PETpla.net Insider 01+02 / 2019

PREFORM PRODUCTION PET planet Insider Vol. 20 No. 01+02/19 www.petpla.net 10 Removal of preform cooling from the injection station to the conditioning station increases productivity Productivity boost With the Zero Cooling technology, Nissei ASB Machine Co., Ltd. intends to push PET moulding efficiency one step further. The technology has been developed to increase productivity and to improve container quality. The company is now applying Zero Cooling as a new standard technology to models in the company’s four-station, one-step ASB Series line-up. The four stations of the ASB Series machines seen in fig.1 operate simultaneously within each cycle. Standard one-step moulding works on the principle that a custom- designed preform is injection moulded and cooled to the point where the PET resin is still above its glass transition temperate (Tg), so it is still flexible as it is transferred to the fol- lowing stations. The residual heat in the preform is then used to allow blow moulding into the finished container shape at the stretch-blow station. Because injection and cooling of the preforms always requires the longest time of these four processes, the injection station dictates the overall cycle time of the moulding machine, and therefore productivity. Nissei ASB sees the advantage of its ASB Series in the second of its four stations, known as the preform conditioning station. It is used to apply a variety of adjustments to the temperature profile and/or the shape of the preform, providing greater flexibility and stability over moulding systems lacking this feature. Improved productivity Now, ASB has reviewed the role of the preform conditioning station to develop an advanced cooling tech- nique called “Zero Cooling”. In standard moulding, preform cooling occupies a significant portion of the total cycle time. By shifting the necessary preform cooling from the injection station to the condition- ing station (fig.2) it can be combined with the appropriate temperature profile adjustment. The injec- tion station is now available to start filling the cavity for the next injection cycle while cooling of the previous shot continues simultaneously in the con- ditioning station. It is this removal of cooling from the injection station that enables average productivity increases of 1.5x and gives rise to the name of “Zero Cooling” for the process, states the company. Physical properties Since the cooling rate of PET resin is a fixed property, in standard moulding the only way to shorten cooling time is to make the preform thinner, which for a given container weight means the pre- form also becomes larger (fig.3). Doing this reduces the overall stretch ratio from preform to finished container so the positive effects of strain hardening from biaxial orientation, that increase the stiffness and tensile strength of PET, are significantly reduced. Nissei ASB claims that smaller preforms have the advantage of pro- viding higher stretch ratios resulting in a good material distribution and topload strength around 15% higher than standard moulding or that of competitor’s products (fig.4). With standard moulding, thicker preforms would require longer cooling resulted in reduced productivity. Fig.1 One-step moulding in 4 stations allows for zero cooling. Fig.2 Cycle reduction with Zero Cooling