Thermoplastics blow moulding

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

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... 

Figure 2.22 shows the supremacy of polyethylene and thermoplastic polyester (PET) in the European bottle and other blow-moulded container market. 

Among the plastics suitable for blow moulding are polyethylenes, polypropylenes, polyacrylonitrile, thermoplastic polyesters, polycarbonates... 

Thermoplastics consist of long chains of molecules, in the case of PE these are unbranched. Many of these chains together form a tangle which is more difficult to unravel the more branched the chains are. The branches are like hooks which cause the molecules to catch. Under the influence of relatively small external forces chains and parts of chains can slide across each other. PE is for instance used to make containers, chemical tubing and blow-moulded bottles. Some other thermoplastics are polypropylene (crates), polyvinyl chloride PVC (pipes) and polystyrene (foam). 

Blow moulding was adapted to making containers from plastics from traditional methods of blowing glass bottles. Essentially, the thermoplastic is heated... 

In this method a mandrel is placed in the mould of an injection moulding machine, the mould heated, and thermoplastic forced in to flow round the mandrel and form a tube with a closed end mandrel and plastic then are removed and passed while still hot to the blowing mould, where air introduced through the mandrel blows the material to the shape required. 

Thermoplastics can be moulded into articles by injection moulding or blow moulding. 

Biodegradable polymers are similar in terms of their chemical structure to conventional thermoplastics such as polyethylene, polypropylene and polystyrene. They can be processed using standard polymer processing methods such as film extrusion, injection moulding and blow moulding. 

Polystyrene and closely related thermoplastics such as the ABS polymers may be processed by such techniques as injection moulding, extrusion and blow moulding. Of less importance is the processing in latex and solution form and the... 

Blow moulding describes any shaping process in which air is used to stretch and form plastic materials and can be compared to inflating a balloon. A hot thermoplastic tube, usually made by extrusion, can be inflated with compressed gas while inside a cooled split mould. Hot thermoplastic tubes or parisons can also be blown into free shapes without the aid of a mould (Figure 3.33). Plastic bottles, drums, car fuel tanks and other containers are often made using blow moulding (Figure 3.34). 

In blow moulding, a pre-formed, thermoplastic tube is reheated and blown to shape in a cooled mould before release. 

Flows can be classified into streamline, when particles in the fluid follow paths (streamlines) that remain constant with time, and turbulent, when vortices cause unpredictable changes in the flow pattern with time. The changeover occurs at a critical value of the Reynolds number, which is defined as the melt velocity, divided by the viscosity times the channel diameter. The high viscosity of thermoplastic melts causes velocities to be low. Hence, the Reynolds number is very low and the flows are streamline. We will consider steady flows, and ignore the start and end of injection and blow-moulding flows, when the melt accelerates and decelerates, respectively. However, in the RIM process (Section 5.6.5), turbulent flow of the low viscosity constituents in the mixing head achieves intimate mixing. 

It is difficult to process aliphatic polyesters having low melting points by conventional techniques for thermoplastic materials, such as film blowing and blow moulding. It has been found that the blending of starch with aliphatic polyesters allows their processability and biodegradability to be improved. 

Polyethersulphone is a true thermoplastic and can be processed by all the traditional techniques we associate with thermoplastics. These include Injection moulding, blow moulding, extrusion of rod and sheet, and vacuum forming sheet into con lex shapes. PES requires slightly higher processing temperatures than those needed for most other thermoplastics but these temperatures are well within the capabilities of most modern screw... 

Terephthalic acid forms linear polyesters with diols. Saturated linear polyesters are thermoplastics to be processed into fibres, films, and more recently, into engineering plastics by injection moulding and blow moulding. Poly(ethylene terephthalate) and poly(butylene terephthalate) are the most important representatives of thermoplastic polyesters. Possibilities for their flame-retardance are discussed in Section 5.I.3.4. 

PHB V is thermoplastic and can be processed by injection moulding, extrusion, blow moulding, film and fibre forming, and lamination techniques. 

The processing conditions of BAK poly(esteramide) are similar to those of pofyolefins [99], BAK 1095 resin can be processed into film and also into extruded or blow-moulded parts on conventional machinery used for processing thermoplastics. Processing conditions are given in Table 3.20. 

Thus, protein-based bioplastics can be obtained by extrusion, calendering, extrusion blow moulding, injection and thermoforming processes. These thermoplastic processes are derived from synthetic material production processes. 

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