PETpla.net Insider 06 / 2017

BOTTLE MAKING 29 PET planet Insider Vol. 18 No. 06/17 www.petpla.net Please order your copy at the PETplanet Insider book shop: www.petpla.net/book3 Stretch Blow Molding Second Edition by Ottmar Brandau € 130,00 320 pages © Copyright Elsevier 2012 rod and blow air provide the stress needed to transform the preform into a bottle. The top right of this and the following diagrams indicates the stage of the preform in the blow mould. Elastic deformation Figure 2.14 Elastic deformation occurs when the stretch rod starts moving mate¬rial toward theblow mould. The first stage is the area of elas- tic deformation, as seen in Fig. 2.14. Here, the material stretches but will retract if the stress is removed. This is similar to the way that metals behave, but the shape of the curve is slightly different. Looking at a preform, this stage can be compared to the stretch rod starting to push on the preform. If the stretch rod was retracted, the preform would shrink back almost to its original length. Yielding The second stage is yielding (Fig. 2.15). With no increase in stress, the material “gives,” elongating easily. This happens in the blow mould when the primary or pre-blow air partially inflates the preform. The preform will continue to inflate until it reaches the natural stretch ratio: the point after which higher stress is needed to achieve further elongation. Figure 2.15 At the yielding plateau, no further stress is required for additional strain. The third stage is called strain hardening (Fig. 2.16). Applied stress levels have to increase exponentially in order to force material to stretch further. This is the point in the blow process when high-pressure air enters the preform and forces it to stretch from a bubble to the blow cavity walls where it is rapidly cooled down. It is during the strain-hardening phase that the material achieves orientation. Figure 2.16 Highblow pressureforces the material to strain harden. PROCESS PILOT ® makes producing a better PET bottle as easy as 2 3 1 MEASURE CONTROL OPTIMIZE every bottle for changes in material distribution process variation, inside the blowmolder material utilization and orientation to achieve maximum bottle performance CONTACT US TODAY TO LEARN MORE! AGRINTL.COM | +1.724.482.2163 | SALES@AGRINTL.COM see us at Booth A4-336