There are numerous methods for manufacturing hollow objects using plastic, and rotational molding (or rotational casting) may be one of the most economical and efficient processes we have at our disposal. This informative guide will cover additional uses of this technology, its key advantages, and other useful information.
What is rotational molding?
Rotational molding (rotational molding) is a manufacturing technology. Over the past 20 years, this technology has undergone significant improvements, and more and more companies are using this versatile process every day. Plastic powder is added to a shell-shaped mold, while rotating and heating to produce hollow parts. In this process, the powder melts into a bubble-free liquid layer, forming the inner surface of the mold. Then the object is cooled and the hollow part is removed. This process is often used to manufacture containers (see the image below), but it can also be used to manufacture complex medical products, toys, leisure crafts, and more.
The waste container lid manufactured using rotational molding technology has better quality.
Working principle of rotational molding
First, powdered polymer (mainly polyethylene) is loaded into a metal mold. Alternatively, metal parts can be placed in the mold and combined into the final shape.
Then, the mold is placed in an oven and rotated along two axes. Depending on the material used, the temperature can be maintained between 500°F and 680°F (260°C and 370°C). During this process, the melted material will adhere to the inner surface of the mold.
After the molten material forms an object, it is cooled and removed. Then, the mold is refilled, and the process is repeated as needed.
Trim the mold to separate (the lines or ridges that appear at the mold separation points). At this stage, you can add some other small parts, such as holes, screws, and slots.
- Add material into the mold
- Melt the material inside the mold
- Cooling mold
- post-processing
Equipment used for rotational molding
Rotational molding equipment includes an oven, a cooling chamber, and a mold spindle. The mold is typically made of aluminum alloy through Computer Numerical Control (CNC) machining or metal casting. This type of part is much thicker than similar parts made of stainless steel. Depending on the size and complexity of the part, the mold can also be made of welded steel plates.
Materials used for rotational molding
Most of the materials used in rotational molding come from polyethylene types (about 80%), among which the most common ones are:
- Cross-linked polyethylene (PEX)
- Low-density polyethylene (LDPE)
- Linear low-density polyethylene (LLDPE)
- High-density polyethylene (HDPE)
These materials also contain other components, such as polyvinyl chloride (PVC) plastisol, nylon, and polypropylene. The main requirements for the materials are:
- High thermal stability
- Sufficient antioxidant properties
- Ductility (easily flowing through all spaces of the mold)
The application of rotational molding
Rotational molding is primarily utilized for manufacturing industrial storage tanks and containers. Additionally, it finds applications in various other fields, including:
- Septic tank
- Chemical storage tank
- Oil tank
- Fuel tank
- Water treatment tank
- Transport tank
- Traffic sign
- Container
- Toys and leisure products
- Material Handling
- Marine industry
Rotational molding or injection molding?
Like other methods, rotational molding has both advantages and disadvantages in manufacturing technology. It is often compared to injection molding (IM). Rotational molding and injection molding are two widely used technologies in various industries. They have many commonalities and can sometimes be interchangeable, but generally, these two technologies are suitable for different situations.
Compared to injection molding, rotational molding has the following disadvantages:
- The complexity of mold design is relatively low
- Low tolerance
Advantages of rotational molding:
Although rotational molding is considered less precise than injection molding and has a longer cycle time (1-2 cycles per hour compared to just a few seconds for injection molding), it still possesses some unique advantages that make it irreplaceable.
- Significant changes in surface polishing and color
- Relatively free design
- uniform wall thickness
- durability
- Stress-free product
- Stable and lightweight simultaneous molding
- There is almost no material waste
- Affordable mold equipment cost
- The wall is very sturdy
In addition to other plastic molding techniques, rotational molding technology can produce products that are stronger, more flexible, have smooth surfaces, and exhibit consistent wall density. Parts manufactured using this technique contain more plastic in the outer corners and sides of the mold. Furthermore, due to the advantages of rotational molding, the finished product experiences less stress, is more stable, and also possesses flexibility. It can also reduce the risk of cracks in the final product. Please refer to our manufacturing guide for more information on injection molding techniques.
- Cost
The mold cost is less than 1/5 of the cost of blow molding and injection molding, which means lower production costs in the medium and short term, with almost no change in quality.
- Quality
The precision, consistency, appearance, and texture of parts produced through rotational molding are impressive, and their quality is comparable to that of parts produced by other processes, with a comparable part wall ratio
Injection molding is better
- Flexibility
Unlike processes such as injection molding, this method can be used to manufacture highly complex shapes and even allows for changes in wall thickness without the need for reprocessing.
- Speed
From idea to manufacturing, the delivery cycle for components made using rotational molding is shorter than most other processes.
- Various surface treatments
Rotational molding can provide a range of smooth or textured surfaces, enhancing the quality of the final product at a relatively low cost.
- Multi-purpose
This is a truly versatile plastic molding technology that can be used to manufacture a wide range of products and is suitable for various market industries.
