Reducing Bottle Weight
A better wall thickness distribution could be achieved even in bottles that do not have an ideal circular geometry if the wall thickness of the parison could be varied around the circumference. Until now, there was no technical solution for small dies. With development of semi-multi-wall Flexring sleeves, which can be deformed in a purely linear elastic manner through application of low force, it is now possible to dynamically vary the flow channels of single- and especially multi-channel dies in the radial direction down to diameters of only 4 mm in blow molding applications. Gross Kunststoff Verfahrenstechnik, Rossdorf, Germany, has for the first time retrofitted one channel of a 12-channel head (die diameter 18 mm) with dynamic wall thickness control. This involved redesign of the mandrel and die, and fabrication of a new die housing. The housing holds two stepping motors that ovalize the Flexring sleeve in the discharge area by means of a lever mechanism. In this way, when producing an oval bottle in the future, the section of the parison intended for the threaded closure at the top can be formed with an ideal round die geometry while the oval body of the bottle is likewise formed with an ideal oval die geometry. This approach allows the weight of the bottles to be reduced significantly. Furthermore, by eliminating unnecessary thick sections in the bottle wall, the cooling time can be shortened. Dynamically deformable Flexring sleeves can be retrofitted easily in almost any existing production die.
Dr. Ing. Heinz Groß Kunststoffverfahrenstechnik
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