PROCESSING OF CERAMICS
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PROCESSING OF CERAMICS AND CERMETS. Processing of Traditional Ceramics Processing of New Ceramics Processing of Cermets Product Design Considerations. Prepared by the IAPD Education Committee (Module 1) Presented courtesy of Modern Plastics, Inc. Overview of Ceramics Particulate Processing.

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Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

PROCESSING OF CERAMICS AND CERMETS

  • Processing of Traditional Ceramics

  • Processing of New Ceramics

  • Processing of Cermets

  • Product Design Considerations

Prepared by the IAPD Education Committee (Module 1)

Presented courtesy of Modern Plastics, Inc.

The IAPD Plastics Primer, Module 1


Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

Overview of Ceramics Particulate Processing

  • Traditional ceramics are made from minerals occurring in nature

    • Products include pottery, porcelain, bricks, and cement

  • New ceramics are made from synthetically produced raw materials

    • Products include cutting tools, artificial bones, nuclear fuels, and substrates for electronic circuits

  • The starting material for all of these items is powder

Prepared by the IAPD Education Committee (Module 1)

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The IAPD Plastics Primer, Module 1


Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

Overview of Ceramics Particulate Processing - continued

  • For traditional ceramics, the powders are usually mixed with water to temporarily bind the particles together and achieve the proper consistency for shaping

  • For new ceramics, substances other than water are used as binders during shaping

  • After shaping, the green parts are fired (sintered), whose function is the same as in powder metallurgy:

    • To effect a solid state reaction which bonds the material into a hard solid mass

Prepared by the IAPD Education Committee (Module 1)

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The IAPD Plastics Primer, Module 1


Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

Preparation of the Raw Material for Traditional Ceramics

  • Shaping processes for traditional ceramics require the starting material to be a plastic paste

    • This paste is comprised of fine ceramic powders mixed with water

  • The raw ceramic material usually occurs in nature as rocky lumps, and reduction to powder is the purpose of the preparation step in ceramics processing

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Ingredients of Ceramic Paste for Shaping

  • Clay (hydrous aluminum silicates) - usually the main ingredient because of ideal forming characteristics when mixed with water

  • Water – creates clay-water mixture with suitable plasticity for shaping

  • Non‑plastic raw materials, such as alumina and silica - reduce shrinkage in drying and firing but also reduce plasticity of the mixture during forming

  • Other ingredients, such as fluxes that melt (vitrify) during firing and promote sintering, and wetting agents to improve mixing of ingredients

Prepared by the IAPD Education Committee (Module 1)

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Shaping Processes

  • Slip casting

    • The clay-water mixture is a slurry

  • Plastic forming methods

    • The clay is plastic

  • Semi‑dry pressing

    • The clay is moist but has low plasticity

  • Dry pressing

    • The clay is basically dry (less than 5% water) and has no plasticity

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Four categories of shaping processes used for traditional ceramics, compared to water content and pressure required to form the clay

Prepared by the IAPD Education Committee (Module 1)

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The IAPD Plastics Primer, Module 1


Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

Slip Casting

Sequence of steps in drain casting, a form of slip casting: (1) slip is poured into mold cavity, (2) water is absorbed into plaster mold to form a firm layer, (3) excess slip is poured out, and (4) part is removed from mold and trimmed

Prepared by the IAPD Education Committee (Module 1)

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Plastic Forming Methods

  • Hand modeling (manual method)

  • Jiggering (mechanized method)

  • Plastic pressing (mechanized method)

  • Extrusion (mechanized method)

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Jiggering

Similar to potter's wheel methods, but hand throwing is replaced by mechanized techniques

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Sequence in jiggering: (1) wet clay slug is placed on a convex mold; (2) batting; and (3) a jigger tool imparts the final product shape

The IAPD Plastics Primer, Module 1


Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

Semi-dry Pressing

Uses high pressure to overcome the clay’s low plasticity and force it into a die cavity

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Semi‑dry pressing: (1) depositing moist powder into die cavity, (2) pressing, and (3) opening the die sections and ejection

The IAPD Plastics Primer, Module 1


Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

Drying

  • The drying process occurs in two stages:

  • Stage 1 - drying rate is rapid and constant as water evaporates from the surface into the surrounding air and water from the interior migrates by capillary action to the surface to replace it

    • This is when shrinkage occurs, with the risk of warping and cracking

  • Stage 2 - the moisture content has been reduced to where the ceramic grains are in contact

    • Little or no further shrinkage occurs

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Firing of Traditional Ceramics

  • Heat treatment process that sinters the ceramic material

  • Performed in a furnace called a kiln

  • Bonds are developed between the ceramic grains, and this is accompanied by densification and reduction of porosity

  • Therefore, additional shrinkage occurs in the polycrystalline material in addition to that which has already occurred in drying

  • In the firing of traditional ceramics, a glassy phase forms among the crystals which acts as a binder

Prepared by the IAPD Education Committee (Module 1)

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The IAPD Plastics Primer, Module 1


Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

Glazing

  • Application of a ceramic surface coating to make the piece more impervious to water and enhance its appearance

  • The usual processing sequence with glazed ware is:

    • Fire the piece once before glazing to harden the body of the piece

    • Apply the glaze

    • Fire the piece a second time to harden the glaze

Prepared by the IAPD Education Committee (Module 1)

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Advanced Ceramics

  • Structural:Wear parts, bioceramics, cutting tools, engine components, armour.

  • Electrical:Capacitors, insulators, integrated circuit packages, piezoelectrics, magnets and superconductors

  • Coatings:Engine components, cutting tools, and industrial wear parts

  • Chemical and environmental:Filters, membranes, catalysts, and catalyst supports

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Processing of New Ceramics

  • The manufacturing sequence for the new ceramics can be summarized in the following steps:

    • Preparation of starting materials

    • Shaping

    • Sintering

    • Finishing

  • While the sequence is nearly the same as for the traditional ceramics, the details are often quite different

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Powder Injection Molding (PIM)

  • Ceramic particles are mixed with a thermoplastic polymer, then heated and injected into a mold cavity

  • The polymer acts as a carrier and provides flow characteristics for molding

  • Upon cooling which hardens the polymer, the mold is opened and the part is removed

  • Because temperatures needed to plasticize the carrier are much lower than those required for sintering the ceramic, the piece is green after molding

  • The plastic binder is removed and the remaining ceramic part is sintered

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Hot Pressing

  • Similar to dry pressing except it is carried out at elevated temperatures so sintering of the product is accomplished simultaneously with pressing

  • This eliminates the need for a separate firing step

  • Higher densities and finer grain size are obtained, but die life is reduced by the hot abrasive particles against the die surfaces

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Sintering of New Ceramics

  • Since the plasticity needed to shape the new ceramics is not normally based on water, the drying step required for traditional green ceramics can be omitted for most new ceramic products

  • The sintering step is still very much required

  • Functions of sintering are the same as before:

    • Bond individual grains into a solid mass

    • Increase density

    • Reduce or eliminate porosity

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Powder Pressing

  • Sintering - powder touches - forms neck & gradually neck thickens

    • add processing aids to help form neck

    • little or no plastic deformation

  • Uniaxial compression - compacted in single direction

  • Isostatic(hydrostatic) compression - pressure applied by fluid - powder in rubber envelope

  • Hot pressing - pressure + heat

Adapted from Fig. 13.16, Callister 7e.

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15m

Sintering: useful for both clay and non-clay compositions.

• Procedure:

-- produce ceramic and/or glass particles by grinding

-- place particles in mold

-- press at elevated T to reduce pore size.

• Aluminum oxide powder:

-- sintered at 1700°C

for 6 minutes.

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Sheet Glass Forming

  • Sheet forming – continuous draw

    • originally sheet glass was made by “floating” glass on a pool of mercury – or tin

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Adapted from Fig. 13.9, Callister 7e.


Prepared by the iapd education committee module 1 presented courtesy of modern plastics inc

before cooling

surface cooling

further cooled

compression

cooler

hot

hot

tension

compression

cooler

--Result: surface crack growth is suppressed.

Heat Treating Glass

• Annealing:

--removes internal stress caused by uneven cooling.

• Tempering:

--puts surface of glass part into compression

--suppresses growth of cracks from surface scratches.

--sequence:

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Pressing

Gob

operation

Parison

mold

• Fiber drawing:

Compressed

• Blowing:

air

suspended

Parison

Finishing

mold

wind up

Ceramic Fabrication Methods

PARTICULATEFORMING

CEMENTATION

GLASS

FORMING

• Pressing:

plates, dishes, cheap glasses

--mold is steel with graphite lining

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Anatomy of a tree

  • Pith

  • Heartwood

  • Sapwood

  • Cambium

  • Phloem

  • Bark

    • 2 growth spurts

      • Earlywood

      • Latewood

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Hardwoods vs. Softwoods

  • Softwoods

    • Coniferous

    • Grow rapidly

    • Wide bands of earlywood

    • Earlywood – large less dense cell structure

  • Hardwoods

    • Deciduous

    • Grow slowly

    • Narrow bands of earlywood

    • Earlywood dense cell structure

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Common Hardwoods

  • Red Oak

  • White Oak

  • Hard Maple

  • Cherry

  • Walnut

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Typical lumber cuts

  • Plain-sawn

    • Maximizes lumber

    • Prone to distortion

  • Through-and-through

    • Simplest method

    • Lumber is unstable

  • Quartersawn

    • Produces less lumber

    • Close, tight, straight grain

    • More expensive

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Lumber Drying Methods

  • ‘Green’ Lumber

  • Air Drying

  • Kiln Drying

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Common Lumber Distortions

  • 4 types of distortion

    • Bow

    • Crook

    • Cup

    • Twist

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Common Lumber Defects

  • Pitch Pockets

  • Spalling

  • Loose Knots

  • Checks

  • Splits

  • Shakes

  • Honeycomb

  • Wormholes

  • Wane

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Sheet Goods

  • Cover large area w/no seams

  • Dimensionally stable

  • Minimise waste

  • Relatively inexpensive

    • Plywood

    • Particleboard

    • Medium-density Fiberboard (MDF)

    • Melamine board

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Prepared by the IAPD Education Committee (Module 1)

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The IAPD Plastics Primer, Module 1


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Veneering

Veneer is a very thin slice of wood. It is cut like a pencil sharpener cutting a pencil. Each slice of wood is about the thickness of an annual ring.

A slice of veneer is called a leaf. As the leaves are cut they are stacked in order. This means you will get the best possible match of grain and colour.

Veneer can be applied to a manufactured board to produce a cheap stable large board or it can be used to produce decorative effects. If an interesting grain pattern is found the veneers can create a pattern. This is called BOOK MATCHING. Examples are shown below.

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layer it …

Bend it …..

turn it …..

slot it together it …..

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Bent wood technology

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The suitable material for bending

Material with good grain condition (with a little shake)

High ductility in characteristic.

Use materials that are free of defects such as knots and checks

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Laminated Wood Bending

Laminating wood to bend it is a fairly simple process.

need a form or mold but you won’t need to build a steam box or risk burns with steam.

Thin pieces of wood bend easier than thicker ones, but aren’t as strong.

So by laminating thin strips of wood together in a mold or form adds strength and when the glue dries it will hold the shape also.

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Kerf-cut Bending

Kerf-cut bending is done by using your saw to cut slots across the stock.

This will allow the stock to be bent because the kerfs can compress together.

The kerfs are usually only used on the inside of the bend.

then you would use a veneer you cover the entire piece.

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Kerf-cut Bending

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Steaming

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Equipment used for bending process

1.Steamer

2.Bending strap

3.Former

4.Shim

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Microwave heating

Bending small pieces of wood becomes a very simple process with the use of a microwave;

Microwave bending is also steam bending but in a much quicker, more manageable way.

To generate steam when microwaving, wrap the wood in a piece of wet paper towel, place it in a microwave oven and microwave it on high.

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Eight basic wood joints

  • Edge

  • Butt

  • Rabbet

  • Dado

  • Miter

  • Lap

  • Mortise and Tenon

  • Dovetail

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Wood Joints

  • The following are common methods of strengthening joints.

    • Biscuits

    • Using thin wood wafers called biscuits can strengthen wood joints by providing more glue bonding area. Biscuit will expand 2X.

    • You can use a biscuit joiner (also called a plate joiner) to cut precision mating slots in boards for the biscuits.

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Wood Joints

  • The following are common methods of strengthening joints.

    • Glue Block-small triangular or square blocks

    • Corner Blocks-larger than a glue block

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Glues

  • White glue (polyvinyl acetate, or PVA): PVA glue is a white liquid, usually sold in plastic bottles.

    • It is recommended for use on porous materials -- wood, paper, cloth, porous pottery, and nonstructural wood-to-wood bonds.

    • It is not water resistant. Clamping is required for 30 minutes to 1 hour to set the glue; curing time is 18 to 24 hours

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Glues

  • Plastic resin glue (urea formaldehyde):

  • Plastic resin glue is recommended for laminating layers of wood and for gluing structural joints.

  • It is water resistant but not waterproof and is not recommended for use on outdoor furniture.

  • This glue is resistant to paint and lacquer thinners.

  • Clamping is required for up to 8 hours; curing time is 18 to 24 hours.

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Glues

  • Polyurethane glue is one of the best waterproof glues…

  • This reaction causes an expansion of the glue, filling all voids and giving an exceptionally solid glue joint.If the material is dry, spraying a light mist onto it before gluing accelerates the curing process.

  • In many ways, polyurethane may be the best wood glue. It both accepts wood stains and sands well in thin coatings, neither of which are true for PVA wood glues.

  • Most other adhesives act as a sealer on the wood surface. And removing these other adhesives can be difficult because they dry to a "gummy" texture that resists removal from the wood by sanding... the second strong reason to consider trying polyurethane glue for your next project.

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Basic Clamping Systems

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The IAPD Plastics Primer, Module 1


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