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Environmental Hazards of Nontraditional Machining

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Environmental Hazards of Nontraditional Machining Proceedings of the 4th IASME / WSEAS International Conference on ENERGY & ENVIRONMENT (EE'09) Environmental Hazards of Nontraditional Machining H. El-Hofy and H. Youssef Production Engineering Department Faculty of Engineering, Alexandria University EGYPT [email protected], [email protected] Abstract: - This paper discusses the environmental impacts generated by some nontraditional machining processes. For each case the mechanism of material removal is explained. Sources of hazards are discussed. Environmental impacts on the workers, machines, air, soil, are discussed. Safety and environmental precautions are also considered Key-Words: - Nontraditional machining (NTM), chemical, electrochemical machining (ECM) , thermal, ultrasonic machining (USM), laser beam machining (LBM), abrasive jet machining (AJM), health hazards 1 Introduction not lead to environmental hazards of a different The increasing sensitivity to environment and nature. Most machining processes uses health issues is reflected in the increasing chemicals and liquids in different as shown in stringent legislations and national and Table 1. Most of machining liquids come from international standards. Scientists and engineers petroleum which is toxic to environment and developed new and alternative manufacturing difficult to dispose. These chemicals can be technologies [1]. Machining processes generate transported by a variety of agents and in a solid, liquid or gaseous by-products that present variety of forms which are defined by Hughes et hazards for workers, machine, and the al [3]. Hazardous substances cause ill health to environment. It is appropriate to understand the people at work. These are classified according environmental hazards created by the NTM to their severity and type of hazard which they processes and analyze their impacts on the may present to the workers. The effect of the environment. These hazards can be considered hazards may be acute of short duration and within acceptable limits through the following appear fairly rapidly, or a chronic one caused by steps: prolonged or repeated exposures to hazardous • Reduction of emissions to air, water, and substances resulting from the machining land. processes. • Compliance with relevant legislations • Pollution prevention. 2 Nontraditional Machining Processes • Efficient use of energy. NTM processes generate solid, liquid or gaseous by-products that cause hazards for the In order to improve the quality of the machining workers, environment, and the equipment [4]. In processes, it is essential to adopt innovative this paper, the sort and level of the hazardous methods that achieve the minimum substances for the NTM methods are discussed. environmental contamination through the Table 2 summarizes the possible hazards of application of near net shape technology that machining processes. reduces machining allowance, volumes of cutting fluids, and provides lower power 2.1 Chemical Machining (CHM) requirements. One of the possibilities for CHM, Figure 1, depends on chemical acids that minimizing environmental contamination is to have severe effects on the surrounding implement dry or machining [2] or replace the environment, difficulties in handling and conventional processes with alternative ones storage, and damaging effect on different (rapid prototyping, laser machining, new cutting materials.. The acidity of an etchant dissolved in tool materials,.. etc). These new technologies do water is commonly measured by the pH ISSN: 1790-5095 140 ISBN: 978-960-474-055-0 Proceedings of the 4th IASME / WSEAS International Conference on ENERGY & ENVIRONMENT (EE'09) number. Solutions with pH values of less than 7 contaminated due to alkalinity and at pH 10 to are described as being acidic. Acid deposition 12 it may be classified as heavily contaminated. attacks structures that are made from steel and Aerosols of solid (Nitrogen and sulfuric oxides) fading paint on machine tools. Chemical acids or liquid corrosive substances are air pollutants, also cause significant corrosion of metals. and so form corrosive gases. These gases may Photochemical machining (PCM) is carried out combine with water to form acids which with aqueous solutions of ferric chloride FeCl3, precipitate with rain. Acid gases and acid used at temperatures over 50 °C. FeCl3 is acidic, fumes damage plants. relatively cheap, and readily available, and versatile. Environmentally, it is attractive as it is 2.2 Electrochemical Machining (ECM) of low toxicity and relatively easy to filter, ECM, Figure 2 is known as an environmental replenish and recycle. During CHM, exposure polluting process. Hazards of ECM include: to hafnium (Hf) occurs through inhalation, ingestion, and eye or skin contact. CHM Hydrogen gas: Explosive hydrogen gas is hazards depend on the properties of the generated during the electrolyzing process - - substance, the concentration, and time of H2O + 2e ==> H2 + 2OH contact with acids and alkalis. The impacts of Fe + 2H2O ==> Fe(OH)2 + H2 CHM include the following: Local exhaust must be provided to prevent the hydrogen gas from reaching its lower Labor: CHM causes health effects on labor flammability limit and remove the mists from which include: the workers breathing zone. • Irritation Electrolyte splash: Electrolytes are aqueous • Corrosive injuries and burns solutions of sodium chloride, sodium nitrate, • Rapid, severe, and often irreversible and other salts that become insoluble damage of the eyes hydroxides that deposit out of the solution as a • Risk of larynx and lung cancer sludge. Skin contact with the electrolyte Machine: Many metals are often affected by contents must be controlled by good work corrosion of many types that include localized practices. The door/cover shall be interlocked attack and uniform corrosion. Traditionally, with the electrolyte supply system and the covering materials (e.g. paints) has been used to machining process should not be started when protect iron and steel from rusting.. Poor surface the interlock of the safeguarding device is preparation is the prime cause of protective opened. coating failure. Chromate: Exposure to trivalent chromium Environment: Improper disposal of CHM compounds occurs through inhalation, etchants changes the level of acidity and ingestion, and eye or skin contact. This affects alkalinity affect the flora and fauna in soil and the skin, liver, and kidneys in humans and water. The change of pH from 7 (neutral water) causes contact dermatitis. has an adverse effect on aquatic life. At pH 6 Nitrate: Nitrates and nitrites are known to cause crustaceans and mollusks start to disappear and several health effects such as: moss increases. At pH 5.5, some fish such as • Reactions with hemoglobin in blood salmon, trout, and whitefish start to die and • Decreased functioning of the thyroid salamander eggs fail to hatch. Acidity of pH 4 gland has a lethal effect on crickets and frogs. Some • Shortages of vitamin A alkalis such as ammonia also have an acute • Fashioning of nitrosamines, which a toxic effect on fish. common causes of cancer (nitrates and nitrites) Soil: It is classified as contaminated when, due Methods that is effective in controlling worker to acidity, it has a pH value of 4 to 5 and exposures to nitrogen and trivalent chromium heavily contaminated when the pH is 2 to 4. include the use of process enclosure, local When soil has a pH value of 9 to 10 it is ISSN: 1790-5095 141 ISBN: 978-960-474-055-0 Proceedings of the 4th IASME / WSEAS International Conference on ENERGY & ENVIRONMENT (EE'09) exhaust ventilation, general dilution ventilation, nitrous oxide, ozone, and harmful aerosols are and personal protective equipment formed. There is an increasing demand for exploring methods that reduce or eliminate the 2.3 Electrodischarge Machining (EDM) adverse effect of the working fluid dielectric of During EDM the work material is removed by a EDM. series of sparks that occur in the dielectric liquid filling the gap between the tool-electrode Due to erosion of the workpiece and tool and workpiece, Figure 3. EDM has several electrodes, inorganic substances such as hazard potentials which are: tungsten carbide, titanium carbide, chromium, • Hazardous smoke, vapors, and aerosols nickel, molybdenum, and barium are released • Decomposition products and heavy and condensate in the air. Emissions of organic metals materials are generated by the vaporization of • Hydrocarbon dielectrics affect the skin. the dielectrics. Additionally, the rising smoke • Sharp-edge metallic particles damages carries organic components from substances in the skin the dielectric liquid. The erosion slurry contains • Possible fire hazard and explosions eroded workpiece and tool material and solid • Electromagnetic radiation decomposition products of the dielectric. In EDM, the total aerosols and vapor Protective measures: In order to reduce the concentrations exceed the limits of 5 mg/m3 if possible hazards that may arise due machining no protective measures are taken. Fumes, by EDM, the following measures should be vapors, and aerosols depend on the material strictly followed: removal process, the dielectric, and the work • Reduce air pollution to the permissible material. In this regard: extent using suitable filters • Incorporate a dielectric cleaning and • Die sinking generates more fumes and recalculating system aerosols than wire EDM • Keep the temperature of the media at o • Material composition that contain toxic 15 C blow flashing or health attacking substances such as • Reduce
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