1.3 Enhancements Of Materials Flashcards
What does brittle mean? How to fix?
Something that cannot be bent easily into shape without fracture - using heat treatment can later this to allow it to become less brittle however improving the toughness of the material of the metal less likely to fracture
Note polymers are mostly inert and will resist most chemical inspect and fungal attack the use of additives helps to improve atheistic and working properties
When using polymers they may be heated and melted to form a shape e.g. via injection moulding which can be done to different polymers which have different properties. The additives which make it easier for the polymer to flow easily into the mould is…
Moulding”
Lubricants - Lower the moulding temps needed for polymers, make them less sticky and reduces the viscosity of the polymer so that they can form complex shapes
Thermal antioxidants - help prevent the polymer from oxidising and discolouring during the heating process
Aesthetics:
Pigments - tiny particles which turn the polymers colour into the desired on linked to the tiny pigments
Product function:
Antistatics - polymers are poor conducting materials and so are good at being insulators such as electrical wiring. But the insulating property could lead up to a build up of static charge attracting dirt and dust
Antistatics allow for a build up of moisture from the room reducing the static charge
Flame retardants - adding chlorine, bromine or metal to a polymer reduce the chance of it catching on fire and spreading important for polymers exposed to car engines
Plasticisers - allow plastics to become less hard and brittle at room temps - used in LDPE for food wraps they also allow them to be easily formed at higher temps
Fillers - provide bulk to the material so less of the actual material is needed and improve properties - most used fillers are sawdust and wood flour
If we use mineral fillers they increase the thermal conductivity of the material - heats up and cools down quickly
Pro long life:
Antioxidants - help with reducing environmental deterioration of the polymer from exposure to oxygen in the air
If exposed to the environment they can be Coe brittle and pigment discolouration
UV light stabilisers - prevent polymer chains from being broken down by sunlight - the use will also attack the polymer and cause colour degradation + more brittle
- used in sport seats and synthetic grass playing fields
Encouraging degradation:
Biodegradable plasticisers - like plasticisers will enhance the strength and reduce brittleness making it more flexible and soft which means faster degradation time
Bio- batch additives - oxy degrade in oxygen, photo in light when exposed to uv, hydro in the presence of water
Help reduce the degradation time from hundreds of years to a few months
E.g. food bags
Note wooden material with knots and splits can affect the material overall and stability. Natural wood can split due to the grain pattern and this is one reason why manufactured bards such as made and plywood have been developed as they have a lack of gran structure and consistent strength
What are some of the disadvantages to the use of natural wood?
- the strength properties decrease when the wood is wet
- natural wood is highly combustible
- natural wood is susceptible to fungal attack and decay + insect attacks
- natural wood is anisotropic which means that it is easier to split along its grain than against the grain
Although for these disadvantages enchantments can be made to enhance the properties of the wood
Wood for buildings is highly sought after after due to their attractive grain and colour schemes as well as being natural renewable resource’s which is also an insulating material. What can be done to enhance natural wood?
Adding preservatives such as copper can help with resisting attack and decay from fungal and insects
- copper has excellent properties for this
Pigments can be added to wood to give it different shades of colour
- often for outdoor furniture
- they can also make wood look more expensive and like hardwoods and make them more affordable and environmentally friendly products
Preservatives can be added for fire retardants such as roof systems
How to make the wood harder?
Impregnating the wood with modified natural polysaccharide like celoluse in timber - which cure the wood to give increase in hardness, toughness and stability
Engineered wood covers the classification of manufactured boards typically 1220 and 2440mm
How are manufactured boards made?
Ike clipboard are made from compressing wood chips with resin like UF - a thermosetting polymer
- properties include: very stable and not affected by temperature and humidity also has uniform strength with no grain problems like with natural wood
What can be done to the resins as well?
We can add fire retardant additives to the resin to stop the spread of fire
What is SCL and LVL? Advantages to both uses
Structural composite lumber and laminated veneer lumber are engineered woods made by either layering veneers or strands of wood with resins such as UF and pressing + heat curing them = wood stable billet
State the advantages:
Less prone to defects like warping and splitting or shrinking + greater load properties
Used for beams and rafters
Note metals are made from tiny particles, with their grain size and nature dependant on the material used and the temperature at which the material has been heated to and the rate of cooling - most of the only ways metal can be enhanced is through heating and cooling
What is work hardening?
Cold worked - rolled hammered or bent the crystals within the metal are distorted and changes leading to improved tensile strength and hardness in the worked areas
This is called work hardening
The metal particles are restricted from moving freely and results in less ductility and cracking/damage to the worked area
To reverse work hardening you do annealing
What is annealing?
Make work hardened metal easy to work with making it less brittle and more ductile.
Metal is heated then slowly cooked all ing the metal crystals to move back into place and grow slowly into place. This process is done industrially with an oven at controlled temperatures
Case hardening is for steel with 0.4 percent content of carbon what occurs?
Causing the steel on the outer layer to have a greater hardness and resistance o surface indentation. Keeping the inner core of the metal to its original softer properties
Used on vehicles and gears, bearings
What are the two stages of case hardening
Carbusing:
Changes the chemical composition of the surface of the steel so that is can absorb more carbon to increase its surface hardness
Place in a ceramic box which is where it gets heated for a predetermined length of time
At this temp the carbon atoms diffuse into the material surface to build up the carbon layer
Depth of carbon Ayer is determined by the amount of time left in the ceramic box heated to about 760 degrees
Quenching:
Hot metal is quenched inn water to allow for fast cooling which seals the hardened surface and doesn’t affect the properties of the inner soft core of the steel
- this can be carried in a workshop as well
What is hardening? what happens when the medium/high carbon steel is hardened?
The process of heating the medium and high carbon steels to alter the crystalline structure holding them at this temp for a given time ad the quenching them in water/oil increases the hardness and also increases brittleness
The steel has large internal stresses and are often much harder than required and too brittle for practical uses
Tempering is used as a heat transfer process for medium to high carbon steel after hardening - this reduces the hardness and increases the ductility in the metal as well as decrease the brittleness
How do so?
Heat the metal to the critical point at a given time slowly and air cooled. The exact temp will determine the amount of hardness removed
Increase temp increase loss of hardness and increase in toughness and increase in ductility
What is hardening?
The process of heating the medium and high carbon steels to alter the crystalline structure holding them at this temp for a given time ad the quenching them in water/oil increases the hardness and also increases brittleness
