PETpla.net Insider 10 / 2017

BOTTLE MAKING 25 PET planet Insider Vol. 18 No. 10/17 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 (see Chapter 6). Ovens can easily be accessed and the distance between lamps and preforms is equal over the whole length of the lamp. Round oven sections were used on some machines at one time but are no longer manufactured except with one particular model that uses microwaves instead of infrared. Blow-mould actuation Most moulds open horizon- tally and have some type of locking mechanism. They differ in the way that the cylinders and locking pins are mounted and whether or not they have so-called pancake cylinders for pressure compensation (see chapter 4). Most mould movements are cam- actuated because their movement never changes, no matter what bottle is running (Fig. 3.19). Figure 3.19 Blow clamp in closed posi- tion with vertical locking pin engaged. Picture courtesy of Krones AG. Preform seal When blow air enters the preform, all blow machines must prevent this air from getting out. There are several ways of doing this: with O-rings at the bottom of the preform seat, or in the side walls of the male connection piece. Distortion of the neck may occur when the neck is getting too warm and the material loses some of its strength, or when the hoop stress (increasing with the square of the diameter) becomes too large, even for a cold neck. A more elegant solution is the so- called blow dome. Instead of sealing somewhere on the inside diameter of the preform, this device seals on the transfer ring. By having air pressure on both the inside and outside of the neck finish, there is no net force on the neck itself. This virtually eliminates any dis- tortion problems and leaves necks as they come from the injection machine. Synchronisation and crash protection The primary advantage of rotary machines is that the movement of all parts is continuous. One motor drives the entire machine and transmits movement through belts and pulleys. As long as belts are at the right tension (a maintenance must-do), synchroni- sation is assured. But what happens when a misformed preform prevents the blow mould from closing? At speeds of 2,000 b/c/h, serious damage would occur if there was no protec- tion. This protection is afforded by a series of clutches that are mounted to every drive pulley that is connected to a rotating machine part. When the torsion force on the clutch exceeds a fixed value, the clutch severs the connection between drive pulley and machine part, allowing free rotation. After the operator clears the jam, he or she can manually rotate the machine part back into the synchronised posi- tion on the clutch (Fig. 3.20). Figure 3.20 Clutches such as this model are used to protect fast-moving parts of blow machines. Drawing courtesy of Mayr Corporation. product development caps & closures design high cavitation moulds multi-component moulds closure production systems after sales service competent – professional – inspiring Hoechster Strasse 8 | 6850 Dornbirn | Austria | www.z-moulds.com FAKUMA 2017 October 17th-21th meet us at booth A7-7502 Mould at FAKUMA 28mm 1881 FlipTop Fontana @KraussMaffei in A7-7303