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ITEC 458 - Materials > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

How is the rubber industry organized?

A
  1. Rubber growing plantations
  2. The petrochemical industry
  3. Fabricators
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2
Q

What is the sequence of processing steps required to produce finished rubber goods?

A
  1. production of the raw rubber
  2. compounding
  3. mixing
  4. shaping
  5. vulcanization
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3
Q

What are some of the additives that are combined with rubber during compounding?

A
  • Vulcanizing chemicals
  • Reinforcing fillers
  • Extenders to reduce cost
  • Antioxidants
  • Coloring pigments
  • Plasticizers to soften the rubber
  • Blowing agents to make foam rubber
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4
Q

Name the four basic categories of processes used to shape rubber

A
  1. Extrusion
  2. Calendering
  3. Coating
  4. Molding
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5
Q

What does vulcanization do to the rubber?

A

Treatment that accomplishes cross-linking of elastomer molecules, rubber becomes stiffer and stronger but reinforces extensibility

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6
Q

Name the three basic tire constructions (Briefly describe them)

A
  1. Diagonal Ply: made up of cords in consecutive sheets that run diagonally but in perpendicular direction
  2. Belted Bias: made up of diagonal plies with opposite bias
  3. Radial Ply: have the cords running radially, instead of diagonally
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7
Q

What are the three basic steps in the manufacture of a pneumatic tire?

A
  1. Preforming of components
  2. Constructing of carcass
  3. Components are molded & cured
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8
Q

What is the purpose of the bead coil in a pneumatic tire?

A

Provide stability to the tire area that is subjected to wear & trajaction

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9
Q

What is TPE?

A

A thermoplastic elastomer

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10
Q

What are the principal polymers used in fiber-reinforced polymers?

A

Unsaturated polymers & Epoxies

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11
Q

What is the difference between a roving and a yarn?

A

Roving: a collection of uninterrupted strands which are parallel
Yarn: a twisted group of filaments

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12
Q

In the context of fiber reinforcement, what is a mat?

A

Short fibers that are oriented randomly

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13
Q

Why are flakes considered to be members of the same basic class of reinforcing material as particles?

A

They are basically particles that have very large lengths & widths when compared with thickness

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14
Q

What is sheet molding compound?

A

A polymer compound that consists of thermoset polymer resin, additives, fillers & glass fibers that are cut into small pieces

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15
Q

How is a prepreg different from a molding compound?

A

Consists of continuous fibers and they increase the mechanical properties of the product

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16
Q

Why are laminated FRP products made by the spray-up method not as strong as similar products made by hand lay-up?

A

Hand lay-up method fibers are orientated correctly which makes them stronger and in the spray-up methods fibers are generally oriented randomly

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17
Q

What are some of the advantages of the closed mold processes for PMCs relative to open mold processes?

A
  • High production
  • The surface finish is higher quality
  • Tolerance control can be controlled much better
  • Complex shapes are achievable
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18
Q

Identify some of the different forms of polymer matrix composite molding compounds

A
  1. Sheet molding compounds
  2. Bulk molding compounds
  3. Thick molding compounds
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19
Q

What is preform molding?

A

Another form of compression molding involves the placement of a precut mat into the lower mold section along with a polymer resin charge

20
Q

Describe reinforced reaction injection molding (RRM)

A

Two reactive ingredients are mixed and immediately injected into a mold cavity where curing & solidification occur rapidly

21
Q

Describe the pultrusion process

A

Continuous fiber rovings are dipped into a resin bath and pulled through a shaping die where the impregnated resin cures

22
Q

Glass is classified as a ceramic material; yet glass is different from the traditional and new ceramics. What is the difference?

A

Glass is vitreous - it is in the glossy state, whereas traditional and new ceramics are, by and large, polycrystalline materials

23
Q

What is the predominant chemical compound in almost all glass products?

A

Silica

24
Q

What are the three basic steps in the glassworking sequence?

A
  1. Raw materials preparation and melting
  2. Shaping
  3. Heat treatment
25
Q

Describe the spinning process in glassworking

A

A gob of molten glass is dropped into a conical mold which spins, causing centrifugal force to spread the glass upward onto the mold surfaces

26
Q

What is the main difference between the press-and-blow and the blow-and-blow shaping processes in glassworking?

A

Press-and-blow: initial forming step is pressing of the part
Blow-and-blow: first step blowing

27
Q

There are several ways of shaping plate of sheet glass. Name and briefly describe one of them.

A
  1. Rolling: the hot glass is squeezed between opposing cylindrical rolls
  2. Float: the melted glass flows onto a molten tin surface to achieve uniform thickness and smoothness
28
Q

Name and briefly describe the two processes for forming glass fibers are discussed in the text

A
  1. Drawing: fine glass fibers are pulled through small orifices in a heated plate
  2. Centrifugal Spraying: Molten glass is forced to flow through small orifices in a rapidly rotating bowl to form glass fibers
29
Q

Describe the type of material that is commonly used to make windshields for automobiles

A

Laminated glass

30
Q

What are some of the reasons why plastic shaping processes are important?

A
  1. Many of the processes net shape processes
  2. Less energy is employed than in metalworking
  3. Lower temps are required to process plastics
  4. Great flexibility in geometry
  5. Painting and other finishing processes are generally not required
31
Q

What does viscoelasticity mean when applied to a polymer melt?

A

a combination of viscous and elastic properties that cause the melt to exhibit memory

32
Q

Define die swell in extrusion

A

The tendency of the extrudate to expand in cross-sectional dimensions immediately

33
Q

The barrel and screw of an extruder are generally divided into three sections; identify the sections

A
  1. The feed section
  2. The compression section
  3. The metering section
34
Q

What are the functions of the screen pack and breaker plate at the die end of the extruder barrel?

A
  1. Filter dirt and lumps
  2. Build pressure
  3. Straighten the flow and remove memory of the polymer melt
35
Q

What are the various forms of extruded shapes and corresponding dies?

A
  1. Solid profiles
  2. Hollow profiles
  3. Wire and cable coating
  4. Sheet and film
  5. Filaments
36
Q

What is the distinction between plastic sheet and film?

A

Sheet stock has a thickness greater than 0.5 mm; film stock is less than 0.5 mm

37
Q

What is the blown-film process for producing film stock?

A

Combines extrusion and blowing to produce a tube of thin film

38
Q

Polymer fibers and filaments are used in several applications; what is the most important commercial applicant?

A

Textiles

39
Q

What is the technical difference between a fiber and a filament?

A

A fiber is a long, thing strand of material whose length is at least 100 times its diameter; a filament is a fiber of continuous length

40
Q

An injection-molding machine is divided into two principal components, name them

A
  1. Injection unit
  2. Clamping unit
41
Q

What is the function of gates in injection molds?

A

To constrict the flow of molten plastic into the cavity

42
Q

What are the advantages of a three-plate mold over a two-plate mold in injection molding?

A

Three-plate molds automatically separates the molded parts from the runner system

43
Q

Discuss some of the defects that can occur in plastic injection molding

A
  1. Short shots
  2. Flashing
  3. Sink Marks
44
Q

What are the significant differences in the equipment and operating procedures between injection molding of thermoplastics and injection molding of thermoset?

A
  1. Shorter barrel length
  2. Lower temps in barrel
  3. Use of a heated mold
45
Q

What kind of products are produced by blow molding?

A

Produces hollow, seamless containers (bottles)

46
Q

What is the form of the starting material in thermoforming?

A

Thermoplastic sheet or film

47
Q

What is the difference between a positive mold and a negative mold in thermoforming?

A

Positive: Convex shape
Negative: Concave shape

ITEC 458 - Materials (3 decks)

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