Astakhov / Joksch Metalworking Fluids (MWFs) for Cutting and Grinding

Fundamentals and Recent Advances
1. Auflage 2012
ISBN: 978-0-85709-530-5
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 424 Seiten

Reihe: Woodhead Publishing Series in Metals and Surface Engineering

Metal working fluids (MWFs) provide important functions such as lubrication and cooling in the machining of metals. This book reviews the issues surrounding the use of fluids for cutting and grinding throughout the metal working process, from selection and testing to disposal.The book opens with chapters considering the mechanism and action, selection and delivery of MWFs to the machining zone before moving onto discuss the many issues surrounding MWFs during machining such as selection of the proper MWF, environmental concerns, supply methods, circulation and monitoring. The final chapters discuss the maintenance, replacement and disposal of MWFs.With its distinguished editors and international team of expert contributors, Metalworking fluids (MWFs) for cutting and grinding is an invaluable reference tool for engineers and organizations using metal cutting/machining in the manufacturing process as well as machine designers/manufacturers and machining fluid/chemical suppliers. - Chapters consider the mechanism and action, selection and delivery of MWFs to the machining zone - Environmental concerns, supply methods, circulation and monitoring are also discussed - Written by distinguished editors and international team of expert contributors

Autoren/Hrsg.

Astakhov, V P

Joksch, S.

Leseproben

1 Mechanisms of action of metalworking fluids in metal cutting
V. Godlevskiy,     Ivanovo State University, Russia Abstract:
This chapter describes current theories on the mechanisms of action of metalworking fluids (MWFs) in the machining zone. Their main functions of cooling and lubrication are analyzed. Special attention is devoted to the new microcapillary theory of lubrication action in the edge cutting process. Key words adsorption boundary lubrication capillary lubrication and cooling mechanisms metalworking fluids (MWFs) 1.1 Introduction
Metalworking fluids (MWFs) are part of a large family of lubricants. Until recently MWFs were among the least expensive components in metal cutting manufacture, because recycling processes for these fluids were not associated with high costs. However, this situation is changing rapidly. Modern MWFs for metal cutting are complex mixes of a number of different components, each of which fulfils specific functions. Many properties of modern lubricants are achieved through the introduction of special chemical substances (additives) without which they could not satisfy the escalating requirements of the industry. Additives to MWFs can, for example, reduce friction, provide anti-wear properties and corrosion stability, and improve the temperature–viscosity dependence, and so on. The manufacture and consumption of additives in the world reaches an estimated several million tonnes, including over 600 different commodities. MWF manufacture, both in terms of scale and technology, is comparable to the manufacture of motor and industrial oils. Alongside the obvious progress that has been made in the creation and application of effective MWFs, many unresolved questions remain, mainly connected to the study of physical and chemical aspects of the environment of the cutting zone. It is clear that the development of a conceptual basis for the design and rational use of MWFs relies on knowledge gained through general tribology, physical and colloid chemistry, and on the development of new theoretical approaches. The development and application of MWFs constitutes an interdisciplinary scientific field which includes the technology of processing of metals, tribology (study of friction, wear and lubrication) and chemmotology (usually called tribochemistry, the study of properties, quality and rational application of combustible and lubricating substances in engineering). The interrelationships between the fields of study are shown in Fig. 1.1. 1.1 Interdisciplinary approach to the MWF problem: 1, branch science concerning MWF; 2, sphere of tribological action of lubricating materials; 3, tribology of cutting process; 4, chemmotology of MWF. Earlier studies on chip-formatting mechanisms were carried out in the 1940s and 1950s and on the whole did not take into account parameters of interaction between the contact zone and the external environment. As a result, many theories proposed in these works had to be revised on the basis of new theories developed in solid state physics and in the field of the physical chemistry of superficial phenomena. Within the last few decades studies to establish scientifically proven principles of MWF development and application have been carried out (with some additional recent research into fluids for non-metals). As the problem under discussion is interdisciplinary, it has been necessary to involve physicists, tribologists, colloid and organic chemists as well as electrochemists, and more recently, industrial hygiene and ecology specialists. The rapid development of modern machine tools and cutting tools has created an increasing need to find effective and environmentally friendly MWFs. At the same time the modern applications of MWFs have brought a number of new problems into the picture: • Increased use of difficult-to-machine materials including composite materials. • Sophistication and wider use of heat treatment processes in various work materials. • Increase in deficiency and cost of mineral oils and, as a related issue, limitations on the application of oil-based MWFs. • A recently observed increase in the occurrence of painful sensitivity (sensitization) in the human body to the large number of components of technological lubricants. • A significant increase in the requirements for recycling and regeneration of used MWFs. Some of the most important issues relating to the current use of MWFs are as follows: • The role and parity of various aspects of the action of MWFs (lubrication, cooling, washing, etc.). • Theoretical support for the choice of components used in the MWF structure: water, hydrocarbons, functional additives. • Identification of the passivation of metal surfaces by active components of the environment and their products. • MWF application technique. • Long-term maintenance of MWF to assure the safety of operators, reliability and efficiency of machining operations and protection of environment. A number of contradictions can thus be observed in the evolution of the issues relating to MWFs. On one hand a number of new special work materials cannot be machined without the use of special active lubricants, but on the other, the activity of these substances is harmful to workers and to the environment. Although, from an economic perspective effective, MWFs improve the results of materials processing, they are also higher in price (new components, more complex application technique) and increasing expenditure on regeneration and recycling of the waste products places an additional burden on the cost of these products. Such dialectics of development have resulted in new scientific research becoming necessary in an area that already seemed well developed, with new theoretical approaches and novel technical decisions being required. This chapter discusses attempts to resolve these problems. 1.2 Short history
Developments in MWFs occurred in parallel with the study of the cutting process. For example, the well-known Taylor’s formula which empirically correlates the cutting speed and tool life was corrected to take the influence of MWFs into account as: [1.1] where v is cutting speed, T is tool life; m is the empirical power factor, Cv is a factor dependent on the properties of the work material and CMWF is a factor taking the application of MWFs into account. Factor CMWF, which accounts for the application of the MWF is purely experimental and thus valid only for a particular operation, particular brand, concentration, purity or other basic properties of the MWF used, MWF delivery technique, its flow rate and a myriad of other operation-specific factors. In modern manufacturing, a scientific approach to studying the effect of MWFs is needed. Such an approach should be based on the physics and chemistry of the processes that take place in the contact zone, taking the environment into account. Earlier studies were concentrated on the cooling action of MWFs, that is, their ability to decrease the tool–chip contact temperature. Further developments resulted in the discovery of the embrittlement action of MWFs. The embrittlement action of the cutting fluid reduces the strain at facture of the work material. This action is based on the Rehbinder effect.1,2,9 This effect was invoked as early as in 1936 as the basis of ‘oiliness’ of boundary lubricants. Conducting tension studies of tin specimens, Rehbinder observed that a boundary lubricant film of oleic acid lowered the stress and stress at fracture. Microscopic examination of the test specimens showed a great increase in the number of active slip planes. He concluded that this resulted from penetration (absorption) of the surface active acid into microcracks and thus lowered the strength of the specimen.31 As a result of this development, MWFs with additives emerged that promote this effect. It was found that chemically active MWFs are especially effective in machining difficult-to-machine materials, particularly when aggressive cutting regimes were used. These chemically active MWFs included chlorinated and sulfonated oils, for example, containing additives such as sulfur, chlorine and phosphorus. After the 1960s, these substances were widely applied in the industry, despite the risk that they pose to human health. In the same period, there was a marked increase in scientific studies to reveal the physical and chemical mechanisms governing the action of MWFs. These studies were based on the ideas developed in general tribilogy, for example the molecular-mechanical model of discrete friction developed by Bowden and Tabor 3 and the theory of a boundary lubrication layer (taking into the account the aspect of adsorption).4,5 In the 1970s books and articles began to appear that outlined scientific approaches and observations and the concepts...