Spherical Slider Research Articles

Self-similarity in abrasion of metals by nanosharp asperities of hard carbon containing films

We discuss a remarkably simple power-law relationship observed between the abrasion rate of an initially spherical slider by hard carbon-containing films and the number of sliding cycles n to which the film has been subjected. The power-law relationship is valid up to 4 orders of magnitude in n. We model this phenomenon by connecting it with nanocharacteristics of the coatings. It is proposed to explain the phenomenon by a statistically self-similar variation of the pattern of relatively sharp nanometer-scale asperities of the films.

F-1308 球面コンタクトスライダのダイナミクス・摩耗特性におよぼす液体潤滑膜厚の影響(S47-3 ヘッド・ディスク・インタフェース)(S47 情報機器コンピュータメカニクス)

F-1308 球面コンタクトスライダのダイナミクス・摩耗特性におよぼす液体潤滑膜厚の影響(S47-3 ヘッド・ディスク・インタフェース)(S47 情報機器コンピュータメカニクス)

Friction of smooth surfaces with ultrafine particles in the clearance

Friction force between a spherical slider and a smooth flat surface of mica, glass, silicon, sitall, sapphire, metal or diamond-like coating has been measured at reciprocating motion. The slider was made of steel or sapphire. It was revealed that higher surface microhardness of the samples gave lower friction coefficient. An attempt to model friction process of a precision joint in the presence of wear particles in the contact zone was undertaken. For this purpose, ultrafine diamond particles (UFD) were introduced into the friction zone. The friction coefficient increased nonmonotonously with the sample surface microhardness. This fact is explained by abrasive action of the particles and prevailing component deformation in friction. A possibility of reducing the effect of hard particles on friction coefficient has been demonstrated with the surface microrelieves, which contain peak textures.

Simulation of surface acoustic wave motor with spherical slider

The operation of a surface acoustic wave (SAW) motor using spherical-shaped sliders was demonstrated by Kurosawa et al. (1994). It was necessary to modify the previous simulation models for usual ultrasonic motors because of this slider shape and the high frequency vibration. A conventional ultrasonic motor has a flat contact surface slider and a hundredth driving frequency; so, the tangential motion caused by the elasticity of the slider and stator with regard to the spherical slider of the SAW motor requires further investigation. In this paper, a dynamic simulation model for the SAW motor is proposed. From the simulation result, the mechanism of the SAW motor was clarified (i.e., levitation and contact conditions were repeated during the operation). The transient response of the motor speed was simulated. The relationships between frictional factor and time constant and vibration velocity of the stator and the slider speed were understood. The detailed research regarding the elastic deformation caused by preload would be helpful to construct an exact simulation model for the next work.

Plowing Friction Under Harmonic Normal Loads

The influence of harmonic normal loads on sliding friction is investigated through analysis of contacts consisting of conical and spherical sliders of hard materials on softer metal surfaces. Friction for such contacts is assumed to result from a plowing component and a shearing component. Calculations and experiments show that the coefficient of friction is essentially independent of normal load for contacts with conical sliders. However, for spherical sliders the relation between the coefficient of friction and normal load is highly nonlinear. In the presence of harmonic variations in normal load, this non-linearity causes a shift in the average coefficient of friction. For ideal lubricated contacts, the shearing component of friction is very small and for this case, it is shown that the maximum average reduction in the coefficient of friction is ten percent. When the shearing component is more significant, as with dry contacts, the shift is less. For example, when the shear strength is one-sixth the hardness of the softer material, the maximum average reduction in the coefficient of friction is five percent.

Tribology of unlubricated sliding contact of ceramic materials and amorphous carbon

This work deals with unlubricated sliding contact of SiC and Al 2O 3 spherical sliders against carbon-coated thin-film magnetic rigid disk in a wide range of sliding velocity of 0.5–16.6 m s −1. Grain detachment from the ceramic slider surface was the most important mechanism controlling the life of the thin carbon coating, especially at low sliding velocity. Silicon carbide provided much longer life of the carbon coating compared with alumina, although the difference decreased with the increasing sliding velocity. At high velocity, a high friction-generated flash temperature was mostly responsible for the coating failure. A film formation of agglomerated ceramic wear particles was observed for both SiC and Al 2O 3. A model which summarizes behavior of wear particles at the contact interface was suggested.

A comparison of friction in hydrogel and polyurethane materials for cushion-form joints

The use of a thin layer of a compliant material as a bearing surface in human replacement joints has been found to promote fluid-film lubrication in the joint during continuous movement. However, during periods of continuous loading and little or no movement the fluid film may break down and the articulating surfaces may come into direct contact. This study considers the friction of three compliant materials under conditions of continuous loading and slow sliding velocities. The friction of a non-porous polyrethane and two porous hydrogel polymers, a terpolymer and a semi-interpenetrating network, was studied. Friction was measured between a hard spherical slider and a thin layer of the compliant material. Sliding was carried out in the presence of deionised water or new-born-calf serum as the lubricant. The friction was measured at the start up of motion, after prolonged periods of static loading, and during the subsequent sliding at a constant velocity. All three materials were found to give lower friction during steady-state sliding than at start up. Friction was also higher when serum was used as a lubricant. However, the porous hydrogels gave lower friction than the non-porous polyurethane, especially at start up. The terpolymer hydrogel gave the lowest friction values of the three materials, both at start up and in the steady state.

The influence of surface finish and strain hardening on near-surface residual stress and the friction and wear behavior of A2, D2 and CPM-10V tool steels

The effect of surface finishing method on near-surface residual stress, relative cold work and sliding friction and wear behavior of commercially available air hardening A2, D2, and CPM-10V tool steels was investigated. Microstructural characterization was accomplished using X-ray diffraction and scanning electron and optical microscopy combined with macrohardness measurements. The wear tests were performed using low load-slow speed reciprocating sliding conditions with tool steel flats in unlubricated contact with a 52100 steel spherical slider. The coefficient of friction and mass loss were measured during the course of wear testing and residual stress measurements were made before and after wear testing. Surface grinding and polishing conditions had a significant effect on surface residual stress but had little effect on tool flat sliding wear rates. Residual stress measurements performed after wear testing showed a decrease in compressive residual stresses as wear rate increased. Tool steel wear rates were a linear function of sliding distance except for the initial run-in period. The low wear rates, the run-in friction behavior, and the constancy of near-surface mechanical properties indicate that during run-in surface finish was wear rate controlling and that sample microstructure and composition controlled long-term sliding friction and wear behavior. The low wear rates and the post wear residual stress measurements also indicate that oxidative wear was the primary mechanism responsible for tool flat material attrition. CPM-10V steel flats exhibited the lowest coefficient of friction and the highest resistance to wear which can be attributed to the high volume fraction and homogeneity of V-Cr-C carbides.

The Detection of Flash Temperatures in a Sliding Contact by the Method of Tribo-Induced Thermoluminescence

A method is presented for measuring short duration flash temperatures in sliding contacts. The method uses a photomultiplier to collect photons emitted by a hot contact spot. The method was used to measure flash temperatures at the contact between a spherical sapphire slider and a rapidly moving thin film magnetic disk. It was found that temperature flashes of over 1000° C, lasting less than 2 μs, can occur at the sliding interface.

HEAD-MEDIA INTERFACE OF STRETCHED RECORDING DISK

Head-media interface of CoCr and metal particle stretched recording disks is investigated using a slotted spherical slider. Acoustic emission output of the stretched disk scarcely depends on the flying height. Frictional coefficient in high speed region of the stretched disks is higher than that of a rigid disk which is almost zero. In contrast the coefficient in low speed region are lower than that of the rigid disk. These peculiar running behavior must be based on elasticity of the stretched medium. The change of spacing is less than 0.1μm below 6m/sec of running speed. Using the slotted spherical slider with the optimal radius of curvature even the CoCr stretched disk shows the durability over 100 million passes. These results suggest the possibility of a high density recording disk system based on such "quasi-contact head-media interface".

A comparison of head-to-disk spacing fluctuation on hard and stretch-surface recording disks

The head-to-disk spacing between the slider and the magnetic recording disk is disturbed by impacting the disk for two different systems: a widely used 5 1/4 inch hard disk with a mini-Winchester type slider, and a developmental 5 1/4 inch stretch-surface recording (SSR) disk with a slotted spherical slider. Motions of the sliders and disks are measured by use of laser Doppler vibrometry, and the head-to-disk spacing variations are measured by use of the read-back signal modulation technique. The head-to-disk spacing is excited by the resonances of the suspension arm or the resonant vibrations of the disk in the hard disk system. On the SSR disk the air bearing resonances are much higher than other mechanical disturbances and the spacing variations are primarily limited to spacing increases from the steady flying height that resemble a bouncing motion of the slider. It is difficult to cause the air bearing to fail in the SSR system if cleanliness is maintained.

Friction and frictional tracks on thick silica films prepared by vacuum deposition

Friction and frictional tracks on 2 µm thick SiO2 films evaporated on polymethylmethacrylate (PMMA) substrate were investigated. Diamond spherical sliders of radius 30 and 100 µm, respectively, were slid on these coatings under a load of 50 to 200g at a sliding speed of 15 cm min−1. The static and dynamic friction coefficients for SiO2 films were found to be 0.1 and 0.06, respectively, depending on the load and radius of the slider. For lower load and small slider radius the tracks on SiO2 film were groove-like, and whisker-like cracks regularly grew from the edges of the tracks. For higher loads and larger slider radius, semicircular cracks in the film were regularly found behind the slider, but in thicker film (6 µm thick), circular cracks occurred. The origin of these cracks is discussed in terms of a tension zone produced around the contact area between the slider and the substrate under frictional force.

Design of flying heads for tensioned flexible recording media

Earlier work has shown that by bonding tensioned flexible recording media to rigid support disks it is possible to have performance features similar to rigid disks, while retaining the advantages of flexible-media technology. The present paper documents the use of a mathematical model of the head, suspension, air bearing, and tensioned medium to design nearly optimal sliders for a given applied tension and medium stiffness. A novel coupled finite difference algorithm for solving the governing partial differential equations is described which allows the medium to be modeled in polar coordinates and the head and air bearing to be modeled in rectangular coordinates. Realistic medium boundary conditions are imposed allowing the head position to vary from the inside radius to the outside radius of the disk. Slotted spherical sliders are modeled and model predictions are compared to white-light interferometric measurements of the head-to-medium spacing. Measured friction and modeled minimum head-to-medium spacing are plotted versus velocity. Modeled minimum spacing becomes greater than the disk surface roughness near the velocity of minimum friction.

The Pivoted, Spherical Cap Slider Bearing

In hydraulic pumps of the positive displacement type, the shoes which guide the piston motion may be designed as pivoted slider bearings. One such design, where the bearing geometry is that of a spherical cap, is analyzed and results are presented for the load carrying capacity and the friction.

Elasticity Effects on the Lubrication of Point Contacts

An experimental study has been conducted of the hydrodynamic lubrication of a spherical slider on a flat surface with low elastic modulus. Optical measurements of lubricant film thickness demonstrate that a transition occurs from EHD to elastic isoviscous lubrication as the speed increases. Observed film thicknesses are in general agreement with recently advanced theoretical predictions. A regime chart is presented which charts the limits of the various regions of lubrication for nominal point contact.

Friction in Scratching without Metal Transfer

Scratch friction has been investigated in which the metallic transfer could be neglected. The scratch tests on some metal surfaces were carried out using conical and spherical sliders of hard materials. the geometric shapes of the scratched groove were examined in detail and a comparison of the friction force with these was made. Experiments showed obviously that there is a good correlation between the friction force and the groove shape. The coefficient of friction on the slider face was found to decrease with a decreasing groove depth under an influence of the surface films on the softer metal. An analysis to determine the friction force quantitatively has been developed. This theory specially includes an effect of the height of front ridge formed in front of the slider during scratching on the friction force. The results of the scratch tests show that the theory is very useful for the derivation of the friction force.

Spherical gas slider bearing with forced pressurization

Spherical gas slider bearing with forced pressurization

Lubrication of polythene by oleamide and stearamide

This paper describes a study of the lubrication of polythene surfaces by oleamide and stearamide. The sliding system consists of a stainless steel or glass spherical slider traversing a flat specimen of low density polythene. With unlubricated surfaces the friction coefficient is of order μ = 0.4. If surface films of oleamide are added by various techniques the friction may be as low as μ = 0.03 to 0.04: with stearamide the friction is not less than μ = 0.15. The lubrication is effective only when the amide achieves complete coverage of the polymer. In a second group of experiments polymer specimens were prepared which contained various amounts of amide in the bulk. On abraded surfaces the friction is μ = 0.4. If the samples are heated to say 45°C for several hours and then examined at room temperature the friction is found to be considerably less. The limiting value is μ = 0.04 for oleamide and μ = 0.15for stearamide. Independent experiments show that the diffusion rates of the two amides are similar and that the presence of the solid amide on the surface, for both amides, inhibits the diffusion process. The lubricating properties of the amides appear to be a simple function of their rheological characteristics. Oleamide is softer than stearamide and is more effectively smeared over the polymer surface. In addition it has a lower shear strength. The final part of the paper describes experiments on the effect of surface roughness.

Friction and Wear of Rutile Single Crystals

Low-speed friction tests with fine diamond styli and spherical sliders of ruby, sapphire, and hardened steel were carried out on the crystallographically prominent planes of synthetic single-crystal rutile at room temperature. The friction against diamond was 0.04–0.10; against sapphire and steel, 0.10–0.15. Ploughing friction was found to be anisotropic. When larger sliders were used so that the contribution by ploughing was minimized, the frictional anisotropy vanished. The anisotropy of ploughing was correlated with plastic deformation by slip in and adjacent to the friction track, as seen and studied with the optical microscope. Surface damage by cleavage and brittle failure was found to be severe during the friction experiments.

Lubricated Friction of Rubber. III. Components of Friction in Mating Surfaces

Abstract Friction is usually discussed in terms of contributions from two processes: deformation and adhesion. This terminology has been retained in discussions of lubricated friction of rubber although there is not apparent any clear mechanism by which adhesion might occur. Our study of wet friction leads us to suggest that the components making up frictional resistance to sliding might more appropriately be referred to as deformation and abrasive components. On this basis, there is an obvious mechanism for both processes, and some of the disagreements about interpretation of certain experimental results may be resolved. The basis for our interpretation is implicit in the literature but was originally expressed somewhat tentatively and has not been restated in recent discussions. Greenwood and Tabor pointed out that hysteretic losses make an important contribution to friction of rubber sliding on a lubricated surface and that this contribution is independent of asperity size or distribution so long as only the asperities support the load and the radius of curvature at the asperity tip is above a critical limit which is remarkably low. Further, the experiments of Sabey showed that it was difficult to obtain coefficients higher than 0.4 with spherical sliders. Mean average local pressures high enough to give high friction coefficients could be obtained only with sharp asperities. In the laboratory experiment these were cones. Greenwood and Tabor found that with these damage to the rubber becomes visible at just the semiangle at which the coefficient began to rise abruptly (Figure 1). It is entirely reasonable to call the process causing this damage abrasive friction.