Rotational Molding

Rotational molding, or more commonly called rotomolding, is an economical way to produce large parts. Different types of plastic such as polyethylene, PVC, nylon, and polypropylene, are broken down into a usable resin. This plastic resin is then loaded into a mold that is combination heated and rotated in a slow, yet constant motion. This simultaneous process of heating and rotation distributes the material on the inner surfaces of the mold and combines it together.

Rotomolding is a four-step process, made up of Loading, Heating, Cooling, and Unloading the mold. In the Loading stage the pre-measured plastic resin is loaded into the mold. The filled molds are then closed and moved into the oven, where they slowly rotate on two axes. As the heat penetrates into the molds, the melting resin adheres to the mold’s inner surface until it is thoroughly fused, evenly coating the entire surface.

During the Cooling stage, the mold continues to be rotated to maintain even walls as a high velocity air current gradually cools the mold. The mold is then opened, the finished part removed, and the mold is ready for its next step. Unlike other plastic molding processes, rotomolding produces seamless parts with consistent wall thickness and more material in corners. This is in order to absorb shocks and stresses where they are most likely to occur.

Common Materials:

  • LLDPE – Linear Low Density Polyethelene
    • Most common material used for items like cargo boxes, furniture bases, water tanks, etc. This material provides a high level of durability through more flexible properties and UV resistance.
  • HDPE – High Density Polyethelene
    • This is a harder plastic that is less flexible. It is also highly UV resistant.
  • Crosslinked Polyethelene
    • Used for diesel and gasoline tanks
  • Nylon

Maximum Part Dimensions:

  • Dowco’s largest rotomolding machine can mold parts up to 120″ wide and 60″ tall. Since the machine rotates the part, there are limitations on exactly what will fit. Please contact Dowco to learn more.

Rotomolding offers outstanding flexibility and precision. Complex contours such as metal inserts and flanges can be made right into the walls requiring fewer steps to produce your finished product. In addition, rotomolded plastic eliminates sharp corners and burrs and results in a smooth and seamless product. This reduces the risk of injury for operators.

A wide spectrum of colors are available with rotomolding. There is also no chipping because the color is solid throughout the whole part. Rotomolding offers many distinct advantages over other types of molding such as blow molding or injection molding. The advantages are:

  • Dramatic Cost Savings
  • Short Production Times
  • Easy Modification
  • Superior Strength
  • Ability to Produce Multi-Wall Moldings

Rotational molding is incredibly versatile and is able to handle a vast variety of shapes and sizes. Toys, play houses, drain tile fittings, automotive parts, kayaks, fuel tanks, and park equipment are only a few of the numerous products that can be made. As you can see in the above list, the products produced are only limited to the imagination.

Although the possibilities for rotomolding are endless, the thermoforming method of molding may be what you need. Read on to find out more!


4230 Clipper Dr
Manitowoc, WI 54220
(920) 682-7796


Manitowoc, WI
Lebanon, MO
Ft. Wayne, IN
Little Falls, MN
Shanghai, China