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The rotational moulding process allows the production of parts of different sizes and shapes, in small, medium and large quantities. The process has the advantage of using less raw material than other casting processes and also allows for customisation of parts.
Rotational moulding technology has many advantages, such as the production of high quality parts, easier mould making and minimised tooling costs. It also allows the production of different colours and textures.
Rotational moulding technology is widely used in various industries such as automotive, electronics, furniture and construction. Plastic rotational moulding is particularly suitable for the production of larger and more complex components such as machine parts, furniture, etc...
Rotational moulding of plastics involves the use of several types of plastic with different properties. One of the most commonly used is polyethylene, which is light, flexible and resistant to alkalis and acids. In addition, polypropylene, PVC and other plastics are also used, which offer different advantages for the specific application.
The rotational moulding process is very flexible, allowing for customisation and even small batch production. Process control and quality control are key to achieving the desired dimensional accuracy and quality in the parts produced.
Making the moulds needed to manufacture products is extremely important, as the quality of the mould affects the quality and accuracy of the parts produced. The mould material is usually aluminium alloy or steel which can have different surface structures.
However, rotational moulding of plastic has its limitations. The process cannot produce very detailed and complex moulds and the production speed is slower than other moulding processes.
Overall, rotational moulding of plastics is an efficient and flexible moulding technology that offers a number of advantages in various industries. The process is a widely used technology in the plastics industry, allowing for customization of parts and low costs while ensuring high quality.
Raw materials that can be used:
Polyethylene - PE. Polyethylene is the most commonly used material for rotational moulding. Polyethylene (PE) can be divided into different densities:
PE-LD 0,915 - 0,935 g/cm³
PE HD 0,940 - 0,970 g/cm³
LLDPE 0,870-0,940 g/cm³
Depending on the application and the desired product, different densities and melt flow indexes (MFI) can be used in rotational moulding. For example, very high density materials are used to make large tanks.
Materials with a particularly high melt flow index are used for visible parts and luminaires where aesthetics are particularly important, meaning that lettering and logos can be reproduced in very high detail, which is difficult with materials with a lower MFI. A big advantage of polyethylene is that it offers a wide range of processing possibilities and is very resistant to aggressive chemicals. Furthermore, the temperature range of the manufactured parts is relatively wide, from -20 °C to +60 °C. Common applications are for example light fittings, as well as kayaks and boats, tanks.
In addition to polyethylene, polypropylene is also very suitable for use in the rotary process. It is also a thermoplastic with better heat resistance than polyethylene. The temperature range of rotationally moulded parts can be from -10°C to 100°C. The density ranges from 0,895 g/cm³ to 0,92 g/cm³. Applications are similar to polyethylene, although depending on the application, the emphasis is often on higher temperature resistance. However, this means that processing temperatures and cycle times in the moulding process are higher/longer, which increases the cost of producing polypropylene.
PVDF is highly valued in the industry for its excellent heat and chemical resistance and is often used in special applications where traditional thermoplastics such as polyethylene and polypropylene have reached their limits. Heat resistance up to 140 °C offers new possibilities for replacing metals with plastics. In addition, the material offers the great advantage of a V0 (3 mm UL94) fire classification. High melting temperatures significantly increase cycle times and processing temperatures. In addition, the raw material cost of PVDF is many times higher than polyethylene or polypropylene. The density of the material is significantly higher than the previously presented materials, 1,71-1,78 g/cm³.
In addition to the materials already mentioned, it is also possible to process polyamide by the rotational method. It is often used in the multilayer production of fuel tanks. Its high stiffness and dyeability offer additional advantages for use in visible areas. Polyamide also has the advantage that moulded parts made from it can be exposed to temperatures up to 140 °C. Többrétegű szerkezet létrehozásával lehetőség nyílik például a polietilén pozitív tulajdonságainak és a poliamid tulajdonságainak kombinálására. Mivel a poliamid vízelnyelő tulajdonsággal rendelkezik (higroszkópos), ezért a feldolgozás előtt az anyagot szárítani kell. Ellenkező esetben a következmények az anyag felületének optikai zavarai, sőt törékenysége, ami tönkreteheti az öntött részt. A poliamid sűrűsége 1,01 g/cm³ és 1,235 g/cm³ között van a kristályosságtól és a kialakítástól függően (PA6 - PA12).
By using modified polyethylenes to which foaming agents are added, the plastic can be made foamable during the process. During moulding, the material is heated and the blowing agent is activated. This allows the polyethylene to foam and expand 4-6 times. The resulting structure contains a large number of air bubbles and has the advantage of providing high volume and thus enormous stability with low mass. The foaming agent is often used in combination with conventional materials (see Multilayer). Intended uses include the manufacture of lightweight boat hulls for increased stability, cool boxes to reduce heat transfer through the insulating layer and objects with sound absorbing properties.
The use of flame retardant additives can reduce the burning rate of products, but does not imply total fire resistance. Additives can be used to reduce the rate of fire spread. This makes the use in public buildings safe. However, the addition of additives also reduces chemical resistance and impact strength.
