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Braeden > L15 Polymer Processes > Flashcards

L15 Polymer Processes Flashcards

1
Q

True or false, isthe processing of polymers similar to metals?

A

True

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2
Q

Unlike metals, polymers require…? Their properties are highly influenced by what two things.

A
  • Less energy to process

* Highly influenced by manufacturing processes and parameters

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3
Q

Polymers typically start out in what form when being processed? And for reinforced plastic parts?

A
  • Pellet form

* Liquids for reinforced plastic parts

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4
Q

Briefly describe the4 stages of Extrusion in the Extruder(Refer to diagram on page 3 of L15)

A
  • The raw thermoplastic materials in the form of pellets are fed into a hopper and then into a barrel
  • Barrel houses a screw that conveys the pellets down the barrel
  • Shearing action of the screw as well as external heaters cause the pellets to melt
  • In the last section of the screw, pressure builds and the polymer is extruded through a die
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5
Q

What happens at the end of the barrel in the Extruder?

A

Once the meltedplastic reaches the end of the barrel, its forced through a die and cooled

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6
Q

How do you minimize distortion in theextrusion die?

A

Uniform Cooling

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7
Q

Various die shapes can produce different…

A
  • Profiles

* Even thin sheets and films

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8
Q

What does the phenomena of Die Swell cause?Such ImportanceIf Alan Doesnt Ask Something About This, I will let Mike Punch MeIf He does, we all get to punch Mike

A

Causes the plastic to be shaped differently than the extrusion die (experience is key in designing extrusion dies)

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9
Q

What is Coextrusion?

A

Involves simultaneous extrusion of multiple polymers/materials through a single die

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10
Q

In Coextrusion, each material has its own characteristics and functions.Name 3 Characteristics

A
  • Barrier to both oil and water
  • Electrical insulation and conduction
  • Sealing and labelling
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11
Q

How are plastic coatedelectrical wires produced?Know this for test

A

Coextrusion

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12
Q

What is the most common polymer process?

A

Injection Molding

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13
Q

Injection Molding is similar to what metal process?

A

Hot Chamber Die Casting

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14
Q

How is the “melt” created in Injection Molding? Then what happens to the melt to reach the mold?

A
  • Polymer pellets are plasticized creating the melt

* The melt is forced through a nozzle into the mold

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15
Q

Mmodern machines use this to carry and inject the plastic in Injection Molding?

A

Reciprocating-Screw Type Injector

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16
Q

What is the difference betweenThermoplastics and Thermosets when used in Injection Moldings?What does each promote?

A

For thermoplastics the mold is usually cool

  • To speed up the processing For thermosets the mold is held hot
  • To promote polymerization and crosslinking
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17
Q

What is a major concern in Injection Molding? What is done to compensate?

A
  • Shrinkage (1-7%)

* Molds are made oversized to compensate

18
Q

Identify the Injection Mold Geometry

A

See page 5 of L15

19
Q

Name the 3 Types of molds that can be used in Injection Molding

A
  • Cold Runner Two-Plate
  • Cold Runner Three-Plate
  • Hot Runner Mold
20
Q

Briefly describe the Cold Runner Two-Plate

A
  • Simplest mold design

* Sprue and runners must be removed by hand

21
Q

Briefly describe the Cold Runner Three-Plate

A
  • Runner system is removed from part via intermediate stripper plate
  • Runners and parts are seperate and solid
22
Q

Briefly describe the Hot Runner Mold

A

Runner system is kept in melted state after parts have solidified

23
Q

What are 2 types ofBlow Molding?

A
  • Extrusion Blow Molding

* Injection Blow Molding

24
Q

Briefly describe theprocess of Extrusion Blow Molding. What is the pressure range it operates in?

A
  • A thin tube (Parison) is extruded and clamped into a mold
  • High Pressure (350-700KPa) then forces parison outward to fill cavity
  • Upon cooling the part is ejected
25
Q

Explain the difference between Extrusion Blow Molding and Injection Blow Molding. Name Applications of Injection Blow Molding

A
  • Instead of extruded, the parison is injection molded then transferred to a blow mold and expanded using high pressure gas
  • Ex. Beverage Bottles, Hollow Containers
26
Q

Rotation Molding is similar to Extrusion and Blow Molding but?

A

At a lower cost

27
Q

Describe the process of Rotation Molding

A
  • A thin walled metal mold is made and powdered plastic is placed insidethe mold
  • The mold is heated and rotated about2 perpendicular axis
  • The powdered plastic coats the mold and is fused from the heat
28
Q

Pros and Cons of Rotational Molding plus Applications

A
  • Large thin walled parts can be made
  • Mold and equipment costs are much lower than blow and extrusion molding
  • Cycles times are much longer than blow and extrusion molding Applications
  • Trash Cans, Boat Hulls, Carrying Cases, Tanks
29
Q

What is Thermoforming?

A

A family of processes where thermoplastic sheet is formed over a mold via the application of heat and pressure (or vacuum)

30
Q

Briefly describe the process of Thermoforming

A
  • A thin plastic sheet is heated in an oven until soft (the sag point)
  • Then placed over a mold and pressure is applied until the plastic solidifies
31
Q

How are hollow parts made in Thermoforming?

A

By forcing 2 thin plastic sheets together against molds and applying a combination of vacuumand pressure

32
Q

What is the major limitationof Thermoforming? Name Applications

A
  • **No Parts with holes****

* Signs, Packaging, DIY

33
Q

What is Compression Molding?

A

A preshaped charge (or powder or viscous liquid) is placed into a heated mold cavity and held under pressure until cured

34
Q

During Compression Molding, what is formed that must be removed?

A

Flash, must be removed in subsequent operations

35
Q

What polymer is usually chosen for Compression Molding and why?

A
  • Thermosets

* Longer cycle times and heated die (Which allows crosslinking)

36
Q

Advantages of Compression Molding and Applications

A
  • Molds generally less complex Undercuts are possible because molds can be made to open sideways Applications
  • Dishes, Handles, Pipe Fittings
37
Q

Which costs lessInjection Molding or Compression Molding?

A

Compression

38
Q

In Polymer Casting, some thermoplastics and thermosets may be cast into…?

A

Rigid or Flexible Molds

39
Q

For Thermoplastics inPolymer Casting, the mixture poured into the moldis made of? When it is poured what happens?

A
  • Mixture of Monomer and Catalyst is poured into mold

* Then allowed to polymerize at ambient pressure

40
Q

In Polymer Casting, what are examples of Flexible Molds and why is it used?

A
  • Polyurethanes
  • Silicones
  • Allow complex, intricate shapes to be formed
41
Q

What makes Polymer Casting more versatile?

A

Inserts and other components may be cast into the part as well, allowing versatility

42
Q

Applications of Polymer Casting

A
  • Form molding of cups
  • Food Containers
  • Packing Materials

Braeden (7 decks)

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