MSE Exam 2
Which of the following processing techniques do not use thermosets?
blow molding
important additive in tires, it reinforces the rubber, serving to increase tensile strength and resistance to tearing and abrasion
carbon black
step-polymerization reactions which involves formation of a small by-product like water is called:
condensation polymerization
What are the types of twin screw extruders? State one function of each type of twin screw extruder.
corotating - highly efficient thermal heating counter rotating - devolatization
Thermoforming temperature of amorphous polymer is (above/below) glass transition temperature
above
Which of the following extrusion blow molding systems is suitable to design large thick walled hollow parts?
accumulator head Ram extrusion
Which of the following gates is preferred while designing hollow parts in injection molding?
diaphragm gate
Which of the following techniques of thermoforming can be used to give highest draw ratio?
drape forming
State one advantage related to the use of hot runner molds
eliminate scrap and waste
Extensional viscosity can be a measure of melt flow index
false
Thermoforming is good for highly crystalline polymers
false
Thermoplastic elastomer must have some crosslinks
false
adiabatic heating in extrusion process is due to the external heating elements
false
shrinkage of amorphous polymers is higher than crystalline polymers
false
Which of the following are associated with injection molding?
flashing short shot shrinkage
What is nylon type screw and how is it different from polyethylene type screw?
for resins with sharp melting point and has very short compression zone
Which of the following thermoforming methods is used to design products with high optical clarity, for example canopies in racing vehicles?
free forming
Which of the following is an indicator of the temp limit above which the material cannot be used for structural applications
heat distortion temp
disadvantage on use of screw with higher L/D ratios:
heats the material longer
High molecular weight polymers have:
high melt strength low melt flow index
What type of extruded shape is related to use of spider die in extrusion molding?
hollow tubes
Which of the following decreases with increase crystallinity of polymers?
impact toughness transparency
Addition of plasticizer will result in which of the following?
improves flexibility decreases glass transition temp
How can we reduce die swell?
increase draw down ratio increase extrudate speed use polymer resin with high MW increase length of die land
With increase in MW of polymer chains:
increase in crystallinity increase in melt strength
Weld line is a line of mechanical weakness in the part. Which processing variable can we change to eliminate weld line?
increase injection pressure
Which of the following can be used to design automotive fuel tanks?
injection molding blow molding
In rotomolding, what mold is used for heat sensitive resins to avoid direct heat?
jacketed
Three desired properties of mold material used for injection molding:
low coefficient of thermal expansion high machinability low specific heat capacity
Which one property makes PET highly desirable to make soda bottles?
low gas permeability
Blow molding molds are made of aluminum unlike injection molding made out of tool steel. Which of the following statements are true?
low injection pressure in blow molding
In extrusion molding, it is beneficial to use polymer resin with (high/low) melt flow index and (narrow/broad) molecular weight distribution
low, broad
The largest volume of thermosets which comprise the plastic market:
phenolic resins
Additives added to a polymer to make it softer and more flexible
plasticizers
The significance of biaxial rotation of mold in rotomolding is related to:
provide uniform heating
The shot sizes are higher, cost is low and used to design larger products in injection molding
ram extrusion
Which of the following methods can be used to make a large trash can such that the product has thick corners on outside?
rotomolding
Which of the following are associated with extrusion molding?
shark skin melt fracture bubbles die swell surging
Three factors that can affect the viscosity of a polymer melt
shear rate temp MW
What are the types of mold release agents used for rotomolding?
silicones teflon semi-permanent coating spray permanent coating
Which of the following statements are true about thermoplastics?
solid materials at room temp, viscous liquids at a few hundred degrees, can be shaped in a wide variety of products
In injection molding, the first channel that leads from the nozzle to the mold (runners) is called:
sprue
which of the following is true or helps to increase crystallization?
stress induced crystallization
Which of the following methods can result to improve crystallinity of PP film?
stress induced crystallization Slow cooling of PP film btwn Tg and Tm
The leading commercial synthetic rubber is which one of the following:
styrene-butadiene rubber
State three factors which affects viscosity of polymer melt:
temperature shear rate molecular weight
Due to strain on extruder, which polymer property improves?
tensile strength
What is die swell?
the ratio of diameter of extrudate to diameter of die orifice
what type of polymers refer to materials whose elastomeric properties are due to physical connection between soft and hard phases of materials and not due to crosslinks?
thermoplastic elastomers
What would you expect a heavily crosslinked polyethylene that has a glass transition temperature of 0 C to be at room temp?
thermoset
Which of the following clamping units in injection machine operates faster but has less control over pressure?
toggle clamping unit
In extrusion blow molding, we have higher trim scrap compared to injection blow molding
true
We will use a longer compression zone in extrusion process for a polymer resin with high molecular weight distribution and amorphous in nature
true
we can use direct flame heating for rock and roll rotomolding machine
true
Which method of thermoforming is used to form parts with hollow regions which may be foam filled?
twin-sheet
The geometries possible with extrusion is limited to:
two dimensions
How do we obtain a thermoforming processing window?
using a stress-strain plot
Die swell can be related to:
viscoelasticity
A broad molecular weight distribution polymer resin makes it more suitable for processes like:
Extrusion molding
Which of the following type of die will you use for blown film extrusion?
Annular dies
The geometries possible with injection molding are limited to:
3 dimensions
Which of the following statements are true about thermosets?
At higher temps, they undergo a chemical rxn that hardens the material Can be shaped in a wide variety of products
Use of a parison is associated with which one of the following plastic shaping processes:
Blow Molding
Which of the following processes are associated with the production of plastic sheet and film?
Blown film extrusion
Which of the following are sections of a conventional extruder barrel for thermoplastics?
Compression section Feed section Metering Section
What type of defect may be observed in extrusion molding when deborah number is greater than 1?
Deborah number is related to the ratio of relaxation time to process time. If this happens, we observe melt fracture
In blow molding which of the following methods provides more design flexibility, can produce large bottles and provides a wider choice of resins
Extrusion blow molding
What is the sequential change in the mechanical state of an amorphous polymer as we increase the temp?
Glass, Rubbery solid, Viscous liquid
advantage on use of screw with higher L/D ratios:
Helps to have better mixing ability
In rotomolding, if we produce an unfused product, which of the following physical properties are highly affected?
Impact strength elongation
Narrow molecular weight distribution polymer resin is more suitable for:
Injection Molding
If you want to design tiger cub figurines which of the following methods will you use?
Injection molding
Sections of injection molding machine
Injection unit mold clamping unit
What polymer production process would you use to manufacture the following: Kayaks and plastic bottles
Kayaks: rotomolding Plastic bottles: blow molding
Series connection between a Hookean spring and dashpot represents
Maxwell Model
As die is the key cost related to extrusion molding machine; what is the key cost related to injection molding machine
Mold
What are the advantages of injection blow molding over extrusion blow molding?
No trim scrap high dimensional accuracy uniform wall thickness No seam lines/pinch marks Better transparencies
If you are processing a highly crystalline polymer in extrusion molding machine which one of the following types of screw would you use?
Nylon type screw
Which of the following is true for higher shot sizes, less expensive, and used to design larger products in injection molding?
Ram extrusion
Which of the following are related to injection molding?
Reciprocating screw Ejector pins Ram injection
Which of these thermoset resins have a higher shelf life?
Stage A resins with no crosslinking
Why is runner design important in injection molding?
Streamlined flow
Injection molding can be used for:
Thermoplastics Thermosets
What are the two basic types of clamping units used in injection molding?
Toggle clamps hydraulic clamps
