Technology
QUALITY | ROTATIONAL MOULDING
Rotational moulding offers a great deal of freedom in design and has fewer restrictions than other processes used for the manufacture of plastic parts. It can be used to produce open or closed items with dimensions that can start from diameters as small as 25-50 mm. The shapes can be simple (spheres, containers) or complex (fuel tanks, automotive components). Parts can be moulded with thicknesses starting from 1.0 mm up to 50mm. The parts may be coloured or transparent, flexible or rigid. Rotational moulding is suitable for small production runs, but it can be used for the production of 50,000 – 100,000 parts/year. Above these values a more automated process should be considered. However, in cases where the rotational moulding is the only viable process, higher production outputs can be obtained using multiple moulds and machines.
THREAD
External and internal threads can be produced. External threads should not to be positioned along the parting line of the mould. Internal threads require additional mould section or cores that have to be unscrewed before removing the part from the mould. Small, narrow threads can be obtained by the use of metal inserts which are introduced into the mould. During the heating/moulding process these are covered by the polymer. In the case of plastic inserts, they become joined onto part during the moulding process. Threads can be obtained:
• directly in the moulding: produced by a movable section inserted in the mould that reproduces the shape of the thread and the related dimensions. To obtain a part without faults, the following recommendations are to be followed at the time of the designing the product: - pitch more than 4 mm;
- threaded section with rounded shape.