Everything You Want to Know about Rotational Molding

Updated on February 28, 2020

Rotational molding refers to a plastic manufacturing process to form hollow parts of any size. It is a cost-effective method to produce significant parts. Rotomolding was developed in the 20th century, and it has been gaining popularity over other plastic manufacturing processes like blow molding, thermoforming, and plastic injection molding. 

Let’s look at some essential aspects of rotational molding

What Are the Materials Used in Rotomolding?

Polyethylene is one of the most popular materials used in rotomolding. The reasons behind the preference for polyethylenes are low costs, a broad range of properties, and processability. 

Some plastic manufacturers also use specially formulated powders like polycarbonate, nylons, polypropylene, and rigid polyvinyl chloride in rotomolding. These powders can be reinforced with fiberglass. 

What Is Entailed In Rotomolding?

Step 1 – Mold Preparation 

You can think about the process, like baking a cake. The hollow mold is filled with desired materials like resin or polymer powder, compounds like nylon, polyvinyl chloride, polyethylene, and some mixtures for hardness properties and color. 

Before filling the material, preheat the mold as per the properties of the material. The next step involves loading of powder in the frame, closing the mold, and moving it to the oven. The amount of preheating depends on polymer selection and mold design. 

Step 2- Mold Heating 

One of the crucial fundamentals of rotational molding is the rotation of the molds on two axes to achieve adequate material spreading and coverage. Rotating the mold on one axis won’t guarantee even dispersal of material, and achieving consistent wall thickness would be difficult.

The speed of rotation of the mold is 20 rotations every minute. This ensures the material is not subjected to centrifugal forces and gets excellent coverage. Timing is also an essential factor in rotomolding as insufficient time will prevent the complete melting of polymer and its adherence to the mold wall. Too much time will also degrade the mechanical properties of the polymer and impact its final form.

Step 3 – Mold Cooling 

Mold cooling is also a vital step in rotomolding. The cooling rate needs to be carefully controlled. Water or air helps to cool the mold from outside, which in turn will cool the polymer inside. 

By maintaining the right rate of cooling, you can avoid shrinkage and wrapping problems that are caused by the fast cooling rate. Inconsistent wall thickness and undesired flow are some of the outcomes of cooling too slow. 

Step 4 – Mold Unloading 

The last part of the rotational molding is to ensure the manufactured parts leave the mold quickly and without any damage. You need to plan and apply for mold release properly for which careful mold design is critical. 

A good mold design would ensure the parts separate from mold cavities easily. After unloading the molds, you can proceed with finishing, inspection, and packaging the final product.

Rotomolding is used in a variety of industries. The medical devices, toys, and other plastic items that use daily are some of the products manufactured by rotational molding. 

Precision control, advanced automation, and advanced polymer materials with great finishes has made rotomolding a highly reliable and efficient method in plastic manufacturing.

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