Rotational molding or rotomolding is a plastic molding technology which is used to make hollow object. It is more of a casting tactic and there is no pressure involved. The molds involved are cheap as they don’t have to tolerate pressure and hence short production rates can be done in a cost effective way. Rotational molding comes in handy to make a wide variety of products. It gives the product designer freedom to design any shape he desires to produce. There is no limit to the molding size and there are a plethora of applications too.
Process of rotomolding
The entire concept is very simple. A plastic material in its powdered form is put into a hollow mold which is made of aluminum or sheet steel. The mold is closed and then rotated gradually in two axis. Then the mold is heated in an oven while it is heating and the polymer melts and layer up inside the mold. Once the polymer powder has melted, the mold is transferred to a cooling station and is cooled with air or sometimes mist of water. As the mold cools, it solidifies. When the final cooling is done, the product is taken out of the mold.
The process may be simple, but the people who work on it will admit that the process is complex. It is a casting process where no pressure is involved. In other words, the material cannot be controlled like the way it is done in injection molding. There are many variables involved that impact the production and the end product like ambient temperature and humidity, mold type, material specification and powder quality.
Nowadays the industry is totally dependent upon Polyethylene (PE) and a whopping 97 percent of rotomolded products are made from PE only. PE is a versatile polymer that has controlled the entire process. Rotomolding is a casting technique which uses powder instead of granules means you need to ground the material first. PE can easily be grinded in ambient temperature. The making of other polymers have always been obstructed by the fact that the process is long and aggressive on polymers, but some amount of PVC, Polypropylene and Polyamide (PA6, PA11 & PA12) are used. Many of these materials are hard to grind and may need to use the cryogenic grinding which is expensive. For similar insight on rotomolding, visit this website.