processes and techniques Flashcards
case hardening
Case hardening is a heat treatment process that can be used to prevent steel or iron from becoming brittle, increase its wear resistance or make it more durable. It is achieved by adding carbon to produce a hardened outer skin while the core of the metal remain relatively
soft.
Alloying
Each of the metals is heated until it becomes a molten liquid; at this point the metals are
mixed, along with any other elements that might be added.
Resin
casting
applications:
Jewellery
● Toys
advantages:
● Small-scale
production
● Low set-up
cost
● No cooling time
● Reusable
mould
dissadvantages:
● Castings are
easily
scratched
● Castings may
not be shiny
equipment:
● Rubber/silicon
mould
sand casting
Sand casting
uses:
● Engine parts
● Fan blades
advantages;
● Sand can be
reused
disadvantages:
● Energy
intensive
equipment:
● Cope & drag
Plaster of
Paris casting
applications:
● Models
● Medical
castings
advantages:
● Low set-up
cost
● Few specialist
tools required
● Has a hard
outer surface
dissadavantages:
● Takes a long
time to solidify
● Incorrect
mixture can
result in brittle
castings
equipment:
● Rubber/silicon
mould
Investment
casting
applications:
● Jewellery
● Complex
components
advantages:
● Little further
processing
needed
dissadvantages:
● Energy
intensive
● Long cooling
time
equipment:
● Cope & drag
● Casting sand
● Parting powder
finishes
– paints, varnishes, sealants,
preservatives, anodising, electro-plating, powder
coating, oil coating, cathodic protection
paints
acrylic, emulsion, enamel, gloss, spray, fabric paint
Varnish
generally only used on hardwoods or softwoods. Varnish
can be clear of have some form of stain included, for example to make the wood look older
than it actually is. Varnish enhances the grain of the wood and can provide a very durable
protective coating to the wood, including making it water resistant.
Sealants
Some absorbent materials, such as MDF or Styrofoam, need to be sealed before they can
have a further paint finish applied to them. The sealant often includes adhesives which
prevent the paint from soaking into material which would leave an uneven finish.
Preservatives
Preservatives help to improve the resistance of wood to such attack
and increase the life span of the timber
Anodising
Anodising is a process that can be used to add a coating to aluminium. This coating improves
resistance to wear and can also be decorative. It is possible to anodise aluminium in a range
of different colours. To anodise aluminium the piece that is going to be treated is made in to
an anode and placed in to an acid solution.
Electro-plating
To electroplate a metal an electric current is passed from one terminal through an electrolyte
liquid to another terminal. As electricity flows through the electrolyte the metal atoms within
it separate and form a thin layer on one of the electrodes.
Powder coating
Powder coating has historically been used on metals such as aluminium alloys to provide them with a tough outside finish that offers more protection than paint. Modern technologies have however made it possible to powder coat other materials. The process is carried out by using an electrostatic charge that attracts the thermosetting plastic powder to the surface that is going to be treated and then heating this so that the plastic melts and flows to form the coating which cures at a higher temperature. Thick protective coats can be applied, and the coating does not run (unlike paint), whilst because no solvents are involved the hazards to health and the environment are lower than alternatives.
Oil coating
Adding a layer of oil to a ferrous metal prevents it from rusting. This is because the oil
prevents air coming in contact with the surface of the metal and therefore stops it oxidising.
