What Is Rotomolding?
Rotational molding, rotomolding, rotomold, or rotocasting is a production process to form hollow parts of limitless size. Rotational molding is best used for large, one-piece hollow parts and double-walled open containers such as tanks, kayaks, hunting blinds, playground slides, furniture, and coolers.
This is a cost-effective method to produce large plastic parts. Resins are added into a mold that’s heated and rotated slowly, both vertically and horizontally. The simultaneous heating and rotation distribute and fuses the resin on the inner surfaces of the mold.
The result is a product that contains seamless parts with a uniform wall thickness with more material in corners to absorb shocks and stresses where they occur most. For example, rotomolded coolers and hunting blinds benefit from the rotomolding process resulting in a leak-proof seeable container.
Rotational molding is a manufacturing process that relies on bi-axle rotation, heating, and cooling to produce parts with exceptional strength. The finished product is a stress-free, lightweight, and seamless design that is very durable.
In 1961, the first polyolefin powder, a low-density polyethylene, was publicly demonstrated to the rotational molding industry. Polyethylenes remain one of the most popular materials for rotomolding, because of the processability, broad range of properties, and low cost.
Major thermoplastic raw material suppliers have investigated specially formulated powders for rotational molding, including polypropylene, nylons, polycarbonate, rigid polyvinyl chloride, and others. These powders can be foamed or reinforced with fiberglass.
In addition to the raw material suppliers, many rotational molders also have used custom grinding services or have in-plant grinding capabilities which have enlarged the material selection for this process.
Overview Of The Rotomolding Process
The plastic powder is placed into a heated hollow mold and is rotated in two perpendicular axes as it melts and disperses evenly around the interior surfaces of the mold. The rotation continues during both the heating and cooling phases.
Once the plastic is stable, it then enters the cooling cycle. After cooling the rotation is stopped and the finished part is removed from the mold.
The Rotational Molding Process:
- A hollow mold is filled with powdered plastic resin.
- The mold begins rotating bi-axially and is transferred into an oven.
- The mold continues to rotate as the resin melts and coats the walls of the mold.
- The mold is cooled until the resin hardens into the desired shape.
- The rotation is stopped, and the mold is opened to remove the finished part.
Given the low-pressure, high-heat nature of the process, rotomold tooling is usually made from soft metal such as aluminum and the majority of the resin used is polyethylene due to its low chemical degradation when exposed to high heat. Inserts, ribs, kiss-offs, undercuts, and foam reinforcements are often incorporated into the part in-mold or utilizing secondary processing.
Advantages of Utilizing Rotational Molding
The advantages of rotational molding include design flexibility, durability, low-cost tooling, and uniform wall thickness. A wide range of sizes and shapes can be molded. Rotomolding also has many options for colors, material selection, and textures. Very little material is wasted during the process, and excess material is often re-used, making it economical and environmentally friendly.
Rotational molding offers design advantages over other molding processes. With proper design, parts assembled from several pieces can be molded as one part, eliminating high fabrication costs.
The process also has inherent design strengths, such as consistent wall thickness and strong outside corners that are virtually stress-free. For additional strength, reinforcing ribs can be designed into the part. Along with being designed into the part, they can be added to the mold.
Rotomolding tools can be machined, cast, or fabricated from materials such as steel, aluminum, or stainless steel. Cast and machined molds are best when tight tolerances are needed, or cosmetic finishes are important to the finished product. Cast molds offer a wide range of finishes from wood grain to a mirror finish. Fabricated molds are more economical than cast or machined molds but offer fewer options for finish.
Rotomolding With Grizzly Coolers
Hard-sided coolers from Grizzly Coolers are made of rotationally molded plastic in Decorah, Iowa. Designed to make exceptionally strong coolers and provide optimum performance.
The rotomolding process Grizzly uses ensures each part has a consistent wall thickness, free of imperfections, and ensures the coolers will hold up to the toughest abuse. Grizzly Coolers offers a zero cost lifetime warranty on all their hard-sided coolers. Due in large part to the rotomolding process used during manufacturing.
Grizzly Coolers also offers soft-sided coolers, insulated drinkware, and innovative hunting blinds. Learn more about all its products, its rigorous product testing process, and where you can buy these quality products at GrizzlyCoolers.com.