Rotational molding (or Rotomolding) is a method that involves the slow tumbling, heating, and melting of a thermoplastic powder in a biaxially rotating mold to produce seamless, hollow plastic parts. This process is typically used to mold hollow parts, especially those with complex and varied shapes not easily obtainable by other hollow-art processes. It is a virtually shear-free and pressure-free process. The wall thickness uniformity and part weight can be easily maintained. There is very little waste of material due to scrap. Rotomolding molds are often less expensive than other types of molds.

• How does rotomolding compare with injection molding and blow molding?

Raw Materials
Lower viscosity resins are typically used in this process as they are more readily sintered to ensure a good surface finish. The material must be capable of being ground into a 35-mesh powder that flows like a liquid. It must also be able to adhere to the hot surface of the cavity and fuse together without pressure. The material should be stabilized to resist oxidation, or a nitrogen purge must be used during processing.

• Polyethylene (Low Density) LDPE, LLDPE
• Polypropylene PP
• Ethylene Vinyl Acetate EVA
• Polyvinyl Chloride (PVC)

Cost
Low tooling costs and high piece prices are typical of this process. Cycle times average around 40-45 minutes.

Advantages

• Very large parts can be manufactured
• Chemical waste and storage tanks up to 2,500 gallons
• Minimum design constraints
• Very low tooling costs
• No polymer weld lines
• Stress-free products

Disadvantages

• Slow cycle times mean high piece prices
• Narrow range of raw materials.
• Some geometrical features (such as ribs) are difficult to mold

Applications

Rotational molding is incredibly versatile, able to handle a vast variety of shapes and sizes. Many parts cannot be readily produced by any other method.

INDUSTRIAL & COMMERCIAL – Agriculture, Health & Science, & Point of Sale (POS):

Specialty tanks and containers for fuel, water, and chemical processing

• Livestock feeders
• Drainage systems
• Food service containers
• Instrument housings
• Vending machines
• Highway barriers and road markers

CONSUMER PRODUCTS – Recreational, Special Application, Toy, & Transportation:

• Boats and kayaks
• Childcare seats
• Light globes
• Tool carts
• Planter pots
• Playing balls
• Playground equipment
• Headrests
• Truck/cart liners
• Air ducts