Injection and blow moulding

By the mid-1990s capacity for polyethylene production was about 50 000 000 t.p.a, much greater than for any other type of plastics material. Of this capacity about 40% was for HDPE, 36% for LDPE and about 24% for LLDPE. Since then considerable extra capacity has been or is in the course of being built but at the time of writing financial and economic problems around the world make an accurate assessment of effective capacity both difficult and academic. It is, however, appeirent that the capacity data above is not reflected in consumption of the three main types of material where usage of LLDPE is now of the same order as the other two materials. Some 75% of the HDPE and LLDPE produced is used for film applications and about 60% of HDPE for injection and blow moulding. 

Another serious effect occurs with liquids which are not in themselves solvents but which may wet the polymer surfaces. These facilitate relief of frozen-in stresses by surface cracking which can be a severe problem in using many injection and blow mouldings with specific chemicals. Examples of this are white spirit with polystyrene, carbon tetrachloride with polycarbonates and soaps and silicone oils with low molecular weight polyethylenes. 

Injection- and blow-moulded parts, seals and gaskets resisting oils, handles of motorbikes, cable guides... 

Injection and blow moulding are by far the most used of the moulding processes but compression is sometimes used for specific cases. 

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. 

In tonnage terms, calcium carbonate is completely dominant a few figures are given in Chapter 6. The great majority of calcium carbonate is used in PVC and to a lesser extent unsaturated polyester thermosetting polymer. Much of it is destined for the construction market or the automotive, domestic appliance and household or consumer products industries. New applications include packaging, especially medical and pharmaceutical packaging, biaxially oriented PP film, flexible film, and injection and blow moulded articles. 

A unique situation exists in the polymer industry whereby a substantial proportion of the effort of the large manufacturing polymer producers involves working in conjunction with the users. This technical service is necessary because of the various applications of the polymers, i.e. they are effect chemicals. Thus, a fabricator will co-operate with the manufacturer as to the optimum method (and, in some cases, which polymer to use) for producing the finished article. Space does not permit discussion of the various techniques used, but they include injection and blow moulding, extrusion and the production of films, vacuum forming, etc. 

Bulk and suspension PVC is mainly used for extruded, injection and blow-moulded articles together with the addition of a plasticizer (section 1.14.2). The morphology of the PVC particle is important in order to ease plasticization with liquid additives. The emulsion produced PVC (obtained using a water-soluble initiator) is generally used as a latex (50-70% solids) for coating fabrics, paper (for wallpaper) etc. 

HOPE is a rugged material, which is easy to mould, has a high resistance to impact, and is not affected by most chemicals. Principally used in injection and blow moulding, it may also be vacuum formed or extruded. The working temperature range is -35 to +65 °C. 

Excellent resistance to mechanical fatigue gives PP its unique hinge property. A service temperature of 120°C allows sterilisation. Polypropylene is available in granules or powder and as sheet in natural (off-white) translucent to opaque colours. It is processable by injection and blow moulding and the sheet can be formed by all techniques in use. PP is also produced in monofilaments and fibres. 

The company, with 250 employees, produces polystyrene resin and impact resistant polystyrene. It has capacity of 20 000 tonnes of PS. The company plans to expand its polystyrene capacity by 10 000 tonnes. Other projects planned by the Foshan government are to manufacture special plastic components for electric appliances and to build a polyester injection and blow-moulding facility for polyester packaging bottles. The planned capacity will be up to 100 million preforms and 50 million packaging bottles per year. 

Comments Data provided for injection and blow moulding grades, bm = blow moulding. ... 

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