Rotomolding: Which machines and molds are used?
Introduction
Rotomolding is a manufacturing technique that creates hollow plastic parts in various shapes and sizes. These objects with complex contours and smooth or textured surfaces are produced ingeniously. Essential machines play a crucial role during the process: they rotate and heat the mold, ensuring uniform plastic material distribution. The molds, in turn, give shape to your ideas by containing the molten plastic and forming the desired contours. Meticulous mold design is essential to achieve perfect results. Discover what you need to know about these indispensable elements of rotomolding.
The first appearance of roto molding dates back over 150 years, to the mid-19th century, when the process was conceived to create artillery munitions. It wasn't until the 1930s that the precursors of today's machines began to be used.
Between three and four main parts are found in these devices:
1. An Oven:
This part heats the mold to melt the plastic. It can operate on gas, electricity, or other energy sources. The oven temperature varies depending on the material used but generally ranges from 260 to 370 degrees Celsius or 500 to 700 degrees Fahrenheit.
2. A Rotation Unit:
This machine part rotates the mold on two perpendicular axes. The biaxial rotation allows for the even distribution of the molten plastic inside the mold. The rotation speed and angles are adjustable according to the shape and size of the part to be produced.
3. A Cooling Area:
This part allows the mold to cool gradually in the air. Cooling is essential as it solidifies the plastic, forming the desired shape.
4. A Loading and Unloading Area:
The mold is opened to remove the formed plastic part after cooling. The mold is then reloaded with plastic to start the heating cycle again.
Different Rotomolding Machines for All Production Needs:
With technological advancements, the equipment used for roto molding has undergone various transformations over time and with the mastery of different materials. Several types of machines, each with its specificities, are now available for designing complex plastic parts using this technique.
Clamshell Machines:
These machines combine the heating, cooling, and loading/unloading units in a single workstation. Clamshell machines have a single rotating arm, offering a relatively quick production cycle and requiring little space for installation. Their investment cost is also lower compared to more complex machines. Clamshell machines are more suitable for producing medium to large parts, such as fuel tanks, storage bins, and gardening equipment. They are less suited for very large parts, and their continuous production cycle is slower than carousel machines.
Shuttle Machines:
This machine moves molds between different units, such as the heating station, cooling station, and loading/unloading area. Shuttle machines use a mobile arm to transfer molds from one part to another. Their tremendous flexibility in production stages allows them to work simultaneously with multiple molds of varying dimensions and shapes. They are highly adaptable to a wide range of production constraints. Shuttle machines are ideal for manufacturing large parts such as water tanks and boats. However, the initial cost of these machines is high, and the space required for their installation is often more extensive.
Rock and Roll Machines:
Rock and roll machines combine axial rotation with a rocking motion to distribute the plastic material evenly. They feature a main arm that rotates the mold along a longitudinal axis and a platform that rocks back and forth. This optimal distribution of plastic is perfect for producing long, narrow parts. Rock and roll machines are commonly used to make canoes, elongated tanks, and water sports equipment. However, this type of machine is less suitable for large-scale production.
Carousel Machines:
Carousel machines have a rotating structure with multiple arms, typically three or four. Each arm can carry one or more molds, rotating around a central axis and passing through different units continuously. These machines are highly productive due to their reduced downtime between cycles. Specialists in plastics using carousel machines are very efficient in producing large series of parts. We do not recommend Carousel machines when frequent mold changes are required.
What to Know About Molds Used in Rotomolding:
Using the right machine is essential in roto molding. Equally crucial are the molds, which determine the final shape and details of the desired parts. The quality of the mold directly influences the quality of the rotomolded piece. Molds are precisely designed to ensure exact dimensions and high-quality finishes, meeting the required technical specifications. The expertise and craftsmanship of mold makers are, therefore, critical.
Custom-Made Iron or Steel Molds:
Various materials can be used to design molds, the most common being aluminum and steel. Aluminum molds are lighter, have better heat transmission, and are easier to work with. Plastics specialists use aluminum molds for producing complex parts with fine details. On the other hand, steel moulds are more robust and durable but heavier and more challenging to work with. Steel molds are more commonly used for producing large parts or when the production volume is very high.
Various Types of Molds for Rotomolding:
Molds are crafted using different methods and technologies, whether in aluminum or steel. We consider several criteria when choosing a mold before manufacturing parts, including cost, durability, or the desired level of precision.
Cast Aluminum Molds:
These are made by pouring molten aluminum into a shape or model. Once cooled and solidified, the mold is machined for final details. This type of mold is less expensive to produce than its counterparts, making it more commonly used for small to medium production runs of plastic parts. Cast aluminum molds also allow for integrating complex details directly during the casting process, although molds made through digital processes are more precise.
CNC Machined Aluminum Molds:
CNC machining involves creating a mold from a solid aluminum block using computer-controlled machines. This technique offers exceptional precision, making it ideal for designing plastic parts with strict tolerances and intricate details. The cost of a CNC-machined mold is higher compared to other mold types.
Aluminum or Steel Plate Molds: This mold requires assembling several plates. Molds are made by cutting and assembling metal plates, often welded or bolted to form the final mold. This technique is the most affordable compared to machined or cast molds. This is particularly recommended for small production runs or prototypes.
CNC Machined Aluminum Molds:
CNC machining involves creating a mold from a solid aluminum block using computer-controlled machines. This technique offers exceptional precision, making it ideal for designing plastic parts with strict tolerances and intricate details. The cost of a CNC-machined mold is higher compared to other mold types.
Aluminum or Steel Plate Molds: This mold requires assembling several plates. Molds are made by cutting and assembling metal plates, often welded or bolted to form the final mold. This technique is the most affordable compared to machined or cast molds. This is particularly recommended for small production runs or prototypes.
Conclusion
Rotomolding machines and molds open up a world of endless possibilities. Modern plastics technologies allow you to manufacture complex, custom plastic parts. High-precision molds ensure superior-quality finished products suitable for various applications. Modern roto-moulding machines, with advanced heating and rotation capabilities, enable efficient and cost-effective production, even for small and medium series. With roto molding, bring your boldest ideas to life.