You may have heard about the process of rotomolding. This technology has become more popular in the last 20 years and has revolutionized the manufacturing process of many common items. Products made by rotomolding include hollow vessels, septic tanks, road signs, and other complex hollow shapes.
Rotomolding, short for rotational molding, is a thermoplastic manufacturing process used to create seamless one-piece items using a unique plastic molding. It is most suitable for large and hollow one-piece parts, hollow parts, and double-walled items such as rotomolded cases. This technology is also used for canoes, toys, industrial equipment, garbage bins, plastic planters and much more. The advantages of rotomolding include cost-effectiveness, the ability to produce complex shapes, and uniform wall thickness.
Here is more information about rotomolding and its use in the packaging industry.
Introduction to Rotational Molding
Rotational molding, often referred to as rotomolding, is a highly adaptable production process designed to form hollow parts of virtually any size. This method stands out for its cost-effectiveness and versatility, making it a preferred choice across a wide range of industries. The process begins by placing resin—typically in powder or pellet form—into a mold. The mold is then heated and slowly rotated on both vertical and horizontal axes. As the mold rotates, the resin melts and evenly coats the inner surfaces, creating seamless parts with uniform wall thickness. This unique approach allows manufacturers to produce hollow parts with consistent wall thickness, making rotational molding ideal for applications that require strength, durability, and precision. Industries such as manufacturing, construction, and consumer products rely on this process to create everything from storage tanks to playground equipment, all benefiting from the efficiency and flexibility of rotational molding.
How is rotomolding done?
Most other plastic processes use high pressure, but rotomolding is quite a long process using low pressure and high heat. This makes it more complicated than it seems because the material cannot be handled the same way. It is also more likely to be affected by factors such as temperature, polymer quality, and more. Despite this, it is a worthwhile production process since it results in a very high-quality, seamless plastic product and offers efficient, scalable production. Managing and reducing cycle time in rotomolding operations is important to enhance efficiency and increase production output.
Unlike injection molding, which uses high pressure to inject melted plastic into a mold and is often preferred for high-volume, small-part manufacturing, rotomolding relies on heating and rotating the mold, making it ideal for producing large, complex parts with lower tooling costs and greater flexibility in production scale.
As an experienced company in the rotomolding industry, Creopack is committed to delivering customer satisfaction and high-quality results.
The rotomolding process involves four main steps:
1. Filling the mold
The loading phase is the step where material is added to the hollow mold. This material can be in the form of plastic pellets, resin, or powders, with resins commonly used for their ability to form seamless, durable products. This polymer is usually in powder form and mainly made of polyethylene. Polypropylene is also used as a specialized raw material in rotational molding, offering various formulation options and compatibility with different fillers and reinforcements to enhance material properties. Once the mold is filled, it can be secured.
2. Heating the mold
The mold is then placed in an oven and heated at a high temperature so the polymer can melt and fill the inside of the mold.
During this entire process, the mold is rotated around multiple axes, or is rotating biaxially, so the plastic can properly form to the mold’s shape. As the mold rotates, more material is distributed to corners and stress points, resulting in uniform wall thickness and durable, seamless surfaces.
3. Cooling
The mold is then transferred to a cooling chamber, where the cooling process begins while it continues to slowly rotate. In the cooling chamber, the mold is cooled using air or a fine mist of water to ensure proper solidification and quality of the final product. The cooling process must be carefully measured so the manufactured part does not get warped. This is usually done with air and sometimes with a fine mist of water.
4. Dismantling
The cooling process is done when the item can be handled and the polymer holds its shape. At this point, the rotation is stopped and the part can be removed from the mold. The finished part has been created and is ready for use, and the mold can be reused to make an identical part.
Rotomolding Machines and Equipment
The rotomolding process relies on specialized machines designed to ensure high-quality results and efficient production. These machines are composed of three main components: the oven, the cooling chamber, and the spiders. The oven is responsible for heating the mold and the material inside, typically reaching temperatures between 260 and 370 degrees Celsius to ensure the resin melts and adheres properly to the mold’s surfaces. Once the heating phase is complete, the mold is transferred to the cooling chamber, where it is gradually cooled to ambient temperature. Cooling can be accelerated using forced air or water, helping to solidify the molded product without causing warping or defects. The spiders are mechanical arms that hold and rotate the mold throughout both the heating and cooling stages, ensuring even distribution of material and consistent wall thickness. Modern rotomolding machines incorporate advanced technology, such as computerized controls and high-velocity air circulation, to optimize heat distribution and enhance the overall quality of the finished product.
Materials used in rotomolding
The success of any rotational molding project depends greatly on the materials chosen for the process. In the rotational molding industry, polyethylene stands out as the most widely used material due to its versatility, durability, and excellent molding capabilities. Polyethylene comes in several forms, including linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and low-density polyethylene (LDPE), each offering unique benefits for producing a wide range of rotomolded products.
Linear low-density polyethylene is especially popular in the rotational molding process because it provides a balance of flexibility and strength, allowing manufacturers to achieve consistent wall thickness and uniform density throughout the molded part. High-density polyethylene is valued for its rigidity and impact resistance, making it ideal for applications that require extra durability, such as large tanks and industrial containers. Low-density polyethylene, on the other hand, offers enhanced flexibility and is often used when a softer finished product is desired.
These materials are specifically chosen for their ability to flow evenly within rotational molds, ensuring that even complex shapes and hollow objects are produced with high quality and precision. The use of polyethylene in rotomolding not only results in products with reliable wall thickness and structural integrity but also allows for the creation of intricate designs that meet the diverse needs of various industries. By selecting the right type of density polyethylene, rotational molders can produce durable, cost-effective solutions tailored to customer requirements.
Quality Control and Assurance in Rotomolding
Ensuring consistent wall thickness and high-quality products is a top priority in the rotational molding industry. Rotational molders employ a variety of quality control techniques throughout the rotomolding process. Biaxial rotation—where the mold rotates on two axes—ensures that the material is evenly distributed, preventing thin spots or weak areas in the final product. Precise temperature control during both the heating and cooling phases is essential to avoid defects such as warping or incomplete fusion. The mold rotates continuously during these stages, which helps maintain the desired shape and uniform wall thickness. In addition to process controls, rotational molding companies conduct regular inspections and rigorous testing of finished products to verify that they meet industry standards and customer expectations. These quality assurance measures are critical for delivering reliable, high-performance products and achieving customer satisfaction in every rotomolding project.
Customization and Design Possibilities
One of the standout advantages of rotational molding is its remarkable flexibility in customization and design. The process is well-suited for producing complex shapes and hollow objects, accommodating a wide range of materials such as linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and other polyethylene resins. Rotational molding companies can develop custom molds and tooling to create unique products tailored to specific requirements, including septic tanks, large tanks, and road signs. The ability to achieve consistent wall thickness, even in intricate designs, allows for the production of hollow parts and objects that meet the diverse needs of various industries. Whether it’s manufacturing durable containers, specialized tanks, or custom signage, the rotomolding process offers unparalleled design freedom and the capability to produce both small and large parts with precision and efficiency.
Why use rotomolding in the packaging industry?
Rotomolding can be used to easily make stackable containers, pallets and tanks. It is often used in the packaging industry for its many benefits.
Perhaps the most appreciated benefit by manufacturers is its cost-efficiency and low cost. Tooling is a significant factor in the overall cost, and molds are often made from steel for durability and longevity. Molds are inexpensive and do not require large quantity purchases for them to be worth your money.
Additionally, items require no assembly. Since they are a uniform product, they are a lot more durable and resistant to deterioration caused by chemicals or environmental factors. The properties of the materials used, such as cross-linked polyethylene, provide superior mechanical strength and chemical resistance compared to other materials, making them ideal for demanding applications.
Rotomolding is also highly customizable with endless design possibilities. It always offers smooth and uniform wall thickness, even when the mold shape is more complex. The corners also tend to be thicker, which contributes to their increased strength and integrity, and helps address additional stress that may occur in these areas by adding more material where needed.
We work closely with our customers to develop custom packaging solutions tailored to their specific needs, which leads to high customer satisfaction.
Finally, rotomolding produces little waste since the exact weight of plastic required is used.
Industries that can benefit from rotomolded packaging
Rotomolding can be used for packaging in a variety of industries such as marine, security, oil and gas, aerospace, and more.
Each rotomolding project can be tailored to the specific needs of different industries.
Food industry
Rotomolded packaging can be used in the food industry to transport and store temperature-sensitive food products or dry ice pellets and blocks.
For example, this can be done with our polar insulated container. Rotomolded with FDA-approved polyethylene with foam insulation, it is ideal for food distribution, fish and wine industries.
Military industry
The military industry requires the use of quality cases to transport their heavy-duty equipment. Rotomolded packaging and cases are perfect for handling materials where delicate equipment needs to be transported or stored safely.
Medical industry
The medical industry involves transporting fragile devices and storing chemicals. Medical and pharmaceutical packagingmust also comply with strict standards and regulations.
At Creopack, we understand that packaging for fragile products of the medical industry must have maximum protection, so quality is our top priority.
No matter your industry, your business is sure to benefit from rotomolded packaging.
One of many packaging options
In conclusion, rotomolding is a manufacturing process that produces sturdy thermoplastic items using high heat and low pressure. It offers many benefits that can be useful in different industries. However, obtaining rotomolded items may require the help of professionals such as Creopack.
Trying to decide if rotomolding is the best packaging option for your needs? Contact us to know more about your different options!
Conclusion and Future Outlook
In summary, rotational molding is a versatile and cost-effective production process that delivers consistent wall thickness, high-quality products, and extensive customization options. The rotational molding industry is poised for continued growth, fueled by technological advancements and the rising demand for complex shapes and hollow objects across multiple sectors. As companies seek to reduce cycle times and enhance production efficiency, rotational molding is set to play an increasingly important role in the manufacturing landscape. With its proven ability to produce large parts, maintain uniform wall thickness, and accommodate a wide range of designs, rotational molding remains a leading solution for industries seeking reliable, innovative, and cost-effective manufacturing processes. The future of the rotational molding industry looks bright, with ongoing developments promising even greater capabilities and broader applications.