Environmental Hazards of Nontraditional Machining - wseas.us

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

not lead to environmental hazards of a different nature. Most machining processes uses chemicals and liquids in different as shown in Table 1. Most of machining liquids come from petroleum which is toxic to environment and difficult to dispose. These chemicals can be transported by a variety of agents and in a variety of forms which are defined by Hughes et al [3]. Hazardous substances cause ill health to people at work. These are classified according to their severity and type of hazard which they may present to the workers. The effect of the hazards may be acute of short duration and appear fairly rapidly, or a chronic one caused by prolonged or repeated exposures to hazardous substances resulting from the machining processes.

1 Introduction The increasing sensitivity to environment and health issues is reflected in the increasing stringent legislations and national and international standards. Scientists and engineers developed new and alternative manufacturing technologies [1]. Machining processes generate solid, liquid or gaseous by-products that present hazards for workers, machine, and the environment. It is appropriate to understand the environmental hazards created by the NTM processes and analyze their impacts on the environment. These hazards can be considered within acceptable limits through the following steps: • Reduction of emissions to air, water, and land. • Compliance with relevant legislations • Pollution prevention. • Efficient use of energy.

2 Nontraditional Machining Processes NTM processes generate solid, liquid or gaseous by-products that cause hazards for the workers, environment, and the equipment [4]. In this paper, the sort and level of the hazardous substances for the NTM methods are discussed. Table 2 summarizes the possible hazards of machining processes.

In order to improve the quality of the machining processes, it is essential to adopt innovative methods that achieve the minimum environmental contamination through the application of near net shape technology that reduces machining allowance, volumes of cutting fluids, and provides lower power requirements. One of the possibilities for minimizing environmental contamination is to implement dry or machining [2] or replace the conventional processes with alternative ones (rapid prototyping, laser machining, new cutting tool materials,.. etc). These new technologies do

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2.1 Chemical Machining (CHM) CHM, Figure 1, depends on chemical acids that have severe effects on the surrounding environment, difficulties in handling and storage, and damaging effect on different materials.. The acidity of an etchant dissolved in water is commonly measured by the pH

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contaminated due to alkalinity and at pH 10 to 12 it may be classified as heavily contaminated. Aerosols of solid (Nitrogen and sulfuric oxides) or liquid corrosive substances are air pollutants, and so form corrosive gases. These gases may combine with water to form acids which precipitate with rain. Acid gases and acid fumes damage plants.

number. Solutions with pH values of less than 7 are described as being acidic. Acid deposition attacks structures that are made from steel and fading paint on machine tools. Chemical acids also cause significant corrosion of metals. Photochemical machining (PCM) is carried out with aqueous solutions of ferric chloride FeCl3, used at temperatures over 50 °C. FeCl3 is acidic, relatively cheap, and readily available, and versatile. Environmentally, it is attractive as it is of low toxicity and relatively easy to filter, replenish and recycle. During CHM, exposure to hafnium (Hf) occurs through inhalation, ingestion, and eye or skin contact. CHM hazards depend on the properties of the substance, the concentration, and time of contact with acids and alkalis. The impacts of CHM include the following:

2.2 Electrochemical Machining (ECM) ECM, Figure 2 is known as an environmental polluting process. Hazards of ECM include: Hydrogen gas: Explosive hydrogen gas is generated during the electrolyzing process H2O + 2e- ==> H2 + 2OHFe + 2H2O ==> Fe(OH)2 + H2 Local exhaust must be provided to prevent the hydrogen gas from reaching its lower flammability limit and remove the mists from the workers breathing zone. Electrolyte splash: Electrolytes are aqueous solutions of sodium chloride, sodium nitrate, and other salts that become insoluble hydroxides that deposit out of the solution as a sludge. Skin contact with the electrolyte contents must be controlled by good work practices. The door/cover shall be interlocked with the electrolyte supply system and the machining process should not be started when the interlock of the safeguarding device is opened. Chromate: Exposure to trivalent chromium compounds occurs through inhalation, ingestion, and eye or skin contact. This affects the skin, liver, and kidneys in humans and causes contact dermatitis. Nitrate: Nitrates and nitrites are known to cause several health effects such as: • Reactions with hemoglobin in blood • Decreased functioning of the thyroid gland • Shortages of vitamin A • Fashioning of nitrosamines, which a common causes of cancer (nitrates and nitrites) Methods that is effective in controlling worker exposures to nitrogen and trivalent chromium include the use of process enclosure, local

Labor: CHM causes health effects on labor which include: • Irritation • Corrosive injuries and burns • Rapid, severe, and often irreversible damage of the eyes • Risk of larynx and lung cancer Machine: Many metals are often affected by corrosion of many types that include localized attack and uniform corrosion. Traditionally, covering materials (e.g. paints) has been used to protect iron and steel from rusting.. Poor surface preparation is the prime cause of protective coating failure. Environment: Improper disposal of CHM etchants changes the level of acidity and alkalinity affect the flora and fauna in soil and water. The change of pH from 7 (neutral water) has an adverse effect on aquatic life. At pH 6 crustaceans and mollusks start to disappear and moss increases. At pH 5.5, some fish such as salmon, trout, and whitefish start to die and salamander eggs fail to hatch. Acidity of pH 4 has a lethal effect on crickets and frogs. Some alkalis such as ammonia also have an acute toxic effect on fish. Soil: It is classified as contaminated when, due to acidity, it has a pH value of 4 to 5 and heavily contaminated when the pH is 2 to 4. When soil has a pH value of 9 to 10 it is

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nitrous oxide, ozone, and harmful aerosols are formed. There is an increasing demand for exploring methods that reduce or eliminate the adverse effect of the working fluid dielectric of EDM.

exhaust ventilation, general dilution ventilation, and personal protective equipment 2.3 Electrodischarge Machining (EDM) During EDM the work material is removed by a series of sparks that occur in the dielectric liquid filling the gap between the tool-electrode and workpiece, Figure 3. EDM has several hazard potentials which are: • Hazardous smoke, vapors, and aerosols • Decomposition products and heavy metals • Hydrocarbon dielectrics affect the skin. • Sharp-edge metallic particles damages the skin • Possible fire hazard and explosions • Electromagnetic radiation

Due to erosion of the workpiece and tool electrodes, inorganic substances such as tungsten carbide, titanium carbide, chromium, nickel, molybdenum, and barium are released and condensate in the air. Emissions of organic materials are generated by the vaporization of the dielectrics. Additionally, the rising smoke carries organic components from substances in the dielectric liquid. The erosion slurry contains eroded workpiece and tool material and solid decomposition products of the dielectric.

Die sinking generates more fumes and aerosols than wire EDM Material composition that contain toxic or health attacking substances such as nickel Dielectric type, composition, and viscosity influence the fume and vapor. Lower viscosity produces less fumes and vapors. The level of the dielectric over the erosion spot condenses and absorbs a considerable part of the vapor and fumes in the dielectric itself. (80 mm is recommended).

Protective measures: In order to reduce the possible hazards that may arise due machining by EDM, the following measures should be strictly followed: • Reduce air pollution to the permissible extent using suitable filters • Incorporate a dielectric cleaning and recalculating system • Keep the temperature of the media at 15oC blow flashing • Reduce the emitted electromagnetic radiation by proper shielding of the machine • Reduce the possibility of fire hazard • Use level sensors for the dielectric level • Avoid dielectrics with flashing point of 65oC • Apply a suitable disposal of the wastes • Raise the operator awareness to the risk of high voltage to avoid severe injury or even death

During EDM using mineral oils or organic dielectric fluids generates hazardous fumes such as polycyclic aromatic hydrocarbons (PAH), benzene, vapor of mineral oil, mineral aerosols, and other products are generated by dissociation of oil and its additives. Hydrocarbon dielectrics, generate the same vapors and aerosols except PAH and benzene. Fore water based solvents, normally used in wire EDM, carbon monoxide,

2.4 Laser Beam Machining (LBM) During machining by lasers, the material is heated, partly vaporized, and chemically transformed, Figure 4. The hazardous materials have the consistency of gasses or aerosols. During laser machining of thermoplastics Toenshoff et al [5] reported that 99% of the particles generated have a diameter less than 10 µm and more than 90% are smaller than 1µm.

In EDM, the total aerosols and vapor concentrations exceed the limits of 5 mg/m3 if no protective measures are taken. Fumes, vapors, and aerosols depend on the material removal process, the dielectric, and the work material. In this regard: • • •

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Most particles are in the range of 0.03 µm to 0.5 µm. High alloyed steels emit 4 to 5 times more aerosols than carbon steel. Almost all particles generated by LBM have a diameter in the range of 0.042 µm to 0.35 µm. The hazard potential is influenced by power density, wave length, exposure time of radiation and if LB is visible or invisible Skin hazards: Repeated or even a single، exposure to certain laser wavelengths causes skin damage of varying degrees more than other parts of the body. Eye hazards: Eye injuries are caused by thermal or photochemical mechanisms that occur when a laser beam interacts with the eye. If the beam enters the eye, its energy is concentrated by the lens of the eye about 100,000 times at the retina. Therefore, a small amount of laser light causes damage. Laser beam machining protective measures are as follows:

Labels and signs that give notice of lasers operating in a given area. Protective equipment: Such as barriers or curtains, clothing, or eyewear should be used if the other control measures do not provide adequate protection. Administrative and procedural controls: Consist of a series of rules, regulations that are designed to minimize the risk of laser beam exposure. One of the most effective administrative controls is the training. 2.5 Ultrasonic Machining (USM) USM, Figure 5, is the removal of hard and brittle materials using an axially oscillating tool at ultrasonic frequency (18-20 kHz). During that oscillation, the abrasive slurry of B4C, Al2O3 or SiC (100 – 800 grit) is continuously fed into the machining zone, between a soft tool (brass or steel) and the hard and brittle workpiece. The process finds applications when machining ceramics, glass, and carbides. However, it has many environmental and health hazards that include the electromagnetic field, ultrasonic wave and abrasive slurry.

Regulations: The principal American National Standards Institute (ANSI), ANSI Z136.1, provides requirements and recommendations for the safe use of lasers in typical industrial and research environments. Laser hazard zones: This is achieved by determining the nominal hazard zone (NHZ), defined as the space within which the level of direct, reflected, or scattered radiation exceeds the level of the applicable maximum permissible exposure (MPE). Beam path controls: Unless they are totally enclosed, interlocked, and there is no beam access during normal system operation. Controlled area: A laser controlled area is required during periods of service a temporary controlled area may be established. Engineering controls: Engineering controls are features designed into the laser machine to minimize the risk of exposure to hazardous beams. The most common engineering controls are: • Protective housings and enclosures that cover the equipment or the beam path • Interlocks are often placed on the protective housings so that if they are removed, the beam is shut off. • Beam stops that provide safe termination of the beam path.

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Electromagnetic field: The effects of the electromagnetic field (EMF) on the health of individuals are of concern to some people. Individuals are advised to stay away from the EMF sources, the strength of which drops quickly just few feet from the source. Ultrasonic noise: Ultrasonic frequencies have been found to produce sound in the audible range from 96-105 dB, although it may not appear noisy to older persons and those with imperfect hearing. Excessive noise levels can be reduced usually by enclosures, and thin layers of common material that gives adequate acoustic insulation at upper audible (and ultrasonic) frequencies. Alternatively, ear protectors can be provided and used. Ultrasound is high-frequency sound that is inaudible, or cannot be heard, by the human ear. However, it may still affect hearing and produce other health effects that include noise-induced temporary threshold shift, noise-induced permanent threshold shift, acoustic trauma, and tinnitus. Other communication and performance

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which are too heavy to be inhaled and captured by the respiratory system to very small particles of respirable size. Silica dust is a major hazard in AJM, generated when the abrasive medium or the cut material contains silica. The major risk from silica dust is silicosis which causes stiffening and scarring of the lung. Symptoms include shortness of breath, coughing and chest pain. This leads to degeneration in the individual’s health and an increased risk of lung cancer. Measures to control silica dust generated include using a jet machining medium which does not contain silica, and ensuring the process is isolated or appropriate administrative strategies are implemented. Operators must wear personal protective equipment and abrasive water jet machining techniques must be used. AJ equipment must be isolated. Dust must be cleaned and collected in an appropriate manner. Methods of cleaning include the wetting down of dust prior to cleanup. Hazardous impacts associated with AJM include:

effects may include isolation, annoyance, difficulty concentrating, absenteeism, and accidents. Additionally, it may cause stress, muscle tension, ulcers, increased blood pressure, and hypertension. Abrasives slurry: Slurry fluids are important causes of occupational contact dermatitis, which may involve either irritant or allergic mechanisms. Mist is generated by the spray from the slurry application. Small droplets may be suspended in the air for several hours or several days possibly in the workers breathing zones. Inhaled particles (with aerodynamic diameters less than 10 µ m) deposit in the various regions of the respiratory system. One acute effect observed is mild and reversible narrowing of airways during exposure to the slurry mist causing chronic bronchitis, asthma and even laryngeal cancer. The OSHA standard for airborne particulate (largely due to fluid mist) is 5 mg/cubic meter, and the United Auto Workers (UAW) has proposed a reduction in the standard to 0.5 mg/cubic meter. Mist can be reduced by adding anti misting compounds to the cutting fluids and using mist collector to prevent mist from entering plant air. Contact hazards: If fingers or hands are put into a ultrasonic machine, a tickling sensation is instantly experienced on the skin surface followed 2-3 seconds later by pain in the joints. Other hazards: Effects such as nausea, dizziness, tiredness and tinnitus can be caused by exposure to sound in the ultrasonic frequencies.

Worker: In addition to the health hazards, generated by the dusty environment, the worker's productivity will be decreased, high physical/mental fatigue, low job satisfaction, and high error rates are possible. Workers are advised to use suitable wearing and safety tools Product: In the dusty atmosphere, the abrasives are imbeded in the work surface thus leading to low product quality. Workplace: Producing dusty air make problems in other machines in the same station. Workplace condition improvement can be achieved through good ventilation, implementing air filtration system, and using a suitable dust collection system.

2.6 Abrasive Jet Machining (AJM) The prime hazard in AJM, Figure 6, is the silica dust. Particles of other cut toxic materials such as lead, mercury, arsenic, zinc and cadmium, may constitute a significant hazard. Workers are provided with appropriate respiratory protective equipment against atmospheres containing substances which are harmful if breathed. Risk factors with dust include the type of particulate involved and its biological effect, concentration of airborne particulate in the breathing zone of the work, the size of the particles present in the breathing zone, the duration of exposure. Generally the dust contains a wide range of particles of different sizes including particles

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3-Conclusions Environmental and health hazards are associated with the use of NTM techniques. Such hazards have a direct impact on the workers in the field. Some processes may affect the machines used and product quality. Machinists should be aware of the type of each hazard, its level, and moreover the necessary precautions

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References: [1]G. Byrne and E. Scholta Environmentally Clean Machining Processes- A Strategic Approach, CIRP Annals, V 42/1,1993, 471-474. [2] K. Weinert, I. Inasaki, J. W. Sutherland, and T. Wakabyashi Dry Machining and Minimum Quantity Lubrication, CIRP Annals, V. 53/2, 2004, 17 p [4] Phil Hughes and Ed. Ferrett Introduction to Health and Safety at Work, Elsevier, 2nd Edition, 2005 [5]Helmi Youssef and Hassan El-Hofy Machining Technology, machine tools and operations, CRC Press, Taylor and Francis Group, USA, 2008 [6] H. K. Toenshoff, R. Egger, and F. Klocke Environmental and safety aspects of Electrophysical and Electrochemical Processes, CIRP Annals, V 45/2, 1996, pp 553-567

Figure 4 Laser beam machining

Figure 5 Ultrasonic machining

Figure 6 Abrasive jet machining Table 1 Machining liquids Liquid/ medium Etchants Electrolytes Dielectric liquids Demonized water Abrasive slurry Air + abrasives

Figure 1 Chemical Machining

Application Chemical machining Electrochemical machining Electrodischarge machining EDM wire cutting Ultrasonic machining Abrasive jet machining

Figure 3 Electrodischarge machining

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X X X

X X

X

X

X

X

X

Magnetic field

Vibrations

Noise

X X X

Electrolyte, Etchant

X X X X

Mist

Liquids

Dust X X

Gas

CHM ECM EDM LBM USM AJM WJM

Chips

Process

Figure 2 Electrochemical machining

Slurry, Dielectric

Table 2 Hazardous materials of NTM processes

X X X X X

X X X

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X X