1.1.4 polymer processes

Question 1

which polymer is used for vacuum forming?

Answer 1

HIPS

Question 2

why is vacuum forming only limited to small scale production?

Answer 2

it is a very slow process

Question 3

how does vacuum forming work?

Answer 3

• the mould is placed on the bed of the machine (the platen)
• a polymer sheet is clamped over the mould and heat is applied to the polymer sheet
• when the polymer sheet has softened, the platen is lifted into the polymer and the heat is removed
• the vacuum pump is switched on to suck the polymer sheet down onto the mould
• once the polymer is cooled, the platen is lowered
• the mould is the then removed and excess material is removed from the polymer

Question 4

advantages of vacuum forming

Answer 4

good for mass production
- simple process
- suitable for large items
- provides a nice finish

Question 5

disadvantages of vacuum forming

Answer 5

• only works for thermoplastics that 6mm thick or thinner
• not great for producing fine details
• inefficient use of material
• a slow process

Question 6

what is thermoforming?

Answer 6

thermoforming is a similar process to vacuum forming however the mould is pressed into the heated plastic sheet from above.
this is carried out by a positive mould pressing the clamped heated plastic down into a negative mould.

Question 7

what are the advantages of thermoforming?

Answer 7

• low cost
• good for large production runs
• suitable for large and lightweight components (eg: baths, dashboards, trays, lids)
• fast production and high efficiency
• can include details and logos as they are pressed into the material

Question 8

disadvantages of thermoforming

Answer 8

limited to thin thermoplastic sheets
-material wastage
- lower strength than injection moulded parts

Question 9

describe calendering

Answer 9

• calendaring is a smoothing and rolling process
• this works by heating pellets of thermoplastic so that it melts into a dough like consistency
• it is then massed through a series of heated rollers to make it thinner
• it is then cooled before being cut into stock sheet sizes
• it is process typically used for continuous production

Question 10

describe line bending

Answer 10

• this creates bends along a piece of acrylic by heating a thin piece of wire
• this is typically used for shelves or boxes
• suited for one off or batch production

Question 11

what are some example products of injection moulding

Answer 11

Casing on electrical products, such as computers, TV’s and vaccuum cleaners.

Question 12

describe the process of injection moulding

Answer 12

• Thermoplastic granules are poured into the hopper
• A screw thread is rotated by a motor, this pulls the granules through the chamber past the electric heaters.
• The heat melts the polymer
• When a sufficient amount of polymer has melted and formed at the end of the screw, a hydraulic ram forces the screw thread forward. This injects the polymer into the mould.
• The mould is water cooled, which enables the molten polymer to harden quickly.
• The mould opens and ejector pins push the moulding out.
• Any excess polymer is trimmed off the moulding.
• Formers or jigs may be used to maintain the dimensional accuracy of the moulding while it cools and hardens completely.

Question 13

what type of production line is injection moulding best suited for?

Answer 13

large scale such as mass or continuous production as the moulds can be easily reused

Question 14

what is blow moulding used to create?

Answer 14

hollow products such as bottles

Question 15

what materials are used for blow moulding?

Answer 15

PET,LPDE,HDPE, PP

Question 17

what production line is blow moulding best suited for?

Answer 17

continuous production as it is expensive to set up

Question 18

describe the process of blow moulding

Answer 18

• 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 sides 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 bottle is ejected.

Question 19

what is an example product for compression moulding?

Answer 19

plug sockets

Question 20

what materials are used in compression moulding?

Answer 20

• thermosetting polymers
• urea formaldehyde
• melamine formaldehyde

Question 21

describe the process of blow compression moulding

Answer 21

• A ‘slug’ of pre-weighed thermoset polymer is inserted into pre-heated moulds
• The moulds are closed and hydraulic pressure is applied. The pressure ensures that the polymer takes shape of the mould.
• The moulds remain closed while cross linking 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.

Question 22

what can lamination (lay-up) produce?

Answer 22

• boats made carbon fibre reinforced plastic (CFRP)
• aerospace and automotive parts
• kayaks
• yachts

Question 23

what materials are used in lamination (Lay-up)?

Answer 23

• fibreglass laminates
• GRP
• carbon - fibre composites
• epoxy resins
• polyester

Question 24

describe the process of lamination (lay-up)

Answer 24

• A mould or former in the shape of the product is prepared usually made of timber, manufactured boards such as plywood or high density foam
• The mould or former is coated with a releases agent such as wax or PVA
• A top layer or gel coat is applied. The gel coat is a coating of polyester resin often mixed with a pigment to give a colour to the moulding. The resin might also have additives included to prevent degradation from UV and hydrolysis.
• Fibreglass matting is cut to size and laid over the former.
• Polyester resin is brushed onto the matting and a small roller is uses to push out any air bubbles that may form and to smooth out the matting
• Repeat step 3 until desired thickness is achieved
• Allow to set

Question 25

what products are made from rotational moulding?

Answer 25

water tanks, kayaks, playground equipment and storage containers

Question 26

what materials are used for rotational moulding

Answer 26

high density polyethylene (HDPE), polypropylene (PP), polyethylene (PE) and nylon