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Title: Processing of Metal Powders and Processing of Ceramics and Glass


1
Processing of Metal Powders and Processing of
Ceramics and Glass
  • Group 10
  • Kevin Burns
  • Jared Adams
  • Chris Chaves
  • Drew Smith
  • James Colovos
  • March 6, 2006

2
Topics
  • Processing of Metal Powders
  • Production of Metal Powders
  • Compaction of Metal Powders
  • Sintering
  • Secondary and Finishing Operations
  • Design Considerations
  • Process Capabilities
  • Economics of Powder Metallurgy
  • Processing of Ceramics, Glass, and
    Superconductors
  • Shaping Ceramics
  • Forming and Shaping of Glass
  • Techniques for Strengthening and Annealing glass
  • Design Considerations for Ceramics and Glasses
  • Processing of Superconductors

3
Processing of Metal Powders
  • Powder Metallurgy Process (P/M process)
  • The process where metal powders are compacted
    into desired and often complex shapes and
    sintered to form a solid piece
  • Process was first used five thousand years ago by
    Egyptians to make iron tools

4
  • Net-shape Forming
  • The ability to produce parts to net dimensions

5
Parts and Components Made with the P/M Process
  • Balls for ballpoint pens
  • Automotive components, makes up 70 of P/M
    process (ex. piston rings, connecting rods, brake
    pads, gears, cams, bushings)
  • Tool steels, tungsten carbides
  • Graphite brushes inserted with copper for
    electric motors
  • Magnetic materials
  • Metal filters and oil-impregnated bearings with
    controlled porosity
  • Metal foams
  • Surgical implants
  • Other items used for aerospace, nuclear and
    industrial applications

6
  • Advances in the P/M process permit structural
    parts of aircraft (ex. landing gear components,
    engine-mount supports, engine disks, impellers,
    engine frames
  • The P/M process has become competitive for
    complex parts made of high strength and hard
    alloys with processes such as casting, forging,
    and machining)
  • Common metals used in the P/M process
  • Iron
  • Copper
  • Aluminum
  • Tin
  • Nickel
  • Titanium
  • Refractory metals

7
Production of Metal Powders
  • The powder metallurgy process
  • Powder production
  • Blending
  • Compaction
  • Sintering
  • Finishing operations

8
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9
Powder Production
  • First step in P/M process
  • Methods
  • Atomization
  • Reduction
  • Electrolytic deposition
  • Carbonyls
  • Comminution
  • Mechanical alloying
  • Miscellaneous methods

10
Atomization
  • Produces a liquid-metal stream by injecting
    molten metal through a small orifice
  • The stream is broken up by jets of inert gas or
    air

11
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13
  • The size and shape of the particles from
    atomization depend on the temperature, flow rate,
    size of nozzle, and the jet characteristics
  • When water is used it creates a slurry metal
    powder and leaves a liquid at the bottom of the
    atomization chamber
  • The water cools the metal faster for a higher
    production rates

14
Centrifugal Atomization
  • The process in which the molten-metal drops onto
    a rapidly rotating disk or cup
  • The centrifugal forces break up the molten-metal
    stream to generate particles
  • Another method is that a consumable electrode is
    rotating rapidly in a helium filled chamber

15
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17
Reduction of Metal Oxides
  • A process that uses gases as a reducing agent
  • Hydrogen and carbon monoxide
  • Also known as the removal of oxygen
  • Very fine metallic oxides are reduced to the
    metallic state
  • Spongy and porous powders are produced

18
Electrolytic Deposition and Carbonyls
  • Electrolytic Deposition utilizes either aqueous
    solutions or fused salts
  • Makes the purest powders that are available
  • Metal carbonyls are formed by letting iron or
    nickel react with carbon monoxide
  • Reaction product is decomposed to iron and nickel
  • Forms small, dense, uniform spherical particles

19
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20
Mechanical Comminution
  • Also known as pulverization
  • Involves roll crushing, milling in a ball mill,
    or grinding of brittle or less ductile metals
    into small particles
  • Brittle materials have angular shapes
  • Ductile metals are flaky and not particularly
    suitable for P/M

21
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22
Mechanical Alloying
  • Powders of two or more pure metals are mixed in a
    ball mill

23
  • Under the impact of the hard balls the powders
    fracture and bond together by diffusion, forming
    alloy powders
  • The dispersed phase can result in strengthening
    of the particles or can impart special electrical
    or magnetic properties

24
Miscellaneous Methods
  • Precipitation from a chemical solution
  • Production of fine metal chips by machining
  • Vapor condensation

25
Types of Powders
  • Nanopowders
  • Consist of mostly copper, aluminum, iron,
    titanium
  • Are pyrophoric (ignite spontaneously)
  • Contaminated when exposed to air
  • The particle size is reduced and becomes porous
    free when subjected to large plastic deformation
    by compression and shear stress
  • Posses enhanced properties
  • Microencapsulated powders
  • Coated completely with a binder
  • The binder acts as an insulator for electrical
    applications preventing electricity from flowing
    between particles
  • Compacted by warm pressing
  • The binder is still in place when used

26
Particle Size, Shape, and Distribution
  • Particle size is measured by a process called
    screening
  • Screening is the passing of metal powder through
    screens of various mesh sizes
  • The main process of screening is Screen Analysis
  • Screen analysis uses a vertical stack of screens
    with mesh size becoming finer as the powder flows
    down through screens

27
Other Screening Methods
  • Sedimentation
  • Involves measuring the rate at which particles
    settle in a fluid
  • Microscopic Analysis
  • Includes the use of transmission and scanning
    electron microscopy
  • Optical
  • Particles block a beam of light and then sensed
    by a photocell
  • Light Scattering
  • A laser that illuminates a sample consisting of
    particles suspended in a liquid medium
  • The particles cause the light to be scattered,
    and a detector then digitizes and computes the
    particle-size distribution
  • Suspending Particles
  • Particles suspended in a liquid and then detected
    by electrical sensors

28
Particle Shape and Shape Factor
  • Major influence on processing characteristics
  • Usually described by aspect ratio and shape
    factor
  • Aspect ratio is the ratio of the largest
    dimension to the smallest dimension
  • Ratio ranges from unity (spherical) to 10
    (flake-like, needle-like
  • Shape factor (SF) is also called the shape index
  • Is a measure of the ratio of the surface area to
    its volume
  • The volume is normalized by a spherical particle
    of equivalent volume
  • The shape factor for a flake is higher than it is
    for a sphere

29
Size Distribution and Other Properties
  • Size distribution is important because it affects
    the processing characteristics of the powder
  • Flow properties, compressibility and density are
    other properties that have an affect on metal
    powders behavior in processing them
  • Flow
  • When metal powders are being filled into dies
  • Compressibility
  • When metal powders are being compressed
  • Density
  • Theoretical density, apparent density, and the
    density when the powder is shaken or tapped in
    the die cavity

30
Blending Metal Powders
  • Blending (mixing) is the next step in P/M process
  • Must be carried out under controlled conditions
    to avoid contamination or deterioration
  • Deterioration is caused my excessive mixing and
    causes the shape to be altered or the particles
    harden causing the compaction process to be
    difficult
  • Is done for several significant reasons

31
Reasons for Blending
  • To impart special physical and mechanical
    properties and characteristics
  • Proper mixing is essential to ensure the
    uniformity of mechanical properties throughout
    the part
  • Even one metal can have powder vary in size and
    shape
  • The ideal mix is one in which all of the
    particles of each material are distributed
    uniformly
  • Lubricants can be mixed with the powders to
    improve flow of metal powder into dies, reduce
    friction between metal particles, and improve the
    die life
  • Binders are used to develop sufficient green
    strength
  • Other additives can be used to facilitate
    sintering

32
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33
Hazards
  • Metal powders are explosive because of the high
    surface area-to-volume ratio (mostly aluminum,
    magnesium, titanium, zirconium, and thorium
  • Most be blended, stored, handled with great care
  • Precautions
  • Grounding equipment
  • Preventing sparks
  • Avoiding friction as a source of heat
  • Avoiding dust clouds
  • Avoiding open flames
  • Avoiding chemical reactions

34
Compaction of Metal Powders
  • The third step in the P/M process which the
    blended powders are pressed into various shapes
    in dies
  • The purpose of compaction is to obtain the
    required shape, density, and particle-to-particle
    contact and to make the part sufficiently strong
    for further processing
  • Green compact is known as pressed powder and is
    very fragile and can be crumbled like chalk

35
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36
  • The density of a green compact depends on the
    pressure applied
  • Important factor in density is the size
    distribution of the particles
  • If all particles are the same size then there
    will always be porosity (ex. box filled tennis
    balls will always have space in between them)

37
  • The higher the density, the higher the strength
    and elastic modulus
  • The higher the density, the higher the amount of
    solid metal in the same volume and then the
    higher the strength

38
Equipment
  • The pressure required for pressing metal powders
    ranges from 70 MPa (10 ksi) to 800 MPa (120 ksi)
  • The compacting pressure required depends on the
    characteristics and shape of the particles, on
    the method of blending, and on the lubricant

39
Presses
  • Press capacities ate on the order of 200 to 300
    tons
  • Most projects require less than 100 tons
  • Small tonnage, crank- or eccentric-type
    mechanical presses are used
  • For higher capacities, toggle or knucklejoint
    presses are employed
  • Hydraulic presses can have capacities up to 5,000
    tons and are used for large parts
  • The type of press selected depends on part size
    and its configuration, density requirements, and
    production rate

40
Isostatic Pressing
41
Cold Isostatic Pressing
  • Mold made of elastomer (neoprene rubber,
    urethane, polyvinyl chloride)
  • Commonly pressurized at 400 MPa, up to 1000 MPa
  • Ex. Automotive cylinder liners

42
Hot Isostatic Pressing (HIP)
  • High-melting-point sheet metal
  • High temp inert gas or vitreous fluid
  • Pressures as high as 100 MPa
  • Temperatures of 1200C (2200F)
  • Used for making high-quality parts
  • Ex. valve lifter

43
Hot Isostatic Pressing (HIP)
  • Advantages
  • 100 density
  • Good metallurgical bonding of the particles
  • Good mechanical properties
  • Compacts of uniform grain structure and density
  • Disadvantages
  • Wider dimensional tolerances
  • Higher equipment cost and production time
  • Small production quantities

44
Powder-injection molding (PIM)
  • Metals melting above 1000C (1830F)
  • (carbon, stainless steels, copper, bronze,
    titanium)
  • Ex. Watches, parts for guns, door hinges surgical
    knives
  • Advantages
  • Complex shapes
  • Dimensional tolerances good
  • High production rates
  • Disadvantage high cost and limited availability
    of fine metal powders

45
PIM Process
46
Spray Deposition
  • Shape-generation process
  • Used to produce seamless tubing and piping
  • Produces 99 solid metal density
  • Osprey Process

47
Other Compacting and shaping processes
  • Powder rolling (roll compaction)
  • Extrusion
  • Pressureless compaction
  • Ceramic molds

48
Punch and Die materials
  • Depends on abrasiveness of the powder metal and
    the number of parts being produced
  • Air- or oil-hardened tool steels
  • Hardness range from 60 to 64 HRC
  • Tungsten-carbide dies used for more severe
    applications
  • Control of die and punch dimensions
  • Die and punch surfaces lapped and polished

49
Sintering
  • Green compacts
  • Temperature within 70-90 of melting point
  • Sintering time from 10 minutes to 8 hours
  • Furnace atmosphere (hydrogen, burned ammonia,
    partially combusted hydrocarbon gases, nitrogen)
  • Diffusion mechanism
  • Vapor-phase transport
  • Liquid-phase sintering
  • Spark sintering

50
Sintering metal powders, sintering products,
sintering furnace
51
Secondary and finishing operations
  • Coining and sizing
  • Impact forging
  • Machining
  • Grinding
  • Plating
  • Heat treating
  • Impregnating
  • Infiltration

52
17.6 Design Considerations
  • Keep the shape simple (Avoid thin sections,
    variations in thickness, and high
    length-to-diameter ratios)
  • P/M parts should be made with the widest
    acceptable tolerances
  • Parts should not be less than 1.5 mm thick
  • Letters can be pressed if oriented perpendicular
    to the direction of the pressing and can be
    raised or recessed
  • A radius cannot be pressed into an edge of a part
    because it would require the punch to be
    feathered to a zero thickness

53
  • 17.6 (Cont.)
  • Notches and grooves can be made if they are
    perpendicular to pressing
  • Dimensional tolerances of sintered P/M parts are
    usually on the order of -.05 to .1 mm
  • To the right Examples of P/M parts showing poor
    and good designs.

54
17.7 Process Capabilities of P/M
  • Capabilities
  • It is a technique for making parts from
    high-melting-point metals
  • High production on relatively complex parts with
    less labor
  • P/M reduces scrap and waste, while eliminating
    machining and finishing
  • Wide range of compositions makes it possible to
    obtain special mechanical and physical properties
    (stiffness, vibration damping, hardness, density,
    toughness, and magnetic properties)

55
17.7 (Cont.)
  • Limitations of P/M
  • High cost of metal powder
  • High cost for tooling and equipment for small
    production runs
  • Limitations on part size and shape
  • Mechanical properties such as strength and
    ductility are lower than by forging.

56
17.8 Economics of P/M
  • P/M can produce parts neat net-shape, eliminating
    secondary manufacturing and assembly operations.
  • Because of initial costs of punches, dies, and
    equipment production of quantities of over
    10,000 pieces are economical.
  • Tooling costs for HIP and powder injection
    molding are higher than powder processing
    (because its near-net-shape manufacturing method,
    the cost of finishing operations in P/M are low
    compared to casting and forging.

57
18.2 Shaping of Ceramics
1- First, the raw materials must be ground or
crushed down into fine particles. 2- Next, the
particles must be mixed with additives, which
include binder- to hold particles
together lubricant- to reduce friction and aid
in removing from mold wetting agent- to improve
mixing process (commonly water) plasticizer- to
improve ease of forming mixture agents- control
of foaming and sintering deflocculent- to create
uniform mixture by applying like charges to
all particles, causing them to repel each
other 3- Finally, the material must be shaped,
dried, and fired.
58
Crushing (a.k.a. comminution or
milling) Crushing is typically done in a ball
mill, in either wet or dry conditions. Wet
milling is preferred because it strengthens
particle bonds and limits dust. For correct
sizing, the crushed particles are passed through
a sieve. Mixing Particles are then mixed
with one of the additives listed and described on
the previous slide.
59
Casting Slip Casting (Drain Casting)-The crushed
particles are first mixed with water, then
are poured into a mold. Pouring must be
done properly to avoid air pockets.
When some of the water has been absorbed, the
remainder of the mixture is poured out of
the top of the mold. The top of
the part can then be trimmed. Advantages-
inexpensive components Disadvantages- limited
control of dimensions low production
rate Doctor-Blade Process- Used to produce
ceramic sheets thinner than 1.5mm. Ceramic
mixture is forced under a blade to create a film,
which is then dried in a drying chamber (usually
attached to the same machine).
60
Plastic Forming Primary method of plastic
forming is extrusion. Extrusion- Ceramic
particles mixed into a solution with 20-30
water. Then mixture is pushed through a
small die opening by a screw- type piece of
equipment. Advantages- low cost, high
production Disadvantages- wall thickness
limited
61
Pressing Dry Pressing- High pressure applied to
ceramic particles with a moisture content
below 4, causing compaction. Require
dies made of hardened steel and highly resistant
to wear, making them very expensive.
Friction causes large variation in density
throughout mixture. Wet Pressing- Part formed in
mold under high pressure from a press.
Moisture content in mixture is typically
10-15. High Production, but high cost
and limited dimensional control. Isostatic
Pressing- Used primarily to attain a uniform
density in a part. Accomplished by the
application of inert gases before pressing.
62
Pressing (continued) Jiggering- Similar to
process of making clay pottery. Ceramic
particles are mixed with water, and then formed
while spinning. Only for axisymetric
parts, and little dimensional control. Injection
Molding- Used mostly in high cost operations
where precision is absolutely necessary.
Ceramic particles are mixed with a binder, which
is then burned out. Sections are usually
less than 15mm thick, because anything thicker
tends to have internal cracks and voids. Hot
Pressing (Pressure Sintering)- Pressure and heat
are applied at the same time. Combination
reduces porosity of the part, which increases its
overall strength and density.
63
Drying and Firing Variations in moisture content
and thickness cause parts to crack while
drying. Moisture loss while drying can result in
a size decrease of 15-20. Green state
describes the state a part is in after it has
been dried and before it is fired because its
softness makes it especially easy to
machine. Firing results in less (but still
existent) shrinkage than drying. Strength and
hardness of ceramics come from firing due to a
bond formed between the oxide particles and
reduced porosity. Nanophase Ceramics- Fired at
lower temperatures than regular ceramics. Easier
to fabricate due to the lower required
temperature.
64
Finishing Operations -Grinding -Lapping and
honing -Ultrasonic machining -Drilling -Electri
cal-discharge machining -Laser-beam
machining -Abrasive water-jet cutting -Tumbling
Glazing- Applying a glaze or enamel to the
ceramic before firing improves both the final
appearance and strength.
65
Forming and Shaping of Glass
Flat Sheet and Plate Glass Float Method- Molten
glass is floated over a bath of molten tin
before it is solidified in a separate chamber. No
additional finishing is necessary. Drawing
Process- Molten glass is squeezed through two
rolls, then moves on o two smaller rolls. Rolling
Process- Similar to drawing process, but patterns
are commonly imprinted from the rolls onto the
glass, leaving a rough finish.
Molten Glass
66
Glass Tubing and Rods Tubing- Molten glass is
wrapped around a mandrel and taken out by two
rolls. Air is blown through the mandrel to
prevent the tube from collapsing into
itself. Some machines manufacture 2000
fluorescent light bulbs per minute using this
method. Rods- Rods are made in exactly the same
way, but without the air blown through the
mandrel. This allows the glass to collapse and
become solid.
67
Discrete glass products
  • Processes used to make discrete glass objects
  • Blowing
  • Pressing
  • Centrifugal casting
  • Sagging

68
Blowing
  • Blowing process Blown air expands a hollow gob
    of heated glass against the inner walls of a
    mold.
  • A parting agent (such as oil or emulsion) is
    usually used to prevent the glass from sticking
    to the mold.

69
Blowing
  • Blow and blow process After blowing a second
    blowing operation can be used for finalizing
    product shape.

70
Blowing
  • Applications Hollow and thin-walled glass items
    (bottles, vases, and flasks)
  • Surface finish Acceptable for most applications

71
Pros and cons of blowing
  • Pros Very economical for high-rate production.
  • Example Highly-automated blowing machines can
    make around 2000 incandescent light bulbs per
    minute.
  • Cons Difficult to control the wall thickness of
    the product

72
Pressing
  • Pressing process A gob of molten glass is placed
    into a mold and pressed by a plunger into a
    confined shape.
  • Molds may be one piece or split. Solidifying
    glass acquires the shape of the mold-plunger
    cavity.
  • Similar to closed-die forging.

73
Pressing
  • One-piece molds cannot be used in pressing if the
    plunger cannot be retracted.
  • One-piece molds cannot be used for thin-walled
    items
  • Split molds can accommodate thin-walled products

74
Pressing
  • Pressing can produce higher dimensional accuracy
    than blowing.

75
Press and blow process
  • After a part is pressed, it is blown to further
    expand the glass into the mold.

76
Centrifugal Casting (Spinning)
  • Centrifugal casting process The centrifugal
    force pushes the molten glass against the wall.
  • TV picture tubes and missile nose cones can be
    made with centrifugal casting.

77
Sagging
  • Sagging process A sheet of glass is placed over
    a mold and heated. The glass sags by its own
    weight and takes the shape of the mold.
  • Typical applications include dishes, sunglass
    lenses, mirrors for telescopes, and lighting
    panels.

78
Glass ceramics manufacture
  • Trade names Pyroceram, Corningware
  • Contain large proportions of several oxides.
  • Manufacturing involves a combination of methods
    used for ceramics and glasses.
  • Shaped into discrete products (such as dishes and
    baking pans) then heat treated.
  • After heat treating glass is devitrified
    (recrystallized).

79
Glass Fibers
  • Continuous glass fibers are drawn through
    multiple orifices (200 to 400 holes) in heated
    platinum plates at speeds as high as 500 m/s
    (1700ft/s).
  • Fiber diameters as small as 2?m (80?in.)
  • Coated with chemicals to protect fiber surface.
  • Short fibers (chopped) are made as compressed air
    or steam passes the fiber as it passes through
    the orifice.

80
Glass Fibers - Glass wool
  • Glass wool is short glass fibers.
  • Glass wool is used for thermal and acoustic
    insulation.
  • Made by a centrifugal spraying process. Molten
    glass is ejected (spun) from a rotating head.
  • Glass wool fiber diameter is typically 20 to 30
    ?m (800 to 1200 ?in.)

81
Techniques for Strengthening and Annealing Glass
  • Glass can be strengthened by thermal tempering,
    chemical tempering, and laminate strengthening.
  • Finishing operations can be used to impart
    desired properties and surface characteristics.

82
Thermal Tempering
  • Surfaces of the hot glass are cooled rapidly by a
    blast of air. The surfaces solidify and are
    forced to contract as the bulk of the glass
    begins to cool.
  • Surfaces develop residual compressive stresses.
  • The interior develops tensile stresses.
  • Compressive surface stresses improve the strength
    of the glass.

83
Thermal Tempering
84
Chemical Tempering
  • The glass is heated in a bath of molten KNO3,
    K2SO4, or NaNO3, depending on the type of glass.
  • Ion exchanges take place and larger atoms replace
    smaller atoms on the surface of the glass.
  • Residual compressive stresses develop on the
    surface.

85
Laminated Glass
  • Glass is strengthened through a method called
    laminate strengthening.
  • Two pieces of flat glass have a thin sheet of
    tough plastic in between.
  • When the glass is cracked, its pieces are held
    together by the plastic sheet.

86
Bulletproof Glass
  • Bulletproof glass basically consists of glass
    laminated with a polymer sheet.
  • Thickness ranges from 7 to 75 mm (.3 to 3 in.)
    Thinner glass is for handguns and the thicker
    glass is for rifles.

87
Finishing Operations
  • Annealing removes residual stresses by heating
    the glass to a certain temperature and then
    cooling gradually.
  • Annealing time ranges from a few seconds to 10
    months.
  • Glass products may be cut, drilled, ground, and
    polished.
  • Care should be exercised in all finishing
    operations to ensure there is no surface damage.

88
Design Considerations for Ceramics and Glasses
  • Ceramic and glass products require careful
    selection of composition, processing methods,
    finishing operations, and methods of assembly
    with other components.

89
References
  • http// www.designinsite.dk/gifs/pb1007.jpg
  • www.cullenconsulting.com.au/ epsi/images/
  • www.scielo.br/.../ jbsmse/v26n1/a07fig03.gif
  • www.turkcadcam.net
  • www.esrf.fr/.../2002/ Materials/MAT3/fig081
  • www.mrf-furnaces.com/ images/4station.jpg
  • met.iisc.ernet.in/ govind/Spray-forming.jpg
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