There are plenty of ways of manufacturing hollow objects using plastic and rotational molding (or rotomolding) is probably one of the most affordable and efficient methods at our disposal. This informative guide attempts to cover what else the technology is used for, what its main advantages are and other useful information.

Rotational molding (or rotomolding) is a manufacturing technology that has improved significantly over the last 20 years, and every day more and more companies are utilizing this multifunctional process. It is used mainly for producing hollow parts by adding plastic powder to a shell-like mold, and then rotating and heating it at the same time. During this process, the powder fuses into a bubble-free liquid layer that takes the form of the inner mold surface. The mass is then cooled and the hollow part is removed. This process is quite often used for the manufacturing of tanks (refer to image below), but it can also be used for making complex medical products, toys, leisure craft, and much much more. rotomolding companies

Tanks and containers manufactured via rotational molding have a wall thickness ranging from 0.5 to 20 mm. Their capacity can reach up to 13,000 gallons.

How rotational molding works

The process begins by loading a metal mold with a powdered polymer (mostly polyethylene). Metal components can also be placed in the mold and incorporated into the final shape.

The mold is put into an oven chamber and rotated along 2-axis. The temperature is kept at 500°F – 680°F (260°C – 370°C) depending on the material used. During this process, the melted material adheres to the inner surface of the mold.

After the molten material has formed the object, it is cooled and removed. The mold is then reloaded, and the process is repeated as many times as it is necessary.

The mold split (line or ridge that appears at the point where the mold is separated) is removed via trimming. Some elements like apertures, holes, screws and slots can be added during this stage.

  1. Loading material inside the mold
  2. Melting the material inside the mold
  3. Cooling the mold
  4. Post processing

Rotational Molding Equipment

Rotational molding machines include an oven, a cooling chamber and mold spindles. Molds are usually made from aluminum alloy with CNC machining or metal casting. Such parts are much thicker than an equivalent made out of stainless steel. The molds can also be fabricated from welded sheet steel depending on the size and complexity of the part.

Chapter 2: Types of Rotational Molding Machines

The standard set-up of a rotational molding operation consists of an arm or cradle, which carries the mold, single or multiple ovens, and cooling chambers. The only difference among the machines is in the direction where the mold travels, following the sequence of the rotational molding process. The machine types used in the rotational molding process are the following:

  • Clamshell Machine: Clamshell machines are single station machines wherein molding and cooling occurs in one chamber. The mold with resin is loaded and unloaded in the chamber through the front panel. The front panel and cover are locked during heating and molding. After molding, the cover is opened to allow cooling, causing the mold to be swung out of the open oven.

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