Polymers - Specialist Technical Principles

• Common polymers and their uses


  Polyethylene terephthalate - PET - Water bottles
• Common polymers and their uses

  High density polythene - HDPE - fabric conditioner bottles
• Common polymers and their uses

  Polyvinyl chloride - PVC - Plastic toys; cling film
• Common polymers and their uses

  Low density polythene - LDPE - Bread bags
• Common polymers and their uses

  Polypropylene - PP - Yoghurt pots; pen lids
• Common polymers and their uses

  Polystyrene - PS - Packaging; coffee cups
• Sources and origins

  Crude oil:

  Drilled and pumped

  v

  oil tanker

  v

  oil distillery

  v

  fractional distillation

  v

  naphtha vented off from distillery column

  v

  cracking into monomers

  v

  polymeristation
• Use of material properties in commercial products

  eg. Chair:

  • can be injection moulded on mass
  • colours can be changed
  • identical shape allows stacking
  • lightweight
  • easy to clean
• Use of material properties in commercial products

  eg. Plug socket:

  • urea formaldehyde - UF - is used
  • can be compression moulded on mass
  • excellent electrical insulator
  • absorbs little water
  • hard outer high-gloss finish
  • heat resistant
• Stock forms, types and sizes

  Polymer: acrylic

  Stock form: sheet

  Uses: menu holders in bars and restaurants
• Stock forms, types and sizes

  Polymer: Polypropylene

  Stock form: granules

  Uses: pen lids; bottle tops
• Stock forms, types and sizes

  Polymer: Polythene

  Stock form: Powder

  Uses: Dip coating metal objects, eg. coat hangers
• Stock forms, types and sizes

  Polymer: Plastazote

  Stock form: foams

  Uses: swimming pool floats
• Stock forms, types and sizes

  Polymer: PVC

  Stock form: Film

  Uses: Food wrapping
• Stock forms, types and sizes

  Polymer: PLA or ABS

  Stock form: Filament

  Uses: 3D printing
• Scales of production

  One-off / prototype:

  • 3D printing used - environmentally friendly as is an additive not subtractive manufacturing process
  • > Technical filaments can be used
  • Custom-made / bespoke items
• Scales of production

  Batch:

  • Could be laser cut
  • Could then be partially bent with a strip wire heater and a colling jig
• Scales of production


  Mass:

  • production line

  Continuous:

  • Injection moulding can be a continuous manufacturing method
  • Extrusion can also be continuous
• Tools equipment and processes

  • "Chinagraph pencil" - wax or grease based pencil - used to mark polymers -> or alcohol based permanent marker
  • Polymers can be cut with a coping saw or a hacksaw and then filed up to the cutting line
  • Strip-wire heater can be used to bend a thermoforming polymer eg. Acrylic
• Tools, equipment and processes

  Vacuum forming:

  • shape to outline the desired shape is called a former, the hollow bit in the former for the polymer (eg. HIPS) to fill is called the mould
  • PROCESS:
  • HIPS heated
  • Solid former is pressed upwards into the HIPS
  • Vacuum is turned on, removing air around the former
  • The HIPS takes the form of the solid former
  • Former needs a draft angle otherwise the product will get stuck in the mould
• Commercial Processes

  Injection Moulding:

  1. Granules of plastic in a hopper
  2. Moved with an Archimedean screw through the heating chamber
  3. One melted, the polymer is pushed into the mould with a hydraulic ram
  4. The hydraulic ram ensures the correct amount of polymer enters each time
  5. Mould is cooled and plastic removed
• Commercial Processes

  Extrusion:

  • Similar to injection moulding but without the hydraulic ram
  • Polymer is passed through a die continuously
  • used for pipes, tubes and guttering
• Accuracy and Quality Control

  • Due to production methods commonly being automated, as long as the machines are maintained, the product is usually accurate
  • Go No go gauges are used: Go side is lower bound of tolerance, No go side is the upper bound
• Surface treatments and finishes

  • If formed in a mould - self-finishing

  Otherwise:

  1. Polymer is marked at the cutting point
  2. Saw is used near to the line
  3. File is used to remove more material up to the line
  4. Wet and dry abrasive paper used to remove file marks
  5. Fine abrasive paper used for a matt finish
  6. An electric buffer can be used for a gloss finish
• Surface treatments and finishes

  • A pattern can be added using a sublimation printer
  • like a regular ink-jet printer but uses sublimation ink

  1. Pattern is printed onto heat-proof paper
  2. Paper is place onto the polymer and heated with a heat press to about 200°C
  3. Polymer is removed. Paper is removed from the polymer, revealing the image