Foreword
Contributors
1.0 Introduction
1.1 A Modern History of
Rotational Molding
1.2 Rotational Molding
Applications
1.3 Rotational Molding Markets
1.3.1 North
America
1.3.2 Europe
1.3.3
Australia and Rest of the World
1.4 The Future of The Industry
1.5 Rotational Molding
Associations Around the World
2.0 Process Basics
2.1 Four Basic Steps
2.2 Advantages of Rotational
Molding
2.3 Limitations of Rotational
Molding
2.4 Rotational Molding from
Within the Mold
3.0 Materials
3.2 Range of Materials Available
3.3.3
Linear Low Density Polyethylene (LLDPE)
3.3.4
Medium Density Polyethylene (MDPE)
3.3.5
High Density Polyethylene (HDPE)
3.3.7
Metallocene Polyethylenes (mLLDPE)
3.3.8
Ethylene Vinyl Acetate (EVA) – Ethylene Butyl Acetate (EBA)
3.3.9
Semi-Conductive Polyethylene
3.3.10
Flame Retardant Polyethylene
3.3.11
Plasma and Radiation Treated Polyethylene
3.3.12
Fluorinated Polyethylene
3.5 Nylon
3.11 Reinforced Materials
3.12 Other Materials
3.12.1 Acetal Copolymer
3.12.2 Acrylic
3.12.3 Cellulosics
3.12.4 Epoxy
3.12.5 Ionomers
3.12.6 Liquid Crystal Polymers
3.12.7 Phenolic
3.12.8 Polybutylene
3.12.9 Polyester
3.12.10 Polystyrene
3.12.11 Polyurethane
3.15 Material Standards
4.0 Molds
4.1 Introduction
4.2 Mold Design Considerations
4.2.1 Reviewing A Part Design
– What Type Of Mold Is Best For An Application?
4.2.2 Mold Elements And Features
4.2.3 Factors
That Affect The Cost Of A Mold
4.2.4 Heat
Transfer Characteristics Of Various Mold Materials
4.2.5 Thermal
Expansion Characteristics Of Various Mold Materials
4.2.6
Specifying A Mold For Ordering
4.3 Fabricated Molds - Sheet
Metal
4.4 Cast Molds – Aluminum
4.5 Other Mold Making Methods
4.5.1 Glass
Fiber (Composite)
4.5.2
Electroforming
4.5.3 Sprayed
Metal
4.5.4
Jacketed Molds
4.6 Mold-Release Systems
4.7
Mold Maintenance
5.0 Machinery
5.1 Introduction
5.1.1
Heating Stage
5.1.2
Cooling Stage
5.1.3
Servicing Stage
5.1.4
Rotation
5.2 Machine Styles
5.2.1
Rock and Roll
5.2.2
Shuttles
5.2.3
Turntable and Trolley Based Systems
5.2.4
Carousels
5.2.5
Independent Arm
5.2.6
Vertical Style (Ferris Wheel)
5.2.7
ClamshellTM
5.2.8
Electrical
5.2.9
Oil Heated
5.2.10
Infrared
5.2.11
Selecting a Machine Style
5.3 Operational Parameters
5.4 Setting Up a Machine for Operation
6.0 Design
Considerations
6.1 Introduction
6.2 Design Development Process
6.3 Computer Aided Design
(CAD)
6.4 Basic Design Guidelines
6.4.1 General
Considerations – Function, Shape and Size
6.4.2 Wall
Thickness
6.4.3 Draft
Angles
6.4.4 Corner
Radii and Angles
6.4.5
Stiffening of Parts
6.4.6 Holes
6.4.7 Bosses
6.4.8
Tolerances and Shrinkage Considerations
6.4.9 Warpage
and Flatness Considerations
6.4.10 Double
Wall Parts
6.4.11
Kiss-Offs
6.4.12
Undercuts
6.4.13
Threads
6.4.14
Inserts
6.4.15
Parting Lines
6.4.16 Vents
6.4.17 Heat
Transfer
6.4.18
Graphics and Texture
6.4.19 Part
Assembly
6.4.20 ESCR
Performance
6.4.21 TRIP
Molding Technology
6.5 Design Calculations
6.5.1
Shotweight of a Rectangular Box
6.5.2
Shotweight of a Cylinder
6.5.3
Calculation of R-value for Insulation
6.5.4 Double
Wall Foam Cross-Section for Constant Weight
6.5.5 Double
Wall Foam Cross-Section for Constant Stiffness
6.5.6 Single
Wall Foam Cross-Section for Constant Weight
6.5.7 Single
Wall Foam Cross-Section for Constant Stiffness
6.5.8
Dimensional Change Due to Thermal Expansion
6.5.9 Design
Wall Thickness of a Cylindrical Tank
6.5.10
Conversion Factors
7.0 Color and Additives
7.1 Introduction
7.2 Basic Types of Colorants
and Additives
7.2.1
Pigments – Organic
7.2.2
Pigments – Inorganic
7.2.3 Special
Effects
7.2.4 Wetting
Agents
7.2.5
Anti-Oxidants
7.2.6 UV
Stabilizers
7.2.7
Antistats
7.2.8 Flow
Enhancers, Internal Lubricants, Internal Mold Releases
7.2.9 Blowing
Agents
7.2.10
Anti-Microbial Additives
7.2.11 Flame
Retardants
7.3 Practical Colorant Loading
Ranges
7.4 Mixing of Colorants and
Additives
7.4.1
Dry-Blending
7.4.2 Liquid
Color
7.4.3 Paste
Dispersions in PVC
7.4.4
Melt-Compounding
7.4.5 Mixing
Equipment
7.5 Effect of Color on
Processing and Part Physical Properties
7.5.1 Effect
on Cycle Time
7.5.2 Effect
on Shrinkage
7.5.3 Effect
of Pigments on Physical Properties
7.6 Effect of Additives on
Processing and Part
Physical
Properties
7.6.1
Anti-Stats
7.6.2
Anti-Oxidants
7.6.3 UV
Stabilizers
7.6.4
Conductive Additives
7.7 Practical Aspects of Color
7.7.1 Powder
Handling Tips
7.7.2 Effect
of Changing Material Suppliers on Color
7.7.3
Selecting a Color Supplier
7.7.4 Color
Match Request Form
7.7.7 Color
Standards
7.7.8 Color
Problems
8.0 Practical
Aspects
8.1 Types of Rotomolding Operations
8.2 Molding From An Operator’s Viewpoint
8.3 The Process of Material Build-Up in the Mold
8.4 Establishing the Optimum Cure Cycle
8.4.1
Impact Strength vs. Oven Temperature and Cycle Time
8.4.2
Tensile and Flexural Strength vs. Internal Air Temperature
8.4.3
Internal Air Temperature Measurements
8.5 Processing Parameters
8.5.1
Polyethylene
8.5.2
Crosslinked Polyethylene
8.5.3
Metallocene Polyethylene
8.5.4
Polypropylene
8.5.5
Nylon
8.5.6
Polycarbonate
8.5.7
ABS
8.5.8
Foaming Materials
8.6 Bubbles
8.7 Rotation Speeds and Ratios
8.8 Part Wall Thickness Control
8.9 Venting
8.10 Release Agents
8.11 Cooling
8.12 Shrinkage and Warpage
8.13 Liquid Materials
8.13.1
Polyvinylchloride (PVC)
8.14 Demolding and Reloading
8.15 Multiple Layer Molding
8.15.1
Co-Rotomolding
8.15.2
Foaming
8.15.4
Rotolining
8.16 Quality Control
8.16.1
Quality Control Points in Production
8.16.2 Impact
Testing
8.17 Troubleshooting
8.17.2
Liquid Materials – Plastisols
9.0 Secondary
Operations and Decoration
9.1 Basic Part Finishing Techniques
9.2 CNC Operations
9.3 Fixtures
9.3.1
CNC Holding Fixtures
9.3.2
Manual Cutting or Drilling Fixtures
9.3.3
Shrink Fixtures
9.4 Graphics and Decoration
9.4.1
Mold-In Graphics®
9.4.2
Mold-On Graphics®
9.4.3
Post-Mold GraphicsTM
9.4.4
Ink Stenciling and Labeling
9.5 Painting and Adhesives
9.6 Welding
10.0 Process
Control
10.1 Introduction
10.2 Basic Control Methods – Heating and
Cooling Systems
10.2.1
Heat Transfer Rates
10.2.2
Oven Performance
10.2.3
Cooler Performance
10.3 Direct Temperature Measurements
10.4 Indirect Temperature Measurements
10.5 Cycle Balancing / Scheduling
10.6 Process Simulations
11.0 Process
Economics
11.1 Rotational Molding
Capabilities vs. Other Processes
11.2 Costing Elements in
Rotational Molding
11.4 Comparative Costing vs.
Other Processes
Glossary of Terms
Index
