How Plastics are Made

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• How Plastics are Made
• Understanding the Physical
• Properties of Plastics

Prepared by the IAPD Education Committee (Module
1) Presented courtesy of Modern Plastics, Inc.
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Processing

• Hand (or spray) lay up
• Laminating
• Filament winding
• Polymer orientation

• Injection molding
• Extrusion
• Ram extrusion
• Screw extrusion
• Coextrusion
• Casting
• Compression molding
• Rotational molding
• Transfer molding
• Calendering

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Injection Molding
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Extrusion

• Ram
• Screw
• Coextrusion

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Casting
Base Material
Reactive Additive
Oven
Casting
Mold
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Compression Molding

• Sheet and block molding
• Parts molding

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Rotational Molding

• Low cost
• Low pressure
• Used in many markets
• Easily adapted for short production runs

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Transfer Molding

• Widely used in the semiconductor industry

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Calendering
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Hand (or Spray) Lay Up

• Used to make large parts
• Used to produce fiberglass boats and camper
  shells

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Laminating
Resin Binder
Reinforcing Substrate
Heat and pressure applied to the top and bottom
of the material
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Filament Winding

• Used to make containers and tubes
• Items used for transportation of liquids or
  gasses

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Polymer Orientation

• Used to manufacture polymer fibers, strapping,
  webbing, film, sheet and profiles

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Plastics Fabrication

• CNC machining centers
• CNC lathes
• Cutting and drilling
• Profiling
• Routing and milling
• Thermoforming
• Forging
• Milling
• Welding
• Bending
• Bonding

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Thermoforming

• Single station thermoforming
• Rotary station thermoformers
• Pressure forming
• Twin sheet thermoforming

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Welding

• Extrusion welding
• Hot gas welding
• Butt welding
• Spin welding
• Solvent welding

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Bonding

• The union of materials by adhesives to unite
  materials by means of an adhesive

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The Performance of a Plastic Part is Affected By

• Type of load
• Size and application of load
• Frequency of application of load
• Speed of load
• Temperature the part will see, and for how long
• Use and environment of load

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Mechanical Properties

• Tensile strength
• Elongation
• Compressive strength
• Creep
• Shear strength
• Flexural strength

• Torsional strength
• Modulus
• Impact strength
• Specific gravity
• Water absorbtion
• Coefficient of Friction (COF)

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Testing Organizations

• AFNOR - Association Francaise de Normalisation
  (France)
• BSI - British Standards Institution (UK)
• IEC - International Electrotechnical Commission
• JIS - Japanese Industrial Standards

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Tensile Strength
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Elongation
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Compressive Strength

• Measured in pounds per square inch (PSI)
• Higher PSI harder to compress

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Creep

• Associated with compressive strength
• Creep at room temperature is called cold flow

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Shear Strength
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Flexural Strength
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Torsional Strength

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Modulus

• Also referred to as stiffness
• Used in conjunction with strengths (flexural
  modulus, tensile modulus, etc.)
• Higher modulus stiffer material
• Measured in PSI

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Impact Strength
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Specific Gravity

• Related to the density of material
• Can be used to determine the weight of material
• Specific gravity of less than 1.0 will float in
  water

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Water Absorption

• Measured by the percentage of swell
• Think of a sponge as having high percentage
  absorption

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Coefficient of Friction (COF)

• Resistance to sliding (slickness)
• Low COF more slippery (think of wet ice as
  having lowest COF)
• Static COF refers to initial movement from rest
• Dynamic COF refers to being already in motion

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Thermal Properties

• Coefficient of thermal expansion
• Heat deflection temperature
• Continuous service temperature
• Melting point
• Thermal conductivity

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Coefficient of Thermal Expansion (CTE)

• Change in size as temperature changes
• Lower value less change with temperature

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Heat Deflection Temperature (HDT)

• Temperature up to which a material can perform,
  under load, without distorting
• Measured in degrees Fahrenheit, usually under 264
  PSI
• Used most widely to predict performance

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Continuous Service Temperature (CST)

• Highest temperature a material can withstand and
  still retain at least 50 of its properties
• Measured in degrees Fahrenheit, in air
• In high temperatures, both CST and HDT must be
  considered

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Melting Point

• Temperature at which a crystalline thermoplastic
• changes from solid to liquid

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Thermal Conductivity

• How much heat a material will conduct
• Most plastics are good insulators (do not
  conduct heat well)
• Higher value more heat conducted
• Thermal conductivity of plastics is 300 to 2,500
  times less than most metals

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Electrical Properties

• Volume resistivity
• Surface resistivity
• Dielectric constant
• Dielectric strength
• Dissipation factor
• Arc resistance
• Flammability

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Volume Resistivity

• Ability of electricity to flow through a material
• Measured in ohms/cm
• Lower value more easily current flows
• Higher value better resistor or insulator

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Surface Resistivity

• Ability of electricity to flow over the surface
  of a material
• Same measurements as volume resistivity
• Used to evaluate material when static discharge
  characteristics are critical

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Surface Resistivity
Insulative Range
Conductive Range
Static Dissipative Range
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9
10
11
12
1
2
3
4
5
1 10 10 10 10 10
10 10 10 10 10
Shielding Range
6
7
8
10 10 10
106 to 108 Critical Range for ESD Control
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Dielectric Constant

• That property of a dielectric that determines the
  electrostatic energy stored per unit volume for
  unit potential gradient

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Dielectric Strength

• Effectiveness of material as an insulator
• Measured in volts/.001 thickness
• Higher value better insulator
• Voltage is increased until material arcs, showing
  a breakdown

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Dissipation Factor

• Tangent of the loss angle of the insulating
  material

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Arc Resistance

• Time required for an arc to establish a
  conductive path on the surface of an organic
  material

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Flammability

• Measured by UL94 ratings
• Most favorable ratings are given to materials
  that extinguish themselves rapidly, and do not
  drip flaming particles
• Scale from highest burn rate gt most flame
  retardant is HB, V-2, V-1, V-0, 5V

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