MSE Exam 2

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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


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