What do you know about Rotomolding Machine?

The Rotomolding Machine is a plastic casting technology machine that produces hollow, seamless and double-walled parts by heating powdered resin in a hollow mold tool while slowly rotating and cooling to cure. The process began hundreds of years ago, became popular in the mid-20th century, and is still evolving. The process has a variety of applications.

• How will the heating step of the Rotomolding Machine work?

• Why is the heating step of the Rotomolding Machine so important?

• How will the cooling of the Rotomolding Machine take place?

How will the heating step of the Rotomolding Machine work?

The Rotomolding Machine heats the powdered resin inside the hollow mold while slowly rotating it until all the resin is melted. As the resin melts, it covers the entire inner wall of the mold. The simultaneous action of heating and rotating ensures a uniform distribution of the resin inside the mold. The mold rotates biaxially, usually at a slow speed (less than 15 rpm).

In order to obtain a good wall thickness distribution, a proper rotation ratio must be determined. This value is the ratio of revolutions per minute (RPM) on the horizontal axis to RPM on the vertical axis. Spheres or cubes can be formed with a 4:1 rotation ratio. For irregular solids, this ratio must be 1:8 or 8:1, depending on how the manufacturer optimizes this factor.

Why is the heating step of the Rotomolding Machine so important?

The heating time of the polymer is critical and is one of the parameters that determines the quality of the finished product.

Too long a heating time in the Rotomolding Machine can lead to thermal degradation of the polymer and can reduce the final mechanical properties, such as reduced abrasion and impact resistance. Conversely, insufficient heating time can lead to incomplete melting of the polymer. The unmelted particles will not bind to the melted resin, resulting in bubble formation. This change has a negative impact on the final mechanical properties of the product.

How will the cooling of the Rotomolding Machine take place?

In this stage, the molten polymer inside the Rotomolding Machine's mold hardens and solidifies into the desired shape. The outside of the rotating mold is cooled by natural or forced convection, usually using air. Sometimes cooling air is supplied to the inside of the mold to maintain dimensional stability during the cooling process. Water spraying can be used to reduce the cooling time, but this can affect the mechanical properties and dimensions of the part.

The cooling time of the polymer is as important as the heating time. Therefore, the proper cooling rate must be determined. Rapid cooling can lead to uncontrolled warpage and shrinkage of the part. On the other hand, slow cooling can lead to molten resin flow, which can result in inconsistent wall thickness.

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