15 - Polymer processes Flashcards
1
Q
Vaccum forming process (6)
A
- Mould is placed on the bed of the platen which is then lowered to the bottom
- Polymer sheet is clamped over the mould and a heater is pulled over the polymer sheet
- When the polymer sheet has softened the platen is raised over the sheet
- Vacuum pump is switched on which sucks the polymer onto the mould
- Once polymer has cooled and returned to a solidified state, the platen is lowered and vacuum is switched off
- Mould is removed from the moulding and excess polymer is trimmed off
2
Q
Vacuum forming:
- Polymer stock form
- Products
A
3
Q
Key features of vacuum forming (3)
A
- Moulds are relatively easy to make but need a draft angle, air holes and rounded corners
- Not cost effective for one-off manufacture
- Small-scale batch and mass production
4
Q
Thermoforming process (2)
A
- Similar to vacuum forming but there is an additional mould that is pressed onto the surface of the polymer sheet at the same time the vacuum is applied
- The two moulds trap the softened polymer in between them giving extra detail to the moulding
5
Q
Thermoforming:
- polymer stock form
- products
A
- Thermoplastic sheet approx 6mm
- Bath, food packaging (fruit punnets, cake boxes, sandwich boxes)
6
Q
Key features of thermoforming
A
- Good for fine detail such as moulding in logos
- Slow process used in industrial production
7
Q
Calendering process (4)
A
- Pellets of thermoplastic is heated so that it melts into a dough-like consistency
- It is then extruded between a series of heated rollers to make it thinner
- Its then finished on cooling rollers
- It is then chopped into standard stock sheet sizes, or in the case of polymer film it is rolled up for storage and distribution
8
Q
Calendering:
- Polymer stock form
- products
A
- Thermoplastic pellets
- Thin polymer sheet and film
9
Q
Key features of calendering
A
- Is an industrial production method, carried out by specialist manufacturers
- Used for continuous production
10
Q
Line bending process
A
Uses an electrically heated element that provides heat along a line to bend sheet of termoplasric shuck as acrylic
11
Q
Line bending:
- Polymer stock form
- Products
A
- Thermoplastic sheet
- Acrylic boxes, sheet or point-of-sale displays
12
Q
Key features of line bending (2)
A
- Quite slow and labour intensive - commonly used in school or college workshops
- Suitable for one-off or limited batch production
13
Q
Lamination (lay-up) process (6)
A
- a mould or former in the shape of the product or component is prepared - made from timber, manufactured boards or high density foam
- Mould or former coated in related agent e.g wax or PVA or parcel tape
- A top layer of gel (gel is polyester resin mixed with a pigment) is applied to give colour and addititives such as prevent UV degradation and hydrolysis
- Fibreglass matting is cut to size and laid over the former then begins the stippling process the matting is available in a range of stock forms including chopped strand, woven and ‘tissue’ which is a fine grade matting for covering the surface
- Step 3 is repeated until the desired thickness is achieved and fine tissue matting is used on the top layers - a vacuum bag may be used to compress the layers of GRP before it sets
- GRP is allowed to set
14
Q
What is the stippling process that takes place during lamination?
A
polyester resin in brushed onto matting and a small roller is used to push out any air bubbles that may form and to smooth out the matting
15
Q
Lamination:
- polymer stock form
- products
A
- Fibre-based composite sheets (GRP, CFRP)
- Boats hulls, kayaks, train carriages, theatre and film props, theme park rides
18
Q
Injection moulding process (5)
A
- Thermoplastic granules are poured into the hopper
- A screw thread is rotated by a motor thus pulling the granules through the chamber and past electric heaters
- The heaters melt the polymer
- When a sufficient charge of polymer has been melted and formed at the end of the screw, a hydraulic ram forces the screw thread forward injecting the polymer into the mould
- The mould is water cooled to allow it to harden quicker
- Any excess polymer is trimmed of the moulding - formers or jigs May be used the dimensional accuracy of the moulding while it cools and gardens completely
21
Q
Blow moulding process (5)
A
- The polymer is fed into the hopper
- An Archimedean screw pulls the polymer through a heated section melting the polymer
- The melted polymer is extruded as a tube called a parison
- The mould slides close around the parison and air is injected into the mould, forcing the polymer to the sides
- The polymer is allowed to cool for a few seconds the mould opens and the finished bottled is ejected
24
Q
Rotational moulding process (4)
A
- Polymer powder or granules are loaded into a mould, which is clamped and sealed
- Mould is transferred to an oven where it is heated to 260-370°c, depending upon the polymer used then the mould is slowly rotated around two axes and as it’s heated it costs the inside of the mould
- Once the polymer has achieved the correct thickness the mould is cooled - usually a fan and/or water is used to cool the polymer
- When polymer has solidified, the part will shrink slightly, allowing it to be removed
27
Q
Extrusion process (6)
A
- Polymer granules are loaded into the hopper
- The Archimedean screw moves the polymer granules past heaters
- The heaters soften the polymer
- When sufficient polymer has melted, the hydraulic ram pushes the Archimedean screw, forcing the polymer through a steel die the shape of the die determines the shape of the extrusion
- The extrusion may be supported by rollers as it leaves the die and is cooled by water or air
- The extrusion is then cut to the desired length
30
Q
Compression moulding process (5)
A
- A ‘slug’ of ore-weighed thermoset polymer is inserted into pre-heated moulds
- The moulds are closed and hydraulic pressure is applied this pressure ensures that the polymer takes the shape of the mould
- The moulds remain closed while cross-linking takes place and the thermoset ‘cures’
- When the moulding has cured, the machine opens and the product is removed
- Excess polymer known as ‘flash’ is removed
