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Rotational Molding

Rotational moulding, also sometimes known as rotomoulding, is a thermoplastic fabrication process by which plastic goods are formed and manufactured using a revolving mold and high heat. Rotomolded products are hollow and have single piece construction, with uniform wall thickness and high tensile strength. They are often inexpensive to manufacture and require little further fabrication work.

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MOD is a design and manufacturing specialist in the conversion of metal, fiberglass, wood and other parts into complete, integrated, rotational molding plastic designs. Award-winning MOD engineers help you cut the parts, count, reduce weight, boost strength and add stunning visual appeal. We create products for applications such as chemical, food, healthcare and more.
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We are a full-service rotational molding manufacturer that takes pride in our state-of-the-art equipment and our long-term employees. We are noted for our custom ability, but have our own standard product line as well. Why buy anything but Quality? Stop in and we are confident that you will agree, Quality is not just our name, it is our business. Call us today or visit our website for a quote!
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Park Plastic Products is ready for your rotomolding needs. We manufacturer the rotational molded tanks you require with exceptional quality and fair prices. We pride ourselves on fast service and complete customer satisfaction. If there is a product you need, inquire with us and we will be happy to work with you on the solution. Do not wait, give us a call today!
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Assmann Corporation is an NSF & ISO certified rotational molder of large and small double wall, vertical, horizontal and conical plastic tanks, and also chemical feed stations plus secondary containment basins. Our rotomolding process and extensive experience makes the difference... We offer many accessories, including full drain outlet, seismic restraints and more.
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We have been producing high quality rotationally molded products for the marine, construction, medical, and irrigation industries since 1994. We are committed to customer satisfaction, making quality and reliability our first priority in everything we do. Call or visit us online for more detailed information about the products and services that we offer. We would love to serve you today!
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Custom rotational molding from Fibertech Inc. includes complete design and manufacturing services. We will help you develop timely, economical solutions and specifications for your custom rotationally molded plastic parts and products. We specialize in custom projects for commercial and industrial products, including fan housings, lockers, bulk handling containers and recreational products. From design through production and delivery, our customers receive high-quality, timely service.
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Industry Information
View A Video on Rotational Molding - A Quick Introduction

Rotational molders employ rotational molding techniques to manufacture plastic parts from stock molds, and rotomolding companies often offer custom rotational molding, which requires the fabrication of a unique rotomold. The molds are usually made out of either stainless steel or aluminum, which are welded together or die cast. The plastic rotational molding process is considered slower than other thermoplastic molding techniques, and parts are usually manufactured in smaller runs. Roto moulders are often able to mold different products simultaneously, as long as they are similar in size. Some are designed to fit many different smaller molds on their spindle arms, while other rotational molders are used to fabricate one large molded product at a time. Rotational moulders are used to fabricate plastic products for a wide range of industries and applications, including food and beverage processing, pharmaceutical, waste water management, agricultural, plumbing, sporting goods, packaging, material handling, chemical, fuel/oil, marine, road construction, automotive and toy manufacturing. Tanks, containers, bins and other hollow plastic products are just a few examples of possible rotationally molded plastics.

The process begins with a rotomoulding machine with arms called spindles. These spindles support the molds in which the plastic material is contained. The molding machine transports the molds from the loading area to a heating chamber and then to a cooling chamber. From start to finish, there are four different stages that are completed in anywhere from 15 to 90 minutes. In the first stage, which is referred to as the charging phase, the metal mold is loaded with raw plastic material and is sealed shut. From there, the mold is heated to high temperatures while slowly revolving on the vertical and horizontal axes of the spindles. This heats the plastic powder until molten, so it evenly coats the interior walls of the mold. Because roto moulders use low pressure, the plastic resin is in the form of fine powder to help it reach all surfaces of the mold cavity evenly. The plastic material can feature additives that contribute to corrosion and static resistance, and the finished molded product assumes these properties when it emerges from the molding process. Phase three is a cooling stage that cures the plastic within the mold, which is accomplished by using cold air and water for about 20 minutes. After the plastic has fully dried, the mold is reopened and the solid plastic part is manually removed. Because shrinking often occurs, removal can prove to be difficult. For applications that require additional strength, reinforcing ribs can be fabricated into the part.
 
Rotational molding services have several advantages over blow molding, thermoforming and injection molding. Molders are able to change colored plastics without extensive line cleanings, which saves on time and additional costs. Rotational molding does not require pressure, so the molds do not endure the same pressure as in injection molding or extrusion, which helps to limit equipment costs as well as energy-related costs. Rotational molding is often the method of choice in the fabrication of large plastic vessels and tanks, which are otherwise welded together with a laser, hot pressurized gas, ultrasonic vibration or a hot plate and pressure. While welding provides an air and water tight seal, bursting and cracking under high pressure is a concern. Rotomolded plastic tanks, however, are seamless and able to withstand higher amounts of pressure. Examples of other rotomolded products include outdoor furniture, kayaks and canoes, playground slides, safety cones, footballs, sports helmets, plastic rotomolded tanks, large trash containers and beverage bottles.

There are many other advantages to the rotational molding process. While being heated and rotated, the plastic resin adheres to the hot mold, coating it very evenly and seamlessly, producing strong outside corners with virtually no stresses. Rotomolding can produce one-piece constructions, and complex parts are formed without any part assembly required. The plastics used for rotomolds are often lightweight and may be high or low in density. For applications in the food and beverage and pharmaceutical industries, the thermoplastics used can be easily fabricated to be FDA approved, meaning they must not contain any recycled plastic or dies and cannot contaminate substances under any conditions, even high temperatures. The low cost of the materials and tooling makes rotational molding just as cost effective for producing prototypes as it is for large production runs. A variety of finishes, colors and textures are available. Companies are able to mold their logo, graphic or labels right into the parts. These imprints will not come off and are parts of the mold construction. Rotomolding is a versatile molding technique that provides durability to products, eliminates costly fabrication and assembly processes and reduces the need for replacement parts.

rotational molded plastic

rotational molding
rotationally molded


Types of Rotationally Molded Plastics and Rotational Molding

  • Cross-linked polyethylene is an ideal material for rotomolded products that will be exposed to extremely cold temperatures. 
  • Custom rotational molding services allow customers to design rotomolded products to their specifications.
  • High-density polyethylene (HDPE) offers high-flow molding and high molecular weight performance in rotationally molded parts. Properly rotomolded HDPE products will have interior gloss development, ductile cold temperature impact performance and an off-gas odor that confirms the chemical cross-linking reaction.
  • Linear low density polyethylene (LLDPE) provides superior fit and finish to rotationally molded products. Rotomolded LLDPE products also have high impact, tensile and dielectric strength. 
  • Plastic rotational molding is the process of rotating molten plastic material in a mold in order to shape it into a useful product.
  • Polyethylene (PE) is a lightweight plastic that has a low modulus of elasticity. Rotationally molded PE products are thick in desired places and have good impact resistance.
  • Polyvinyl chloride (PVC), also referred to as "vinyl," has excellent transparency, chemical resistance, long-term stability, good weatherability, flow characteristics and stable electrical properties. PVC can be either rigid or flexible. 
  • Rotational molders, also known as rotational moulders or roto moulders, are used to fabricate hollow plastic parts.
  • Rotational moulding is the low pressure process used to create hollow plastic components.
  • Rotationally molded fuel tanks are seamless polyethylene (PE) tank structures that retain molded-in logos, warnings, serial numbers and other full color graphics when exposed to salt water, sunlight, solvents, cold weather and other severe conditions.
  • Rotationally molded plastics are one-piece products created on a rotational molding machine.
  • Rotomolds are machines used to make hollow, one-piece plastic parts.
  • Rotomolded products are hollow plastic parts formed by rotational plastic molding processes.
  • Rotomolded tanks are hollow plastic containers used for the storage of materials, often in bulk quantities.
  • Rotomolding, also known as rotomoulding, is the four-step process used to make hollow plastic components.

Rotational Molding Terms

Blow Molding - A common process used to form hollow, thermoplastic shapes, such as bottles and containers. Two general types of blow molding are extrusion and injection blow molding.
 
Chemical Cross Linking - The process in which individual polymer particles are joined together by a molecular bond.
 
Chemical Resistance - The ability of a material to withstand various chemical agents. Plastic is capable of enduring many of these chemicals, making it very useful for holding tanks and other containers.
 
Corrosion - The oxidation and deformation of a material, such as the rusting of iron, due to a chemical reaction.
 
Cycle Time - The time it takes from the first stage of rotational molding, in which the plastic is loaded, until the plastic completes its final stage and is removed from the mold.
 
Deflashing - The removal of unwanted material from a molded product, especially from the areas where parting lines of the mold may have caused excess material to be formed.
 
Density - A significant parameter for polyethylene (PE) that affects the properties, such as stiffness and impact strength, of the end product.
 
Elasticity - The ability of a material to return to its original form after stress has been applied and quickly removed.
 
Fusion Temperature - The temperature at which the plastic resin melts and begins to adhere to the surface of the mold.
 
Grind Ability - The ability of a plastic to be ground into a fine powder. Most plastics are ground prior to being loaded into the mold.
 
Impact Resistance - The measure of the ability of a plastic to withstand fracture by shock.
 
Plastic - A generic name for semi-synthetic or synthetic materials that can be extruded or molded into films or objects. Plastic materials are also used for coatings and adhesives.
 
Polymer - A chain of molecules that is formed by the bonding of individual repeating units (monomers).
 
Pour Ability - The measure of the speed of a plastic powder when poured through a funnel. For a plastic powder to be acceptable for rotomolding, it must be capable of flowing at least 185 grams/minute.
 
Resin - Any of various semisolid or solid natural organic materials that are usually translucent or transparent. Resins are mostly utilized in plastics, adhesives and coatings.
 
Spindles - The "arms" of the rotational molding machine that are responsible for moving the molds between different stages. Spindles also spin on the horizontal and vertical axes to create a uniform filling within the mold.
 
Thermal Stability - The ability of a resin to withstand specified temperatures. Less thermally stable materials can be rotomolded only under controlled conditions with extreme care.
 
Thermoplastic - A material that will soften when repeatedly heated and cooled. Examples of thermoplastics include polyethylenes, polypropylene (PP), vinyl and nylons.




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