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Introduction to Polymer Processing
Published in F. Joseph Schurk, Pradeep B. Deshpande, Kenneth W. leffew, Vikas M. Nadkarni, Control of Polymerization Reactors, 2017
One of the major reasons for the phenomenal growth of plastics in engineering applications has been the design flexibility offered by the molding processes to produce parts of complex shapes and geometries at high rates of production. The most common molding processes are injection molding, blow molding, and rotational molding. The injection molding process is used for large-volume production of components such as gears, lighting fixtures, valves, impellers, appliance housings, small toys, plumbing fixtures, etc., mainly with transition and engineering plastics. Blow molding produces hollow plastic containers ranging in capacities from baby milk bottles of a few ounces capacity to large 55-gal drums used for chemicals. The most commonly used materials for blow molding include commodity plastics such as high density polyethylene, PP copolymers, PVC, and engineering plastics such as polyethylene terephthalate and polycarbonate. The rotational molding technique is used for producing hollow articles of complex shapes and large volume, such as water storage tanks, rocking horse toys, automotive fuel tanks, etc., mainly with HOPE and LLDPE.
Plastics
Published in Sherif D. El Wakil, Processes and Design for Manufacturing, 2019
Rotational molding is a process by which hollow objects can be manufactured from thermoplastics and sometimes thermosets. It is based upon placing a charge of solid or liquid polymer in a mold. The mold is heated while being rotated simultaneously around two perpendicular axes. As a result, the centrifugal force pushes the polymer against the walls of the mold, thus forming a homogeneous layer of uniform thickness that conforms to the shape of the mold, which is then cooled before the product is ejected. The process, which has a relatively long cycle time, has the advantage of offering almost unlimited product design freedom. Complex parts can be molded by employing low-cost machinery and tooling.
Fabrication Processes
Published in Manas Chanda, Plastics Technology Handbook, 2017
Essentially four steps are involved in rotational molding: loading, melting and shaping, cooling, and unloading. In the loading stage a predetermined weight of powdered plastic is charged into a hollow mold. The mold halves are closed, and the loaded mold is moved into a hot oven where it is caused to simultaneously rotate in two perpendicular planes. A 4:1 ratio of rotation speeds on minor and major axes is generally used for symmetrically shaped objects, but wide variability of ratios is necessary for objects having complicated configurations.
Machine-based production scheduling for rotomoulded plastics manufacturing
Published in International Journal of Production Research, 2021
Mark Baxendale, James M. McGree, Aaron Bellette, Paul Corry
Rotational moulding (Rotomoulding) is a production process commonly used to create hollow plastics. The market for rotomoulding powder, the raw material for rotomoulding, has been forecast to grow at a compound annual growth rate of 18.2% until 2026 (Credence Research 2018), with the market value of rotomoulded products expected to grow beyond that. Whilst rotomoulded products vary widely, all follow the same general production process. Material is placed into a hollow mould which is attached to the arm of a rotomoulding machine. Generally, multiple fixing points exist on an arm, allowing for multiple moulds to be attached and processed simultaneously provided there is enough room available. Rotomoulding machines contain an oven, capable of housing one arm and its attached moulds. When heated, the powder melts and the arm rotates the attached moulds on all axes to evenly distribute material around the walls of the moulds. The arm is taken out of the oven once moulds are sufficiently cooked, and the arm continues to rotate whilst moulds are cooled to ensure material sets evenly before moulds are removed from the machine and products are finished (Association of Rotational Moulders Australasia, Inc. 2016). It is noted that moulds can stay attached to the machine, and products removed directly from the mould, if the same products are to be immediately produced again. However, no real time is saved by doing so. Any time saved by avoiding full mould removal is offset by the time lost by having to prepare the mould (i.e. clean, refill material) on the arm as moulds are normally pre-prepared in the case for a full changeover. This process is detailed in a Gantt chart in Figure 1, depicting the processing of 3 batches on a 2-arm rotomoulding machine.
An approach toward augmenting materials, additives, processability and parameterization in rotational molding: a review
Published in Materials and Manufacturing Processes, 2020
Nikita Gupta, PL. Ramkumar, Vrushang Sangani
Many researchers have given a detailed description of the materials that can be utilized for rotational molding process. The various materials that can be used are polyethylene, polyvinyl chloride, nylon, polycarbonate, etc., for rotational molding process. The properties associated with each material with its merits and demerits are enlisted in Table 1.