Enhancement of Materials Flashcards
Why add lubricants to polymer stock?
reduces viscosity of molten polymer making it less sticky and allowing more intricate shapes to be formed
also allow moulding temperature to be lowered saving energy
Why add thermal antioxidants to polymer stock?
prevent polymer oxidising or discolouring during excessive heat during processing
Why add pigments to polymer stock?
give colour
Why add anti-statics to polymer stock?
reduce likelihood of polymer building us a static charge
Why add flame retardants to polymer stock?
reduce likelihood of combustion or spread of fire
Why add plasticisers to polymer stock?
allow plastics to become less hard and brittle at normal temp use e.g. added to LDPE food wrap allowing wrapping to stretch
also allow polymers to be easily formed at higher temperatures
Why add fillers to polymer stock?
provide bulk so less polymer required
some minerals e.g. chalk help increase thermal conductivity (=shorter mould cycle)
Why add biodegradable plasticisers to polymer stock?
more flexible, softer and easier to break down
Why add biobatch additive to polymer stock?
oxy,photo and hydro degradable
Why add antioxidants to polymer stock?
reduce environmental deterioration of polymer
also help prevent increased brittleness
often used in garden furniture
Why add UV light stabilisers to polymer stock?
prevent polymer chains being broken down by sunlight
Why add resins and laminations to wood?
enhance properties of usable parts of trees such as sawdust
e.g chipboard
Give an application for resins with fire retardants
cladding
Why add laminations to wood?
enhance aesthetics
Why add preservatives to wood?
protection from fungal and insect attack
e.g. preheated with copper based preseravtives
Why add pigment to wood?
colour
can also be used on softwoods to look like hardwood
Why add fire retardant preservatives to wood?
used to pressure treat woods
can also give resistance to high-wear use
Why add modified natural polysaccharide to wood?
cure within wood cell structure
=increase hardness, stability etc.
Why add structural composite lumber and laminated veneer lumber to wood?
less prone to defects
great load bearing properties
What is work hardening?
when metal is cold worked (such as bending or rolling)
crystals within metal are distorted = improved tensile strength and hardness
less ductility
effects can be removed by annealing
What is annealing?
used to make word hardened metal easier to work
metal heated then cooled very slowly (allowing metal crystals to grow and slowly move into place)
What is case hardening used for?
used for hardening surface of steel with less than 0.4% carbon content
produces outer casing while inner retains original softer properties
Explain the two steps of case hardening
- Carburising - changes chemical composition of surface of low carbon steel so it can absorb more carbon to increase surface hardness
placed in ceramic box packed with carbon and heated causing carbon atoms to diffuse into materials structure to build up surface content
longer the time, thicker the carbon - Quenching - hot metal is quenched in water to fast cool it and seal hard surface case
What is hardening?
medium and high carbon steels are heated to alter crystalline structure, hold then quench
