4.2

Alloying

Alloying

Alloys are a mixture that contains at least one metal.

• Alloying increases strength and hardness

• Alloying reduces malleability and ductility, of alloys compared to pure metals.

• This is due to the presence of “foreign” atoms which interfere with the movements of atoms in the crystals during plastic deformation

Work hardening (Cold working or Strain Hardening)

Is the process of toughening the a metal through plastic deformation.

Tempering

Tempering is a heat treatment process

• Usually carried out after hardening of a metal to:

  • increase its toughness and ductility

  • decrease hardness and brittleness

Superalloys

Exhibits excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion.

Creep

Creep is the tendency of a metal (or material) to slowly move or deform permanently due to the long term exposure of stress that are below the yield strength or ultimate strength of the metal.

Oxidation resistance

• Oxidation is the interaction between oxygen and different substances when they make contact, such as rust Fe2O3

• Oxidation resistance is the ability of a material to resist the direct and indirect attack of oxygen (oxidation) and degradation.

Ferrous Alloys

Mild Steel

Carbon content of 0.1 to 0.3% and Iron content of 99.7 – 99.9%. Used for engineering purposes and in general, none specialised metal products.

Ferrous Alloys

Stainless Steel

Made up of Iron, nickel and chromium. Resists staining and corrosion and is therefore used for the likes of cutlery and surgical instrumentation.

Ferrous Alloys

Cast Iron

Carbon 2 – 6% and Iron at 94 to 98%. Very strong but brittle. Used to manufacture items such as engine blocks and manhole covers.

Non-ferrous Alloys

Aluminum

An alloy of aluminum, copper, and manganese. Very lightweight and easily worked. Used in aircraft manufacture, window frames, and some kitchenware. Pure Aluminum can be used in drink cans.

Non-ferrous Alloys

Copper

Copper is a natural occurring substance. The fact that it conducts heat and electricity means that it is used for wiring, tubing and pipe work.

Non-ferrous Alloys

Brass

A combination of copper and zinc, usually in the proportions of 65% to 35% respectively. Is used for ornamental purposes and within electrical fittings.

Non-ferrous Alloys

Silver

Mainly a natural substance, but mixing with copper creates sterling silver. Used for decorative impact in jewellery and ornaments, and also to solder different metals together.

Non-ferrous Alloys

Lead

Lead is a naturally occurring substance. It is heavy and very soft and is often used in roofing, in batteries and to make pipes. (from CastleMetalsEurope)

Natural Timber

A natural composite material comprising cellulose fibres in a lignin matrix.

Seasoning

Seasoning is the commercial drying of timber which reduces the moisture content of wood.

Air-drying

Stacks of sawn timber in the open or in large sheds. There is little control over the drying process as the weather elements have affects.

Kiln-drying

Stacks of sawn timber in a kiln, to reduce the moisture content in wood, where the heat, air circulation, and humidity is closely controlled.

Timber Defects

Warping

Distortion in wood caused by uneven drying, which results in the material bending or twisting.

Timber Defects

Bowing

Is the warping along the length of the face of the wood.

Timber Defects

Cupping

Warping across the width of the face of wood, in which the edges are higher or lower than the center.

Timber Defects

Twisting

Warping where the two ends of a material do not lie on the same plane.

Timber Defects

Knots

Imperfections in timber, caused by the growth of branches in the tree that reduces its strength.

Natural Timber

Is timber that is sawn from the tree and is used as is (ie not made into plywood, etc). This includes hardwood and softwood trees.

Characteristics of natural timber

• Tensile Strength: The tensile strength of natural timber is greater along the grain than across the grain.

• Resistance to damp environments: is very resistant.

• Longevity: Hardwoods very good. Softwoods good.

• Aesthetic properties: natural colours range (red, purple, cream and brown). The grain can add to its aesthetics.

Man-made timbers

Plywood

(very thin slices of wood) glued together perpendicularly.

Man-made timbers

Particle board (Chipboard)

Made from different sizes of wood chips, joined with glue and pressed.

Man-made timbers

MDF (Medium Density Fibre Board)

Strands of fibre ruled together and pressed into sheets.

Lamination

Covering the surface with a thin sheet of another material (plastic laminate, wood veneer, etc) typically for protection, preservation or aesthetic reasons.

Characteristics of man-made timber

• Tensile strength: depends on the man-made timber

  • Plywood – high tensile strength in all directions

  • Particle board and MDF – very low

• Resistance to damp environments: depends on the man-made timber.

  • Exterior plywood – excellent.

  • Interior plywoods very low

  • Particle board and MDF – very low

• Longevity:

  • Plywood is high

  • Particle board and MDF is low to medium

• Aesthetic properties:

  • Plywood if the top layer is of a nice timber like Beech will be good

  • Particle board and MDF requires finishing or a sheet of lamination (see previous section)

Creosote

A material that penetrates the timber fibres protecting the integrity of the wood from attack from borer, wood lice and fungal attack.

Reasons for Treating and finishing timbers

• Reducing attack by insects, fungus and marine borers by making the wood poisonous

  • Creosote: A material that penetrates the timber fibers protecting the integrity of the wood from attack from borer, wood lice and fungal attack.

• Protection from the weather

• Protection from Dry rot.

• Where timber is subjected to decay and attack by fungus.

• Improving chemical resistance

• Enhancing aesthetic properties

• Modifying other properties

Glass

Glass is primarily composed of silca sand (silicon dioxide) together with limestone (calcium carbonate) and Soda Ash (sodium carbonate) and small quantities of a few other chemicals.

Characteristics of glass

• Transparency, allows light to pass through thus allowing you to see the contents of a jar or through a window.

• Colour, colour can de deigned in my adding chemicals

• Strength – low tensile strength but high compressive strength

• Brittleness, it has a low impact strength and thus will shatter easily (low toughness).

• Hardness, high hardness and wont scratch readily.

• Un-reactivity – is chemically inert so leaching of acid based contents is not a problem.

• Non-Toxic due to its un-reactivity therefore suitable for food storage.

• Non-porous, thus will hold liquids or stop moisture seeping from outside.

• Insulator.

• 100% recyclable and is continuously recyclable

Recycling of Glass

• Recycled glass is known as cullet which is added to new raw materials to make new glass.

• It reduces the energy required thus the costs in producing new glass.

• When recycled the glass is separated into the same colours groups (due to chemical compounds) then are crushed .

Applications of glass

Soda Glass

This commercial glass and is the most commonly used. Has medium to low thermal shock, in other words it will shatter going from cold to hot or the other way.

Applications of glass

Borosilicate (Pyrex)

Commonly known as Pyrex. The chemical composition  of Soda Glass is altered by the addition of oxides which improve thermal conductivity.

Applications of glass

Toughened

Is heated up to the point of melting then blasted with cold air. This makes the outside is in compression and the slower cool interior is in tension. When it is impacted it shatters into little pieces rather than sharp shards.

Applications of glass

Laminated

It is layers of glass and plastic sheets between them. When impacted, the glass fragments are held in place. This prevents cracks from growing

Application of glass

Glass Fibre

Is a very long strand of glass. Sometimes these are woven into mats and used as glass fiber reinforced plastic when combined with a resin (polymer).

Thermoplastics

Are linear chain molecules with weak secondary bonds between the chains.

General for thermoplastics characteristics include:

• • ductile

  • low stiffness – squishy water bottles for example

  • easily injected into a mould

  • can be reshaped after heating

  • easily and cost effectively manufactured

PP (Polypropene)

• lowest density of thermoplastics

• good toughness

• resistant to fats

• high resistance to temperature

• good fatigue resistance

• semi-rigid

• translucent

• recyclable

PE (Polyethene)

• low stiffness (semi-rigid, flexible)

• high toughness

• translucent

• commonly HDPE and LDPE

• recyclable

PET (Polyethylene terephthalate)

• high strength

• rigid

• thermal resistant

• recyclable

ABS (Acrylonitrile butadiene styrene)

• high impact resistance

• high toughness

• dimensional stability

• good stiffness

• good workability properties

• versatile material

• repayable – not all centres will receive it.

HIPS (High Impact PolyStyrene)

• easy of fabrication

• high impact strength

• good aesthetics-various colours

• rigid/stiff

• low cost

• dimensional stability

• good workability properties

• non-biodegradable

PVC (Polyvinyl chloride)

• Can be stiff or flexible (when a plastizeer is added)

• good aesthetics – colours

• low cast

• non-biodegradable

Type of thermoset:

Polyurethane

• It can be hard like fibreglass or soft and spongy

• wide range of hardness

• good tensile and compressive strength

• toughness – impact resistant

• good electrical resistivity

• good bonding properties

• good resistant to damp environments

Type of thermoset:

Urea-formaldehyde

• high (surface) hardness

• high tensile strength

• good

• electrical resistivity

• low resistance to damp environments

• deterioration of indoor are quality

Type of thermoset:

Melamine resin

• high hardness (one of the highest)

• high chemical resistance resin

• medium fire and heat resistant (will decompose under great heat)

• resistant to moisture (damp environments)

Type of thermoset:

Epoxy resin

• high thermal resistance

• high chemical resistance

• high toughness

Recovery and disposal of plastics

• Nearly all plastics can be recycled it mostly depends on economic, technical and logistical factors

• Thermoplastics can be easily recycled.

  • come in a range of chemical compounds and therefore need to be sorted for recycling

• Thermosets not so easy (and expensive to do so)

  • need to be ground into a powder which adds time and costs.

  • Often get sent to landfill

Natural fibres

Materials produced by plants or animals that can be spun into a thread, rope or filament.\

Common examples include:

• Wool

• Cotton

• Silk

Synthetic fibres

Fibres made from a man-made material that are spun into a thread; the joining of monomers into polymers by the process of polymerisation.

Acrylic, nylon, polyester, lyrca, rayon, acetate, spandex, and Kevlar

Properties of natural fibres

• Absorbency – is very high

• Strength – low tensile strength

• Elasticity – not very elastic

• Effect of temperature – will burn but does not melt.

Properties of synthetic fibres

• Absorbency –  is very low

• Strength – high tensile strength

• Elasticity – highly elastic (like stockings, socks etc)

• Effect of temperature – will burn and melt.

Conversion of yarns into fabrics:

Weaving

• The act of forming a sheet like material by interlacing long threads passing in one direction with others at a right angle to them.

Conversion of yarns into fabrics:

Knitting

• A method for converting a yarn into fabric by creating consecutive rows of interlocking loops of yarn.

Conversion of yarns into fabrics:

Lacemaking

• A method for creating a decorative fabric that is woven into symmetrical patterns and figures.

Conversion of yarns into fabrics:

Felting

• A method for converting yarn into fabric by matting the fibres together.

What is a composite?

A mixture composed of two or more materials with one acting as the matrix (glue) the other acts as a reinforcement (fibres/sheet/particles).

Composition and structure of composites

Concrete

Water, Portland cement, and aggregates (gravel etc)

Composite and structure of composites

Engineered wood

Also called composite wood, man-made wood, or manufactured board. gluing sheets (veneer), particles or stands of wood together.

Composite and structure of composites

Plywood

Sheets of venner glued together with the grain perpendicular to each sheet.

Composite and structure of composites

Particleboard

Chips of wood glued together (see above image).

Composite and structure of composites

Fibreglass

Stands of glass, formed into a matt and then covered in resin (polymer/thermoset plastic).

Composite and structure of composites

Kevlar

Para-aramid synthetic fiber covered in a resin

Composite and structure of composite

Carbon

Reinforced plastic – carbon fibres formed into a matt (see above image) then covered in resin.

Composite and structure of composite

Laminated veneer lumber (LVL)

Uses multiple layers of thin wood assembled with adhesives