Rotomoulding moulds are crucial for producing high-quality products as they determine the details of the exterior of the finished item. The moulds are hollow, as the rotomoulding process does not rely on pressure to shape the plastic resin. This allows for lightweight and slim moulds. Moulds can consist of two separate parts that open up or multiple components opening in different directions for more complex designs, all resulting in a seamless, hollow plastic product.
The base part of the mould is securely attached to the arm of the rotomoulding machine, while the other parts of the mould are clamped to this base part, enabling fast and efficient demoulding. Typically, moulds for rotomoulding are made of aluminium or steel and are heated in an oven to melt the plastic resin inside.
Aluminium moulds for rotational moulding
Aluminium moulds are commonly used in rotational moulding due to their great design freedom combined with heat conductivity. They can withstand the high temperatures involved in the rotational moulding process. Aluminium moulds also are relatively easy to manufacture, making them a popular choice. Additionally, aluminium moulds are lightweight, which is an advantage for larger moulds and for the rotational moulding machine. Overall, aluminium moulds are a cost-effective, lightweight, and durable solution for rotational moulding process.
The moulds can be made in two ways: by casting aluminium or by machining aluminium. In the casting method, molten aluminium is poured into a mould to create the desired shape. In the machining method, a block of aluminium is cut and shaped on a CNC machine using various tools and machinery to create the desired mould.
Cast aluminium moulds
Cast aluminium moulds for rotomoulding are made by pouring molten aluminium into a mould to create the desired shell which has a typical wall thickness of 8 mm. Cast aluminium moulds can be designed with intricate and multi-faceted shapes, including areas that might otherwise be difficult to remove, or even impossible undercuts. This is because rotomoulding allows for the separation of the mould into various parts during the demoulding process, allowing for easy release of the final product, including any undercuts. A mould surface finish can be created by blasting or polishing to create the desired effects on the part. Cast aluminium moulds can also replicate stone structures, or a wood grain, or any structure that is on the model used to cast the aluminium.
Machined aluminium moulds
Machined aluminium moulds for rotomoulding are created by routing or milling a block of aluminium on a CNC machine, using various tools to produce the desired shape. This method allows for a high level of detail in the finished product. The precision of a machined aluminium tool also is very high, making it the ideal choice for projects that require high accuracy.
Like cast moulds, machined aluminium moulds can include parts like threads and undercuts that might otherwise be impossible to demould. Machined aluminium moulds typically have a thickness of 8 mm, resulting in an even heat distribution and a constant part wall thickness. Local variations in thickness within the mould can influence the final wall thickness of the rotomoulded product. This variation of heat transfer in the mould results in areas of increased or decreased resin build-up, leading to thicker or thinner areas in the final product where these are required.
Steel moulds for rotomoulding
Steel moulds for rotomoulding are made by cutting and shaping sheets of steel. These steel parts are then welded together to create a mould. Sheet steel moulds are typically used for producing large parts and parts with relatively simple geometries. Like aluminium moulds, they are also lightweight and easy to handle. However, the level of detail and precision that can be achieved with sheet steel moulds is not as high as with machined or cast aluminium moulds.
Moulds with integrated heating
A specific type of mould has integrated heating, required for rotomoulding machines that do not use ovens. These moulds have built-in electrical heating elements, which are embedded into the mould’s shell, allowing them to be heated directly. The heating elements are positioned on the mould in a specific pattern. They can be placed closer together in areas where thicker walls are needed, while other areas may not be heated to create openings or cut-outs in the final product. These moulds can be made from cast and from machined aluminium, presenting all the technical possibilities of aluminium moulds.
Proper tools are essential
Proper tools are essential for achieving high-quality results, and we will guide you in selecting the most suitable mould for your product. Based on factors such as finish quality, product size, and required precision, we will recommend the appropriate type of sheet steel, aluminium casting, machined aluminium, or heating-integrated mould.