Rotational molding, also known as roto molding, is one of the affordable and efficient methods used to produce hollow plastic objects that require high-quality finishes, consistent wall thickness, and high stability. This process is used across a wide range of industries for its various benefits. The article will help you learn more about rotational molding.
What is Rotational Molding ?
Rotational Molding Process Image Credit:
https://en.m.wikipedia.org/wiki/Rotational_molding
Rotational molding is a versatile manufacturing process used to create hollow parts. It involves filling the heated mold with the plastic powder. The mold is then rotated around two perpendicular axes as it is heated.This makes the plastic melt, spread evenly and coat the interior of the mold. The rotation continues during both the heating and cooling phases, avoiding sagging or deformation. After cooling, the material hardens, and the hollow part with the desired shape can be removed from the mold. Rotational molding can be more cost-effective when the production demands are lower than 3,000 units a year. The process can be used to form hollow parts with uniform wall thickness,intricate geometries, and superior strength.
Materials used for Rotational Molding
Materials that are commonly used:
Materials that are occasionally used :
Types of Rotational Molding Machines
Turret Machines (offer uniform heating and consistent product quality)
Carousel Machines (allow for different-size molds, with different cycle
times and thickness needs)
Swing Machines ( contribute to production efficiency)
Vertical Wheel Machines (energy-efficient, can mold small to
medium-sized parts)
Rock and Roll Machines ( designed mainly to produce long, narrow parts,
best for large parts that have a large length-to-width ratio)
Clamshell Machines ( used in low-volume manufacturing, ideal for
locations with limited space)
Open-Flame Machines (well-suited to producing cylindrical parts,
optimizing gas consumption)
Shuttle Machines ( productive, cost-efficient,advantageous in maximizing
floor space)
Advantages of Rotational Molding
Rotational molding has some distinct advantages:
Inexpensive tooling
Low operating pressures enable the mold to be manufactured with low-cost materials such as aluminum. It allows for less investment for the tooling.
Almost no material waste
There is almost no material waste during the process, which improves cost effectiveness.
Uniform wall thickness
The continuous rotation of the mold evenly coats the walls during both the heating and cooling phases, ensuring a uniform wall thickness throughout the molded product.
High stability
Without the exposure to external pressure, the material stability can be enhanced and the risk of defects in the finished parts can be reduced.
High durability
The parts manufactured with rotational molding are seamless and on-piece constructed, which eliminates the need for joining techniques. As a result, the likelihood of weak spots can be reduced, and products can be more durable.
Ease of producing double-walled parts
Double-walled parts can be easily produced without the need for additional post-processing steps such as welding and joint fabrication.
Disadvantages of Rotational Molding
Rotational molding has some disadvantages, including:
Longer production cycles
Rotational molding is not a great choice for high-volume manufacturing due to its longer production cycles. The speed of eight rotations per minute means that completing one rotationally molded part requires about three hours.
High costs
Additional cost is required in the process for the cooling water or air systems. In addition,rotational molding can be more labor intensive because of the limited availability of mechanization and automation.
Limited choices for materials
Materials used in rotational molding require the use of additives or being converted into powdered form, increasing the raw material cost. They also must have a certain level of thermal stability, which limits poly-based resins to be selected.
Low repeatability
Due to a lack of repeatability, the soft metal used in rotational molding must be replaced or repaired after 3,000 cycles, which results in quality problems.
Voids
Voids in the end product are possible.
Some details and designs are difficult to mold
Rotational molding machines fail to mold high-tolerance parts and sharp edges.
Applications of Rotational Molding
Rotational molding is mainly used for the manufacturing of tanks,but it can also be used for many other applications.Some common applications include:
Automotive parts such as fuel tanks and fenders
Storage tanks and containers
Materials handling equipment
Medical devices
Road signs and bollards
Gardening and agricultural tools used for planting
Furniture
Toys and Leisure
Watercraft and marine products
Small shelters and housing (i.e. pet houses,tornado shelters)
FAQs
1.What are the alternatives to rotational molding ?
Injection molding.
Injection molding and rotational molding are similar in that both of them offer design flexibility and can be used to create complex parts. Injection
molding is preferred over rotational molding in terms of producing large volumes of more complex parts.
Blow molding.
Blow molding and rotational molding have some similarities in that they can be used to create hollow plastic products. Though blow molding has less
flexibility and higher tooling cost, it is favored over rotational molding in large scale production, shorter cycles and longer mold life.
2.What is the best material for rotational molding ?
Polyethylene (PE). 97% of rotomoulded products are made from polyethylene (PE) because this material has excellent chemical resistance, impact strength, and ease of processing.
3.What are the factors that may affect the rotational molding process?
Draft angles, wall thickness, large flat surfaces or parallel walls, material flow around corners and aesthetics.
4.What are the rotational moulding parameters?
Heating time, cooling rate, and rotation ratio. They are critical to determine the mechanical properties and dimensional quality of the parts to be produced.
5.What are the common defects of rotational molding products?
Shrinkage and deformation, reduced Impact strength,bubbles and perforations.
6.What is the thickness of rotational molding ?
It can range from 1/32 inch to 1 inch (0.8mm to 25mm). 
7.Is rotational moulding sustainable?
There isn’t a definite answer. Strictly speaking, it isn’t sustainable due to the use of non-renewable plastics made from petroleum.However, it can be environmentally-friendly when compared with other manufacturing processes, because no chemicals or dangerous toxins are released and minimal material waste is created during production.
Conclusion
This article explained what is rotational molding, discussed its advantages and disadvantages, and applications in detail. You can learn a lot through reading this article. Echofast offers custom injection molding and die casting services from product development to production, addressing your concerns and lessening project risks.
Table of Contents
Collapse
Page navigation
Contact Us