1.3-Material Enhancement Flashcards
Name some polymer additives
Antistatics
Fillers
Flame retardants
Plasticisers
Stabilisers
Antioxidants
How do preservatives enhance wood?
they penetrate the wood to give the enhanced properties throughout the wood section. They often use a copper based preservative as it is a naturally occurring mineral with excellent fungicidal properties. Pigments can be added to the the preservative to give different shades. Preservatives with fire retardant properties can also be used to treat wood for roofs.
Why is the use of pigments in wood positive?
inexpensive softwoods can be coloured to look like hardwoods so that manufacturers can sell more affordable and environmentally friendly products
What do polysaccharides do in wood?
they cure within the wood cell structure to produce wood that has increased hardness, toughness and stability
How are resins used in manufactured boards?
act as the glue in chipboard and MDF to keep it together. They can be impregnated with fire retardant additives so the boards can be used for cladding, structural components and flooring
What are structural composite lumber (SCL) and laminated veneer lumber (LVL)?
engineered woods made by layering either veneers or strands of wood with resins such as , pressing and heat curing them.
Advantages of boards over natural wood
less prone to defects like warping, splitting or shrinking
greater load bearing properties
resins can be impregnated with fire retardant additive
not affected by temperature or humidity as much
What is work hardening?
when a metal is cold worked (bending, rolling or hammering), the crystals within are distorted and changed, leading to improved tensile strength and hardness in the worked area. It can result in less ductility, cracking or damage in the worked area
What is annealing?
used to make work hardened metal easier to work by making it less brittle and more ductile. Metal is heated and then slowly cooled, allowing crystals to grow and slowly move into place
What is case hardening?
a process used for hardening the surface of steels with low carbon content. It provides an outer casing of greater hardness. There are two stages: carburising and quenching
What is carburising?
changes chemical composition of the surface of low carbon steel so it can absorb more carbon to improve surface hardness. The steel is placed in a ceramic box filled with carbon and is then heated to 950 degrees c
What is quenching?
hot metal is quenched in water. A fast cooling process which seals the hard surface case while not affecting the inner core
What is hardening?
heating steels to alter crystalline structure, holding them at this temperature and then quenching them in water
What is tempering?
heat treatment for steels after hardening to remove excess hardness and increase ductility
