Production using a rotational moulding technology consists generally of four basic stages: filling a mould with plastic, thermal treatment, cooling, demoulding and machining. However, thanks to the solutions used in the technological line and the fact that it is equipped with a mill and a pulveriser, there is an additional stage in our company besides the elements typical of rotational moulding, namely the stage of recovering material unused in the production process. Thanks to this solution, our production is practically waste-free, and thus environment-friendly.
The first stage of production is filling a mould with plastic in the form of thermoplastic powder, usually polyethylene, either in natural form or with admixtures of colours or other additives as well as elements to be embedded in the plastic, all that depending on product requirements. Then the product mould is closed by operators and entered into a furnace; at this stage, the mould already rotates in two perpendicular planes.
The mould is heated up to the temperature at which the powder in the mould becomes liquid. During this process, the mould is constantly rotated along two perpendicular axes. Properly selected heating time, temperature and speed of the mould rotation ensure even distribution of the liquid material inside the mould, giving the desired product shape. After this process, the mould leaves the furnace to start the cooling process.
The constantly rotating mould is cooled by air, thanks to which the plastic solidifies in the mould, and the continuous rotation of the mould causes that the material doesn’t settle in an undesirable manner, thanks to which the product achieves the required thickness and uniformity on the entire surface. The important elements that affect the length of cooling are the product size and the required thickness of its walls.
Once the mould has been cooled, it is dismantled by the operators, and the product is removed and carefully machined to remove excess material using specialized tools dedicated to the processing of plastic products. A machine operator checks and cleans the mould, and then they can proceed with refiling it, thanks to which the cycle can be repeated.
The material that remains after the processing is transferred to a special mill for grinding plastics. Thanks to correctly profiled knives, this mill processes the delivered material at a speed of 1600 kg/h into even flakes with a diameter of 6 mm. Then the material so processed is transferred to a pulveriser, which further processes it and grinds the material to form a powder with a grain diameter of about 500 microns, so we can use it as an additive in further production.