PUBH 4310 Test 4
Annealing -Nitrate salt baths
-are powerful oxidizers •Nitrate salts will decompose at 400 ºC (750 ºF), •At 650 ºC (1200 ºF) breakdown can be violent and release nitrogen oxide (flammable) and nitrogen dioxide (toxic)
Hard soldering
-Hard soldering uses metals (solder) with melting points ranging 316-427 ºC (600-800 ºF)
Liquid Penetrant Inspection
-Identifies flaws and failures on non-magnetic materials
Soldering exposures
-Lead-tin solder at controlled temperatures does not generate significant lead fume •Automated and manual soldering exposures are generally well below TLV -Thermal degradation products from rosin fluxing can be irritating -Cleaning solder dross and maintenance work can expose workers to lead dust
To transport product streams, including initial chemical streams, process streams, and waste streams, piping systems are used. Pipe manifolds allow for movement of these streams to different area needs. Because pipe manifolds are connected together, these are possible areas where leakage can occur. a. What is the issue if there are many leaks from these systems within a work area? b. What is the purpose of pipe connection jackets on pipe manifolds? What is a limitation of them?
-Leaks may seem trivial when considering single pieces of equipment, but hundreds of leaks become major exposure concerns -Leaks from flanges or fittings can be serious if corrosive or toxic liquids are being carried •Primary leak control is maintenance, but use of pipe connection jackets that cover the connection during failures prevents spraying but not dripping
In the drying process, what part of the process would you expect possible solvent exposure? Why? At what part of the process would you expect exposure to dusts? Why?
-Loading the dryer with Solvent laden cake -Dust from unloading dryer and packaging dry product
Three classes of welding
-pressure -non-pressure -brazing
Vapor area of vapor-phase degreaser
-where parts sit during process -vapor accumulates in this area
Hard chrome plating
-Plating for tools, worn parts, and gauges -Thick chrome layer deposited directly on base metal -Creates highest exposure to chromic acid mist
How is polishing different than grinding?
-Polishing removes work piece surface imperfections such as tool marks -Grinding To remove scale from finished metal in the forging industry
Annealing Hazards
-Possible explosion/fire if hot nitrate salts come in contact with organic materials(carbon or grease)
Soft Soldering
-Soft soldering uses metals (solder) with melting points <316 ºC (600 ºF)
Resistance Welding
-Used for fabrication of light sheet metal parts •Electric current passes through workpieces held together under pressure •Current heats workpiece surfaces causing them to melt -Seam, spot, projection, and flash welding use this technique •No flux or filler metal used
Rotary Blasting Table
•Used for cleaning moderately sized parts or heavily soiled parts •Parts to be blasted are placed on large swing table attached to access door •Centrifugal impeller shoots metal shot or grit onto the workpiece surface •Dust controlled through local exhaust at a 500 fpm inside the enclosure
Tumble or Barrel Blasting
•Used for large lots of small parts •Horizontal barrel tumbles at low speeds while air blasting parts •Common abrasives are silicon carbide or aluminum oxide •Equipment locally exhausted at 500 fpm through all openings •Good work practices and respiratory protection are needed for most maintenance and cleanout activities
Brush plating
•Used to fix worn metal machine parts and defective plated parts •Workpiece serves as the cathode and a graphite tool (anode) covered with an absorbent is used to deposit metal onto the workpiece •Process operates at a low DC voltage, and generally done by hand •Hazards -Skin contact when preparing/handling the chemically saturated absorbent pads-Release of cyanide with inadvertent mixing of acid and cyanide chemicals
Plasma Arc Welding and Cutting - PAW and PAC
•Welding head flows gas, like Argon, through an orifice under high voltage to make a highly ionized gas stream •Interaction of mechanical and electromagnetic forces creates arc temperatures > 33,400ºC (60,000ºF) •Widely used for metal cutting and metallizing
Annodizing
(is not Electroplating) •Workpiece is now the anode and a lead slab is the cathode •Used for decoration, corrosion resistance, and electrical insulation •Process (done mostly to aluminum) -Oxygen released on the workpiece to cause a controlled surface oxidation -Bath usually a chromic acid mixture under high current -Problem with this method is its low efficiency and high rate of misting
What is smut?
(residue) must be removed before metal can be finished -Smut is removed using: •Anodic electro-pickle, •Alkaline electro-cleaning, or •Ultrasonic cleaning with an alkaline solution
Laser Welding
-2 common lasers used for welding are the Nd: YAG and CO2
How would you describe the Plate and Frame Filter Press process?
-A series of polypropylene support plates in a parallel configuration (as many as 10-30 plates) -Filter placed over each plate, then a hydraulic ram compresses plates to obtain a seal -Feed slurry from reactor is pressed into each filter causing a solid-liquid separation -Filtrate drains, then cake is washed in place with a solvent -As wash is completed, pressure is released and plates separated -Operator scrapes cake off of each plate by hand
Abrasive Blasting - Centrifugal Impeller
-Abrasive flows to center of wheel and discharged at high velocity -Used primarily in glove box enclosures and rotary blasters
Abrasive Blasting - Compressed air
-Abrasive pot is pressurized forcing abrasive into the throat of the abrasive nozzle or siphoned into the throat of the nozzle. •Abrasive velocities exceed 200 fps (feet per second) -Used for indoor and outdoor projects
•Electrolytic alkaline cleaning
-An aggressive cleaning method that removes soil and smut from dirty parts -Bath is an electrolytic cell powered with direct current using the tank as the anode and the work piece as the cathode.
Grinders can be portable or fixed, can you name some uses/industries that we have discussed where grinders are used to finish/clean workpieces?
-Any metal working
Bright Dipping
-Applications •Acid bright dips remove light oxides and give metal surface a mirror-like appearance. -Bright dips: •Are mixtures of nitric and sulfuric acid, •Are used to clean the surfaces of cadmium, magnesium, copper, copper alloys, silver, and sometimes stainless steel -Nitrogen oxide gases are common release products Bright
Submerged Arc Welding - SAW
-Arc shielded from atmosphere by covering weld with a granular fusible flux •Granular flux is fed onto the metal ahead of the arc •Arc sinters flux to form a molten slag cover over the weld-Flux shields the arc, adds alloy, stabilizes the arc, and shapes the weld bead •Arc made from a filler metal that serves as the wire electrode •This technique can be semi- or fully-automated
Gas Tungsten Arc Welding
-Arc using an inert gas (Ar or He) environment •Prevents O2 and H2 from entering the weld •Welds aluminum, magnesium, stainless steel, nickel alloys, copper-nickel brasses, silver bronze, and other low alloy steels •Arc between non-consumable tungsten electrode and the workpieces creates enough heat to melt metals together •Arc is created inside an inert gas environment
Can you describe the Centrifuge Process and relate it to a common appliance that people use every day?
-Can be operated in a batch or semi-continuous mode -Perforated basket is lined with a backing screen lined with a synthetic fabric -Feed liquor is added to the centrifuge, where particulate deposits on the filter while filtrate drains through the side then pumped to a holding tank for re-use -When enough cake builds onto the centrifuge, the feed from the reactor is slowed, and cake is removed using a plow or peeler knife(90% product removal) -Remaining product is usually removed by hand with a plastic spade -clothes dryer
Of the three separation techniques, which is the most effective at removing the liquids from the solids?
-Centrifuge
What does heat treating do?
-Changing the crystal lattice of steel will harden it •2 general methods: -Add carbon or nitrogen to the metal surface of a low carbon steel to harden it -Heat medium carbon steel above a critical temp to increase strength and hardness •These methods harden the surface of the metal, not the entire mass
Quenching
-Controlled cooling or "quenching" is required after furnace and salt bath processes -Quench baths may be water, oil, molten salt, liquid air, or brine
Machining Fluids Purposes
-Cool the cutting tool, and to lubricate the cutting tool/workpiece interface -Flush metal chips and debris away from cutting process
Annealing
-Cooling and heating cycles that modify workpiece's metal properties to soften it
Storage tanks can be underground or above ground, what are 4 advantages to install above ground tanks instead of underground tanks?
-Cost less to install -can be moved later if necessary -Can inspect for defects and repair before leaks develop -less regulation because EPA regulates under ground tanks
Who regulates gamma ray sources?
-Design, manufacture, and use of radioisotope sources and exposure devices are regulated by the US NRC, and 26 "Agreement States" •Organizations that perform radioisotope radiography must be licensed by the NRC (Nuclear Regulatory Commission) or the "Agreement State" where the work is being done
Magnetic Particle Inspection
-Detects surface flaws, especially cracks -Simple low cost procedure used in metal fabrication
Case Hardening
-Diffuses carbon or nitrogen into workpiece surface •Takes from 1 to 20 hrs and can be a thickness of 0.1 to 0.25 inches
"Electroless Plating"
-Done by depositing metal onto a workpiece through a catalytic reaction in a bath -Plastics suited for "electroless plating" include nylon and polycarbonate -Common metals plated onto plastic include nickel, copper, cobalt, gold, and palladium
Electrochemical Machining
-ECM is the opposite of electroplating •Electroplating - Metal deposits on workpiece (cathode) from plate stock (anode) in an electrolytic bath at low voltage/high current •ECM - cutting tool is the cathode and workpiece is the anode -As electrolyte passes between the workpiece and the tool ,metal ions are removed from the workpiece and swept away by the electrolyte
The "X-ray Generator"
-Electrons are accelerated in an evacuated tube from a cathode to anode •Electrons hit the target and rapidly decelerate causing bremsstrahlung(braking radiation) which produces x-rays -Activated from a remote location to limit worker exposure -Generally in fixed locations due to size, weight, and service requirements (x-ray room)
Industrial Radiography
-Examines metal for flaws and cracks on welds, castings, and forgings •Can be done in shop, off-site, aboard ships, and on pipelines -expose one side of object then measure amount transmitted through object -Defects (areas of low density or thickness) allow more radiation to pass through which creates a darker image on the film
•Non-electrolytic cleaning
-Excellent for rust removal but not scale and uses high concentration of caustic soda and various chelating and sequestering agents
What is a Fab and how does a fab maintain a clean room environment but also provide the materials needed to support the clean room?
-Fabrication buildings (Fabs) •Contain clean rooms, subfabs, and huge ventilation systems -Fab controls that maintain a "clean room" environment also minimize worker exposure -Hazards include: •Chemicals, IR and non-IR radiation, ergonomic stressors, noise, and lasers
Induction Heating
-For high production of small parts with well defined surface geometry -Current induced through part heats it to desired temperature for hardening
•Abrasive Blasting Room
-For very large work pieces -Operator does blasting from inside room •Wears specialized equipment that provides protection from the dust, noise, impact, and vibration-Room exhausted at 100 fpm from ceiling to floor or from exhaust slots at wall bottom -Exhausted air passes through a settling chamber then a fabric filter(bag house)
Conventional Metal Machining
-Forcing the point of a cutting tool against a work piece at a controlled speed and force •Remove parts of work piece by shearing or abrading •Lubricant also controls temperature and flushes away debris-Pressure of cutting tool on workpiece creates high temperatures
Detonation Thermal Spraying
-Gas fed to a combustion chamber ignites fuel by a spark plug (260 firings/minute) •Metal powder is fed to the chamber where the explosion drives melted powder to the work piece at a velocity of about 760 m/sec
Health Hazards of SMA Welding
-Health Hazards •Depends on the metal being welded and contents of the electrode -Exposure Profile •Metal Fume Components -Iron oxide is the major metal fume from welding mild steel, •Can deposit in the lungs to cause a benign condition called "siderosis" •Siderosis is not a functional impairment and doesn't develop fibrous tissue -Fume is also made up of manganese, zinc, and occasionally lead -Steel alloys can produce Ni, Cr, oxides of molybdenum and Cu, and fluoride fume •Metal Fume Concentration -Depends on parent metal, electrode, current density, wire feed rate, arc time, power configuration (ac or dc), and polarity (straight or reversed) -Other exposure contributors are ventilation, indoor or outdoor, or if in an enclosure •Gases and Vapors -Includes: nitrogen dioxide, CO, CO2, acrolein, and ozone -Low concentrations unless in an enclosed or confined space •Radiation -"SMA welding" exposes workers from IR to UV •Acute UV absorption at the cornea causes photokeratitis (a.k.a., "arc eye," "sand in the eye," or "flash burn") - Pain occurs 5-6 hrs after exposure, clears up in about 24 hrs •UVexposure can causeskin erythema (burn)
Steps for soldering
-Includes base metal clean, fluxing, soldering, and final clean •Base metal cleaning -Removes oil, grease, wax, or other debris so flux can react with tarnished metal •Flux -Removes tarnish from metal -Available in solid, paste, and liquid form -Applied by brush, roll, spray, foam, dip, or wipe •Soldering -Melted to flow around connected work pieces fastening them together -Common techniques are: solder iron, solder pot, drag solder, wave solder, reflow soldering •Cleaning -Flux residue and degradation products on base metal are removed by brushing or wiping with water or solvents
What occurs at the Reactor? Why might you request that a reactor have glass lining? Some safety features include "rupture disks", "inerted headspace", or installing "bottom sampling loop". What advantage or safety control does each provide?
-Major design features divided into production and safety -Glass lining in vessel stops trace metals from interfering with reaction -Rupture Disks: Pressure relief valves that use rupture disks mounted in a pipe leading from top of vessel to an empty discharge point -Inerted headspace: Inert the head space (vapor/air) with N2 or CO2 for fire protection -Bottom sampling loop: eliminates headspace exposure
Gas Metal Arc Welding
-More commonly known as Metal Inert Gas (MIG) Welding -consumable wire electrode fed from a reel/spool that maintains the arc as it melts •Gas flow maintained around electrode, and is a concentration of He, Ar, CO2, N2, or a blend of these
Decorative Chromium electroplating
-Part plated with nickel, then thin chromium layer -Used for plumbing fixtures and automotive parts
Plasma Thermal Spraying
-Plasma arc is created in a controlled atmosphere of a special nozzle •Argon gas is ionized as it passes through the arc then as it continues through the nozzle it recombines to create high temperatures 16,700 ºC (30,000 ºF) •High temperature melts metal alloy, ceramic, and carbide powders in the air stream, then deposits them on the workpiece surface at velocities of 300-600 m/sec
Ultrasonic Inspection
-Pulse-echo and transmission-type ultrasonic inspections have a wide range of application for flaw detection and structural analysis •Can detect voids much smaller than all other testing methods -Works by using a transducer to pass ultrasound waves through it to reflect pulses back to the transducer as flaws are found
How does the Nutsche separate product? What is the mother liquor and what is done with it?
-Reactor contents sent to Nutsche to befiltered by gravity, vacuum, or pressure -Particles collected on the filter media, while filtrate or mother liquor is pumped back to a holding tank for reuse
Shielded Metal Arc Welding - SMA Welding
-Shielded metal arc welding, a.k.a. "stick" or "electrode" welding -Most common type of non-pressure welding Electric arc drawn between welding rod and workpiece •Molten metal forms a common puddle, which cools to form the weld •Slag forms at the surface of the weld -Electrode coating •Releases a shielding gas like CO2 to prevent air from entering the arc puddle which weakens the weld •Provides flux to form slag and to react with oxygen to remove it, •Adds alloying metal to the weld, and •Controls the viscosity of the molten metal
Condenser of vapor-phase degreaser
-Stops solvent vapor from exiting the tank by condensing vapor to liquid -Can be a water jacket, coil, or both that extend completely around tank -Creates top of vapor blanket and limits solvent escape into workroom
Open Air Blasting Worker protection and dust is controlled through
-Temporary enclosures, -Respiratory protection, and -Good work plans •Other contaminants often get mixed in with the abrasive dust
Machine Tools: Milling Machine
-The work piece is fixed while cutting tool moves across face of workpiece -Workpiece is mechanically clamped in place
When polishing or buffing a workpiece, what is the most likely source of dust exposure? Why?
-The workpiece is the major source of airborne particulate during grinding, -The abrasive and wheel are the principal contaminant during buffing/polishing
If a material is stored in a larger vessel and must be transferred to a smaller and portable vessel, why is it important to bond the portable vessel to the larger vessel? Why is this important when transferring flammable solids or liquids?
-To prevent a spark that ignites the contents of the vessel
Electrical Discharge Machining
-Used for large precise complex work: •blanking die, extrusion die, and carbide punching- Process: •Spark-gap technique using a graphite tool as the cathode and workpiece as the anode •Workpiece immersed in a dielectric oil bath using low-voltage DC •Voltage increased across the gap until a spark produces enough heat to erode a small amount of metal from the workpiece •Repeated until machining is complete -Hazards •Dielectric oils-As dielectric oils get pyrolysed they form hydrogen gas, methane, carbon monoxide, and traces of other gases, which are released in the mists-Oil gets contaminated with small hollow spheres of the machined metal
Oxyacetylene or Methylacetylene-Propadiene Torch
-Used on small specialty parts to harden metal by direct flame on select areas
Brazing
-Used to make refrigerators, electronics, jewelry, and aerospace components to join both similar and dissimilar components •Similar to soldering, but the American Welding Society considers it a welding process because: -In brazing, metals are heated above 450 ºC (840 ºF),whereas soldering occurs below that -Joint look like solder bonds, but are much stronger and require less cleaning -Flux used to prevent oxidation of base metal, not to prepare surface metal as in soldering •Common fluxes are made from fluorine, chlorine, and phosphorous -Uses filler metals to create a chemical bond (like soldering) to join two similar or dissimilar pieces together -Exposure Profile •Brazing flux, like solder flux, is a skin corrosive and respiratory irritant
Gas Welding and Cutting
-Used widely for light sheet metal and repair work •Fusing metals by heat of combustion from oxygen and gas: -acetylene, methylacetylene-propadiene (MAPP), propane, butane, or H2 •Flame melts workpiece as filler rod is fed into the joint -Filler rod generally the same as base metal, except bronze is used for iron
Abrasive Blasting - Hydro-blasting
-Uses a high pressure stream of water to carry the abrasive. -Pressures are 1000 - 20,000 psig (lbs/sq. inch gauge) -Mostly done outdoors
Laser Heat Treating
-Uses coatings to absorb optical radiation into metal-Hazards include typical laser hazards -Possible air contaminants from degraded coating
Freeboard of vapor-phase degreaser
-Vertical distance between point at which vapors can escape degreaser and the highest normal vapor level -Ratio of freeboard height to degreaser width should be at least 1, but BKM is at 1.25 -As freeboard height increases, it creates difficulty for operator to load degreaser, •Eliminated by installing a work platform or placing degreaser in a pit
Water jet cutting
-Water mixed with various abrasives is shot onto an object at pressures up to 65,000 psig to cut up to 1-inch thick mild steel •Abrasives can be garnet, aluminum oxide, or silicon carbide -Principle hazard is contact with water stream •At nozzle, the water stream can amputate limbs •At 3 feet from nozzle the stream can still cause serious injury
Liquid Carburizing
-Workpiece immersed into molten salt bath of sodium or potassium cyanide (or cyanate) and salts of Na, K, Ba chloride (15-30 hrs) to add mostly C to surface
Pack Carborizing
-Workpiece placed in a metal box covered with an organic carburizing compound -Gas tight box put in furnace where compound degrades to CO to diffuse C into metal -Part quenched to complete hardening
In descending order (worst to least) are those that cause skin cancer:
-mineral oil, emulsified oil, and synthetic machining fluid
In making nitric acid, what is the purpose of the catalyst? How is NO2 converted to nitric acid (HNO3)?
-oxidizing ammonia to nitric oxide -NO2 is absorbed into water through a column yielding 50-70% nitric acid
•Alkaline cleaners include
-sodium hydroxide, potassium hydroxide, -sodium carbonate, sodium meta- or ortho-silicate, tri-sodium phosphate, -borax, and tetra-sodium pyrophosphate
What is the Pig (gamma ray sources)
-source is placed inside a shielded container called a pig -containers weigh up to 50-lbs for Ir-192 sources, and up to 300-lbs for Co-60
What is considered the most serious cutting tool exposure?
Cobalt
Four techniques of Metal Thermal Spraying
Combustion, Thermal Arc, Plasma, and Detonation
Special problems associated with stainless steel welding
•70% of stainless steel welding is done by SMA welding using coated chromium -nickel alloy electrodes or by MIG welding using uncoated chromium-nickel wire -MIG welding releases high conc. Cr (III), while SMA releases Cr (VI) -Nickel has been found in the air, but at concentrations less than the allowable exposure limits
Alkaline Treatment - Salt Baths
•Cast iron, steel alloys, copper, aluminum, and nickel are often cleaned using a molten caustic (NaOH) bath •Molten caustic is used to: -Remove oxides of chromium, nickel, and iron -Remove oils, graphite, carbon, sand, and scale •Contaminant Removal -Oxides and surface debris collect and sink to bottom as sludge -Other contaminants will float to surface or volatize as a vapor or fume
Combustion Spraying-Wire
•Coating material (wire form), is fed to a gun operated with air or combustible gas, such as acetylene, propane, or natural gas •Wire is melted in the flame, disintegrated to a molten particulate then compressed airpropels itat 240 m/sec onto workpiece
Annealing -High temp neutral baths
•Contain potassium and sodium chloride and barium nitrate•Baths neutral so no chemical reaction with workpiece
Annealing -Low temp salt bath
•Contain potassium nitrate and sodium nitrate
Heat Treating
•Designed to strengthen and harden ferrous/non-ferrous alloys -Hardening and annealing define the final properties of the metal
Open Air Blasting
•For really large equipment: -Ships, trucks, trains, bridges, and water towers, or -Any other equipment that is so large that it must be cleaned outdoors •Major challenge of this process is protecting the worker and the environment from the abrasive dust and the equipment coatings
Gas Carborizing
•Gas Carburizing -Adds carbon to the steel's surface -Workpiece in a furnace with high concentrations of CO at high temp. 870-980 ºC (1600-1800 ºF) -Carbon concentration of mild steel can go from 0.1% to 1.2% carbon-CO Exposures •Furnace can have up to 40% (400,000 ppm) CO, common to release 100 ppm into work area (TLV 25 ppm)
-Primary hazards in abrasive blasting rooms are? What are some controls?
•High dust concentrations(10-100 mg/m3) from abrasive and surface debris •Vibration from the hand-held nozzle •Noise which can exceed 110 dBA. -Common engineering control is a "dead-man switch" on hand-held nozzle to prevent injury •If dropped "dead-man switch" shuts off air supply to prevent nozzle from whipping around
What are the three types of carborizing?
Gas, Pack, and Liquid
What is the most significant chronic injury that can be caused by long term use of hand held grinders? Why does this occur?
Grinders can be exposed to excessive hand-tool vibration leading to finger blanching
Hard Metal Tool and Cutter Grinding
Hard Metal Tool and Cutter Grinding -Manufacturing Process •Cutting tools in metal machining must be: -Hard enough to cut the workpiece, -Strong enough to withstand mechanical shock, and -Run at high temps with/without machining fluids while staying sharp •Common cutting tools contain metal carbides with a cobalt binder
Why must a grinding wheel be "dressed" periodically?
Wheel must be "dressed" to work properly.
What is closed circuit unloading?
When a liquid is pumped out of a tank, fumes must be replaced to prevent high vapor pressure within the tank
When using a vapor phase degreaser, you want to avoid solvent drag, what is solvent drag? Also, provide three examples that can cause solvent drag to occur.
When solvent comes out of a vapor phase degreaser after removing the product -removing solvents too quickly -don't overload degreaser -Only spray workpiece when below the vapor level
What has caused radiation incidents?
have occurred when operators failed to properly return source to a shielded position and then approached the source stop without a radiation survey
What is welding?
heating metals to a temperature that joins them together. -In this process •Metal is vaporized then condensed to form a fume that agglomerates rapidly •Fume made of base metal, workpiece metal, coating, electrode, and flux
Heating element of vapor-phase degreaser
heats solvent to become a vapor
Why would operators decide to use a "day drum" for the transfer of chemicals to a reactor or other equipment?
in the event of a malfunction or power outage, chemicals can still be used for a whole day so production does not stop for the day
What does it mean when a part looks dry in the vapor phase degreaser?
it appears dry because vapor stops condensing on parts
For an immersion tank or a vapor phase degreaser, why would one want a sliding cover instead of a hinged cover?
it pulls out vapor when opened and pushes out vapors when closed
Why should you put small parts in a wire basket?
keep all parts at freeboard height till drained
Special problems associated with welding fumes
•90% of welding particulate < 1 μm, and 60% of welding fume < 0.25 μm suggesting that most of the inhaled welding fume ends up in the lower respiratory tract
What is acid pickling?
•Acid Pickling probably derived from early practice of cleaning metal in vinegar -Pickling removes scale, rust, corrosion, and oxide films but leaves a smut •Sulfuric, hydrochloric, and phosphoric acids are used
Acid Pickling and Bright Dipping-Health Hazards
•Acid mists and gases released during pickling and bright dipping •Corrosive effects to skin, mucosa, and eyes include:-Burns, ulcers, and necrosis(tissue death), severe exposures can be lethal •Airborne mists, gases, and vapors can be serious upper and lower respiratory irritants -High exposure to nitric acid can cause pulmonary edema(fluid in lungs) and death-Epi studies (1980's) showed excess laryngeal cancer in steel workers using sulfuric and other acids during pickling operations
Gas nitriding
•Adding nitrogen to the metal surface -A furnace atmosphere of ammonia makes a nitrogen rich environment when ammonia passes over a catalyst to dissociate to an atmosphere of 25% nitrogen and 75% hydrogen -Workpiece then loaded in a vacuum vessel with a low pressure nitrogen environment and high -voltage dc field -Vessel wall acts as the anode and the workpiece as the cathode where nitrogen ions accelerate to cathode (workpiece) to form a nitride hardened case
Degreasing:
•Removes grease, oil, wax, or other contaminants from metal •A common cleaning operation of manufacturing/service industries •Cleaning and workload determines solvent and cleaning process -Small shops often clean parts using cold liquid solvents •Usually by dipping, brushing or wiping -Large shops use large dip tanks with mechanical agitators and spray nozzles -Vapor-phase degreasing often uses halogenated hydrocarbons on parts where residue is unacceptable
There are 8 major semiconductor fabrication processes steps listed in lecture that are distinct in what is done to the wafer, what are those 8 process steps?
•Silicon Crystal (Ingot) Formation •Cutting and Polishing •Oxidation •Layering-Photo Lithography, -Developing, -Etching •Doping •Additional Layering •Wafer Testing •Packaging
Gamma Ray
•Source of gamma rays are through radioactive decay -Principle radioisotopes are Iridium-192 and Cobalt-60
Machine Tools: Lathe
•The cutting tool usually fixed while work piece moves •The workpiece held in place with a "collet" or a "chuck"
Chlorine is made from two very different processes, both use sodium chloride (NaCl) and water (H2O) to create chlorine gas. Which of the two processes are most used in the United States? In understanding how chlorine is made, why would you expect one to be used so much less? (2 likely reasons).
•The diaphragm cell process, 75% of US market, •The mercury cell chloralkali process, 25% of market -Diaphragm cell takes up less room -Long steel chamber4-ft wide, 40-ft long,1-ft deep, contains about 3-tons of mercury and is sloped
Controls for Salt Baths
•Use auto shutoffs to prevent over heating •Place rods in salt bath to create vent holes before salt cools and solidifies at room temperatures -Prevents explosions or blowouts when reheating •Workpiece must be clean/dry as residual grease, oil, or paint can create explosive atmospheres
X-ray
•X-ray radiography is classed as "electronic product radiation" because produced electrically
Why electroplate?
•to prevent rusting and corrosion, •for appearance, •to reduce electrical contact resistance, •as a base for soldering operations, •to provide electrical insulation, and •to improve wear-ability
what was used instead of TCE, PCE, and methylene chloride?
1,1,1-trichlorethane and chlorofluorocarbon 113 -Both showed low toxicity, non-photochemical activity, and superior performance -But during the 1980's, both were linked as contributors to ozone layer depletion
Major chemicals used in vapor-phase degreasing were
:-trichloroethylene (TCE), -perchloroethylene (PCE), and -methylene chloride •Only TCE was photo-chemically reactive, so smog was reduced.
Ammonia is one of the chief product in making nitric acid, under what condition can ammonia become an explosive hazard?
> 16% in air it can become an explosion hazard
What is the purpose of Acid and Alkali cleaning?
After removal of soil, oil, and grease, acid and alkaline baths prepare metal surfaces for electroplating or other finishes
Acid Pickling and Bright Dipping -Controls
Air contaminant concentrations vary depending on: -Tank geometry, surface area, and bath temperature -Electrolytic process, work rate, and worker practices -Ventilation control and to control misting by use of inhibitors to create a foam blanket
1)The U.S Clean Air Act requires industry to do what by Jan 2030?
All hydrochlorfluorcarbons to be completely phased out by Jan. 2030
1)Although there are many degreasing processes or methods, what is still the most common way to clean parts?
Cold Degreasing: Still the most common cold degreasing technique is transport of small amounts of solvent to the worker's work space.
How is buffing different than grinding or polishing?
Creates high-luster appearance, with very little metal removed
When grinding an object, what is the most likely source of dust exposure? Why?
Dressing removes much of the wheel as course dust but produces very little respirable dust
What is a "clean room", why is it important to maintain in this industry? Does this set up also protect workers from chemical exposures? In what way?
Fab controls that maintain a "clean room" environment also minimize worker exposure
Sulfur dioxide, a waste stream of mining operations, is often converted to sulfuric acid, through a 3 step process. When sulfur dioxide is converted via a catalyst, it becomes sulfur trioxide, why can't this be directly mixed with water to sulfuric acid (H2SO4)?
If SO3 is added directly to water, it forms sulfuric acid mist, but when added to sulfuric acid (mix is called Oleum), it allows for direct mixing with water to make sulfuric acid.
what can be electroplated?
Metal, plastic and rubber
Most ammonia that is marketed for use is made industrially and not from animal waste. What is the primary source of nitrogen and what is the primary source of hydrogen in making ammonia?
Natural gas is the source of Hydrogen and air is the source of nitrogen
What kind of machining oil causes folliculitis (oil acne)?
Oil based machining fluid
What does a gamma radiation operator wear?
Operators wear a direct reading pocket dosimeter and a film badge or thermo-luminescent dosimeter, and use a calibrated radiation survey meter during all radiographic operations
What purpose do pipe manifolds server in the transfer of chemicals?
Pipe lines run from each storage tank into the facility where they terminate at a manifold, then distribute to reactors by hard pipe or flex lines
Metal Thermal Spraying
Process where a fine mesh metal powder or wire is melted then sprayed at high velocity onto a workpiece surface to adhere and solidify
why would you suggest that these tanks be covered when not in use?
So fumes do not escape
Why should a degreasing tank be at least 3 feet high?
So workers don't lean over the tank
In chemical processing, raw materials are used or mixed to create a new product. a. What modes are used to bring these materials on site for processing, warehousing, or storage? b. What kinds of storage packaging or containment might be used to store these raw materials?
a - Bags, drums, totes, bins, tankers/rail cars, or large tanks b- above or underground tanks, totes, bins, bags
Disadvantages of Gamma Ray sources
can't be turned off and continuously emits gamma rays
•Thermal Arc Spraying
consumable metal wire electrodes made of material (metal) to be sprayed are energized by a low volt-high amp DC power supply -Power supply creates an arc similar to conventional arc welding then compressed air sprays the molten metal onto the workpiece
What are the Principle hazards of acid and alkali cleaning?
exposure to alkali or acid mist from •Heating, •Air agitation, •Gassing from electrolytic operations, •Cross contamination between baths
Advantages of Gamma Ray sources
external energy isn't needed like with X-ray generators
Alkaline Immersion Cleaning
remove oil and gas residue, buffing compounds, certain soils, and paint.
Why is it necessary that the freeboard be at a height equal to the tank width?
so it does not tip over
3 types of machining fluids responsible for dermatitis in descending order (worst to least) are
synthetic machining fluid, emulsified oil, and mineral oil,
Explain how a vapor-phase degreaser works
•As cold metal parts are lowered into the hot vapor, the vapor condenses on the cold parts dissolving the grease and oils. •Oily condensate drops back into the liquid solvent sump at base of tank •Solvent evaporates continuously to replace the condensed vapor and maintain the vapor blanket •Oils do not vaporize, so form a sludge at bottom of the tank, which is periodically removed •Scrubbing action of condensing vapor continues until part reaches vapor temperature •When part reaches vapor temp, it appears dry because vapor stops condensing on parts, at this time process is now complete
Machine Tools: Grinding Machine
•Both tool and workpiece can move at high speeds •Can use magnets to keep workpiece stationary
Plastics Electroplating
•Canplate plastic with the same quality as metal plating
Cyaniding
•Carbon and Nitrogen added to workpiece surface -Workpiece immersed in a sodium chloride salt bath mixed with sodium and potassium cyanide for 30-60 min at > 870 ºC (1600 ºF) -A quenching step finishes hardening
Carbon Nitriding
•Carbon and nitrogen added to workpiece surface -An Endogas Generator (produces endothermic gas) uses 5% natural gas (carbon source) and 5% ammonia (nitrogen source)
Electroplating process
•Electrolyte consists of plating metal dissolved in salt water •Uses two electrodes powered by low voltage DC electricity •Work piece is the cathode (-) which absorbs (plates) metal ions •While the anode (+) if active, is a slab or basket as the plating metal source; if inactive, metal salts are added as a metal source •As power is applied, positively charged metal ions deposit out of salt and onto a negatively charged workpiece (cathode) -Hydrogen (cathode) and oxygen (anode) are released during the process
Magnetic Particle Inspection steps
•Ferromagnetic particles are applied to metal's surface by an air gun or dipped into a bath that contains particles suspended in water or a light petroleum oil •Magnetic field is generated through metal part which causes magnetic particles to gather at the flaw-Magnetic particles can be designed to fluoresce under a UV-A mercury vapor lamp to highlight flaws
Liquid Penetrant Inspection steps
•Fluorescent or visible die suspended in liquid is applied to the workpiece by brush, dip, or spray •Dye absorbs into the flaw by capillary action, •Workpiece is rinsed, then dipped or dusted with an absorbent powder •Dye in workpiece absorbs into powder which is visible or fluoresces under a UV lamp
-Cabinet (aka - Glove Box) Blasting
•For blasting small parts •Heavy duty rubber gloves to hold abrasive nozzle and parts to be cleaned •Exhausted at a minimum flow rate of 4 air changes per minute •Air goes through a cyclone collector, a bag house, then exhausted outside •Abrasives used for cabinets include silicon carbide and aluminum oxide, - Use low toxicity abrasives, never use Silica in a "Glove Box" •With proper maintenance, exposure to blaster is minimal •Periodic inspection needed to maintain dust control •Respiratory protection and good work practices needed for maintenance and clean out •Worker exposures include:- Vibration from the hand-held nozzle and Noise from the blast. - A good working cabinet keeps noise levels below 85 dBA
Soldering
•Joining metal by surface adhesion without melting base metal •Temperature range differentiate soldering (<450 ºC) from brazing (>450 ºC) •Soldering (and brazing) hold metals together through chemical bonding (covalent) •Composition of solder and flux determines potential hazards •Most common solder contain 65% Tin (Sn) and 35% lead (Pb), •Melting point of solders are quite low and generally do not create inhalable fume, since lead fume is only created at >450 ºC
Flux
•Made from organic and inorganic materials •Usually a corrosive cleaner used with a volatile solvent or vehicle
-Principle hazards of metal thermal spraying are:
•Metal fumes -Deposition efficiency of application determines metal fume generation:•Combustion spraying with wire, deposition from90% for Al, and 55% for Pb •Plasma arc is from 50% for chromium carbideand90% for aluminum-titania •Gases-High velocity of gases through the spray gun can be injected into the skin •Noise-Noise from 107 - 119 dBA, and 2 to 4 kHz noise caused by flow through spray nozzle •Non-ionizing radiation (NIR)-NIOSH study showed that UV, IR, and visible radiation can exceed the ACGIH TLVs
Combustion Spraying-Powdered
•Powdered metal is sprayed by an oxygen fuel stream into a fuel gas (acetylene or hydrogen) to melt then projected onto the workpiece at velocities below 30 m/sec
Patenting
•Quenching operation that uses molten lead baths for thin cross-sectional parts like wire
What must a gamma radiation operator do before testing?
•Radiographic operators receive formal radiation safety training •Must post radiation warning signs and secure access to the area
What are the two methods to make hydrochloric acid? Which method is the most common source of hydrochloric acid?
•Reacting sulfuric acid with sodium chloride to form sodium bisulfite, Reacting sodium bisulfite with sodium chloride to form hydrogen chloride and sodium sulfate -In the US, hydrochloric acid is mostly formed as a by-product in the chlorination of organics •Hydrogen, benzene, chlorine, and a catalyst react to form chlorobenzene, leaving hydrogen chloride as a by-product •Hydrogen chloride can be mixed with water to make hydrochloric acid
Most chemical components/products result from 3 major process steps: reaction, separation, then drying. It can be said that these step mimic typical chemical synthesis in a chemistry lab. Using this scenario, what would be the equivalent of the round bottom flask, the Buchner funnel, and the convection oven?
•Reaction: Reactor -Chemicals added to a heated round bottom flask that is monitored by a temperature probe and mixed with a magnetic stirrer, reaction occurs with liquid being distilled, leaving solids at bottom •Separation: Nutsche -Solids separated by pouring fluid with solids through a filter and into a Buchner funnel •Drying: Oven -The remaining solid is placed in a convection oven to dry
