Kiss-Off Ribbing and Rotational Molding

Kiss-Off Ribbing
Kiss-Off Ribbing

Kiss-off ribbing is a term that’s used in rotational molding to describe a solid, reinforcing structure that transmits a load from one nominal wall to another. Because rotational molding produces hollow parts, engineers and product designers need to consider what will happen to a plastic part if it’s flexed. Examples of rotomolded parts include plastic tanks, ducts, bins, pallets, spine boards, and baby-changing stations.

Kiss-Off Ribbing Advantages and Applications

During the rotational molding process, kiss-off ribbing is formed when powder bridges the gap between the male part of the lower-mold half and the surface of the upper-mold half. This bridge or solid structure supports loading and can help prevent damage during part usage. For example, if the surface of a rotomolded door is pushed and flexed, the kiss-off ribbing transfers the load from one side to the other.

Kiss-off ribbing also prevents warpage across large, flat surfaces. Added strength and dimensional stability are also benefits. Specialized applications can include the baffling inside of fuel tanks. Without baffles, the pickup point for a fuel tank may not stay submerged if fuel suddenly sloshes backward, such as during a steep uphill climb. Without the constant pumping of fuel, a vehicle’s engine could stall or fail.

Design and Manufacturing Considerations

For engineers and product designers who want to include kiss-off ribbing, the thickness of the kiss-off area is an important dimension to consider.  According to the Association of Rotational Molders (ARM), 175% of the nominal wall thickness is a good starting point. These proportions provide a good weld line and also leave enough room for the plastic to move over all of the mold’s surfaces.

Engineers and product designers also need to consider the distance between the two nominal walls. If the distance is great, heating the mold surfaces in the kiss-off area can be challenging. Additional heating can increase cycle times and costs. Designing a hole through the mold and the part in the kiss-off area can help to direct hot oven air towards the kiss-off surface.

Rotational Molding and Your Plastics Project

Gregstrom Corporation provides rotational molding services that create strong, hollow plastic parts in a variety of shapes, sizes, textures, and colors. We also provide value-added services such as design assistance and tooling.  To learn more about kiss-off ribbing and other part features, contact us at our Made in the USA manufacturing facility in Woburn, Massachusetts (USA).