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Pub Health 4310 Health Hazards in Industry

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Title: Pub Health 4310 Health Hazards in Industry


1
Pub Health 4310Health Hazards in Industry
  • John Flores
  • Lecture 15
  • Metal Fabrication

2
Lecture 15Metals Fabrication
  • Chapters 7-12
  • Metals Fabrication
  • Forging
  • Foundry Operations
  • Metal Machining
  • Welding
  • Heat Treating
  • Nondestructive Testing

3
Metals Fabrication Metal Machining
  • Introduction
  • Metal machining is the fabrication of metal parts
    from solid stock
  • Machining is done a variety of ways, but since
    all associated occupational hazards are similar,
    focus will be on conventional machining
  • 5 special machining techniques will be discussed
    in further detail
  • Electrochemical machining, electrical discharge
    machining, hard metal tool grinding, laser
    cutting, and water jet cutting
  • Major occupational health issues associated with
    metal machining are attributable to machining
    fluids causing health hazards through dermal
    contact and inhalation exposures
  • The association between skin contact with mineral
    oil-based machining fluids and squamous cell
    carcinoma was described in the UK in the 1800s
  • Mineral oil was classified as a carcinogen by
    IARC in 1987
  • Eisen et al. (1982) showed a twofold excess of
    larynx cancer for machinists exposed to mineral
    oil based machining fluids
  • There have also been increased digestive tract
    cancers in machinists using machining fluids
  • Bronchitis and asthma are also associated with
    inhalation exposures to machining fluid aerosols
  • The most common occupational disease in metal
    machining is dermatoses from skin contact with
    machining fluids, and will affect one in three
    machinists each year.
  • Machining of specialized metals such as beryllium
    can create additional hazards to protect against

4
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice
  • All dimensional machining operations are done by
    forcing the point of a cutting tool against a
    work piece in a controlled speed and force
  • The cutting element removes some of the work
    piece by shearing or abrading action
  • The piece comes off as a fine continuous wire
    chip, a heavy short chip, or as individual
    particles
  • Because of extreme temperature and pressure build
    up at the interface of the cutting tool and work
    piece, lubricants are needed to control
    temperature and help flush away particles or
    chips
  • Machining fluid is supplied at the work
    piece/cutting tool interface by a steady stream
    or spray
  • Common groupings of available machining fluids
    are Straight Oil, Emulsified Oil, Synthetic
    Fluid, and Machining Fluid
  • Theses fluids can be oil, soluble oils,
    water-based fluids, synthetic fluids, and
    coolants
  • There are 4 components of machining operations
    which need further discussion in application,
    hazards, and controls
  • The 4 operations are
  • Machine Tools
  • Cutting Tools
  • Work Piece Metal
  • Machining Fluids

5
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Machine Tools
  • A large number of machine tools have been
    designed to accomplish dimensional cutting on a
    range of metals and plastics
  • The principle tools that health and safety person
    should be familiar with are the lathe, the
    milling machine, and the grinder
  • The cutting tool may be fixed and the work piece
    move (lathe),
  • The work piece fixed and the cutting tool move
    across the face of the work piece (milling
    machine), or
  • Both the tool and the workpiece move at high
    speeds (grinding operation)
  • The workpiece may be held in place by an
    adjustable collet or chuck as on a lathe,
    mechanically clamped on the bed of a milling
    machine, or held in place by a magnet on the work
    bed of a surface grinder
  • The cutting tool position, the workpiece speed,
    and the cutting tool speed may be controlled
  • Manually by the machinist,
  • By a numerical control (NC),
  • Or by a computer-assisted numerical control (CNC)
    system

6
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Machine Tools (cont.)
  • Work places may consist of a one-man one
    tool, or a large production area in which one
    worker may tend numerous semi-automatic machine
    tools
  • In old machine shops, machines were belt driven
    from overhead pulleys, but in modern shops each
    tool is driven by its individual motor
  • On a lathe the power train rotates the chuck and
    workpiece
  • On a milling machine (planar) the power is
    delivered to the bed on which the workpiece is
    positioned
  • And for a grinding operations, both the grinding
    wheel and the workpiece bed are powered on
    surface grinders
  • Hazards
  • Noise in small to medium size machine shops can
    be as low as 85 dBA, but in larger machine shops
    or as the density of the tools increases,
    exposures greater than 90 dBA begin to occur
  • The most effective noise control is to specify
    machining tools be at 80 dBA at the operators
    position

7
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Cutting Tools
  • Special alloys have been developed for the
    manufacture of cutting tools, they include
  • High carbon steels with alloying elements of
    vanadium, chromium, and manganese
  • High speed steels containing manganese and
    tungsten
  • Special cobalt steels
  • Cast alloys of tungsten, chromium, and cobalt
    and
  • Tungsten carbide
  • The loss of material from the cutting tool is
    insignificant during conventional machining and
    is not a potential air contaminant
  • On grinding operations, the cutting tools are
    individual grains of abrasive embedded in a
    matrix and can create potential airborne hazards
  • Common abrasives include aluminum oxide, silicon
    carbide, diamonds, and cubic boron nitride
  • During the manufacture of cutting tools, there
    are metal dusts created during grinding and
    dressing operations that can become airborne
    hazards
  • Local exhaust ventilation should be provided

8
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Work Piece Metal
  • Metal machined in industry ranges from mild steel
    (low toxicity) to various high-temperature and
    stainless alloys containing chromium, nickel, and
    cobalt, and highly toxic metals
  • Chromium, nickel, and cobalt can present a health
    hazard depending on the machining technique
  • Highly toxic metals such as beryllium must have
    special controls in place to protect workers from
    exposure
  • Common view by health professionals is that there
    is little exposure to airborne metal
    concentrations when machining mild steel and its
    alloys with cutting tools
  • Explosive concentrations of dusts can be created
    when machining magnesium and titanium requiring
    suitable ventilation control and air cleaning
  • Machining of cast iron does not create hazardous
    dusts, but it does create dust build up if
    housekeeping problems is not prioritized
  • Machining fluids can become contaminated with
    trace quantities of base metals which may lead to
    sensitization of workers to chromium, nickel, and
    cobalt if hands are immersed into or splashed by
    machining fluids

9
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Machine Fluids
  • Machining fluids are designed to cool and
    lubricate the interface between the cutting tool
    and the workpiece, and to flush away metal chips
    or pieces
  • Using the proper machining fluid will extend tool
    life, surface finish, and improve dimensional
    stability of the workpiece during machining
  • Machining fluid composition
  • Fluids are available available in the form of
  • Mineral oils which contain greater than 80
    mineral oils with the balance consisting of
    various additives
  • Emulsified oils consisting of 3-10 mineral oil,
    emulsifiers and other additives, and water
  • Synthetic machining fluids which are based on a
    complex group of water-soluble chemicals that
    result in a fluid that is basically non-corrosive
    fluid with cooling and lubricant properties
  • Semi-synthetic fluids are based on emulsified
    oils with the addition of chemicals used in
    synthetic oils

10
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Machine Fluids (cont.)
  • Exposure Data
  • A series of studies conducted by the UAW-GM
    National Joint Committee on Health and Safety
    (Hallock et al., 1994) showed the following
    results
  • In 3 machining facilities exposures prior to 1970
    had arithmetic mean concentrations of 5.42 mg/m3,
    from 1970 to 1989 the arithmetic mean was 1.82
    mg/m3
  • This reduction is attributable to plant control
    measures such as local exhaust ventilation,
    general exhaust ventilation, air cleaning,
    enclosure of cutting tools, and increased use of
    water based machining fluids
  • To inhibit corrosion and adjust pH, a mixture of
    ethanolamines (EA) are added to most machining
    fluids with the exception of straight mineral
    oils
  • Studies have been conducted to evaluate potential
    exposures, but the data is limited due to MSDS
    information being incomplete, the volatility of
    some of the ethanolamines, and differences in
    machining oils being used.
  • Studies of machining fluids aerosols in an
    automotive transmission plant showed that large
    particles (gt 8um) were created from spraying and
    splashing, and fine aerosols (0.1 1.0um) were
    produced at the cutting point due to shear forces
    and high temperature
  • Depending on the type of machining fluid being
    used anywhere from 19 55 of the aerosol is of
    the respirable fraction

11
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Machine Fluids (cont.)
  • Health Effects
  • Extensive studies have been conducted in 1989 by
    the University of Birmingham in England
  • The majority of occupational dermatitis in
    machinists is due to water based machining
    fluids, including emulsified oils and synthetic
    machining fluids
  • The irritant emulsifiers and the high pH of
    machining fluids seem to account for 7-80 of the
    cases,
  • Sensitization may account for the rest which is
    due to formaldehyde-containing release agents,
    rosin uses as a base for the emulsifier, and
    steel leachates of chromium, nickel, and cobalt
  • Oil based machining fluids can cause folliculitis
    (oil acne) in rare cases, but can be controlled
    with good hygienic measures
  • The three types of machining fluids in descending
    order of the potential to cause dermatitis are
    synthetics, emulsified oil, and mineral oil, in
    descending order to cause skin cancer are mineral
    oil, emulsified oil, and synthetic machining
    fluid
  • Respiratory effects of exposure to machining
    fluids are
  • Inconsistent results in linking respiratory
    cancer with machining fluid exposures
  • Eisen et al. (1994) study showed a two-fold
    excess of larynx cancer in machinist in the
    automotive industry

12
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Machine Fluids (cont.)
  • Health Effects (cont.)
  • Respiratory effects (cont)
  • Machinists are at risk for bronchitis,
    occupational asthma initiated by sensitization to
    machining fluid aerosols.
  • Exposure to mineral oil based mists is not
    believed to cause fibrotic changes in lung tissue
  • Microbial contamination
  • Emulsified oil and synthetic machining fluids
    provide the right environment to promote
    microbial growth
  • Organisms include aerobic bacteria which drop the
    machining fluid pH, anaerobic bacteria which can
    create hydrogen sulfide, yeast, and fungus
  • Although fecal and urinary pathogens have been
    found in machining fluids, this has not been a
    documented source of disease
  • Skin pathogens have not been found to be viable
    in machining fluids
  • Pseudomonas Aeroginosa can be present in high
    concentrations in water-based machining fluids,
    it is a potent producer of endotoxin and has
    become a respiratory concern it also produces
    keratinolase, which softens the skin and may
    promote dermatitis

13
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Control of Exposures to Machining Fluids
  • Machine Design There are 2 types of systems
    that handle machining fluids in the machine shop
  • Small shops have individual systems for each tool
  • Fluid flows from an adjustable nozzle over the
    cutting tool, and drains into a collection pan
  • The collection pan catches metal debris as the
    fluid flows through the pan into a 5-50 gal sump,
    from the sump machining fluids are pumped back up
    to the application nozzle
  • Metal chips are removed by hand by the machinist
  • Due to the small capacity of this system,
    contaminants build up quickly requiring periodic
    maintenance
  • Large facilities use a central system which
    supplies machining fluids to numerous tools
  • The machining fluids are pumped from a large
    reservoir (up to 20,000 gallons) to each
    individual tool providing fluid flow over each
    cutting point, the excess fluid returns to the
    machine tool sump which empties into a trench
    returning the fluid back to the central reservoir
  • A conveyor placed below the tools, removes metal
    chips instead of requiring operator handling
  • The large volume of these systems allows for
    better quality maintenance of the machining
    fluids
  • Mechanical splash guards are designed to keep
    fluids and metal chips inside of the tool
    enclosure
  • Splash guards should be designed to slide out of
    the way for access inside the tool during
    maintenance, and not be of the removable type to
    ensure that they remain in place when tool is in
    use
  • Although enclosure of the tool is effective at
    controlling machining fluid mists, increasing
    fluid flow to maintain low temperatures at the
    cutting point can significantly reduce mist
    generation

14
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Control of Exposures to Machining Fluids (cont.)
  • Machining Fluid Design
  • Emulsifiers are common skin irritants, so
    minimizing the concentration of emulsifiers in
    water-based machining fluids should be a goal
  • Control alkalinity of the fluids, high pH causes
    defatting of the skin and respiratory irritation
  • Be aware that machining fluids containing both
    nitrates and amines have the potential to
    generate carcinogenic nitrosamines
  • Personal Protective Equipment
  • For hands, use PPE as appropriate, gloves may not
    always be safe to use even though they provide a
    protective barrier from the cutting fluids,
    barrier creams are not very effective
  • Use of after work skin conditioning creams are
    only useful if they are consistently used
  • Soaps and cleansers need to be a balance between
    effectiveness and adverse effect on skin
  • To protect against splashing, protective
    coveralls or aprons protect the skin, but may
    create heat stress depending on the materials
    adopted
  • Evaluate the effectiveness of safety glasses or
    goggles against the splash potential of the fluids

15
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Control of Exposures to Machining Fluids (cont.)
  • Work Practice
  • Elimination of machining fluids is the ultimate
    control approach to eliminate mists
  • Some shops now conduct dry machining on cast
    iron, nodular iron, steel, and considering its
    use for other metals
  • Conducting grinding and machining work at the
    lowest speed compatible with production and
    quality minimizes mist generation
  • Installed safeguards including splash guards
    should be used by the machinist
  • Maintain the machining fluid dilution rate as
    recommended by the manufacturer
  • Special attention must be given to add the
    correct concentration of biocide dont overdose
    the fluid

16
Metals Fabrication Metal Machining
  • Conventional Metal Machining Practice (cont.)
  • Control of Exposures to Machining Fluids (cont.)
  • Ventilation
  • Exhaust hoods used to capture metal dust during
    machining include conventional exterior hoods,
    high-velocity-low-volume capture hoods, and
    enclosures
  • Some metals, such as beryllium, require local
    exhaust on all machining operations
  • Use of machining fluids under conditions of high
    load may create machining fluid mists, which
    would then require the use of general or local
    exhaust ventilation
  • If general (dilution) exhaust is used to control
    mists, then the air must be monitored and cleaned
    to ensure it is suitable for circulation
  • When numerically controlled or computer assisted
    numerically controlled systems are used for high
    precision machining on elaborate workpieces, the
    tool may be tested using styrene, urethane, or
    epoxy proofing boards to inexpensively ensure
    that the machine works properly
  • Control of the dusts generated from this
    procedure is necessary to for housekeeping, fire
    protection, and worker health

17
Metals Fabrication Metal Machining
  • Electrochemical Machining (ECM)
  • The ECM process is similar to conventional
    electroplating
  • In electroplating, metal is deposited onto the
    workpiece (cathode) from a solid piece of plating
    stock (anode) utilizing a DC electrolytic bath
    operating at low voltage and high current density
  • In the ECM process, the workpiece is the anode,
    and the cutting tool serves as the cathode
  • Electrolyte is pumped through the space between
    the workpiece and the tool, as DC current flows,
    metal ions are removed from the workpiece and
    swept away by the electrolyte
  • The metal particles react with the electrolyte
    instead of depositing on the cathode (tool)
  • Electrolytes are usually an aqueous solution of
    sodium chloride, sodium nitrate, and other salts
    that become insoluble hydroxides that will
    deposit out of solution as sludge
  • Since the ECM method is fast, produces an
    excellent finish, does not produce burrs, and
    causes little tool wear, it is widely used for
    cutting irregularly shaped holes in hard, tough
    metals
  • Electrolyte from the ECM method releases hydrogen
    at the cathode, and misting results at the bath
    surface
  • The magnitude of this problem depends on the bath
    composition and the power density of the system
  • 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
  • The low DC voltage and high current of the
    equipment will normally not become an electrical
    hazard
  • Skin contact with the bath contents must be
    controlled by good work practices and PPE

18
Metals Fabrication Metal Machining
  • Electrical Discharge Machining (EDM)
  • EDM is a popular machining technique for large
    precise work such as die sinking, or the drilling
    of small holes in complex parts
  • EDM is basically a spark-gap technique which uses
    a graphite tool as the cathode and the workpiece
    as the anode immersed in a dielectric oil bath
    powered by a low-voltage DC power supply.
  • Voltage across the gap increases until breakdown
    occurs and there is a spark discharge across the
    gap which produces high temperature at the
    discharge point eroding a small quantity of metal
    from the workpiece, and is repeated until the
    machining is complete
  • Hazards
  • Dielectric oils represent the bulk of hazards
    associated with EDM
  • Petroleum distillates (e.g. Stoddard Solvent) are
    used for light cutting, while mineral oil is used
    for large projects
  • As dielectric oils get pyrolyzed, they breakdown
    to form hydrogen gas, methane, carbon monoxide,
    and traces of other gases, which are released
    into the workplace air as mists
  • The oil eventually gets contaminated with small
    hollow spheres of the metal being machined which
    can contribute to their ability to cause
    dermatitis
  • Controls
  • Oil mist should be controlled through local
    exhaust ventilation using a partially enclosed
    hoods
  • An ultra high efficiency filter should be placed
    in the oil re-circulating line to remove any
    metal particulate

19
Metals Fabrication Metal Machining
  • Hard Metal Tool and Cutter Grinding
  • Manufacturing Process
  • The cutting tools in metal machining must have a
    hardness that will permit cutting of the
    workpiece, strength to withstand the mechanical
    shock, and the ability to run at high
    temperatures with and without machining fluids
    while maintaining sharpness
  • The most common materials used for cutting tools
    are metal carbides with a cobalt binder
  • The material make up of a typical cutting tool
    is 80 tungsten carbide, 10 other metal
    carbides (e.g. tantalum, chromium, niobium, and
    titanium), and 10 cobalt binder
  • Some applications will substitute a nickel binder
    for the cobalt binder
  • Weighing and blending the cutting tool material
    presents the greatest potential for exposure
    which can be controlled with local exhaust
    ventilation at the workstation
  • Exposure Data
  • Various studies of cutting tool materials show
    cobalt to be the most serious exposure hazard
  • Health Effects
  • A series of papers attributes progressive
    interstitial pulmonary fibrosis in grinding room
    workers exposed to airborne cobalt in excess of
    the TLV
  • Sprince (1992) found that workers who wet/dry
    grind tungsten carbide have a decrease in
    pulmonary function as compared to worker who are
    exposed to the material, but dont grind them
  • The occurrence of asthma in hard metal workers is
    believed to due to true sensitization to cobalt

20
Metals Fabrication Metal Machining
  • Laser and Water Jet Cutting
  • Two new processes for metal cutting are done with
    lasers or a water jet
  • Both systems are being evaluated for numerical
    control systems, since they can be used for both
    plastics and metal and be produced at a high rate
  • Laser cutting
  • The laser system uses a NdYAG laser for copper,
    brass, and aluminum
  • A CO2 laser for steel and other alloy
  • Hazards associated with lasers systems are due to
    the metal fume created during the cutting
    process, these fume can be controlled through
    local exhaust ventilation
  • Water jet cutting
  • Is basically used in the same type of
    applications that a laser system is used
  • Water pressures up to 65,000 psig used in
    conjunction with abrasives such as garnet,
    aluminum oxide, or silicon carbide are able to
    cut up to 1-inch mild steel
  • Principle hazards are contact of the worker with
    the water stream
  • 3 feet from the nozzle the stream is erosive and
    will cause serious injury
  • At the nozzle, the water stream can amputate
    limbs
  • Interestingly, water jet cutting is used in some
    surgical procedures

21
Metals Fabrication Welding
  • Introduction
  • Welding is the process of heating metals to a
    suitable temperature to join them together.
  • In the US it is estimated that there are
  • 185,000 welders, brazers, and cutters
  • 700,000 who weld as part of their job
  • Welding processes can be classed as pressure,
    non-pressure, or brazing
  • Non-pressure welding, which involves the fusing
    (melting) together of metals, is the most
    dominant type of welding and will be discussed in
    detail.
  • In this process metal is vaporized and then
    condensed to form a fume in the 0.01 0.1 um
    particle size range that agglomerates rapidly
  • The fume is made up of the base metal, workpiece
    metal coating, electrode, and the fluxing agents
  • Welding also forms a range of gases and vapors,
    and can include ozone and nitrogen dioxide
  • Electromagnetic radiation is generated during
    welding with varied intensity dependant on the
    process
  • Disease or Injury associated with Welding
  • IARC has classed welding fume as a Group 2A
    carcinogen, meaning its a possible human
    carcinogen
  • A number of studies have shown pulmonary disease,
    small airway disease, chronic bronchitis, and
    x-ray abnormalities
  • Reduced sperm count has been found in welders
  • Acute conditions include pulmonary edema from
    confined spaces, photokeratitis from UV exposure
    to the unprotected eye, and metal fume fever from
    welding and cutting copper and zinc coated metals

22
Metals Fabrication Welding
  • Shielded Metal Arc Welding SMA Welding
  • Shielded metal arc welding also known as stick
    or electrode welding is the most common type of
    non-pressure welding
  • Process
  • An electric arc is drawn between the welding rod
    and the workpiece which melts the metal and
    electrode
  • The molten metal forms a common puddle, which
    cools together to form the weld
  • Slag forms at the surface of the weldment from
    the flux and other metal impurities and is
    removed from the weldment either manually or with
    a pneumatic chipper
  • AC or DC power is used straight (electrode
    negative, workpiece positive) or reverse polarity
  • The electrodes contain the same basic metal as
    the parent alloy and are of 3 basic coating
    types
  • Cellulosic TiO2, sand, and magnesium silicate
  • Rutile TiO2, CaCO3, and cellulose
  • Basic high content of calcium carbonate or
    fluoride
  • The principle function of the electrode coating
    is to release a shielding gas such as CO2 to
    insure that air does not enter the arc puddle
    which weakens the weld
  • The coating also stabalizes the arc, provides a
    flux and slag producer to remove oxygen from the
    weld, adds alloying metal to the weld, and
    controls the viscosity of the molten metal
  • The composition of the electrode and coating is
    listed through and AWS classification number that
    is stamped onto the electrode

23
Metals Fabrication Welding
  • Shielded Metal Arc Welding SMS Welding (cont.)
  • The potential health hazards associated with
    metal fume from shielded metal arc welding
    depends on the metal being welded and the
    composition of the welding electrode
  • Exposure Profile
  • Metal Fumes
  • The principle component of the metal fumes from
    mild steel welding is iron oxide, which can
    deposit in the lungs to cause a benign condition
    called siderosis
  • Siderosis does not cause any functional
    impairment or the development of fibrous tissue
  • A study by Stokinger in 1984 concluded that iron
    oxide is not carcinogenic to humans
  • The concentration of metal fume exposure depends
    on the composition of the parent metal, the
    electrode, the current density, the wire feed
    rate, the arc time, the power configuration (ac
    or dc), and the polarity (straight or reversed)
  • Other contributors to metal fume exposure include
    the ventilation rate, indoor or outdoor work, or
    whether the work is done in an enclosure such as
    a confined space
  • Welding fume sampling can be done with air and
    biological sampling (urinary)
  • Welding fume samples consist mostly of iron
    oxides, manganese, zinc, and occasionally lead
  • Some alloys of steel can produce nickel,
    chromium, molybdenum and copper oxides, and
    fluorides

24
Metals Fabrication Welding
  • Shielded Metal Arc Welding SMA Welding (cont.)
  • Exposure Profile (cont.)
  • Gases and Vapors
  • Some gases and vapors produced during welding
    include nitrogen dioxide, carbon monoxide,
    carbon dioxide, acrolein, and ozone
  • Contaminants are usually at low concentrations,
    unless work being done in an enclosed or confined
    space
  • Radiation
  • Radiation generated by shielded metal arc
    welding exposes the worker to wavelengths from
    IR-C to UV-C
  • To date there has been no evidence of IR
    radiation causing damage from SMA welding
  • The acute exposure to arc welding called arc
    eye, sand in the eye, or flash burn is
    caused by exposure to the UV-B radiation range
    because the corneal epithelium completely absorbs
    this range causing severe photokeratitis in about
    5-6 hrs after exposure, and will clear up in
    about 24 hrs (very painful)
  • SMA welding can cause skin erythema due to
    exposure to the UV-C and UV-B ranges
  • Magnetic radiation can be generated by a 60-Hz
    welding generator can create up to 2-200 uT
    (micro Tesla), while current pulses up to 100,000
    amps can produce fields of up to 10,000 uT at 0.2
    1.0 meters from the welding transformer cables

25
Metals Fabrication Welding
  • Gas Tungsten Arc Welding
  • To weld aluminum, magnesium and other reactive
    metals an inert gas is added to the arc
    environment to prevent oxygen and hydrogen from
    entering the weld
  • Process
  • In gas tungsten arc welding, the arc is
    established between a non-consumable tungsten
    electrode and the workpiece to create heat which
    melts the metal edges together
  • Argon or helium is then added around the
    electrode to maintain an inert environment
  • The gas tungsten arc welding technique is used
    for aluminum and magnesium, but is also used for
    welding stainless steel, nickel alloys,
    copper-nickel brasses, silver bronze, and other
    low alloy steels
  • Exposure Profile
  • Welding fume concentrations in gas tungsten arc
    welding are lower than in manual stick welding
    and gas metal arc welding
  • However the inert gas technique produces
    electromagnetic energy an order of magnitude
    greater than shielded arc welding
  • The energy in the UV-B and UV-C ranges,
    especially at 270 nm region, are the most
    biologically effective radiation and will produce
    skin erythema and photokerititis
  • At 200 nm (UV-C) oxygen can be converted into
    ozone
  • To evaluate gas tungsten arc welding exposures,
    air sampling for ozone and nitrogen oxide would
    be required

26
Metals Fabrication Welding
  • Gas Metal Arc Welding - GMA
  • Gas Metal Arc Welding is more commonly known as
    Metal Inert Gas (MIG) Welding
  • Process
  • The welding torch has a center consumable wire
    fed from a reel or spool that maintains the arc
    as it melts into the weld puddle
  • A flow of gas is maintained around the consumable
    electrode, the gas is usually helium, argon,
    carbon dioxide, nitrogen, or a blend of these
  • The wire electrode is similar to the base metal
    being welded
  • It often has a flash coating of copper to insure
    electrical contact and to prevent rusting
  • Some wire contains fillers to help deoxidize the
    weld
  • Manganese, silicon, and aluminum are used in
    steel filler wire,
  • Titanium and silicon are used in nickel alloy
    wire, and
  • Titanium, silicon, and phosphorus are used in
    copper alloy wire
  • The use of flux-cored consumable electrodes have
    have improved Gas Metal Arc Welding
  • The electrode is a hollow wire with the core
    filled with various deoxidizers, fluxing agents,
    and metal powders
  • Sometimes the flux core creates an inert gas
    shield for the weld, this type of process is
    called self-shielding
  • Because there is no slag created by the Gas Metal
    Arc (GMA) Welding, the duty cycle is much higher
    than Shielded Metal Arc (SMA) Welding

27
Metals Fabrication Welding
  • Gas Metal Arc Welding GMA (cont.)
  • Exposure Profile
  • Gas Metal Arc (GMA)Welding produces higher
    concentrations of ozone than Shielded Metal Arc
    (SMA) Welding
  • The arc length and inert gas flow rate do not
    impact ozone generation rate
  • Ozone generation rate is the highest when GMA
    welding of aluminum-silica alloys
  • Nitrogen dioxide concentration are about the same
    as SMA
  • Iron oxide fume is generally less than SMA
  • When CO2 is used, depending on the current
    density, the gas flow rate, and the base metal,
    significant concentrations of CO can be generated
  • With reasonable ventilation, hazardous CO
    concentrations should not be present in the
    breathing zone
  • Radiation hazards in GMA can be an order of
    magnitude more than SMA
  • Radiation source is UV-C and UV-B
  • UV emissions from GMA can breakdown chlorinated
    hydrocarbons vapors, such as trichloroethylene,
    into chlorine, hydrogen chloride, and phosgene
  • Dilution ventilation or local ventilation
    generally control concentrations within
    acceptable levels

28
Metals Fabrication Welding
  • Submerged Arc Welding - SAW
  • The arc is shielded from the atmosphere by
    covering the weld with a granular, fusible flux
  • Process
  • The arc is conducted through a filler metal which
    is usually a bare wire electrode, the granular
    flux is fed onto the metal ahead of the arc path,
    which sinters to form a molten slag cover over
    the weld metal
  • The flux shields the arc, adds alloy metal,
    stabilizes the arc, and defines the weld bead
    shape
  • This technique is used is used in either a semi-
    or fully-automated mode for welding thick
    sections on plain carbon and low-alloy steel
  • Exposure Profile
  • Metal fume concentration is much lower for SAW,
    than it is for SMA or GMA welding because of the
    blanketing action of the flux
  • Hydrogen fluoride and soluble fluoride
    particulates released from the welding flux are
    the principle exposures of concern
  • The SAW process usually relies on dilution
    ventilation and has has little study from an IH
    point of view
  • Dust exposure is a concern when filling the flux
    hopper since the dust may contain titanium,
    calcium, barium, potassium, aluminum, sodium, and
    chlorine compounds

29
Metals Fabrication Welding
  • Plasma Arc Welding and Cutting PAW and PAC
  • Process
  • In the plasma arc process the welding head is
    designed to provide a flow of gas such as argon
    through an orifice under a high voltage gradient
    creating a highly ionized gas stream
  • The interaction of mechanical and electromagnetic
    forces produces creates arc temperatures greater
    than 33,400ºC (60,000ºF)
  • This technique is widely used for metal cutting
    and metallizing
  • Exposure Profile
  • The UV spectrum for PAW is much more intense than
    other inert gas welding systems
  • Major skin and eye hazards are created by PAW and
    requires special clothing and eye protection
  • The rich UV-B spectrum creates high ozone
    generation rates and nitrogen dioxide
  • Can easily exceed the TLV if local exhaust
    ventilation isnt maintained
  • Noise at the operators position can range from
    110-120 dBA
  • The noise is principally aerodynamic in origin so
    is difficult to control
  • Work is often done in a enclosed operating booth
    to control noise which is equipped with a
    downdraft hood to remove air contaminants

30
Metals Fabrication Welding
  • Laser Welding
  • Both gas and solid state lasers are being used in
    production facilities
  • 2 common lasers used for welding are the NdYAG
    and CO2
  • Process
  • An optically focused beam of coherent light from
    a laser is used to melt a well defined workpiece
    area
  • Since the beam cross section is very small it is
    very effective for precision welding or cutting
  • There are 3 major components of a laser welding
    system
  • The laser, the workstation (which includes the
    beam delivery system and the work handling
    equipment), and the computer control system
  • Exposure Profile
  • Generally laser welding produced less metal fume,
    but when cutting stainless steel the same fume
    generation rate was the same as GMA welding
  • Eye and skin contact from the laser beam are the
    main hazard as they can cause serious injury
  • Depending on the laser strength, there can be
    spectral, diffuse, or direct exposure hazards
  • Both UV, blue and visible light can be emitted
    from the laser plume during beam workpiece
    interaction (e.g., CO2 lasers)
  • Other plume concerns include polycyclic
    hydrocarbons released when cutting/welding
    plastics
  • There are also hazards of noise, vibration, and
    electricity associated with laser usage.

31
Metals Fabrication Welding
  • Resistance Welding
  • Used widely for the assembly of light sheet metal
    fabrications
  • Process
  • An electric current passe through workpieces held
    together under pressure, localized heating at the
    contact surfaces due to contact resistance causes
    the metal to coalesce
  • Seam, spot, projection, and flash welding are
    based on this technique
  • No flux or filler metal is used in this process
  • Exposure Profile
  • Hazards are minimal with this welding process
  • The major complaint from this process arises from
    parts with residual surface oils, which when
    welded, degrades and forms aldehydes
  • Aldehydes can cause olfactory, respiratory, and
    eye irritation
  • Ozone can also be generated during the welding
    process at levels exceeding the TLV
  • Nitrogen dioxide and welding fume were found to
    be below the TLV (NIOSH, 1990)

32
Metals Fabrication Welding
  • Gas Welding and Cutting
  • Used widely for light sheet metal and repair work
  • Process
  • The heat of fusion is created from the combustion
    of oxygen and one of several gases
  • acetylene, methylacetylene-propadiene (MAPP),
    propane, butane, or hydrodgen
  • The flame melts the workpiece and filler rod is
    fed manually into the joint
  • Filler rod is generally the same composition of
    the metal being welded with the exception of iron
    in which bronze rod is used
  • Exposure Profile
  • Metal fume originates from the base metal, the
    flux, and filler metal, but since temperatures
    are much lower than arc welding, excessive
    concentrations are rare, except when welding
    zinc, lead, and cadmium
  • The principle hazard of Gas Welding is the
    formation of nitrogen dioxide in confined spaces
  • The highest concentration of nitrogen dioxide
    occurs when the torch is burning without active
    welding
  • Although not considered chief hazards, phosphine
    may be present as a contaminant in acetylene and
    CO may form when heating up cold metal with a gas
    burner
  • Hazards from gas welding radiation emissions are
    in the visible to infrared regions (IR-A, -B, -C)

33
Metals Fabrication Welding
  • Scarfing and Cutting Processes
  • Used to cut slab steel, remove gates and riser
    systems on castings, gouge out defective metal in
    castings, and remove surface scale on billets
  • Process
  • Arcair process uses a copper-clad,
    boron-graphite electrode in a manual electrode
    holder that contains a compressed air supply to
    blow away the molten metal as it is melted
  • Can remove up to 0.9 kg (2.0 lbs) of metal per
    minute
  • Powder burning process uses an oxygen-acetylene
    torch on iron powder which creates a high
    temperature flame that can cut through very thick
    steel
  • Exposure Profile
  • Metal fume is the principle hazard associated
    with Scarfing and Cutting Processes (UK,
    Sanderson, 1968)
  • In ventilated work areas the principle hazards
    were iron oxide fume from the workpiece and
    copper fume from the electrode
  • In enclosed operations lead, copper, iron oxide
    fumes, ozone, and CO were high

34
Metals Fabrication Welding
  • Brazing
  • Widely used in the manufacture of refrigerators,
    electronics, jewelry, and aerospace components to
    join both similar and dissimilar components
  • Process
  • Is very similar to soldering operations, but the
    American Welding Society considers it a welding
    process becau
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