They are known for their impact resistance, high tensile strength and wide design range. Rotational molding is an inexpensive process that uses rotation, heat and a mold to form many different products, the most popular of which are plastic tanks.
Rotomolded tanks exhibit uniform wall thickness, the ability to have threads, fittings or hardware attached and many different color options. They are mostly used in industrial applications for the food and beverage processing, fuel and oil, chemical, pharmaceutical, marine, wastewater treatment, agricultural and medical industries.
Their seamless, single part construction protects against fractures and leaks, which leads to a longer lifespan. They have many benefits over metal tanks, which can corrode and oxidize and are difficult to install. Rotational molding is also the most beneficial method of producing plastic tanks, compared to other thermoplastic fabrication processes like welding.
There is also very little material wasted, unlike thermoforming, injection molding and blow molding, all of which have extra scrap pieces of plastic that are removed from the newly formed tanks and require costly assembly.
Rotationally molded tanks are made of a few different thermoplastic materials, including polyethylene, polypropylene, Halar and polyvinylidene fluoride, all of which are high purity plastics. To enhance properties like strength, moisture, chemical and temperature resistance, color and flame retardancy, the plastic resin often contains additive materials, depending on the product’s application.
Since plastic tanks are generally some of the largest products fabricated from rotational molding, manufacturers employ the largest rotomolders to produce them. They require a large amount of space, an area where high heat can be reached and a cooling location, both of which must be big enough for the rotational molding machine to revolve around two different axes if necessary.
To fabricate the tanks, the polymer resin is always in fine powder form, in order to better reach all corners and sides of the tank-shaped mold. Since the process is carried out under low speeds and low pressure, even distribution of the plastic is sometimes a concern. However, if the plastic granules are fine enough, complex designs such as two-compartment tanks are possible.
Rotomolded tanks are designed to be either horizontal or vertical in orientation, and may hold anywhere from a few gallons to several thousand gallons.