Journal of Materials Processing Technology 152 (2004) 215–220 Cutting fluid emulsions produced by dilution of a cutting fluid concentrate containing a cationic/nonionic surfactant mixture H. Bataller, S. Lamaallam, J. Lachaise, A. Graciaa, C. Dicharry ∗ Laboratoire des Fluides Complexes, Centre Universitaire de Recherche Scientifique, Université de Pau et des Pays de l’Adour, 64000 Pau, France Received 27 April 2003; accepted 10 March 2004 Abstract A cutting fluid concentrate has been formulated from a paraffinic oil, a hard water, MonoEthanolamine Borate (MEAB) and a cationic/nonionic surfactant mixture. Its dilution with hard water yields very stable oil-in-water emulsions, the so-called cutting fluid emulsion, with an average droplet diameter of 50 nm, independently of both the hardness of water and the weight ratio of hard water to concentrate. The high stability of these emulsions results from the existence of a strong repulsive potential between droplets which is caused in particular by the presence of the cationic surfactant at their surface. From a practical point of view, the ability to produce stable cutting fluid emulsions for a wide range of dilution, whatever the hardness of water, might allow the user to fine-tune the lubricating and cooling abilities of the fluids and therefore optimize their performances during the metal working process. © 2004 Elsevier B.V. All rights reserved. Keywords: Cutting fluid concentrate; Dilution; Hard water; Cutting fluid emulsion; Stability 1. Introduction Heat dissipation and lubrication are common problems that faces the metal processing industry. In machining pro- cesses such as metal/turning, milling, drilling and in par- ticular when the metal removal operations are conducted at high speeds and low pressures, the regulation of heat gen- eration and the lubrication of the contact point are achieved by pouring an oil-in-water emulsion, the so-called cutting fluid emulsion, over the cutting surface. Such a fluid has the particular advantage that it combines the cooling property of water and the lubrication property of oil. It is usually ob- tained by diluting a cutting fluid concentrate with mains wa- ters at a weight ratio of water to concentrate ranging from approximately 98/2 to 95/5 depending on the machining op- eration [1,2]. A cutting fluid concentrate usually contains a mineral oil, a surfactant mixture, in some cases water and vari- ous additives which are included to meet the specifications of commercial concentrates such as resistance to bacterial growth and low corrosion capacity [1,2]. For easiness of use, the concentrate must be stable and not viscous. Its ap- pearance has to be monophasic and its dilution with water ∗ Corresponding author. E-mail address: christophe.dicharry@univ-pau.fr (C. Dicharry). associated with gentle mixing must produce an oil-in-water emulsion. An emulsion is a nonequilibrium system which will fi- nally separate in two phases. A short time of separation will restrict the use of the emulsion as a cutting fluid because lubrication capacity decreases with stability. The stability of an emulsion can be increased by using ionic surfactants because their adsorption at the surface of the oil droplets yields electric repulsion between them [3]. A commercial cutting fluid concentrate generally con- tains a mixture of anionic and nonionic surfactants [4]. Mixed surfactants increase the solubilization capacity of surfactants [5] and in some cases may facilitate the sponta- neous formation of an emulsion when the system is brought into contact with water [4]. The presence of an anionic surfactant in the surfactant mixture gives a negative electric charge to the oil droplets of the emulsion [6]. However, the stability of this emulsion will often depend on the metal- lic ion (Ca 2+ and Mg 2+ ) contents of the water used for dilution. When the ion concentration is high enough, the anionic surfactants may form insoluble compounds with them and then precipitate [7]. This causes the decrease of the surface charge of droplets and the emulsion may be destabilized. The total concentration of calcium and magne- sium ions in water defines the hardness of water. A water is said hard if the concentration is greater than 1.5 mmol/l [8]. The hardness of water may vary from one region to another 0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2004.03.027