Rotationally molded plastics are thermoplastic products fabricated through the process of rotational molding, or rotomolding for short. (A thermoplastic is a plastic material that will soften when repeatedly heated and cooled.) The rotomolding process is very simple and inexpensive–in short, it involves a revolving mold and high heat. Rotationally molded plastics are hollow, with the high tensile strength and uniform wall thickness that comes from single piece construction.
The process to form rotationally molded plastics starts with a metal mold into raw plastic material is loaded and supported by arms called spindles. This is called the charging phase. From here, the loaded molds are transported to a heating chamber, where the mold is heated and revolved the on the spindles’ horizontal and vertical axes until molten. This low-pressure method allows the molten plastic, which may be enhanced with corrosion and static resistant additives, to coat the interior walls of the mold cavity evenly. The third phase of rotomolding is the cooling stage, during water and air cool and dry it for about twenty minutes. The last step is to reopening the fully dried mold and manually removing the new plastic part. Read More…
The list of plastics that can be rotationally molded is quite long. Some of these include: polyethylene (PE) cross-linked polyethylene, high-density polyethylene (HDPE), linear low density polyethylene (LLDPE) and polyvinyl chloride (PVC). Polyethylene is a lightweight plastic that has a low modulus of elasticity.
Rotationally molded polyethylene products have good impact resistance and are thick in desired areas. Cross-linked polyethylene is type of PE that is perfect for products that will be exposed to extremely low temperatures. High-density polyethylene also promises to perform and adapt well to cold temperatures. In addition, this high-flow molding, high molecular weight thermoplastic offers products with interior gloss development. The benefits of rotationally molded linear low density polyethylene parts are superior fit and finish and high impact, tensile and insulatory strengths. Finally, polyvinyl chloride, commonly called PVC or vinyl, offers excellent chemical resistance, high transparency, long-term stability, good weatherability, superior flow characteristics and stable electrical properties. Also, it can be either flexible or rigid.
The metal mold used for rotomolding, which can be custom-made, is usually made from aluminum or stainless steel. Because rotomolding is a slower process than other thermoplastic molding techniques, it is usually only used for shorter manufacturing runs. Despite this setback, rotational molding services offer many benefits that processes like thermoforming, injection molding and blow molding do not. First, roto molders can often mold different products at the same time, as long as they are similarly sized. Second, because rotational molding doesn’t require pressure, manufacturers save on energy related costs and equipment costs, because their molds aren’t put under so much stress. Third, molders can switch colored plastics without lengthy line cleanings. In addition, since rotationally molded plastics are seamless, they can endure higher amounts of pressure without fracturing. This fact makes rotomolding a popular method for the fabrication of canoes, kayaks, large plastic vessels and tanks, playground slides, sports helmets and more. Another advantage of rotomolded plastics is that they can easily be fabricated to meet FDA standards for use in the pharmaceutical, food and beverage industries. Also, it is very easy to design a mold to form a logo, graphic or label into a rotomolded plastic product. Rotomolded parts are lightweight and versatile in density, color, finish and texture.
With all these advantages and more, it’s no wonder that rotomolding is popular industries like road construction, agriculture, plumbing, sporting goods, packaging, material handling, automotives, toy manufacturing, wastewater management, pharmaceuticals, food and beverage processing, fuel and oil, chemical handling and marine manufacturing.