1. materials (plastics) Flashcards
What are plastics?
they are made of polymers and are mostly refined from oil
What are most polymers?
synthetic (man-made by chemical engineers)
What are the two categories of polymers?
- thermoset
- thermoplastic
What are thermosetting polymers?
- A polymer, that once set, cannot be reheated or remoulded
- this is because they undergo a chemical change when they set
What are thermoplastic polymers?
A polymer that can be heated and shaped multiple times
What is a polymer?
a plastic
What is plastic memory?
when a polymer is heated and they return to their original shape
What are the characteristics of thermoplastic polymers?
- soft when heated, harden once cooled
- they can be recycled as they can be reheated many times
- plastic memory
What are 3 examples of thermoplastics?
- acrylic
- polypropylene (PP)
- high impact polystyrene (HIPS)
What are the properties of acrylic?
- hard wearing
- will not shatter
- can be coloured
What are 3 examples of thermosetting plastics?
- urea formaldehyde
- melamine formaldehyde
- epoxy resin
What are the uses for acrylic?
- bathtubs
- school projects
- display signs
What are the properties of polypropylene?
- high impact strength
- softens at 150 degrees celcius
- can be flexed many times without breaking
What are the uses of polypropylene?
- school chairs
- crates
What are the properties of high impact polystyrene? (HIPS)
- light but strong
- widely available in sheets
What are the uses of high impact polystyrene? (HIPS)
casings of electronic products
What are the properties of polythene (LDPE)?
- weaker and softer than HPDE
- lightweight
What are the uses for polythene (LDPE)?
- carrier bags
- squeezy bottles
What are the properties of polythene (HDPE)?
- stiff, strong plastic
- used for pipes and bowls
What are the uses for polythene (HDPE)?
buckets
What are the properties of urea formaldehyde?
- colourless plastic
- can be coloured
What are the uses of urea formaldehyde?
- door and cupboard handles
- electrical fittings
What are the steps for injection moulding?
- Clamping
- Injection can begin after the two plates of the mould are clamped together
- Dwelling - the melted plastic fills the entire mould
- Cooling
- Mold opening
- Ejection
What are the steps for blow moulding?
- parison ready
- Mould closes over parison
- Parison inflated to fill mould. Extruder forming new parison
- Bottle removed and trimmed
What are the steps for vacuum forming?
- Mould is made from MDF or expanded polystyrene
- The mould is placed in the bottom of the vacuum former
- The sheet of plastic is placed above the mould and clamped in place
- The electric element (heater) is turned on and begins to warm the plastic sheet
- The thermoplastic becomes flexible as it is heated. The mould is moved up to the plastic using the handle
- The pump is turned on and the air is removed from under the plastic, sucking the plastic over the mould
What are the types of manufacturing processes for plastics?
- Vacuum forming
- Injection moulding
- Blow moulding
