engineering

What is normalising

a heat treatment that results in tough metal with some ductility

What metal is normalising carried out on

carried out on work hardened steel which is heated and allowed to cool in the air

How does normalising work

allows atoms to rearrange within existing grains

doesn't allow grains to grow so steel doesn't soften that much

What metals is annealing used for

both ferrous and non - ferrous metals

what does annealing do

allows grains to grow in metal relieving internal stresses and relocating dislocations to new grain boundaries

what is the process of annealing in steel

furnance is switched off and it is allowed to cool slowly after annealing

what is the process of annealing in aluminium

annealing temperature most be closely monitored ( 350 - 400 degrees) as it melts at 660 degrees

heated to dull red and then cooled in water.

what is the process of annealing in copper

Black scale may appear from corrosion so a process called pickling (where a metal is put in dilute acid) is performed

what is the process of annealing in brass

similar to copper

must be cooled slowly as it is brittle

pickling is also performed to it

What are the two types of arc welding

Tungsten inert gas (TIG)

Metal inert gas (MIG)

What is the difference between MIG and TIG

TIG:

spark created between non consumable electrode and work piece with filler added separately if needed

MIG:

spark is made using a consumable electrode and workpiece

How does arc welding work

Heat source moves along the joint melting the weld pool

Area behind the weld pool solidifies quickly

A shielding gas flows over the arc and joint preventing oxidation

In MMA welding flux from filler rod covers the weld instead

This must be cleaned off after the joint has been cooled

What is annealing

heat treatment that makes a metal softer and easier to work

metal is heated to a temperature the grains can grow within

What is quenching

the rapid cooling of a hot metal by immersing it in a liquid often oil or brine

What is tempering

a heat treatment to remove some of the brittleness in hardened steel at the cost of some hardness

What is carburising

the addition of carbon to the surface of low carbon steel to improve hardness and strength

What is hardening

a heat treatment that increases hardness and the strength of a metal due to change in arrangement of its atoms

what is cold working

repeatedly bending or hammering a material

what is corrosion

the reaction between the surface of a material and its environment that eats away at some of the material

coating can be added (eg. painting, dip coating, plating\0 to prevent this as corrosion reduces the appearance of a material

how does cold working work

when a material isn't heated before work is done to it the grains in the affected area of the metal stretch out making them thinner and smaller

what is work hardening

an increase in the strength or hardness to a metal due to cold working

this is because many metals get harder as work is done to them

how can carburising be part of the hardening process

heating steel to red hot then dipping it in carbon powder

steel part packed in charcoal granules then heating it

steel is held in temperature for a few hours and allowed to "soak" so carbon diffuses through surface

steel part heated in furnace containing carbon rich gas

steel is then left to soak for several hours

What is an alloy

a mixture of 2 or more metals

what are the two types of metals

ferrous

non ferrous

What are ferrous metal examples

cast iron (good compressive strength. Used for engine blocks and vices)

Low carbon steel (tough and low cost stronger than most non ferrous metals. Used for car bodies, nails and screws)

High carbon steels (strong and hard. Difficult to form)

Stainless steel ( strong and hard. Good corrosion resistance. Expensive. Used for cutlery, sinks)

what are some non ferrous metal examples

Aluminium (light, soft, ductile, malleable, Good conductor of heat and electricity and corrosion resistant. Used for aircraft bodies and cooking utensils)

Copper (malleable, ductile, tough. Good conductor of heat and electricity, corrosion resistant. Casts well and joins easily. Used for castings and ornaments)

Brass (tough, hard wearing, corrosion resistant. Used for bearings and coins)

Lead (soft, malleable and heavy. Corrosion resistant, easy to work and melts at low temperatures. Used for roof coverings and soft solders)

Zinc (low melting point, very corrosion resistant, easily worked. Used for galvanising steel)

What is strength

the ability for a material to withstand a force being applied it

What are the three types of strength

Tensile strength: how well a material resists a pulling force

Compressive strength: How well a material resists a squeezing force

Torsional strength: how well a material withstands a twisting force

What is yield strength

the amount of stress at which a material will permanently start to deform

the material will return to original size and shape once the stress is removed

What is ultimate tensile stress

the amount of stress at which a material breaks

What is ductility

the amount an object can be deformed

what is malleability

the ability of a material to be deformed without rupturing

what is hardness

the ability of a material to resist wear and abrasion

what is toughness

the ability of a material to withstand impact without breaking

What is brittleness

the opposite of toughness

a brittle material will shatter or crack at a response to impact

what is stiffness

a materials ability to resist bending

How is stiffness calculated

using youngs modulus

what is a composite

a type of material made by combining two or more different types of material which remain physically distinct in structure (they aren't chemically combined)

what makes up a composite

a reinforcement (provides strength)

the matrix (holds the reinforcement making it rigid)

Composite examples

MDF (made from wood fibres + adhesive matrix smooth finish, easily machined, cheap)

GRP (made from glass fibres + resin matrix high strength, low density, chemical resistant)

Structural concrete (better tensile strength than pure concrete)

OSB (made from wood strands + adhesive matrix similar to plywood)

Types of reinforcements

Fibres and strands

Plies or laminates

Particles

What effects the properties of a reinforcement

Size, shape, quantity and distribution of reinforcement

Eg. if the reinforcement is all aligned in the same direction it will be strong in that direction but weak in others

Are composites recyclable

No

What is soldering

joining process where metal parts are attached together using a filler wire which melts and runs between them

What are the two types of soldering

Soft
Hard

What is soft soldering

used to attach components onto a PCB

Solder wire is pushed into the joint

The solder then melts and flows into the space between metal parts

What is hard soldering

also called silver soldering

used for making jewellry

solder melts at 620 - 740 degrees

melted using a flame

flux is applied directly to the joint to prevent oxidation of metals

What is brazing

joining process where metal parts are attached together using a filler wire which melts and runs between them with heat provided by a flame or oven

How does brazing work

the surface is cleaned of oxides, rust, paint and grease

a flux is applied to prevent oxidation

joint is heated to 400 - 1200 degrees melting metal filler

then allowed to cool and harden

What is welding

joining process for metal parts where the edges of the parts are melted together and form the joint with additional filler metal if needed

How does welding work

joint is thoroughly cleaned

flame or electric spark is used as a heat source

what are threaded fastenings

products like screws, nuts and bolts that can be used to make temporary joints

what are rivets

used to hold sheets of metal, polymers and different materials together.

How are rivets used

hole is drilled into overlapping sheets of material

a rivet is inserted through the hole

ends are hammered over
Access to both sides of the joint is needed for this joining process

How does a pop rivet work

hole is drilled into overlapping sheets of material

a pin is pulled through the rivet that is in the hole joining the sheets

the pin then breaks away

what is surface finishing

modifying the surface of a part

What is painting

A type of surface finish

a coloured substance which is spread over a surface and dries to leave a thin coating

can increase corrosion resistance and appearance

applied manually using a paintbrush

quick and low cost

what is dip coating

A type of surface finish

a polymer coating is applied to the metal (eg. PVC, nylon, polythene)

provides shiny, wear resistant and corrosion preventitive finish

How does dip coating work

dipped in a fluidised bed of polymer particles

polymer particles stick to surface and melt until required thickness is achieved

coated part is reheated to ensure polymer powder has melted

what is electroplating

process where a part to be coated is placed in a chemical bath and current is passed through it to build a coating

How does electroplating work

A thing metal coat (eg. zinc, copper, nickel or tin) is produced

the part to be coated is put in a bath containing a solution of chemical salts and then attached to the negative side of the electricity supply

the metal for the coating becomes the anode creating a circuit

the anode dissolves and a thin part builds up as the current flows through

the strength of current and concentration of the solution controls the amount of metal disposition

What is anodising

An electroplating process where a protective oxide layer is formed on the metal part being plated

colour can be added to tint the coating for attractiveness

used for jewelry and dental implants

What is galvanising

applying a coating to steel by dipping it in molten zinc

zinc is a good corrosion resistant coating

used for car body panels, buckets and dustbins

what is polishing

the process of smoothing the surface if a part by removing or wearing away a small amount of the material

used for metals and edges of polymer products

a buffing wheel or non abrasive cloth is used

gives material a shinier appearance and surface is smoother

what is a linkage

a system consisting of rods connected via pivots - used to change to the size of a force, the direction of motion and/or the type of motion

Linkage examples

a system consisting of rods connected via pivots - used to change to the size of a force, the direction of motion and/or the type of motion

Linkage examples

reverse motion linkage: reverse the direction of movement

parallel motion linkages: use parallel connecting links. the input and output movement are the same direction

bell cranks: change horizontal movement to vertical movement or vice versa

What are the four main types of motion

Linear motion: motion in a straight line

rotary motion: motion that turns in a circle

reciprocating motion: motion that goes back and forth in a straight line

oscillating motion: a swinging motion from side to side

What is a cam and follower

a type of mechanism that converts rotary motion to reciprocating motion

used to control intake and exhaust valves in internal combustion engines ensuring they operate in time with the pistons

what is a rack and pinion mechanism

changes rotary motion to linear motion

what is a crank and slider mechanism

used to convert rotary motion to reciprocating motion

What is a gear train

two or more spur gears that mesh together to transmit rotary motion and drive

What do different gear trains do

A large gear driving a small gear results in increased speed but less torque

a small gear driving a large gear will increase torque but decrease speed

What is a pulley system

a system consisting of pulley wheels and a belt or rope. Used to transmit drive or reduce effort when lifting objects

What is an alternative to a gear system

Chain and sprocket mechanism

It has less parts and is less complex than a gear train

However chain can jump out or break if system isn't properly maintained

What do bearings do

control motion and reduce friction between moving parts

plain bearings provide a sliding contact with the other parts of the machine

a rolling element bearing are placed between two bearings known as races (eg. ball bearings, roller bearings)