Tribological element

The HH, HL, HM, HR, HV and HG hydraulic lubricants are the most important and widely used. As viscosity is one of their most important properties, they are produced in a wide range of viscosities, ISO VG 10-100. For a given application, viscosity should be as low as possible to give a rapid response for the hydraulic system, meaning that the oil should be sufficiently fluid for efficient power transmission. A minimum viscosity level is necessary to eliminate or minimize leakage losses and ensure lubrication of all tribological elements of the hydraulic system. 

For accurate transmission of the motion, stable and relatively high friction at the contact inter ce is required. Moreover high wear resistance of both tribological elements is essential to maintain accurate performance, sinee wear causes a decrease in the mechanieal accuracy of the system. 

The parts and materials directly involved in wear are described as elements of the tribosystem. They characterize the structure of the tribosystem together with their key tribological characteristics and interactions . 

Vol. 14 Tribological Design of Machine Elements (Dowson et al.. Editors)... 

Among the various compounds of carbon, the carbides of different elements have a special significance from the tribological point of view. Many of these materials, for instance WC, SiC, and TiC, are mechanically hard and have found use in the tribological industry. The carbonitride (or what can also be called the carbide of nitrogen) is an important constituent of this class of materials. In the last decade or so, the theoretical prediction of crystalline carbonitride phases that could be harder than diamond has generated much interest in the synthesis of this material. 

Hartley claims that the effects of ion implantation on wear reduction are due to physical rather than chemical mechanisms . This is probably true for the systems considered in this model. But there are certainly cases where chemical effects are important too, especially in tribological systems, including lubrication. For fluid lubricants it is well known that certain chemical elements improve the adhesion of the lubricating films. These elements may be introduced by ion implantation. This is also possible for high-temperature lubrication where the lubricant is incorporated in the material. Here chemical methods for the production of surface films (oxides, fluorides, sulfides) are common. Ion implantation is an alternative method of incorporating the effective element into the surface region of the material. 

Most real solids, and hence surfaces, are not perfectly periodic but contain a certain degree of disorder. This can change the tribological properties of a system qualitatively. There are many ways to introduce the effects of disorder into the FK model. One possibility is to assume that the substrate potential contains random elements, while another possibility is to assume that the bond lengths or the spring stiffnesses fluctuate around a mean value. 

CNT has already been exploited in NEMS as the basis for a rotary element for a magnetically actnated nano-plate [96] and additional NEMS devices relying on both the novel mechanical and electrical properties of CNTs wiU continne to be developed in the years to come. Composite materials containing CNTs, especially inorganic material/CNT blends, have been demonstrated to have enhanced mechanical and tribological properties, unattainable with current metallurgical techniques [97]. These electroless and electrodeposited composites wiU provide a new class of materials available for MEMS and NEMS devices. 

Surface texture and roughness play central roles in the theory of tribology, and we will explore them in the surface characterization section. One of the interesting elements that emerge is that the notion of roughness is interwoven with the perspective of scale (both in regard to physical dimensions and time). So it will be of use to review the scales that are encountered in CMP technology.34... 

The element of indeterminateness in this definition is to a certain extent advantageous, as the borderline between surface interactions which can be regarded as tribological and those which cannot is not firmly established. For example, the interaction between two charged surfaces as they approach each other is ordinarily thought of as electrical behavior. However, as we shall find when we come to the examination of contacting... 

Two basic factors should be considered in assessing the role of chemical reactivity in additive action (a) the nature of the additive— X.e. its structure and the reactive elements therein (b) the reactivity of the rubbing surfaces, which includes their state of activation as well as the intrinsic reactivity of the constituent materials. In tribological processes, additive reactions occur at surfaces that are being rubbed or have just been rubbed. For the most part the sequence of events is so complex that the reactivity of the surfaces cannot even be estimated, let alone be specified precisely. Nevertheless it is valuable background to know how surfaces of known composition and properties react generally with chemical groups typical of additive substances as well as with specific substances of established utility. 

The intrinsic complexity of additive/metal interactions under dynamic rubbing conditions probably means that the description and analysis of additive action even in fairly simple tribological situations will not be entirely free of conjecture. The difficulties in the elucidation of additive/metal interaction are illustrated by the work of Buckley [7, 8, 13] for no matter how elegantly the presence of the active element (sulfur, chlorine, carbon) in the surface of the metal is demonstrated, it does not reveal the path by which that element got there from the additive substance as originally put into the system. The appropriateness of a conjecture or an experimental investigation can be tested by questions such as the following How is the initial encounter of the additive molecule with the metal surface treated What is known about the interaction immediately subsequent to the initial encounter How is the interaction affected by the duration of contact and by the local temperature Is there further interaction, of the additive and secondary products or of secondary products directly, with the metal surface ... 

The most important use of XV is its telomerization with fluoride ion to give a linear hydrofluoroacyl fluoride (XVI), that is fluorinated with elemental fluorine to give a linear perfluorinated polyether (XVIII), which is sold by Daikin as Demnum (Eq 13.18). Note that Demnum and Krytox are isomeric materials. In general, their properties are quite similar, but there are subtle differences in physical properties and in chemical stability in tribological applications. 

The elements of such a system consist of the primary body, the counter body, the interfacial medium and surrounding medium. Wear is a result of the action of the collective stress on the structure respectively on the elements of the tribological system and manifests itself in energetic and material interactions between these elements. It is defined by the wear parameters. Basically all wear mechanisms can occur abrasion, adhesion, tribo-chemical reactions or wear caused by fatigue. In the case of the extrusion of ceramic bodies, corrosion must be considered as another harmful mechanism. When determining the elements of the tribosystem for the... 

In machine elements such as friction bearings with a tribological function, process-related influences are highly desirable. Heated molds are a possible solution, also in injection molding. 

Applications of DLC films in several fields like optics, magnetic disks, tribology and machine elements or biomedical purposes have been reported in the literature. A review on this topic was given by Matthews and Eskildsen [78]. 

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