Basics of Thermosets, Scientific Molding, and Steel Selection

2

Fundamental Differences between Thermoplastics and Thermosets

• Thermoplastics are Supplied as Chemically Finished and Stable Compounds

• Thermoplastics Must Be Melted and Converted at Relatively High Temperatures

• Thermoplastics Can Be Repeatedly Softened and Solidified• The Bulk of Thermoplastic Materials Are Supplied As Unfilled Products

Thermosets Are Supplied As Partially Formed Polymers• Processing Is Designed to Complete the Polymerization Process and Make

the Molded Part At the Same Time• Conversion Temperatures Are Relatively Low• Finished Product Consists of a Network Solid That Cannot Be Re-melted• Almost All Thermoset Compounds Are Highly Filled

3

General Advantages of Thermosets

• Low Initial Viscosity Allows for Long Flow Paths and Production of Large Parts• High Electrical Insulation Properties• Low Processing Temperatures Allow the Use of Organic and Thermally Unstable Fillers and

Modifiers– Cotton Flock– Wood Flour– Polyester Fabric– Walnut Shells– Alumina Trihydrate (ATH)– Hemp

• Good Cost/Performance Balance for Elevated Temperature Properties • Wide Range of Processes and Forms for Raw Material Provide Good Versatility in

Design/Performance Equation• Cannot Melt or Soften in Catastrophic Thermal Runaway Events• High Levels of Filler Tend to Result in Materials That Shrink and Warp Less than Reinforced

Thermoplastics • Excellent Compressive Properties• Batch Process Allows for Creative Material Modifications• More Creep Resistance Than Thermoplastic

4

General Disadvantages of Thermosets

• Material Properties are Not as Developed as Thermoplastic• Low Initial Viscosity of Materials Results in Flash and the Need for Secondary

Operations• Low Tensile Strength and Ductility Tend to Result in Parts Designed with Thick

Walls• Compounds Are Reactive Systems – Results in Shelf Life Problems• Batch Processes Result in More Inconsistent Lot-to-Lot Consistency• High Levels of Some Fillers Result in Excessive Tool Wear• The Unique Nature of Each Thermoset Family Does Not Help Thermoset to

Thermoset Replacements for Future Cost Reduction• Compound Formulations Overly Secretive• Some Material Suppliers Compete with Their Molding Customers• Product Quality Dependent Upon the Degree of Crosslinking Established

During the Molding Cycle• Breakdown in High Vibration Applications• Poor Thermal Conductivity for Housing Replacements

5

Generic Specific Gravity

Material Value

Magnesium 1.74

Aluminum 2.75

Zinc 7.14

Nylon 6/6 – 33% Glass Fiber 1.39

PPS – 40% Glass Fiber 1.65

Polyethersulfone – 30% Glass Fiber 1.58

Thermoset Polyester 1.75-1.95

Vinyl Ester 1.75-1.95

General Purpose Phenolic 1.40-1.75

High-Performance Phenolic 1.40-1.80

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Cost Analysis – Price/Pound (March 2008)

Al, 1.6

Mg, 2.38

Zn, 2.5

PPS, 5

PEEK, 33

Nylon 6/6, 1.6

Melamine, 0.9

Phenolic, 1.6

Polyester, 1.48

Vinyl Ester, 2.2

Silicone, 6

DAP, 3.5

0

5

10

15

20

25

30

35

($)

7

Cost Analysis – Price/Cubic Inch (March 2008)

Al, 0.16

Mg, 0.15

Zn, 0.65

PPS, 0.30

PEEK, 1.73

Nylon 6/6, 0.15

Melamine, 0.06

Phenolic, 0.10

Polyester, 0.10

Vinyl Ester, 0.14

Silicone, 0.39

DAP, 0.25

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

($)

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Material Choices in Thermosets

• Phenolics• Aminos (Melamine, Urea)• Unsaturated Polyesters• Polyurethane• Allyls (DAP, DAIP)• Polyimides• Silicones• Epoxy• Casein

Cross Over point is Phenolic equals PPS

9

Phenolic

• Two-Stage (Novalac)-Shelf Life Infinite (normal storage)– Produced with Acid Catalyst and a portion of the required

Formaldehyde– Product is a brittle compound that will not cure with heat and is

considered a thermoplastic– Hardener is required to complete cure which is usually Formaldehyde in

the form hexamethyleneteramine (hexa), which upon heatings forms ammonia and formaldehyde

• Two-Stage (Novalac) Properties– Broken down in to General Purpose, Non-bleeding, Heat Resistant,

Impact, and Electrical– They Maintain dimension stability for an indefinite amount of time at

normal atmospheric conditions– High degree of resistance to deformation under load

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Phenolics – Advantages

• Excellent Dimensional Stability – Low Coefficient of Thermal Expansion• Very High Surface Hardness – Good Wear and Friction Properties• Excellent retention of physical properties at high temperature (300F continuous,

500F short bursts-Post Bake 340F Continuous)• Good Insulator both electrically and thermally • Multiple Fillers (Inorganic and Polymeric)• Highly Resistant to Solvents and Automotive Fluids

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Phenolics - Disadvantages

• Single Stage Resins Unstable at Temperatures Above 45 F Making Production Sensitive

• Two-Stage Resins Available Only in Black and Dark Colors Such As Brown, Dark Blue, Dark Red and Green

• Susceptible to Electrical Tracking• Usually Require Post-Baking to Achieve Optimal Properties (Two-Stage Resins)

• Very Low Impact Resistance• Two-Stage expels Ammonia

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Urea – Properties

• Any Color• High gloss and durable• High mechanical strength, heat resistance, fire resistance, good electrical arc, and arc tracking

• Scratch Resistant• Readily used in compression and transfer, requires modification for injection molding to extend flow “life”

• Heat Resistance up to 170F

13

Melamine - Properties

• Similar to Urea but Higher heat resistance, chemical, moisture, electrical, and scratch resistance

• Multiple fillers can be used (wood flour, minerals, and cellulose fiber)

• FDA approved for food contact even at high temperature• High surface gloss• Bright sharp colors that are light fast• Extreme Hardness• Excellent Arc Resistance

14

Polyester Chemical Forms

•Ortho: Most widely used• Iso: Better mechanical properties and chemical resistance than Ortho more costly

•Bisphenol A fumarates: Very good chemical and thermal properties – considered high performance

•Chlorendics: Excellent chemical properties combined with some flame retardancy

•Vinyl esters: Exceptional mechanical and chemical properties but higher cost

15

Polyester - Forms

•Free-flowing granular•Pelletized (PMG)•Putty or rope-type extrudates•Sheet molded compound (SMC)•High bulk factor compounds (BMC)•Thick molding compounds (TMC)

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Polyesters - Advantages

•Available In A Wide Range of Colors•Excellent Electrical Properties Combined with Ignition Resistance

•Good Toughness for Thermosets•Can be Molded in to Complex Shapes

17

Polyesters - Disadvantages

•Maturation Process Required Prior to Molding

•Styrene Crosslinking Agent Is Volatile Causing Viscosity Changes As A Function of Storage Time

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Thermoset Injection

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