Product features related to processing

The aim is to recognise design features associated with processes. The diagrams in Chapter 5 show the major processes. Both the product shape and surface marks provide clues for process identification. 

Abbreviations Polymer Density (kgm T, CQ T , CQ Event if bent through 90° 

P4MP Poly (4-methyl-pentene-l) 830 25 238 Semi-brittle 

crystal melting temperature Tg, glass transition temperature. 

These are hollow containers, usually with an opening of smaller diameter than the body. Both ends of the moulding may be cut off to produce a tubular product, or one end cut off for a bucket-shaped container. The wall thickness varies with position, and there is a weld Hue across the closed end of the container (Fig. 1.12). Sometimes near-parallel lines are visible on the inner surface. These indicate the extrusion direction when the parison (tubular preform) emerged from a die. Look for the weld location on the base of an HDPE milk bottle this aligns with the external surface line from the mould split. Section the milk bottle vertically, in a plane perpendicular to the weld line, and measure the thickness at the weld line compared with elsewhere. Note the threads in the neck are corrugated. 

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