Nominal wall thickness in rotational molding refers to the standard wall thickness of a rotomolded part. Rotational molding produces walls with a uniform thickness, even for plastic parts with unusual shapes. Non-uniform wall thicknesses can be produced within limits, but a uniform thickness helps to avoid warping and promotes structural integrity

Part Strength and Part Costs

The thickness of the nominal wall, along with the type of plastic material, determines the strength and load bearing capacity of a rotomolded part. In addition, wall thickness affects part costs. Rotomolded parts with thicker walls require more material: an added expense. Parts with thicker walls also have longer cycle times and require more energy to heat and cool the plastic.

Additional Considerations

With heat-sensitive materials, there’s a risk that the prolonged heating cycles needed for thicker walls could cause the plastic material to degrade. Thermal degradation, a form of molecular degradation caused by overheating, changes a polymer’s properties and can result in embrittlement, chalking, color changes, or cracking. Thinner walls can help mitigate this risk.

Polyethylene Rotational Molding

Polyethylene, a commonly used rotomolding material, supports wall thicknesses that typically range from .125” to .25”, according to the Association of Rotational Molders (ARM). However, large parts that are rotomolded from cross-linked polyethylene can have wall thicknesses up to 2.5”. With polyethylene rotational molding, a wall thickness of 1” is not uncommon.

Kiss-Off Ribs and Nominal Wall Thickness

Rotational molding supports thick walls, but part designers can use other strengthening techniques instead. For example, kiss-off ribs are solid, reinforcing structures that transmit a load from one nominal wall to another. These bridge-like structures increase stiffness and provide dimensional stability. They can also prevent warpage across large, flat surfaces.

Design Assistance for Rotomolding

Gregstrom is an experienced rotomolder that can help you define the best nominal wall thickness for your plastic parts. Even after a mold has been built and sampled, rotational molding supports adjustments to part wall thickness. Few other plastics processes offer designers this advantage, which is just one of many that rotational molding provides.

Contact Gregstrom to learn more and discuss your application.