Plastics : Rotational molding

Rotational molding (also called rotomolding) is a manufacturing process used to create hollow plastic parts by rotating heated molds that contain plastic powder or resin, allowing the material to coat and form along the mold's inner walls.

In-Depth Explanation:

Process Steps:

• Loading: Plastic powder/resin is placed into a hollow mold
• Heating: The mold is heated while rotating on two perpendicular axes
• Cooling: The mold continues rotating while cooling
• Release: The finished part is removed from the mold

Key Advantages:

• Creates hollow parts with uniform wall thickness
• Low tooling costs compared to other methods
• Minimal material waste
• Ability to mold large parts
• No weld lines or internal stresses

Common Materials Used:

• Polyethylene (PE)
• Polypropylene (PP)
• PVC plastisols
• Nylon

Polyethylene (PE) is a lightweight, durable plastic material commonly used in packaging, bottles, and containers. It's known for its flexibility, chemical resistance, and comes in different densities (low-density PE and high-density PE).

Polypropylene (PP) is a versatile thermoplastic polymer known for its good chemical resistance, high melting point, and strength. It's commonly used in food containers, car parts, and textile fibers.

PVC plastisols are liquid mixtures of PVC (polyvinyl chloride) particles suspended in plasticizers (chemical additives that increase the flexibility, workability, and durability of plastics) that form a solid when heated. They're used for coatings, dip molding, and making flexible products like gloves and toys.

Nylon is a strong, heat-resistant synthetic polymer known for its high durability and wear resistance. It's commonly used in textiles, machine parts, and high-performance components due to its excellent mechanical properties.

Real-World Examples:

Storage Products:

• Water tanks
• Fuel tanks
• Chemical storage containers
• Industrial bins

Recreational Items:

• Kayaks
• Playground equipment
• Traffic barriers
• Outdoor furniture

Industrial Applications:

• Material handling containers
• Agricultural tanks
• Automotive parts
• Marine buoys

Consumer Products:

• Toy parts
• Pet houses
• Garden planters
• Coolers

Design Considerations:

• Draft angles for easy part removal
• Proper wall thickness distribution
• Location of parting lines
• Venting requirements
• Surface finish requirements

Limitations:

• Relatively long cycle times
• Limited to hollow parts
• Higher unit costs for small production runs
• Material options more limited than injection molding