Polymer processing techniques Flashcards
(27 cards)
name the main high volume techniques used to manufacture polymer products (7)
Extrusion, injection moulding, blow moulding, compression moulding, thermoforming, coating, rotational moulding
what is the difference between batch and continuous manufacturing?
Batch processes are completed in defined cycles, producing a number of components per cycles
Continuous involves processes that generate product continuously, requiring cutting to discrete lengths
What are the basic steps/necessities involved in any polymer manufacture process
=Polymer preparation-mixing and heating
=polymer flow forming-processed as a viscous liquid or softened solid
=part shape definition
=solidification-cure of a TS or solidification of a TP
Describe the 3 sections in an extruder
Feeder: used to convey solid pellets away from hopper towards compression
Compression: compresses material, heat conduction and shearing causes melting, air and volatiles are forced out of melt
Metering section: provides strong mixing and ensures homogeneity of melt. shearing provides pressure required at die/ mould
What are the three main things an extruder does
- melting of the TP (from pellet form)
- Removal of air and volatiles from the melt
- provides driving force
Why would you use twin screws in an extruder?
for materials that require thorough mixing or high volumes
wat is the difference between corotating and counterrotating screws in an extruder?
counterrotating-majority of material gathers at intersections and is pushed along quickly (suitable for high flowrates)
-corotating:Material takes along path resulting in more thorough mixing
Describe the extrusion process (production rate,continuous/batch, capital expense, typical materials)
rate: medium to high (continuous)
capital expense: extruder and supporting equipment is expensive
typical material: TP’s with lw to medium viscosity
Describe the injection moulding process (production rate,continuous/batch, capital expense, typical materials)
Batch, medium to high production
Capital expense: moulds cost (increases with part quality, size, and production rate)
typical material: TP with low to medium viscosity
Describe the blow moulding process (production rate,continuous/batch, capital expense, typical materials)
rate: very high
capital: machinery is high cost
typical materials: commodity TP
Descirbe the compression moulding process (production rate,continuous/batch, capital expense, typical materials)
Rate: low to medium
Capital expense: prodominantly through the press, moulds are relatively cheap
Material: typically TS in powdered form
Describe the thermoforming process (production rate,continuous/batch, capital expense, typical materials)
rate: low to high
expense: reasonably economical, can be performed using modest through to complex machinery
Material: TP sheets + films
Describe the rotational moulding process (production rate,continuous/batch, capital expense, typical materials)
Rate: low to medium
expense: relatively low due to low pressure low cost moulds
Material: majority powdered polyethlene, other TP and liquid TS possible
Describe the coating process (production rate,continuous/batch, capital expense, typical materials)
Rate: high
Expense: extruder based for TP, cheaper for TS (dip)
material: Low viscosity extrudable TP, and variety of TS liquid resins
Name and briefly describe four different types of Extrusion processes?
Profile: A die is used to extrude complex shapes
Sheet: Produces flat sheets and films, utilises a coat hanger die
Blown film: Die produces a continuous film of melt, air is blown through the centre
Filament: produces synthetic fibres for cloth or rope
What are the four basic steps in an injection moulding cycle?
Mould closes, melt injection, part cooling, part ejection
What are the three main parts to an injection moulding unit?
Injection unit, mould, clamping unit
What are the three main steps in blow moulding?
melting the polymer, creating a preform, blowing the preform tube into the desired shape
How would you improve the standard steps in a blow mouliding cycle to increase production rate?
larger production rates achieved by working multiple moulds through cycles. a single extruder is used to feed the moulds. ( picture is circular with moulds at different steps i.e. blow, cooling, eject, clean etc
List some main advantages between extrusion and injection blow moulding
ext: tooling cost lower, shorter cycle time, wider choice of polymers, more flexibility in part design
Inj: better accuracy, uniform wall thickness, no seam lines or pinch marks, more transparent part as better control of crystallisation
List the main disadvantages between extrusion and injection moulding
ext: requires significant part trimming, requires additional equipment to grind scrap and reintroduce extruder
inj: higher tooling costs, limited choice of polymers
Name the 5 main steps in compression moulding
placement of charge mould closure squeeze to dimensions polymer solidifies demoulding
What material charge forms are moulded in compression moulding?
powder and sheet TP and TS
Describe the 5 basic steps in thermoforming
load blank into diaphragm heat blank clamp into mould draw down into mould de-mould and trim
