ROTATIONAL BLOW MOULDING

Injection/compression moulding - Thermoplastics and thermosets Blow moulding - Thermoplastics Rotational moulding - Thermoplastics... 

The process is attractive for a number of reasons. Firstly, since it is a low pressure process the moulds are generally simple and relatively inexpensive. Also the moulded articles can have a very uniform thickness, can contain reinforcement, are virtually strain free and their surface can be textured if desired. The use of this moulding method is growing steadily because although the cycle times are slow compared with injection or blow moulding, it can produce very large, thick walled articles which could not be produced economically by any other technique. Wall thicknesses of 10 mm are not a problem for rotationally moulded articles. 

Table 2.17 analyses some examples of the relative processing cost versus the annual production in units. The various technologies listed are not suitable for all materials or parts machining is used with numerous materials rotational moulding uses liquid resins vacuum forming uses thermoplastic sheets blow moulding uses special grades of thermoplastics... 

Extrusion, injection, compression, blown film, blow moulding, rotational moulding, foam, coating, powdering, co-extrusion, for thin or thick parts, for crosslinking, electrowelding. .. 

ETFE can be processed by conventional molten-state methods such as extrusion, injection, compression, transfer, rotational and blow moulding. 

Blowing The preform mould opens and the core rod is rotated and clamped into the hollow, chilled blow mould. The core rod opens and allows compressed air into the perform, which inflates into the finished article shape. 

Ejection After a cooling period the blow mould opens and the core rod is rotated to the ejection position. The finished article is stripped off the core rod and leak-tested prior to packing. The preform and blow mould can have many cavities, typically three to sixteen depending on the article size and the required output. There are three sets of core rods, which allow concurrent preform injection, blow moulding and ejection. 

In iiyection blow moulding the parison is injection moulded on to a steel rod (see Figure 7.45, station 1). The rod and parison ate then rotated to station 2 (the blow mould) wnere air is blown into the parison to cause it to take up the shape of the mould. The rod and bottle are next rotated to station 3, at which the mould opens and the bottle is ejected. 

Foam production is compatible with injection and compression moulding, extrusion, thermoforming, rotational and blow moulding, and with the spread coating of PVC. 

Assumptions Injection moulding Reaction Injection moulding Blow moulding Thermo- forming Rotational moulding Hand lay-up Fabrication... 

Johnson, N.C. Cost comparison of rotational casting with injection moulding and blow moulding. Brit. Blast., July 1974, p. 376. 

Extrusion blow moulding Injection blow moulding Injection moulding Rotational moulding Extrusion. 

---