Deck 10: Shaping Processes for Plastics

Question 1

A polymer melt exhibits which of the following properties and characteristics (three correct answers):

A)becomes less resistant to flow at high shear rates
B)becomes more resistant to flow at high shear rates
C)high viscosity
D)low viscosity
E)Newtonian fluid
F)viscoelasticity

Answer 1

becomes less resistant to flow at high shear rates
high viscosity
viscoelasticity

Question 2

The die swell ratio for a polymer melt has a value that is never less than one:

Answer 2

True

Question 3

Extrusion is a compression process in which material is forced to flow through a die orifice to provide long continuous product whose cross-sectional shape is determined by the shape of the orifice:

Answer 3

True

Question 4

Which of the following are sections of a conventional extruder barrel for thermoplastics (three correct answers):

A)compression section
B)die section
C)feed section
D)heating section
E)metering section
F)shaping section

Question 5

The forward movement of polymer melt in an extruder barrel is resisted by drag flow, which is caused by the resistance to flow through the die orifice:

Question 6

Bambooing is a more severe case of which one of the following defects in plastic extrusion:

A)melt fracture
B)sharkskin
C)viscoelasticity

Question 7

Which of the following processes are used to produce plastic sheet and film (three correct answers):

A)blown-film extrusion process
B)calendering
C)chill-roll extrusion
D)doctor blade method
E)spinning
F)thermoforming
G)transfer molding

Question 8

Injection molding is a process in which a polymer is heated to a highly plastic state and forced to flow under high pressure into a mold cavity, where it solidifies and is then removed from the cavity:

Question 9

The principal components of an injection molding machine are which two of the following:

A)clamping unit
B)hopper
C)injection unit
D)mold
E)part ejection unit

Question 10

The parting line in injection molding is which one of the following:

A)the lines formed where polymer melt meets after flowing around a core in the mold
B)the narrow gate sections where the parts are separated from the runner
C)where the clamping unit is joined to the injection unit in the molding machine
D)where the two mold halves come together

Question 11

The function of the ejection system in injection molding is which one of the following:

A)move polymer melt into the mold cavity
B)open the mold halves after the cavity is filled
C)remove the molded parts from the runner system after molding
D)separate the part from the mold cavity after molding

Question 12

A three-plate mold offers which of the following advantages when compared to a two-plate mold (two best answers):

A)automatic separation of parts from runners
B)gating is usually at the base of the part to reduce weld lines
C)sprue does not solidify
D)stronger molded parts

Question 13

Which of the following defects are associated with injection molding (three correct answers):

A)bambooing
B)die swell
C)drag flow
D)flash
E)melt fracture
F)short shots
G)sink marks

Question 14

Which of the following are reasons why injection molding of thermosets is more difficult than injection molding of thermoplastics (two best answers):

A)allowances must be made for cross-linking of thermosets
B)barrel temperatures must be hotter for thermosets
C)cycle times are longer because of curing
D)thermosets are denser
E)two injection units are required

Question 15

Reaction injection molding is used for which one of the following plastic types:

A)thermoplastics
B)thermosets

Question 16

Compression molding differs from injection molding in which of the following respects (two correct answers):

A)faster production rates
B)molds are simpler
C)part geometries are generally more complex
D)presses are oriented vertically rather than horizontally
E)shorter cycle times

Question 17

Compression molding and transfer molding can be used on both thermosets and elastomers:

Question 18

Use of a parison is associated with which one of the following plastic shaping processes:

A)bi-injection molding
B)blow molding
C)compression molding
D)pressure thermoforming
E)sandwich molding

Question 19

Stretch blow molding is a variation of which one of the following:

A)extrusion blow molding
B)injection blow molding
C)rotational blow molding

Question 20

In rotational molding, centrifugal force is used to force the polymer melt against the surfaces of the mold cavity where solidification occurs:

Question 21

Thermoforming is limited to which one of the following plastic types:

A)elastomers
B)thermoplastics
C)thermosets

Question 22

A thermoforming mold with a convex form is called which one of the following:

A)a die
B)a negative mold
C)a positive mold
D)a three-plate mold

Question 23

Which one of the following thermoforming processes requires the most expensive mold:

A)mechanical thermoforming
B)pressure thermoforming
C)vacuum thermoforming

Question 24

The term encapsulation refers to which one of the following plastics shaping processes:

A)casting
B)compression molding
C)extrusion of hollow forms
D)injection molding in which a metal insert is encased in the molded part
E)vacuum thermoforming using a positive mold

Question 25

The two most common polymer foams are which of the following:

A)polyacetal
B)polyethylene
C)polystyrene
D)polyurethane
E)polyvinylchloride

Question 26

In which of the following properties do plastic parts often compare favorably with metals (two best answers):

A)impact resistance
B)resistance to ultraviolet radiation
C)stiffness
D)strength
E)strength-to-weight ratio
F)temperature resistance

Question 27

Which of the following processes would be applicable to produce hulls for small boats (three best answers):

A)blow molding
B)compression molding
C)injection molding
D)rotational molding
E)vacuum thermoforming