- To see some of our Rotational Molding projects, visit the Rotational Molding section of our blog -

We utilize the Rotational Molding (or Rotomolding) method for creating many kinds of mostly hollow, plastic items. The metal molds are either cast (for smaller, highly detailed items) or fabricated (floats, storage tanks). Plastic is placed into the mold in powder form.  The amount of plastic depends on desired wall thickness of the part.  The mold is then heated, which causes the plastic powder within to melt and form a puddle at the bottom of the mold cavity. The mold is then slowly rotated (usually around two perpendicular axes) causing the melted material to flow into to the mold and stick to its walls. In order to maintain even thickness throughout the part, the mold continues to rotate during the cooling phase. Once cooled, the mold is taken apart, revealing the finished plastic part.

The plastic used is usually a polyethylene; however other materials can also be used.

Advantages

• Rotational Molds are far cheaper to produce than similar plastics applications.
• Rotomolded parts are extremely strong and durable.  UV inhibitors can also be added to the plastic to prevent fading.
• Having a solid color throughout the parts will also help to hide scratching and wear.  Rotomolded parts generally have a long life.
• Very little wasted material, and what isn’t used can usually be recycled to use again.
• Consistent wall thickness, with very strong (and virtually stress free) outside corners.
• Prefinished pieces (metal threads, inserts) can be added to the mold before molding.

Disadvantages

• Long cycle times—only one or two cycles an hour can typically occur.   
• Large flat surfaces will warp if not supported
• Because of the way the part is formed, the molecules of the plastic are largley unpredictable. For example, 2 identical parts may act totally differently when exposed to UV rays.
• Because it is a low pressure process, hard to reach areas in a mold can go un-molded if not dealt with properly.

Typical Uses

Product Design Considerations

• Shrinkage - Rotomolded parts usually shrink 3-3.5% from the size of the mold.
• Draft Angles - Depending on the depth of the mold, draft will have to be added on vertical surfaces.   Draft on rotomolds will usually require a minimum of 1°.   
• Undercuts - With the Rotational Molding process, you can usually get away with small undercuts.  It’s best to consult us before hand in this case.

 

 

 

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Industrial Shape & Form Ltd. | 100 - 1638 Langan Avenue | Port Coquitlam | BC | Canada | V3C 1K5
Phone: 604.468.7750 | Fax: 604.468.7751 | info@industrialshapeandform.com

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