Rotational molding, also known as rotomolding, is a plastics molding technology which is ideal for making hollow articles. It is a casting technic but unlike most other plastics processes there is no pressure involved. Molds for the process are relatively inexpensive as they do not have to withstand pressure and therefore relatively short production runs can be made very economically.
Rotomolding is used to make a very diverse range of products. The process offers the product designer exceptional freedom as just about any shape can be produced. There is almost no limit to the size of moldings and there are literally thousands of applications.
Various types of conventional plastic resins may be used in the Rotational Molding process to achieve the desired characteristics, depending on the final product’s application like producing water, fuel, and other tanks, boats, toys, traffic warning signs, etc.
Polyethylene is the most often used material for rotational molding. Polyethylene itself is classified into several types, such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear low-density polyethylene.
HDPE is frequently selected for rotational molding due to its favorable features. To begin, HDPE has good mold flow properties, which means it melts readily and uniformly covers the interior of the mold during the rotational molding process. This results in constant wall thickness and helps with the overall uniformity of the product.
Second, HDPE has excellent impact resistance and toughness, making it perfect for applications requiring endurance, such as the manufacture of tanks, containers, and outdoor items like boats or traffic signs. Its tolerance to chemicals, moisture, and environmental conditions makes it ideal for rotational molding applications.
Furthermore, HDPE is relatively lighter than other materials, allowing for the manufacture of lightweight yet strong pieces. Its recyclability and low cost make it a desirable choice for producers seeking environmentally friendly and cost-effective solutions.
Rotational Molding Procedure
The rotational molding process is a high-temperature, low-pressure method for producing plastics that uses heat and biaxial rotation to manufacture hollow, one-piece objects such as septic tanks, water tanks, toys, and any other plastic products having a hollow body.
The rotational molding method is really simple: A hollow mold that determines the final shape is filled with a light weight of plastic resin. The mold begins to rotate biaxially while also being heated in an oven. As a result of the heating, the resin melts and coats the mold walls. Immediately after that, the mold should be cooled so that the resin forms in its proper shape without deformation. Finally, the rotation stops and the mold is opened to release the finished product.
Schematic of rotational molding procedure
Applications of Rotational Molding
Rotational molding is the most effective method for producing hollow, large-scale plastic parts and components. Here are some typical applications using the rotational molding method: Tanks and containers include fuel, water, industrial, and recovery tanks, as well as toys, boats and canoes, and traffic warning signs.
Tanks and Containers
This technique has various benefits for tank and container manufacture. First of all, it enables the production of hollow components with complicated forms, lowering the danger of leakage and improving structural integrity. Second, rotational molding enables the immediate incorporation of elements like inserts and fittings into the component, which speeds up production and improves functioning. Furthermore, its design versatility allows for adjustment of wall thickness, material composition, and design aspects to fulfill unique needs. Finally, rotational molding’s scalability makes it cost-effective for both short and big production runs, meeting the demands of a wide range of sectors such as agricultural and chemical processing, and water treatment.
These advantages make rotational molding ideal for producing a variety of tanks and containers, including portable water tanks, fuel tanks, large agricultural tanks, small tanks, septic tanks, and other similar tanks.
Toys
Rotational molding is widely employed in the toy industry due to its versatility and cost-effectiveness. As said before, it allows for the production of complex shapes and designs, including intricate details and textures, enhancing the toy’s aesthetic appeal. Secondly, it enables the creation of durable yet lightweight toys, suitable for both indoor and outdoor play. Additionally, rotational molding permits the incorporation of features like handles, wheels, and internal compartments directly into the toy design. This process is scalable, facilitating efficient production of toys in various sizes and quantities, making it a preferred choice for toy manufacturers worldwide.
Boats and Canoes
Rotational molding is a popular technology for making boats and canoes because it can produce smooth, hollow structures with complicated shapes. This continuous design maintains water tightness and improves structural integrity, which is critical for boats. The method results in lightweight yet strong boats, improving performance and fuel economy. Furthermore, its cost-effectiveness and scalability make it suitable for manufacturing boats and canoes of varying sizes and numbers to fulfill the varying demands of recreational and commercial uses.
Traffic Warning Signs
Rotational molding is an important technology for creating traffic warning signs because of its capacity to construct long-lasting, weather-resistant structures. Its structure assures durability and resistance to tough outdoor conditions including UV rays and high temperatures. Furthermore, rotational molding enables the insertion of reflective materials directly into the sign design, guaranteeing good visibility for drivers even in low-light settings.
Polyethylene Rotational grades
| Grade | MFI | Density | Application |
|---|---|---|---|
| HD-3840UA | 4 (190°C / 2.16kg) | 0.954 | Scpetic tanks - Potable water tanks - Large agricultural tanks - Toys - Wide variety consumer articles - Canoes and Boats |
| HD-3030UA | 3 (190°C / 2.16kg) | 0.93 | Small Containers(Max 500Lit) - Septic Tanks(max 500Lit) - Toy - Pleasure boats - Traffic warning signs |
