 Posted: Fri 6:11, 13 May 2011 Post subject: Machining Fluids, Coolants from Chicago Cutting To |
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Cutting Fluids Cutting fluids are required to do many things simultaneously. These functions include: Cooling the work and cutting tool. Improving surface finish quality. Lubricating to reduce friction and cutting forces, thereby extending tool life. Minimizing material buildup on tool cutting edges. Protecting machined surface against corrosion. Flushing away chips. In addition, cutting fluids must comply with all federal, state, and local regulations for human safety, air and water pollution, waste disposal, and shipping restrictions. Types of Cutting Fluids Cutting fluids fall into four basic types: Mineral oils. Emulsifiable oils. Chemical and semichemical fluids. Gaseous fluids. Mineral Cutting Oils Cutting oils made from mineral oil may be used straight or combined with additives. Straight mineral oils are best suited for light-duty (low speed, light feed) operations where high levels of cooling and lubrication are not required. They are noncorrosive and are usually used with high machinability metals, such as aluminum, magnesium, brass, and free-cutting steel. Mineral oils are often combined with animal and vegetable oils and contain sulfur, chlorine, and/or phosphorus. Their use is limited by high cost,cutting tools, operator health problems, and danger from smoke and fire. Mineral oils also stain some metals. They have a tendency to become rancid, so the tank containing them must be cleaned periodically and the fluid replaced. When working in situations where cutting fluid mists or vapors are present, always wear an approved respirator. A simple dust mask is not sufficient protection. Emulsifiable Oils Emulsifiable oils are also known as soluble oils. They are composed of oil droplets that are suspended in water by blending the oil with emulsifying agents and other materials. Emulsifiable oils range in appearance from milky to translucent. They are available in many variations for metal removal applications that generate considerable heat. Emulsifiable oils offer a number of advantages over straight cutting oils. They provide increased cooling capacity in some applications. They are cleaner to work with than other cutting fluids, and provide cooler and cleaner parts for the machinist to handle. These oils reduce the misting and fogging that are health hazards for machine operators. Because they are diluted with water, they offer increased economy and present no fire hazard. Emulsifiable cutting oils can be used in most light- and moderate-duty machining operations. For economy and best machining results, these oils must be mixed according to the manufacturer’s recommendations. These take into account the material being machined and the machining operation performed. Fluid maintenance must be performed on a routine basis to control rancidity. Water-based cutting fluids must never be used when machining magnesium. Chemical and Semichemical Cutting Fluids Chemical cutting fluids generally contain no oil. They have various rates of dilution depending upon use. A wetting agent is often added to provide moderate lubricating qualities. Semichemical cutting fluids may have a small amount of mineral oil added to improve the fluid 51 lubricating qualities. Semichemical cutting fluid’s incorporate the best qualities of both chemical and emulsifiable cutting fluids. Chemical and Semichemical cutting fluids offer the following advantages: Fluids dissipate heat rapidly. They are clean to use. After machining, residue is easy to remove. The fluids are easy to mix and do not become rancid. Their disadvantages are: Some formulas have minimal lubricating qualities. Fluids may cause skin irritation in some workers. When they become contaminated with other oils, disposal can be a problem. Gaseous Fluids Compressed air is the most commonly used gaseous fluid coolant. It cools by forced convection In addition to cooling the workpiece and tool, compressed air also blows chips away at high velocity. Workers in surrounding areas must be shielded from the flying chips. Application of Cutting Fluids Machining and grinding applications require continuous flooding of fluid around the cutting tool and work to provide efficient removal of the heat generated. Coolant nozzles must be positioned carefully so that, in addition to cooling the work area, the cutting fluid will also carry the chips away. In some machining operations, a conveyor system is used to remove chips and cutting fluid from the cutting area. The cutting fluid is filtered to remove contaminants and is returned to the machine’s coolant tank for reuse. Evaluation of Cutting Fluids It is not possible in this text’s limited space to -over all cutting fluids, nor does space permit recommending specific cutting fluids for every machining operation. This information can be obtained from data published by cutting fluid manufacturers. Recommendations for cutting fluid use are included in the chapters of this text dealing with each type of machine tool. In general, however, cutting fluids (gaseous fluids excepted) are compatible with HSS (high-speed steel) and carbide tooling. Since carbide tooling operates at higher cutting speeds and generates higher cutting temperatures, cutting fluids that have high cooling rates should be used in such applications. Machining with ceramic tooling is usually accomplished without the use of cutting fluids. |
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