High Sliding Speeds Research Articles

Friction of Methyl-Branched Fatty Acid Layers at Low and High Sliding Speeds.

The friction of methyl-branched fatty acids was studied with a surface forces apparatus (SFA) with attachments for low-speed (μm/s) and high-speed (cm/s) sliding. The systems studied were isooleic acid, a mixture of unsaturated C-18 isomers with one methyl group located along the chain, and isostearic acid, which consisted of saturated C-18 isomers with one methyl branch. The methyl group was expected to disrupt the close packing of the molecules in the pure substance and when adsorbed on a surface. The friction forces and friction coefficients were compared with results for stearic and oleic acid. Isostearic acid showed low friction at low speeds. At high speeds, a peak was found in the friction coefficient of both isostearic and isooleic acid layers, whereas a gradual increase in friction coefficient with speed was seen for oleic acid, suggesting different relaxation times of the structures formed on the surfaces.

Design of Fe–SiC–Cu–G Composite Alloy and Optimization of Graphite Contribution for High Sliding Speed Applications

Design of Fe–SiC–Cu–G Composite Alloy and Optimization of Graphite Contribution for High Sliding Speed Applications

Improving Lubrication Efficiency at High Sliding Speeds by Plasma Surface Texturing

Improving Lubrication Efficiency at High Sliding Speeds by Plasma Surface Texturing

Research on the delamination wear properties of the pure carbon strip at the high-sliding speed with electric current

PurposeThis paper aims to investigate the delamination wear properties of a carbon strip in a carbon strip rubbing against a copper wire at the high-sliding speed (380 km/h) with or without electrical current.Design/methodology/approachThe friction and wear properties of a carbon strip in a carbon strip rubbing against a copper wire are tested on the high-speed wear tester whose speed can reach up to 400 km/h. The test data have been collected by the high-speed data collector. The worn surfaces of the carbon strip are observed by the scanning electron microscope.FindingsIt was found that there was a significant increase of the delamination wear with the decrease of the normal load when the electric current is applied. The size of the flake-like peeling also increases with the decrease of normal load. The delamination wear extends gradually from the edge of the erosion pits to the surrounding area with the decrease of the normal load. However, the delamination wear never appears in the absence of electric current. It is proposed that the decreased normal load and the big electrical current are the major causes of the delamination wear of the carbon strip.Originality valueThe experimental test at high-sliding speed of 380 km/h was performed for the first time, and the major cause of the delamination was discovered in this paper.

Measurement and Characterization of “Resonance Friction” at High Sliding Speeds in a Model Automotive Wet Clutch

The friction forces between various lubricated “friction materials” and sapphire disks were measured using a new “high-speed” rotating disk attachment to the surface forces apparatus (SFA). Two different clutch lubricants and two different friction materials were tested at sliding speeds and normal loads from 5 to 25 m/s, and 0.2 to 1 N (nominal pressures ~1 MPa), respectively. The results show that “resonance friction”—characterized by large amplitude oscillatory (i.e., sinusoidal) vibrations, also known as shudder or chatter—dominates dynamical considerations at high sliding speed, replacing the smooth sliding or low-amplitude stick–slip that is characteristic of low speed/low load sliding. The characteristic (rotational) speeds or frequencies at which resonance friction occurs depend only on the coupled/uncoupled mechanical resonance frequencies of the loading and friction-sensing mechanisms. In contrast, the intensity of and time to enter/exit shudder depends strongly on the lubricating oil and, to a lesser extent, on the friction material. Physical–chemical analyses of the friction materials before and after testing showed that the samples undergo primarily structural rather than chemical changes. Our results provide new fundamental insights into the resonance friction phenomenon and suggest means for its control.

Effect of sliding speed and contact pressure on the oxidative wear of austempered ductile iron

The dry tribo-oxidative sliding wear of an ADI was investigated as a function of sliding speed and applied pressure, using a pin-on-disc apparatus. The wear rates, steady-state friction coefficients and contact temperatures were measured for each sliding conditions, and the acting wear mechanism were investigated by means of metallographic observations of worn surfaces and subsurface damaged regions. Two friction and wear regimes were identified. In the first one, at low sliding speeds (0.5–1 m/s), friction coefficient and wear rates were found to decrease with sliding speed and applied pressure. In the second one, at high sliding speeds (1.5–2.6 m/s), friction and wear were found to decrease with sliding speed but to increase with applied pressure. The observed behaviour and the transition from the low-sliding speed regime to the high-sliding speed regime were explained by considering the formation of a surface white layer that is controlled by the attainment of a critical flash temperature during sliding.

Friction Modifier Behaviour in Lubricated MEMS Devices

Low viscosity fluids could provide reliable lubrication for certain microelectromechanical system’s (MEMS) applications where high-sliding speeds and/or high sliding distances occur. However, while the use of low viscosity fluids leads to reduced hydrodynamic friction, high boundary friction can be a significant issue at low entrainment speeds. This article describes a series of tests of low viscosity fluids, blended with a friction modifier additive so as to provide a combination of both low hydrodynamic and low boundary friction at MEMS scales. The low viscosity fluids tested were hexadecane, low viscosity silicone oil, toluene and water. With the exception of water, the addition of the organic friction modifier octadecylamine to all these lubricating fluids produced a significant reduction in boundary friction. For a MEMS contact lubricated with silicone oil for instance, boundary friction was reduced from 0.5 to close to 0.05. The presence of the amine dissolved in the toluene had the effect of reducing boundary friction from 0.75 to 0.55; this was further reduced to 0.25 after the specimens had been immersed in the toluene-additive blend for 48 h. A water-soluble additive, diethylamine, was added to de-ionized water, at 0.1% by weight concentration. Although an initial reduction in boundary friction was observed (0.45–0.25), under these conditions the rapid onset of severe wear negated these effects. It is suggested that corrosion of silicon by water, followed by abrasion, is the cause of this accelerated wear.

Influence of Contacting Pressure on Current Stability and Tribological Properties of CPMM Collector Materials against Cu/Cr Alloy under High Sliding Speed with Electric Current

Dry sliding tests with electric current were carried out on a pin-on-disc system tribometer in this study, where copper-base powder metallurgy material and copper alloy QCr0.5 were used as the pin and the disc respectively. The researches were aimed at exploring relation between tribological properties and current stability of the couple under different loads. The results indicate that the current stability and friction coefficient increases with current and load. Moreover, co-effect between the current stability and tribological behavior has been found, which behaves in the way that the higher the current stability, the higher dynamic current collection capability and tribological properties.

Tribological Behavior of Ceramics at High Sliding Speeds in Steam

Three sets of tests were conducted using a pin-on-disk tribometer to determine the tribological behavior of ceramics at high sliding speeds in steam. In the first set, the speed was increased from 4000rpm to 10,000rpm in 1000 rpm increments. Constant rotational speeds of 4000rpm, 6000rpm, 8000 rpm and 10,000 rpm were used in the second test series. In the third series of tests, the rotational speed was slowly increased to 10,000rpm and allowed to coast down to zero. While the coefficient of friction for silicon nitride/YTZP pair varied between 0.2 and 0.4 without a clear pattern as the speed was increased in the first two test series, it decreased from about 0.6 to 0.2 when the speed was raised to 10,000 rpm in the third test series. This behavior is attributed to the general phenomena of powder lubrication as the wear debris provides an interfacial layer leading to reduced friction at high speeds. The coefficient of friction for silicon nitride/silicon carbide pair was substantially reduced to about 0.02 as the speed was raised. The low coefficient of friction, however, increased to a high level as the speed was further increased. The drop in friction is explained based on analysis of elasto-hydrodynamic lubrication assuming that a water film containing solid particles exists at the interface. Several possible mechanisms are suggested for the transition to a higher friction as the speed is raised: thermal effects at high flash temperatures, low residence times (for water adsorption on surface), collapse of the lubricant film and starvation effects.

Friction and Wear with Surface Melting at High Sliding Speed and High Contact Pressure (1st Report,An Experimental Approach to the Condition of the transition to a Melting Lubrication)

Based on the recent demands for higher sliding velocity of components, the excessive wear of the slider due to it has been discussed. However, since R. S. Montgomery reported his experimental work on the wear at high sliding speeds, no one has reported theoretical analysis of the slider wear. In this study, the frictional resistance was examined with static intrusion and dynamic acceleration tests. In the static intrusion test, the static frictional resistance increases linearly as the slider travel increase until the slider come to fully contact the cylinder. Meanwhile, the dynamic acceleration test revealed that the dynamic frictional resistance is about 30-40% of the static one with the slider travel up to approximately 50 mm, and that it then falls to the level of about 10% as the slider travel further increases. Such the sudden change corresponds to the estimated values of the friction coefficient : the friction coefficient estimated from the dynamic acceleration test results is about 0.1 in the earlier stage and falls to about 0.03 in the later stage, while the static intrusion test results only show a constant coefficient value of about 0.3. This drastic reduction of the friction coefficient in the dynamic test is considered to be attributable to the surface liquefaction of the slider material, where a melting lubrication may occur. The transitional condition to such a melting lubrication can be quantitatively expressed and evaluated by means of the melting lubridcation index, BLI.

Friction and Wear with Surface Melting at High Sliding Speed and High Contact Pressure (3rd Report,An Analytical Approach to the Condition of the Transition to a Melting Lubrication)

An analyzing method to estimate sliding resistance is proposed. In this method, variation of contact pressure caused by plastic deformation of the slider in intrusion process and variation of friction coefficient caused by surface melting are considered. The sliding resistances calculated with this method are agree well with those reported previously. The surface melting phenomena appears in the calculated result too. Based on this method, it allows us to estimate sliding resistance in high sliding speed and high contact pressure conditions without large-scale experiments.

Friction and Wear with Surface Melting at High Sliding Speed and High Contact Pressure (2nd Report,A Melting Wear Analysis Based on the Non-Steady Heat Conduction Equation)

A new melting wear analyzing method of the slider is proposed based on the non-steady heat conduction equation. The friction coefficients calculated with the theory agreed well with those reported by previous workers. The estimated values of the slider wear also agree well with those obtained experimentally. The melting wear analyzing method is confirmed to estimate the melting wear quantitatively from thermal properties of sliders. Based on the method, a practical selection method of slider material has been established.

Scuffing Performance of M50 Bearing Steel Lubricated with a Gas Turbine Engine Oil at High Sliding Speeds

The paper describes the results of scuffing tests carried out in a special high speed rig using M50 bearing steel rollers prepared to simulate the ball and raceway elements of gas turbine angular contact thrust bearings. The lubricant was Mobiljet2, a typical 5 cSt gas turbine engine oil, and sliding speeds of up to 30 m/s were simulated. It was found that the concept of “PV” (product of contact pressure and sliding speed) as a predictor of scuffing was not appropriate and a better indicator of failure under these conditions was the calculated value of oil film thickness in relation to the surface roughness of the rollers. In general the scuffing performance of M50 steel was found to be consistent with earlier work on ground and superfinished case-carburized steels when run with the same lubricant. Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

Friction and Wear of Cast Iron under High Sliding Speed and High Contact Pressure. 2nd Report. The Condition of the Transition from Mild Wear to Severe Wear.

The dry friction and wear characteristics of cast iron at high sliding speed and high contact pressure are described with a focus on the conditions of transition from mild wear to severe wear and the friction characteristics in the mild wear region. Wear tests were carried out using a pin on-disk test device in which the cast iron pin slid on a mild steel disk, and the variations of the friction force, the wear rate and the temperature rise with the sliding distance were measured. From the experimental results, the following points were clarified. First, the transition from mild wear to severe wear occurs when the friction induced temperature rise of the cast iron pin reaches a certain value which is strongly related to the decrease in hardness of the cast iron pin. Secondly, the mean coefficient of friction in the case of mild wear can be determined from the temperature rise at the transition point or the mean friction power in the mild wear region. It also depends on the PV value, i.e. it decreases with increasing PV value.

Conditions for Scuffing Failure of Ground and Superfinished Steel Disks at High Sliding Speeds Using a Gas Turbine Engine Oil

This paper describes the results of an experimental investigation to compare the scuffing performance of conventionally ground and superfinished hardened steel disks operating at sliding speeds of up to 26 m/s and lubricated with a gas turbine engine oil at a temperature of 100° C. The ground disks were finished in the axial direction to simulate the orientation of surface finish found on involute gears. Superfinishing was found to give a significant increase in the load at which scuffing occurred. Frictional traction was also measured in the experiments and was found to be significantly lower for the superfinished disks in the loading stages preceding scuffing failure.

Friction and Wear of Cast Iron under High Sliding Speed and High Contact Pressure. 1st Report. Coefficient of Friction and Wear Rate in the State of Thermal Wear.

To clarify the dry friction and wear characteristics of cast iron under the conditions of high sliding speed and high contact pressure, especially those in the state of the thermal wear, wear tests of sliding a cast iron pin on a mild steel disk were carried out with using a pin-on-disk test device. The variations of friction force and wear rate with sliding distance were measured. The temperature changes of the sliding pin were also measured using the infrared imaging system. After some sliding, the temperature of the cast iron pin near the sliding surface rose sufficiently for thermal wear to occur. In the state of thermal wear, the coefficient of friction of cast iron is independent of the contact pressure but is considerably influenced by the sliding speed and decreases with higher speed. On the other hand, the wear rate of the cast iron pin increases proportionally with the increment of contact pressure, but it is little affected by the sliding speed.

The Influence of Lubricant Visco-Plastic Character on the Line Contact EHL Under High Sliding Speeds

By using the first-order small parameter perturbation method, a form of the Reynolds equation has been derived for non-Newtonian lubricants based on the Bair & Winer's visco-plastic model. The Newton-Raphson iteration method has been adopted to obtain full numerical solutions for the line contact EHL. The changes of the slide/roll ratio, limiting shear stress and viscosity, which mainly reflect the non-Newtonian behavior of lubricants, have been widely investigated. The effects on the line contact EHL are discussed. Furthermore, the partial thermal EHL solutions have been presented for the temperature and shear stress distributions as well as the coefficients of friction on the surfaces. The results of theoretical analyses compare well with the experimental data. Presented at the 45th Annual Meeting In Denver, Colorado May 7–10, 1990

An Application of the Finite Element Method to the Thermohydrodynamic Analysis of a Thin Film Cylindrical Bore Bearing Running at High Sliding Speed

A finite element model of the thermohydrodynamic behavior of a cylindrical bore bearing is presented. The predicted behavior is compared with experimental evidence where possible and favorable correlation is obtained. The analysis is extended to include thermoelastic behavior in both the shaft and bush and it is demonstrated that this mechanism can influence bearing behavior considerably.

The Thermal Control of Friction at High Sliding Speeds

It is proposed that thermal effects govern friction in high speed unlubricated contact. The general principle can be found from a manipulation of Blok’s flash temperature theory to give the coefficient of friction as a dependent parameter. The principal factors controlling friction, provided the conditions are sufficiently severe, appear to be the decomposition temperature, hardness and thermal properties of the materials. The same mechanism appears from a numerical model of thermal effects in sliding. The model is compared with several sets of experimental results in different configurations.

Friction and Wear at High Sliding Speeds

Sliding tests have been carried out using a variety of soft metal and nonmetal pins on a rotating steel disk at speeds up to 150 m/s. A new high-speed friction apparatus in which the normal force, the friction force and the friction coefficient are recorded, was used. In general, the wear rate increased drastically, and the friction coefficient decreased moderately as the sliding speed was raised, these changes being especially pronounced when pin materials of low melting temperature were used. The friction data are in good agreement with those obtained by others using the pin-on-disk geometry. However, although in many cases the interface reached the melting temperature of the lower melting sliding material, the very low friction coefficient values of under 0.05 reported by some investigators were not reached.