Rotational Molding Wall Thickness Problems: Causes and Solutions

In rotational molding, it is difficult to produce plastic parts with abrupt wall thickness changes. The average wall thickness of a rotomolded product depends mainly on the amount of material charged into the mold, while wall thickness uniformity is strongly influenced by mold design, mold structure, temperature distribution, and the rotational molding process itself. If uneven wall thickness occurs during production, the cause is usually related to part geometry, mold temperature, or rotational speed.

From the perspective of product and mold structure, the wall thickness at concave corners of a rotomolded part, which correspond to convex areas of the mold, is usually thinner. In contrast, the wall thickness at convex areas of the product, which correspond to concave areas of the mold, is usually thicker. However, if the angle of a convex section is too sharp, the material may not fully reach that area, which can result in defects such as voids or pinholes. For this reason, rotomolded parts should avoid sharp corners whenever possible, and smooth radius transitions are generally recommended.

The melting and adhesion behavior of plastic materials is also closely related to mold temperature. In areas where the mold temperature is higher, the plastic melts earlier and adheres more easily to the mold surface, resulting in greater material buildup in those sections. In lower-temperature areas, less resin adheres to the mold surface, which can lead to uneven wall thickness across the final product.

Wall thickness is also affected by rotational speed. If the rotational speed is unstable, it can easily cause irregular wall thickness variation throughout the part. To maintain consistent wall thickness, manufacturers generally use constant-speed or constant-torque motors with automatic control to keep both the main and secondary axes rotating steadily. When the wall thickness of one area differs significantly from other sections and mold modification is not practical, the issue must be addressed through process optimization and technical adjustment.