低速可达0.05″/s,位置精度RMS值为0.009″左右.正弦运动幅值30′,最大速度36″/s,最大加速度为0.18″/s2.这些指标满足了LAM OST天文望远镜的技术要求.克服了由于安装等原因导致旋转轴线之间存在扭转角,进而使得天文望远镜所跟踪的目标在视场中出现抖动,甚至严重会漂移出视场的局限,实现了外圆摩擦传动主、从动轮旋转轴线在空间平行的理想位置.     

Tribological characterization of alumina and silicon carbide under lubricated sliding

The aim of this study was to investigate the tribological properties of four different advanced ceramics - monolithic alumina, SiC whisker-reinforced alumina, monolithic silicon carbide and SiSiC-during lubricated sliding. Advanced techniques of electron microscopy and spectroscopy have been used to characterize the materials before and after testing. Tests have been performed where two flat discs were rotated against each other under closed contact in an environment of oil and water. The main wear mechanisms of the four ceramics are identified and discussed. What clearly emerges from these studies is the much more reliable performance of the silicon carbides than the aluminas. The silicon carbides have a low wear rate where microfracture and oxidation are the main deteriorating mechanisms. The capability to maintain smooth surfaces and thus also a high degree of hydrodynamic lubrication is largely due to the potential of the water to dissolve formed wear debris. The main wear mechanism of the aluminas is surface fracture. The rough fracture surfaces and the fact that the wear fragments form a discontinuous surface film will reduce the effect of the lubrication, thus accelerating the wear. Furthermore, a deformation layer with microcracks develops in the contact which decreases wear resistance.     

Tribological characterization of thin hard coatings by reciprocating sliding tests

Thin hard coatings on metal or ceramic surfaces offer a large spectrum of improvements of the friction and/or wear behaviour of tribosystems. The development of coatings and the tailoring of their properties require test methods providing information about their friction and wear behaviour. A new wear test standard (ASTM) is under development for the evaluation of friction and wear quantities for sliding motions using the reciprocating sliding mode. The applicability of this test method to coated specimens was checked by testing uncoated and coated steel specimens in contact with alumina balls, whereby lower loads were used than in the ASTM proposal for bulk materials. Additionally, the influence of the relative humidity of the surrounding air at room temperature on friction and wear results was examined.     

Relationship between wear of friction materials and dissipated power density

Specific tribometric tests showed both the effect and relevance of the power dissipated by friction upon the transition from mild wear to severe wear for friction materials. The dissipated power density could be viewed as an important variable either to identify the critical wear characteristics of friction materials or to make comparisons among different types of friction materials. The scanning electron microscopy analysis showed some correspondence between the sliding surface morphology after the friction tests and the wear rate obtained. Moreover, the phenomena observed are related to known mechanochemical wear mechanisms.     

Tribological behavior and tribofilm composition in lubricated systems containing surface-capped molybdenum sulfide nanoparticles

The tribological behavior of surface-capped MoS₃ nanoparticles (nano-MoS₃) in hydrocarbon oils was studied both alone and in combination with ZDDP. It was found that the nano-MoS₃ additive alone demonstrates pro-wear properties and decreases the friction coefficient only at high temperatures. The combination with ZDDP demonstrates synergism in antiwear and antifriction activity even at low ZDDP content. X-ray Absorption Near Edge Structure (XANES) spectroscopy at the sulfur, molybdenum and phosphorus edges was used to identify the chemical species in tribochemical films. It was established that the nano-MoS₃-formed tribofilms are composed of oxidized sulfur and molybdenum species while tribofilms formed by combination with ZDDP are composed of phosphate layers incorporating MoS₂-type fragments providing friction reduction.     

Sliding velocity dependency of the friction coefficient of Si-containing diamond-like carbon film under oil lubricated condition

In this study we investigated the sliding velocity dependency of the coefficient of friction for a Si-containing diamond-like carbon (DLC-Si) film in an automatic transmission fluid (ATF) under a wide range of contact pressures. The DLC-Si film and a nitrided steel with a surface roughness, Rz_JIS, of around 3.0 μm were used as disk specimens. A high-carbon chromium steel (JIS-SUJ2) bearing ball was used as a ball specimen. Friction tests were conducted using a ball-on-disk friction apparatus under a wide range of sliding velocites (0.1-2.0 m/s) and contact pressures (P_max: 0.42-3.61 GPa) in ATF. The friction coefficients for the nitrided steel had a tendency to decrease with an increase in sliding veloicity under all the contact pressure conditions; however, the friction coefficients for the DLC-Si film were stable with respect to sliding velocities under all the contatct pressures. These results indicate that the DLC-Si film suppresses the stick-slip motion during sliding againt steel in ATF, which is a desired frictional characteristic for the electromagnetic clutch disks used under lubrication. Furthermore, the DLC-Si film showed a higher wear resistance and lower aggression on the steel ball specimen than the nitrided steel. There were less hydrodynamic effects on the friction coefficient for the DLC-Si film possibly due to maintenance of the initial surface roughness and its poorer wettability with the fluid. X-ray photoelectron spectroscopy (XPS) analysis of the sliding surfaces revealed that the adsorption film derived from the succinimide on the sliding surfaces of the DLC-Si film and the mating steel ball also contributed to the sufficient and less sliding-velocity-dependant friction coefficients.     

钢丝绳摩擦传动防滑计算的新方法

通过钢丝绳摩擦传动的受力分析,得出不打滑状态下的广义欧拉公式和接触弧内任一截面上钢丝绳张力的分布规律,提出了一种引入许用防滑角进行钢丝绳摩擦传动防没计算的新方法。