Name the types of additives.
antistatic agents
coupling agents
fillers
flame retardents
hat stabilizers
lubricants
pigments
plasticisers
reinforcements
stabilizers
nucleating agents
Why are Stabilizers added to a polymer blend?
To prevent detoriation due to enviromental factors
Why are coupling agents added to a polymer blend?
To improve the bonding between filler and polymer
What is understood under compounding?
Mixing and dispersing the components of the final polymer product
Is compounding a hot or cold process?
It can be both
Why are shear stresses important for the mixing?
aggregates break up
polymer chains elongate in flow direction
On what do the shearing stresses depend during mixing?
Temperature
stresses induced by mixer
What is important for liquid/solid mixing?
The consideration of the relative densities.
How does the viscosity normally behave in compounding?
Due to the low pressures: Newtonian
What are the two mechanisms of particle dispersion in compounding?
simple shear flow -> low deformation rates
elongation flow -> high deformation rate
Name two examples for mixers and describe them briefly
Kenics mixer: Liquid/liquid, for similar viscosities
Coulete centrifugal mixer: for different viscosities, mixing effect depends on relative viscocities
What is a step that can be necessary before polymer mixing?
Drying near Tg to avoid evolution of gasses
What are typical materials for extrusion?
PVC, PE, PP, PMMA, PC
What are the steps of Extrusion?
melting
forming by being pushed through profile
cooling
cut off
Name the components
What are the processing temperatures (tp) for extrusion?
Tg+(100 to 150) for amorphous
Tm+(20 to 50) for crystalline
On what parameter depends the type of cooling type chosen?
The thickness of the final product
What is the prequisit for coextrusion?
That the components can stick together in the molten state
What are the important diameters of an extrusion screw and why?
length and outer diameter for the modeling of the melt flow
What is the advantage of using twin screws in extrusion?
better compounding and mixing while melting
better maintenance
geometry changes along the line of extruder easier
What are the three zones of a screw from start to finish?
feed zone, compression zone, metering zone
What is the compression ratio?
What causes the melting of the polymer in extrusion?
The high energy from the sheer stresses, heaters
How can the swelling of the melt after extrusion be avoided?
adjusting the die geometry
What tool is used for the extrusion of flat products? What are the controlling parameters?
Coat hanger die
parameters: lip thickness, rate of extrusion & rate of collection
What are the steps in Thermoforming?
heating
forming
What are the main types of thermoforming?
Vacuum forming (drawing pressure from underneath)
Pressure forming (e.g. blow molding)
Mechanical forming (molds)
What happens to the residual product after trimming the final product?
The residual material goes back into the cycle.
Name the marked components
How is the total drawing ratio calculated?
How is the point of halt in extention in a blow foil extruder called?
Frostline
How is the drawing ratio in film blowing calculated?
Which materials are uesd for blow foil extrusion
PE, PET
Describe, how coextrusion work in film blowing.
How are foils created for polymers that cant be melted (e.g. Cellophane)?
Solvent solution casting (analogous to ceramic tape casting)
for which species is the permeability measured?
oxygen
carbon dioxide
water
How is the permeation constant meassured?
Q volume of liquid passing through
A exposed area
t Time
p pressure difference
What are the steps in blow molding?
Heating
Forming
stretching
blowing
Cooling
Out of what material are blow molding forms constructed?
Aluminium, due to high thermal conductivity
What are the two types of blow molding and their respective polymers?
injection blow molding (PET, PC)
extrusion blow molding (HDPE, PP, PVC)
What are the differences between injection and extrusion blow molding?
Extrusion:
continous
low orientation
welding line
Injection:
discontinous
high orientation
injection point
What are the stages of roto molding?
Loading
Unloading
Which materials are used for Roto molding?
Polyethylene (85%)
PVC
PP
PA
Describe the process of Roto molding
Plastic powder is melted in a mold, which is rotated until every surface is covered.
What is Envriomental stress cracking resistance and how is it induced?
Cracking due to enviromental factors like UV radiation, oxidation, heat.
How is the thickness of the product determined in Rotomolding?
by the amount of introduced material
What are possible draw backs in Roto molding
discoloration due to high temperature
poor stiffness
unfused parts
Which materials can be processed in an ejection molding machine?
Thermosplastics
Thermosets
Elastomers
Describe the injection molding cycle.
What is the major difference between a injection molding plasticizing unit and an extruder plasticizing unit?
The injection molding plasticizer has a backflow stop valve
How does the ram position and pressure evolve over time in injection molding?
Name components of a injection mold
Gate
Ejectors
Runners
Spuce
What is a hot runner mold?
A mold that keeps the plastic in the runners above melting point and therefore reduces material waste.
What is a cold junction and a hot junction in injection molding?
hot: parallel flow border
cold: perpendicular flow border
What is the effect of excessive or insufficient temperature or pressure in injection molding?
What is reactive injection molding?
Mixing the two reactants just before injection
the reaction finished in the mold
What is the spruce?
The sprue is the channel along which the molten plastic enters the mold
What is the runner?
The runner is the flow path from the sprue to the cavity
What is the gate?
The gates are the small orifices which connect the runner to the cavity
Last changed7 months ago
