Engineering Materials Chapter 13 Shaping processes for plastics

Common gases used in polymer foams are which three of the following?

air, carbon dioxide, and nitrogen

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. True or false?

False

The distribution channel in an injection mold consists of which three of the following components?

gates, runners, and sprue

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

injection blow molding

Relative to conventional injecting molding, the injection pressures in structural foam molding are higher, lower, or the same?

lower

The amount of polymer melt injected into the mold during each injection molding cycle is called which one of the following?

shot

Thermoforming can only be used on which one of the following polymer types?

thermoplastics

In a reciprocating-screw injection molding machine, the injection of polymer melt into the mold cavity is accomplished by the rotation of the screw in the barrel. True or False?

False

In rotational molding, centrifugal force is used to force the polymer melt against the surfaces of the mold cavity where solidification occurs. True or False?

False

Polymers with low melt viscosities are the best candidates for extrusion, because they hold shape better during cooling. True or false?

False

Which three of the following defects are associated with injection molding?

Flash, short shots, and sink marks

The die characteristic indicates that flow rate through the die orifice increases as head pressure decreases or increases?

Increases

The die swell ratio for a polymer melt has a value that is never less than than one. True or False?

True

The product of an extrusion process is called the extrudate. True or False?

True

To compensate for die swell, the extrudate is often stretched to offset expansion from die swell. True or False?

True

The screw-preplasticizer machine is also known by which one of the following names?

Two-stage machine

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

Where the mold halves open to remove the part(s)

Which two of the following are reasons why injection molding of thermosets is more difficult than injection molding of thermoplastics?

allowances must be made for cross-linking of thermosets, cycle times are longer because of curing

Which two of the following factors will reduce the amount of shrinkage during solidification and cooling in thermoplastic molding?

Higher injection pressure, higher molding temperature, and higher proportion of filler in the plastic

In which two of the following properties do plastic parts often compare favorably with metals?

Impact resistance and strength-to-weight ratio

Toggle-clamp units on injection-molding machines are most suited to which one of the following tonnages?

Low

Compression molding differs from injection molding in which two of the following respects?

molds are simpler, and presses are oriented vertically rather than horizontally

Casting can only be used for thermosetting plastics, not thermoplastic polymers. True or False?

False

Blow molding can only be used on which one of the following polymer types?

Thermoplastics

In which one of the following spinning processes is the starting polymer in solution and the solvent is separated by evaporation by pulling the filament through a heated chamber?

Dry Spinning

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

A positive mold

A polymer melt exhibits which four of the following properties and characteristics?

Becomes less resistant to flow as temperature increases, becomes less resistant to flow at high shear rates, high viscosity, and viscoelasticity.

Which three of the following processes are used to produce plastic sheet and film?

Blown-film extrusion process, calendering, and chill-roll extrusion.

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

Casting

The amount of molding compound loaded into the heated mold during each compression molding cycle is called which one of the following?

Charge

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

Clamping unit, and injection unit

Which three of the following are sections of a conventional extruder barrel for thermoplastics?

Compression section, feed section, and metering section

The extruder characteristic indicates that flow rate in the extruder barrel increases as head pressure decreases or increases?

Decreases

Following parameters is increased:

Diameter of the barrel, rotational speed of screw

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

Mechanical thermoforming

Turbulent flow of polymer melt through the die orifice is likely to cause which one of the following defects in plastic extrusion?

Melt fracture

The coating of a flat plastic or rubber film onto materials such as fabrics, paper, and cardboard is called which of the following?

Planar coating

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

Polystyrene and polyurethane

Which one of the following is not a function of the breaker plate and screen pack through which the polymer melt flows just before entering the die?

Reduce the viscosity of the melt

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

Separate the part from the mold cavity after molding

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

Sharkskin

The coefficient shear viscosity is defined as which one of the following?

Shear stress divided by shear rate

As the term is used in the production of synthetic fibers and filaments, spinning involves the extrusion of a polymer melt through which one of the following?

Spinneret

Injection molding can be used for elastomers, thermoplastics and thermosets. True or false?

True

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

Thermosets

A fiber is defined as a long, thin strand of material whose length is at least 100 times its cross-sectional dimension, whereas a filament is a fiber of continuous length. True or False?

True

Blow molding is a molding process in which air pressure is used to inflate a soft plastic parison inside a mold cavity to produce hollow parts such as bottles. True or False?

True

Compression molding and transfer molding can be used on both thermosets and elastomers. True or false?

True

Contour coating involves the application of a polymer coating onto a solid three-dimensional object. True or false.

True

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. True or False?

True

Extrusion is a used for thermoplastics and elastomers but rarely for thermosets. True or False?

True

Structural foam molding and sandwich molding both produce plastic parts that haven an inner core that is foam surrounded by a dense outer skin, but only produces a smooth part surface; which one: sandwich molding or structural foam molding?

sandwich molding

Plastic sheet refers to stock thickness thinner than 0.5 mm (0.020 in), whereas plastic film refers to thickness greater than 0.5 mm (0.020 in). True or false?

False

Shrinkage of high-density polyethylene is lower than for low-density polyethylene because of HDPE's greater crystallinity. True or False?

False

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. True or False?

True