The friction of clean crystal surfaces

1966 ◽  
Vol 295 (1442) ◽  
pp. 233-243 ◽  
Keyword(s):  
Coefficient Of Friction ◽  
High Surface ◽  
High Vacuum ◽  
Surface Films ◽  
Surface Adhesion ◽  
Crystal Surfaces ◽  
Deformation And Fracture ◽  
The Coefficient Of Friction ◽  
Molecular Layers ◽  
Frictional Behaviour

A study is made of the frictional behaviour of crystals (diamond, magnesium oxide, sapphire) sliding on themselves in high vacuum (10 -10 torr). The surface films normally present on these crystals are very tenacious but they may be worn away by repeated sliding in the same track. Under these conditions the friction of the clean crystals may increase by a factor of ten so that the coefficient of friction may rise to μ ≈ 1. The frictional rise is limited because of the elastic and brittle behaviour of the contact regions. Under these conditions subsurface deformation and fracture of the crystal occurs and this, combined with the high surface adhesion, causes pronounced wear. Adsorption of a few molecular layers of gas can again reduce the friction to a low value. The results are relevant to the operation of bearings and to the wear of surfaces in space.

Tribological Properties of Polyoxymethylene Composites Against Aluminum

2003 ◽  
Vol 125 (3) ◽  
pp. 661-669 ◽  
Author(s):  
Masaya Kurokawa ◽  
Yoshitaka Uchiyama ◽  
Tomoaki Iwai ◽  
Susumu Nagai
Keyword(s):  
Wear Rate ◽  
Coefficient Of Friction ◽  
Tribological Properties ◽  
High Surface ◽  
Surface Hardness ◽  
Disk Surface ◽  
Optical Microscope ◽  
Transfer Film ◽  
The Other ◽  
The Coefficient Of Friction

Tribological properties of several kinds of polyoxymethylene (POM) composites were evaluated for the purpose of developing a polymeric tribomaterial especially suited for mating with aluminum parts having low surface hardness. POM composites containing small amounts of silicon carbide (SiC), POM/SiC; those containing a small amount of calcium octacosanonoate besides SiC, POM/SiC/Ca-OCA; and the one blended with 24 wt % of polytetrafluoroethylene, POM/PTFE(24); were injection-molded into pin specimens and their tribological properties were tested by means of a pin-on-disk type wear apparatus using an aluminum (A5056) mating disk in comparison with a 303 stainless steel (SUS303) disk. Evaluation was focused on observation of the sliding surfaces of the pin specimens and the mating disks by a scanning electron microscope and an optical microscope together with the measurement of surface roughness. In the case of mating against a SUS303 disk having high surface hardness, all pin specimens did not roughen the disk surfaces even after long time of rubbing. Only POM/PTFE(24) composite obviously made a transfer film on the disk surface, while the other composites made an extremely thin one on it. POM/SiC(0.1)/Ca-OCA(1) composite, containing SiC 0.1 wt. % and Ca-OCA 1 wt. %, was found to show the lowest coefficient of friction and the lowest wear rate forming extremely thin transfer film on the mating disk. On the other hand, against an A5056 disk which has lower surface hardness than that of SUS303 disk, unfilled POM and POM composites except POM/SiC(0.1)/Ca-OCA(1) composite roughened the disk surfaces. However, the sliding surface of the A5056 disk rubbed with POM/SiC(0.1)/Ca-OCA(1) composite was significantly smoother and that of the pin specimen was also quite smooth in comparison with other pin specimens. Further, when each POM composite was rubbed against the A5056 disk, formation of transfer film was not obvious on the disk surfaces. For POM/SiC(0.1)/Ca-OCA(1) composite, the wear rate was the lowest of all POM composites, and the coefficient of friction was as low level as 60 percent of that of unfilled POM, but slightly higher than that of POM/PTFE(24) composite. For POM/SiC(0.1)/Ca-OCA(1) composite, the nucleating effect of SiC and Ca-OCA, which accelerated the crystallization of POM during its injection molding to form a matrix containing fine spherulites, must have resulted in increasing the toughness of the matrix and lowering the wear rate. Also, the lubricant effect of Ca-OCA should have lowered the coefficient of friction of the same matrix for rubbing against aluminum mating disk. POM/SiC(0.1)/Ca-OCA(1) composite was concluded as an excellent tribomaterial for mating with aluminum parts.

Variation with load of the coefficient of friction and metallic transfer under conditions of boundary lubrication

1952 ◽  
Vol 212 (1111) ◽  
pp. 516-519 ◽  
Keyword(s):  
Coefficient Of Friction ◽  
Boundary Lubrication ◽  
General Pattern ◽  
Copper Plate ◽  
Experimental Conditions ◽  
Average Hardness ◽  
Boundary Lubricant ◽  
The Coefficient Of Friction ◽  
Fixed Load ◽  
Molecular Layers

Several papers have been published recently which show for a number of metals that, under certain experimental conditions, several molecular layers of boundary lubricant are necessary to give effective lubrication, i.e. a coefficient of friction of 0.1 or less. Recent experiments by the authors suggest that these results represent parts of a more general pattern. In the previous work, the experiments were carried out at a fixed load; in the present, the load has been varied. The apparatus used was a copy of that described by Bowden & Leben (1939) for studying friction at low speeds of sliding. A hemispherical copper slider of radius 0-45 cm was caused to slide upon a flat copper plate at a speed of approximately 1 cm/min. Several specimens were used; their average hardness was 100 v .p .h .

scholarly journals The Influence of Surface Texturing on the Frictional Behaviour in Starved Lubricated Parallel Sliding Contacts

Lubricants ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 68 ◽  
Author(s):  
Bijani ◽  
Deladi ◽  
Rooij ◽  
Schipper
Keyword(s):  
Coefficient Of Friction ◽  
Surface Texturing ◽  
Geometrical Parameters ◽  
Textured Surfaces ◽  
Tribological Behaviour ◽  
Sliding Contacts ◽  
Cavitation Effect ◽  
The Coefficient Of Friction ◽  
Starved Lubrication ◽  
Frictional Behaviour

Starvation occurs when the lubricated contact uses up the lubricant supply, and there is not enough lubricant in the contact to support the separation between solid surfaces. On the other hand, the use of textures on surfaces in lubricated contacts can result in a higher film thickness. In addition, a modification of the surface’s geometrical parameters can benefit the tribological behaviour of the contacts. In this article, for parallel sliding surfaces in starved lubricated conditions, the effect of surface texturing upon the coefficient of friction is investigated. It is shown that surface texturing may improve film formation under the conditions of starvation, and as a result, the frictional behaviour of the parallel sliding contact. Furthermore, the effect of starved lubrication on textured surfaces with different patterns in the presence of a cavitation effect, and its influence on frictional behaviour, is investigated. It is shown that surface texturing can reduce the coefficient of friction, and that under certain conditions, the texturing parameter could have an influence on the frictional behaviour of parallel sliding contacts in the starved lubrication regime.

Effect of surface structure, composition and texture on friction under boundary conditions

1952 ◽  
Vol 212 (1111) ◽  
pp. 508-512
Keyword(s):  
Oxide Film ◽  
Boundary Conditions ◽  
Coefficient Of Friction ◽  
Substrate Material ◽  
Pure Aluminium ◽  
Surface Layers ◽  
The Coefficient Of Friction ◽  
The Difference ◽  
Frictional Behaviour ◽  
Effect Of Surface

The coefficient of friction of surfaces lubricated under boundary conditions may be profoundly affected by such factors as the degree of working of the substrate material, the nature of the oxide film and the degree of roughness of the surface. Experiments are described wherein the frictional behaviour of surfaces of stainless steel specimens prepared in various ways was compared. The worked surface layers in these particular experiments appear to increase the value of the coefficient of friction, but the effect of surface texture is of predominant importance. The effect of different oxide films is best illustrated by reference to pure aluminium, the surface of which has been oxidized under different environmental conditions. The constitution of the oxide film formed is modified with a consequent effect on boundary friction. When the friction of rough and smooth surfaces is compared, the difference in behaviour appears to be qualitative rather than quantitative.

Influence on Friction Force of Adhesion Force between Vulcanizates and Sliders

1994 ◽  
Vol 67 (5) ◽  
pp. 797-805 ◽  
Author(s):  
Kunio Mori ◽  
Satoshi Kaneda ◽  
Kentaro Kanae ◽  
Hidetoshi Hirahara ◽  
Yoshiyuki Oishi ◽  
...  
Keyword(s):  
Free Energy ◽  
Surface Free Energy ◽  
Friction Force ◽  
Coefficient Of Friction ◽  
Adhesion Force ◽  
High Surface ◽  
Low Surface Energy ◽  
Polar Groups ◽  
Slider Surface ◽  
The Coefficient Of Friction

Abstract The effects of vulcanizate and slider surface free energy—as well as the adhesion force (P) between them—on friction the force (F) and the coefficient of friction (μ) has been investigated. SBR and NBR vulcanizates were prepared using three molds differing in surface free energy. The mold with a high surface free energy gave a vulcanizate surface possessing polar groups. The mold with low surface energy gave a vulcanizate surface with many nonpolar groups. The coefficient of friction increased with the surface free energy of SBR and NBR vulcanizates. With SBR vulcanizate (surface free energy, 31.3 mJ·m−2) and teflon slider (surface free energy, 28.1 mJ·m−2) combination having the least surface free energy, the coefficient of friction was constant at greater than a 0.2N load. With vulcanizates and an aluminum slider with high surface free energy, friction force could be detected even at zero load because of the adhesion force at the interface. Friction force increased linearly with adhesion force between vulcanizates and sliders when the physical properties of the vulcanizates and net work chain density were constant. The present results clearly demonstrate the contribution of adhesion force to the friction of vulcanizates.

Friction of clean metals and the influence of adsorbed films

1951 ◽  
Vol 208 (1094) ◽  
pp. 311-325 ◽  
Keyword(s):  
Room Temperature ◽  
Physical Adsorption ◽  
Surface Films ◽  
Metallic Contact ◽  
Adsorbed Films ◽  
Real Area Of Contact ◽  
Molecular Layers ◽  
Very High ◽  
Frictional Behaviour ◽  
Real Area

An experimental Study has been made of the frictional behaviour of thoroughly degassed metal surfaces. An apparatus is described, in which friction can be measured at any desired temperature up to 1200° C or more, either in vacuo or in a particular gas. It is found that when sufficiently clean metals are allowed to touch, even at room temperature, complete seizure occurs. Over the real area of contact the specimens adhere with the bulk strength of the metal, and this area increases greatly with continued sliding or attempted sliding. Various gases and vapours have been adsorbed on to the clean specimens, and their in­fluences on friction determined. These specific contaminants are most effective as lubricants where they can react with the metal to form a solid and chemically attached film which is several molecular layers in thickness. Otherwise the friction remains very high, although seizure is prevented. It is shown that physical adsorption may occur in addition, with a significant reduction in the friction. The results support the view that the friction of metals is due mainly to adhesion at the points of real contact, and is governed by the extent to which even the thinnest of surface films can reduce this metallic contact.

Brush Dynamics: Models and Characteristics

2006 ◽  
Author(s):  
Libardo V. Vanegas Useche ◽  
Magd M. Abdel Wahab ◽  
Graham A. Parker
Keyword(s):  
Surface Roughness ◽  
Coefficient Of Friction ◽  
Rotational Speed ◽  
Surface Finishing ◽  
Stick Slip ◽  
Street Sweeping ◽  
The Coefficient Of Friction ◽  
Dynamics Models ◽  
Frictional Behaviour ◽  
Duct Cleaning

This paper reviews investigations into the dynamics and modelling of brushes. They include brushes for surface finishing operations, removal of fouling, post-CMP brushing processes, air duct cleaning, and street sweeping. The methods that have been proposed to model brush dynamics are described, and the results of the research into brush mechanics are presented and discussed. Some conclusions of the paper are as follows: brush dynamics is very complex, as it depends on the interaction among many phenomena and variables. The bristle oscillations that occur in some brushes constitute a complexity for modelling brush behaviour and are not normally addressed. Additionally, the literature reveals that the coefficient of friction is not a constant value that depends only on the materials and surface roughness of the two contacting bodies. Frictional behaviour strongly depends on many variables, such as brush setup angles and rotational speed, which play a part in the development of stick-slip friction cycles. Finally, it is concluded that brush behaviour and the phenomena involved in brushing have not been fully studied or understood and more research into this field is needed.

scholarly journals The influence of temperature on boundary lubrication

1942 ◽  
Vol 181 (984) ◽  
pp. 23-42 ◽  
Keyword(s):  
Oleic Acid ◽  
Coefficient Of Friction ◽  
Boundary Lubrication ◽  
Surface Film ◽  
Adsorbed Layer ◽  
Surface Measurement ◽  
Polar Group ◽  
The Coefficient Of Friction ◽  
Low Speeds ◽  
Frictional Behaviour

The frictional behaviour between mild steel surfaces lubricated with excess of pure hydrocarbons, ketones, alcohols, amides, acids and esters has been investigated at low speeds and under high loads. In all cases a transition from smooth sliding to irregular stick and slip motion takes place at a temperature characteristic of the lubricant employed. Experiments in which lubricant films one or more molecules thick were built up by the Langmuir-Blodgett technique have shown that the transition from smooth sliding to stickslips occurs when the adsorbed surface film of lubricant breaks down and becomes disoriented. Acids and esters are shown to be strongly adsorbed, while hydrocarbons, ketones, alcohols and amides are not appreciably adsorbed. It is shown that adsorption of acids and esters occurs by the interaction of the dipoles in their polar group with the metal atoms in the surface. The results also suggest that molecules of long-chain compounds are oriented on a metal surface in the same way as they have been shown to be arranged on an aqueous surface. Measurement of the coefficient of friction between surfaces lubricated with films one and many molecules thick has shown that under conditions of ‘ boundary lubrication ’ prevailing at high loads and low speeds, excess of lubricant is squeezed out, and lubrication is effected by a unimolecular film adsorbed on each surface. The variation of the coefficient of friction with load in the case of oleic acid shows that orientation with this lubricant extends beyond the primary adsorbed layer. This result accounts for the low values of the coefficient of friction obtained by previous workers, and explains the good lubricating properties of oleic acid. These experiments show that a study of the frictional behaviour provides a m ethod of investigating the properties of surface films on metals.

Dry Forming of Aluminium Sheet Metal: Influence of Different Types of Forming Tool Microstructures on the Coefficient of Friction

2015 ◽  
Vol 651-653 ◽  
pp. 516-521 ◽  
Author(s):  
Peter Scholz ◽  
Richard Börner ◽  
Ralf Kühn ◽  
Roland Müller ◽  
Andreas Schubert
Keyword(s):  
Sheet Metal ◽  
Coefficient Of Friction ◽  
Metal Forming ◽  
Process Chains ◽  
Different Types ◽  
Strip Drawing ◽  
The Coefficient Of Friction ◽  
Surface Microstructures ◽  
Forming Tools ◽  
Frictional Behaviour

In the sheet metal forming industry lubricants are applied in forming processes to expand the technological boundaries by reducing friction and wear. The friction between tool and sheet metal is crucial to the deep drawing process. Due to economic and ecological reasons the aim of the manufacturers is to reduce or even avoid the use of lubricants. Consequently, this approach enables both a shortening of the process chains and an essential saving of resources. The advantages of structured forming tools in lubricated processes concerning the reduction of the coefficient of friction by the appearance of lubricating micro pockets are well-known. However, without using any lubricant this effect does not work. In this case the contact area is reduced by structuring the forming tool which affects the tribological system.In this paper the influence of microstructures with different geometries and surface treatments (uncoated / a-C:H:Si-coating) on the coefficient of friction in dry metal forming of the alloy AA5182 is compared to the frictional behaviour of unstructured forming tools using lubricant as reference. Before coating, the forming tools are machined by milling to generate tribologically effective microstructures. With the use of a strip drawing plant the effects of different surface microstructures and materials on the coefficient of friction are investigated.

Paper 4: An Experimental Study of the Frictional Behaviour of Steels at Elevated Temperatures

1966 ◽  
Vol 181 (15) ◽  
pp. 1-10
Author(s):  
L. A. Mitchell ◽  
T. S. Crawford
Keyword(s):  
Experimental Study ◽  
Coefficient Of Friction ◽  
Elevated Temperatures ◽  
Oxide Films ◽  
Hardened Steel ◽  
Material Combination ◽  
Severe Wear ◽  
Mild Wear ◽  
The Coefficient Of Friction ◽  
Frictional Behaviour

Many investigators, by the manner of presentation of results, have implied that for any given material combination and atmosphere, the coefficient of friction is a function of temperature alone. Experiments are described which were designed to evaluate the importance of the sliding and temperature histories on the unlubricated sliding performance of steels at temperatures up to 500°C. Only for a hardened steel, when mild wear prevailed, was the specimen history unimportant, and, in this case, μ was virtually independent of temperature. With materials exhibiting severe wear, sliding produced changes in friction which were attributed to hardening of the surfaces and when the thickness of oxide films became comparable with the size of transferred particles, exposure to temperature could modify subsequent frictional behaviour.

Sign in / Sign up

Export Citation Format

Share Document