Plastic has been taking a lot of heat over the years, not from its manufacturing process but from environmentalists. It was mostly a losing battle, especially in the arena of public perception. The industry responded resoundingly in recent years, coming up with more environmental bio-based plastics and improving its manufacturing processes. Rotational molding, in particular, is one production method that has seen significant developments in its operation gaining a wider range of applications along the way.
What is Rotational Molding?
Rotational or rotomolding is unique in that it can create seamless and continuous hollow plastic products. Its name is mainly derivative of its molding process where the raw material is rotated inside a metal mold as it is heated then cooled. It has an extensive array of applications from toys, to plastic containers, and even in the aerospace industry.
What is the Process of Rotomolding?
The molding process starts by filling the hollow mold with a predetermined amount of powdered resin, usually organic polyethylene. The mold, on the other hand, is commonly made of aluminum shaped on a CNC machine.
After filling, the mold moves on to the next stage of the process, which is heating. The mold goes into an oven preheated to around 300 degrees Celsius as it rotates on two axes. The heat makes the polymer fluid enough to be forced against the walls of the mold by the spinning motion. The time it spends inside the oven is critical. Too much heating will degrade the polymer and reduce the product’s impact strength while too little will create large bubbles.
After achieving a uniform thickness, the mold moves on to the cooling stage using air or water or a combination of both. In this stage, the polymer solidifies and shrinks just enough, so removing it from the mold becomes easy. After it has cooled thoroughly enough to be handled, the mold is opened, the product is removed, and the whole process starts again.
What are the Advantages of Rotomolding?
Most hollow plastic manufacturers prefer rotational molding over other processes for two important reasons:
Rotomolding has lower production costs. The molds used are cheaper and have lower residual stress levels. The process is also straightforward. Once the mold is set up, only the polymer and the oven are needed. The process is also cost-efficient. The rotation is slow and requires minimal energy, and there are no losses in raw material since the mold is closed.
Rotational molding gives manufacturers unlimited design options. Intricate shapes can be molded as a whole, which is much better than fabricating separate parts to be assembled later. Product thickness can also be varied quickly by adjusting the amount of polymer used and the parameters of the production process. More drastic changes in the design can be easily accommodated by using metal inserts, and even these can be done at a low cost.
Why Plastic is a Necessity
The reputation of plastics as an enemy of the environment is slowly fading, which is a good thing since its use could not be abandoned altogether. Besides, they reduce fuel consumption and carbon footprint for the transportation of many products when used as primary packaging. With more advancements in technology, plastic will become even more eco-friendly and eventually shed its notoriety completely.
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