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Plastic rotational moulding and injection moulding, blow moulding are all processes that can be used to manufacture plastic products. Although the use of each technology is widespread, there are some differences that may make rotational moulding preferable.
One of the main advantages of plastic rotational moulding is the amount of waste generated during production. In rotational moulding, the plastic is placed in a mould and then the whole mould is rotated to distribute the plastic evenly. The final product contains minimal waste and is typically 100% recycled.
Rotational moulding is also more suitable for large and complex products. While injection moulding, blow moulding technology is suitable for the production of larger quantities of smaller and simpler shaped products, rotational moulding allows the production of larger and more dimensional products in special moulds.
Another advantage of rotational moulding is that the wall thickness of the product is more uniform. In the injection moulding process, the material is poured into a mould, the mould is cooled and the product is removed. However, if the product is too thick, cracks or air pockets may appear on the surface of the material during cooling. With rotational moulding, on the other hand, the material is continuously moved around in the mould, so it is evenly distributed and less likely to form air pockets or cracks in products.
Parts produced by rotational moulding technology are more resistant to weather conditions and chemicals. This feature is very useful in industries such as automotive, electronics and construction, where parts need superior durability and resistance.
Rotational moulding technology offers a more flexible solution, as moulds can be more easily modified and adapted to customer needs.
Overall, plastic rotational moulding technology has many advantages over other plastic moulding technologies. Rotational moulding enables the production of small, medium and large parts, provides higher quality and more flexible manufacturing options, and the parts it produces are more resistant to weathering and chemicals. Rotational moulding technology can be a more economical and efficient way to produce larger quantities of plastic parts in a variety of industries.
The process is a thermoplastic rotational moulding, as the plastic powder is rotated during heating. This rotational movement takes place on two axes. Firstly through a horizontal axis, where the entire machine arm rotates, and then through a vertical axis, where the arm on which the mould is mounted rotates by itself. Thanks to this rotary movement, the melted plastic is distributed on the inner walls and the wall thickness is evenly distributed, preventing the material from stretching at the edges. The rotational moulding process described below creates a seamless plastic hollow body consisting of one part without any stressed areas. This makes the plastic part very robust and dimensionally stable and durable. The entire rotation process is carried out without pressure, solely by the force of gravity, resulting in stress-free hollow bodies. The pressureless rotational moulding process is divided into four different manufacturing stages:
First, the steel or aluminium tool is attached to its machine arm. Unlike other processes, several tools can be mounted on the same machine arm, increasing production capacity. The tool is then filled with plastic material. Since powder is used in most cases, the rotational moulding process is also called powder process. Several materials can be used in the same mould and a unique wall thickness can be achieved by varying the amount of plastic loaded. Depending on the product, different components such as threaded inserts or metal inserts such as nuts can be incorporated into the product The mould, depending on its complexity, consists of two or more parts, which are closed by quick-release fasteners and/or screw fasteners.
In the next step, the tool is placed in the heating furnace. During the heating phase, the plastic is heated uniformly at a temperature between 150°C and 200°C. The next step is the heating of the tool. During the entire heating phase, the tool holder arm rotates uniformly around two perpendicular axes. During rotation, both the entire arm rotates and the clamping plate on the end of the arm on which the tool is mounted rotates separately. During the two-axis rotation, the molten plastic in the mould is only distributed uniformly by gravity and adheres to the mould wall when the melting temperature is reached. Due to the continuous biaxial rotation, the wall thickness builds up layer by layer throughout the component until the material is completely melted. Thanks to this pressure-free manufacturing process, a uniform wall thickness distribution can be achieved in each individual area without stress.
Once the material has finished melting, the tool is automatically transferred from the heating chamber to the cooling chamber. The machine arm maintains a continuous two-axis rotary motion. In the cooling chamber, the molten plastic is cooled to a temperature of approximately 90 degrees Celsius. The mould is in continuous motion during cooling. Cooling is done exclusively by air cooling to ensure uniform and slow cooling of the part, preventing distortion or "stressing" of the plastic part. Cooling templates can be used to further control the shrinkage of the products coming out of the mould in order to ensure the required tolerance.
After cooling, the tool is sent to the assembly station. After cooling, the product is removed from the mould. Since manual force is used to remove the product, minor undercuts that can cause problems with other plastic moulding processes are not a problem with rotational moulded products. After the product has been removed, the tools are refilled with raw material. For more complex parts, where the mould consists of more than two parts, each part must first be disassembled so that the finished product can be completely removed. Multi-part moulds can also be used to produce complex moulds.
Benefits, features:
Thermoplastic rotational moulding has many advantages over other processes: Particularly large and seamless plastic parts can be produced in a fully enclosed mould in sizes from 20 to 40,000 litres in small and large series. We can create any number of openings in the plastic part directly during our manufacturing process, with plastic or metal internal and external threads as required. During the process, we can create geometric features such as complex shapes with undercuts, ribs, indentations, recessed handles. We also offer modular tooling options to create multiple parts with a single tool. Metal inserts, inserts can be moulded in plastic or can be placed directly after manufacture. This improves assembly time, as the structures can be bolted directly, without the need for complex thread-forming, post-forming of fixing points. In terms of design, the products can be made with single walls, e.g. tanks, panels, cladding, etc. The products can be made with double walls, which, when filled with insulating material, provide extremely high thermal insulation and greatly increase the stability and strength of the product.
Injection moulding is mainly used in the plastics industry. The appropriate plastic is liquefied in the injection moulding machine and injected under pressure into the injection moulding tool. The liquid plastic cools down in the mould to return to a solid state and is then removed from the mould as a finished product. The inner cavity of the mould is completely filled with plastic, which determines the final shape of the product. Injection moulding allows a wide variety of shapes and surface structures, such as the smoothest surfaces, patterns and engravings. Injection moulding allows the production of large quantities of injection moulded parts at low cost. Given that the cost of the mould is considerable, the use of this technology can be said to be economical for the production of thousands of products. Injection moulded parts can be produced in weights ranging from a few milligrams to around 150 kg.
Production process:
At the beginning of the production process, the plastic is fed in the form of granules into the extrusion screw of the injection moulding machine. The plastic granules are heated through the screw and thus melted. The melted plastic is injected into the mould at high pressure. The tool is then cooled with water or oil and the finished product can then be removed. Injection moulding produces high quality, high precision and uniformly sized parts and can be used in many industries such as automotive, electronics and household appliances.
Blow moulding is a process that produces hollow bodies from various thermoplastics. The materials most commonly used in extrusion blow moulding are polyethylene (PE) and polypropylene (PP).
Pending:
First, the plastic is melted by an extruder and conveyed to a nozzle by a conveyor screw. There, the raw material is pushed through the nozzle to form a tube. This tube of material is also called a preform. The mould, consisting of two halves, is then closed around the preform. Inside the mould is a negative, or reverse, impression of the desired shape of the finished product. A separation tool, such as a knife, is used to separate the preform from the material exiting the nozzle. This process produces jagged seams at the bottom of the moulded part, typical of the bottom of a shampoo bottle, for example. Once the preform is separated from the nozzle and the two closed moulds are half-closed, a tubular device is dipped into the material hose. The compressed air flows through this device into the hose. This causes the preform to inflate and lie against the inner walls of the mould. In addition, a thread is formed through the pipe, for example at the plastic neck. When the preform is fully inflated and the inner walls of the mould are precisely formed, the cooling process can begin. The heat of the mould is reduced by the built-in cooling circuits. The air between the mould and the inflated product can escape through the mould parting lines or through additional ventilation openings in the blow mould. Once the blown moulded part has reached its removal temperature due to the cooling process, the mould halves can be opened and the blown moulded part can be removed. The process can then be repeated and the mould halves are closed around a new preform. Finally, the moulded part is transferred to a screw separation station. There the edges, which have not been blown because they have overstretched the mould, are separated from the blown parts by a punching or cutting tool. These residues, after being finely ground, can be reintroduced into the production process.
Their use:
Plastic blow moulding is used in a wide range of industries where plastic products of different shapes, sizes and thicknesses are required. These include food, packaging, automotive, electronics, healthcare, construction and many others.
In the food industry, plastic blow moulding is a commonly used technology for the production of beverage bottles, dairy cartons and other food packaging. In the automotive industry, it is used to manufacture fuel tanks, engine oil tanks, air filters, headlights, window washer tanks and other components. In the electronics industry, it is used to manufacture products such as cable protection tubes, battery cases, laptop cases and phone cases.
In the healthcare industry, plastic blow moulding is used to make blood glucose meter cases, inhalers and sterilisation boxes. In the construction industry, plastic blow moulding is used in the manufacture of sewer systems, water storage tanks and insulation materials.
Overall, plastic blow moulding has a wide range of applications and allows the production of plastic products in many shapes and sizes.
